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Transmitter Release (transmitter + release)
Selected AbstractsDOES NITRIC OXIDE MODULATE TRANSMITTER RELEASE AT THE MAMMALIAN NEUROMUSCULAR JUNCTION?CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 4 2007Travis J Nickels SUMMARY 1Application of the nitric oxide (NO) donor, sodium nitrite and the NO synthase substrate l -arginine had no effect on nerve-evoked transmitter release in the rat isolated phrenic nerve/hemidiaphragm preparation; however, when adenosine A1 receptors were blocked with the adenosine A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) prior to application of sodium nitrate or l -arginine, a significant increase in transmitter release was observed. In addition, the NO donor s -nitroso- N -acetylpenicillamine (SNAP) significantly increased transmitter release in the presence of DPCPX. In the present study, we have made the assumption that these NO donors elevate the level of NO in the tissue. Future studies should test other NO-donating compounds and also monitor the NO concentrations in the tissue to ensure that these effects are, in fact, NO induced. 2Elevation of cGMP in this preparation with the guanylyl cyclase activator 3-(5,-hydroxymethyl-2,-furyl)-1-benzyl indazole (YC-1) significantly enhanced transmitter release. In the presence of DPCPX and the selective guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), which blocks the production of cGMP, the excitatory effects of sodium nitrite and l -arginine were abolished. 3These results suggest that NO serves to enhance transmitter release at the rat neuromuscular junction (NMJ) via a cGMP pathway and this facilitation of transmitter release can be blocked with adenosine. Previously, we demonstrated that adenosine inhibits N-type calcium channels. Because NO only affects transmitter release when adenosine A1 receptors are blocked, we suggest that NO enhances transmitter release by enhancing calcium influx via N-type calcium channels. Further studies are needed to confirm that NO alters transmitter release via cGMP and that this action involves the N-type calcium channel. 4The results of the present study are consistent with a model of NO neuromodulation that has been proposed for the mammalian vagal,atrial junction. This model suggests that NO acts on NO-sensitive guanylyl cyclase to increase the intracellular levels of cGMP. In turn, cGMP inhibits phosphodiesterase-3, increasing levels of cAMP, which then acts on the N-type calcium channels to enhance calcium influx, leading to an increase in transmitter release. Our only modification to this model for the NMJ is that adenosine serves to block the modulation of transmitter release by NO. [source] Differential Ca2+ -dependence of transmitter release mediated by P/Q- and N-type calcium channels at neonatal rat neuromuscular junctionsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2002Marcelo D. Rosato-Siri Abstract N- and P/Q-type voltage dependent calcium channels (VDCCs) mediate transmitter release at neonatal rat neuromuscular junction (NMJ). Thus the neonatal NMJ allows an examination of the coupling of different subtypes of VDCCs to the release process at a single synapse. We studied calcium dependence of transmitter release mediated by each channel by blocking with ,-conotoxin GVIA the N-type channel or with ,-agatoxin IVA the P/Q-type channel while changing the extracellular calcium concentration ([Ca2+]o). Transmitter release mediated by P/Q-type VDCCs showed steeper calcium dependence than N-type mediated release (average slope 3.6 ± 0.09 vs. 2.6 ± 0.03, respectively). Loading the nerve terminals with 10 µm BAPTA-AM in the extracellular solution reduced transmitter release and occluded the blocking effect of ,-conotoxin GVIA (blockade ,2 ± 9%) without affecting the action of ,-agatoxin IVA (blockade 85 ± 4%). Both VDCC blockers were able to reduce the amount of facilitation produced by double-pulse stimulation. In these conditions facilitation was restored by increasing [Ca2+]o. The facilitation index (fi) was also reduced by loading nerve terminals with 10 µm BAPTA-AM (fi = 1.2 ± 0.1). The control fi was 2.5 ± 0.1. These results show that P/Q-type VDCCs were more efficiently coupled to neurotransmitter release than were N-type VDCCs at the neonatal neuromuscular junction. This difference could be accounted for by a differential location of these channels at the release site. In addition, our results indicate that space,time overlapping of calcium domains was required for facilitation. [source] Functions of glutamate transporters in cerebellar Purkinje cell synapsesACTA PHYSIOLOGICA, Issue 1 2009Y. Takayasu Abstract Glutamate transporters play a critical role in the maintenance of low extracellular concentrations of glutamate, which prevents the overactivation of post-synaptic glutamate receptors. Four distinct glutamate transporters, GLAST/EAAT1, GLT-1/EAAT2, EAAC1/EAAT3 and EAAT4, are distributed in the molecular layer of the cerebellum, especially near glutamatergic synapses in Purkinje cells (PCs). This review summarizes the current knowledge about the differential roles of these transporters at excitatory synapses of PCs. Data come predominantly from electrophysiological experiments in mutant mice that are deficient in each of these transporter genes. GLAST expressed in Bergmann glia contributes to the clearing of the majority of glutamate that floods out of the synaptic cleft immediately after transmitter release from the climbing fibre (CF) and parallel fibre (PF) terminals. It is indispensable to maintain a one-to-one relationship in synaptic transmission at the CF synapses by preventing transcellular glutamate spillover. GLT-1 plays a similar but minor role in the uptake of glutamate as GLAST. Although the loss of neither GLAST nor GLT-1 affects cerebellar morphology, the deletion of both GLAST and GLT-1 genes causes the death of the mutant animal and hinders the folium formation of the cerebellum. EAAT4 removes the low concentrations of glutamate that escape from uptake by glial transporters, preventing the transmitter from spilling over into neighbouring synapses. It also regulates the activation of metabotropic glutamate receptor 1 (mGluR1) in perisynaptic regions at PF synapses, which in turn affects mGluR1-mediated events including slow EPSCs and long-term depression. No change in synaptic function is detected in mice that are deficient in EAAC1. [source] Activity-dependent formation and functions of chondroitin sulfate-rich extracellular matrix of perineuronal netsDEVELOPMENTAL NEUROBIOLOGY, Issue 5 2007Alexander Dityatev Abstract Extracellular matrix molecules,including chondroitin sulfate proteoglycans, hyaluronan, and tenascin-R,are enriched in perineuronal nets (PNs) associated with subsets of neurons in the brain and spinal cord. In the present study, we show that similar cell type-dependent extracellular matrix aggregates are formed in dissociated cell cultures prepared from early postnatal mouse hippocampus. Starting from the 5th day in culture, accumulations of lattice-like extracellular structures labeled with Wisteria floribunda agglutinin were detected at the cell surface of parvalbumin-expressing interneurons, which developed after 2,3 weeks into conspicuous PNs localized around synaptic contacts at somata and proximal dendrites, as well as around axon initial segments. Physiological recording and intracellular labeling of PN-expressing neurons revealed that these are large fast-spiking interneurons with morphological characteristics of basket cells. To study mechanisms of activity-dependent formation of PNs, we performed pharmacological analysis and found that blockade of action potentials, transmitter release, Ca2+ permeable AMPA subtype of glutamate receptors or L-type Ca2+ voltage-gated channels strongly decreased the extracellular accumulation of PN components in cultured neurons. Thus, we suggest that Ca2+ influx via AMPA receptors and L-type channels is necessary for activity-dependent formation of PNs. To study functions of chondroitin sulfate-rich PNs, we treated cultures with chondroitinase ABC that resulted in a prominent reduction of several major PN components. Removal of PNs did not affect the number and distribution of perisomatic GABAergic contacts but increased the excitability of interneurons in cultures, implicating the extracellular matrix of PNs in regulation of interneuronal activity. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007 [source] The structure and mode of action of different botulinum toxinsEUROPEAN JOURNAL OF NEUROLOGY, Issue 2006J. O. Dolly The seven serotypes (A,G) of botulinum neurotoxin (BoNT) are proteins produced by Clostridium botulinum and have multifunctional abilities: (i) they target cholinergic nerve endings via binding to ecto-acceptors (ii) they undergo endocytosis/translocation and (iii) their light chains act intraneuronally to block acetylcholine release. The fundamental process of quantal transmitter release occurs by Ca2+ -regulated exocytosis involving sensitive factor attachment protein-25 (SNAP-25), syntaxin and synaptobrevin. Proteolytic cleavage by BoNT-A of nine amino acids from the C-terminal of SNAP-25 disables its function, causing prolonged muscle weakness. This unique combination of activities underlies the effectiveness of BoNT-A haemagglutinin complex in treating human conditions resulting from hyperactivity at peripheral cholinergic nerve endings. In vivo imaging and immunomicroscopy of murine muscles injected with type A toxin revealed that the extended duration of action results from the longevity of its protease, persistence of the cleaved SNAP-25 and a protracted time course for the remodelling of treated nerve,muscle synapses. In addition, an application in pain management has been indicated by the ability of BoNT to inhibit neuropeptide release from nociceptors, thereby blocking central and peripheral pain sensitization processes. The widespread cellular distribution of SNAP-25 and the diversity of the toxin's neuronal acceptors are being exploited for other therapeutic applications. [source] Adenosine drives recycled vesicles to a slow-release pool at the mouse neuromuscular junctionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2010Paula P. Perissinotti Abstract The effects of adenosine on neurotransmission have been widely studied by monitoring transmitter release. However, the effects of adenosine on vesicle recycling are still unknown. We used fluorescence microscopy of FM2-10-labeled synaptic vesicles in combination with intracellular recordings to examine whether adenosine regulates vesicle recycling during high-frequency stimulation at mouse neuromuscular junctions. The A1 adenosine receptor antagonist (8-cyclopentyl-1,3-dipropylxanthine) increased the quantal content released during the first endplate potential, suggesting that vesicle exocytosis can be restricted by endogenous adenosine, which accordingly decreases the size of the recycling vesicle pool. Staining protocols designed to label specific vesicle pools that differ in their kinetics of release showed that all vesicles retrieved in the presence of 8-cyclopentyl-1,3-dipropylxanthine were recycled towards the fast-release pool, favoring its loading with FM2-10 and suggesting that endogenous adenosine promotes vesicle recycling towards the slow-release pool. In accordance with this effect, exogenous applied adenosine prevented the replenishment of the fast-release vesicle pool and, thus, hindered its loading with the dye. We had found that, during high-frequency stimulation, Ca2+ influx through L-type channels directs newly formed vesicles to a fast-release pool (Perissinotti et al., 2008). We demonstrated that adenosine did not prevent the effect of the L-type blocker on transmitter release. Therefore, activation of the A1 receptor promotes vesicle recycling towards the slow-release pool without a direct effect on the L-type channel. Further studies are necessary to elucidate the molecular mechanisms involved in the regulation of vesicle recycling by adenosine. [source] L-type calcium channels are involved in fast endocytosis at the mouse neuromuscular junctionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2008Paula P. Perissinotti Abstract We used fluorescence microscopy of FM dyes-labeled synaptic vesicles and electrophysiological recordings to examine the functional characteristics of vesicle recycling and study how different types of voltage-dependent Ca2+ channels (VDCCs) regulate the coupling of exocytosis and endocytosis at mouse neuromuscular junction. Our results demonstrate the presence of at least two different pools of recycling vesicles: a high-probability release pool (i.e. a fast destaining vesicle pool), which is preferentially loaded during the first 5 s (250 action potentials) at 50 Hz; and a low-probability release pool (i.e. a slow destaining vesicle pool), which is loaded during prolonged stimulation and keeps on refilling after end of stimulation. Our results suggest that a fast recycling pool mediates neurotransmitter release when vesicle use is minimal (i.e. during brief high-frequency stimulation), while vesicle mobilization from a reserve pool is the prevailing mechanism when the level of synaptic activity increases. We observed that specific N- and L -type VDCC blockers had no effect on evoked transmitter release upon low-frequency stimulation (5 Hz). However, at high-frequency stimulation (50 Hz), L -type Ca2+ channel blocker increased FM2-10 destaining and at the same time diminished quantal release. Furthermore, when L -type channels were blocked, FM2-10 loading during stimulation was diminished, while the amount of endocytosis after stimulation was increased. Our experiments suggest that L -type VDCCs promote endocytosis of synaptic vesicles, directing the newly formed vesicles to a high-probability release pool where they compete against unused vesicles. [source] Severely impaired neuromuscular synaptic transmission causes muscle weakness in the Cacna1a -mutant mouse rolling NagoyaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2007Simon Kaja Abstract The ataxic mouse rolling Nagoya (RN) carries a missense mutation in the Cacna1a gene, encoding the pore-forming subunit of neuronal Cav2.1 (P/Q-type) Ca2+ channels. Besides being the predominant type of Cav channel in the cerebellum, Cav2.1 channels mediate acetylcholine (ACh) release at the peripheral neuromuscular junction (NMJ). Therefore, Cav2.1 dysfunction induced by the RN mutation may disturb ACh release at the NMJ. The dysfunction may resemble the situation in Lambert,Eaton myasthenic syndrome (LEMS), in which autoantibodies target Cav2.1 channels at NMJs, inducing severely reduced ACh release and resulting in muscle weakness. We tested neuromuscular function of RN mice and characterized transmitter release properties at their NMJs in diaphragm, soleus and flexor digitorum brevis muscles. Clinical muscle weakness and fatigue were demonstrated using repetitive nerve-stimulation electromyography, grip strength testing and an inverted grid hanging test. Muscle contraction experiments showed a compromised safety factor of neuromuscular transmission. In ex vivo electrophysiological experiments we found severely impaired ACh release. Compared to wild-type, RN NMJs had 50,75% lower nerve stimulation-evoked transmitter release, explaining the observed muscle weakness. Surprisingly, the reduction in evoked release was accompanied by an ,,3-fold increase in spontaneous ACh release. This synaptic phenotype suggests a complex effect of the RN mutation on different functional Cav2.1 channel parameters, presumably with a positive shift in activation potential as a prevailing feature. Taken together, our studies indicate that the gait abnormality of RN mice is due to a combination of ataxia and muscle weakness and that RN models aspects of the NMJ dysfunction in LEMS. [source] Mechanisms of ATP action on motor nerve terminals at the frog neuromuscular junctionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2005S. Grishin Abstract We have shown previously that ATP inhibits transmitter release at the neuromuscular junction through the action on metabotropic P2Y receptors coupled to specific second messenger cascades. In the present study we recorded K+ or Ca2+ currents in motor nerve endings or blocked K+ or Ca2+ channels in order to explore the nature of downstream presynaptic effectors. Endplate currents were presynaptically depressed by ATP. Blockers of Ca2+ -activated K+ -channels, such as iberiotoxin, apamin or tetraethylammonium, did not change the depressant action of ATP. By contrast, K+ channel blocker 4-aminopyridine (4-AP) and raised extracellular Ca2+ attenuated the effect of ATP. However, these effects of 4-AP and high Ca2+ were reversed by Mg2+, suggesting Ca2+ -dependence of the ATP action. Ba2+ promoted the depressant action of ATP as did glibenclamide, a blocker of ATP-sensitive K+ channels, or mild depolarization produced by 7.5 mm K+. None of the K+ channel blockers affected the depressant action of adenosine. Focal recording revealed that neither ATP nor adenosine affected the fast K+ currents of the motor nerve endings. However, unlike adenosine, ATP or UTP, an agonist of P2Y receptors, reversibly reduced the presynaptic Ca2+ -current. This effect was abolished by suramin, an antagonist of P2 receptors. Depressant effect of ATP on the endplate and Ca2+ -currents was mimicked by arachidonate, which precluded the action of ATP. ATP reduced acetylcholine release triggered by ionomycin or sucrose, suggesting inhibition of release machinery. Thus, the presynaptic depressant action of ATP is mediated by inhibition of Ca2+ channels and by mechanism acting downstream of Ca2+ entry. [source] Stabilizing effects of extracellular ATP on synaptic efficacy and plasticity in hippocampal pyramidal neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2005Eduardo D. Martín Abstract The role of adenosine triphosphate (ATP) as a neurotransmitter and extracellular diffusible messenger has recently received considerable attention because of its possible participation in the regulation of synaptic plasticity. However, the possible contribution of extracellular ATP in maintaining and regulating synaptic efficacy during intracellular ATP depletion is understudied. We tested the effects of extracellular ATP on excitatory postsynaptic currents (EPSCs) evoked in CA1 pyramidal neurons by Schaffer collateral stimulation. In the absence of intracellular ATP, EPSC rundown was neutralized when a low concentration of ATP (1 µm) was added to the extracellular solution. Adenosine and ATP analogues did not prevent the EPSC rundown. The P2 antagonists piridoxal-5,-phosphate-azophenyl 2,,4,-disulphonate (PPADS) and reactive blue-2, and the P1 adenosine receptor antagonist 8-cyclopentyltheophylline (CPT) had no detectable effects in cells depleted of ATP. However, the protective action of extracellular ATP on synaptic efficacy was blocked by extracellular application of the protein kinase inhibitors K252b and staurosporine. In contrast, K252b and staurosporine per se did not interfere with synaptic transmission in ATP loaded cells. Without intracellular ATP, bath-applied caffeine induced a transient (< 35 min) EPSC potentiation that was transformed into a persistent long-term potentiation (> 80 min) when 1 µm ATP was added extracellularly. An increased probability of transmitter release paralleled the long-term potentiation induced by caffeine, suggesting that it originated presynaptically. Therefore, we conclude that extracellular ATP may operate to maintain and regulate synaptic efficacy and plasticity in conditions of abnormal intracellular ATP depletion by phosphorylation of a surface protein substrate via activation of ecto-protein kinases. [source] Kv3 voltage-gated potassium channels regulate neurotransmitter release from mouse motor nerve terminalsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2004Ruth E. Brooke Abstract Voltage-gated potassium (Kv) channels are critical to regulation of neurotransmitter release throughout the nervous system but the roles and identity of the subtypes involved remain unclear. Here we show that Kv3 channels regulate transmitter release at the mouse neuromuscular junction (NMJ). Light- and electron-microscopic immunohistochemistry revealed Kv3.3 and Kv3.4 subunits within all motor nerve terminals of muscles examined [transversus abdominus, lumbrical and flexor digitorum brevis (FDB)]. To determine the roles of these Kv3 subunits, intracellular recordings were made of end-plate potentials (EPPs) in FDB muscle fibres evoked by electrical stimulation of tibial nerve. Tetraethylammonium (TEA) applied at low concentrations (0.05,0.5 mm), which blocks only a few known potassium channels including Kv3 channels, did not affect muscle fibre resting potential but significantly increased the amplitude of all EPPs tested. Significantly, this effect of TEA was still observed in the presence of the large-conductance calcium-activated potassium channel blockers iberiotoxin (25,150 nm) and Penitrem A (100 nm), suggesting a selective action on Kv3 subunits. Consistent with this, 15-µm 4-aminopyridine, which blocks Kv3 but not large-conductance calcium-activated potassium channels, enhanced evoked EPP amplitude. Unexpectedly, blood-depressing substance-I, a toxin selective for Kv3.4 subunits, had no effect at 0.05,1 µm. The combined presynaptic localization of Kv3 subunits and pharmacological enhancement of EPP amplitude indicate that Kv3 channels regulate neurotransmitter release from presynaptic terminals at the NMJ. [source] 5-HT inhibits N-type but not L-type Ca2+ channels via 5-HT1A receptors in lamprey spinal neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2003Russell H. Hill Abstract 5-HT is a potent modulator of locomotor activity in vertebrates. In the lamprey, 5-HT dramatically slows fictive swimming. At the neuronal level it reduces the postspike slow afterhyperpolarization (sAHP), which is due to apamin-sensitive Ca2+ -dependent K+ channels (KCa). Indirect evidence in early experiments suggested that the sAHP reduction results from a direct action of 5-HT on KCa channels rather than an effect on the Ca2+ entry during the action potential [Wallén et al., (1989) J. Neurophysiol., 61, 759,768]. In view of the characterization of different subtypes of Ca2+ channels with very different properties, we now reinvestigate if there is a selective action of 5-HT on a Ca2+ channel subtype in dissociated spinal neurons in culture. 5-HT reduced Ca2+ currents from high voltage activated channels. N-type, but not L-type, Ca2+ channel blockers abolished this 5-HT-induced reduction. It was also confirmed that 5-HT depresses Ca2+ currents in neurons, including motoneurons, in the intact spinal cord. 8-OH-DPAT, a 5-HT1A receptor agonist, also inhibited Ca2+ currents in dissociated neurons. After incubation in pertussis toxin, to block Gi/o proteins, 5-HT did not reduce Ca2+ currents, further indicating that the effect is caused by an activation of 5-HT1A receptors. As N-type, but not L-type, Ca2+ channels are known to mediate the activation of KCa channels and presynaptic transmitter release at lamprey synapses, the effects of 5-HT reported here can contribute to a reduction in both actions. [source] Rapid and long-term alterations of hippocampal GABAB receptors in a mouse model of temporal lobe epilepsyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2003Andrea Straessle Abstract Alterations of ,-aminobutyric acid (GABA)B receptor expression have been reported in human temporal lobe epilepsy (TLE). Here, changes in regional and cellular expression of the GABAB receptor subunits R1 (GBR1) and R2 (GBR2) were investigated in a mouse model that replicates major functional and histopathological features of TLE. Adult mice received a single, unilateral injection of kainic acid (KA) into the dorsal hippocampus, and GABAB receptor immunoreactivity was analysed between 1 day and 3 months thereafter. In control mice, GBR1 and GBR2 were distributed uniformly across the dendritic layers of CA1,CA3 and dentate gyrus. In addition, some interneurons were labelled selectively for GBR1. At 1 day post-KA, staining for both GBR1 and GBR2 was profoundly reduced in CA1, CA3c and the hilus, and no interneurons were visible anymore. At later stages, the loss of GABAB receptors persisted in CA1 and CA3, whereas staining increased gradually in dentate gyrus granule cells, which become dispersed in this model. Most strikingly, a subpopulation of strongly labelled interneurons reappeared, mainly in the hilus and CA3 starting at 1 week post-KA. In double-staining experiments, these cells were selectively labelled for neuropeptide Y. The number of GBR1-positive interneurons also increased contralaterally in the hilus. The rapid KA-induced loss of GABAB receptors might contribute to epileptogenesis because of a reduction in both presynaptic control of transmitter release and postsynaptic inhibition. In turn, the long-term increase in GABAB receptors in granule cells and specific subtypes of interneurons may represent a compensatory response to recurrent seizures. [source] Anandamide regulates neuropeptide release from capsaicin-sensitive primary sensory neurons by activating both the cannabinoid 1 receptor and the vanilloid receptor 1 in vitroEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2003Jatinder Ahluwalia Abstract The effect of anandamide, which activates both the cannabinoid 1 (CB1) receptor and the vanilloid receptor 1 (VR1), was studied on calcitonin gene-related peptide (CGRP) release from cultured primary sensory neurons, the majority of which coexpress the CB1 receptor and VR1. Concentrations of anandamide <,1 µm produced a small but significant CB1 receptor-mediated inhibition of basal CGRP release while higher concentrations induced VR1-mediated CGRP release. The excitatory effect of anandamide was potentiated by the CB1 receptor antagonist SR141716A. In the presence of SR141716A at concentrations <,100 nm, anandamide was equipotent with capsaicin in stimulating CGRP release. However, at higher concentrations anandamide produced more CGRP release than equimolar concentrations of capsaicin. Three and ten nanomolar anandamide inhibited the capsaicin-evoked CGRP release. In the presence of SR141716A, treatments which activated protein kinase A, protein kinase C and phospholipase C significantly potentiated the anandamide-evoked CGRP release at all anandamide concentrations. Although this potentiation was reduced when the CB1 receptor antagonist was omitted from the buffer, the CGRP release evoked by 300 nm and 1 µm anandamide was still significantly larger than that seen with nonpotentiated cells. These data indicate that anandamide may regulate CGRP release from capsaicin-sensitive primary sensory neurons in vivo, and that the net effect of anandamide on transmitter release from capsaicin-sensitive primary sensory neurons depends on the concentration of anandamide and the state of the CB1 receptor and VR1. These findings also suggest that anandamide could be one of the molecules responsible for the development of inflammatory heat hyperalgesia. [source] Differential Ca2+ -dependence of transmitter release mediated by P/Q- and N-type calcium channels at neonatal rat neuromuscular junctionsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2002Marcelo D. Rosato-Siri Abstract N- and P/Q-type voltage dependent calcium channels (VDCCs) mediate transmitter release at neonatal rat neuromuscular junction (NMJ). Thus the neonatal NMJ allows an examination of the coupling of different subtypes of VDCCs to the release process at a single synapse. We studied calcium dependence of transmitter release mediated by each channel by blocking with ,-conotoxin GVIA the N-type channel or with ,-agatoxin IVA the P/Q-type channel while changing the extracellular calcium concentration ([Ca2+]o). Transmitter release mediated by P/Q-type VDCCs showed steeper calcium dependence than N-type mediated release (average slope 3.6 ± 0.09 vs. 2.6 ± 0.03, respectively). Loading the nerve terminals with 10 µm BAPTA-AM in the extracellular solution reduced transmitter release and occluded the blocking effect of ,-conotoxin GVIA (blockade ,2 ± 9%) without affecting the action of ,-agatoxin IVA (blockade 85 ± 4%). Both VDCC blockers were able to reduce the amount of facilitation produced by double-pulse stimulation. In these conditions facilitation was restored by increasing [Ca2+]o. The facilitation index (fi) was also reduced by loading nerve terminals with 10 µm BAPTA-AM (fi = 1.2 ± 0.1). The control fi was 2.5 ± 0.1. These results show that P/Q-type VDCCs were more efficiently coupled to neurotransmitter release than were N-type VDCCs at the neonatal neuromuscular junction. This difference could be accounted for by a differential location of these channels at the release site. In addition, our results indicate that space,time overlapping of calcium domains was required for facilitation. [source] Nerve growth factor expression in parasympathetic neurons: regulation by sympathetic innervationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2000Wohaib Hasan Abstract Interactions between sympathetic and parasympathetic nerves are important in regulating visceral target function. Sympathetic nerves are closely apposed to, and form functional synapses with, parasympathetic axons in many effector organs. The molecular mechanisms responsible for these structural and functional interactions are unknown. We explored the possibility that Nerve Growth Factor (NGF) synthesis by parasympathetic neurons provides a mechanism by which sympathetic,parasympathetic interactions are established. Parasympathetic pterygopalatine ganglia NGF-gene expression was examined by in situ hybridization and protein content assessed by immunohistochemistry. Under control conditions, NGF mRNA was present in ,,60% and NGF protein was in 40% of pterygopalatine parasympathetic neurons. Peripheral parasympathetic axons identified by vesicular acetylcholine transporter-immunoreactivity also displayed NGF immunoreactivity. To determine if sympathetic innervation regulates parasympathetic NGF expression, the ipsilateral superior cervical ganglion was excised. Thirty days postsympathectomy, the numbers of NGF mRNA-positive neurons were decreased to 38% and NGF immunoreactive neurons to 15%. This reduction was due to a loss of sympathetic nerve impulse activity, as similar reductions were achieved when superior cervical ganglia were deprived of preganglionic afferent input for 40 days. These findings provide evidence that normally NGF is synthesized by parasympathetic neurons and transported anterogradely to fibre terminals, where it may be available to sympathetic axons. Parasympathetic NGF expression, in turn, is augmented by impulse activity within (and presumably transmitter release from) sympathetic axons. It is suggested that parasympathetic NGF synthesis and its modulation by sympathetic innervation provides a molecular basis for establishment and maintenance of autonomic axo-axonal synaptic interactions. [source] Neurobehavioral abnormalities in the dysbindin-1 mutant, sandy, on a C57BL/6J genetic backgroundGENES, BRAIN AND BEHAVIOR, Issue 4 2009M. M. Cox Sandy mice have a deletion mutation in the gene encoding dysbindin-1, Dtnbp1, with consequent reduction of the protein in heterozygotes and its loss in homozygotes. The sandy mouse thus serves as an animal model of dysbindin-1 function. As this protein is concentrated in synaptic tissue and affects transmitter release, it may affect neuronal processes that mediate behavior. To investigate the neurobehavioral effects of the Dtnbp1 mutation, we studied littermate sandy and wild-type controls on a C57BL/6J genetic background. The three animal groups were indistinguishable in their external physical characteristics, sensorimotor skills and indices of anxiety-like behaviors. In the open field, however, homozygous animals were hyperactive and appeared to show less habituation to the initially novel environment. In the Morris water maze, homozygous animals displayed clear deficits in spatial learning and memory with marginal deficits in visual association learning. Apart from the last mentioned deficits, these abnormalities are consistent with hippocampal dysfunction and in some cases with elevated dopaminergic transmission via D2 dopamine receptors. As similar deficits in spatial learning and memory have been found in schizophrenia, where decreased dysbindin-1 has been found in the hippocampus, the sandy mouse may also model certain aspects of cognition and behavior relevant to schizophrenia. [source] Axon-glia communication evokes calcium signaling in olfactory ensheathing cells of the developing olfactory bulbGLIA, Issue 4 2007Anne Rieger Abstract Olfactory ensheathing cells (OECs) accompany receptor axons in the olfactory nerve and promote axonal growth into the central nervous system. The mechanisms underlying the communication between axons and OECs, however, have not been studied in detail yet. We investigated the effect of activity-dependent neuronal transmitter release on Ca2+ signaling of OECs in acute mouse olfactory bulb slices using confocal Ca2+ imaging. TTX-sensitive axonal activity upon electrical nerve stimulation triggers a rise in cytosolic Ca2+ in OECs, which can be mimicked by application of DHPG, an agonist of metabotropic glutamate receptors (mGluRs). Both stimulation- and DHPG-induced Ca2+ transients in OECs were abolished by depletion of intracellular Ca2+ stores with cyclopiazonic acid (CPA). The mGluR1 -specific antagonist CPCCOEt completely inhibited DHPG-evoked Ca2+ transients, but reduced stimulation-induced Ca2+ transients only partly, suggesting the involvement of another neurotransmitter. Application of ATP evoked CPA-sensitive Ca2+ transients in OECs, which were inhibited by the P2Y1 -specific antagonist MRS2179. Co-application of CPCCOEt and MRS2179 almost completely blocked the stimulation-induced Ca2+ transients, indicating that they were mediated by mGluR1 and P2Y1 receptors. Our results show that OECs are able to respond to olfactory nerve activity with an increase in cytosolic Ca2+ due to glutamate and ATP release. © 2006 Wiley-Liss, Inc. [source] Information processing and transmission in glia: Calcium signaling and transmitter releaseGLIA, Issue 7 2006Joachim W. Deitmer No abstract is available for this article. [source] Role of glial amino acid transporters in synaptic transmission and brain energeticsGLIA, Issue 3 2004Païkan Marcaggi Abstract This article reviews how the uptake of neurotransmitter by glial amino acid transporters limits the spatial spread of transmitter to preserve the independent operation of nearby synapses, temporally shapes postsynaptic currents, and regulates the effects of tonic transmitter release. We demonstrate the importance of amino acid uptake and recycling mechanisms for preventing the loss of energetically costly neurotransmitter from the brain, and also examine the suggestion that glutamate uptake into glia plays a key role in regulating the energy production of the brain. Finally, we assess the role of glial amino acid transporters in transmitter recycling pathways. © 2004 Wiley-Liss, Inc. [source] Ultrastructural correlates of synapse withdrawal at axotomized neuromuscular junctions in mutant and transgenic mice expressing the Wld geneJOURNAL OF ANATOMY, Issue 3 2003Thomas H. Gillingwater Abstract We carried out an ultrastructural analysis of axotomized synaptic terminals in Wlds and Ube4b/Nmnat (Wld) transgenic mice, in which severed distal axons are protected from Wallerian degeneration. Previous studies have suggested that axotomy in juvenile (< 2 months) Wld mice induced a progressive nerve terminal withdrawal from motor endplates. In this study we confirm that axotomy-induced terminal withdrawal occurs in the absence of all major ultrastructural characteristics of Wallerian degeneration. Pre- and post-synaptic membranes showed no signs of disruption or fragmentation, synaptic vesicle densities remained at pre-axotomy levels, the numbers of synaptic vesicles clustered towards presynaptic active zones did not diminish, and mitochondria retained their membranes and cristae. However, motor nerve terminal ultrastructure was measurably different following axotomy in Wld transgenic 4836 line mice, which strongly express Wld protein: axotomized presynaptic terminals were retained, but many were significantly depleted of synaptic vesicles. These findings suggest that the Wld gene interacts with the mechanisms regulating transmitter release and vesicle recycling. [source] Pregnenolone sulfate induces NMDA receptor dependent release of dopamine from synaptic terminals in the striatumJOURNAL OF NEUROCHEMISTRY, Issue 2 2008Matthew T. Whittaker Abstract Neuromodulators that alter the balance between lower-frequency glutamate-mediated excitatory and higher-frequency GABA-mediated inhibitory synaptic transmission are likely to participate in core mechanisms for CNS function and may contribute to the pathophysiology of neurological disorders such as schizophrenia and Alzheimer's disease. Pregnenolone sulfate (PS) modulates both ionotropic glutamate and GABAA receptor mediated synaptic transmission. The enzymes necessary for PS synthesis and degradation are found in brain tissue of several species including human and rat, and up to 5 nM PS has been detected in extracts of postmortem human brain. Here, we ask whether PS could modulate transmitter release from nerve terminals located in the striatum. Superfusion of a preparation of striatal nerve terminals comprised of mixed synaptosomes and synaptoneurosomes with brief-duration (2 min) pulses of 25 nM PS demonstrates that PS increases the release of newly accumulated [3H]dopamine ([3H]DA), but not [14C]glutamate or [3H]GABA, whereas pregnenolone is without effect. PS does not affect dopamine transporter (DAT) mediated uptake of [3H]DA, demonstrating that it specifically affects the transmitter release mechanism. The PS-induced [3H]DA release occurs via an NMDA receptor (NMDAR) dependent mechanism as it is blocked by D-2-amino-5-phosphonovaleric acid. PS modulates DA release with very high potency, significantly increasing [3H]DA release at PS concentrations as low as 25 pM. This first report of a selective direct enhancement of synaptosomal dopamine release by PS at picomolar concentrations via an NMDAR dependent mechanism raises the possibility that dopaminergic axon terminals may be a site of action for this neurosteroid. [source] Calcium channel subtypes differentially regulate fusion pore stability and expansionJOURNAL OF NEUROCHEMISTRY, Issue 4 2007Alvaro O. Ardiles Abstract Various studies have focused in the relative contribution of different voltage-activated Ca2+ channels (VACC) to total transmitter release. However, how Ca2+ entry through a given VACC subtype defines the pattern of individual exocytotic events remains unknown. To address this question, we have used amperometry in bovine chromaffin cells. L, N, and P/Q channels were individually or jointly blocked with furnidipine, ,-conotoxin GVIA, ,-agatoxin IVA, or ,-conotoxin MVIIC. The three channel types contributed similarly to cytosolic Ca2+ signals induced by 70 mmol/L K+. However, they exhibited different contributions to the frequency of exocytotic events and they were shown to differently regulate the final steps of the exocytosis. When compared with the other VACC subtypes, Ca2+ entry through P/Q channels effectively induced exocytosis, it decreased fusion pore stability and accelerated its expansion. Conversely, Ca2+ entry through N channels was less efficient in inducing exocytotic events, also slowing fusion pore expansion. Finally, Ca2+ entry through L channels inefficiently induced exocytosis, and the individual blockade of this channel significantly modified fusion pore dynamics. The distance between a given VACC subtype and the release sites could account for the differential effects of the distinct VACC on the fusion pore dynamics. [source] Loss of SNAP-25 and rabphilin 3a in sensory-motor cortex in Huntington's diseaseJOURNAL OF NEUROCHEMISTRY, Issue 1 2007Ruben Smith Abstract Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG-expansion in the gene encoding the protein huntingtin. The disease is characterized by progressive motor disturbances, cognitive defects, dementia, and weight loss. Using western blotting and immunohistochemistry we have assessed the expression levels and patterns of a number of proteins involved in neurotransmitter release in post-mortem frontal cortex samples from 10 HD cases with different disease grades. We report a loss of the soluble N -ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein, synaptosome-associated protein 25 (SNAP 25) in HD brains of grades I,IV. Moreover, in brains of grade III and IV we found a reduction in rabphilin 3a, a protein involved in vesicle docking and recycling. These losses appear to be specific and not due to a general loss of synapses in the HD cortex. Thus, levels of synaptobrevin II, syntaxin 1, rab3a or synaptophysin are unaltered in the same patient samples. SNAP 25 and rabphilin 3a are crucial for neurotransmitter release. Therefore, we suggest that a deficient pre-synaptic transmitter release may underlie some of the symptoms of HD. [source] Regulation of Neurotransmitter Release by Metabotropic Glutamate ReceptorsJOURNAL OF NEUROCHEMISTRY, Issue 3 2000Jayne Cartmell Abstract: The G protein-coupled metabotropic glutamate (mGlu) receptors are differentially localized at various synapses throughout the brain. Depending on the receptor subtype, they appear to be localized at presynaptic and/or postsynaptic sites, including glial as well as neuronal elements. The heterogeneous distribution of these receptors on glutamate and nonglutamate neurons/cells thus allows modulation of synaptic transmission by a number of different mechanisms. Electrophysiological studies have demonstrated that the activation of mGlu receptors can modulate the activity of Ca2+ or K+ channels, or interfere with release processes downstream of Ca2+ entry, and consequently regulate neuronal synaptic activity. Such changes evoked by mGlu receptors can ultimately regulate transmitter release at both glutamatergic and nonglutamatergic synapses. Increasing neurochemical evidence has emerged, obtained from in vitro and in vivo studies, showing modulation of the release of a variety of transmitters by mGlu receptors. This review addresses the neurochemical evidence for mGlu receptor-mediated regulation of neurotransmitters, such as excitatory and inhibitory amino acids, monoamines, and neuropeptides. [source] A2A Adenosine Receptor Facilitation of Neuromuscular TransmissionJOURNAL OF NEUROCHEMISTRY, Issue 6 2000Influence of Stimulus Paradigm on Calcium Mobilization Abstract: The influence of stimulus pulse duration on calcium mobilization triggering facilitation of evoked [3H]acetylcholine ([3H]ACh) release by the A2A adenosine receptor agonist CGS 21680C was studied in the rat phrenic nerve-hemidiaphragm. The P-type calcium channel blocker ,-agatoxin IVA (100 nM) decreased [3H]ACh release evoked with pulses of 0.04-ms duration, whereas nifedipine (1 ,M) inhibited transmitter release with pulses of 1-ms duration. Depletion of intracellular calcium stores by thapsigargin (2 ,M) decreased [3H]ACh release evoked by pulses of 1 ms, an effect observed even in the absence of extracellular calcium. With short (0.04-ms) stimulation pulses, when P-type calcium influx triggered transmitter release, facilitation of [3H]ACh release by CGS 21680C (3 nM) was attenuated by both thapsigargin (2 ,M) and nifedipine (1 ,M). With longer stimuli (1 ms), a situation in which both thapsigargin-sensitive internal stores and L-type channels are involved in ACh release, pretreatment with either ,-agatoxin IVA (100 nM) or nifedipine (1 ,M) reduced the facilitatory effect of CGS 21680C (3 nM). The results suggest that A2A receptor activation facilitates ACh release from motor nerve endings through alternatively mobilizing the available calcium pools (thapsigargin-sensitive internal stores and/or P- or L-type channels) that are not committed to the release process in each stimulation condition. [source] Target-dependent modulation of neurotransmitter release in cultured Helix neurons involves adhesion moleculesJOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2001Mirella Ghirardi Abstract The secretory capabilities of the serotonergic neuron C1 of cerebral ganglion of Helix pomatia were markedly reduced when it was cultured in contact with the wrong target neuron, C3. When the neuron B2, one of its physiological targets, was micromanipulated within the network made of intermingled neurites originating from the axonal stumps of both C1 and C3 neurons, C1 increased the amount of the evoked transmitter release, which, after 30 min, reached the level observed when cocultured with the appropriate target. The removal of the appropriate target brought C1 back to the low release condition. By imaging C1 neurites with a fluorescent dye, morphological changes involving a local increase in the number of varicosities could be observed as early as 30 min after contact with the appropriate target. Monoclonal antibody 4E8 against apCAM, a family of Aplysia adhesion molecules, recognizes apCAM-like molecules of the Helix central nervous system on immunocytochemistry and Western blot analysis. The contact with the appropriate target previously incubated in a 4E8 solution, which did not interfere with its capacity to respond to serotonin, failed to increase the transmitter release of C1 cocultured in the presence of the wrong target, C3. These results suggest that the apCAM-like antigens bound to the target membrane participate in the molecular processes responsible for the assembly of the "release machinery" present in the functional presynaptic structure. J. Neurosci. Res. 65:111,120, 2001. © 2001 Wiley-Liss, Inc. [source] Recent Advances in Intravesical Treatment of Overactive BladderLUTS, Issue 1 2009Hann-Chorng KUO The traditional medication for overactive bladder (OAB) is antimuscarinic agent, which targets muscarinic receptors. Recent investigations have revealed that muscarinic receptors are present in the urothelium and suburothelial sensory fibers, as well as in the detrusor. Urothelial dysfunction and abnormality of sensory receptor expression or transmitter release in suburothelial nerves could contribute to OAB refractory to antimuscarinics. Intravesical treatment to inhibit abnormal receptor expression or transmitter release in the sensory nerve terminals in the suburothelial space might provide beneficial therapeutic effects in the treatment of OAB. Intravesical resiniferatoxin (RTX) instillation and intravesical botulinum toxin A (BoNT-A) injection are two promising treatment alternatives for refractory OAB. RTX at a high dose may cause undesired adverse events, such as hematuria, bladder pain or autonomic dysreflexia. RTX at a low concentration can decrease sensory urgency without influencing detrusor contractility; multiple instillations of low-dose RTX may be required to achieve adequate desensitization of OAB. BoNT-A, however, has a beneficial effect on detrusor contractility and causes large post-void residual after injection in some patients. Therefore, careful dosage and injection site adjustment is mandatory to achieve satisfactory results using intravesical therapy. [source] Presynaptic modulation of cholinergic and non-cholinergic fast synaptic transmission in the myenteric plexus of guinea pig ileumNEUROGASTROENTEROLOGY & MOTILITY, Issue 3 2004K. J. LePard Abstract, These studies investigated receptors modulating release of mediators of fast excitatory postsynaptic potentials (fEPSPs) in guinea pig ileum myenteric plexus using electrophysiological methods. Fast EPSPs inhibited by >95% by hexamethonium (100 ,mol L,1) were cholinergic; mixed fEPSPs were inhibited <95% by hexamethonium. Non-cholinergic fEPSPs were studied in the presence of hexamethonium. The ,2-adrenergic receptor agonist UK 14304 inhibited cholinergic (maximum inhibition = 76%, EC50 = 18 nmol L,1), mixed (81%, 21 nmol L,1) and non-cholinergic (76%, 44 nmol L,1) fEPSPs equally. The 5-HT1 receptor agonist 5-carboxamidotryptamine inhibited cholinergic, mixed and non-cholinergic fEPSPs equally. Renzapride, increased non-cholinergic (33%) less than mixed (97%, 13 ,mol L,1) fEPSPs. Renzapride inhibited the purely cholinergic fEPSPs (,29%) but potentiated the cholinergic component of mixed fEPSPs (39%). Prucalopride potentiated all fEPSPs equally (30,33%). 5-HT (0.1 ,mol L,1) induced potentiation of cholinergic (75%), mixed (97%) and non-cholinergic (84%) fEPSPs was not statistically different. The potentiating effects of renzapride and 5-HT on fEPSPs were inhibited by the 5-HT4 receptor antagonist, SB 204070 (10 nmol L,1). Renzapride (0.3 ,mol L,1) blocked 5-HT-induced increases in cholinergic fEPSPs. ,2-Adrenergic and 5-HT1 receptors mediate inhibition of transmitter release from cholinergic and mixed terminals. 5-HT and prucalopride, acting at 5-HT4 receptors, facilitate all fEPSPs; renzapride facilitates the cholinergic and non-cholinergic components of mixed fEPSPs but not purely cholinergic fEPSPs. Cholinergic synapses may express few 5-HT4 receptors or a renzapride-insensitive 5-HT4 receptor isoform. [source] Differences in circular muscle contraction and peristaltic motor inhibition caused by tachykinin NK1 receptor agonists in the guinea-pig small intestineNEUROGASTROENTEROLOGY & MOTILITY, Issue 2 2000Shahbazian The tachykinin NK1 receptor agonist substance P methyl ester (SPOME) impedes intestinal peristalsis by releasing nitric oxide (NO) from inhibitory motor neurones. Since NK1 receptor agonists differ in their receptor interaction, we set out to compare a range of NK1 receptor agonists including SPOME, septide and GR-73 632 in their effects on propulsive peristalsis and circular muscle activity in the guinea-pig isolated small intestine. SPOME (100,300 n M) inhibited peristalsis by a rise of the pressure threshold at which peristaltic waves were triggered, whereas septide and GR-73 632 (30,300 n M) interrupted peristalsis by causing circular muscle spasms. Separate experiments showed that all three NK1 receptor agonists caused contraction of the circular muscle, which was enhanced by the NO synthase inhibitor NG -nitro- L -arginine methyl ester (300 ,M) and the P2X purinoceptor antagonist suramin (300 ,M). In contrast, tetrodotoxin (300 n M) augmented the contractile effect of septide and GR-73 632 but not that of SPOME. It is concluded that the motor response to NK1 receptor agonists involves release of NO and adenosine triphosphate from inhibitory motor neurones. However, the NK1 receptor agonists differ in the mechanism by which they cause inhibitory transmitter release, which corresponds to differences in their antiperistaltic action. [source] | |||||||||||||||||||||||||