Immunocytochemical features of the vestibular nuclei in the monkey and cat.

Immunocytochemical studies of the vestibular nuclei (VN) were done in the squirrel monkey and cat using polyclonal antisera. Brain stem sections were processed using the Avidin-Biotin peroxidase complex with diaminobenzidine as the chromagen. Choline acetyltransferase immunoreactivity (ChAT-IR) was most prevalent in the caudal medial (MVN), inferior (IVN) and peripheral superior (SVN) VN. Nearly all cells of groups x and z were ChAT-positive. None of the giant cells of the lateral vestibular nucleus (LVN) was ChAT-IR. Glutamate immunoreactivity (GLU-IR) was abundant in all VN and in cells of the vestibular ganglion (VG). Gamma-aminobutyric acid immunoreactivity (GABA-IR), was found in cells of rostral MVN, cell group y and in granules about giant cells in dorsal LVN. Substance P immunoreactive (SP-IR) was present in a small cells in MVN, IVN and the VG and in granules surrounding all large cells in LVN in both monkey and cat; SP-IR granules were most intense in ventral LVN in the monkey. Some cells in the dorsal parts of the fastigial nucleus (FN) were outlined by SP-IR granules in both species. Leucine-enkephalin immunoreactivity (ENK-IR) was identified only in granules surrounding cells of group x in the monkey. GLU was the only immunoreactive substance found in the giant cells of LVN. The disposition of ChAT-IR in the VN suggested participation in commissural systems, as well as projections to spinal cord and/or cerebellum. Small GABA-IR neurons in MVN probably represented both commissural and projection neurons; GABA-IR granules about cells in dorsal LVN and some cells in MVN and SVN appeared to represent Purkinje cell (PC) terminals. SP-IR granules surrounding cells in ventral LVN appeared to represent terminals of small SP-positive VG cells. The source of SP-IR granules around cells in dorsal LVN and some cells in FN and SVN remains unknown, but these fibers may originate from portions of the reticular formation known to contain large numbers of SP-positive neurons.     

Afferent and efferent connections of the medial, inferior and lateral vestibular nuclei in the cat and monkey

Attempts were made to determine the afferent and efferent connections of the medial (MVN), inferior (IVN) and lateral (LVN) vestibular nuclei (VN) in the cat and monkey using retrograde and anterograde axoplasmic transport technics. Injections of HRP and [3H]amino acids were made selectively into MVN, IVN and LVN and into: (1) MVN and IVN, (2) LVN and IVN and (3) all 4 VN. Contralateral afferents to MVN arise from (1) the nuclei prepositus (NPP) and intercalatus (NIC), (2) all parts of MVN and cell group 'y' and (3) parts of the superior vestibular nucleus (SVN), IVN and the fastigial nucleus (FN). Ipsilateral projections to MVN arise from: (1) a central band of the flocculus and the nodulus and uvula, (2) the interstitial nucleus of Cajal (INC), and (3) visceral nuclei of the oculomotor nuclear complex (OMC). Efferent projections of MVN are to: (1) the ipsilateral supraspinal nucleus (SSN), and (2) the contralateral central cervical nucleus (CCN), MVN, SVN, cell group 'y', the rostroventral region of LVN, the trochlear nucleus (TN) and the INC. Projections to the abducens nuclei (AN) and the OMC are bilateral. Some ascending fibers in the cat cross within the OMC. In the monkey fibers from MVN end in a central band of the ipsilateral flocculus. Afferents to IVN arise ipsilaterally from SVN, the nodulus, the uvula and the anterior lobe vermis. Contralateral afferents arise from: (1) parts of CCN, MVN, SVN, IVN and cell group 'y' and (2) the central third of the FN. IVN receives bilateral projections from the perihypoglossal nuclei (PH) and the visceral nuclei of the OMC. Efferents from IVN project: (1) ipsilaterally to nucleus beta of the inferior olive, (2) contralaterally to parts of MVN, SVN and cell group 'y' and (3) bilaterally to the paramedian reticular nuclei. No commissural fibers interconnect cell groups 'f' and 'x'. Ascending fibers from IVN terminate contralaterally in the TN and the OMC. In the monkey fibers from IVN terminate in the ipsilateral nodulus, uvula and anterior lobe vermis; no fibers project to FN in either the cat or the monkey. Afferents to the LVN arise primarily from the ipsilateral anterior lobe vermis and bilaterally from rostral parts of the FN. No commissural fibers interconnect the LVN. Projections of the LVN are primarily to spinal cord via the vestibulospinal tract (VST); collaterals of the VST terminate in the lateral reticular nucleus (LRN). Ascending uncrossed projections from LVN in the cat terminate in the medial rectus subdivision of the OMC.(ABSTRACT TRUNCATED AT 400 WORDS)     

Immunocytochemistry of oculomotor afferents in the squirrel monkey (Saimiri sciureus).

Attempts were made to co-define afferents of the oculomotor nuclear complex (OMC) and their putative neurotransmitters in the squirrel monkey. Wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) and wheat germ agglutinin conjugated to enzymatically inactive HRP and coupled to colloidal gold (WGAapoHRP-AU) were used as retrograde tracers in combination with immunocytochemical methods. Primarily unilateral injections were made into portions of the OMC. Stabilized tetramethylbenzidine (TMB) and silver enhanced sections were immunoreacted with antisera for choline acetyltransferase (ChAT), glutamate (GLU), aspartate (ASP), aminobutyric acid (GABA), serotonin (5-HT) and cholecystokinin (CCK). Moderate numbers of ChAT-IR neurons in caudal regions of the medial vestibular nuclei (MVN) projected to the OMC. Tracer labeled ChAT-IR cells in the MVN projected ipsilaterally to the ventral nucleus (medial rectus subdivision) of the OMC and bilaterally with contralateral dominance to other OMC subdivisions. Cholinergic neurons in the dorsal paragigantocellular reticular nucleus (DPG) projected bilaterally to each half of the OMC. Cells of the DPG, considered to contain inhibitory burst neurons impinging upon the contralateral abducens nucleus, were shown to project to virtually all subdivision of the OMC. Abducens motor neurons were ChAT-IR, but abducens internuclear neurons were not. Cells in caudal parts of the nucleus prepositus (NPP) projecting to the ipsilateral ventral nucleus of the OMC were not ChAT-positive; ChAT-IR cells in rostral NPP did not project to the OMC. Unilateral OMC injections labeled cells ipsilaterally in the RiMLF, contralaterally in the pretectal olivary nucleus, the interstitial nucleus of Cajal and the infracerebellar nucleus and bilaterally in the superior vestibular nucleus, none of which were ChAT-IR. A small number of cells in the locus ceruleus projected ipsilaterally to the OMC. Although large numbers of vestibular neurons were GLU-IR and ASP-IR, only a few tracer labeled ASP-IR neurons in the contralateral MVN projected to the OMC. No other GLU- or ASP-positive neurons were immunoreactive for GABA, 5-HT or CCK, but cells of the lateral vestibular nucleus were surrounded by CCK-IR fibers and terminals.     

Brain stem afferents to the fastigial nucleus in the cat demonstrated by transport of horseradish peroxidase.

Although retrograde and anterograde degeneration studies have provided important information concerning brain stem afferents to the fastigal nucleus (FN), these data may be incomplete and should be confirmed by axonal transport methods. Attempts were made to inject horseradish peroxidase (HRP) unilaterally into the FN in a series of adult cats. Animals were perfused with dextran and a fixative solution of paraformaldehyde and glutaraldehyde in 0.1 M phospate buffer. Representative sections were treated by the Graham and Karnovsky ('66) method. Selective HRP injections in one FN resulted in retrograde transport of the marker to Purkinje cells of the ipsilateral vermis and distinctive appendages of the contralateral medial accessory olivary (MAO) nucleus (nucleus beta and the dorso-medial cell column). Retrograde transport of the label was found bilaterally in cells of the medial (MVN) and inferior (IVN) vestibular nuclei, in cell group x and in the nucleus prepositus (PP). Labeled vestibular neurons, most numerous in MVN, were identified in dorsal, caudal and lateral regions, with a slight ipsilateral preponderance. Only a few neurons in caudal, dorsal and lateral regions of the IVN were labeled and none of these included cells of group f. Labeled cells in the caudal third of PP were greatest ipsilaterally. Rostral and caudal injections of FN labeled smaller numbers of cells in MVN, IVN, cell group x and PP. HRP injections of FN and portions of lobules VIII and IX resulted in bilateral retrograde labeling of larger numbers of cells in MVN, IVN and cell group x, and ipsilateral labeling of cells in group y and the interstitial nucleus of the vestibular nerve. Injections of HRP into basal folia of lobules V and VI resulted in retrograde transport of the marker to cells of the medial and dorsal accessory olivary nuclei contralaterally, and to cells of the ipsilateral accessory cuneate nucleus. Transport of label injected into portions of the pyramis was detected in parts of the contralateral MAO and bilaterally in parts of the pontine and reticulotegmental nuclei. This study suggests that the principal afferents of the fastigial nucleus arise from: (1) Purkinje cells of the ipsilateral vermis, (2) restricted portions of the contralateral MAO (nucleus beta and dorsomedial cell column), (3) portions of the MVN and IVN (bilaterally) and (4) caudal parts of the PP. Secondary vestibular inputs to the fastigial nucleus probably are relayed mainly by Purkinje cells in the cerebellar cortex.     

Distribution of primary vestibular fibers in the brainstem and cerebellum of the monkey

Attempts were made to determine the central projections of ganglion cells innervating individual semicircular ducts in the monkey by implanting or injecting tritiated amino acids (leucine and/or proline), or horseradish peroxidase (HRP), selectively into a single ampulla. Central transport via the vestibular ganglion in animals receiving isotope implants or injections fell into three categories: (1) transport from ganglion cells innervating all receptive elements of the labyrinth, (2) transport from ganglion cells innervating the three semicircular ducts, and (3) transport from cells of the inferior vestibular ganglion innervating the posterior semicircular duct. Transneuronal transport of isotope was observed in secondary vestibular fibers in animals where proline was used and survival exceeded 12 days. Transneuronal labeling of secondary auditory fibers was independent of the [³H]amino acid used, and occurred with survivals of 10 or more days. HRP implanted into the ampulla of the lateral semicircular duct in several animals produced retrograde transport to efferent vestibular and cochlear neurons, but did not result in transganglionic labeling of primary vestibular or auditory fibers.Primary vestibular fibers terminate throughout the superior (SVN) and medial vestibular nuclei (MVN). Within SVN, terminals are most pronounced in its central large-celled portion, but extend into peripheral parts of the nucleus, except for a small medial area near its junction with the oral pole of MVN. Primary projections to MVN are homogenously distributed throughout the nucleus excepting a small circular area of sparse terminals along its ventral margin. Primary vestibular afferents terminate mainly in rostral and caudal portions of the inferior vestibular nucleus (IVN), but do not reach cell group ‘f’. Projections to the lateral vestibular nucleus (LVN) are restricted to its ventral part. Primary projections to the accessory vestibular nuclei reach the interstitial nucleus of the vestibular nerve (NIVN) and cell group ‘y’. Fibers project beyond the vestibular nuclei (VN) to terminate ipsilaterally in the accessory cuneate nucleus (ACN), the subtrigeminal lateral reticular nucleus (SLRN), and well-defined portions of the reticular formation (RF). Projections to SVN and MVN are derived primarily from ganglion cells innervating the semicircular ducts, while projections to caudal IVN, cell group ‘y’ and ACN are related mainly to macular portions of the vestibular ganglion. NIVN receives both macular and duct afferents. Posterior duct afferents terminate in medial portions of SVN, in rostrolateral portions of MVN, and in rostral IVN.Transneuronal transport of isotope increases the volume of terminal label in the ipsilateral VN, but not in dorsal LVN, or cell groups ‘f’ or ‘x’. The quality of transneuronal transport in secondary vestibular fibers is dependent upon: (1) survival time, (2) proximity to the VN, and (3) the excitatory or inhibitory nature of the projection.Primary vestibulocerebellar fibers terminate heavily in the ipsilateral nodulus and ventral uvula. Lesser projections reach the flocculus, deep folia of vermal lobules V and VI, and the lingula. Primary vestibulocerebellar projections terminate as mossy fiber rosettes in the granular layer of these cortical areas. No primary vestibular fibers terminate in the primate fastigial nuclei.     

Organization of the coeruleo-vestibular pathway in rats, rabbits, and monkeys

Inputs from locus coeruleus (LC) appear to be important for altering sensorimotor responses in situations requiring increase vigilance or alertness. This study documents the organization of coeruleo-vestibular pathways in rats, rabbits and monkeys. A lateral descending noradrenergic bundle (LDB) projects from LC to the superior vestibular nucleus (SVN) and rostral lateral vestibular nucleus (LVN). A medial descending noradrenergic bundle (MDB) projects from LC to LVN, the medial vestibular nucleus (MVN), group y and rostral nucleus prepositus hypoglossi (rNPH). There is a characteristic, specific pattern of innervation of vestibular nuclear regions across the three species. A quantitative analysis revealed four distinct innervation density levels (minimal, low, intermediate and high) across the vestibular nuclei. The densest plexuses of noradrenergic fibers were observed in the SVN and LVN. Less dense innervation was observed in the MVN, and minimal innervation was observed in the inferior vestibular nucleus (IVN). In monkeys and rabbits, rostral MVN contained a higher innervation density than the rat MVN. In monkeys, the rNPH also contained a dense plexus of fibers. Selective destruction of terminal LC projections (distal axons and terminals) by the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) resulted in a dramatic reduction of immunoreactive fibers within the vestibular nuclear complex of rats, suggesting that the source of these immunoreactive fibers is LC. Retrograde tracer injections into the vestibular nuclei resulted in labeled cells in the ipsilateral, caudal LC and adjacent nucleus subcoeruleus. It is hypothesized that the regional differences in noradrenergic innervation are a substrate for differentially altering vestibulo-ocular and vestibulo-spinal responses during changes in alertness or vigilance.     

Projections from the parabrachial nucleus to the vestibular nuclei: potential substrates for autonomic and limbic influences on vestibular responses

Previous anatomical studies in rabbits and rats have shown that the superior vestibular nucleus (SVN), medial vestibular nucleus (MVN) and inferior vestibular nucleus (IVN) project to the parabrachial nucleus (PBN) and K?lliker-Fuse (KF) nucleus. Adult male albino rabbits and Long-Evans rats received iontophoretic injections of biotinylated dextran amine, Phaseolus vulgaris leucoagglutinin, Fluoro-Gold or tetramethylrhodamine dextran amine into either the vestibular nuclei or the PBN and KF nuclei. The results were similar in both rats and rabbits. Injections of retrograde tracers into the vestibular nuclei produced retrogradely labeled neurons bilaterally in caudal third of the medial, external medial, and external lateral PBN in both species, with more variable labeling in KF. Rats also had consistent bilateral (predominantly contralateral) labeling in the ventrolateral PBN. The most prominent labeling was produced from injections that included the SVN, with fewer labeled neurons observed from injections in the caudal MVN and the IVN. Anterograde transport of BDA from injections into the PBN and KF nuclei of rabbits revealed prominent projections to the SVN, dorsal aspect of the rostral MVN, caudal MVN, pars beta of the LVN and IVN. These connections appear to contain a component that is reciprocal to the vestibulo-parabrachial pathway and a non-reciprocal component to regions connected with the vestibulocerebellum and vestibulo-motor reflex pathways. These connections support the concept that a synthesis of autonomic, vestibular and limbic information is an integral property of pathways related to balance control in both the brain stem and forebrain. It is suggested that these projections may contribute broadly to both performance tradeoffs in vestibular-related pathways during variations in the behavioral context and affective state and the close association between anxiety and balance function.     

The vestibulothalamic connections in the rat: A morphological analysis using wheat germ agglutinin-horseradish peroxidase

The vestibulothalamic connections were studied in the rat using wheat germ agglutinin-horseradish peroxidase (WGA-HRP). The distributions of anterograde labelling of fibers and terminals in the brainstem and the thalamus were analyzed by injecting WGA-HRP into the superior (SVN) and lateral (LVN) vestibular nuclei, and the medial (MVN) and inferior (IVN) vestibular nuclei. The distributions of retrograde labelling of cells were analyzed in the vestibular nuclear complex by injecting WGA-HRP into the thalamus centered in the central lateral nucleus (CL), ventral posterolateral nucleus (VPL), and rostral part of the dorsal medial geniculate nucleus (rMGd). The vestibular projection to the CL via the medial longitudinal fasciculus (MLF) and the ascending tract of Deiters (ATD) originates mainly in the contralateral MVN and ipsilateral SVN. The vestibular projections to the VPL and the ventral lateral nucleus (VL) via MLF, ATD and superior cerebellar peduncle (SCP) originate mainly in the MVN and SVN, bilaterally. The projection to the rMGd via the lateral lemniscus-inferior collicular brachium, and MLF (and SCP) originates in the contralateral IVN.     

Connections and oculomotor projections of the superior vestibular nucleus and cell group ‘y’

Attempts were made to determine brainstem and cerebellar afferent and efferent projections of the superior vestibular nucleus (SVN) and cell group 'y' ('y') in the cat using axoplasmic tracers. Injections of HRP, WGA-HRP and [3H]amino acids were made into SVN and 'y' using two different infratentorial stereotaxic approaches. Controls were provided by unilateral HRP injections involving the oculomotor nuclear complex (OMC), the interstitial nucleus of Cajal (INC) and the deep cerebellar nuclei (DCN). Large injections of SVN almost invariably involved 'y' and dorsal parts of the lateral vestibular nucleus (LVN). Smaller injections involved central and ventral peripheral parts of SVN. Discrete injections of 'y' involved small dorsal parts of LVN. Afferents to SVN are derived mainly from the vestibular nuclei (VN) and parts of the vestibulocerebellum. SVN receives afferents: bilaterally from caudal portions of the medial (MVN) and inferior (IVN) vestibular nuclei and 'y'; contralaterally from ventral and lateral parts of SVN and rostral MVN; and ipsilaterally from the nodulus, uvula and medial parts of the flocculus. Purkinje cells (PC) in medial parts of the flocculus project to central regions of SVN, while PC in the nodulus and uvula appear to project mainly to dorsal peripheral regions of SVN. SVN receives sparse projections from the ipsilateral INC, the contralateral central cervical nucleus (CCN) and virtually no projections from the reticular formation. SVN projects via the medial longitudinal fasciculus (MLF) to the ipsilateral trochlear nucleus (TN), the inferior rectus subdivision of the OMC, the INC, the nucleus of Darkschewitsch (ND) and the rostral interstitial nucleus of the MLF (RiMLF). Contralateral projections of SVN cross in the ventral tegmentum caudal to most of the decussating fibers of the superior cerebellar peduncle and terminate in the dorsal rim of the TN and the superior rectus and inferior oblique subdivisions of the OMC; sparse crossed projections enter the INC and the ND. Cerebellar projections of SVN end as mossy fibers in the ipsilateral nodulus, uvula and in medial parts of the flocculus bilaterally. Retrograde transport from unilateral injections of the OMC indicate that afferents from SVN arise ipsilaterally from central and dorsal regions and contralaterally from dorsal peripheral regions. Ventral cell group 'y' receives small numbers of afferent fibers from caudal central parts of the ipsilateral flocculus. No fibers from ventral 'y' could be traced to other vestibular nuclei, the OMC or the cerebellum.(ABSTRACT TRUNCATED AT 400 WORDS)     

Morphology of single primary vestibular afferents originating from the horizontal semicircular canal in the cat

The central projections of physiologically characterized vestibular nerve fibers originating from the horizontal semicircular canal were studied in the vestibular nuclei of adult cats after intracellular staining with horseradish peroxidase (HRP). First, primary nerve fibers were physiologically classified as regular or irregular types on the basis of the regularity of the spontaneous discharge pattern. Then, these two types of fibers were morphologically analyzed and compared following HRP intraaxonal injection. The two types of axons showed a basically similar trajectory in the four major vestibular nuclei. They bifurcated into an ascending and a descending branch in the ventrolateral part of the lateral vestibular nucleus (LVN). The ascending branch extended rostrally and gave off one or two collaterals in the superior vestibular nucleus (SVN), although some of the ascending branches further ran rostrally into the cerebellum. The collaterals, while running medially, gave rise to fine terminal branches with en passant boutons in the SVN, and further coursing caudally, they entered the rostral part of the medial vestibular nucleus (MVN). The descending branch, while running caudally in the lateral part of the LVN and the inferior vestibular nucleus (IVN), gave off several thick collaterals to the MVN and extensive terminals were present in the IVN and MVN. In each primary axon, about one-third of the total terminal boutons were distributed in each of the SVN, the MVN, and the IVN. In contrast to this similarity of the overall axonal trajectory within the vestibular nuclei, both types of axons exhibited several marked differences in diameter and in the mode of terminal arborization. In almost every part of the ramification, the irregular-type fibers were thicker than the regular-type fibers. In the regular-type axons, many small terminal boutons (mean size, 2.4 x 1.4 microns, N = 2,739) were located in close proximity (100-150 microns) to the parent collateral. In the irregular-type axons, slightly larger terminal boutons (mean size, 3.0 x 1.7 microns, N = 1,287), were spread more widely (200-300 microns) around their collaterals. These clear morphological differences between the regular-type and the irregular-type terminal axons were consistently observed in any vestibular nucleus.     

Vestibular and cochlear efferent neurons in the monkey identified by immunocytochemical methods

Attempts were made to identify vestibular (VEN) and cochlear (CEN) efferent neurons in the squirrel monkey using retrograde transport of horseradish peroxidase (HRP) and immunocytochemical methods. HRP implants in the ampulla of the lateral semicircular duct retrogradely labeled cells of VEN bilaterally and some cells of CEN. VEN located lateral to the rostral part of the abducens nucleus formed a compact collection of cells, all of which were immunoreactive only to antisera for choline acetyltransferase (ChAT). CEN, identified by immunoreactivity to ChAT were located at the hilus of the lateral superior olive (LSO), along the lateral border of the LSO and sparsely near lateral parts of the ventral trapezoid nucleus (VTN). A small number of cells and fibers near the border of the VTN and lateral to the LSO were immunoreactive for leucine enkephalin (L-ENK). Fibers immunoreactive for L-ENK also were identified in the hilus of the LSO. No cells of the superior olivary complex were immunoreactive for antisera to ChAT, L-ENK, substance P, gamma-aminobutyric acid or glutamic acid decarboxylase. Cells of VEN and CEN can be identified by their immunoreactivity to ChAT, and some cells and fibers of CEN also contain L-ENK.     

Trigeminovestibular and trigeminospinal pathways in rats: retrograde tracing compared with glutamic acid decarboxylase and glutamate immunohistochemistry

This study identified neurons in the sensory trigeminal complex with connections to the medial (MVN), inferior (IVN), lateral (LVN), and superior (SVN) vestibular nuclei or the spinal cord. Trigeminovestibular and trigeminospinal neurons were localized by injection of retrograde tracers. Immunohistochemical processing revealed gamma-aminobutyric acid (GABA)- and glutamate-containing neurons in these two populations. Trigeminovestibular neurons projecting to the MVN and the IVN were in the caudal principal nucleus (5P), pars oralis (5o), interpolaris (5i), and caudalis (5c) and scattered throughout the rostral 5P. Projections were bilateral to the IVN, with an ipsilateral dominance to the MVN, except from the rostral 5P, which was contralateral. Neurons projecting to the LVN were numerous in the ventral caudal 5P and the 5o and less abundant in the rostral 5P, 5i, and 5c. Our results suggested that only 5P and 5o project to the dorsal LVN. Neurons projecting to the SVN were in the dorsal 5P, 5o, and 5i but not in 5c. Trigeminospinal neurons were mainly in the ventral 5o and 5i and in the lateral 5c, rarely or never in 5P. Among trigeminovestibular neurons, most of the somas were immunoreactive for glutamate, but some reacted for GABA. Among trigeminospinal neurons, the number of somas immunoreactive for each of the two amino acids was similar. Trigeminal terminals were observed in contact with vestibulospinal neurons in the IVN and LVN, giving evidence of a trigeminovestibulospinal pathway. Therefore, inhibitory and excitatory facial inputs may contribute through trigeminospinal or trigeminovestibulospinal pathways to the control of head/neck movements.     

Fastigial efferent projections in the monkey: an autoradiographic study.

Because fastigial efferent fibers partially decussate within the cerebellum and cerebellar corticovestibular projections pass near, or through, the fastigial nucleus (FN), degeneration studies based on lesions in the nucleus leave unresolved questions concerning fastigial projections. Attempts were made to determine fastigial projections in the monkey using autoradiographic tracing technics. Cells in rostral, caudal and all parts of the FN were labeled with [³H] amino acids. Selective labeling of neurons in either rostral or caudal parts of the FN results in transport of isotope primarily via fibers of the contralateral uncinate fasciculus (UF) and the ipsilateral juxtarestiform body (JRB). Fastigial projections to the vestibular nuclei are mainly to ventral portions of the lateral (LVN) and inferior (IVN) vestibular nuclei, are nearly symmetrical and are quantitatively similar on each side. Fastigiovestibular projections to cell groups f and x arise from all parts of the FN and are mainly crossed; modest projections to the medial vestibular nucleus are uncrossed. No fastigial efferent fibers end in the superior vestibular nucleus on either side, or in dorsal regions of the LVN. Crossed fibers descending in IVN terminate in the nucleus parasolitarius. Fastigioreticular fibers arise predominately from rostral regions of the FN, are entirely crossed and project mainly to: (1) medial regions of the nucleus reticularis gigantocellularis, (2) the dorsal paramedian reticular nucleus and (3) the magnocellular part of the lateral reticular nucleus. Fastigiopontine fibers, emerge with the UF, bypass the vestibular nuclei and terminate upon the contralateral dorsolateral pontine nuclei. Crossed fastigiospinal fibers separate from fastigiopontine fibers and descend in the ventrolateral tegmentum beneath the spinal trigeminal tract; in the medulla and upper cervical spinal cord these fibers are intermingled with those of the vestibulospinal tract. Fastigiospinal fibers terminate in the anterior gray horn at C-1 and probably descend further. Ascending fastigial projections arise from caudal parts of the FN, are entirely crossed and ascend in dorsal parts of the midbrain tegmentum. Label is transported bilaterally to the superior colliculi and the nuclei of the posterior commissure. Contralateral fastigiothalamic projections terminate in the ventral posterolateral (VPLc and VPLo) and in parts of the ventral lateral (VLo) thalamic nuclei. The major region of termination of fastigiothalamic fibers is in VPLo. Fastigiothalamic projections, probably conveying impulses concerned with equilibrium and somatic proprioception, appear to impinge upon thalamic neurons receiving inputs from less specialized receptors that signal information concerning position sense and body movement. More modest fastigial projections to VLo could directly influence activity of neurons in the primary motor cortex.     

Gamma amino butyric acid (GABA) immunoreactivity in the vestibular nuclei of normal and unilateral vestibular neurectomized cats

Recent neurochemical investigations of the central vestibular pathways have demonstrated that several neurotransmitters are involved in various operations required for stabilizing posture and gaze. Neurons of the vestibular nuclei (VN) receive GABAergic inhibitory afferents, and GABAergic neurons distributed throughout the vestibular complex are implicated in inhibitory vestibulo-ocular and vestibulo-spinal pathways. The aim of this study was to analyse the modifications of GABA immunoreactivity (GABA-ir) in the cat VN after unilateral vestibular neurectomy (UVN). Indeed, compensation of vestibular deficits is a good model for studying adult central nervous system (CNS) plasticity and the GABAergic system is involved in CNS plasticity. We studied GABA-ir by using a purified polyclonal antibody raised against GABA. Light microscopic preparations of thin (20 microm) sections of cat VN were used to quantify GABA-ir by an image analysing system measuring GABA-positive punctate structures and the number of GABA-positive neurons. Both the lesioned and intact sides were analysed in three populations of UVN cats killed at different times after injury (1 week, 3 weeks and 1 year). These data were compared to those collected in normal unlesioned and sham-operated cats. Results showed a spatial distribution of GABA-ir in the control cats that confirmed previous studies. GABA-ir neurons, fibres and nerve terminals were scattered in all parts of the VN. A higher concentration of GABA-positive neurons (small cells) was detected in the medial and inferior VN (MVN and IVN) and in the dorsal part of the lateral VN (LVNd). A higher level of GABA-positive punctate structures was observed in the MVN and in the prepositus hypoglossi (PH) nucleus. Lesion-induced changes were found at each survival time. One week after injury the number of GABA-positive neurons was significantly increased in the MVN, the IVN and the dorsal part of the LVN on the lesioned side and in the ventral part of the LVN on the intact side. One year later a bilateral increase in GABA-positive neurons was detected in the MVN whilst a bilateral decrease was observed in both the SVN and the ventral part of the LVN. Changes in the GABA-staining varicosities did not strictly coincide with the distribution of GABA-ir cells, suggesting that GABA-ir fibres and nerve terminals were also modified. One week and later after injury, higher GABA-staining varicosities were seen unilaterally in the ipsilateral MVN. In contrast, bilateral increases (in PH) and bilateral decreases (in SVN and the ventral part of the LVN) were recorded in the nearly (3 weeks) or fully (1 year) compensated cats. At this stage GABA-staining varicosities were significantly increased in the lesioned side of the MVN. These findings demonstrate the reorganization of the GABAergic system in the VN and its possible role in recovery process after UVN in the cat. The changes seen during the acute stage could be causally related to the VN neuron deafferentation, contributing to the static vestibular deficits. Those found in the compensated cats would be more functionally implicated in the dynamic aspects of vestibular compensation.     

Afferents to the flocculus of the cerebellum in the rhesus macaque as revealed by retrograde transport of horseradish peroxidase

To investigate the afferent projections to the flocculus in a nonhuman primate, we injected horseradish peroxidase into one flocculus of six rhesus macaques (Macaca mulatta) and processed their brains according to the tetramethylbenzidine protocol to reveal retrogradely labeled neurons. Labeled neurons were found in a large set of nuclei within the rostral medulla and the pons. The greatest numbers of labeled neurons were in the vestibular complex and the nucleus prepositus hypoglossi. There were neurons labeled bilaterally throughout all the vestibular nuclei except the lateral vestibular nucleus, but most of the labeled neurons were in the caudal parts of the medial and inferior vestibular nuclei and in the central part of the superior vestibular nucleus; the nucleus prepositus was also labeled bilaterally, primarily caudally. Modest numbers of labeled neurons were found in the y-group, most ipsilaterally, and many neurons were labeled in the interstitial nucleus of the vestibular nerve. No labeled neurons were found in the vestibular ganglion following a large injection into the flocculus. A second large source of afferents to the flocculus was the medial, paramedial, and raphe reticular formation. Dense aggregates of labeled neurons were located in several pararaphe nuclei of the rostral medulla and the rostral pons and in the nucleus reticularis paramedianus of the medulla and several component nuclei of the nucleus reticularis tegmenti pontis bilaterally. Several groups of cells within and abutting upon the medial and rostral aspects of the abducens nucleus were labeled bilaterally. There was a modest projection from two parts of the pontine nuclei. Both a dorsal midline nucleus ventral to the nucleus reticularis tegmenti pontis and a collection of nuclei in a laminar region adjacent to the contralateral middle cerebellar peduncle contained labeled neurons whose numbers, while modest, were large compared to the projections to the flocculus in other animals. This generic difference may be due to the greater development of the smooth pursuit system in monkeys and the consequent need for a more substantial input from the cerebral cortex. As in other genera, the inferior olive projected to the flocculus via the dorsal cap of Kooy and the contiguous ventrolateral outgrowth. The projection was completely crossed and large injections labeled virtually every neuron in the dorsal cap, suggesting that the dorsal cap is the principal source of climbing fiber afferents.(ABSTRACT TRUNCATED AT 400 WORDS)     

Distribution of choline acetyltransferase immunoreactivity in the brain of an elasmobranch, the lesser spotted dogfish (Scyliorhinus canicula)

Although the distribution of cholinergic cells is remarkably similar across the vertebrate species, no data are available on more primitive species, such as cartilaginous fishes. To extend the evolutionary analysis of the cholinergic systems, we studied the distribution of cholinergic neurons in the brain and rostral spinal cord of Scyliorhinus canicula by immunocytochemistry using an antibody against the enzyme choline acetyltransferase (ChAT). Western blot analysis of brain extracts of dogfish, sturgeon, trout, and rat showed that this antibody recognized similar bands in the four species. Putative cholinergic neurons were observed in most brain regions, including the telencephalon, diencephalon, cerebellum, and brainstem. In the retrobulbar region and superficial dorsal pallium of the telencephalon, numerous small pallial cells were ChAT-like immunoreactive. In addition, tufted cells of the olfactory bulb and some cells in the lateral pallium showed faint immunoreactivity. In the preoptic-hypothalamic region, ChAT-immunoreactive (ChAT-ir) cells were found in the preoptic nucleus, the vascular organ of the terminal lamina, and a small population in the caudal tuber. In the epithalamus, the pineal photoreceptors were intensely positive. Many cells of the habenula were faintly ChAT-ir, but the neuropil of the interpeduncular nucleus showed intense ChAT immunoreactivity. In the pretectal region, ChAT-ir cells were observed only in the superficial pretectal nucleus. In the brainstem, the somatomotor and branchiomotor nuclei, the octavolateral efferent nucleus, and a cell group just rostral to the Edinger-Westphal (EW) nucleus contained ChAT-ir neurons. In addition, the trigeminal mesencephalic nucleus, the nucleus G of the isthmus, some locus coeruleus cells, and some cell populations of the vestibular nuclei and of the electroreceptive nucleus of the octavolateral region exhibited ChAT immunoreactivity. In the reticular areas of the brainstem, the nucleus of the medial longitudinal fascicle, many reticular neurons of the rhombencephalon, and cells of the nucleus of the lateral funiculus were immunoreactive to this antibody. In the cerebellum, Golgi cells of the granule cell layer and some cells of the cerebellar nucleus were also ChAT-ir. In the rostral spinal cord, ChAT immunoreactivity was observed in cells of the motor column, the dorsal horn, the marginal nucleus (a putative stretch-receptor organ), and in interstitial cells of the ventral funiculus. These results demonstrate for the first time that cholinergic neurons are distributed widely in the central nervous system of elasmobranchs and that their cholinergic systems have evolved several characteristics that are unique to this group.     

Cholecystokinin octapeptide-like immunoreactive material in neurons of the intralaminar nuclei of the cat''s thalamus

Cholecystokinin-like immunoreactive material (CCK-IR) was revealed in the cat's thalamus by using the peroxidase-antiperoxidase method. The most dense collection of perikarya containing CCK-IR was seen in the rostral group of the intralaminar nuclei, in rostral parts of the rhomboid nucleus and the anterodorsal nucleus. Cells with CCK-IR were also found in the caudal group of the intralaminar nuclei, in the paraventricular nucleus and the parataenial nucleus. The remaining thalamic nuclei were void of CCK-IR. By combining immunohistochemistry with retrograde transport of horseradish peroxidase, CCK-IR was shown to be present in neurons of the intralaminar nuclei projecting to the neocortex. Our findings suggest that CCK might act as a transmitter in the efferent projections of the intralaminar and midline nuclei of the cat's thalamus.     

Mesodiencephalic projections to the vestibular complex in the cat

The distribution of cells in the rostral medial mesencephalon and caudal diencephalon which project to the vestibular complex was mapped in the cat by using retrograde axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Subsequent experiments using anterograde transport of WGA-HRP clarified the position of the terminations of the mesodiencephalic-derived afferents in the vestibular complex. After large injections which involved the entire vestibular complex, retrogradely labeled cells were seen in both the ipsilateral and contralateral interstitial nucleus of Cajal (INC) and were more numerous in its rostral pole. Labeled cells also occurred in the perifascicular region, both immediately adjacent to the fasciculus retroflexus and rostroventral to it. Fusiform midline cells of the Edinger-Westphal nucleus were also labeled, as well as a number of cells in the adjacent somatic portion of the oculomotor complex (OMC). Another group of labeled cells was observed within the contralateral medial terminal nucleus of the accessory optic tract (MTN) and in the posterior hypothalamic nucleus. Injections limited to subregions of the vestibular complex resulted in similar but slightly varying distributions and numbers of retrogradely labeled cells. After injections covering the caudal half of the medial vestibular nucleus (MVN) and descending vestibular nucleus (DVN), labeled cells in the INC and tegmentum dorsal to it were especially prominent, but none was seen in the MTN or OMC. Injections placed in the rostral MVN, lateral vestibular nucleus, y group, and superior vestibular nucleus resulted in a distribution of labeled cells similar to that seen following global vestibular injections, but these cells were fewer in number. After an injection confined to the y group, a small number of retrogradely labeled cells were seen in the rostral pole of the INC and immediately ventral to the fasciculus retroflexus. Projections from the rostral medial mesencephalon and caudal diencephalon to the MVN, DVN, and y group were confirmed by using anterograde transport of WGA-HRP. Direct projections from the INC-perifascicular regions and somatic neurons of the OMC to the caudal vestibular complex could play a role in eye-head coordination. Those projections from the rostral INC and MTN to the rostral vestibular complex may play a role in vertical eye movements and responses to visual stimuli which move in the vertical plane.     

Transneuronal transport in the vestibular and auditory systems of the squirrel monkey and the arctic ground squirrel. I. Vestibular system

Transneuronal transport of [3H]proline, [3H]fucose, and [3H]leucine in various combinations from pledgets implanted in the ampulla of a single semicircular duct was studied in the squirrel monkey and arctic ground squirrel after long survival periods. Tritiated amino acids implanted in any single ampulla resulted in labeling of nearly all vestibular and auditory receptors, nearly all cells of the vestibular and spiral ganglia and central transport via nearly all root fibers of both nerves. Primary vestibular fibers were distributed to the vestibular nuclei (VN) and specific parts of the cerebellum in the pattern previously described. Transneuronal transport of [3H]proline by vestibular neurons was present in all known secondary pathways, except those projecting to thalamic nuclei. Observations were similar in both species, except for small differences in commissural vestibular projections. Major commissural transport was to all parts of the opposite medial vestibular nucleus (MVN) and to peripheral parts of the superior vestibular nucleus (SVN), but some transport was present in all contralateral VN, including ventral cell group y. Descending transneuronal transport was evident in vestibulospinal tract (VST) ipsilaterally and in the medial longitudinal fasciculus (MLF) bilaterally. Both [3H]proline and [3]fucose were transported transneuronally to the ipsilateral abducens nucleus (AN); with long survivals [3H]proline was transported peripherally via the ipsilateral abducens nerve root. Ascending transport in the MLF was bilateral, asymmetric and greatest contralaterally. Fibers entered the contralateral MLF near the AN and the lateral wing of the ipsilateral MLF rostral to most of the VN. Terminals in the trochlear nuclei (TN) were bilateral and greatest contralaterally. In the monkey terminals in ipsilateral oculomotor complex (OMC) were distributed uniformly in all subdivisions, except for the medial rectus subdivision (MRS), where terminals were more numerous. The greatest density of terminals was present contralaterally in the superior rectus subdivision (SRS) of the OMC; only sparse terminals were present in the MRS on that side. Transport in the ipsilateral abducens nerve roots in the monkey and the virtual absence of transport to the MRS of the contralateral OMC suggested transneuronal transport to abducens motor neurons, but not to internuclear neurons (AIN). The AIN project only to the MRS of the contralateral OMC and do not appear to receive vestibular input. Comparable observations were made in the AN, TN and OMC of the ground squirrel, although the representation of the extraocular muscles in the OMC is unknown.(ABSTRACT TRUNCATED AT 400 WORDS)     

Distribution of choline acetyltransferase immunoreactivity in the vestibular nuclei of normal and unilateral vestibular neurectomized cats

Post‐lesion recovery of vestibular functions is a suitable model for studying adult central nervous system plasticity. The vestibular nuclei complex (VN) plays a major role in the recovery process and neurochemical reorganizations have been described at this brainstem level. The cholinergic system should be involved because administration of cholinergic agonists and antagonists modify the recovery time course. This study was aimed at analysing the postlesion changes in choline acetyltransferase immunoreactivity (ChAT‐Ir) in the VN of cats killed 1 week, 3 weeks or 1 year following unilateral vestibular neurectomy. ChAT‐positive neurons and varicosities were immunohistochemically labelled and quantified (cell count and surface measurement, respectively) by means of an image analysing system. The spatial distribution of ChAT‐Ir within the VN of control cats showed darkly stained neurons and varicosities mainly located in the caudal parts of the medial (MVN) and inferior (IVN) VN, the nucleus prepositus hypoglossi (PH) and, to a lesser extent, in the medial part of the superior vestibular nucleus (SVN). Lesion‐induced changes consisted in a significant increase in both the number of ChAT‐positive neurons (IVN, SVN) and the surface of ChAT‐positive varicosities (IVN, SVN, PH). They were observed bilaterally in the acute (1 year and 3 weeks) and compensated (1 year) cats for the SVN and PH, while they persisted only in the IVN on the lesioned side in the compensated cats. These findings demonstrate vestibular lesion‐induced reorganization of the cholinergic system in the IVN, SVN and PH which could contribute to postural and oculomotor function recovery.