Cervical Nucleus Research Articles

Multiplicity of vestibulospinal projections to the upper cervical spinal cord of the cat: A study with the anterograde tracer Phaseolus vulgaris leucoagglutinin

The distribution and frequency of vestibulospinal axons and boutons in the upper cervical spinal cord of the cat were investigated. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was injected into discrete regions of the vestibular nuclei, including the medial and descending nuclei, as well as small regions of the lateral vestibular nucleus along its medial border with the medial vestibular nucleus. In contrast to previous reports, labelled vestibulospinal axons were not found to be restricted to the ventromedial and ventrolateral funiculi, but were also observed bilaterally in the lateral funiculi, the dorsolateral funiculi and the dorsal columns. The diameter of these axons ranged from 0.5 to 7.4 microns. Labelled boutons were found bilaterally from lamina IV to IX as well as in lamina X. Contralateral to the injection site, boutons were frequently found as far dorsal as lamina II. Ipsilaterally, boutons were found this far dorsal in only one experiment. There was a dense projection to the contralateral central cervical nucleus, while very few, if any, boutons were observed in the ipsilateral central cervical nucleus. In each experiment, the density of boutons was greater in the rostral cervical segments than in more caudal segments. The "new" vestibulospinal projections to the dorsal horn and central cervical nucleus were confirmed in separate experiments using retrograde transport of horseradish peroxidase. These results show that vestibulospinal axons project to the upper cervical spinal cord via multiple funicular paths. The rich terminations of these axons outside of the ventral horn, as well as in the neck motoneuron nuclei, indicate that vestibulospinal projections must play a wide variety of functions in addition to their well-documented role in the direct control of head movement.

Cells of origin of ascending and descending as well as branching fibers in the cervical spinal cord of the pigeon

Ascending and descending projections of spinal neurons (cervical enlargement) were studied with the retrograde transport of horseradish peroxidase (HRP) and with the fluorescent tracers Fast blue and rhodamine isothiocyanate (single and double labeling). Ascending and descending projections arise from the same laminae of the spinal grey except for neurons in contralateral lamina I and avian cervical Clarke's column which have ascending fibers only. A significant number of cervical nucleus proprius neurons (lamina IV) descends to the lumbar enlargement. Neurons with branching fibers were rare (less than 10 per cent).

Ascending afferents to the lateral cervical nucleus are enriched in glutamate-like immunoreactivity: a combined anterograde transport-immunogold study in the cat

To investigate whether glutamate (Glu) may be a transmitter in terminals of ascending afferents to the lateral cervical nucleus (LCN), these terminals were identified by anterograde transport of wheatgerm agglutinin-horseradish peroxidase from the spinal cord, and their content of Glu-like immunoreactivity (Glu-LI) was assessed at the ultrastructural level by the immunogold technique. The gold particle density over the peroxidase-positive terminals of the spinocervical tract (SCT) was significantly higher (by a factor of 2.44) than over a reference terminal population containing flattened or pleomorphic vesicles. Further, LCN neurons were densely labeled by the Glu antiserum, although the gold particle density over neuronal cell bodies was not as high as in the SCT terminals. Previous investigations have shown enrichment of Glu-LI in putative glutamatergic terminals in other parts of the CNS. Hence, the present observations indicate that Glu may be a transmitter in the synapses between SCT terminals and LCN neurons. The cell body labeling in the LCN is more difficult to interpret because of possible interference of metabolic pools of glutamate.

Propriospinal neurons with ascending collaterals to the dorsal medulla, the thalamus and the tectum: a retrograde fluorescent double-labeling study of the cervical cord of the rat

Branching neurons with descending propriospinal collaterals and ascending collaterals to the dorsal medulla, the thalamus and the tectum were studied in the rat's cervical spinal cord (C1-C8), using the retrograde fluorescent double-labeling technique: Diamidino Yellow Dihydrochloride (DY) was injected in the cord at T2, True Blue (TB) was injected in the brain stem. DY-labeled descending propriospinal neurons were present in all laminae, except lamina IX. They were concentrated in lamina I, laminae IV to VIII, and in the lateral spinal nucleus, LSN. TB-labeled neurons projecting to the dorsal medulla were concentrated in lamina IV and the medial parts of laminae V and VI (probably representing postsynaptic dorsal column--PSDC--neurons), but were also present in lamina I, the LSN, the lateral dorsal horn, and in laminae VII and VIII. DY-TB double-labeled neurons giving rise to both a descending propriospinal collateral and an ascending collateral to the dorsal medulla were intermingled with the TB single-labeled neurons. About 4% of the descending propriospinal neurons gave rise to an ascending collateral to the dorsal column nuclei; these double-labeled cells constitute a sizable fraction (10%) of the PSDC neurons. TB-labeled spinothalamic and spinotectal neurons were located in lamina I, the lateral cervical nucleus (LCN), and LSN, the lateral lamina V, lamina VII and VIII, lamina X and in the spinal extensions of the dorsal column nuclei, predominantly contralateral to the TB injections. DY-TB double-labeled neurons were present throughout C1-C8 in the LSN, lateral lamina V, lamina VIII, ventromedial lamina VII, and lamina X. Only very few were observed in lamina I and the LCN, and none in the spinal extensions of the dorsal column nuclei. The double-labeled neurons constituted only a minor fraction of all labeled neurons; 3-5% of the spinothalamic neurons and about 1-7% of the spinotectal neurons were double-labeled. Conversely, only about 1% of the labeled descending propriospinal neurons gave rise to an ascending spinothalamic collateral, and even fewer (0.1 to 0.6%) to a collateral to the dorsal midbrain. The LSN displayed the highest relative content of branching neurons. Up to 20% of its ascending spinothalamic and spinotectal neurons and up to 8% of its descending propriospinal neurons were found to be branching neurons, indicating that the LSN constitutes an unique cell-group in the rat spinal cord.

Degeneration of spinocerebellar neurons in amyotrophic lateral sclerosis

The selective involvement of spinocerebellar neurons in sporadic amyotrophic lateral sclerosis was investigated using two monoclonal antibodies that have neuronal subset specificity in human spinal cord. In normal control subjects, monoclonal antibody 6A2 showed specificity for neurons of the dorsal nucleus of Clarke, the cells of origin of the dorsal spinocerebellar tract. Immunoreactive neurons were also observed in locations corresponding to the central cervical nucleus and spinal border region, containing neurons of the cervicospinocerebellar and ventral spinocerebellar tracts, respectively. The latter two neuronal subsets are indistinguishable from surrounding neurons when conventional histological stains are used. Antigen 6A2 was distributed on surfaces of neuronal somas and proximal neurites and extended into the extracellular space. A second antibody, monoclonal antibody 44.1, labeled the cytoplasm of neuronal somas and neurites, including all monoclonal antibody 6A2-reactive cells and alpha motoneurons. In spinal cords of all 5 patients with amyotrophic lateral sclerosis, monoclonal antibody 6A2 reactivity in the majority of spinocerebellar neurons was absent or localized to the somal cytoplasm, which still stained with monoclonal antibody 44.1. In more severely involved tissues, there was loss of some spinocerebellar neurons and a corresponding loss of monoclonal antibody 44.1 reactivity. These findings confirm involvement of the spinal cord components of the spinocerebellar system at all levels in sporadic amyotrophic lateral sclerosis and suggest that some surface molecules are modified during the degenerative process.

Central projections of C4–C8 dorsal root ganglia in the rat studied by anterograde transport of WGA‐HRP

Injections of WGA-HRP were made in the rat C4-C8 dorsal root ganglia (DRGs) individually to study the central projections and their relations to each other. The main dorsal horn projections from these DRGs to the dorsal horn lamina II extended for about two segments rostrally and caudally to the injected DRG, whereas the projections to laminae I, III, and IV were less restricted rostrocaudally. Comparisons of the dorsal horn projections from the DRGs investigated indicated a tendency for a somatotopic organization, which was most prominent in lamina II. Labeled central branches from the C4-8 DRGs could be traced in the dorsal column as far caudally as 12-17 segments caudal to the level of entrance. Most of these fibers appeared to end in the medial dorsal horn base, including the column of Clarke. Labeling of primary afferents in the ventral horn generally extended for at least 3-4 segments rostral and caudal to the level of the injected DRG. Projections to the central cervical nucleus were most prominent from the C4 DRG and gradually became less prominent from the more caudal DRGs. Heavy projections to the cuneate nucleus (Cun) originated from the C7 and C8 DRG, whereas those from the C4-C6 DRGs were less extensive. The Cun projections from the different DRGs appeared to overlap, and the same was true for the projections to the external cuneate nucleus. Projections to the gracile nucleus, the vestibular nuclear complex, including nucleus X, and to trigeminal sensory nuclei were seen from all DRGs investigated.

Serotonergic innervation of the lateral cervial nucleus: An immunohistochemical study in cats and monkeys (Aotus trivirgatus)

A serotonergic input to the lateral cervical nucleus of cats and monkeys (Aotus trivirgatus) was demonstrated with immunohistochemical methods. In both species, the lateral cervical nucleus was found to contain a network of serotonin-immunoreactive fibers. However, the density of labeled fibers was greater in the monkeys than in the cats. Most labeled fibers were thin and had irregularly spaced varicosities. Electron microscopic examination showed that labeled varicosities were in apposition with dendrites, neuronal somata and unlabeled terminals, but synapses were rare. The results demonstrate that the lateral cervical nucleus receives a serotonergic innervation, as is the case with other somatosensory relay structures such as the spinal dorsal horn and the dorsal column nuclei. The presence of a serotonergic innervation suggests that the transmission of somatosensory information through the lateral cervical nucleus is modulated by a descending pathway. However, its effect on the response properties of neurons in the lateral cervical nucleus is unknown.

Cytoarchitectonic organization of the spinal cord in the rat: II. The cervical and upper thoracic cord.

A laminar cytoarchitectonic scheme of the cervical and upper thoracic segments of the rat spinal cord is presented in which Rexed's principles for the cat are applied. The material examined in the current investigation consists of 50-80 microns-thick unstained or Nissl-stained sections, and 2 microns-thick plastic-embedded sections stained with paraphenylenediamine. The cytoarchitectonic organization was found to be basically similar to that of the cat. As in our previous study of the cytoarchitectonic organization of the lower thoracic and lumbosacral spinal cord (Molander et al.; J. Comp. Neurol. 230:133-141, '84), the borderlines between the laminae were often found to be ambiguous, suggestive of zones of transition rather than sharp borders. In addition to the laminar scheme, the distribution of certain important cell groups, including the column of Clarke, the central cervical nucleus, the lateral cervical nucleus, the lateral spinal nucleus, and the internal basilar nucleus, is described.

Substance P–like immunoreactivity in the lateral cervical nucleus of the owl monkey (Aotus trivirgatus): A comparison with the cat and rat

The location of substance P (SP) in the lateral cervical nucleus (LCN) of monkeys (Aotus trivirgatus), cats, and rats was investigated with immunohistochemical methods. Light microscopic analysis showed that SP-positive fibers and terminals are evenly distributed throughout the LCN of the monkey and rat, whereas the SP labeling in the LCN of the cat is concentrated in the medial part of the nucleus, with only very sparse labeling in the lateral part. Electron microscopic examination of the monkey LCN revealed the presence of SP-like immunoreactivity within terminal boutons and unmyelinated axons. The SP-positive boutons are in synaptic contact with dendrites and, occasionally, cell bodies; they contain densely packed, clear, round synaptic vesicles, as well as dense-core vesicles. The distribution of SP-like immunoreactivity in the LCN of monkeys, cats, and rats is similar to that of nociceptive-responsive neurons demonstrated in electrophysiological experiments. The possible role of the SP-containing fibers in the transmission of nociceptive information through the LCN is discussed.

A reinvestigation of the spinovestibular projection in the cat using axonal transport techniques

There are numerous discrepancies within the literature concerning the sources of spinovestibular fibers and their distribution in the vestibular complex. Sources of afferents from all spinal levels were sought using the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. Following injections of this tracer in all portions of the vestibular complex retrograde labelling was densest at upper cervical levels, especially within the contralateral central cervical nucleus. Labelling was also observed in laminae VI (ipsilaterally), IV, V, VII, and VIII (bilaterally). At progressively more caudal levels, numbers of labelled cells decreased but were similarly distributed in these laminae. The terminal distribution of spinal efferent fibers within the vestibular complex was revealed by injecting wheat germ agglutinin conjugated to horseradish peroxidase or tritiated amino acids into various levels of the spinal cord. These studies showed that all spinal levels project to the descending vestibular nucleus and group x. The f-tail of the descending vestibular complex receives projections from upper cervical and thoracic levels. Terminations within the medial vestibular nucleus arise from both upper cervical and lumbar levels. No conclusive evidence was found supporting the presence of substantial direct spinal projections to the lateral vestibular nucleus, superior vestibular nucleus, or group z. Possible functional roles for the spinovestibular projection in posture and gaze are discussed.

Receptive fields and in-field afferent inhibition of neurones in the cat's lateral cervical nucleus.

1. Extracellular microelectrode recordings were made from projection neurones of the lateral cervical nucleus (LCN) in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. 2. The receptive fields of eight-five units were analysed. Most units had excitatory receptive fields similar in size and shape to those of spinocervical tract (SCT) cells. A few (14%) had either very large fields or 'stocking-like' fields. The majority of the LCN neurones (fifty-five, 65%) were excited by hair movement and, in addition, by noxious mechanical stimulation within the skin area responding to hair movement. Twenty-five units (29%) were excited by hair movement alone. For seven of these twenty-five neurones, noxious mechanical stimulation within the excitatory receptive field produced inhibition of the background discharge. One unit was excited by noxious mechanical stimulation and for the remaining four units no receptive field could be found. In six units inhibitory receptive fields outside the excitatory field were found. 3. Air-jet stimuli were used to define the excitatory profiles of the units' receptive fields to hair movement. In general, receptive fields had single regions of greatest sensitivity usually at or near the centre of the field, where that was oval in shape, with the sensitivity declining towards the field's circumference. In some units with very large fields that included parts of one or two limbs and the trunk there could be more than one highly sensitive region. 4. Pairs of air-jet stimuli were used to investigate in-field afferent inhibition in LCN cells. One jet was used to condition the responses to another jet located at a different position within the excitatory receptive field and occurring 200 ms later. Sixteen units were tested and significant in-field inhibition was observed in all sixteen. 5. The in-field afferent inhibition was organized spatially in the sense that inhibition was generally strongest when the conditioning and testing stimuli were close together and became weaker as they were moved apart. The afferent inhibition was not simply a function of the response produced by the conditioning stimulus. Furthermore, increasing the strength of the stimuli did not in general lead to larger areas from which the inhibition could be produced. The inhibitory areas defined in these experiments were generally less than 120 mm in length in units with receptive fields much longer than 100 mm.(ABSTRACT TRUNCATED AT 400 WORDS)

The morphology of cat spinal neurons projecting to both the lateral cervical nucleus and the dorsal column nuclei.

Morphological features of physiologically characterized doubly projecting spinocervical tract-dorsal column postsynaptic (SCT-DCPS) neurons were examined following intracellular injections of horseradish peroxidase. Their cell bodies and majority of dendrites were located in laminae III-IV. The SCT-DCPS neurons have rostrocaudally elongated dendritic trees with spiny fine caliber dendrites, and issue local axon collaterals that are studded with varicosities. The results show that the doubly projecting SCT-DCPS neurons do not represent a morphologically distinct subset of the spinocervical tract (SCT) or dorsal column postsynaptic (DCPS) cells.

GABA‐immunoreactive neurons and terminals in the lateral cervical nucleus of the cynomolgus monkey

An antiserum against the inhibitory transmitter substance gamma-aminobutyric acid (GABA) was used to investigate the distribution of GABAergic nerve terminals and cell bodies in the lateral cervical nucleus (LCN) of the cynomolgus monkey. Light microscopic immunohistochemistry demonstrated GABA-immunoreactive puncta, suggestive of nerve terminals, scattered throughout the LCN. The terminal-like profiles are often present along the somata of unlabeled neurons, but most are located in the neuropil. GABA-immunoreactive neurons are present in the LCN, but constitute a very small number of the LCN neurons. Electron microscopy showed that the GABA-positive neurons are small with a relatively large nucleus. They are contacted by few somatic boutons. Numerous GABA-immunoreactive terminals containing densely packed round to oval synaptic vesicles were also found. Most GABA-positive terminals make synaptic contact with dendrites, but synapses with cell bodies are also present. Synaptic contacts between labeled and unlabeled terminals were not observed. Some GABA-positive terminals make contact with GABA-positive neurons. The present findings suggest that GABA is a major inhibitory transmitter substance in the LCN of the monkey. However, in comparison with other somatosensory relay nuclei, there are few GABA-immunoreactive neurons in the LCN. This may imply that the GABA-positive neurons branch extensively in the LCN or that an extrinsic source of GABAergic input exists.

Spinocerebellar neurons and propriospinal neurons in the cervical spinal cord: a fluorescent double-labeling study in the rat and the cat.

In the cervical spinal cord of the rat and the cat, the distributions of spinocerebellar and of descending propriospinal neurons were investigated using the retrograde fluorescent double-labeling technique. Moreover, a search was made for the presence of neurons with both ascending spinocerebellar and descending propriospinal axoncollaterals. Diamidino Yellow Dihydrochloride (DY) was injected at T2, while True Blue (TB) (in rats) or Fast Blue (FB) (in cats) was injected in the cerebellum. The distributions of labeled neurons were very similar in the rat and the cat. DY-labeled propriospinal neurons, projecting to T2 or below, were most numerous in lamina I and laminae IV to VIII. In the rat, such neurons were also present in the lateral spinal nucleus (LSN). TB- or FB-labeled spinocerebellar neurons were concentrated in the central cervical nucleus (CCN) at C1-C4, in the central part of lamina VII at C5-T1, in the medial part of lamina VI and the adjoining dorsomedial part of lamina VII at C2/C3-T1, and in Clarke's column. They were also found in lamina V at C1 and C7-T1, and in lamina VIII at all levels. In both species only very few DY-TB/FB double-labeled neurons, representing neurons with branching axons, were observed; in C1-T1, only about 0.5% of all TB/FB-labeled spinocerebellar neurons and about 0.05% of all DY-labeled descending propriospinal neurons were double-labeled. The double-labeled neurons were all located centrally in lamina VII at C5-T1, but even in that area they constituted not more than 1.5% (rat) and 4% (cat) of the labeled spinocerebellar neurons. These findings indicate that, in the cervical cord of the rat and the cat, descending propriospinal neurons and spinocerebellar neurons are to a large extent separate populations.

Fluorescent histochemical localization of neutral endopeptidase-24.11 (enkephalinase) in the rat spinal cord.

The localization of neutral endopeptidase-24.11 (E.C. 3.4.24.11; enkephalinase) in rat spinal cord was investigated by a novel fluorescent histochemical method. Enkephalinase was localized by using a coupled enzyme assay based upon the sequential cleavage of the synthetic peptide substrate glutaryl-ala-ala-phe-4-methoxy-2-naphthylamide by enkephalinase and exogenous aminopeptidase M. Enzyme distribution was examined in segments from cervical, thoracic, lumbar, and sacral cord. At all spinal cord levels, enkephalinase was localized to discrete regions of the gray matter. The substantia gelatinosa displayed rich enkephalinase staining which overlapped the inner and outer zones of lamina II. A staining pattern similar to that observed in lamina II was observed in the spinal trigeminal nucleus in the medulla. In lamina III the enzyme was associated with small and medium-sized cells. Lamina IV showed staining associated with medium-sized and large cell bodies. The medial boundary of the dorsal gray of laminae IV and V had medium-sized fusiform cells which stained for enkephalinase. In the lateral reticulated areas of lamina V, enkephalinase reaction product was localized to scattered medium-sized and large cells compressed against the white matter of axon bundles. Staining in lamina VI was similar in appearance to lamina V. Enkephalinase reaction product was widely distributed in the ventral horn. Numerous ventral horn motor neurons of varied size and morphology in laminae VIII and XI stained richly for the enzyme. The enzyme was also localized to medium-sized and large cells in lamina X and to cells of the central cervical nucleus. The size and morphology of the cell types associated with the enzyme supported a neuronal association for enkephalinase. The regional distribution of the enzyme overlapped that of enkephalin- and substance-P rich regions of the spinal cord. These findings support a role for enkephalinase in the metabolic regulation of centrally acting neuropeptides.

Central distribution of cervical primary afferents in the rat, with emphasis on proprioceptive projections to vestibular, perihypoglossal, and upper thoracic spinal nuclei

The projections of primary afferents from rostral cervical segments to the brainstem and the spinal cord of the rat were investigated by using anterograde and transganglionic transport techniques. Projections from whole spinal ganglia were compared with those from single nerves carrying only exteroceptive or proprioceptive fibers. Injections of horseradish peroxidase (HRP) or wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) were performed into dorsal root ganglia C2, C3, and C4. Free HRP was applied to the cut dorsal rami C2 and C3, greater occipital nerve, sternomastoid nerve, and to the C1/2 anastomosis, which contains afferents from suboccipital muscles and the atlanto-occipital joint. WGA-HRP injections into ganglia C7 and L5 were performed for comparative purposes. Injections of WGA-HRP or free HRP into rostral cervical dorsal root ganglia and HRP application to C2 and C3 dorsal rami produced labeling in dorsal and ventral horns at the level of entrance, the central cervical nucleus, and in external and main cuneate nuclei. From axons ascending to pontine and descending to upper thoracic spinal levels, medial collaterals were distributed to medial and descending vestibular, perihypoglossal and solitary nuclei, and the intermediate zone and Clarke's nucleus dorsalis in the spinal cord. Lateral collaterals projected mainly to the trigeminal subnucleus interpolaris and to lateral spinal laminae IV and V. Results from HRP application to single peripheral nerves indicated that medial collaterals were almost exclusively proprioceptive, whereas lateral collaterals were largely exteroceptive with a contribution from suboccipital proprioceptive fibers. WGA-HRP injections into dorsal root ganglia C7 and L5 failed to produce significant labeling within vestibular and periphypoglossal nuclei, although they demonstrated classical projection sites within the brainstem and spinal cord. The consistent collateralisation pattern of rostral cervical afferents along their whole rostrocaudal course enables them to contact a variety of precerebellar, vestibulospinal, and preoculomotor neurons. These connections reflect the well-known significance of proprioceptive neck afferents for the control of posture, head position, and eye movements.

Central projections of the rat radial nerve investigated with transganglionic degeneration and transganglionic transport of horseradish peroxidase.

Transganglionic degeneration and transganglionic transport of HRP were used for investigation of the spinal cord and brainstem projections from the superficial, cutaneous (SR) and deep, muscular (DR) branches of the radial nerve. The HRP study included a numerical and size analysis of labelled dorsal root ganglion (DRG) cells. In degeneration experiments the SR nerve was found to project somatotopically to laminae III-IV, but degeneration was also found in lamina I and inconsistently in lamina II. Transection of the DR nerve was found to give rise to a small amount of degeneration, which in "sham" operations was established to result from the skin injury during dissection of the DR nerve. With the HRP method, the SR nerve was found to project somatotopically to laminae I-IV, whereas the DR nerve projected more diffusely to the medial part of laminae V-VII. HRP application to the SR and DR nerves resulted in labelling of a mean of 1,024 and 310 DRG cells, respectively. These labelled neurons had a median cell area of 381 and 562 micron 2 for the SR and DR nerves, respectively, and both small and large cells were labelled in both types of experiments. In the lower brainstem, projections from the SR nerve were found only in the ipsilateral dorsal part of the main cuneate nucleus (MCN) with both methods. Brainstem projections from the DR nerve that were found only with the HRP method were found in the ipsilateral ventral part of the MCN together with a projection to the ipsilateral external cuneate nucleus. No projections were found to the central cervical nucleus. The present results indicate that cutaneous compared to muscular primary sensory neurons are much more prone to react with transganglionic degeneration after peripheral nerve transection. Furthermore, in the rat the SR nerve projects somatotopically, whereas the DR nerve does not. Both nerve branches are connected to small and large spinal ganglion cells, although the median cell area is larger in muscular neurons.

Synaptic connections of GABA-containing boutons in the lateral cervical nucleus of the cat: An ultrastructural study employing pre- and post-embedding immunocytochemical methods

The lateral cervical nucleus receives input from the spinocervical tract and projects to the thalamus and mesencephalon. The organization of this nucleus was examined using two immunocyto-chemical methods. Pre-embedding immunolabelling was performed using an antibody against glutamate decarboxylase, and post-embedding immunogold-reaction was performed with an antibody to glutaraldehyde-fixed GABA. Light microscopic analysis of material reacted for glutamate decarboxylase revealed that punctate structures were present throughout the nucleus and were associated with large cells in the dorsolateral region of the nucleus. Electron microscopy demonstrated that the punctate structures were synaptic boutons which formed symmetrical synaptic junctions with dendrites and somata of cells in the nucleus. The ultrastructural preservation of material prepared for the post-embedding immunogold technique was superior to that prepared for pre-embedding immunostaining. Positively labelled synaptic boutons exhibited high colloidal gold density and, like those prepared for the pre-embedding method, formed symmetrical synaptic junctions with dendrites and somata of neurons. Labelled boutons were densely packed with irregularly-shaped synaptic vesicles. They displayed characteristics which were distinct from those unlabelled boutons. Boutons, revealed by both immunolabelling methods, were not observed to form synaptic associations with other axon terminals and were presynaptic to dendrites and somata only. Therefore, it is probable that such boutons are responsible for postsynaptic inhibition of cells in the nucleus. In view of this evidence, it is concluded that the lateral cervical nucleus is not simply a relay but is actively involved in processing sensory information.

Light and electron microscopical studies of the GABA innervation of the dorsal column nuclei and the lateral cervical nucleus in the primate species Macaca fascicularis and Papio anubis.

In 4 monkeys of the species Macaca fascicularis (2 animals) and Papio anubis (2 animals) the three dorsal column nuclei and the lateral cervical nucleus have been investigated immunocytochemically with antiserum against gamma-aminobutyric acid (GABA). Light microscopic studies demonstrated the presence of GABA-positive cells in the gracile nucleus, the internal cuneate nucleus and the lateral cervical nucleus but not in the external cuneate nucleus. Although labeled cells seemed fairly evenly spread in the nuclei there was an increased amount between the clusters of the internal cuneate nucleus and in the border zone between the gracile and the cuneate nucleus. Electron microscopical investigation showed GABA labeling in fairly small neurons with relatively large cell nuclei and low somatic bouton covering. GABA-positive terminals with rounded synaptic vesicles were present in all the investigated nuclei also the external cuneate one. No apparent difference in number of such boutons in the different nuclei or parts of the nuclei was found. GABA-positive boutons mostly synapsed with dendrites but in the dorsal column nuclei also with other larger boutons. Axosomatic contacts between labeled terminals and neuronal perikarya were more common in the lateral cervical nucleus than in the dorsal column nuclei. The results from the different nuclei in the monkey were compared with the results of similar investigations in the cat. It is concluded that there are important species differences especially on the light microscopical level in the lateral cervical nucleus. Thus the GABA labeled cells is rather evenly spread over the nucleus in the monkey whereas in the cat they are concentrated to the ventromedial region.

Spinocerebellar tract neurons with axons passing through the inferior or superior cerebellar peduncles. A retrograde horseradish peroxidase study in rats.

Using the retrograde horseradish peroxidase (HRP) method, we determined whether axons of the spinocerebellar tract (SCT) neurons pass through the superior (SCP) or the inferior (ICP) cerebellar peduncle in rats. Following bilateral section of either the SCPs or the ICPs, HRP was injected into the cerebellar anterior lobe and lobule VI, and the resulting labeled neurons were quantitatively examined throughout the length of the spinal cord. Almost all SCT neurons in the central cervical nucleus, Clarke's column and lamina VII of the third cervical (C3) to third thoracic (T3) segments and the T11 to fifth lumbar (L5) segments, and the majority of SCT neurons in the ventrolateral part of the anterior horn of the L6 to caudal (Ca) segments and laminae V of the C8-L5 segments and VII of the L6-Ca segments project their axons through the ICPs. The majority of spinal border cells (T11-L5) and a large number of SCT neurons in lamina VII of the C3-T3, T11-L5 and L6-Ca segments project their axons through the SCPs. A nearly equal number of SCT neurons in lamina VIII (C1-L6) send axons through the SCPs or the ICPs. The proportion of SCT neurons projecting via the SCPs versus those projecting via the ICPs was approximately 1:5.