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Synapses
Kinds of Synapses Selected AbstractsVisual Signals in the Retina: From Photons to SynapsesEXPERIMENTAL PHYSIOLOGY, Issue 1 2000Leon Lagnado The ability to see the world around us is an immediate and striking example of the abilities of the nervous system, and perhaps for this reason, vision is one of the most intensively studied aspects of brain function (Hubel, 1995). This paper examines some of the earliest steps in vision occurring in the retina (Dowling, 1987; Rodieck, 1998). [source] Increased Galanin Synapses onto Activated Gonadotropin-Releasing Hormone Neuronal Cell Bodies in Normal Female Mice and in Functional Preoptic Area Grafts in Hypogonadal MiceJOURNAL OF NEUROENDOCRINOLOGY, Issue 6 2002G. Rajendren Abstract Galanin synaptic input onto gonadotropin-releasing hormone (GnRH) neuronal cell bodies was analysed in female mice using the presynaptic vesicle-specific protein, synaptophysin (Syn) as a marker. In the first experiment, forebrain sections from normal ovariectomized ovarian steroid-primed mice exhibiting a surge of luteinizing hormone were processed for immunohistochemical labelling for GnRH, synaptophysin, galanin and Fos. Two representative sections from each brain, one passing through the anterior septum (anterior section) and the other through the organum vasculosum lamina terminalis-preoptic area (posterior section), were analysed under the confocal microscope. None of the GnRH cells analysed in the anterior sections were Fos immunoreactive (IR) or received input from galanin-IR fibres. In contrast, the majority of GnRH cells in the posterior sections analysed were Fos-positive. The number of galanin synapses onto the Fos-positive GnRH cells was significantly higher than that in the Fos-negative cells in this area of the brain, even though the number of Syn-IR appositions was comparable to each other. Transplantation of preoptic area (POA) into the third cerebral ventricle of hypogonadal (HPG) mice corrects deficits in the reproductive system. In the second experiment, synaptic input to GnRH cells was compared between HPG/POA mice with (functional graft) or without (nonfunctional graft) gonadal development. The mean numbers of Syn-IR appositions and galanin synapses per GnRH cell and the proportion of GnRH cells with galanin input were significantly higher in the functional than in the nonfunctional grafts. The results suggest that galanin can act directly on the GnRH cell bodies and may have an important regulatory role on the GnRH system. [source] Synaptic structure, distribution, and circuitry in the central nervous system of the locust and related insectsMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2002Alan Hugh David Watson Abstract The Orthopteran central nervous system has proved a fertile substrate for combined morphological and physiological studies of identified neurons. Electron microscopy reveals two major types of synaptic contacts between nerve fibres: chemical synapses (which predominate) and electrotonic (gap) junctions. The chemical synapses are characterized by a structural asymmetry between the pre- and postsynaptic electron dense paramembranous structures. The postsynaptic paramembranous density defines the extent of a synaptic contact that varies according to synaptic type and location in single identified neurons. Synaptic bars are the most prominent presynaptic element at both monadic and dyadic (divergent) synapses. These are associated with small electron lucent synaptic vesicles in neurons that are cholinergic or glutamatergic (round vesicles) or GABAergic (pleomorphic vesicles). Dense core vesicles of different sizes are indicative of the presence of peptide or amine transmitters. Synapses are mostly found on small-diameter neuropilar branches and the number of synaptic contacts constituting a single physiological synapse ranges from a few tens to several thousand depending on the neurones involved. Some principles of synaptic circuitry can be deduced from the analysis of highly ordered brain neuropiles. With the light microscope, synaptic location can be inferred from the distribution of the presynaptic protein synapsin I. In the ventral nerve cord, identified neurons that are components of circuits subserving known behaviours, have been studied using electrophysiology in combination with light and electron microscopy and immunocytochemistry of neuroactive compounds. This has allowed the synaptic distribution of the major classes of neurone in the ventral nerve cord to be analysed within a functional context. Microsc. Res. Tech. 56:210,226, 2002. © 2002 Wiley-Liss, Inc. [source] Synaptic connections of cholinergic antennal lobe relay neurons innervating the lateral horn neuropile in the brain of Drosophila melanogasterTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 3 2003Kouji Yasuyama Abstract Presumed cholinergic projection neurons (PNs) in the brain of the fruit fly Drosophila melanogaster, immunoreactive to choline acetyltransferase (ChAT), convey olfactory information between the primary sensory antennal lobe neuropile and the mushroom body calyces, and finally terminate in the lateral horn (LH) neuropile. The texture and synaptic connections of ChAT PNs in the LH and, comparatively, in the smaller mushroom body calyces were investigated by immuno light and electron microscopy. The ChAT PN fibers of the massive inner antennocerebral tract (iACT) extend into all portions of the LH, distributing in a nonrandom fashion. Immunoreactive boutons accumulate in the lateral margins of the LH, whereas the more proximal LH exhibits less intense immunolabeling. Boutons with divergent presynaptic sites, unlabeled as well as ChAT-immunoreactive, appear to be the preponderant mode of synaptic input throughout the LH. Synapses of ChAT-labeled fibers appear predominantly as divergent synaptic boutons (diameters 1,3 ,m), connected to unlabeled postsynaptic profiles, or alternatively as a minority of tiny postsynaptic spines (diameters 0.05,0.5 ,m) among unlabeled profiles. Together these spines encircle unidentified presynaptic boutons of interneurons which occupy large areas of the LH. Thus, synaptic circuits in the LH differ profoundly from those of the PNs in the mushroom body calyx, where ChAT spines have not been encountered. Synaptic contacts between LH ChAT elements were not observed. The synaptic LH neuropile may serve as an output area for terminals of the ChAT PNs, their presynaptic boutons providing input to noncholinergic relay neurons. The significance of the postsynaptic neurites of the ChAT PNs is discussed; either local or other interneurons might connect the ChAT PNs within the LH, or PNs might receive inputs arising from outside the LH. J. Comp. Neurol. 466:299,315, 2003. © 2003 Wiley-Liss, Inc. [source] Synapses on NG2-expressing progenitors in the brain: multiple functions?THE JOURNAL OF PHYSIOLOGY, Issue 16 2008Vittorio Gallo Progenitor cells expressing the proteoglycan NG2 represent approximately 5% of the total cells in the adult brain, and are found both in grey and white matter regions where they give rise to oligodendrocytes. The finding that these cells receive synaptic contacts from excitatory and inhibitory neurons has not only raised major interest in the possible roles of these synapses, but also stimulated further research on the developmental and cellular functions of NG2-expressing (NG2+) progenitors themselves in the context of neural circuit physiology. Here we review recent findings on the functional properties of the synapses on NG2+ cells in grey and white matter regions of the brain. In this review article we make an attempt to integrate current knowledge on the cellular and developmental properties of NG2+ progenitors with the functional attributes of their synapses, in order to understand the physiological relevance of neuron,NG2+ progenitor signal transmission. We propose that, although NG2+ progenitors receive synaptic contact in all brain regions where they are found, their synapses might have different developmental and functional roles, probably reflecting the distinct functions of NG2+ progenitors in the brain. [source] Modulation and metamodulation of synapses by adenosineACTA PHYSIOLOGICA, Issue 2 2010J. A. Ribeiro Abstract The presence of adenosine in all nervous system cells (neurones and glia) together with its intensive release following insults makes adenosine as a sort of ,regulator' of synaptic communication, leading to the homeostatic coordination of brain function. Besides the direct actions of adenosine on the neurosecretory mechanisms, to tune neurotransmitter release, adenosine receptors interact with other receptors as well as with transporters as part of its attempt to fine-tune synaptic transmission. This review will focus on examples of the different ways adenosine can use to modulate or metamodulate synapses, in other words, to trigger or brake the action of some neurotransmitters and neuromodulators, to cross-talk with other G protein-coupled receptors, with ionotropic receptors and with receptor kinases as well as with transporters. Most of these interactions occur through A2A receptors, which in spite of their low density in some brain areas, such as the hippocampus, may function as amplifiers of the signalling of other mediators at synapses. [source] Orexins/hypocretins control bistability of hippocampal long-term synaptic plasticity through co-activation of multiple kinasesACTA PHYSIOLOGICA, Issue 3 2010O. Selbach Abstract Aim:, Orexins/hypocretins (OX/Hcrt) are hypothalamic neuropeptides linking sleep,wakefulness, appetite and neuroendocrine control. Their role and mechanisms of action on higher brain functions, such as learning and memory, are not clear. Methods:, We used field recordings of excitatory post-synaptic potentials (fEPSP) in acute mouse brain slice preparations to study the effects of orexins and pharmacological inhibitors of multiple kinases on long-term synaptic plasticity in the hippocampus. Results:, Orexin-A (OX-A) but not orexin-B (OX-B) induces a state-dependent long-term potentiation of synaptic transmission (LTPOX) at Schaffer collateral-CA1 synapses in hippocampal slices from adult (8- to 12-week-old) mice. In contrast, OX-A applied to slices from juvenile (3- to 4-week-old) animals causes a long-term depression (LTDOX) in the same pathway. LTPOX is blocked by pharmacological inhibition of orexin receptor-1 (OX1R) and plasticity-related kinases, including serine/threonine- (CaMKII, PKC, PKA, MAPK), lipid- (PI3K), and receptor tyrosine kinases (Trk). Inhibition of OX1R, CaMKII, PKC, PKA and Trk unmasks LTDOX in adult animals. Conclusion:, Orexins control not only the bistability of arousal states and threshold for appetitive behaviours but, in an age- and kinase-dependent manner, also bidirectional long-term synaptic plasticity in the hippocampus, providing a possible link between behavioural state and memory functions. [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] Neuronismo y reticulismo: neuronal,glial circuits unify the reticular and neuronal theories of brain organizationACTA PHYSIOLOGICA, Issue 1 2009A. Verkhratsky Abstract The neuronal doctrine, which shaped the development of neuroscience, was born from a long-lasting struggle between reticularists, who assumed internal continuity of neural networks and neuronists, who defined the brain as a network of physically separated cellular entities, defined as neurones. Modern views regard the brain as a complex of constantly interacting cellular circuits, represented by neuronal networks embedded into internally connected astroglial syncytium. The neuronal,glial circuits endowed with distinct signalling cascades form a ,diffuse nervous net' suggested by Golgi, where millions of synapses belonging to very different neurones are integrated first into neuronal,glial,vascular units and then into more complex structures connected through glial syncytium. These many levels of integration, both morphological and functional, presented by neuronal,glial circuitry ensure the spatial and temporal multiplication of brain cognitive power. [source] Could chronic pain and spread of pain sensation be induced and maintained by glial activation?ACTA PHYSIOLOGICA, Issue 1-2 2006E. Hansson Abstract An injury often starts with acute physiological pain, which becomes inflammatory or neuropathic, and may sometimes become chronic. It has been proposed recently that activated glial cells, astrocytes and microglia within the central nervous system could maintain the pain sensation even after the original injury or inflammation has healed, and convert it into chronic by altering neuronal excitability. Glial cell activation has also been proposed to be involved in the phenomenon of spread of pain sensation ipsilaterally or to the contralateral side (i.e. mirror image pain). Substance P and calcitonin gene-related peptide, released due to an inflammatory process, interact with the endothelial cells of the blood,spinal cord and blood,brain barriers. The barriers open partially and substances may influence adjacent glial cells. Such substances are also released from neurones carrying the ,pain message' all the way from the injury to the cerebral cortex. Pro-inflammatory cytokines may be released from the microglial cells, and astroglial Ca2+ -transients or oscillations may spread within the astroglial networks. One theory is that Ca2+ -oscillations could facilitate the formation of new synapses. These new synapses could establish neuronal contacts for maintaining and spreading the pain sensation. If this theory holds true, it is possible that Ca2+ waves, production of cytokines and growth factors could be modified by selective anti-inflammatory drugs to achieve a balance in the activities of the different intercellular and intracellular processes. This paper reviews current knowledge about glial mechanisms underlying the phenomena of chronic pain and spread of the pain sensation. [source] Assembling microtubules disintegrate the postsynaptic density in vitroCYTOSKELETON, Issue 1 2007Li-Ping Lo Abstract The postsynaptic density (PSD), a disk-shaped protein aggregation of several hundred nm in diameter, plays important roles in the signal transduction and molecular organization of the excitatory synapses in mammalian CNS. The PSD resides in the microfilament-enriched cytoplasm of dendritic spines where the transient appearance of microtubules has been reported. When PSD isolated from porcine brain was incubated with polymerizing ,,,-tubulins, its turbidity became greater than that of the original PSD, suggesting that the PSD's structure was altered upon incubating with assembling microtubules. By transmission electron microscopy, smaller PSD fragments and several novel structures, including holes and finger-like extensions, were found in the PSD after incubation with assembling microtubules, but not in the original PSD or in the PSD incubated with ,,,-tubulins pretreated with vincristine. The results suggest that the interactions with assembling microtubules may result in the formation of holes in the PSD, and the rupture of these holes subsequently leads to the formation of smaller PSD fragments. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source] How does premenstrual dysphoric disorder relate to depression and anxiety disorders?DEPRESSION AND ANXIETY, Issue 3 2003Mikael Landén M.D., Ph.D. Abstract Premenstrual dysphoric disorder (PMDD) is a severe variant of premenstrual syndrome that afflicts approximately 5% of all women of fertile age. The hallmark of this condition is the surfacing of symptoms during the luteal phase of the menstrual cycle, and the disappearance of symptoms shortly after the onset of menstruation. Whereas many researchers have emphasized the similarities between PMDD and anxiety disorders, and in particular panic disorder, others have suggested that PMDD should be regarded as a variant of depression. Supporting both these notions, the treatment of choice for PMDD, the serotonin reuptake inhibitors (SRIs), is also first line of treatment for depression and for most anxiety disorders. In this review, the relationship between PMDD on the one hand, and anxiety and depression on the other, is being discussed. Our conclusion is that PMDD is neither a variant of depression nor an anxiety disorder, but a distinct diagnostic entity, with irritability and affect lability rather than depressed mood or anxiety as most characteristic features. The clinical profile of SRIs when used for PMDD, including a short onset of action, suggests that this effect is mediated by other serotonergic synapses than the antidepressant and anti-anxiety effects of these drugs. Although we hence suggest that PMDD should be regarded as a distinct entity, it should be emphasized that this disorder does display intriguing similarities with other conditions, and in particular with panic disorder, which should be the subject of further studies. Also, the possibility that there are subtypes of PMDD more closely related to depression, or anxiety disorders, than the most common form of the syndrome, should not be excluded. Depression and Anxiety 17:122,129, 2003. © 2003 Wiley-Liss, Inc. [source] Advanced microscopic imaging methods to investigate cortical development and the etiology of mental retardationDEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 4 2005Tarik F. Haydar Abstract Studies on human patients and animal models of disease have shown that disruptions in prenatal and early postnatal brain development are a root cause of mental retardation. Since proper brain development is achieved by a strict spatiotemporal control of neurogenesis, cell migration, and patterning of synapses, abnormalities in one or more of these events during prenatal development can lead to cognitive dysfunction after birth. Many of underlying causes of mental retardation must therefore be studied in developing brains. To aid in this research, live imaging using laser scanning microscopy (LSM) has recently allowed neuroscientists to delve deeply into the complex three-dimensional environment of the living brain to record dynamic cellular events over time. This review will highlight recent examples of how LSM is being applied to elucidate both normal and abnormal cortical development. © 2005 Wiley-Liss, Inc. MRDD Research Reviews 2005;11:303,316. [source] The effects of seizures on the connectivity and circuitry of the developing brainDEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 2 2004John W. Swann Abstract Recurring seizures in infants and children are often associated with cognitive deficits, but the reason for the learning difficulties is unclear. Recent studies in several animal models suggest that seizures themselves may contribute in important ways to these deficits. Other studies in animals have shown that recurring seizures result in dendritic spine loss. This change, coupled with a down-regulation in NMDA receptor subunit expression, suggests that repetitive seizures may interrupt the normal development of glutamatergic synaptic transmission. We hypothesize that homeostatic, neuroprotective processes are induced by recurring early-life seizures. These processes, by diminishing glutamatergic synaptic transmission, are aimed at preventing the continuation of seizures. However, by preventing the normal development of glutamatergic synapses, and particularly NMDA receptor-mediated synaptic transmission, such homeostatic processes also reduce synaptic plasticity and diminish the ability of neuronal circuits to learn and store memories. MRDD Research Reviews 2004;10:96,100. © 2004 Wiley-Liss, Inc. [source] Presynaptic secretion of mind-the-gap organizes the synaptic extracellular matrix-integrin interface and postsynaptic environmentsDEVELOPMENTAL DYNAMICS, Issue 3 2009Emma Rushton Abstract Mind-the-Gap (MTG) is required during synaptogenesis of the Drosophila glutamatergic neuromuscular junction (NMJ) to organize the postsynaptic domain. Here, we generate MTG::GFP transgenic animals to demonstrate MTG is synaptically targeted, secreted, and localized to punctate domains in the synaptic extracellular matrix (ECM). Drosophila NMJs form specialized ECM carbohydrate domains, with carbohydrate moieties and integrin ECM receptors occupying overlapping territories. Presynaptically secreted MTG recruits and reorganizes secreted carbohydrates, and acts to recruit synaptic integrins and ECM glycans. Transgenic MTG::GFP expression rescues hatching, movement, and synaptogenic defects in embryonic-lethal mtg null mutants. Targeted neuronal MTG expression rescues mutant synaptogenesis defects, and increases rescue of adult viability, supporting an essential neuronal function. These results indicate that presynaptically secreted MTG regulates the ECM-integrin interface, and drives an inductive mechanism for the functional differentiation of the postsynaptic domain of glutamatergic synapses. We suggest that MTG pioneers a novel protein family involved in ECM-dependent synaptic differentiation. Developmental Dynamics 238:554,571, 2009. © 2009 Wiley-Liss, Inc. [source] Visualizing neurons one-by-one in vivo: Optical dissection and reconstruction of neural networks with reversible fluorescent proteinsDEVELOPMENTAL DYNAMICS, Issue 8 2006Shinsuke Aramaki Abstract A great many axons and dendrites intermingle to fasciculate, creating synapses as well as glomeruli. During live imaging in particular, it is often impossible to distinguish between individual neurons when they are contiguous spatially and labeled in the same fluorescent color. In an attempt to solve this problem, we have taken advantage of Dronpa, a green fluorescent protein whose fluorescence can be erased with strong blue light, and reversibly highlighted with violet or ultraviolet light. We first visualized a neural network with fluorescent Dronpa using the Gal4-UAS system. During the time-lapse imaging of axonal navigation, we erased the Dronpa fluorescence entirely; re-highlighted it in a single neuron anterogradely from the soma or retrogradely from the axon; then repeated this procedure for other single neurons. After collecting images of several individual neurons, we then recombined them in multiple pseudo-colors to reconstruct the network. We have also successfully re-highlighted Dronpa using two-photon excitation microscopy to label individual cells located inside of tissues and were able to demonstrate visualization of a Mauthner neuron extending an axon. These "optical dissection" techniques have the potential to be automated in the future and may provide an effective means to identify gene function in morphogenesis and network formation at the single cell level. Developmental Dynamics 235:2192,2199, 2006. © 2006 Wiley-Liss, Inc. [source] Activity of nAChRs containing ,9 subunits modulates synapse stabilization via bidirectional signaling programsDEVELOPMENTAL NEUROBIOLOGY, Issue 14 2009Vidya Murthy Abstract Although the synaptogenic program for cholinergic synapses of the neuromuscular junction is well known, little is known of the identity or dynamic expression patterns of proteins involved in non-neuromuscular nicotinic synapse development. We have previously demonstrated abnormal presynaptic terminal morphology following loss of nicotinic acetylcholine receptor (nAChR) ,9 subunit expression in adult cochleae. However, the molecular mechanisms underlying these changes have remained obscure. To better understand synapse formation and the role of cholinergic activity in the synaptogenesis of the inner ear, we exploit the nAChR ,9 subunit null mouse. In this mouse, functional acetylcholine (ACh) neurotransmission to the hair cells is completely silenced. Results demonstrate a premature, effusive innervation to the synaptic pole of the outer hair cells in ,9 null mice coinciding with delayed expression of cell adhesion proteins during the period of effusive contact. Collapse of the ectopic innervation coincides with an age-related hyperexpression pattern in the null mice. In addition, we document changes in expression of presynaptic vesicle recycling/trafficking machinery in the ,9 null mice that suggests a bidirectional information flow between the target of the neural innervation (the hair cells) and the presynaptic terminal that is modified by hair cell nAChR activity. Loss of nAChR activity may alter transcriptional activity, as CREB binding protein expression is decreased coincident with the increased expression of N-Cadherin in the adult ,9 null mice. Finally, by using mice expressing the nondesensitizing ,9 L9,T point mutant nAChR subunit, we show that increased nAChR activity drives synaptic hyperinnervation. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2009 [source] Glutamate drives the touch response through a rostral loop in the spinal cord of zebrafish embryosDEVELOPMENTAL NEUROBIOLOGY, Issue 12 2009Thomas Pietri Abstract Characterizing connectivity in the spinal cord of zebrafish embryos is not only prerequisite to understanding the development of locomotion, but is also necessary for maximizing the potential of genetic studies of circuit formation in this model system. During their first day of development, zebrafish embryos show two simple motor behaviors. First, they coil their trunks spontaneously, and a few hours later they start responding to touch with contralateral coils. These behaviors are contemporaneous until spontaneous coils become infrequent by 30 h. Glutamatergic neurons are distributed throughout the embryonic spinal cord, but their contribution to these early motor behaviors in immature zebrafish is still unclear. We demonstrate that the kinetics of spontaneous coiling and touch-evoked responses show distinct developmental time courses and that the touch response is dependent on AMPA-type glutamate receptor activation. Transection experiments suggest that the circuits required for touch-evoked responses are confined to the spinal cord and that only the most rostral part of the spinal cord is sufficient for triggering the full response. This rostral sensory connection is presumably established via CoPA interneurons, as they project to the rostral spinal cord. Electrophysiological analysis demonstrates that these neurons receive short latency AMPA-type glutamatergic inputs in response to ipsilateral tactile stimuli. We conclude that touch responses in early embryonic zebrafish arise only after glutamatergic synapses connect sensory neurons and interneurons to the contralateral motor network via a rostral loop. This helps define an elementary circuit that is modified by the addition of sensory inputs, resulting in behavioral transformation. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009 [source] Dopamine modulation of the In vivo acetylcholine response in the Drosophila mushroom bodyDEVELOPMENTAL NEUROBIOLOGY, Issue 11 2009Vitold Tsydzik Abstract Olfactory sensory information in Drosophila is transmitted through antennal lobe projections to Mushroom Body neurons (Kenyon cells) by means of cholinergic synapses. Application of acetylcholine (ACh) and odors produce significant increases in intracellular calcium ([Ca2+]i) in these neurons. Behavioral studies show that Kenyon cell activity is modulated by dopaminergic inputs and this modulation is thought to be the basis for an olfactory conditioned response. However, quantitative assessment of the synaptic inputs to Kenyon cells is currently lacking. To assess neuronal activity under in vivo conditions, we have used the endogenously-expressed camgaroo reporter to measure [Ca2+]i in these neurons. We report here the dose-response relationship of Kenyon cells for ACh and dopamine (DA). Importantly, we also show that simultaneous application of ACh and DA results in a significant decrease in the response to ACh alone. In addition, we show inhibition of the ACh response by cyclic adenosine monophosphate. This is the first quantitative assessment of the effects of these two important transmitters in this system, and it provides an important basis for future analysis of the cellular mechanisms of this well established model for associative olfactory learning. © 2009 Wiley Periodicals, Inc. Develop Neurobiol, 2009 [source] Watching moving images specifically promotes development of medial area of secondary visual cortex in ratDEVELOPMENTAL NEUROBIOLOGY, Issue 9 2009Baonan Sun Abstract It is generally accepted that the cortex can be divided into numerous regions depending on the type of information each processes, and that specific input is effective in improving the development of related regions. In visual cortex, many subareas are distinguished on the basis of their adequate information. However, whether the development of a subarea can be specifically improved by its particular input is still largely unknown. Here, we show the specific effects of motion information on the development of the medial area of secondary visual cortex (V2M), a subarea associated with processing the movement component of visual information. Although watching a moving or a still image had similar effects in primary visual cortex, the moving image induced multistage development of V2M in dark-reared rats: both mRNA and protein levels of GluR2 were upregulated, the density and protein content of GluR2-positive synapses increased, and the spine density and the frequency of spontaneous excitatory postsynaptic currents (EPSCs) of pyramidal neurons in Layer 5 were elevated. Our results suggest that rats are able to identify motion information, distribute it to V2M, and then use this input to specifically improve the development of V2M. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009 [source] Bilirubin as a determinant for altered neurogenesis, neuritogenesis, and synaptogenesisDEVELOPMENTAL NEUROBIOLOGY, Issue 9 2009Adelaide Fernandes Abstract Elevated levels of serum unconjugated bilirubin (UCB) in the first weeks of life may lead to long-term neurologic impairment. We previously reported that an early exposure of developing neurons to UCB, in conditions mimicking moderate to severe neonatal jaundice, leads to neuritic atrophy and cell death. Here, we have further analyzed the effect of UCB on nerve cell differentiation and neuronal development, addressing how UCB may affect the viability of undifferentiated neural precursor cells and their fate decisions, as well as the development of hippocampal neurons in terms of dendritic and axonal elongation and branching, the axonal growth cone morphology, and the establishment of dendritic spines and synapses. Our results indicate that UCB reduces the viability of proliferating neural precursors, decreases neurogenesis without affecting astrogliogenesis, and increases cellular dysfunction in differentiating cells. In addition, an early exposure of neurons to UCB decreases the number of dendritic and axonal branches at 3 and 9 days in vitro (DIV), and a higher number of neurons showed a smaller growth cone area. UCB-treated neurons also reveal a decreased density of dendritic spines and synapses at 21 DIV. Such deleterious role of UCB in neuronal differentiation, development, and plasticity may compromise the performance of the brain in later life. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009 [source] A critical step for postsynaptic F-actin organization: Regulation of Baz/Par-3 localization by aPKC and PTENDEVELOPMENTAL NEUROBIOLOGY, Issue 9 2009Preethi Ramachandran Abstract Actin remodeling has emerged as a critical process during synapse development and plasticity. Thus, understanding the regulatory mechanisms controlling actin organization at synapses is exceedingly important. Here, we used the highly plastic Drosophila neuromuscular junction (NMJ) to understand mechanisms of actin remodeling at postsynaptic sites. Previous studies have suggested that the actin-binding proteins Spectrin and Coracle play a critical role in NMJ development and the anchoring of glutamate receptors most likely through actin regulation. Here, we show that an additional determinant of actin organization at the postsynaptic region is the PDZ protein Baz/Par-3. Decreasing Baz levels in postsynaptic muscles has dramatic consequences for the size of F-actin and spectrin domains at the postsynaptic region. In turn, proper localization of Baz at this site depends on both phosphorylation and dephosphorylation events. Baz phosphorylation by its binding partner, atypical protein kinase C (aPKC), is required for normal Baz targeting to the postsynaptic region. However, the retention of Baz at this site depends on its dephosphorylation mediated by the lipid and protein phosphatase PTEN. Misregulation of the phosphorylation state of Baz by genetic alterations in PTEN or aPKC activity has detrimental consequences for postsynaptic F-actin and spectrin localization, synaptic growth, and receptor localization. Our results provide a novel mechanism of postsynaptic actin regulation through Baz, governed by the antagonistic actions of aPKC and PTEN. Given the conservation of these proteins from worms to mammals, these results are likely to provide new insight into actin organization pathways. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009 [source] Efficient copackaging and cotransport yields postsynaptic colocalization of neuromodulators associated with synaptic plasticityDEVELOPMENTAL NEUROBIOLOGY, Issue 10 2008J.E. Lochner Abstract Recent data suggest that tissue plasminogen activator (tPA) influences long-term plasticity at hippocampal synapses by converting plasminogen into plasmin, which then generates mature brain-derived neurotrophic factor (mBDNF) from its precursor, proBDNF. Motivated by this hypothesis, we used fluorescent chimeras, expressed in hippocampal neurons, to elucidate (1) mechanisms underlying plasminogen secretion from hippocampal neurons, (2) if tPA, plasminogen, and proBDNF are copackaged and cotransported in hippocampal neurons, especially within dendritic spines, and (3) mechanisms mediating the transport of these neuromodulators to sites of release. We find that plasminogen chimeras traffic through the regulated secretory pathway of hippocampal neurons in dense-core granules (DCGs) and that tPA, plasminogen, and proBDNF chimeras are extensively copackaged in DCGs throughout hippocampal neurons. We also find that 80% of spines that contain DCGs contain chimeras of these neuromodulators in the same DCG. Finally, we demonstrate, for the first time, that neuromodulators undergo cotransport along dendrites in rapidly mobile DCGs, indicating that neuromodulators can be efficiently recruited into active spines. These results support the hypothesis that tPA mediates synaptic activation of BDNF by demonstrating that tPA, plasminogen, and proBDNF colocalize in DCGs in spines, where these neuromodulators can undergo activity-dependent release and then interact and/or mediate changes that influence synaptic efficacy. The results also raise the possibility that frequency-dependent changes in extents of neuromodulator release from DCGs influence the direction of plasticity at hippocampal synapses by altering the relative proportions of two proteins, mBDNF and proBDNF, that exert opposing effects on synaptic efficacy. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008. [source] Neural agrin increases postsynaptic ACh receptor packing by elevating rapsyn protein at the mouse neuromuscular synapseDEVELOPMENTAL NEUROBIOLOGY, Issue 9 2008Jennifer Brockhausen Abstract Fluorescence resonance energy transfer (FRET) experiments at neuromuscular junctions in the mouse tibialis anterior muscle show that postsynaptic acetylcholine receptors (AChRs) become more tightly packed during the first month of postnatal development. Here, we report that the packing of AChRs into postsynaptic aggregates was reduced in 4-week postnatal mice that had reduced amounts of the AChR-associated protein, rapsyn, in the postsynaptic membrane (rapsyn+/, mice). We hypothesize that nerve-derived agrin increases postsynaptic expression and targeting of rapsyn, which then drives the developmental increase in AChR packing. Neural agrin treatment elevated the expression of rapsyn in C2 myotubes by a mechanism that involved slowing of rapsyn protein degradation. Similarly, exposure of synapses in postnatal muscle to exogenous agrin increased rapsyn protein levels and elevated the intensity of anti-rapsyn immunofluorescence, relative to AChR, in the postsynaptic membrane. This increase in the rapsyn-to-AChR immunofluorescence ratio was associated with tighter postsynaptic AChR packing and slowed AChR turnover. Acute blockade of synaptic AChRs with ,-bungarotoxin lowered the rapsyn-to-AChR immunofluorescence ratio, suggesting that AChR signaling also helps regulate the assembly of extra rapsyn in the postsynaptic membrane. The results suggest that at the postnatal neuromuscular synapse agrin signaling elevates the expression and targeting of rapsyn to the postsynaptic membrane, thereby packing more AChRs into stable, functionally-important AChR aggregates. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008 [source] Electron microscopic 3D-reconstruction of dendritic spines in cultured hippocampal neurons undergoing synaptic plasticityDEVELOPMENTAL NEUROBIOLOGY, Issue 7 2008Wladimir Ovtscharoff Jr. Abstract Dendritic spines are assumed to constitute the locus of neuronal plasticity, and considerable effort has been focused on attempts to demonstrate that new memories are associated with the formation of new spines. However, few studies that have documented the appearance of spines after exposure to plasticity-producing paradigms could demonstrate that a new spine is touched by a bona fida presynaptic terminal. Thus, the functional significance of plastic dendritic spine changes is not clearly understood. We have used quantitative time lapse confocal imaging of cultured hippocampal neurons before and after their exposure to a conditioning medium which activates synaptic NMDA receptors. Following the experiment the cultures were prepared for 3D electron microscopic reconstruction of visually identified dendritic spines. We found that a majority of new, 1- to 2-h-old spines was touched by presynaptic terminals. Furthermore, when spines disappeared, the parent dendrites were sometime touched by a presynaptic bouton at the site where the previously identified spine had been located. We conclude that new spines are most likely to be functional and that pruned spines can be transformed into shaft synapses and thus maintain their functionality within the neuronal network. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008. [source] Derailed regulates development of the Drosophila neuromuscular junctionDEVELOPMENTAL NEUROBIOLOGY, Issue 2 2008Faith L.W. Liebl Abstract Neural function is dependent upon the proper formation and development of synapses. We show here that Wnt5 regulates the growth of the Drosophila neuromuscular junction (NMJ) by signaling through the Derailed receptor. Mutations in both wnt5 and drl result in a significant reduction in the number of synaptic boutons. Cell-type specific rescue experiments show that wnt5 functions in the presynaptic motor neuron while drl likely functions in the postsynaptic muscle cell. Epistatic analyses indicate that drl acts downstream of wnt5 to promote synaptic growth. Structure,function analyses of the Drl protein indicate that normal synaptic growth requires the extracellular Wnt inhibitory factor domain and the intracellular domain, which includes an atypical kinase. Our findings reveal a novel signaling mechanism that regulates morphology of the Drosophila NMJ. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2008 [source] Arachidonic acid as a retrograde signal controlling growth and dynamics of retinotectal arborsDEVELOPMENTAL NEUROBIOLOGY, Issue 1 2008B.H. Leu Abstract In the developing visual system, correlated presynaptic activity between neighboring retinal ganglion cells (RGC) stabilizes retinotopic synapses via a postsynaptic NMDAR (N -methyl- D -aspartate receptor)-dependent mechanism. Blocking NMDARs makes individual axonal arbors larger, which underlies an unsharpened map, and also increases branch turnover, as if a stabilizing factor from the postsynaptic partner is no longer released. Arachidonic acid (AA), a candidate retrograde stabilizing factor, is released by cytoplasmic phospholipase A2 (cPLA2) after Ca2+ entry through activated NMDARs, and can activate presynaptic protein kinase C to phosphorylate various substrates such as GAP43 to regulate cytoskeletal dynamics. To test the role of cPLA2 in the retinotectal system of developing zebrafish, we first used PED6, a fluorescent reporter of cPLA2 activity, to show that 1,3 min of strobe flashes activated tectal cPLA2 by an NMDAR-dependent mechanism. Second, we imaged the dynamic growth of retinal arbors during both local inhibition of tectal cPLA2 by a pharmacological inhibitor, arachidonic tri-fluoromethylketone, and its suppression by antisense oligonucleotides (both injected intraventricularly). Both methods produced larger arbors and faster branch dynamics as occurs with blocking NMDARs. In contrast, intraocular suppression of retinal cPLA2 with large doses of antisense oligos produced none of the effects of tectal cPLA2 inhibition. Finally, if AA is the retrograde messenger, the application of exogenous AA to the tectum should reverse the increased branch turnover caused by blocking either NMDARs or cPLA2. In both cases, intraventricular injection of AA stabilized the overall branch dynamics, bringing rates down below the normal values. The results suggest that AA generated postsynaptically by cPLA2 downstream of Ca2+ entry through NMDARs acts as a retrograde signal to regulate the dynamic growth of retinal arbors. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2008. [source] A role for acetylcholine receptors in their own aggregation on muscle cellsDEVELOPMENTAL NEUROBIOLOGY, Issue 8 2007Rebecca B.R. Milholland Abstract Both neurotrophic factors and activity regulate synaptogenesis. At neuromuscular synapses, the neural factor agrin released from motor neuron terminals stimulates postsynaptic specialization by way of the muscle specific kinase MuSK. In addition, activity through acetylcholine receptors (AChRs) has been implicated in the stabilization of pre- and postsynaptic contacts on muscle at various stages of development. We show here that activation of AChRs with specific concentrations of nicotine is sufficient to induce AChR aggregation and that this induction requires the function of L-type calcium channels (L-CaChs). Furthermore, AChR function is required for agrin induced AChR aggregation in C2 muscle cells. The same concentrations of nicotine did not induce observable tyrosine phosphorylation on either MuSK or the AChR , subunit, suggesting significant differences between the mechanisms of agrin and activity induced aggregation. The AChR/L-CaCh pathway provides a mechanism by which neuromuscular signal transmission can act in concert with the agrin-MuSK signaling cascade to regulate NMJ formation. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007. [source] Splice-isoform specific immunolocalization of neuronal nitric oxide synthase in mouse and rat brain reveals that the PDZ-complex-building nNOS, ,-finger is largely exposed to antibodiesDEVELOPMENTAL NEUROBIOLOGY, Issue 4 2007Kristina Langnaese Abstract Knock out mice deficient for the splice-isoform ,, of neuronal nitric oxide synthase (nNOS,,) display residual nitric oxide synthase activity and immunosignal. To attribute this signal to the two minor neuronal nitric oxide synthase splice variants, ,, and ,,, we generated isoform-specific anti-peptide antibodies against the nNOS,, specific ,,-finger motif involved in PDZ domain scaffolding and the nNOS,, specific N-terminus. The nNOS,, ,,-finger-specific antibody clearly recognized the 160-kDa band of recombinant nNOS,, on Western blots. Using immunocytochemistry, this antibody displayed, in rats and wild-type mice, a labeling pattern similar to but not identical with that obtained using a commercial pan-nNOS antibody. This similarity indicates that the majority of immunocytochemically detectable nNOS is not likely to be complexed with PDZ-domain proteins via the ,,-finger motif. This conclusion was confirmed by the inhibition of PSD-95/nNOS interaction by the nNOS,, ,,-finger antibody in pull-down assays. By contrast, nNOS,, ,,-finger labeling was clearly reduced in hippocampal and cortical neuropil areas enriched in NMDA receptor complex containing spine synapses. In nNOS,, knock out mice, nNOS,, was not detectable, whereas the pan-nNOS antibody showed a distinct labeling of cell bodies throughout the brain, most likely reflecting ,,/,,-isoforms in these cells. The nNOS,, antibody clearly detected bacterial expressed nNOS,, fusion protein and nNOS,, in overexpressing HEK cells by Western blotting. Immunocytochemically, individual cell bodies in striatum, cerebral cortex, and in some brain stem nuclei were labeled in knock out but not in wild-type mice, indicating an upregulation of nNOS,, in nNOS,, deficient animals. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007 [source] Subcellular compartmentalization of aromatase is sexually dimorphic in the adult zebra finch brainDEVELOPMENTAL NEUROBIOLOGY, Issue 1 2007Kevin N. Rohmann Abstract The vertebrate brain is a source of estrogen (E) via the expression of aromatase (E-synthase). In the zebra finch (Taeniopygia guttata), despite documented dimorphisms in E-action, no differences are detectable in circulating E, or the neural levels of aromatase transcription, activity, or somal protein expression. Studies of aromatase expression at the light- and electron-microscope levels reveal greater numbers of fibers and presynaptic boutons in adult males relative to females. We assayed aromatase activity and content in synaptosomes and microsomes from the anterior [containing lMAN and Area X (males)] and posterior telencephalon (containing HVC and RA) of adult birds. In contrast to non-song birds and mammals, both cell fractions contain abundant aromatase measurable in terms of activity (enzyme assays) and content (Western blots) with minimal enrichment in microsomes. From brain homogenates of identical concentration, aromatase activity was higher in the synaptosomal relative to the microsomal fraction, in males relative to females, and in the posterior compared to anterior telencephalon. These effects were driven by high levels of synaptosomal aromatase in the male posterior telencephalon. These data suggest that males possess more aromatase per presynaptic bouton, or a greater number of aromatase-containing presynaptic boutons than females in the posterior telencephalon. Further, the present report reveals synaptic aromatization as a considerable source of E in the zebra finch brain, and supports the idea that telencephalic synapses in and around the adult male song production nuclei may be exposed to higher levels of E compared to the female brain. © 2006 Wiley Periodicals, Inc. J Neurobiol 67: 1,9, 2007 [source] | |||||||||||||||||||||||||||||||