Connection Input Mapping and 3D Reconstruction of the Brainstem and Spinal Cord Projections to the CSF-Contacting Nucleus.

Objective: To investigate whether the CSF-contacting nucleus receives brainstem and spinal cord projections and to understand the functional significance of these connections. Methods: The retrograde tracer cholera toxin B subunit (CB) was injected into the CSF-contacting nucleus in Sprague-Dawley rats according the previously reported stereotaxic coordinates. After 7-10 days, these rats were perfused and their brainstem and spinal cord were sliced (thickness, 40 µm) using a freezing microtome. All the sections were subjected to CB immunofluorescence staining. The distribution of CB-positive neuron in different brainstem and spinal cord areas was observed under fluorescence microscope. Results: The retrograde labeled CB-positive neurons were found in the midbrain, pons, medulla oblongata, and spinal cord. Four functional areas including one hundred and twelve sub-regions have projections to the CSF-contacting nucleus. However, the density of CB-positive neuron distribution ranged from sparse to dense. Conclusion: Based on the connectivity patterns of the CSF-contacting nucleus receives anatomical inputs from the brainstem and spinal cord, we preliminarily conclude and summarize that the CSF-contacting nucleus participates in pain, visceral activity, sleep and arousal, emotion, and drug addiction. The present study firstly illustrates the broad projections of the CSF-contacting nucleus from the brainstem and spinal cord, which implies the complicated functions of the nucleus especially for the unique roles of coordination in neural and body fluids regulation.

Neurochemical organization of the vestibular brainstem in the common chimpanzee (Pan troglodytes).

Chimpanzees are one of the closest living relatives of humans. However, the cognitive and motor abilities of chimpanzees and humans are quite different. The fact that humans are habitually bipedal and chimpanzees are not implies different uses of vestibular information in the control of posture and balance. Furthermore, bipedal locomotion permits the development of fine motor skills of the hand and tool use in humans, suggesting differences between species in the structures and circuitry for manual control. Much motor behavior is mediated via cerebro-cerebellar circuits that depend on brainstem relays. In this study, we investigated the organization of the vestibular brainstem in chimpanzees to gain insight into whether these structures differ in their anatomy from humans. We identified the four nuclei of vestibular nuclear complex in the chimpanzee and also looked at several other precerebellar structures. The size and arrangement of some of these nuclei differed between chimpanzees and humans, and also displayed considerable inter-individual variation. We identified regions within the cytoarchitectonically defined medial vestibular nucleus visualized by immunoreactivity to the calcium-binding proteins calretinin and calbindin as previously shown in other species including human. We have found that the nucleus paramedianus dorsalis, which is identified in the human but not in macaque monkeys, is present in the chimpanzee brainstem. However, the arcuate nucleus, which is present in humans, was not found in chimpanzees. The present study reveals major differences in the organization of the vestibular brainstem among Old World anthropoid primate species. Furthermore, in chimpanzees, as well as humans, there is individual variability in the organization of brainstem nuclei.

Vestibular nuclei characterized by calcium-binding protein immunoreactivity and tract tracing in Gekko gecko.

Immunohistochemical techniques were used to describe the distribution of the calcium binding proteins calretinin, calbindin and parvalbumin as well as synaptic vesicle protein 2 in the vestibular nuclei of the Tokay gecko (Gekko gecko). In addition, tract tracing was used to investigate connections between the vestibular nerves and brainstem nuclei. Seven vestibular nuclei were recognized: the nuclei cerebellaris lateralis (Cerl), vestibularis dorsolateralis (Vedl), ventrolateralis (Vevl), ventromedialis (Vevm), tangentialis (Vetg), ovalis (VeO) and descendens (Veds). Vestibular fibers entered the brainstem with the ascending branch projecting to Vedl and Cerl, the lateral descending branch to Veds, and the medial descending branch to ipsilateral Vevl. Cerl lay most rostral, in the cerebellar peduncle. Vedl, located rostrally, was ventral to the cerebellar peduncle, and consisted of loosely arranged multipolar and monopolar cells. Vevl was found at the level of the vestibular nerve root and contained conspicuously large cells and medium-sized cells. Veds is a large nucleus, the most rostral portion of which is situated lateral and ventral to Vevl, and occupies much of the dorsal brainstem extending caudally through the medulla. VeO is a spherically shaped cell group lateral to the auditory nucleus magnocellularis and dorsal to the caudal part of Vevl. Vevm and Vetg were small in the present study. Except for VeO, all other vestibular nuclei appear directly comparable to counterparts in other reptiles and birds based on their location, cytoarchitecture, and connections, indicating these are conserved features of the vestibular system.

Precerebellar and vestibular nuclei of the short-beaked echidna (Tachyglossus aculeatus).

The monotremes are a unique group of living mammals, which diverged from the line leading to placental mammals at least 125 million years ago. We have examined the organization of pontine, inferior olivary, lateral reticular and vestibular nuclei in the brainstem of the short-beaked echidna (Tachyglossus aculeatus) to determine if the cyto- and chemoarchitecture of these nuclei are similar to that in placental mammals and marsupials. We have used Nissl staining in conjunction with enzyme-histochemistry for acetylcholinesterase, cytochrome oxidase and NADPH diaphorase as well as immunohistochemistry for non-phosphorylated neurofilament protein (SMI-32 antibody) and calcium binding proteins (parvalbumin, calbindin, calretinin). Homologies could be established between the arch shaped inferior olivary complex of the echidna and the principal, dorsal and medial accessory subdivisions of the therian inferior olivary complex. The pontine nuclei of the echidna included basilar and reticulotegmental components with similar cyto- and chemarchitectural features to therians and there were magnocellular and subtrigeminal components of the lateral reticular nucleus, also as seen in therians. Subdivisions and chemoarchitecture of the vestibular complex of the echidna were both similar to that region in rodents. In all three precerebellar nuclear groups studied and in the vestibular nucleus organization, the cyto- and chemoarchitecture of the echidna was very similar to that seen in therian mammals and no "primitive" or "reptilian" features were evident.

Characterization of neuronal subsets surrounded by perineuronal nets in the rhesus auditory brainstem.

The distribution of perineuronal nets and the potassium channel subunit Kv3.1b was studied in the subdivisions of the cochlear nucleus, the medial nucleus of the trapezoid body, the medial and lateral superior olivary nuclei, the lateral lemniscal nucleus and the inferior colliculus of the rhesus monkey. Additional sections were used for receptor autoradiography to visualize the patterns of GABAA and GABAB receptor distribution. The Kv3.1b protein and perineuronal nets [visualized as Wisteria floribunda agglutinin (WFA) binding] were revealed, showing corresponding region-specific patterns of distribution. There was a gradient of labelled perineuronal nets which corresponded to that seen for the intensity of Kv3.1b expression. In the cochlear nucleus intensely and faintly stained perineuronal nets were intermingled, whereas in the medial nucleus of the trapezoid body the pattern changed to intensely stained perineuronal nets in the medial part and weakly labelled nets in its lateral part. In the inferior colliculus, intensely labelled perineuronal nets were arranged in clusters and faintly labelled nets were arranged in sheets. Using receptor autoradiography, GABAB receptor expression in the anterior ventral cochlear nucleus was revealed. The medial part of the medial nucleus of the trapezoid body showed a high number of GABAA binding sites whereas the lateral part exhibited more binding sites for GABAB. In the inferior colliculus, we found moderate GABAB receptor expression. In conclusion, intensely WFA-labelled structures are those known to be functionally involved in high-frequency processing.

The anatomy of the vestibular nuclei.

The vestibular portion of the eighth cranial nerve informs the brain about the linear and angular movements of the head in space and the position of the head with respect to gravity. The termination sites of these eighth nerve afferents define the territory of the vestibular nuclei in the brainstem. (There is also a subset of afferents that project directly to the cerebellum.) This chapter reviews the anatomical organization of the vestibular nuclei, and the anatomy of the pathways from the nuclei to various target areas in the brain. The cytoarchitectonics of the vestibular brainstem are discussed, since these features have been used to distinguish the individual nuclei. The neurochemical phenotype of vestibular neurons and pathways are also summarized because the chemical anatomy of the system contributes to its signal-processing capabilities. Similarly, the morphologic features of short-axon local circuit neurons and long-axon cells with extrinsic projections are described in detail, since these structural attributes of the neurons are critical to their functional potential. Finally, the composition and hodology of the afferent and efferent pathways of the vestibular nuclei are discussed. In sum, this chapter reviews the morphology, chemoanatomy, connectivity, and synaptology of the vestibular nuclei.

[Distribution of Fas and FasL in the central nervous system of adult rhesus].

OBJECTIVE: To investigate the distribution of Fas and FasL in the CNS of adult rhesus. METHODS: Frozen sections were incubated in polyclonal anti-Fas and anti-FasL antibody by the immunohistochemical SP method. RESULTS: The Fas and FasL immunopositive neurons were observed in many areas. Fas immunoreactivity could be seen in the cytoplasm and processes of Purkinje cells and in the brain stem nuclei, including vestibular nucleus, dorsal nucleus of vagus and spinal nucleus of trigeminal nerve. FasL immunopositive neurons were observed in cerebral cortex, especially in pyramidal neurons of lamina I and V, cerebellar nuclei, diencephalon, and brain stem nuclei involving pontine nucleus, vestibular nucleus, cochlear nucleus, spinal nucleus of trigeminal nerve, hypoglossal nucleus, nucleus ambiguous and reticular formation. Fas and FasL immunoreactivity mainly distributed in motor neurons of spinal ventral horn and neural fibers and glia cells in white matter. They all took on brown staining in the cytoplasm and process. CONCLUSION: The distribution profiles of Fas and FasL in various areas of CNS indicate that they may fill some roles in the immune and physical function of the aforesaid anatomic

Polysynaptic pathways from the vestibular nuclei to the lateral mammillary nucleus of the rat: substrates for vestibular input to head direction cells.

The activity of some neurons in the lateral mammillary nucleus (LMN) of the rat corresponds with the animal's current head direction (HD). HD cells have been studied extensively but the circuitry responsible for the generation and maintenance of the HD signal has not been established. The present study tested the hypothesis that a polysynaptic pathway connects the vestibular nuclei with the LMN via one or more relay nuclei. This circuitry could provide a substrate for the integration of sensory input necessary for HD cell activity. This hypothesis is based upon the prior demonstration that labyrinthectomy abolishes HD selectivity in thalamic neurons. Viral transneuronal tracing with pseudorabies virus (PRV) was used to test this hypothesis. We injected recombinants of PRV into the LMN and surrounding nuclei of adult male rats and defined the patterns of retrograde transneuronal infection at survival intervals of 60 and 72 h. Infected medial vestibular neurons (MVN) were only observed at the longest postinoculation interval in animals in which the injection site was localized largely to the LMN. Robust infection of the dorsal tegmental nucleus (DTN) and nucleus prepositus hypoglossi (PH) in these cases, but not in controls, at both survival intervals identified these nuclei as potential relays of vestibular input to the LMN. These data are consistent with the conclusion that vestibular information that contributes to the LMN HD cell activity is relayed to this caudal hypothalamic cell group via a polysynaptic brainstem circuit.

Microarray analysis of gene expression in the rat vestibular nucleus complex following unilateral vestibular deafferentation.

To investigate the molecular background of vestibular compensation, a model of lesion-induced plasticity, we used a microarray analysis to examine genes that show asymmetrical expression between the bilateral vestibular nucleus complexes (VNCs) 6 h following unilateral vestibular deafferentation (UVD). Asymmetrical gene expression was then validated by a real-time quantitative PCR. Among the 88 genes for which the ipsilateral (ipsi) : contralateral (contra) was > 1.35, the number of known genes was 33 (38%), and the number of expressed sequence tag (EST) sequences was 55 (62%). Among the 130 genes for which the contra : ipsi was > 1.35, the number of known genes was 55 (42%), and the number of EST sequences was 75 (58%). Changes in some of the genes were consistent with previous studies; however, we found several new genes which could be functionally related to the molecular basis of the electrophysiological asymmetry between the VNCs following UVD. Ipsi > contra genes included the GABA(A) receptor rho subunit, regulatory proteins of G protein signaling, calcium signaling related molecules such as the voltage-dependent calcium channel alpha2/delta subunit 1, calcineurin subunit Abeta and Ca(2+) pump. Contra > ipsi genes included the neuronal high affinity glutamate transporter, 5-hydroxytryptamine receptor 1D, mitogen-activated protein kinase 12 and ubiquitin carboxy-terminal hydrolase L1.

Plasticity of histamine H3 receptor expression and binding in the vestibular nuclei after labyrinthectomy in rat.

BACKGROUND: In rat, deafferentation of one labyrinth (unilateral labyrinthectomy) results in a characteristic syndrome of ocular and motor postural disorders (e.g., barrel rotation, circling behavior, and spontaneous nystagmus). Behavioral recovery (e.g., diminished symptoms), encompassing 1 week after unilateral labyrinthectomy, has been termed vestibular compensation. Evidence suggesting that the histamine H3 receptor plays a key role in vestibular compensation comes from studies indicating that betahistine, a histamine-like drug that acts as both a partial histamine H1 receptor agonist and an H3 receptor antagonist, can accelerate the process of vestibular compensation. RESULTS: Expression levels for histamine H3 receptor (total) as well as three isoforms which display variable lengths of the third intracellular loop of the receptor were analyzed using in situ hybridization on brain sections containing the rat medial vestibular nucleus after unilateral labyrinthectomy. We compared these expression levels to H3 receptor binding densities. Total H3 receptor mRNA levels (detected by oligo probe H3X) as well as mRNA levels of the three receptor isoforms studied (detected by oligo probes H3A, H3B, and H3C) showed a pattern of increase, which was bilaterally significant at 24 h post-lesion for both H3X and H3C, followed by significant bilateral decreases in medial vestibular nuclei occurring 48 h (H3X and H3B) and 1 week post-lesion (H3A, H3B, and H3C). Expression levels of H3B was an exception to the forementioned pattern with significant decreases already detected at 24 h post-lesion. Coinciding with the decreasing trends in H3 receptor mRNA levels was an observed increase in H3 receptor binding densities occurring in the ipsilateral medial vestibular nuclei 48 h post-lesion. CONCLUSION: Progressive recovery of the resting discharge of the deafferentated medial vestibular nuclei neurons results in functional restoration of the static postural and occulomotor deficits, usually occurring within a time frame of 48 hours in rats. Our data suggests that the H3 receptor may be an essential part of pre-synaptic mechanisms required for reestablishing resting activities 48 h after unilateral labyrinthectomy.

Immunohistochemical detection of phosphorylated form of extracellular signal-regulated kinase 1/2 in rat vestibular nuclei following hemorrhagic hypotension.

The purpose of this study was to evaluate the expression of the phosphorylated form of extracellular-regulated protein kinase 1/2 (pERK1/2), which is one of the major regulatory factors for transcription of the c-fos oncogene in neurons, within the vestibular nuclei (VN) of rats following acute arterial hypotension. Following acute arterial hypotension induced by rapid hemorrhage, a significant number of pERK1/2-immunoreactive neurons appeared bilaterally in the caudal aspect of the medial and inferior VN. No labeling of pERK1/2 was observed in the lateral VN. The peak expression of pERK1/2-immunoreactive neurons in these nuclei occurred within 5 min after hemorrhage. In bilaterally labyrinthectomized rats, the appearance of pERK1/2-immunoreactive neurons was eliminated in the VN. These results suggest that, following acute hypotension, afferent signals from the peripheral vestibular receptors are required for activation of extracellular signal-regulated kinase 1/2 in the VN.

Glutamate release in the rat medial vestibular nucleus following unilateral labyrinthectomy using in vivo microdialysis.

We investigated the changes in glutamate release from the ipsi- and contra-lesional medial vestibular nucleus (MVN) following unilateral labyrinthectomy (UL) by in vivo microdialysis study. The concentration of glutamate in the ipsi-lesional MVN was decreased until 4 h. Twelve hours after UL, the concentration of glutamate was restored back to the basal level, after which the release did not show any change between 24 and 48 h post-UL. In contrast, the concentration of glutamate in the contra-lesional MVN, which increased immediately after UL, decreased gradually to the basal level until 3-4 h post-UL, followed by no further change. The difference in the glutamate concentration between ipsi- and contra-lesional MVN increased immediately after UL and gradually decreased accompanied by a reduction in the frequency of nystagmus, although spontaneous nystagmus had not disappeared by the time the imbalance of glutamate release diminished. These results suggest that the imbalance of glutamate release between bilateral nuclei induced the nystagmus, and the change in release is concerned with the rapid development of vestibular compensation.

Neurotrophin receptor immunostaining in the vestibular nuclei of rats.

The distribution of high-affinity neurotrophin receptors in cells of the vestibular nuclear complex and its subnuclei of adult rats was examined. We noted a high density of tyrosine kinase (Trk) A- and B- and a lower density of TrkC-immunostained cells. In particular, long, intensely labelled immunostained-TrkB fibres formed networks in the neuropil. Both TrkA- and TrkB-immunostained cells were widely distributed in the lateral, medial and spinal vestibular nuclei, and were less frequently seen in the superior vestibular nucleus, x and y subnuclei. However, immunostaining for TrkC was weak in many cells within the vestibular nuclei. The widespread and abundant neuronal distribution of Trk receptors predicts that their associated neurotrophins exert significant effects on individual cells within the vestibular nuclei.

Vestibulotrigeminal and vestibulospinal projections in rats: retrograde tracing coupled to glutamic acid decarboxylase immunoreactivity.

Immunohistochemical experiments were performed using glutamic acid decarboxylase (GAD) to identify gamma-aminobutyric acid (GABA)ergic neurons in the vestibular nuclei (VN). VN neurons projecting to the sensory trigeminal complex (STC) or to the C1-C2 segments of the spinal cord were identified by injection of wheat germ agglutinin-apo-horseradish peroxidase coupled to colloidal gold (gold-HRP), a retrogradely transported tracer, in these structures. The experiments combining injection of gold-HRP in spinal cord and GAD immunohistochemistry revealed the existence in the medial, inferior and lateral VN of GAD immunoreactive neurons projecting to the spinal C1-C2 level. Experiments combining injection of gold-HRP in the STC and GAD immunohistochemistry demonstrated that, at least, 30-50% of the vestibulo-trigeminal neurons also contained GAD. Injections of two different retrograde tracers (gold-HRP and Biotinylated dextran amine) in the STC and the spinal cord demonstrated that some VN neurons project by axon collaterals to both structures. Because of the GABAergic spinal and STC vestibular projections we assume that these VN neurons with collateral projection are GABAergic. Therefore primary afferents from the face, neck or hindlimb could be modulated by inhibitory influences from GABAergic vestibular neurons.

Modulation of the voltage-gated sodium- and calcium-dependent potassium channels in rat vestibular and facial nuclei after unilateral labyrinthectomy and facial nerve transsection: an in situ hybridization study.

We investigated whether the expression in the vestibular and facial nuclei of the voltage-dependent Na alpha I and Na alpha III channels and of the Ca(2+)-activated K(+)-channel subunits, small-conductance (SK) 1, SK2 and SK3, is affected by unilateral inner-ear lesion including both labyrinthectomy and transsection of the facial nerve. Specific sodium (Na alpha I, Na alpha III) and potassium (SK1, SK2, SK3) radioactive oligonucleotides were used to probe sections of rat vestibular and facial nuclei by in situ hybridization methods. The signal was detected with films or by emulsion photography. Animals were killed at various times following the lesion: 1 day, 3 days, 8 days or 30 days. In normal adult animals, mRNAs for Na alpha I, and SK1, SK2, and SK3 channels were found in several brainstem regions including the lateral, medial, superior and inferior vestibular nuclei and the facial nuclei. In contrast, there was little Na alpha III subunit mRNA anywhere in the brainstem. Following unilateral inner ear lesion in rats, the medial vestibular nuclei were probed with Na alpha I, Na alpha III, SK1, SK2 and SK3 oligonucleotide probes: autoradiography indicated no difference between the two sides, at any of the times studied. Na alpha I and SK2 mRNAs were less abundant and Na alpha III, SK1 and SK3 mRNAs were more abundant in the axotomized facial nuclei motoneurons than in controls. Removal of vestibular input did not affect the abundance of the mRNAs for the sodium- or calcium-dependent potassium channels in the deafferented vestibular nuclei. There is thus no evidence that modulation of these conductances contributes to the recovery of a normal resting discharge of the deafferented vestibular neurons and consequently to the functional recovery of the postural and oculomotor deficits observed at the acute stage. However, facial axotomy induced a long-term modulation of both Na and SK conductances mRNAs in the facial motoneurons ipsilateral to the lesion. Presumably, retrograde injury factors resulting from axotomy were able to alter durably the membrane properties and thus the excitability of the facial motoneurons.

Plurisegmental vestibulocerebellar projections and other hindbrain cerebellar afferents in midterm chick embryos: biotinylated dextranamine experiments in vitro.

The vestibular neuronal groups that project to the cerebellum were mapped in midterm chick embryos (10-11 days in "ovo") through "in vitro " retrograde tracing experiments. Massive unilateral deposits of biotin-dextranamine were placed at the basis of the cerebellum to label the cerebellar peduncles. Separate rostral and caudal vestibulo-cerebellar groups were identified, with predominance of contralateral neurons. We tentatively identified the rhombomeric location of both groups, as well as their topography within the conventional cytoarchitectonically-defined vestibular nuclei, by comparison with previously established segmental fate maps. The rostral group extended from rhombomeres 1-4 (r1-r4) and was restricted mainly to the superior vestibular nucleus. The caudal group stretched from r6 to pseudorhombomere "r8" and was related to the descending and medial vestibular nuclei. The less abundant ipsilateral vestibulocerebellar neurons had a similar topography. The crossing axons of the rostral vestibulocerebellar neurons formed a distinct rostral vestibulocerebellar decussation, restricted to the floorplate of rhombomere 2. The axons of the caudal vestibulocerebellar population mostly decussated associated to the deep cochlear commissure. The present results extend the "segmental hodological mosaic" of defined projection-neuron groups identified within the avian vestibular nuclear complex: The vestibulocerebellar projecting neurons as a type appear iterated from r1 to r4 and from r6 to pseudorhombomere "r8," albeit showing in their arrangement peculiarities related to single segmental domains, particularly rostrally. In contrast, the vestibulospinal groups are located more restrictedly in r4-r6, while the vestibulo-ocular projecting neurons extend from r1 to "r7." Only r4 and r6 contain elements of all three hodological types. The organization of the three vestibular projection populations studied to date seems comparable in chicken and frogs and may be a conserved feature in vertebrates.

Calcium-binding proteins map the postnatal development of rat vestibular nuclei and their vestibular and cerebellar projections.

We investigated whether three calcium-binding proteins, calretinin, parvalbumin, and calbindin, could identify specific aspects of the postnatal development of the rat lateral (LVN) and medial (MVN) vestibular nuclei and their vestibular and cerebellar connections. Calretinin levels in the vestibular nuclei, increased significantly between birth and postnatal day (P) 45. In situ hybridization and immunocytochemical staining showed that calretinin-immunoreactive neurons were mostly located in the parvocellular MVN at birth and that somatic and dendritic growth occurred between birth and P14. During the first week, parvalbumin-immunoreactive fibers and endings were confined to specific areas, i.e., the ventral LVN and magnocellular MVN, and identified exclusively the maturation of the vestibular afferents. Calbindin was located within the dorsal LVN and the parvocellular MVN and identified the first arrival of the corticocerebellar afferents. From the second week, in addition to labeling vestibular afferents in their specific target areas, parvalbumin was also found colocalized with calbindin in mature Purkinje cell afferents. Thus, the specific spatiotemporal distribution of parvalbumin and calbindin could correspond to two successive phases of synaptic remodeling involving integration of the vestibular sensory messages and their cerebellar control. On the basis of the sequence of distribution patterns of these proteins during the development of the vestibular nuclei, calretinin is an effective marker for neuronal development of the parvocellular MVN, parvalbumin is a specific marker identifying maturation of the vestibular afferents and endings, and calbindin is a marker of the first appearance and development of Purkinje cell afferents.

NMDA and AMPA receptor subunit protein expression in the rat vestibular nucleus following unilateral labyrinthectomy.

We examined the expression of the NR1 and NR2A subunits of the N-methyl-D-aspartate (NMDA) receptor, and the GluR2 subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor, in the ipsilateral and contralateral vestibular nucleus complexes (VNCs) at 10 h and 2 weeks following unilateral vestibular deafferentation (UVD) in rats, in order to directly test the hypothesis that the behavioural recovery following UVD ('vestibular compensation') is associated with an up-regulation of NMDA receptors. We found no significant changes in NR1 or NR2A expression at 10 hs or 2 weeks post-op. compared to sham and anesthetic controls. We did find a significant (p < 0.01 and p < 0.05) increase in GluR2 expression in both VNCs at 10 h but not 2 weeks post-op. compared to sham and anesthetic controls; however, comparison over time post-UVD failed to detect a significant difference, suggesting that it was small and transient at best. These results add further evidence to the conclusion that NMDA receptors do not undergo up-regulation in the ipsilateral VNC during vestibular compensation.

Dexamethasone attenuates by colchicine induced Fos expression in the rat deep cerebellar and vestibular nuclei.

1. The intent of the present study was to find out whether dexamethasone pretreatment may affect the induction of Fos protein in cell nuclei of the cerebellar vestibular neuronal complex (CVNC) elicited by central administration of colchicine. Specifically, the rate of the dexamethasone-sensitive cell population was analyzed and compared at different levels of the CVNC using a light microscopic avidin-biotin peroxidase immunohistochemistry. 2. Male Wistar rats were pretreated with dexamethasone 3 days prior (2.5 mg/kg/day, s.c.) and 24 h after an intracerebroventricular delivery of colchicine (60 microg/10 microL). Animals were sacrificed 48 h after colchicine treatment by a transcardial perfusion with fixative. 3. Dexamethasone in itself had no effect on the activity of cells of the CVNC. However, in colchicine treated animals, which exhibited a large number of Fos-positive cells over the entire CVNC, the dexamethasone elicited a substantial reduction in the number of the Fos-immunoreactive cells over the CVNC. Distinct dexamethasone dependent reduction (50-90%) of Fos-immunoreactivity was observed in each of the deep cerebellar nuclei. On the other hand, less number of dexamethasone-sensitive cells were recognized in the vestibular structures. From these, maximal Fos-inhibition by dexamethasone was recognized in the medial vestibular nucleus, however, even in this case the number of suppressed cells did not exceed 50%. 4. The results provide for the first time evidence about the dexamethasone dependent reduction of Fos-immunoreactivity in the cells of the CVNC in response to stimulation elicited by colchicine. The data also indicate that the glucocorticoids might be involved in the regulation of some functions of the CVNC under stress conditions.

Voltage-gated calcium channels contribute to the pattern of the resting discharge in guinea pig medial vestibular nucleus neurons.

In brainstem slices of guinea pigs perfused with artificial cerebro-spinal fluid (ACSF), the discharge of all the spontaneously active neurons of the medial vestibular nucleus (MVN) is regular. It has been reported that prolonged exposure to a low Ca(2+) medium could induce these neurons to fire bursts of spikes. In this study, we performed a systematic exploration of the spontaneous activity of the guinea pig MVN neurons by extracellular recordings in slices perfused either with a low Ca(2+)-high Mg(2+) medium, or with ACSF added with omega-agatoxin-IVA and with omega-conotoxin-GVIA. The percentage of recorded neurons which fired bursts, was 67% in low Ca(2+)-high Mg(2+) medium and 34% under the action of Ca(2+) channel blockers. These results show that the sensitivity of the firing properties to divalent cations is not shared by all of the MVN neurons and that the regularity of firing of a class of MVN neurons depends on the Ca(2+) channels they express in their membranes.