Topographical projections from the cerebral cortex to the nucleus of the solitary tract in the cat

Summary The distribution of cerebral cortical neurons sending projection fibers to the nucleus of the solitary tract (NST), and the topographical distribution of axon terminals of cortico-NST fibers within the NST were examined in the cat by two sets of experiments with horseradish peroxidase (HRP) and HRP conjugated with wheat germ agglutinin (WGA-HRP). First, HRP was injected into the NST. In the cerebral cortex of these cats, neuronal cell bodies were labeled retrogradely in the deep pyramidal cell layer (layer V): After HRP injection centered on the rostral or middle part of the NST, HRP-labeled neuronal cell bodies were distributed mainly in the orbital gyrus and caudal part of the infralimbic cortex, and additionally in the rostral part of the anterior sylvian gyrus. After HRP injection centered on the caudal part of the NST, labeled neuronal cell bodies were seen mainly in the caudoventral part of the infralimbic cortex, and additionally in the orbital gyrus, posterior sigmoid gyrus and rostral part of the anterior sylvian gyrus. The labeling in the infralimbic cortex, orbital gyrus and anterior sylvian gyrus was bilateral with a predominantly ipsilateral distribution, while that in the posterior sigmoid gyrus was bilateral with a clear-cut contralateral dominance. In the second set of experiments, WGA-HRP was injected into the cerebral cortical regions where neuronal cell bodies had been retrogradely labeled with HRP injected into the NST: After WGA-HRP injection into the orbital gyrus, presumed axon terminals in the NST were labeled in the rostral two thirds of the nucleus bilaterally with an ipsilateral predominance. After WGA-HRP injection into the rostral part of the anterior sylvian gyrus, a moderate number of presumed axon terminals were labeled throughout the whole rostrocaudal extent of the NST bilaterally with a slight ipsilateral dominance. After WGA-HRP injection into the middle and caudal parts of the anterior sylvian gyrus, no labeling was found in the NST. After WGA-HRP injection into the caudal part of the infralimbic cortex, presumed terminal labeling in the NST was seen throughout the whole rostrocaudal extent of the nucleus bilaterally with a dominant ipsilateral distribution. After WGA-HRP injection into the posterior sigmoid gyrus, however, no terminal labeling was found in the NST. The results indicate that cortico-NST fibers from the orbital gyrus terminate in the rostral two thirds of the NST, while those from the infralimbic cortex and the rostral part of the anterior sylvian gyrus project to the whole rostrocaudal extent of the NST.     

Topographical organization of amygdaloid projections to the caudatoputamen, nucleus accumbens, and related striatal-like areas of the rat brain.

The topographical organization of amygdaloid projections to the caudatoputamen, nucleus accumbens, and lateral portions of the bed nucleus of the stria terminalis and central amygdaloid nucleus was investigated, in the rat, using the retrograde transport of wheat germ agglutinin-conjugated horseradish peroxidase. Although the caudatoputamen and nucleus accumbens are the principal components of the striatum, there is evidence that lateral portions of the bed nucleus of the stria terminalis and central amygdaloid nucleus may be striatal-like structures. The basolateral nucleus was the main source of amygdaloid fibers to all of these structures. In many instances labeled areas of the basolateral nucleus were continuous with labeled areas in the adjacent lateral and basomedial nuclei. Amygdaloid neurons projecting to the striatum and striatal-like areas exhibited an overlapping topographical organization. In general, the medial-to-lateral coordinate in the striatum corresponds to the medial-to-lateral coordinate in the basolateral nucleus. There was also a partial reversed sagittal topography in that the caudal caudatoputamen receives its principal projection from the rostral basolateral nucleus. However, the rostral basolateral nucleus had a stronger projection to the rostral caudatoputamen and lateral nucleus accumbens than the caudal basolateral nucleus. The principal striatal projection of the caudal basolateral nucleus was to the medial nucleus accumbens. Amygdaloid labeling produced by injections into the medial nucleus accumbens was very similar to that seen with injections into the lateral portions of the bed nucleus of the stria terminalis and central amygdaloid nucleus. The retrograde amygdaloid labeling seen in this investigation, when compared to labeling seen with cortical injections in previous studies, suggests that specific amygdaloid domains project to particular cortical areas as well as to the principal striatal targets of the same areas.     

Topographic organization of projections from the amygdala to the visual cortex in the macaque monkey

The topography of amygdaloid projections to the visual cortices in the macaque monkey was examined by injecting the fluorescent tracers Fast Blue and Diamidino Yellow at different locations in the occipital and temporal lobes and mapping the distribution of retrogradely labeled cells in the amygdala. Injections involving regions from rostral area TE to caudal area V1 all resulted in labeled cells within the basal nucleus of the amygdala. Relatively few double-labeled cells were observed even when the two injections were separated by less than 3 mm. The projections were rostrocaudally organized such that projections to caudal visual areas originated from dorsal and caudal portions of the magnocellular division of the basal nucleus while projections to more rostrally situated visual areas originated in more rostral and ventral portions of the basal nucleus. When injections involved rostral and medial portions of area TE, retrogradely labeled cells were observed in the accessory basal and lateral nuclei in addition to the basal nucleus. These data confirm that the amygdala gives rise to feedback projections to all levels of the "ventral stream" visual pathway. The projections do not appear to be diffusely distributed since few double-labeled cells were observed. The largest cells of the basal nucleus, those located in the magnocellular division, project the farthest in the visual system and innervate all occipital and temporal levels. The smaller cells, in the intermediate and parvicellular regions, project to more rostral and medial portions of the visual cortex. These results suggest that the amygdala may have substantial modulatory control over sensory processing at all stages of the ventral-stream visual cortical hierarchy.     

Topographic principles in the spinal projections of serotonergic and non-serotonergic brainstem neurons in the rat

The spinal projections from the raphe-associated brainstem areas containing serotonergic neurons were studied with aldehyde-induced fluorescence in combination with the retrograde fluorescent tracer True Blue in the rat. This technique makes it possible to determine simultaneously the projections of individual neurons and to detect whether serotonin is present in the same neurons. After tracer injections into the spinal cord retrogradely labeled serotonergic and non-serotonergic neurons were found in the medullary raphe nuclei and adjacent regions and to a lesser extent in association with the dorsal and median raphe nuclei in the mesencephalon. Large True Blue injections that covered one side of the spinal cord at mid-cervical level labeled about 60% of the ipsilaterally situated serotonergic neurons in the medullary raphe regions while the corresponding figure contralaterally was about 25%. On both sides a larger number of labeled non-serotonergic neurons were found; these were sometimes located dorsal to, but often intermingled with, the serotonergic cells. While the serotonergic projection from the mesencephalon could not be labeled from injections below cervical levels, the labeling in more caudal brainstem regions exhibited only minor variations depending on the rostrocaudal level of the spinal segment injected. Furthermore, quantitative data from injections at different levels indicate that the majority of the spinal-projecting neurons traverse most of the length of the cord. Summarizing the results obtained from small injections restricted to subregions of the cord we feel that it is possible to distinguish three fairly distinct pathways for spinal projections from the medullary raphe and adjacent regions: The dorsal pathway originates mainly from cells in the caudal pons and rostral medulla oblongata (rostral part of nucleus raphe magnus, nucleus raphe magnus proper, nucleus reticularis gigantocellularis pars alpha and nucleus paragigantocellularis). This pathway, which contains a large non-serotonergic component, descends through the dorsal part of the lateral funiculus and terminates mainly in the dorsal horn at all spinal cord levels. The intermediate pathway is largely serotonergic with its cell bodies located within the arcuate cell group (situated just ventral and lateral to the pyramids very close to the ventral surface of the brainstem) and in the nucleus raphe obscurus and pallidus and terminates in the intermediate grey at thoracolumbar and upper sacral levels.(ABSTRACT TRUNCATED AT 400 WORDS)     

DARPP-32在大鼠全脑的定位分布

目的 探讨DARPP-32在大鼠全脑的表达分布特点.方法 应用免疫组织化学染色技术对大鼠脑内DARPP-32的表达分布进行观察.结果 免疫组织化学染色结果显示,强阳性的DARPP-32染色大部分分布于基底节区和前嗅皮质区,主要分布在伏隔核、尾壳核及杏仁核复合体的神经元胞体内,以及苍白球、腹侧苍白球、脚间核及黑质网状部的...     

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)     

The cerebellar projection from the reticular formation of the brain stem in the rabbit

Summary By retrograde transport of horseradish peroxidase the reticulocerebellar projections were examined in twenty-six rabbits.After injections in the cerebellum retrogradely labeled neurons were more numerous in the caudal reticular formation (ventral and gigantocellular reticular nuclei) than in its rostral part (caudal and oral pontine reticular nuclei). The labeled cells were of all sizes, large, medium-sized and small. Giant cells were labeled only after injections in the posterior lobe vermis.After injections in the anterior lobe, the posterior vermis, the fastigial nucleus and the flocculus, retrogradely labeled neurons were found bilaterally in the ventral reticular nucleus, the gigantocellular reticular nucleus and the caudal pontine reticular nucleus. Some cases with posterior vermal and fastigial injections in addition showed labeled neurons bilaterally in the oral pontine reticular nucleus. There were no major side differences. The cases with injections in the anterior part of the paramedian lobule gave rise to only a few labeled cells in the gigantocellular reticular nucleus.Negative findings were consistently made in the mesencephalic reticular formation.     

Parvalbumin in respiratory neurons of the ventrolateral medulla of the adult rat

A column of parvalbumin immunoreactive neurons is closely associated with the location of respiratory neurons in the ventrolateral medulla of the rat. The majority (66%) of bulbospinal neurons in the medullary ventral respiratory column (VRC) that were retrogradely labeled by tracer injections in the phrenic nucleus were also positive for parvalbumin. In contrast, only 18.8% of VRC neurons retrogradely labeled after a tracer injection in the VRC, also expressed parvalbumin. The average cross-sectional area of VRC neurons retrogradely labeled after VRC injections was 193.8 m² ± 6.6 SE. These were significantly smaller than VRC parvalbumin neurons (271.9 m² ± 12.3 SE). Parvalbumin neurons were found in the Bötzinger Complex, the rostral ventral respiratory group (VRG), and the caudal VRG, areas which all contribute to the bulbospinal projection. In contrast, parvalbumin neurons were sparse or absent in the preBötzinger Complex and in the vicinity of the retrotrapezoid nucleus, areas that have few bulbospinal projections. Parvalbumin was rarely colocalized within Neurokinin-1 receptor positive (NK1R) VRC neurons, which are found in the preBötzinger complex and in the anteroventral part of the rostral VRG. Parvalbumin neurons in the Bötzinger Complex and rostral VRG help define the rostrocaudal extent of these regions. The absence of parvalbumin neurons from the intervening preBötzinger complex also helps establish the boundaries of this region. Regional boundaries described in this manner are in good agreement with earlier physiological and anatomical studies. Taken together, the distributions of parvalbumin, NK1R and bulbospinal neurons suggest that the rostral VRG may be subdivided into distinct, anterodorsal, anteroventral, and posterior subdivisions.     

大鼠中脑导水管周围灰质向三叉神经脊束核尾侧亚核的5-羟色胺能投射

大鼠中脑导水管周围灰质(PAG)向三又神经脊束核尾侧亚核(Sp 5 C)投射的起源细胞在其吻、中、尾三个部分的分布不同,且由尾段向吻段有从腹侧向背侧移行的趋势。尾段的HRP逆标细胞主要位于PAG的腹外侧区、内侧区腹侧部;中段的标记细胞较多,主要见于腹外侧区、背侧区和背外侧区腹侧部,尚可见一些顺行标记的终末;吻段的标记细胞主要位于背外侧区,在上丘深层、Cajal氏中介核、Darkschewitsch氏核内,也可见标记细胞。标记细胞和终末均主要位于注射侧的PAG内。PAG向Sp 5 C投射的5-羟色胺(5-HT)样神经元主要位于PAG的中、尾段的腹外侧区和内侧区腹侧部。中段的双标细胞占全部双标细胞数的57％,尾段占41％,吻段占2％。在背中缝核(DR)内,亦可见到一些双标细胞。PAG内的双标细胞占其HRP标记细胞总数的37％,但仅占5-HT样阳性细胞总数的4.5％。标记细胞主要为中型(20—30μm)梭形及三角形,小型(<20μm)梭形和大型(>30μm)多角形细胞较少见。     

An anterograde and retrograde tract-tracing study on the projections from the thalamic gustatory area in the rat: distribution of neurons projecting to the insular cortex and amygdaloid complex

Projections from the thalamic gustatory nucleus, i.e. the parvicellular part of the posteromedial ventral thalamic nucleus (VPMpc) to the forebrain regions were studied in the rat by the tract-tracing methods with anterograde tracer (biotinylated dextran amine, BDA) and anterograde/retrograde tracer (wheat-germ agglutinin-horseradish peroxidase, WGA-HRP). After BDA injection into the VPMpc, terminal labeling was observed in the insular cortex, amygdaloid complex, and fundus striati. The terminal labeling in the amygdaloid complex was distributed in dorsolateral area of the rostral part of the lateral amygdaloid nucleus and the rostral part of the lateral subdivision of the central amygdaloid nucleus. The terminal labeling in the central amygdaloid nucleus extended to the fundus striati. The retrograde tracing study with WGA-HRP revealed that the projection fibers from the VPMpc to the amygdaloid complex originated from the medial part of the VPMpc and also from the thalamic area medial to the VPMpc. In the rats injected with Fluoro-Gold and WGA-HRP, respectively into the insular cortex and amygdaloid complex, no double-labeled neuronal cell bodies were found in the VPMpc, although neurons labeled singly with Fluoro-Gold were intermingled with those singly labeled with WGA-HRP in the medial part of the VPMpc. The results indicated that VPMpc neurons projecting to the amygdaloid complex constituted a population different from VPMpc neurons projecting to the insular cortex.     

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.     

Morphometric and experimental studies of the red nucleus in the albino rat

Cytoarchitectural observations showed that the red nucleus of the albino rat consists of three distinct neuronal populations. Neurons with coarse Nissl bodies occupy the caudal end of the red nucleus and extend in diminishing number to the rostral tip. Neurons with finely granular Nissl material are the predominant cell type at the rostral tip of the red nucleus and interdigitate with the coarse neurons except at the caudal end of the nucleus. Coarse neurons, in contrast to fine neurons, are multiangular in contour and tend to be larger, although the two populations overlap in size. A population of interneurons, almost entirely smaller than the other cell types and less numerous, is ubiquitous within the red nucleus. Injections of horseradish peroxidase (HRP) at different levels of the spinal cord established that the coarse neurons on the contralateral side are the source of the rubrospinal tract and are topographically organized. The dorsal-medial part of the red nucleus emits axons which project to the cervical cord and the ventral-ventrolateral part of the nucleus to the lumbar cord. The thoracic cord receives projections from rubral neurons at intermediate positions. Further, coarse neurons from the entire rostrocaudal axis of the red nucleus contribute fibers to the rubrospinal tract.     

Noradrenergic neurons with divergent projections to the motor trigeminal nucleus and the spinal cord: a double retrograde neuronal labeling study

Double retrograde axonal tracing was combined with the indirect immunofluorescence antibody method to determine whether noradrenergic neurons have divergent projections to the motor nucleus of the trigeminal nerve and the spinal cord. Rhodamine-labeled microspheres were injected into the motor trigeminal nucleus and True Blue was deposited into lumbar segments of the spinal cord. After a 10-18-day survival period, brainstem sections were processed for immunofluorescence staining of noradrenergic neurons using antibodies to rat dopamine-beta-hydroxylase. Rhodamine-labeled noradrenergic neurons were observed ipsilaterally throughout the A5 and A7 groups; the contralateral A5 and A7 groups contained few rhodamine-labeled cells. A few rhodamine-labeled noradrenergic neurons were observed in the locus coeruleus and subcoeruleus. True Blue-labeled noradrenergic neurons were identified in the A5 and A7 groups, in the ventral part of the locus coeruleus and in the subcoeruleus. Double retrogradely labeled noradrenergic neurons were observed in the A5 and A7 groups but not in the locus coeruleus and subcoeruleus. Of the total number of rhodamine-labeled noradrenergic cells, a large percentage also contained True Blue: 54% in the caudal A5 group, 59% in the rostral A5 group, and 72% in the A7 group. Of the total number of True Blue-labeled noradrenergic neurons, the percentage of double retrogradely labeled cells was 33% in the caudal A5 group, 46% in the rostral A5 group, and 56% in the A7 group. The findings of this study provide the first anatomic evidence for the existence of a prominent population of noradrenergic cells in the A5 and A7 groups with divergent projections to the motor trigeminal nucleus and the spinal cord. We propose that this subpopulation of noradrenergic neurons in the A5 and A7 groups influences motoneurons at multiple levels of the neuraxis.     

Cortical projections from the suprasylvian gyrus to the reticular thalamic nucleus in the cat

The cat's suprasylvian gyrus was injected iontophoretically with either 4% wheat germ agglutinin-horseradish peroxidase, 4% dextran-fluororuby or 4% dextran-biotin. The locations of labelled fibres, presumed terminals and cell bodies were determined with the aid of a camera lucida attachment and computer aided stereometry. Cells from the crown of the suprasylvian gyrus project to the dorsal-most portion of the rostral half of the reticular nucleus. The region or 'sector' is distinct, albeit with some overlap, from the visual sector of the reticular nucleus defined by projections from adjacent extrastriate visual cortices. The projection from the suprasylvian gyrus to the reticular nucleus has a rough topography such that the caudal areas project to the more caudal aspects of the sector and rostral areas project to the more rostral areas of the reticular nucleus. There is a large degree of overlap of rostrocaudal projections from the suprasylvian gyrus within the sector, however, the projections originating from rostral sites are situated in a more ventral location compared to the projection originating from the caudal suprasylvian gyrus. Analysis of the distribution of biotin labelled presumptive terminals did not support the notion of 'slabs' or regional variation in terminal density across the mediolateral thickness of the reticular nucleus. In addition, a number of presumptive terminals were found within the internal capsule which coincided with the position of retrogradely labelled cells in the internal capsule following thalamic injections and appears to be part of the perireticular nucleus.The results suggest that the reticular nucleus may be segregated into sectors connected with modality specific cortical areas (e.g. striate and extrastriate visual areas) and nonspecific sectors connected with polymodal (e.g. area 7) cortical regions. The reticular nucleus and its connections with the suprasylvian gyrus may form an important link in binding eye movements to sensory integrative process through visuomotor and auditory thalamic connections.     

Serotonin-immunoreactive axons in the cell column of sympathetic preganglionic neurons in the spinal cord of the filefish Stephanolepis cirrhifer

Serotonin-immunoreactive axonal components were observed in the central autonomic nucleus (CAN), a cell column of sympathetic preganglionic neurons in the rostral spinal cord of the filefish Stephanolepis cirrhifer. Serotonin-positive axonal varicosities were seen around neuronal perikarya through the whole rostrocaudal extent of the CAN, although their distribution pattern in the rostral CAN was different from that in the caudal CAN. Electron microscopically, serotonin-positive axonal varicosities were found to make axodendritic and axosomatic synapses on CAN neurons. Many serotonin-positive neuronal cell bodies were seen in the raphe nuclei in the lower brainstem, whereas only a few were found in the spinal cord. Thus most of serotoninergic axons within the CAN were considered to originate from the raphe nuclei in the lower brainstem.     

Connections of the caudal ventrolateral medullary reticular formation in the cat brainstem

 A region of the caudal ventrolateral medullary reticular formation (CVLM) participates in baroreceptor, vestibulosympathetic, and somatosympathetic reflexes; the adjacent retroambigual area is involved in generating respiratory-related activity and is essential for control of the upper airway during vocalization. However, little is known about the connections of the CVLM in the cat. In order to determine the locations of terminations of CVLM neurons, the anterograde tracers Phaseolus vulgaris leucoagglutinin and tetramethylrhodamine dextran amine were injected into this region. These injections produced a dense concentration of labeled axons throughout the lateral medullary reticular formation (lateral tegmental field), including the retrofacial nucleus and nucleus ambiguus, regions of the rostral ventrolateral medulla, the lateral and ventrolateral aspects of the hypoglossal nucleus, nucleus intercalatus, and the facial nucleus. A smaller number of labeled axons were located in the medial, lateral, and commissural subnuclei of nucleus tractus solitarius, the A5 region of the pontine reticular formation, the ventral and medial portions of the spinal and motor trigeminal nuclei, locus coeruleus, and the parabrachial nucleus. We confirmed the projection from the CVLM to both the rostral ventrolateral medulla and lateral tegmental field using retrograde tracing. Injections of biotinylated dextran amine or Fluorogold into these regions resulted in retrogradely labeled cell bodies in the CVLM. However, the neurons projecting to the lateral tegmental field were located mainly dorsal to those projecting to the rostral ventrolateral medulla, suggesting that these neurons form two groups, possibly with different inputs. Injections of retrograde tracers into the lateral tegmental field and rostral ventrolateral medulla also produced labeled cell bodies in other regions, including the medial and inferior vestibular nuclei and nucleus solitarius. These data are consistent with the view that the CVLM of the cat is a multifunctional area that regulates blood pressure, produces vocalization, affects the shape of the oral cavity, and elicits contraction of particular facial muscles. Received: 18 February 1997 / Accepted: 27 March 1997     

The rostrocaudal organization in the dorsal root ganglia of the rat: a consequence of plexus formation?

The dorsal root ganglia (DRGs) of the rat have a rostrocaudal organization. This organization can most easily be demonstrated in fetal and neonatal rats because the spatial relationships of their DRGs are maintained better in tissue sections than those of mature rats. This review is concerned with the way in which the rostrocaudal organization of the DRGs is generated. Wheat germ agglutinin — horseradish peroxidase/horseradish peroxidase labeling of peripheral nerves of the brachial and lumbar plexuses shows that the position of the somata of the sensory neurons of the labeled nerves can be restricted to rostral or caudal halves of DRGs. Labeling of the thoracic nerve or its branches always results in labeling throughout the entire thoracic DRG. After application of the marker to forelimb nerves, it was observed that whenever a DRG is labeled only partially, its spinal nerve is correspondingly labeled partially as well. These data suggest that the rostrocaudal organization in the DRG is related to the formation of the plexuses. During development nerve fibers can be segmentally labeled, using the subdivision of the DRGs into a rostral and a caudal half to keep together as they find their way through the plexus. Application of label to forelimb skin, hindlimb skin and even thoracic skin can result in labeling of rostral or caudal halves of a DRG. A possible explanation might be that each dermatome can be divided into a skin area innervated by the rostral half of a DRG and a skin area innervated by the caudal half of the same dorsal root ganglion. In the rat, the segmental sensory innervation of muscles during development has not yet been investigated. The question of whether the segmental unit of innervation of a muscle is a whole DRG or half a DRG therefore still remains unanswered.     

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.     

Anatomical re-evaluation of the corticostriatal projections to the caudate nucleus: a retrograde labeling study in the cat

The distribution of cortical neurons projecting to the cat caudate nucleus (CN) was examined using retrograde labeling methods. Single injections of either horseradish peroxidase conjugated with wheat germ agglutinin (HRP-WGA), or the fluorescent tracers Fast Blue (FB) or Diamidino Yellow (DY) were made into different regions of the CN. This study confirms the following previous findings. (1) Labeled neurons were observed in the frontal and parieto-temporal cortices. (2) The corticocaudate cells were mainly located in layer V, although some cells were also observed in layer III and occasionally in layers II and VI. (3) Dorsal injections into the rostral CN yielded more dorsal labeling in the cerebral cortex. However, ventral cortical areas such as the ventral part of the prelimbic (PL) cortical area and the insular cortex (sylvian anterior (SA), agranular and disgranular insular areas) presented retrograde labeling after both dorsal and ventral injections into the CN. (4) Dorsal injections into the CN labeled all subdivisions of areas 4 and 6 whereas the ventral ones labeled only the areas 4delta, 6alphabeta, 6aalpha, 6iffu. The novel findings of this study are as follows. (1) The cortical area 6betabeta and the dorsolateral prefrontal area (PfDl) were labeled in all our cases. In addition, PL, anterior limbic, SA and rostral part of cingulate (Cg) cortical areas were also labeled in most of our cases. (2) Ventral injections into the CN elicited a higher number of retrogradely labeled neurons in the ventral prefrontal area than dorsal injections. (3) A topographical relationship was found between the caudal CN and the dorsomedial prefrontal area so that dorsal injections in the caudal CN elicited retrograde labeling in the rostral PfDl, whereas ventral injections labeled the caudal PfDl. (4) A topography from dorsal to rostral and ventral to caudal was also observed between injections into the CN and PL and Cg. (5) A mediolateral topography was observed in the presylvian, cruciate and splenial sulci.     

Parvalbumin-containing neurons mediate the feedforward inhibition of rat rubrospinal neurons

The calcium-binding protein, parvalbumin and glutamic acid decarboxylase immunohistochemistry were used to locate candidate neurons mediating the inhibition of rat rubral neurons. A group of cells with small to medium-sized cell bodies that reacted positively to both were found in the red nucleus and its immediate vicinity. At the caudal nuclear level, these neurons gathered in the reticular formation, the pararubral area dorsolateral to the nucleus. As the nucleus expanded in size rostrally these neurons started to incorporate into the nucleus at about the anterior half of the middle nucleus and were all located within the rostral nucleus. Since these neurons were spatially segregated from the caudal nucleus we tested their connection by applying anterograde tracer to the pararubral area at the caudal red nuclear level. Labeled fibers with bouton-like swellings were found to enter the caudal nucleus and closely apposed rubrospinal neuronal cell bodies. These findings are consistent with our earlier observation that stimulating the pararubral area elicited a monosynaptic gamma-aminobutyric-acid(A) receptor-mediated inhibition on rubrospinal neurons in brainstem slices. In addition, the present study also shows that these inhibitory neurons remained unaltered in rats subjected to unilateral upper cervical rubrospinal tractotomy, suggesting that the reduction of pararubral stimulus-induced inhibition on rubrospinal neurons following spinal axonal injury resulted from causes other than the loss of these inhibitory neurons. In the rats, sensorimotor cortical fibers are known to reach the rostral red nucleus and the pararubral area but not the caudal nucleus. This prompted us to propose that neocortical inputs inhibit rubrospinal neurons through the activation of these PV-containing neurons. The proposed feedforward inhibitory circuit enables the cerebral cortex to disynaptically modulate the rubrospinal control over flexor motor execution.