Journal of Comparative Neurology
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An experimental study of the ventral striatum of the golden hamster. I. Neuronal connections of the nucleus accumbens Abstract As part of an experimental study of the ventral striatum, the horseradish peroxidase (HRP) method was used to examine the afferent and efferent neuronal connections of the nucleus accumbens. Following iontophoretic applications or hydraulic injections of HRP in nucleus accumbens, cells labeled by retrograde transport of HRP were observed in the ipsilateral telencephalon in the posterior agranular insular, perirhinal, entorhinal, and primary olfactory cortices, in the subiculum and hippocampal field CA1, and in the anterior and posterior divisions of the basolateral amygdaloid nucleus. In the diencephalon, labeled neurons were present ipsilaterally in the central medial, paracentral and parafascicular intralaminar nuclei, and in the midline nuclei parataenialis, paraventricularis, and reuniens. Retrograde labeling was observed in the ipsilateral brainstem in cells of the ventral tegmental area and dorsal raphe. Many of these projections to nucleus accumbens were found to be topographically organized. Anterograde transport of HRP from nucleus accumbens demonstrated ipsilateral terminal fields in the ventral pallidum and substantia nigra, pars reticulata. The afferent projections to nucleus accumbens from the posterior insular and perirhinal neocortices, intralaminar thalamus, and the dopamine‐containing ventral tegmental area are analogous to the connections of the caudatoputamen, as are the efferents from nucleus accumbens to the substantia nigra and ventral globus pallidus. These connections substantiate the classification of nucleus accumbens as a striatal structure and provide support for the recently proposed concept of the ventral striatum. Furthermore, the demonstration that a number of limbic system structures, including the amygdala, hippocampal formation, entorhinal cortex, and olfactory cortex are important sources of afferents to the nucleus accumbens, suggests that the ventral striatum may serve to integrate limbic information into the striatal system.
Journal of Comparative Neurology - Tập 191 Số 2 - Trang 167-192 - 1980
An experimental study of the ventral striatum of the golden hamster. II. Neuronal connections of the olfactory tubercle Abstract As part of an experimental study of the ventral striatum, the horseradish peroxidase (HRP) method was used to examine the afferent and efferent neuronal connections of the olfactory tubercle. Following iontophoretic applications or hydraulic injections of HRP in the tubercle, neurons labeled by retrograde transport of HRP were observed ipsilaterally in the telencephalon in the main olfactory bulb, the medial, lateral, ventral, and posterior divisions of the anterior olfactory nucleus, and in the orbital, ventral, and posterior agranular insular, primary olfactory, perirhinal, and entorhinal cortices. Labeled cells were also present in the basolateral, basomedial, anterior cortical, and posterolateral cortical amygdaloid nuclei, and bilaterally in the nucleus of the lateral olfactory tract. In the diencephalon, ipsilateral HRP‐containing neurons were observed in the midline nuclei paraventricularis, parataenialis, and reuniens, and in the parafascicular intralaminar nucleus. Retrograde labeling was present in the ipsilateral brainstem in cells of the ventral tegmental area, substantia nigra, and dorsal raphe. Many of the above projections to the tubercle were found to be topographically organized. Anterograde axonal transport of HRP from the olfactory tubercle labeled terminal fields ipsilaterally in all parts of the anterior olfactory nucleus, in the ventral pallidum, and in the substantia nigra, pars reticulata. Contralaterally, terminal fields were present in the dorsal and lateral divisions of the anterior olfactory nucleus. The projections to the tubercle from the orbital, ventral, and posterior agranular insular, and perirhinal neocortices, intralaminar thalamus, and dopamine‐containing areas of the ventral mesencephalon are analogous to the connections of the caudatoputamen, as are the efferents from the tubercle to the ventral globus pallidus and substantia nigra. These connections substantiate the recent suggestion that the olfactory tubercle is a striatal structure, and provide support for the ventral striatal concept. In the present study of the olfactory tubercle, and in the first study in this series on the nucleus accumbens, the ventral striatum was found to receive projections from a number of limbic system structures, including the main olfactory bulb, anterior olfactory nucleus, amygdala, hippocampus, and subiculum, and the entorhinal and primary olfactory cortices. These findings suggest that the ventral striatum is concerned with integrating limbic information into the striatal system.
Journal of Comparative Neurology - Tập 191 Số 2 - Trang 193-212 - 1980
Dual serotoninergic projections to forebrain in the rat: Morphologically distinct 5‐HT axon terminals exhibit differential vulnerability to neurotoxic amphetamine derivatives Abstract The cerebral cortex of the rat and other mammals is innervated by two morphologically distinct classes of serotoninergic (5‐HT) axon terminals: fine axons with minute varicosities and beaded axons characterized by large, spherical varicosities. Fine and beaded 5‐HT axons exhibit different regional and laminar distributions in forebrain and arise from separate brainstem nuclei, the dorsal and median raphe nuclei, respectively. Tha present neuroanatomic study, based on immunocytochemical methods to visualize 5‐HT axons, demonstrates that the two axon types differ markedly in their vulnerability to the neurotoxic amphetamine derivatives, methylenedioxyamphetamine (MDA), and p‐chloroamphetamine (PCA). While both drugs cause extensive degeneration of fine 5‐HT axons throughout forebrain, beaded 5‐HT axons are consistently spared. Fine 5‐HT axons, which richly innervate most regions of dorsal forebrain in control rats, are rarely seen 2 weeks after treatment with MDA or PCA; this loss of fine axons reflects a marked denervation that persists for months after drug administration. The serotoninergic axon terminals remaining after MDA or PCA administration are almost entirely of the beaded type and appear to be unaffected by both drugs. Over a wide range of doses (2.5–40 mg/kg PCA) and survival times (2 weeks to 2 months), these spared 5‐HT axons with large, spherical varicosities cannot be distinguished from the normal, beaded 5‐HT axons in control rats by morphologic criteria. Moreover, beaded 5‐HT axons exhibit a highly characteristic regional distribution which is the same in control as in MDA‐ and PCA‐treated rats: these axons innervate specific zones or layers within parietal and occipital cortex, hippocampus, cingulate cortex, entorhinal cortex, and the olfactory bulb, among other forebrain areas, and they form a dense plexus lining the ventricular system. Taken together, the results of this study demonstrate that fine 5‐HT axons are highly vulnerable to the neurotoxic effects of the amphetamine derivatives MDA and PCA, while beaded 5‐HT axons are markedly resistant. These findings are consistent with the hypothesis that there are two anatomically and functionally distinct sets of serotoninergic neurons projecting to forebrain. While both of these neuronal systems utilize 5‐HT as a neurotransmitter, they differ in several features: (1) origin from separate nuclei in the brainstem (the dorsal and median raphe), (2) two types of morphologically distinct axon terminals, (3) markedly different distribution and innervation patterns in forebrain, and (4) dissimilar pharmacological properties. The results further suggest that psychotropic amphetamine derivatives have a selective action upon fine serotoninergic axons that arise from the dorsal raphe nucleus.
Journal of Comparative Neurology - Tập 314 Số 3 - Trang 558-586 - 1991
GABA<sub>A</sub>‐receptor heterogeneity in the adult rat brain: Differential regional and cellular distribution of seven major subunits Abstract GABAA ‐receptors display an extensive structural heterogeneity based on the differential assembly of a family of at least 15 subunits (α1–6, β1–3, γ1–3, θ, ρl–2) into distinct heteromeric receptor complexes. The subunit composition of receptor subtypes is expected to determine their physiological properties andipharmacological profiles, thereby contributing to flexibility in signal transduction and allosteric modulation. In heterologous expression systems, functional receptors require a combination of α‐, β‐, and γ‐subunit variants, the γ2‐subunit being essential to convey a classical benzodiazepine site to the receptor. The subunit composition and stoichiometry of native GABAA ‐receptor subtypes remain unknown. The aim of this study was to identify immunohistochemically the main subunit combinations expressed in the adult rat brain and to allocate them to identified neurons. The regional and cellular distribution of seven major subunits (α1, α2, α3, α5, β2,3, γ2, δ) was visualized by immunoperoxidase staining with subunit‐specific antibodies (the β2‐ and β3‐subunits were covisualized with the monoclonal antibody bd‐17). Putative receptor subtypes were identified on the basis of colocalization of subunits within individual neurons, as analyzed by confocal laser microscopy in double‐ and triple‐immunofluoreseence staining expeximents. The results reveal an extraordinary heterogeneity in the distribution of GABAA ‐receptor subunits, as evidenced by abrupt changes in immunoreactivity along well‐defined cytoarchitectonic boundaries and by pronounced differences in the cellular distribution of subunits among various types of neurons. Thus, functionally and morphologically diverse neurons were characterized by a distinct GABAA ‐receptor subunit repertoire. The pultiple staining experiments identified 12 subunit combinations in defined neurons. The most prevalent combination was the triplet α1/β2,3/γ2, detected in numerous cell types throughout the brain. An additional subunit (α2, α3, or δ) sometimes was associated with this triplet, pointing to the existence of receptors containing four subunits. The triplets α2/β2,3/γ2, α3/β2,3/γ2, and α5/β2,3/γ2 were also identified in discrete cell populations. The prevalence of these seven combinations suggest that they represent major GABAA‐receptor subtypes. Five combinations also apparently lacked the β2,3‐subunits, including one devoid of γ2‐subunit (α1/α2/γ2, α2/γ2, α3/γ2, α2/α3/γ2, α2/α5/δ). These combinations were selectively associated with small neuron populations, thereby representing minor GABAA receptor subtypes. These results provide the basis for a functional analysis of GABAA ‐receptor subtypes of known subunit composition and may open the way for unproved therapeutic approaches based on the development of subtype‐selective drugs. © 1995 Wiley‐Liss, Inc.
Journal of Comparative Neurology - Tập 359 Số 1 - Trang 154-194 - 1995
The organization of projections from the cortes, amygdala, and hypothalamus to the nucleus of the solitary tract in rat Abstract Direct projections from the forebrain to the nucleus of the solitary tract (NTS) and dorsal motor nucleus of the vagus in the rat medulla were mapped in detail using both retrograde axonal transport of the fluorescent tracer True Blue and anterograde axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP). In the retrograde tracing studies, cell groups in the medial prefrontal cortex, lateral prefrontal cortex (primarily ventral and posterior agranular insular cortex), bed nucleus of the stria terminalis, central nucleus of the amygdala, paraventricular, arcuate, and posterolateral areas of the hypothalamus were shown to project to the NTS and in some cases also to the dorsal motor nucleus of the vagus. The prefrontal cortical areas projecting to the NTS apparently overlap to a large degree with those cortical areas receiving mediodorsal thalamic and dopaminergic input. The retrogradely labeled cortical cells were situated in deep layers of the rat prefrontal cortex. The anterograde tracing studies revealed a prominent topography in the mediolateral termination pattern of forebrain projections to the rostral part of the NTS and to the dorsal pons. The projections to the NTS were generally bilateral, except for projections from the central nucleus of the amygdala and bed nucleus of the stria terminalis which were predominantly ipsilateral. The prefrontal cortical projections to the NTS travel through the cerebral peduncle and pyramidal tract and terminate throughout the rostrocaudal extent of the NTS. Specifically, the prefrontal cortex innervates dorsal portions of the NTS (lateral part of the dorsal division of the medial solitary nucleus, dorsal part of the lateral solitary nucleus and the caudal midline region of the commissural nucleus), areas which receive relatively sparse subcortical projections. These dorsal portions of the NTS receive major primary afferent projections from the vagal and glossopharyngeal nerves. In contrast, the subcortical projections, which travel through the midbrain and pontine tegmentum, terminate most heavily in the ventral portions of the NTS, i.e., the area immediately dorsal and lateral to the dorsal motor nucleus of the vagus. Only the paraventricular hypothalamic nucleus has substantial terminals throughout the dorsal motor nucleus of the vagus. Hypothalamic cell groups innervate the area postrema and, along with the prefrontal cortex, innervate the zone subjacent to the area postrema. We suggest that direct projections to the NTS and dorsal motor nucleus of the vagus are one criterion that can be used to define the visceral fore‐brain. The organization of the forebrain terminations in the solitary complex described here may eventually allow a better understanding of how the brain controls visceral function.
Journal of Comparative Neurology - Tập 224 Số 1 - Trang 1-24 - 1984
Anatomy of hierarchy: Feedforward and feedback pathways in macaque visual cortex ABSTRACT The laminar location of the cell bodies and terminals of interareal connections determines the hierarchical structural organization of the cortex and has been intensively studied. However, we still have only a rudimentary understanding of the connectional principles of feedforward (FF) and feedback (FB) pathways. Quantitative analysis of retrograde tracers was used to extend the notion that the laminar distribution of neurons interconnecting visual areas provides an index of hierarchical distance (percentage of supragranular labeled neurons [SLN]). We show that: 1) SLN values constrain models of cortical hierarchy, revealing previously unsuspected areal relations; 2) SLN reflects the operation of a combinatorial distance rule acting differentially on sets of connections between areas; 3) Supragranular layers contain highly segregated bottom‐up and top‐down streams, both of which exhibit point‐to‐point connectivity. This contrasts with the infragranular layers, which contain diffuse bottom‐up and top‐down streams; 4) Cell filling of the parent neurons of FF and FB pathways provides further evidence of compartmentalization; 5) FF pathways have higher weights, cross fewer hierarchical levels, and are less numerous than FB pathways. Taken together, the present results suggest that cortical hierarchies are built from supra‐ and infragranular counterstreams. This compartmentalized dual counterstream organization allows point‐to‐point connectivity in both bottom‐up and top‐down directions. J. Comp. Neurol. 522:225–259, 2014. © 2013 Wiley Periodicals, Inc.
Journal of Comparative Neurology - Tập 522 Số 1 - Trang 225-259 - 2014
The nerve ring of the nematode <i>Caenorhabditis elegans</i>: Sensory input and motor output Abstract The general organization and structure of the nerve ring, the main mass of central nervous system neuropil, in the small soil nematode Caenorhabditis elegans is described. The nerve ring receives sensory input from the anterior tip of the animal by means of six nerve bundles, all nerve fibers of which have centrally located cell bodies. The anterior sensory structures are classically divided into two types, papillary and amphidial, and are assumed responsible for mechano‐ and chemoreception, respectively. Papillary fibers enter directly into the nerve ring, whereas amphidial fibers enter the ventral ganglion, a posterior extension of the nerve ring, in a circuitous manner which is not discussed in detail. Of those papillary fibers which project into the nerve ring neuropil, 22 end in easily characterized sensory structures whereas 14 terminate distally near sensory organs but have no function which can be deduced on the basis of comparative morphology. After entering the ring the fibers maintain their identity and do not anastamose with one another. Cell bodies of each papillary sensory neuron have been mapped around the nerve ring. The cephalic musculature is shown to consist of 32 muscle cells which form four longitudinal submedial groups of eight muscles each. Innervation of this musculature occurs wholly within the CNS by means of processes of the muscle cells which are sent centrally. The anterior 16 cephalic muscle cells are innervated by the ring only, in well delimited regions termed muscle plates. The posterior 16 are dually innervated by means of processes sent both to the nerve ring plates and to their nearest medial longtitudinal nerve cord. The nerve ring neuropil is characterized as having fibers containing one of four morphologically distinct vesicle types. Gap junction contacts are observed within the main neuropil involving one of these fiber types and within the muscle plate regions among muscle processes, which do not contain vesicles. An evolutionarily primitive sensory‐motor synapse within the nerve ring is described from an identified sensory neuron onto an identified cephalic muscle cell process. Comparisons are made with the nervous system of Ascaris lumbricoides , the only other nematode to be extensively studied, to illustrate the conservativeness of the nemic nervous system.
Journal of Comparative Neurology - Tập 162 Số 1 - Trang 71-110 - 1975
Electron microscopical reconstruction of the anterior sensory anatomy of the nematode <i>caenorhabditis elegans</i> Abstract The complete structure of the anterior sensory nervous system of the small nematode C. elegans has been determined by reconstruction from serial section electronmicrographs. There are 58 neurons in the tip of the head. Fifty‐two of these are arranged in sensilla. These include six inner labial sensilla, six outer labial sensilla, four cephalic sensilla and two amphids. Each sensillum consists of ciliated sensory neurons ending in a channel enclosed by two nonneuronal cells, the sheath and socket cells. The amphidial channel opens to the outside as does that of the inner labial sensilla so that these probably contain chemoreceptive neurons. The endings of the other sensilla are embedded in the cuticle and may be mechanoreceptive. The cell bodies of all the neurons lie near the nerve ring and their axons project into the ring or into ventral ganglia. One of the ciliated sensory neurons in each of the six inner labial sensilla makes direct chemical synapses onto a muscle making these sensory‐motor neurons. The anatomy of four isogenic animals was compared in detail and found to be largely invariant. The anatomy of juveniles is nearly identical to that of the adult, but males have four additional neuron processes.
Journal of Comparative Neurology - Tập 160 Số 3 - Trang 313-337 - 1975
The central projection of masticatory afferent fibers to the trigeminal sensory nuclear complex and upper cervical spinal cord Abstract Retrograde and anterograde transport of horseradish peroxidase‐wheat germ agglutinin (HRP‐WGA) conjugate was used to study the organization of primary afferent neurons innervating the masticatory muscles. HRP applied to the nerves of jaw‐closing muscles–the deep temporal (DT), masseter (Ma), and medial pterygoid (MP)–labeled cells in the trigeminal ganglion and the mesencephalic trigeminal nucleus (Vmes), whereas HRP applied to nerves of the jaw‐opening muscles–anterior digastric (AD) and mylohyoid (My)–labeled cells only in the trigeminal ganglion. Cell bodies innervating the jaw‐closing muscles were found with greater frequency in the intermediate region of the mandibular subdivision, while somata supplying the jaw‐opening muscles were predominant posterolaterally. The distribution of their somatic sizes was unimodal and limited to a subpopulation of smaller cells. Projections of the muscle afferents of ganglionic origin to the trigeminal sensory nuclear complex (TSNC) were confined primarily to the caudal half of pars interpolaris (Vi), and the medullary and upper cervical dorsal horns. In the Vi, Ma, MP, AD, and My nerves terminated in the lateral‐most part of the nucleus with an extensive overlap in projections, save for the DT nerve, which projected to the interstitial nucleus or paratrigeminal nucleus. In the medullary and upper cervical dorsal horns, the main terminal fields of individual branches were confined to laminae I/V, but the density of the terminals in lamina V was very sparse. The rostrocaudal extent of the terminal field in lamina I differed among the muscle afferents of origin, whereas in the mediolateral or dorsoventral axis, a remarkable overlap in projections was noted between or among muscle afferents. The terminals of DT afferents were most broadly extended from the rostral level of the pars caudalis to the C3 segment, whereas the MP nerve showed limited projection to the middle one‐third of the pars caudalis. Terminal fields of the Ma, AD, and My nerves appeared in the caudal two‐thirds of the pars caudalis including the first two cervical segments, the caudal half of the pars caudalis and the C1 segment, and in the caudal part of the pars caudalis including the rostral C1 segment, respectively. This rostrocaudal arrangement in the projections of muscle nerves, which corresponds to the anteroposterior length of the muscles and their positions, indicates that representation of the masticatory muscles in lamina I reflects an onion‐skin organization. These results suggest that primary muscle afferent neurons of ganglionic origin primarily mediate muscle pain. In addition, the distribution patterns of the afferent neurons of jaw‐closing muscles in the mesencephalic trigeminal nucleus (Vmes) and their central projections were examined. The Vmes neurons from the DT and Ma nerves were bimo‐dally distributed, with larger numbers in the rostra1 half of the nucleus, whereas those from the MP nerve were sparsely and evenly distributed. Individual central axons of the Vmes neurons innervating the three jaw‐closing muscles projected to the trigeminal motor nucleus (Vmo), supra‐ and intertrigeminal regions, and lateral reticular formation of the medulla extending to the upper spinal cord. There were, however, differences in the caudal extent of the axons from the different muscles.
Journal of Comparative Neurology - Tập 268 Số 4 - Trang 489-507 - 1988
Intrinsic and commissural connections of the rat inferior colliculus Abstract This study analyzes the distribution of the intrinsic and commissural fiber plexuses originating in the central nucleus of the inferior colliculus in the rat. The anterograde tracer Phaseolus vulgaris ‐leucoagglutinin (PHA‐L) was injected iontophoretically at different places along the tonotopic axis of the central nucleus and visualized immunohistochemically. In coronal sections the terminal fields of axons originating at each injection site are seen to create four well‐defined bands across the rostrocaudal extent of the inferior colliculus, two in the ipsilateral and two in the contralateral side. The “ipsilateral main band” extends dorsomedially and ventrolaterally from the injection site, in register with the known isofrequency contours of the central nucleus, spanning this nucleus and extending into the dorsal cortex of the inferior colliculus. The “ipsilateral external band” is located in the external cortex, where it is oriented dorsoventrally, slightly oblique to the pial surface. In caudal sections, the ventral portion of these two bands appear to join. The two bands in the contralateral inferior colliculus occupy a symmetric position to those of the ipsilateral side, forming a mirror‐like image. The position of the four bands changes as the position of the injection site is varied along the frequency gradient axis of the central nucleus. After ventromedial (high frequency area) injections, the main band is ventral and medial, and the external band ventral and lateral. After more dorsolateral (lower frequency) injections, the main band is more dorsal and lateral, whereas the external band is more dorsal but more medial. Thus, the change in the position of the external band is separate and opposite to that of the main band. We suggest that the main bands represent isofrequency contours. Since the projection from the central nucleus to the external cortex of the inferior colliculus also appears to be tonotopic, we also propose a tonotopic organization for the external cortex. The main bands overlap the terminal field of the lemniscal fibers in the central nucleus; thus, it is concluded that the intracollicular fibers contribute to the formation of the known fibrodendritic laminae of the central nucleus. A possible role in preservation of frequency information and integration of other different acoustic parameters is proposed for the main bands. The external bands could participate in polysensory integration, and the commissural connections could be involved in hitherto unknown stages of binaural processing of sound. Based on our results, several modifications are proposed for delineating the subdivisions of the inferior colliculus. © 1992 Wiley‐Liss, Inc.
Journal of Comparative Neurology - Tập 319 Số 3 - Trang 417-437 - 1992
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