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Afferent Input (afferent + input)

Distribution by Scientific Domains

Life Sciences	83%
Medical Sciences	16%

Distribution within Life Sciences

Neuroscience	60%
Anatomy & Physiology	31%
2 Other Subdomains	9%

Selected Abstracts

GABAergic modulation of primary gustatory afferent synaptic efficacy

DEVELOPMENTAL NEUROBIOLOGY, Issue 2 2002
Andrew A. Sharp
Abstract Modulation of synaptic transmission at the primary sensory afferent synapse is well documented for the somatosensory and olfactory systems. The present study was undertaken to test whether GABA impacts on transmission of gustatory information at the primary afferent synapse. In goldfish, the vagal gustatory input terminates in a laminated structure, the vagal lobes, whose sensory layers are homologous to the mammalian nucleus of the solitary tract. We relied on immunoreactivity for the GABA-transporter, GAT-1, to determine the distribution of GABAergic synapses in the vagal lobe. Immunocytochemistry showed dense, punctate GAT-1 immunoreactivity coincident with the layers of termination of primary afferent fibers. The laminar nature and polarized dendritic structure of the vagal lobe make it amenable to an in vitro slice preparation to study early synaptic events in the transmission of gustatory input. Electrical stimulation of the gustatory nerves in vitro produces synaptic field potentials (fEPSPs) predominantly mediated by ionotropic glutamate receptors. Bath application of either the GABAA receptor agonist muscimol or the GABAB receptor agonist baclofen caused a nearly complete suppression of the primary fEPSP. Coapplication of the appropriate GABAA or GABAB receptor antagonist bicuculline or CGP-55845 significantly reversed the effects of the agonists. These data indicate that GABAergic terminals situated in proximity to primary gustatory afferent terminals can modulate primary afferent input via both GABAA and GABAB receptors. The mechanism of action of GABAB receptors suggests a presynaptic locus of action for that receptor. © 2002 Wiley Periodicals, Inc. J Neurobiol 52: 133,143, 2002 [source]

Nociceptive spinothalamic tract and postsynaptic dorsal column neurons are modulated by paraventricular hypothalamic activation

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2008
Gerardo Rojas-Piloni
Abstract Previously, we demonstrated that stimulation of the paraventricular hypothalamic nucleus diminishes the nociceptive dorsal horn neuronal responses, and this decrease was mediated by oxytocin in the rat. In addition, we have proposed that oxytocin indirectly inhibits sensory transmission in dorsal horn neurons by exciting spinal inhibitory GABAergic interneurons. The main purpose of the present study was to identify which of the neurons projecting to supraspinal structures to transmit somatic information are modulated by the hypothalamic-spinal descending activation. In anaesthetized rats, single-unit extracellular and juxtacellular recordings were made from dorsal horn lumbar segments, which receive afferent input from the toe and hind-paw regions. The projecting spinothalamic tract and postsynaptic dorsal column system were identified antidromically. Additionally, in order to label the projecting dorsal horn neurons, we injected fluorescent retrograde neuronal tracers into the ipsilateral gracilis nucleus and contralateral ventroposterolateral thalamic nucleus. Hence, juxtacellular recordings were made to iontophoretically label the recorded neurons with a fluorescent dye and identify the recorded projecting cells. We found that only nociceptive evoked responses in spinothalamic tract and postsynaptic dorsal column neurons were significantly inhibited (48.1 ± 4.6 and 47.7 ± 8.2%, respectively) and non-nociceptive responses were not affected by paraventricular hypothalamic nucleus stimulation. We conclude that the hypothalamic-spinal system selectively affects the transmission of nociceptive information of projecting spinal cord cells. [source]

Developmental changes in the BDNF-induced modulation of inhibitory synaptic transmission in the Kölliker,Fuse nucleus of rat

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2007
Miriam Kron
Abstract The Kölliker,Fuse nucleus (KF), part of the pontine respiratory group, is involved in the control of respiratory phase duration, and receives both excitatory and inhibitory afferent input from various other brain regions. There is evidence for developmental changes in the modulation of excitatory inputs to the KF by the neurotrophin brain-derived neurotrophic factor (BDNF). In the present study we investigated if BDNF exerts developmental effects on inhibitory synaptic transmission in the KF. Recordings of inhibitory postsynaptic currents (IPSCs) in KF neurons in a pontine slice preparation revealed general developmental changes. Recording of spontaneous and evoked IPSCs (sIPSCs, eIPSCS) revealed that neonatally the ,-aminobutyric acid (GABA)ergic fraction of IPSCs was predominant, while in later developmental stages glycinergic neurotransmission significantly increased. Bath-application of BDNF significantly reduced sIPSC frequency in all developmental stages, while BDNF-mediated modulation on eIPSCs showed developmental differences. The eIPSCs mean amplitude was uniformly and significantly reduced following BDNF application only in neurons from rats younger than postnatal day 10. At later postnatal stages the response pattern became heterogeneous, and both augmentations and reductions of eIPSC amplitudes occurred. All BDNF effects on eIPSCs and sIPSCs were reversed with the tyrosine kinase receptor-B inhibitor K252a. We conclude that developmental changes in inhibitory neurotransmission, including the BDNF-mediated modulation of eIPSCs, relate to the postnatal maturation of the KF. The changes in BDNF-mediated modulation of IPSCs in the KF may have strong implications for developmental changes in synaptic plasticity and the adaptation of the breathing pattern to afferent inputs. [source]

Induction of rapid, activity-dependent neuronal,glial remodelling in the adult rat hypothalamus in vitro

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2003
Sarah L. Langle
Abstract The hypothalamic oxytocinergic system offers a remarkable model of morphological plasticity in the adult because its neurons and astrocytes undergo mutual remodelling in relation to differing physiological conditions. Among various factors involved in such plasticity, oxytocin (OT) itself appears of primary importance as its central administration resulted in morphological changes similar to those brought on by physiological stimuli. In the present study, we applied OT on acute hypothalamic slices from adult rats that included the supraoptic nucleus. Using ultrastructural morphometric analyses, we found that it induced a significant reduction of astrocytic coverage of OT neurons, leaving their surfaces directly juxtaposed, to an extent similar to that detected in vivo under conditions like lactation. These neuronal,glial changes were rapid and reversible, occurring within a few hours, and specifically mediated via OT receptors. They were potentiated by oestrogen and depended on calcium mobilization and de novo protein synthesis. Moreover, they depended on concurrent neuronal activation brought on by hyperosmotic stimulation or blockade of inhibitory GABAergic neurotransmission; they were inhibited by blockade of glutamatergic receptors. Taken together, our observations show that intrahypothalamic release of OT affects not only neuronal activation of the OT system but its morphological plasticity as well. Moreover, the activity dependence of the OT-induced changes strongly suggests that astrocytes can sense the level of activity of adjacent neurons and/or afferent input and this can subsequently act as a signal to bring on the neuronal and glial conformational changes. [source]

Distribution of mossy fibre rosettes in the cerebellum of cat and mice: evidence for a parasagittal organization at the single fibre level

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2001
Fahad SultanArticle first published online: 20 DEC 200
Abstract Mossy fibres are the main afferent input to the granular layer of the cerebellar cortex. In this study, the spatial distribution of the mossy fibres' presynaptic enlargements , the so-called rosettes , were analysed on the single fibre level. Data obtained from the cerebella of cat and mice were compared to look for species differences, and the cerebella of the adult and young mice were also compared to look for developmental changes. The results show that there is a spatial anisotropy in all mossy fibres studied, with neighbouring rosettes being about three times further away from each other along the parasagittal axis and closer to each other in the mediolateral direction. Furthermore, these results suggest that this anisotropy is established at an early developmental stage. The anisotropic orientation of mossy fibres at the single fibre level supports the hypothesis of a timing mechanism in cerebellar function. [source]

The isochronic band hypothesis and climbing fibre regulation of motricity: an experimental study

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2001
Masaji Fukuda
Abstract The dynamic organization of the olivocerebellar afferent input to Purkinje cells was examined in rat cerebellar cortex. The distribution of synchronous Purkinje cell complex spike activity was characterized, bilaterally, utilizing multiple electrode recordings in crus IIa folium under ketamine anaesthesia. The results confirmed the existence of rostrocaudal complex spike isochronicity bands with a mediolateral width of 500 µm. For a given band, no finer spatial submicrostructures could be discerned at a first-order approximation (two-dimensional projection). Closer analysis determined that isochronicity between bands is not continuous in space but demonstrates discrete discontinuities at the mediolateral boundaries. Principal component multivariate analysis revealed that the first principal component of the spatio-temporal variance is synchronicity along the rostrocaudal band with a decreased level of coupling in the mediolateral direction at the band boundary. Furthermore, this discrete banding isochronicity is organized by the distribution of feedback inhibition from the cerebellar nuclei on to the inferior olive nucleus. The usual multiple band structure can be dynamically altered to a single wide-band dynamic architecture, or to other patterns of activity, as may be required by movement coordination. [source]

Nerve growth factor expression in parasympathetic neurons: regulation by sympathetic innervation

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2000
Wohaib 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]

Modifications of retinal afferent activity induce changes in astroglial plasticity in the hamster circadian clock

GLIA, Issue 2 2001
Monique Lavialle
Abstract The circadian clock, located in the suprachiasmatic nucleus (SCN) of the hypothalamus in mammals, exhibits astroglial plasticity indicated by GFAP expression over the 24-h period. In this study, we evaluated the role of neuronal retinal input in the observed changes. Modifications of retinal input, either by rearing animals under darkness (DD) or under constant light (LL), or by suppressing afferent input (bilateral enucleation), induced drastic changes in astroglial plasticity. In enucleated animals, a dramatic decrease in GFAP expression was evident in the area of the SCN deprived of retinal projections, whereas persistence of a rhythmic variation was in those areas still exhibiting GFAP expression. By contrast, no changes in astrocytic plasticity were detected in hamsters maintained under LL. These data suggest two fundamental roles for astrocytes within the SCN: (1) to regulate and mediate glutamate released by retinal terminals throughout the neuronal network to facilitate photic signal transmission; (2) to contribute to synchronization between suprachiasmatic neurons. GLIA 34:88,100, 2001. © 2001 Wiley-Liss, Inc. [source]

Retraining cervical joint position sense: The effect of two exercise regimes

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2007
Gwendolen Jull
Abstract This study compared the effects of conventional proprioceptive training and craniocervical flexion (C-CF) training on cervical joint position error (JPE) in people with persistent neck pain. The aim was to evaluate whether proprioceptive training was superior in improving proprioceptive acuity compared to another form of exercise, which has been shown to be effective in reducing neck pain. This may help to differentiate the mechanisms of effect of such interventions. Sixty-four female subjects with persistent neck pain and deficits in JPE were randomized into two exercise groups: proprioceptive training or C-CF training. Exercise regimes were conducted over a 6-week period, and all patients received personal instruction by an experienced physiotherapist once per week. A significant pre- to postintervention decrease in JPE, neck pain intensity, and perceived disability was identified for both the proprioceptive training group (p,<,0.001) and the C-CF training group (p,<,0.05). Patients who participated in the proprioceptive training demonstrated a greater reduction in JPE from right rotation compared to the C-CF training group (p,<,0.05). No other significant differences were observed between the two groups. The results demonstrated that both proprioceptive training and C-CF training have a demonstrable benefit on impaired cervical JPE in people with neck pain, with marginally more benefit gained from proprioceptive training. The results suggest that improved proprioceptive acuity following intervention with either exercise protocol may occur through an improved quality of cervical afferent input or by addressing input through direct training of relocation sense. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 2007 [source]

Impaired heteronymous somatosensory motor cortical inhibition in dystonia

MOVEMENT DISORDERS, Issue 11 2003
Laura Bertolasi MD
Abstract A typical pathophysiological abnormality in dystonia is cocontraction of antagonist muscles, with impaired reciprocal inhibitory mechanisms in the spinal cord. Recent experimental data have shown that inhibitory interactions between antagonist muscles have also a parallel control at the level of the sensorimotor cortex. The aim of this work was to study heteronymous effects of a median nerve stimulus on the corticospinal projections to forearm muscles in dystonia. We used the technique of antagonist cortical inhibition, which assesses the conditioning effect of median nerve afferent input on motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) in ipsilateral forearm extensor muscles at rest. Nine healthy subjects and 10 patients with torsion dystonia participated in the study. MEPs and somatosensory evoked potentials were normal in patients. In healthy subjects, median nerve stimulation at 15- to 18-msec intervals inhibited the test MEPs in forearm extensors. In dystonic patients, median nerve stimulation delivered at the same conditioning,test intervals elicited significantly less inhibition of the test MEP. On the whole, these data suggest an impaired sensory,motor integration in dystonia and, more specifically, the decreased antagonistic cortical inhibition could suggest that functional interactions between antagonist muscles are primarily impaired at the cortical level. © 2003 Movement Disorder Society [source]

Sensorimotor integration in movement disorders

MOVEMENT DISORDERS, Issue 3 2003
Giovanni Abbruzzese MD
Abstract Although current knowledge attributes movement disorders to a dysfunction of the basal ganglia,motor cortex circuits, abnormalities in the peripheral afferent inputs or in their central processing may interfere with motor program execution. We review the abnormalities of sensorimotor integration described in the various types of movement disorders. Several observations, including those of parkinsonian patients' excessive reliance on ongoing visual information during movement tasks, suggest that proprioception is defective in Parkinson's disease (PD). The disturbance of proprioceptive regulation, possibly related to the occurrence of abnormal muscle-stretch reflexes, might be important for generating hypometric or bradykinetic movements. Studies with somatosensory evoked potentials (SEPs), prepulse inhibition, and event-related potentials support the hypothesis of central abnormalities of sensorimotor integration in PD. In Huntington's disease (HD), changes in SEPs and long-latency stretch reflexes suggest that a defective gating of peripheral afferent input to the brain might impair sensorimotor integration in cortical motor areas, thus interfering with the processing of motor programs. Defective motor programming might contribute to some features of motor impairment in HD. Sensory symptoms are frequent in focal dystonia and sensory manipulation can modify the dystonic movements. In addition, specific sensory functions (kinaesthesia, spatial,temporal discrimination) can be impaired in patients with focal hand dystonia, thus leading to a "sensory overflow." Sensory input may be abnormal and trigger focal dystonia, or defective "gating" may cause an input,output mismatch in specific motor programs. Altogether, several observations strongly support the idea that sensorimotor integration is impaired in focal dystonia. Although elemental sensation is normal in patients with tics, tics can be associated with sensory phenomena. Some neurophysiological studies suggest that an altered "gating" mechanism also underlies the development of tics. This review underlines the importance of abnormal sensorimotor integration in the pathophysiology of movement disorders. Although the physiological mechanism remains unclear, the defect is of special clinical relevance in determining the development of focal dystonia. [source]

Enhanced expression of mast cell growth factor and mast cell activation in the bladder following the resolution of trinitrobenzenesulfonic acid (TNBS) colitis in female rats,

NEUROUROLOGY AND URODYNAMICS, Issue 6 2007
Ruomei Liang
Abstract Aims Chronic pelvic pain disorders often overlap. We have shown that acute colonic irritation can produce acute irritative micturition patterns and acutely sensitize bladder afferent responses to mechanical and chemical stimuli. We hypothesize that with time, colonic irritation can lead to neurogenic changes in the bladder and the development of chronic bladder sensitization. Methods Micturition patterns were measured in rats 60,90 days after the induction of trinitrobenzenesulfonic acid (TNBS) colitis in the resolution phase of this model. Total and activated mast cells (MCs) were quantified in the bladder, while mRNA levels of stem cell factor (SCF; a.k.a. MC growth factor) and nerve growth factor (NGF; a MC and nociceptive C-fiber stimulator) were quantified in the bladder and L6-S1 dorsal root ganglia (DRG). Results Following intra-rectal TNBS, voiding volume was reduced (P,<,0.005), while voiding frequency was increased (P,<,0.05), both by ,50%. Furthermore, both the percentage and density of activated bladder MCs were significantly elevated (P,<,0.05), although total MC counts were not statistically increased. At the molecular level, urinary bladder SCF expression increased twofold (P,<,0.005), as did NGF (P,<,0.01), while L6-S1 DRG levels were not significantly elevated. Conclusions Chronic cystitis in the rat as evidenced by changes in micturition patterns and the recruitment of activated MCs can occur during the resolution phase of TNBS colitis. These changes, of which MCs may play an important role, appear to be maintained over time and may occur via stimulation of convergent pelvic afferent input resulting in the upregulation of neurotrophic factors in the target organ. Neurourol. Urodynam. 26:887,893, 2007. © 2007 Wiley-Liss, Inc. [source]

Regulation of Kv channel expression and neuronal excitability in rat medial nucleus of the trapezoid body maintained in organotypic culture

THE JOURNAL OF PHYSIOLOGY, Issue 9 2010
Huaxia Tong
Principal neurons of the medial nucleus of the trapezoid body (MNTB) express a spectrum of voltage-dependent K+ conductances mediated by Kv1,Kv4 channels, which shape action potential (AP) firing and regulate intrinsic excitability. Postsynaptic factors influencing expression of Kv channels were explored using organotypic cultures of brainstem prepared from P9,P12 rats and maintained in either low (5 mm, low-K) or high (25 mm, high-K) [K+]o medium. Whole cell patch-clamp recordings were made after 7,28 days in vitro. MNTB neurons cultured in high-K medium maintained a single AP firing phenotype, while low-K cultures had smaller K+ currents, enhanced excitability and fired multiple APs. The calyx of Held inputs degenerated within 3 days in culture, having lost their major afferent input; this preparation of calyx-free MNTB neurons allowed the effects of postsynaptic depolarisation to be studied with minimal synaptic activity. The depolarization caused by the high-K aCSF only transiently increased spontaneous AP firing (<2 min) and did not measurably increase synaptic activity. Chronic depolarization in high-K cultures raised basal levels of [Ca2+]i, increased Kv3 currents and shortened AP half-widths. These events relied on raised [Ca2+]i, mediated by influx through voltage-gated calcium channels (VGCCs) and release from intracellular stores, causing an increase in cAMP-response element binding protein (CREB) phosphorylation. Block of VGCCs or of CREB function suppressed Kv3 currents, increased AP duration, and reduced Kv3.3 and c- fos expression. Real-time PCR revealed higher Kv3.3 and Kv1.1 mRNA in high-K compared to low-K cultures, although the increased Kv1.1 mRNA was mediated by a CREB-independent mechanism. We conclude that Kv channel expression and hence the intrinsic membrane properties of MNTB neurons are homeostatically regulated by [Ca2+]i -dependent mechanisms and influenced by sustained depolarization of the resting membrane potential. [source]

Learning to breathe: control of the inspiratory,expiratory phase transition shifts from sensory- to central-dominated during postnatal development in rats

THE JOURNAL OF PHYSIOLOGY, Issue 20 2009
Mathias Dutschmann
The hallmark of the dynamic regulation of the transitions between inspiration and expiration is the timing of the inspiratory off-switch (IOS) mechanisms. IOS is mediated by pulmonary vagal afferent feedback (Breuer,Hering reflex) and by central interactions involving the Kölliker,Fuse nuclei (KFn). We hypothesized that the balance between these two mechanisms controlling IOS may change during postnatal development. We tested this hypothesis by comparing neural responses to repetitive rhythmic vagal stimulation, at a stimulation frequency that paces baseline breathing, using in situ perfused brainstem preparations of rats at different postnatal ages. At ages < P15 (P, postnatal days), phrenic nerve activity (PNA) was immediately paced and entrained to the afferent input and this pattern remained unchanged by repetitive stimulations, indicating that vagal input stereotypically dominated the control of IOS. In contrast, PNA entrainment at > P15 was initially insignificant, but increased after repetitive vagal stimulation or lung inflation. This progressive adaption of PNA to the pattern of the sensory input was accompanied by the emergence of anticipatory centrally mediated IOS preceding the stimulus trains. The anticipatory IOS was blocked by bilateral microinjections of NMDA receptor antagonists into the KFn and PNA was immediately paced and entrained, as it was seen at ages < P15. We conclude that as postnatal maturation advances, synaptic mechanisms involving NMDA receptors in the KFn can override the vagally evoked IOS after ,training' using repetitive stimulation trials. The anticipatory IOS may imply a hitherto undescribed form of pattern learning and recall in convergent sensory and central synaptic pathways that mediate IOS. [source]

Sublinear summation of afferent inputs to the nucleus accumbens in the awake rat

THE JOURNAL OF PHYSIOLOGY, Issue 8 2009
John A. Wolf
The mechanisms by which the nucleus accumbens integrates afferent input from limbic and cortical structures have been influential in the development of models of psychiatric disorders such as schizophrenia. Previous studies of the response of nucleus accumbens (Nacb) cells to the stimulation of afferent inputs from hippocampus (HC) and prefrontal cortex (PFC) have demonstrated that PFC throughput can be modulated by preceding HC input. Examination of the post-synaptic potential size has suggested, however, that summation of these inputs is sublinear. All studies to date examining Nacb integration of inputs via stimulation of afferents have been performed in the anaesthetized rat. The present experiments compare the response of Nacb cells to different combinations of PFC and HC stimulation in awake and isoflurane-anaesthetized rats that were chronically implanted with both stimulating and recording electrodes. The results of these experiments suggest that summation of afferent input in the Nacb of the awake rat is predominantly sublinear, with only a minority of neurons demonstrating modulation of PFC inputs by the HC in the awake or the anaesthetized animal. The response profile of many cells changed during anaesthesia when compared to the awake condition, and on average showed suppression to PFC input 50 and 150 ms following HC stimulation while under deep isoflurane anaesthesia. These results suggest that sublinear integration of afferent input from the PFC and HC is the dominant mode of integration of Nacb cells in the awake animal, which has implications for corticostriatal models of psychiatric dysfunction. [source]

Role of cardiac-renal neural reflex in regulating sodium excretion during water immersion in conscious dogs

THE JOURNAL OF PHYSIOLOGY, Issue 1 2002
Kenju Miki
The present study was undertaken to determine the role of cardiopulmonary mechanoreceptors in inducing the sustained reduction of renal sympathetic nerve activity (RSNA) and concomitant changes in sodium excretion occurring during water immersion (WI) in intact dogs. Seven cardiac-denervated dogs were chronically instrumented for measuring RSNA, systemic arterial (Pa), central venous (Pcv) and left atrial pressures (Pla). WI initially decreased RSNA in cardiac denervated dogs by 10.0 ± 5.5 %; thereafter the RSNA fell to a nadir of 18.5 ± 5.6 % (P < 0.05) at 40,80 min of WI and then returned toward the pre-immersion level. Renal sodium excretion increased significantly by 211 ± 69 % (P < 0.05) only during the first 20,40 min of WI. WI increased Pa, Pcv and Pla in a step manner from 94 ± 3 to 108 ± 3 mmHg (P < 0.05), from 1.4 ± 0.5 to 12.3 ± 1.0 mmHg (P < 0.05) and from 4.9 ± 0.6 to 15.4 ± 1.2 mmHg (P < 0.05), respectively. These responses in RSNA and sodium excretion to WI in the cardiac-denervated dogs were significantly (P < 0.05) attenuated compared with those in a previous group of intact dogs. These data suggest that the attenuated responses of neural and excretory response to WI observed in cardiac-denervated dogs can be attributed to an interruption of afferent input originating from the cardiopulmonary mechanoreceptors to the central nervous system. [source]

Probing the corticospinal link between the motor cortex and motoneurones: some neglected aspects of human motor cortical function

ACTA PHYSIOLOGICA, Issue 4 2010
N. C. Petersen
Abstract This review considers the operation of the corticospinal system in primates. There is a relatively widespread cortical area containing corticospinal outputs to a single muscle and thus a motoneurone pool receives corticospinal input from a wide region of the cortex. In addition, corticospinal cells themselves have divergent intraspinal branches which innervate more than one motoneuronal pool but the synergistic couplings involving the many hand muscles are likely to be more diverse than can be accommodated simply by fixed patterns of corticospinal divergence. Many studies using transcranial magnetic stimulation of the human motor cortex have highlighted the capacity of the cortex to modify its apparent excitability in response to altered afferent inputs, training and various pathologies. Studies using cortical stimulation at ,very low' intensities which elicit only short-latency suppression of the discharge of motor units have revealed that the rapidly conducting corticospinal axons (stimulated at higher intensities) drive motoneurones in normal voluntary contractions. There are also major non-linearities generated at a spinal level in the relation between corticospinal output and the output from the motoneurone pool. For example, recent studies have revealed that the efficacy of the human corticospinal connection with motoneurones undergoes activity-dependent changes which influence the size of voluntary contractions. Hence, corticospinal drives must be sculpted continuously to compensate for the changing functional efficacy of the descending systems which activate the motoneurones. This highlights the need for proprioceptive monitoring of movements to ensure their accurate execution. [source]

Afferent-induced facilitation of primary motor cortex excitability in the region controlling hand muscles in humans

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2009
H. Devanne
Abstract Sensory inputs from cutaneous and limb receptors are known to influence motor cortex network excitability. Although most recent studies have focused on the inhibitory influences of afferent inputs on arm motor responses evoked by transcranial magnetic stimulation (TMS), facilitatory effects are rarely considered. In the present work, we sought to establish how proprioceptive sensory inputs modulate the excitability of the primary motor cortex region controlling certain hand and wrist muscles. Suprathreshold TMS pulses were preceded either by median nerve stimulation (MNS) or index finger stimulation with interstimulus intervals (ISIs) ranging from 20 to 200 ms (with particular focus on 40,80 ms). Motor-evoked potentials recorded in the abductor pollicis brevis (APB), first dorsalis interosseus and extensor carpi radialis muscles were strongly facilitated (by up to 150%) by MNS with ISIs of around 60 ms, whereas digit stimulation had only a weak effect. When MNS was delivered at the interval that evoked the optimal facilitatory effect, the H-reflex amplitude remained unchanged and APB motor responses evoked with transcranial electric stimulation were not increased as compared with TMS. Afferent-induced facilitation and short-latency intracortical inhibition (SICI) and intracortical facilitation (ICF) mechanisms are likely to interact in cortical circuits, as suggested by the strong facilitation observed when MNS was delivered concurrently with ICF and the reduction of SICI following MNS. We conclude that afferent-induced facilitation is a mechanism which probably involves muscle spindle afferents and should be considered when studying sensorimotor integration mechanisms in healthy and disease situations. [source]

Facilitation of corticospinal excitability in the tibialis anterior muscle during robot-assisted passive stepping in humans

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2009
Kiyotaka Kamibayashi
Abstract Although phasic modulation of the corticospinal tract excitability to the lower limb muscles has been observed during normal walking, it is unclear to what extent afferent information induced by walking is related to the modulation. The purpose of this study was to test the corticospinal excitability to the lower limb muscles by using transcranial magnetic stimulation (TMS) and transcranial electrical stimulation of the motor cortex while 13 healthy subjects passively stepped in a robotic driven-gait orthosis. Specifically, to investigate the effect of load-related afferent inputs on the corticospinal excitability during passive stepping, motor evoked potentials (MEPs) in response to the stimulation were compared between two passive stepping conditions: 40% body weight unloading on a treadmill (ground stepping) and 100% body weight unloading in the air (air stepping). In the rectus femoris, biceps femoris and tibialis anterior (TA) muscles, electromyographic activity was not observed throughout the step cycle in either stepping condition. However, the TMS-evoked MEPs of the TA muscle at the early- and late-swing phases as well as at the early-stance phase during ground stepping were significantly larger than those observed during air stepping. The modulation pattern of the transcranial electrical stimulation-evoked MEPs was similar to that of the TMS-evoked MEPs. These results suggest that corticospinal excitability to the TA is facilitated by load-related afferent inputs. Thus, these results might be consistent with the notion that load-related afferent inputs play a significant role during locomotor training for gait disorders. [source]

Developmental changes in the BDNF-induced modulation of inhibitory synaptic transmission in the Kölliker,Fuse nucleus of rat

Discharge patterns of neurons in the medial pontobulbar reticular formation during fictive mastication in the rabbit

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2001
K.-G. Westberg
Abstract In this study, we describe functional characteristics of neurons forming networks generating oral ingestive motor behaviours. Neurons in medial reticular nuclei on the right side of the brainstem between the trigeminal and hypoglossal motor nuclei were recorded in anaesthetized and paralysed rabbits during two types of masticatory-like motor patterns induced by electrical stimulation of the left (contralateral) or right (ipsilateral) cortical masticatory areas. Sixty-seven neurons in nucleus reticularis pontis caudalis (nPontc), nucleus reticularis parvocellularis (nParv), and nucleus reticularis gigantocellularis (Rgc) were studied. These were classified as phasic or tonic depending on their firing pattern during the fictive jaw movement cycle. Phasic neurons located in the dorsal part of nPontc were active during the jaw opening phase, whilst those in dorsal nParv tended to fire during the closing phase. In most neurons, burst duration and firing frequency changed between the two motor patterns, but there was little change in phase of firing. Tonic units were mainly recorded in the ventral half of nPontc, and at the junction between Rgc and caudal nParv. Cortical inputs with short latency from the contralateral masticatory area were more frequent in phasic (82%) than tonic (44%) neurons, whilst inputs from the ipsilateral cortex were equal in the two subgroups (57% and 56%). Phasic neurons had significantly shorter mean contralateral than ipsilateral cortical latencies, whilst there was no difference among tonic neurons. Intra- and perioral primary afferent inputs activated both types of neurons at oligo-synaptic latencies. Our results show that subpopulations of neurons in medial reticular nuclei extending from the caudal part of the trigeminal motor nucleus to the rostral third of the hypoglossal motor nucleus are active during the fictive masticatory motor behaviour. Unlike masticatory neurons in the lateral tegmentum, the medial subpopulations are spatially organized according to discharge pattern. [source]

Exercise-induced neuronal plasticity in central autonomic networks: role in cardiovascular control

EXPERIMENTAL PHYSIOLOGY, Issue 9 2009
Lisete C. Michelini
It is now well established that brain plasticity is an inherent property not only of the developing but also of the adult brain. Numerous beneficial effects of exercise, including improved memory, cognitive function and neuroprotection, have been shown to involve an important neuroplastic component. However, whether major adaptive cardiovascular adjustments during exercise, needed to ensure proper blood perfusion of peripheral tissues, also require brain neuroplasticity, is presently unknown. This review will critically evaluate current knowledge on proposed mechanisms that are likely to underlie the continuous resetting of baroreflex control of heart rate during/after exercise and following exercise training. Accumulating evidence indicates that not only somatosensory afferents (conveyed by skeletal muscle receptors, baroreceptors and/or cardiopulmonary receptors) but also projections arising from central command neurons (in particular, peptidergic hypothalamic pre-autonomic neurons) converge into the nucleus tractus solitarii (NTS) in the dorsal brainstem, to co-ordinate complex cardiovascular adaptations during dynamic exercise. This review focuses in particular on a reciprocally interconnected network between the NTS and the hypothalamic paraventricular nucleus (PVN), which is proposed to act as a pivotal anatomical and functional substrate underlying integrative feedforward and feedback cardiovascular adjustments during exercise. Recent findings supporting neuroplastic adaptive changes within the NTS,PVN reciprocal network (e.g. remodelling of afferent inputs, structural and functional neuronal plasticity and changes in neurotransmitter content) will be discussed within the context of their role as important underlying cellular mechanisms supporting the tonic activation and improved efficacy of these central pathways in response to circulatory demand at rest and during exercise, both in sedentary and in trained individuals. We hope this review will stimulate more comprehensive studies aimed at understanding cellular and molecular mechanisms within CNS neuronal networks that contribute to exercise-induced neuroplasticity and cardiovascular adjustments. [source]

To breathe or not to breathe?

EXPERIMENTAL PHYSIOLOGY, Issue 1 2009
That is the question
Our understanding of the role of the brain in respiratory rhythm generation and regulation began the early nineteenth century. Over the next 150 years the neuronal groups in the medulla oblongata and pons that were involved in eupnoea and in gasping were identified by techniques involving the lesioning of areas of the lower brainstem, several transections across the brainstem and focal electrical stimulation. An incomplete picture emerged that stressed the importance of the ventral medulla. Subsequent electrophysiological studies in in vivo, in situ and in vitro preparations have revealed the importance of restricted groups of neurones in this area, within the Bötzinger and pre-Bötzinger nuclei, that are the essential kernel for rhythm generation. The outputs to the spinal motoneurones responsible for the patterning of inspiratory and expiratory discharge are shaped by inputs from these neurones and others within the respiratory complex that determine the activity of respiratory bulbospinal neurones. It is clear that the developmental stage of the preparation is often critical for the pattern of respiratory activity that is generated and that these patterns have important physiological consequences. The models that are currently considered to explain rhythmogenesis are critically evaluated. The respiratory network is subject to regulation from peripheral and central chemoreceptors, amongst other afferent inputs, which act to ensure respiratory homeostasis. The roles of peripheral chemoreceptors as primarily O2 sensors are considered, and the evolution of ideas surrounding their roles is described. New insights into the transduction mechanisms of chemoreception in the carotid body and chemosensitive areas of the ventral medullary surface, specifically in monitoring CO2 levels, are reviewed. As new experimental tools, both genetic and cellular, are emerging, it can be expected that the detailed network architecture and synaptic interactions that pattern respiratory activity in relation to behavioural activity will be revealed over the next years. [source]

Sensorimotor integration in movement disorders

Elicited ponto-geniculo-occipital waves by auditory stimuli are synchronized with hippocampal ,-waves

PSYCHIATRY AND CLINICAL NEUROSCIENCES, Issue 3 2002
AKIHIRO KARASHIMA
Abstract The study demonstrated that ponto-geniculo-occipital (PGO) waves are phase-locked with hippocampal ,-waves during rapid eye movement (REM) sleep. A possible mechanism for influencing a PGO wave generator by hippocampal ,-waves was hypothesized. The generator is known to receive afferent inputs such as auditory input. To test this hypothesis, the temporal relationship between hippocampal ,-waves and elicited PGO waves (PGOE) by auditory stimuli was analysed. The analysis showed that PGOE were synchronized with ,-waves, but did not reset the phase of a ,-wave. Because the occurrence of PGOE and spontaneous PGO waves shared the same phase-dependency on ,-waves, the results strongly suggest that the PGO wave generator was driven by ,-waves, as originally hypothesized. [source]

Altered balance of ,-aminobutyic acidergic and glutamatergic afferent inputs in rostral ventrolateral medulla-projecting neurons in the paraventricular nucleus of the hypothalamus of renovascular hypertensive rats

THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 5 2010
Vinicia Campana Biancardi
An imbalance of excitatory and inhibitory functions has been shown to contribute to numerous pathological disorders. Accumulating evidence supports the idea that a change in hypothalamic ,-aminobutyic acid (GABA)-ergic inhibitory and glutamatergic excitatory synaptic functions contributes to exacerbated neurohumoral drive in prevalent cardiovascular disorders, including hypertension. However, the precise underlying mechanisms and neuronal substrates are still not fully elucidated. In the present study, we combined quantitative immunohistochemistry with neuronal tract tracing to determine whether plastic remodeling of afferent GABAergic and glutamatergic inputs into identified RVLM-projecting neurons of the hypothalamic paraventricular nucleus (PVN-RVLM) contributes to an imbalanced excitatory/inhibitory function in renovascular hypertensive rats (RVH). Our results indicate that both GABAergic and glutamatergic innervation densities increased in oxytocin-positive, PVN-RVLM (OT-PVN-RVLM) neurons in RVH rats. Despite this concomitant increase, time-dependent and compartment-specific differences in the reorganization of these inputs resulted in an altered balance of excitatory/inhibitory inputs in somatic and dendritic compartments. A net predominance of excitatory over inhibitory inputs was found in OT-PVN-RVLM proximal dendrites. Our results indicate that, along with previously described changes in neurotransmitter release probability and postsynaptic receptor function, remodeling of GABAergic and glutamatergic afferent inputs contributes as an underlying mechanism to the altered excitatory/inhibitory balance in the PVN of hypertensive rats. J. Comp. Neurol. 518:567,585, 2010. © 2010 Wiley-Liss, Inc. [source]

Twitch and nontwitch motoneuron subgroups in the oculomotor nucleus of monkeys receive different afferent projections

THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 2 2004
Richard Wasicky
Abstract Motoneurons in the primate oculomotor nucleus can be divided into two categories, those supplying twitch muscle fibers and those supplying nontwitch muscle fibers. Recent studies have shown that twitch motoneurons lie within the classical oculomotor nucleus (nIII), and nontwitch motoneurons lie around the borders. Nontwitch motoneurons of medial and inferior rectus are in the C group dorsomedial to nIII, whereas those of inferior oblique and superior rectus lie near the midline are in the S group. In this anatomical study, afferents to the twitch and nontwitch subgroups of nIII have been anterogradely labeled by injections of tritiated leucine into three areas and compared. 1) Abducens nucleus injections gave rise to silver grain deposits over all medial rectus subgroups, both twitch and nontwitch. 2) Laterally placed vestibular complex injections that included the central superior vestibular nucleus labeled projections only in twitch motoneuron subgroups. However, injections into the parvocellular medial vestibular nucleus (mvp), or Y group, resulted in labeled terminals over both twitch and nontwitch motoneurons. 3) Pretectal injections that included the nucleus of the optic tract (NOT), and the olivary pretectal nucleus (OLN), labeled terminals only over nontwitch motoneurons, in the contralateral C group and in the S group. Our study demonstrates that twitch and nontwitch motoneuron subgroups do not receive identical afferent inputs. They can be controlled either in parallel, or independently, suggesting that they have basically different functions. We propose that twitch motoneurons primarily drive eye movements and nontwitch motoneurons the tonic muscle activity, as in gaze holding and vergence, possibly involving a proprioceptive feedback system. J. Comp. Neurol. 479:117,129, 2004. © 2004 Wiley-Liss, Inc. [source]