Distribution of neuropeptide Y immunoreactivity in the basal forebrain and upper brainstem of the squirrel monkey (Saimiri sciureus)

The distribution of neuropeptide Y (NPY) immunoreactivity in the brain of the squirrel monkey (Saimiri sciureus) was studied by means of the indirect immunofluorescence, peroxidase-antiperoxidase, and avidin-biotin-complex methods. The antiserum used was raised in rabbits and did not show any significant crossreactivity with related peptides including peptide YY and avian pancreatic polypeptide. In the upper brainstem of the squirrel monkey a dense NPY-immunoreactive terminal field is seen in lateral parabrachial area, locus coeruleus, and interpeduncular nucleus. A small group of NPY-immunoreactive cell bodies is present in the lateral habenula and a moderate number of NPY-immunoreactive fibers occurs in periaqueductal gray and nucleus raphe pallidus. The substantia nigra (SN) appears mostly devoid of NPY immunoreactivity whereas the ventral tegmental area contains a few reactive fibers. In the hypothalamus the medial preoptic area as well as the arcuate and paraventricular nuclei receive a strikingly dense NPY innervation. In addition, numerous NPY-positive cell bodies are found within the dorsomedial half of the supraoptic nucleus but very few are seen in paraventricular nucleus. A large number of NPY-immunoreactive cell bodies is also present in arcuate nucleus. In the basal telencephalon NPY-immunoreactive cells abound mostly in striatum, but some are also found in the amygdala (particularly basal, central, and lateral amygdaloid nuclei), the claustrum, and in the bed nucleus of the stria terminalis. Intensely reactive network of NPY-immunoreactive fibers is also present in all of these structures. In striatum, the numerous, fine and non-varicose NPY-immunoreactive fibers, as well as the NPY-positive cell bodies, are slightly more abundant in caudate nucleus than in putamen. The globus pallidus (GP) is mostly devoid of NPY-immunoreactive fibers and terminals. The fact that the two major recipient structures of striatal outflow (SN and GP) do not receive significant NPY input suggests that the striatal NPY-containing neurons are intrinsically organized.     

Distribution of high affinity choline transporter immunoreactivity in the primate central nervous system

A mouse monoclonal antibody (clone 62-2E8) raised against a human recombinant high-affinity choline transporter (CHT)-glutathione-S-transferase fusion protein was used to determine the distribution of immunoreactive profiles containing this protein in the monkey central nervous system (CNS). Within the monkey telencephalon, CHT-immunoreactive perikarya were found in the striatum, nucleus accumbens, medial septum, vertical and horizontal limb nuclei of the diagonal band, nucleus basalis complex, and the bed nucleus of the stria terminalis. Dense fiber staining was observed within the islands of Calleja, olfactory tubercle, hippocampal complex, amygdala; moderate to light fiber staining was seen in iso- and limbic cortices. CHT-containing fibers were also present in sensory and limbic thalamic nuclei, preoptic and hypothalamic areas, and the floccular lobe of the cerebellum. In the brainstem, CHT-immunoreactive profiles were observed in the pedunculopontine and dorsolateral tegmental nuclei, the Edinger-Westphal, oculomotor, trochlear, trigeminal, abducens, facial, ambiguus, dorsal vagal motor, and hypoglossal nuclei. In the spinal cord, CHT-immunoreactive ventral horn motoneurons were seen in close apposition to intensely immunoreactive C-terminals at the level of the cervical spinal cord. CHT immunostaining revealed a similar distribution of labeled profiles in the aged human brain and spinal cord. Dual fluorescent confocal microscopy revealed that the majority of CHT immunoreactive neurons contained the specific cholinergic marker, choline acetyltransferase, at all levels of the monkey CNS. The present observations indicate that the present CHT antibody labels cholinergic structures within the primate CNS and provides an additional marker for the investigation of cholinergic neuronal function in aging and disease.     

Distribution and ultrastructural features of the serotonin innervation in rat and squirrel monkey subthalamic nucleus

The main purpose of this light and electron microscopic immunocytochemical study was to characterize and compare the serotonin (5‐HT) innervation of the subthalamic nucleus (STN) in rats and squirrel monkeys (Saimiri sciureus) following labeling with an antibody against the 5‐HT transporter (SERT). Unbiased counts of SERT+ axon varicosities revealed an average density of 5‐HT innervation higher in monkeys (1.52 × 10⁶ varicosities/mm³) than rats (1.17 × 10⁶), particularly in the anterior half of the nucleus (1.70 × 10⁶). As measured by electron microscopy, SERT+ axon varicosity profiles in the STN of both species were smaller than unlabeled profiles. The number of SERT+ profiles displaying a synaptic junction indicated that, in both rat and monkey STN, approximately half of 5‐HT axon varicosities were asynaptic. In monkeys, all synaptic junctions made by SERT+ varicosities were asymmetrical, as opposed to only 77% in rats. Despite the higher density of 5‐HT innervation in the anterior half of monkey STN, the ultrastructural features of its SERT+ varicosities, including synaptic incidence, did not significantly differ from those in its posterior half. These findings suggest that, throughout the rat and monkey STN, 5‐HT afferents may exert their influence via both synaptic delivery and diffusion of 5‐HT, and that an ambient level of 5‐HT maintained in STN by these two modes of transmission might also modulate neuronal activity and influence motor behavior. A better understanding of the factors governing the complex interplay between these signaling processes would greatly improve our knowledge of the physiopathology of the STN.     

Distribution and morphological characteristics of dopamine-immunoreactive neurons in the midbrain of the squirrel monkey (Saimiri sciureus)

The distribution and morphological characteristics of dopamine (DA) neurons in the midbrain of the squirrel monkey (Saimiri sciureus) were investigated by peroxidase-antiperoxidase (PAP) immunohistochemistry with a highly specific antiserum raised against DA-glutaraldehyde-lysyl-protein conjugate (donated by M. Geffard). Four contiguous areas contained DA-immunostained nerve cell bodies: (1) the substantia nigra, pars compacta (SNc), (2) the ventral tegmental area (VTA), (3) the retrorubral area (RRA), and (4) the periaqueductal gray (PAG). The SNc composed the vast majority of DA-immunostained neurons. Most of these neurons were relatively large (mean diameters: 35 x 15 micron) and varied in shape from fusiform to polygonal, but a few smaller (16 x 10.5 micron) globular cells were dispersed among them. The caudal two-thirds of the SNc was particularly rich in DA somata. Rostrally, these DA cells formed several distinct columns impinging deeply upon the underlying pars reticulata. Large oval sectors mostly devoid of immunoreactivity were delineated by these trabeculae. The long dendritic processes of DA neurons in the SNc were generally oriented in prominent dorsoventral bundles the ventralmost portion of which arborized diffusely along the dorsal surface of the cerebral peduncle. In the VTA, the DA neurons were regrouped in a triangular zone located dorsal to the interpeduncular nucleus, medial to the substantia nigra and ventral to the oculomotor nucleus. These DA cells were of medium size (19 x 10.5 micron), globular or fusiform, and usually showed one or two thick primary dendrites oriented dorsoventrally. The DA cells in the RRA lay in continuity with the most caudal DA-containing elements of the substantia nigra but could be distinguished by their smaller size (26 x 12 micron), shorter and more profusely branched dendrites, and darker immunostaining. These DA neurons were characteristically scattered among and medial to the fibers of the medial lemniscus, and a few could be observed as far caudally as the pedunculopontine nucleus. In the PAG, DA-immunostained neurons were seen in the rostral half of the mesencephalic central gray and predominated in its ventral half. These cells were of medium size (22.5 x 10 micron) and some of them were found in proximity to the ventricular lining. At caudal levels, the DA-positive cells in the PAG did not intermingle with dorsal raphe neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Localization of cholinergic neurons in the forebrain and brainstem that project to the suprachiasmatic nucleus of the hypothalamus in rat

In mammals, the suprachiasmatic nucleus is responsible for the generation of most circadian rhythms and their entrainment to environmental cues. Cholinergic agents can alter circadian rhythm phase, and fibres immunoreactive for choline acetyltransferase, the biosynthetic enzyme for acetylcholine, are present in the suprachiasmatic nucleus. Since there are no cholinergic somata in the suprachiasmatic nucleus, these fibres must represent the terminals of cholinergic neurons whose cell bodies are located elsewhere in the brain. This study was aimed at locating the cholinergic neurons that project to the suprachiasmatic nucleus by retrograde and anterograde tract-tracing and immunohistochemistry for choline acetyltransferase in the rat. After injection of fluorogold, a retrograde tracer, into the suprachiasmatic nucleus, retrogradely labelled neurons that were immunopositive for choline acetyltransferase were located throughout the rostrocaudal extent of the cholinergic basal nuclear complex, with highest densities in the substantia innominata and the nucleus basalis magnocellularis. A few cells were also located in the medial septum and in the vertical and horizontal limbs ofthe diagonal band of Broca. In the brainstem, double-labelled neurons were located in the laterodorsal tegmental nucleus, pedunculopontine tegmental nucleus and the parabigeminal nucleus. Injections of the anterograde tracer biocytin in these three brainstem nuclei resulted in fibre labelling in the suprachiasmatic nucleus, consistent with the retrograde findings. No clearly double-labelled cells were located in the retina. These results suggest that the suprachiasmatic nucleus receives cholinergic afferents from both the basal forebrain and mesopontine tegmentum which may mediate cholinergic effects on circadian rhythms. © 1993 Wiley-Liss, Inc.     

N-methylaspartate: an effective tool for lesioning basal forebrain cholinergic neurons of the rat

The ability of the excitotoxin, N-methyl-D,L-aspartic acid (NMA), to destroy basal forebrain cholinergic (BFC) neurons was evaluated. NMA (100 nmol) was directly injected into the peripallidum, a region containing a proportionately large number of cortically-projecting BFC neurons. Cholineacetyltransferase (ChAT) activity 10 days later was markedly and significantly reduced (up to 62%) in the cortex ipsilateral to the lesion. NMA induced a focal lesion affecting BFC neurons without damaging axons of passage or causing lesions distant from the site of injection. ChAT immunohistochemistry (IHC) was used to directly demonstrate loss of ChAT-positive neurons from the lesion site. This loss persisted at all survival times examined, from 2 days to 7.5 months post-injection.     

Neurogenesis of the magnocellular basal forebrain nuclei in the rhesus monkey

The time of origin of the neurons that comprise the magnocellular basal forebrain nuclei in rhesus monkeys was determined by using [3H]thymidine autoradiography. Thirteen pregnant animals received an injection of [3H]thymidine between embryonic days 27 (E27) and E50 of their 165 day gestation, and their offspring were sacrificed during the early postnatal period. Neurons within this region were generated in a biphasic pattern. An initial burst of [3H]thymidine-labeled magnocellular neurons was first observed throughout short quiescent period, cells of the remaining anterior basal forebrain (inclusive of magnocellular neurons comprising the vertical limb of the diagonal band and the anteromedial and anterolateral regions of the nucleus basalis) were generated between E36 and E45 with a peak of neurogenesis seen on E40-E43. The intermediate division of the nucleus basalis was generated about the same time, but the peak period of neurogenesis in this region occurred slightly earlier (E36 and E40) and was completed by E43. During the second phase of neurogenesis, neurons within the posterior division of the basal forebrain were generated first, with their genesis virtually completed between E33 and E36. The genesis of all neurons comprising the magnocellular basal forebrain nuclei was completed by E48 of gestation. A general caudal to rostral gradient of neurogenesis was observed within this telencephalic region. In contrast, a neurogenic gradient was not discerned in the radial direction. The present data demonstrate that neurons comprising the basal forebrain magnocellular nuclei in monkeys are generated early in gestation with two peak times of neuronal genesis. These nuclei are among the earliest to be generated in the entire telencephalon, which, like neurons of the thalamus and cortical neurons giving rise to cortical-cortical connections, places them in a strategic position to potentially influence their target neurons within the cortical mantle that are generated later in gestation.     

Strain-dependent variations in the number of forebrain cholinergic neurons

The morphological organization of putatively cholinergic neurons was studied in the forebrain of two inbred mouse strains (C57BL/6 and DBA/2) by means of acetylcholinesterase pharmacohistochemistry. In both strains, putatively cholinergic perikarya were seen in the caudato-putamen, medial septum, diagonal band, and basal nucleus of Meynert: in all these regions, their distribution was similar in both strains, but their density was significantly higher (from 20 to 32%) in DBA/2 mice. The present data demonstrate the existence of genetically determined differences in the organization of forebrain cholinergic systems.     

Neuropeptide Y-immunoreactive neurons in the striatum of cat and monkey: Morphological characteristics, intrinsic organization and co-localization with somatostatin

A detailed study of the distribution of neuropeptide Y (NPY) in the striatum of squirrel monkey (Saimiri sciureus) and cat was undertaken by means of indirect immunofluorescence and peroxidase-antiperoxidase (PAP) methods. In monkey, the NPY-immunoreactivity is homogeneously distributed along the entire extent of the caudate nucleus (CD) and putamen (PUT), while in cat marked heterogeneities are noted. In the CD of cat, the NPY-immunoreactive fibers and cell bodies are concentrated in numerous patches of various sizes, which can be readily distinguished from zones of poor NPY-immunostaining. In the CD and PUT of squirrel monkey the NPY-positive neurons are either triangular, fusiform or globular, with long and smooth dendrites branching infrequently. The numerical density of NPY-immunoreactive cell bodies is greater in the CD than in the PUT, and it increases markedly along the rostrocaudal extent of the striatum. In the rostral CD and PUT the densities are 23 cells/mm2 and 14 cells/mm2, respectively, whereas the values for caudal CD and PUT are 35 cells/mm2 and 20 cells/mm2, respectively. Quantitative measurements reveal that these NPY-immunoreactive cells belong to a single subset of striatal neurons having a maximum diameter of 19.2 +/- 0.1 micron and a cross-sectional area of 145.5 +/- 0.6 micron2 (mean +/- S.E.M.; n = 1238 CD cells and 1169 PUT cells). Furthermore, experiments combining the use of lectin-conjugated HRP as retrograde tracer with PAP immunohistochemical method demonstrate that striatal NPY-immunoreactive neurons in squirrel monkey and cat do not project outside the striatum. Finally, co-localization studies in monkey reveal that the vast majority of striatal NPY-positive neurons also contains somatostatin. These results show that the NPY-immunoreactive neurons in mammalian striatum form a subpopulation of medium-sized interneurons containing somatostatin.     

Quantitative and ultrastructural study of serotonin innervation of the globus pallidus in squirrel monkeys

The present immunohistochemical study was aimed at characterizing the serotonin (5‐HT) innervation of the internal (GPi) and external (GPe) pallidal segments in the squirrel monkey (Saimiri sciureus) with an antibody against the 5‐HT transporter (SERT). At the light microscopic level, unbiased counts of SERT+ axon varicosities showed that the density of innervation is similar in the GPi (0.57 ± 0.03 × 10⁶ varicosities/mm³ of tissue) and the GPe (0.60 ± 0.04 × 10⁶), with the anterior half of both segments being more densely innervated than the posterior half. Dorsoventral and mediolateral decreasing gradients of SERT varicosities occur in both pallidal segments, but are statistically significant only in the GPi. The neuronal density being significantly greater in the GPe (3.41 ± 0.23 × 10³ neurons/mm³) than in the GPi (2.90 ± 0.11 × 103), the number of 5‐HT axon varicosities per pallidal neuron was found to be superior in the GPi (201 ± 27) than in the GPe (156 ± 26). At the electron microscopic level, SERT+ axon varicosities are comparable in size and vesicular content in GPi and GPe, where they establish mainly asynaptic contacts with unlabeled profiles. Less than 25% of SERT+ varicosities display a synaptic specialization, which is of the symmetrical or asymmetrical type and occurs exclusively on pallidal dendrites. No SERT+ axo‐axonic synapses are present, suggesting that 5‐HT exerts its well‐established modulatory action upon various pallidal afferents mainly through diffuse transmission, whereas its direct control of pallidal neurons results from both volumic and synaptic release of the transmitter.     

Synaptic organization of cholinergic neurons in the monkey neostriatum

Cholinergic neurons in the monkey neostriatum were examined at the light and electron microscopic level by immunohistochemical methods in order to localize choline acetyltransferase (ChAT), the synthesizing enzyme for acetylcholine. At the light microscopic level a sparse distribution of cholinergic neurons was identified throughout the caudate nucleus. Neurons had large (25-30 microns) somata, eccentric invaginated nuclei, primary dendrites of unequal diameters, and varicosities on distal dendritic branches. Ultrastructural study showed that the cholinergic cells had a cytoplasm abundant in organelles. Within dendritic branches, mitochondria and cisternae were localized primarily to varicosities. Synaptic inputs were distributed mostly to the dendrites and at least four types that formed symmetric or asymmetric synapses were observed. Immunoreactive fibers were relatively numerous within the neuropil and exhibited small diameters (0.1-0.15) micron) and swellings at frequent intervals. Cholinergic boutons that formed synapses were compared to unlabeled terminals making asymmetric synapses with dendritic spines. Results showed that ChAT-positive axons had significantly smaller cross-sectional areas, shorter synaptic junctions, and a higher density and surface area of mitochondria than the unlabeled boutons. Cholinergic axons formed symmetric synapses mostly with dendritic spines (53%) and the shafts of unlabeled primary and distal dendrites (37%). A relatively small proportion of the boutons contacted axon initial segments (1%) and cell bodies (9%) that included medium-sized neurons with unindented (spiny) and indented (aspiny) nuclei. The majority of dendritic spines contacted by cholinergic axons were also postsynaptic to unlabeled boutons forming asymmetric synapses. The results suggest that cholinergic neurons in the primary neostriatum belong to a single morphological class corresponding to the large aspiny (type II) interneuron identified in previous Golgi studies. Present results along with earlier Golgi-electron microscopic observations from this laboratory suggest that neostriatal cholinergic cells integrate many sources of intrinsic and extrinsic inputs. The observed convergence of ChAT-immunoreactive boutons and unlabeled axons onto the same dendritic spines suggests that intrinsic cholinergic axons modulate extrinsic inputs onto neostriatal spiny neurons at postsynaptic sites close to the site of afferent input.     

Choline acetyltransferase-like immunoreactivity in the forebrain of the red-eared pond turtle (Pseudemys scripta elegans)

Choline acetyltransferase (ChAT) immunohistochemistry was used to map the cholinergic neurons in the forebrain of Pseudemys turtles. Cell bodies with ChAT-like immunoreactivity were seen in the septum, the nucleus of the diagonal band, and embedded within the medial and lateral forebrain bundles. The region of the medial and lateral forebrain bundles contained the greatest concentration of ChAT-positive neurons. Virtually no ChAT-like immunoreactivity was seen in the areas composing the reptilian homologue of the mammalian striatum. It is suggested that the turtle basal forebrain cholinergic neurons may represent the evolutionary precursors to the mammalian cholinergic neurons of the basal forebrain and even the striatum.     

Distribution of neurotensin-containing fibers in the frontal cortex of the macaque monkey.

The distribution of neurotensin-containing fibers was examined in the frontal cortex of the monkey Macaca fuscata using the immunoperoxidase histochemical technique. An extremely dense network of neurotensin-containing fibers was observed in the medial prefrontal regions. The majority of cortical neurotensin fibers was observed in the anterior cingulate cortex (Walker's area 24) and adjacent medial prefrontal regions (areas 6 and 32). In area 24, the fiber density was similar to that in the nucleus accumbens. Immunoreactive fibers were particularly dense in two pyramidal layers (III, V). The medial prefrontal regions, areas 6 and 32, contained a moderate density of immunoreactive fibers. This regional distribution of neurotensin-containing fibers was not observed in other cortical fiber systems that contained substance P, somatostatin, or tyrosine hydroxylase. No neurotensin-containing cell bodies were observed in the frontal cortex. The present study demonstrates that the laminar and regional distributions of neurotensin-containing fibers are unique when compared to those of substance P- or somatostatin-containing fibers, and also distinct from that of catecholaminergic fibers. The distribution of telencephalic neurotensin fibers points to a relationship with limbic structures.     

Effect of basal forebrain somatostatin and parvalbumin neurons in propofol and isoflurane anesthesia

AimsThe basal forebrain (BF) plays an essential role in wakefulness and cognition. Two subtypes of BF gamma‐aminobutyric acid (GABA) neurons, including somatostatin‐expressing (GABA^SOM) and parvalbumin‐positive (GABA^Parv) neurons, function differently in mediating the natural sleep–wake cycle. Since the loss of consciousness induced by general anesthesia and the natural sleep–wake cycle probably share similar mechanisms, it is important to clarify the accurate roles of these neurons in general anesthesia procedure.MethodsBased on two transgenic mouse lines expressing SOM‐IRES‐Cre and PV‐IRES‐Cre, we used a combination of genetic activation, inactivation, and chronic ablation approaches to further explore the behavioral and electroencephalography (EEG) roles of BF^SOM and BF^Parv neurons in general anesthesia. After a single intravenous injection of propofol and the induction and recovery times of isoflurane anesthesia, the anesthesia time was compared. The changes in cortical EEG under different conditions were also compared.ResultsActivation of BF GABA^SOM neurons facilitates both the propofol and isoflurane anesthesia, manifesting as a longer anesthesia duration time with propofol anesthesia and a fast induction time and longer recovery time with isoflurane anesthesia. Moreover, BF GABA^SOM‐activated mice displayed a greater suppression of cortical electrical activity during anesthesia, showing an increase in δ power bands or a simultaneous decrease in high‐frequency power bands. However, only a limited and nuanced effect on propofol and isoflurane anesthesia was observed with the manipulated BF GABA^Parv neurons.ConclusionsOur results suggested that BF GABA^SOM neurons play a critical role in propofol and isoflurane general anesthesia, while BF GABA^Parv neurons appeared to have little effect.     

基底前脑Nestin+胆碱能神经元能较好耐受秋水仙素的细胞毒性

微管破坏剂秋水仙素注射于SD大鼠侧脑室,拟观察其对基底前脑不同类型神经元数量的影响,寻找抗损伤能力更强的神经元。与正常大鼠相比,1d后Nestin+胆碱能神经元数量下降,3d后Nestin+胆碱能神经元数量开始增加,至14,28d时增加达到峰值。而Nestin-胆碱能神经元、细小清蛋白神经元和胆碱乙酰转移酶神经元在注射秋水仙素后,数量逐渐下降。提示Nestin+胆碱能神经元对秋水仙素神经毒性具有较好的耐受性。     

Distribution of GABA-immunoreactive neurons in the basal ganglia of the squirrel monkey (Saimiri sciureus)

The distribution of GABA-immunoreactive neurons was visualized in the basal ganglia of the squirrel monkey (Saimiri sciureus), by using a highly specific antiserum raised against GABA-glutaraldehyde-lysyl-protein conjugate and revealed by the indirect peroxidase-antiperoxidase immunohistochemical method. In the dorsal striatum, GABA-immunoreactive nerve cell bodies were small to medium in size (sectional area ranging from 90 to 125 microns2), but some larger ones (500-600 microns2) were also found. These cells displayed no obvious clustering but were significantly more numerous in the caudate nucleus than in the putamen; their number was also markedly greater at caudal than at rostral striatal levels. A moderate number of evenly distributed positive axon terminals were visible in both the caudate nucleus and the putamen. In the ventral striatum, GABA-immunoreactive nerve cell bodies and axon terminals were seen in fair number within the nucleus accumbens and in the deep layers of the olfactory tubercle. Many positive terminals but no somata were found in the islands of Calleja. In the globus pallidus, virtually all nerve cell bodies were GABA-immunoreactive and the neuropil exhibited a multitude of positive terminals. In the substantia innominata, clusters of small, globular GABA-immunoreactive somata were scattered among aggregates of larger, nonimmunoreactive neurons belonging to the nucleus basalis, and the whole region showed a low to moderate number of evenly spread GABA-positive terminals. In the subthalamic nucleus, nerve cell bodies were generally surrounded by several GABA-positive terminals but were not themselves immunoreactive. The substantia nigra showed many GABA-immunoreactive somata, which predominated in the pars lateralis and diminished progressively in number along the lateromedial axis of the pars reticulata. These cells formed a rather pleomorphic group comprising round, fusiform, or polygonal elements of relatively large size (sectional area ranging from 200 to 800 microns2). In the pars compacta and ventral tegmental area, a few GABA-immunoreactive neurons of small size were dispersed among larger, unreactive neurons. In both pars lateralis and pars reticulata of the substantia nigra, the number of GABA-positive terminals was high and their distribution was rather uniform; a smaller number were visible in the pars compacta of the substantia nigra and in the ventral tegmental area. The present results demonstrate that GABA-containing neurons are widely and heterogeneously distributed in the various components of the squirrel monkey's basal ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)     

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.