Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Projection”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,441 records · Page 80Linked to original sources
PubMed1986

Functional organization of thalamic projections to the motor cortex. An anatomical and electrophysiological study in the rat.

In rats, horseradish peroxidase crystals were injected in motor cortical foci functionally identified by means of the motor effects evoked by electrical stimulations. The location in the thalamus of the neurons linked to different motor cortical foci was studied. Thalamic neurons were retrogradely labeled in both "motor" (ventralis lateralis and ventralis medialis) and "non-motor" nuclei: centralis lateralis, lateralis posterior, mediodorsalis and posterior thalamic nuclear group, as well as the ventrobasal complex. The ventrobasal complex was labeled after horseradish peroxidase injections in hindlimb and trunk motor areas. The ascending projections toward the motor cortex from both "motor" and "non-motor" thalamic nuclei are organized more precisely and more elaborately than previously reported. The motor cortical afferents from the nucleus ventralis lateralis are organized in three planes, rostrocaudally, dorsoventrally and mediolaterally. An inverted relation exists in the rostrocaudal plane between the nucleus ventralis lateralis and the motor cortex: the caudal motor cortex region (hindlimb) receives fiber inputs from the rostral region of the nucleus ventralis lateralis, whereas the caudal zone of the nucleus ventralis lateralis projects to the rostral motor cortex region (forelimb and vibrissae). A dorsoventral organization has also been observed in the rostral region of the nucleus ventralis lateralis: the ventral aspect is the source of fibers directed to the distal hindlimb region, whereas fibers originating from the dorsal aspect are directed to the proximal hindlimb area. A mediolateral relationship exists between medial and lateral sides of the nucleus ventralis lateralis and, respectively, proximal and distal forelimb cortical areas. There is some overlap between the various nuclear regions thus delineated. Four functional zones were found in the lateral half of the nucleus ventralis medialis and were classified according to their projection to the motor cortex; these are involved in motor control of the proximal and distal forelimb, vibrissae and ocular movements. The projection is topographically organized according to both an inverted rostrocaudal and a direct dorsoventral-mediolateral arrangement. Caudally, dorsal and ventral nuclear parts project to rostromedial (vibrissae) and rostrolateral (distal forelimb) regions of the motor cortex, respectively. More rostral nuclear zones project to more caudal (proximal forelimb, eye) cortical regions. There is little overlap between these four nuclear subdivisions. The nucleus centralis lateralis projects to vibrissae and proximal, as well as distal, forelimb areas.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Origin and trajectory of the cerebello-olivary projection: an experimental study with radioactive and fluorescent tracers in the cat.

It was demonstrated with autoradiographic methods that a tract of thin fibers, which is for the most part distinct from the brachium conjunctivum and its crossed descending limb, can be followed from the cerebellar nuclei to the inferior olive. Neurons from all regions of the interposed and dentate nuclei contribute to this tract. With two fluorescent tracers, Fast Blue and Diamidino Yellow Dihydrochloride, the perikarya of neurons in the cerebellar nuclei that project to the inferior olive or thalamus were identified and the possibility of collateral projections from single neurons to both regions was investigated. Numerous retrogradely labeled neurons were seen in the contralateral interposed and dentate nuclei but no double-labeled cells were ever encountered. The mean diameters of the cells projecting to the inferior olive were between 15 and 20 microns while the mean diameters for those projecting to the nucleus ventrolateralis of thalamus were between 25 and 35 microns. Differences in the morphology of the two cell populations were noted. It was also found that the fastigio-olivary projection is small, terminating mainly contralaterally, in the caudal medial accessory olive and subnucleus beta. It is concluded that cerebello-olivary fibers are not collaterals of the cerebellothalamic projection and that there are two different populations of neurons in the cerebellar nuclei that give rise to these distinct efferent projections.

Amidines↗
PubMed1987

Brainstem projections to spinal motoneurons: an update.

1. The existence of direct projections to spinal motoneurons and interneurons from the raphe pallidus and obscurus, the adjoining ventral medial reticular formation and the locus coeruleus and subcoeruleus is now well substantiated by various anatomical techniques. 2. The spinal projections from the raphe nuclei and the adjoining medial reticular formation contain serotonergic and non-serotonergic fibres. These projections also contain various peptides, several of which are contained within the serotonergic fibres. Whether still other transmitter substances (e.g. acetylcholine) are present in the various descending brainstem projections to motoneurons remains to be determined. 3. The spinal projections from the locus coeruleus and subcoeruleus are mainly noradrenergic, but there also exists a non-noradrenergic spinal projection. 4. Pharmacological, physiological and behavioural studies indicate an overall facilitatory action of noradrenaline and serotonin (including several peptides) on motoneurons. This may lead to an enhanced susceptibility for excitatory inputs from other sources. 5. The brainstem areas in question receive an important projection from several components of the limbic system. This suggests that the emotional brain can exert a powerful influence on all regions of the spinal cord and may thus control both its sensory input and motor output.

Animals↗
PubMed1987

Organization of the projections from the subiculum to the ventral striatum in the rat. A study using anterograde transport of Phaseolus vulgaris leucoagglutinin.

The projections of the subiculum, as the main output structure of the hippocampal formation, to the striatum were studied in the rat using the anterograde tracer Phaseolus vulgaris leucoagglutinin. It appears that not only the entire nucleus accumbens, part of the so-called ventral striatum, receives fibres from the subiculum, but that the hippocampal projection area in the striatum includes also the most medial, ventral, rostral and caudal parts of the caudate-putamen complex. Moreover, a relatively small number of fibres and terminals are present in the striatal elements of the medial part of the olfactory tubercle. The projections to the ventral and caudal parts of the caudate-putamen are predominantly derived from the ventral subiculum, whereas the projections to the rostral part of the caudate-putamen are derived from the dorsal subiculum. Furthermore, with respect to the subiculum-accumbens pathway a topographical organization could be established. Thus, the ventral or temporal part of the subiculum projects predominantly to the caudomedial part of the nucleus accumbens, and to a lesser degree to its rostromedial portion, whereas progressively more dorsal or septal parts of the subiculum send fibres to successively more lateral and rostral portions of the nucleus accumbens. Very sparse projections are found to the contralateral nucleus accumbens, arranged in a topographical manner similar to the ipsilateral projections. An important observation with respect to the structure of the nucleus accumbens is that the subicular terminations are inhomogeneously distributed, although a relation with earlier described mosaic patterns in the connectivity and neurochemical composition of the nucleus is not yet clear. Subicular fibres have their densest terminations in relatively cell-poor regions of the nucleus accumbens, and in particular tend to avoid small cell clusters.

Animals↗
PubMed1988

Bulbospinal thyrotropin-releasing hormone projections to the intermediolateral cell column: a double fluorescence immunohistochemical-retrograde tracing study in the rat.

Whereas the neurochemistry of the peripheral autonomic nervous system has been well characterized, less is known concerning the neurotransmitters utilized by medullary projections onto sympathetic preganglionic neurons residing in the thoracolumbar spinal intermediolateral cell column. Retrograde transport of rhodamine-labeled fluorescent microspheres following discrete microinjection into the thoracic intermediolateral cell column was combined with immunohistochemistry to determine neuroanatomic location of thyrotropin-releasing hormone-immunoreactive neurons which project to the intermediolateral cell column in the rat. The ventromedial group of raphe nuclei including the nucleus raphe pallidus, obscurus, and magnus possessed the greatest number of medullary thyrotropin-releasing hormone-immunoreactive neurons which also contained rhodamine-labeled microspheres. High numbers of intermediolateral cell column-projecting thyrotropin-releasing hormone-immunoreactive neurons were also observed in nucleus reticularis paragigantocellularis lateralis and magnocellularis, the lateral reticular nucleus, and the superficial ventral (arcuate) medullary surface. Despite the observations that nucleus reticularis gigantocellularis, paramedianus, and ventralis pars beta project to the intermediolateral cell column, double-labeled cells were not observed in these nuclei. Furthermore, whereas the nucleus reticularis magnocellularis and gigantocellularis, and the lateral reticular nucleus displayed strong ipsilateral predominance in projecting to the intermediolateral cell column, other medullary reticular and raphe nuclei displayed bilateral projections. The present findings support the hypothesis that thyrotropin-releasing hormone-containing neurons in the ventral medulla project to the intermediolateral cell column, and may influence sympathetic preganglionic neurons.

Animals↗
PubMed1989

The organization of dorsal medullary projections to the central amygdaloid nucleus and parabrachial nuclei in the rabbit.

The amygdaloid central nucleus and the pontine parabrachial nucleus receive direct, ascending projections from autonomic regulatory nuclei of the dorsal medulla and are recognized as important components of a forebrain system which contributes to autonomic regulation. The present study was designed to provide more detailed information on the anatomical organization of this ascending system in the rabbit by determining (a) the extent to which separate populations of neurons within the solitary complex project to the central nucleus and parabrachial nucleus, (b) the topographical distribution of the projections of the solitary complex within the amygdaloid central nucleus and parabrachial nucleus and (c) the extent to which projections from the solitary complex to the parabrachial nucleus terminate in the region of origin of projections from the parabrachial nucleus to the amygdaloid central nucleus. A fluorescent dye, double retrograde-labeling technique demonstrated that separate populations of neurons in the solitary complex projected to the amygdaloid central nucleus and parabrachial nucleus. Neurons of both populations were more heavily concentrated within the caudal two thirds of nucleus of the solitary tract and were most numerous within the commissural, medial and dorsomedial subnuclei. Labeled neurons were also located within the dorsal motor nucleus of the vagus nerve. Autoradiographic experiments demonstrated that injections of amino acids into the solitary complex resulted in terminal labeling in the central nucleus. This labeling extended rostrally into the adjacent sublenticular substantia innominata and lateral component of the bed nucleus of the stria terminalis. Label was also observed within the lateral, medial, and Kolliker-Fuse regions of the parabrachial nucleus. A particularly dense field was observed overlying cells located within the ventrolateral region of the lateral parabrachial nucleus. This region contained the majority of labeled neurons within the parabrachial nucleus following fluorescent dye injections into the central nucleus. Furthermore, injections of amino acids into this region resulted in terminal labeling within the central nucleus, with a particularly dense area observed within the medial aspect of the nucleus. The results demonstrate that separate populations of neurons within the solitary complex of the rabbit project to the central amygdaloid and parabrachial nuclei and that the majority of these are located within the caudal two-thirds of the complex.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1990

Single cholinergic mesopontine tegmental neurons project to both the pontine reticular formation and the thalamus in the rat.

Microinjections of the cholinergic agonist carbachol into a caudal part of the pontine reticular formation of the rat induce a rapid eye movement sleep-like state. This carbachol-sensitive region of the pontine reticular formation is innervated by cholinergic neurons in the pedunculopontine and laterodorsol tegmental nuclei. The same population of cholinergic neurons also project heavily to the thalamus, where there is good evidence that acetylcholine facilitates sensory transmission and blocks rhythmic thalamocortical activity. The present study was undertaken to examine the degree to which single cholinergic neurons in the mesopontine tegmentum project to both the carbachol-sensitive region of the pontine reticular formation and the thalamus, by combining double fluorescent retrograde tracing and immunofluorescence with a monoclonal antibody to choline acetyltransferase in the rat. The results indicated that a subpopulation (5-21% ipsilaterally) of cholinergic neurons in the mesopontine tegmentum projects to both the thalamus and the carbachol-sensitive site of the pontine reticular formation, and these neurons represented the majority (45-88%) of cholinergic neurons projecting to the pontine reticular formation site. The percentage of cholinergic neurons with dual projections was higher in the pedunculopontine tegmental nucleus (6-27%) than in the laterodorsal tegmental nucleus (4-11%). In addition, mixed with cholinergic neurons in the mesopontine tegmentum, there was a small population of dually projecting neurons that did not appear to be cholinergic. Mesopontine cholinergic neurons with dual projections may simultaneously modulate neuronal activity in the pontine reticular formation and the thalamus, and thereby have the potential of concurrently regulating different aspects of rapid eye movement sleep.

Animals↗
PubMed1990

Origin of serotonin-containing projections to the ventral respiratory group in the rat.

The major purpose of the present study was to determine the origin of the serotonin-containing neurons which project to the rostral ventral respiratory group in the rat. This was accomplished by using the technique of retrograde tracing with rhodamine-labeled latex microspheres (beads) combined with immunochemistry. The rhodamine-labeled beads were microinjected into electrophysiologically identified groups of inspiratory neurons in the rostral ventral respiratory group to retrogradely label neurons projecting to this site. Immunohistochemical processing of the tissue was then done to determine if serotonin was present in the retrogradely-labeled neurons. Serotonin-containing neurons projecting to the rostral ventral respiratory group were found in the raphe magnus, raphe obscurus, raphe pallidus and in the paraolivary region extending to the ventral medullary surface. No serotonin-containing neurons in more rostrally located raphe nuclei were found to project to the rostral ventral respiratory group. The findings suggest that caudal raphe serotonergic projections may affect the activity of respiratory neurons in the rostral ventral respiratory group. Projections to the rostral ventral respiratory group from other pontomedullary nuclei were also identified. Rhodamine-labeled neurons were found in the area of the Kölliker-Fuse nucleus, lateral and medial parabrachial nuclei, retrofacial nucleus, nucleus ambiguus/retroambigualis, nucleus tractus solitarius, A5 region, nucleus paragigantocellularis lateralis, retrotrapezoid nucleus, area postrema and spinal trigeminal nucleus. The projections to the rostral ventral respiratory group in the rat are similar to those previously described in the cat and suggest a common circuitry for the CNS control of breathing.

Animals↗
PubMed1991

A comparison of the distribution and morphology of thalamic, cerebellar and spinal projection neurons in rat trigeminal nucleus interpolaris.

The retrograde transport of horseradish peroxidase was used to examine and compare the distribution and morphology of thalamic, cerebellar and spinal projecting neurons in rat trigeminal nucleus interpolaris following large injections into their respective targets. The regional distribution of these three populations was evaluated in relation to the six cytoarchitecturally distinct regions which characterize the nucleus. Cerebellar projecting neurons were distributed throughout the rostrocaudal extent of trigeminal nucleus interpolaris, but were infrequently present in its dorsolateral region and in the rostral pole of the nucleus. Thalamic projecting neurons exhibited a distribution pattern that extensively overlapped with that of the trigeminocerebellar neurons: however, they were particularly concentrated in caudal, dorsomedial and rostral, ventrolateral regions of the nucleus. Trigeminospinal projecting neurons exhibited a more restricted distribution within ventral and lateral regions of trigeminal nucleus interpolaris. Although the three populations of projection neurons could not be distinguished solely on the basis of somatic size or shape, distinct regional variations in the distribution and somatodendritic and axonal morphology of these neurons indicated that they arise largely from independent cell populations. However, several regions were identified in which specific cell types were likely to contribute to axonal collaterilization among these pathways. In the ventrolateral magnocellular region of the nucleus, for example, more than half of the large multipolar-shaped neurons were retrogradely labeled after injections into each of the three target sites. The results of the present study indicate that the thalamic, cerebellar and spinal projections of trigeminal nucleus interpolaris arise from a morphologically heterogeneous group of neurons. In addition, regional variations in the distribution and morphology of these neurons provide evidence for the existence of functionally distinct regions that parallel the cytoarchitecturally defined regions of the nucleus. This study also provides indirect evidence for and against collateralization among these three projections within specific regions of the nucleus.

Animals↗
PubMed1991

Topographical organization of the tecto-olivo-cerebellar projection in the cat.

The superior colliculus sends a climbing fiber output to cerebellar vermal lobules VI-VII through the inferior olive. The present study in cats morphologically clarified the existence of a topographical organization in the tecto-olivo-cerebellar projection. A horseradish peroxidase study on the tecto-olivary projection showed that the rostral and caudal superior colliculus projected mostly contralaterally to the caudal and rostral areas of the caudomedial part of the medial accessory olive, respectively. The lateral superior colliculus was found to project more laterally than was the medial superior colliculus. Investigation on the olivocerebellar projection demonstrated that the rostral and caudal areas of the caudomedial part of the medial accessory olive sent climbing fiber terminals contralaterally to the lateral and medial parts of vermal lobules VI-VII, respectively. Thus, it was revealed that the rostral superior colliculus projected mostly to the medial part of ipsilateral vermal lobules VI-VII while the caudal superior colliculus projected mostly to the lateral part of ipsilateral vermal lobules VI-VII.

Afferent Pathways↗
PubMed1992

Collateralized projections from neurons in the rostral medulla to the nucleus locus coeruleus, the nucleus of the solitary tract and the periaqueductal gray.

We have examined collateral projections of locus coeruleus afferent neurons in the rostral medulla to the caudal nucleus of the solitary tract or to the periaqueductal gray using double retrograde labeling techniques in the rat. The present findings confirm previously reported connections to the locus coeruleus, the nucleus of the solitary tract and the lateral periaqueductal gray from the nucleus paragigantocellularis in the rostral ventral medulla. Our results also reveal previously unreported projections from the rostral dorsomedial medulla (in a similar region as locus coeruleus-projecting neurons) to the lateral periaqueductal gray. Following retrograde tracer injections into the nucleus of the solitary tract and the locus coeruleus, doubly labeled neurons were seen in both the nucleus paragigantocellularis and in the rostral dorsomedial medulla. Cell counts revealed that approximately 25% of locus coeruleus-projecting neurons in the nucleus paragigantocellularis, and 12% in the dorsomedial medulla, also innervate the caudal nucleus of the solitary tract. In contrast, no doubly labeled neurons within the rostral ventral medulla were found following injections into the lateral periaqueductal gray and the locus coeruleus, although singly labeled neurons for the two tracers were interdigitated in some regions. Following these injections, numerous neurons were also retrogradely labeled in the dorsomedial medulla in the region of the medial prepositus hypoglossi and the perifascicular reticular formation. A small percentage of locus coeruleus afferents in the dorsal medulla (approximately 10%) also projected to the lateral periaqueductal gray. These results indicate that neurons in both the ventrolateral and dorsomedial rostral medulla frequently send collaterals to both the locus coeruleus and the caudal nucleus of the solitary tract. A small number of neurons in the dorsomedial medulla project to both the locus coeruleus and the lateral periaqueductal gray, but separate populations of neurons project to the locus coeruleus and the lateral periaqueductal gray from the ventrolateral medulla. These results functionally link the locus coeruleus and the nucleus of the solitary tract by virtue of common afferents, and support other studies indicating the importance of central autonomic circuitry in the afferent control of locus coeruleus neurons.

Animals↗
PubMed1992

Direct projections from the central amygdaloid nucleus to the globus pallidus and substantia nigra in the cat.

Employing both anterograde and retrograde axonal tracing, we investigated direct projections from the central amygdaloid nucleus to the basal ganglia in the cat. The anterograde axonal tracing of Phaseolus vulgaris-leucoagglutinin revealed that projection fibers from the central amygdaloid nucleus to the basal ganglia ended in the globus pallidus (the feline homolog to the external segment of the globus pallidus of primates) and substantia nigra. The amygdalopallidal fibers terminated chiefly in the medial most part of the globus pallidus at its caudal level. The amygdalonigral fibers terminated densely in the substantia nigra pars lateralis, and moderately in the dorsolateral part of the substantia nigra pars reticulata; none of them were found to end in the substantia nigra pars compacta. Both of the amygdalopallidal and amygdalonigral projections were ipsilateral. These neuronal connections were confirmed by retrograde axonal tracing of cholera toxin B subunit in the second set of the experiments: The cells of origin of the amygdalopallidal and amygdalonigral projections were located predominantly in the lateral part of the central amygdaloid nucleus, and additionally in the intercalated cell islands of the amygdala. Most of them were of small bipolar or multipolar type. The cells projecting to the globus pallidus were preferentially distributed at the rostral levels of the central nucleus and intercalated cell islands of the amygdaloid complex, while those projecting to the substantia nigra were mainly located at the caudal levels of these amygdaloid subdivisions. In the third set of the experiments, sequential double-antigen immunofluorescence histochemistry for transported cholera toxin B subunit and horseradish peroxidase showed that some single neurons in the lateral part of the central amygdaloid nucleus, particularly at its middle level, issued axon collaterals to both the globus pallidus and substantia nigra pars lateralis. The results of the present study indicate that the central amygdaloid nucleus sends projection fibers to the globus pallidus and substantia nigra possibly to exert a limbic influence upon forebrain motor mechanisms.

Amygdala↗
PubMed1993

Lower thoracic upper lumbar spinocerebellar projections in rats: a complex topography revealed in computer reconstructions of the unfolded anterior lobe.

The topography of wheatgerm agglutinin-horseradish peroxidase/horseradish peroxidase-labeled mossy fiber terminals of lower thoracic-upper lumbar (T12-L3) spinal projections to the cerebellar anterior lobe was quantitatively analysed in adult rats. Computer-based image analysis mapped the orthogonal (parallel to the surface) distribution of labeled terminals in two-dimensional reconstructions of the unfoled anterior lobe cortex. The radial (perpendicular to the surface) distribution of terminals within the granule cell layer was mapped by computing whether the terminals were in either the outer- or inner-halves of this layer. The number of labeled terminals in each lobule was calculated. In the anterior lobe, lower thoracic-upper lumbar spinocerebellar projections terminate primarily in lobules II (mean 27.14%), III (mean 38.68%), and IV (mean 19.31%). Different-sized bilateral injections restricted to L1 were used to study the organization of intrasegmental spinocerebellar projections. Small injections into L1 labeled a limited number of terminals which were located either in clusters or were spatially isolated. Intermediate-sized intrasegmental injections resulted in additional clusters of labeled terminals. Many of the terminal clusters were spatially related and formed larger irregularly shaped patches. Large intrasegmental injections labeled terminal clusters and patches that were discontinuous but aligned parallel to the longitudinal (transverse) axis of lobules II-IV. Injections including segments rostral and caudal to L1 were used to study the topography of intersegmental lower thoracic-upper lumbar spinocerebellar projections. Multisegmental injections increased the number of labeled terminal clusters and patches which obscured the pattern of segmental input, but there was still a transversely oriented pattern of termination. Distinct transversely aligned terminal free areas remained apparent. Lower thoracic-upper lumbar spinocerebellar projections terminated in both the outer- and inner-halves of the granule cell layer, but overall were more numerous in the outer-half of this layer. In serially spaced sagittal sections, however, the majority of terminals alternated between the outer- and inner-halves of the granule cell layer. Outer- and inner-terminals were not spatially segregated in their orthogonal distribution. These results indicate lower thoracic-upper lumbar spinocerebellar projections have a complex three-dimensional topography in the anterior lobe. These findings are discussed in relation to previous findings for a sagittally oriented topography for lower thoracic-upper lumbar spinocerebellar projections and in the context of how cerebellar somatosensory afferent input may be organized.

Animals↗
PubMed1995

Distribution and morphological characterization of viscerofugal projections from the large intestine to the inferior mesenteric and pelvic ganglia of the male rat.

Viscerofugal neurons are enteric neurons in the myenteric plexus of the stomach and intestine that project to the prevertebral ganglia as the afferent limb of intestino-intestinal reflexes. This study characterizes viscerofugal projections to the inferior mesenteric ganglion and investigates the possibility of similar projections to the major pelvic ganglia in the male rat. The colon and rectum were examined for retrogradely labelled neurons following the injection of retrograde tracer into the inferior mesenteric or major pelvic ganglia, or following the application of tracer to the caudal end of the cut intermesenteric nerves, or either end of the cut hypogastric nerves. All labelled viscerofugal neurons were found in the myenteric plexus and were often grouped near the mesenteric attachment. The number of viscerofugal neurons projecting to the inferior mesenteric ganglion via the lumbar colonic nerves increases along the length of the large intestine with the maximum number of viscerofugal neurons found in the rectum. Some viscerofugal neurons from the distal colon and rectum reach the inferior mesenteric ganglion via the hypogastric nerves. A similar number and distribution of viscerofugal neurons project via the inferior mesenteric ganglion into the intermesenteric nerves as terminate in the inferior mesenteric ganglion. Very few viscerofugal neurons project to the neurons of the major pelvic ganglia via the rectal nerves, and no viscerofugal neurons project caudally in the hypogastric nerves to these ganglia. The majority of labelled neurons resembled Dogiel type I morphology. Thus the inferior mesenteric ganglion receives a substantial innervation from viscerofugal neurons of the large intestine, with the greatest supply from the distal colon and rectum.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

The organization of midbrain projections to the ventral striatum in the primate.

Because the dopaminergic neurons of the midbrain form a continuum, boundaries between the ventral tegmental area, substantia nigra pars compacta, and retrorubral area are difficult to distinguish in the primate. Therefore, dopaminergic neurons have been subdivided into more readily discernible dorsal and ventral tiers. The projections from these dorsal and ventral tier neurons of the ventral mesencephalon to the ventral striatum were labeled by injections of horseradish peroxidase conjugated to wheatgerm agglutinin and Lucifer Yellow conjugated to dextran amines into different regions of the nucleus accumbens, the ventral caudate nucleus, and the rostral, ventral putamen in the primate. Neurons projecting to the ventral striatum are not topographically organized in the ventral mesencephalon. Retrogradely labeled neurons are found in the medial densocellular zone of the ventral tier following injections into all regions of the ventral striatum except the ventromedial shell region of the nucleus accumbens. These medial nigral neurons have diverging projections throughout the mediolateral extent of the ventral striatum. In addition, neurons of the dorsal tier project to all ventral striatal regions examined. Notably, neurons projecting to the shell region of the nucleus accumbens are limited to the dorsal tier, throughout the rostrocaudal extent of the substantia nigra. Both dorsal and ventral tier neurons innervate the ventral striatum. Not only do neurons of the ventral tegmental area project to the ventral striatum, but also many of the pars compacta. The projections to the shell region of the nucleus accumbens are more restricted, suggesting that the dopaminergic regulation of this accumbens subterritory is distinct from the rest of the ventral striatum.

Amygdala↗
PubMed1995

Intra-amygdaloid projections of the basolateral and basomedial nuclei in the cat: Phaseolus vulgaris-leucoagglutinin anterograde tracing at the light and electron microscopic level.

The amygdaloid complex plays an essential role in auditory fear conditioning of the Pavlovian type. The available evidence suggests that the lateral nucleus is the input station of the amygdala for auditory conditioned stimuli, whereas the central medial nucleus is the output for conditioned fear responses. However, the intrinsic pathway transmitting auditory information about the conditioned stimulus from the lateral to the central medial nuclei is unknown as there are no direct projections between these nuclei. The present study was undertaken to determine if the main intra-amygdaloid targets of the lateral nucleus, namely the basomedial and basolateral nuclei, project to the central medial nucleus. To this end, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were performed in these nuclei. To rule out the possibility that the anterograde labeling reflected passing fibers merging with the major fiber bundles that course in and around the central medial nucleus, labeled terminals and varicosities were observed in the electron microscope. It was determined that the basolateral and basomedial nuclei have partially overlapping intraamygdaloid targets. They both project to the central medial nucleus, nucleus of the lateral olfactory tract and peri-amygdaloid cortex, but have limited projections to each other. Small Phaseolus vulgaris-leucoagglutinin injections in both nuclei gave rise to prominent intranuclear projections but only the basomedial nucleus was found to project to the lateral and anterior cortical nuclei. At the electron microscopic level, all labeled axon terminals and varicosities formed asymmetric synapses (n = 245) with dendritic spines (83%) or with dendritic shafts (17%). This is the first unambiguous demonstration that the basolateral and basomedial nuclei project to the central medial nucleus. Since these nuclei constitute the main intra-amygdaloid targets of the lateral nucleus, they represent likely candidates for the transmission of auditory conditioned stimuli to the central medial nucleus in auditory fear conditioning.

Amygdala↗
PubMed1994

Topographical organization of subicular neurons projecting to subcortical regions.

Direct projections from the subiculum to the septum, thalamus, and hypothalamus were studied in the rat by the fluorescent retrograde double-labeling technique with Fast blue and Diamidino yellow. The results confirm and extend the previously reported findings. The dorsal subiculum projects primarily to the lateral septum, anterior and midline thalamus, and mammillary complex. The distribution areas of cell bodies of these projection neurons are substantially segregated, depending on their target region, and few single neurons project to two of the target regions by way of axon collaterals. The ventral subiculum projects mainly to the lateral septum, midline thalamus, and ventromedial hypothalamic area. The distribution areas of cell bodies of these projection neurons are considerably overlapped with one another, and a number of single neurons send axon collaterals to two of the lateral septum, midline thalamus, and ventromedial hypothalamic area. It is, thus, indicated that the populations of subicular neurons projecting to each of the subcortical structures examined are more distinctly segregated in the dorsal subiculum than in the ventral subiculum.

Amidines↗
PubMed1988

Layer V in rat auditory cortex: projections to the inferior colliculus and contralateral cortex.

This study compares the form and distribution within layer V of cells projecting to the inferior colliculus with that of commissural cells of origin in adult rat auditory cortex after horseradish peroxidase injections in the ipsilateral inferior colliculus or auditory cortex. The goal of this work was to determine whether every part of layer V participates equally in both projections, and if the cortical neurons in each pathway were similar. The types of neurons were defined in Golgi-Cox preparations and matched with the profiles of retrogradely labeled cells from architectonically defined cortical area 41. Inferior colliculus and commissural neurons form two populations that differ in their distribution in layer V, in somatic area, and in the form of their apical dendritic arbors. Corticocollicular neurons include the largest pyramidal cells, whose robustly filled apical dendrites ascend into layer II or farther. Commissural cells are smaller and have a more heterogeneous form. Their apical dendrites do not usually extend above layer IV, and a few of these cells may be non-pyramidal. Small pyramidal cells and inverted pyramidal cells project to the opposite cortex, but not to the inferior colliculus. Medium-sized pyramidal cells project in both systems. In addition, certain callosal cells of origin in layers V and III were morphologically similar. More than one-third of the commissural cells originate in the superficial part of layer V, where only 7% of the inferior colliculus projection neurons arise. Most corticocollicular cells lie deeper in layer V, where there are fewer commissural neurons. These findings suggest that the efferent systems projecting to telencephalic and mesencephalic targets are morphologically distinct and spatially segregated in layer V. However, the commissural projection includes similar cells in different cortical layers. The types of these efferent neurons may be more closely related to their target than to their laminar origin.

Animals↗