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PubMed1984

Telencephalic connections in lizards. II. Projections to anterior dorsal ventricular ridge.

Three distinct cytoarchitectonic regions were identified within the anterior dorsal ventricular ridge (ADVR) of two species of lizards, Gekko gecko and Iguana iguana. These regions have been named according to their general topographical positions: medial area, caudolateral area, and rostrolateral area. Injections of horseradish peroxidase throughout the ADVR demonstrated that each of the three areas of the ADVR receives projections from specific thalamic nuclei which are associated with specific sensory modalities. The medial area receives an auditory thalamic projection from nucleus medialis. The caudolateral area receives thalamic projections from nucleus medialis posterior and nucleus posterocentralis. The latter two nuclei were shown to receive projections from the spinal cord and, therefore, are presumed to be associated with body somatosensory information. The rostrolateral area receives a thalamic projection from nucleus rotundus, which receives visual information. In addition, the mesencephalic tegmentum and the thalamic nucleus dorsomedialis project to the entire ADVR. The latter projection is similar to the diffuse cortical projections of the intralaminar thalamic nuclei in mammals. These findings support previous suggestions that the ADVR is comparable to sensory regions of the mammalian neocortex.

Afferent Pathways↗
PubMed1985

Cholinergic projections from the basal forebrain to the basolateral amygdaloid complex: a combined retrograde fluorescent and immunohistochemical study.

We have examined the location of cholinergic and non-cholinergic neurons that project to the rat basolateral amygdaloid nucleus by using choline acetyltransferase (ChAT) immunohistochemistry in combination with retrograde fluorescent tracing on the same tissue section. Since many tracer-and ChAT-positive neurons were identified in basal forebrain areas, including the ventral pallidum, we also stained many of the sections for glutamate decarboxylase, a suitable marker for the delineation of pallidal areas. Cholinergic neurons projecting to the basolateral amygdaloid nucleus were observed in a continuous territory stretching from the dorsal part of ventral pallidum, through sublenticular substantia innominata to ventral parts of globus pallidus and peripallidal areas. Non-cholinergic neurons projecting to the basolateral amygdaloid nucleus were found intermixed within the same structures and constitute approximately 25% of the amygdalopetal projection neurons in these ventral forebrain structures. Since amygdalopetal cholinergic neurons were demonstrated in areas generally recognized as giving rise to cholinergic projections to cerebral cortex, several retrograde double-labeling experiments with two different fluorescent tracers were performed for the purpose of detecting the possible existence of collateral projections. The results obtained showed that the cholinergic basal forebrain neurons in general project to only one forebrain region, and, furthermore, that the cholinergic system consists of partially overlapping subsets of neurons that project to various neocortical and allocortical areas and to the amygdaloid body.

Amygdala↗
PubMed1985

Topographical projections of the cerebral cortex to the subthalamic nucleus.

Corticosubthalamic projections in the rat were investigated using the autoradiographic anterograde axonal tracing technique. After unilateral injections of tritiated amino acids in the cerebral cortex, projections to the ipsilateral subthalamic nucleus (STH) could be found arising only from the frontal agranular cortex and the zone of MI-SI overlap. Injections into granular areas of the cortex (e.g., somatosensory and visual areas) did not result in labeling in STH. Following injections in the frontal agranular cortex, labeling was present in the ipsilateral but not the contralateral STH. In general, injections that involved the lateral agranular field of frontal cortex, as defined by Donoghue and Wise ('82), resulted in a greater amount of labeling in STH than injections within the medial agranular area or the zone of MI-SI overlap. The projection from the frontal agranular areas to STH is topographically organized. The rostral part of the lateral agranular cortex projects to the lateral portion of the rostral two-thirds of STH, and the caudal part of this field projects to the ventral aspect of the middle third of STH. Injections in the rostral part of the medial agranular cortex resulted in labeling throughout the ventral two-thirds of the medial half of STH. The caudal part of the medial agranular cortex projects to the dorsolateral part of the caudal two-thirds of STH. The present results reveal projections from only the frontal agranular cortex and the zone of MI-SI overlap to STH in the rat. The cortico-STH projection is ipsilateral and terminates in a topographical manner in all parts of STH.

Animals↗
PubMed1985

Intrinsic projections of the retrohippocampal region in the rat brain. I. The subicular complex.

The intrahippocampal projections of the subicular complex were studied in the rat with the aid of the anterogradely transported lectin Phaseolus vulgaris leucoagglutinin (PHA-L). After iontophoretic injections of the lectin into the subiculum proper, presubiculum, or the parasubiculum, axons and terminal processes immunoreactive for PHA-L were traced to their respective terminal fields within the hippocampal region. After subicular injections PHA-L-stained axons could be followed both in a caudal and a rostral direction. The caudally directed fibers course around or within the angular bundle to enter layers VI and V of the medial entorhinal area (MEA). Many fibers penetrate through these layers to terminate in layer IV of the medial and the lateral entorhinal area, which contains a major terminal field of this projection. At more ventral levels, all layers of the entorhinal area are innervated by cells located in the subiculum. Other retrohippocampal projections of the subiculum proper include the deep and the outer two layers of the presubiculum and the medial sector of the parasubiculum, in addition to a massive projection which terminates in the retrosplenial cortex. The rostrally directed projections from the subiculum form a dense innervation of strata lacunosum, radiatum, oriens, and of individual pyramidal cells in the regio superior of the Ammon's horn. All these projections of the subiculum are exclusively ipsilateral. After injections of PHA-L into layers II and III of the presubiculum, both ipsi- and contralateral projections were traced to the outer three layers of the medial entorhinal area; the lateral entorhinal area apparently receives no innervation from the presubiculum. The innervation of layer III is very dense while in layer II and deep layer I, restricted zones of innervation are found. The fibers reach these layers via the deep layers of the MEA and through the molecular layer after first coursing around the parasubiculum. In addition, a minor projection from the presubiculum to the pyramidal cell layer of the subiculum and to the molecular layer of the hippocampal formation was found. PHA-L injections into the parasubiculum labeled fibers that form a dense innervation of layer II in the MEA and the medial part of the lateral EA, and of the most medial sector of layer III in the MEA. Layer I and the superficial part of layer II of the contralateral MEA also contain a dense terminal network after PHA-L injections into the parasubiculum.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

The efferent projections from the reticular formation and the locus coeruleus studied by anterograde and retrograde axonal transport in the rat.

Following injections of [3H]leucine into the formatio reticularis gigantocellularis (Rgc), reticularis pontis caudalis (Rpc), reticularis pontis oralis (Rpo), reticularis mesencephali (Rmes), or the locus coeruleus (LC) of the rat, autoradiographic study revealed prominent reticuloreticular projections from all areas and secondary projections onto cranial nerve motor nuclei from most areas within the brain stem. Common long descending projections extended the full length of the spinal cord terminating in the ventromedial ventral horn and intermediate zone and more sparsely in the base of the dorsal horn and (particularly from Rgc) the region of the motoneurons. Common long ascending projections extended into the forebrain via Forel's tegmental fascicles. A dorsal branch of fibers innervated the intralaminar and midline nuclei of the thalamus. The major fiber system continued forward through Forel's fields and ascended into the pallidum from Rpo, Rmes, and LC and into the neostriatum from Rmes and LC. Fascicles from all areas also ascended in the medial forebrain bundle through the lateral hypothalamus to the lateral preoptic area, substantia innominata, and nuclei of the diagonal band. From Rpo, Rmes, and LC, fibers continued forward to reach the cerebral cortex, where the innervation was sparse and discrete from Rpo and Rmes but moderate and ubiquitous from LC. Retrograde transport of true blue and/or nuclear yellow revealed inverse gradients along the brain stem longitudinal axis of interdigitated cells respectively projecting caudally into the spinal cord (with the greatest number of cells in Rgc, Rpc, and Rpo) and rostrally into the diencephalon (with the greatest number of cells in Rmes and LC), with very few cells projecting both to the spinal cord and the diencephalon. From the basal forebrain, a large number of reticular and LC cells were retrogradely labelled, whereas from the frontal cortex, a much smaller number of reticular cells was labelled. These results document the widespread efferent projections from the reticular formation and overlapping, yet more extensive, projections from the LC.

Amidines↗
PubMed1985

Projections to the subcortical forebrain from anatomically defined regions of the medial geniculate body in the rat.

Although the auditory cortex is believed to be the principal efferent target of the medial geniculate body (MG), our recent behavioral studies indicate that in rats the conditioned coupling of emotional responses to an acoustic stimulus is mediated by subcortical projections of the MG. In the present study we have therefore used WGA-HRP as an anterograde and retrograde axonal marker to (1) define the full range of subcortical efferent projections of the MG; (2) identify the cells of origin within the MG of each projection; and (3) determine whether the subregions of the MG that project to subcortical areas receive inputs from acoustic relay nuclei of the mid-brain, particularly the inferior colliculus. The rat MG was first parcelled into three major cytoarchitectural areas: the ventral, medial, and dorsal divisions. The suprageniculate nucleus, located within the body of the MG just dorsal to the medial division, was also identified. Efferent projections of the MG were determined by combined anterograde and retrograde tracing methods. Injections of WGA-HRP in the MG produced anterograde transport to cortex and several subcortical areas, including the posterior caudate-putamen and amygdala, the ventromedial nucleus of the hypothalamus, and the subparafascicular thalamic nucleus. The cells of origin of the subcortical projections were then mapped retrogradely after injections in the anterogradely labeled areas. Injections in the caudate-putamen or amygdala retrogradely labeled the medial division of the MG and the suprageniculate nucleus, as well as several adjacent areas of the posterior thalamus surrounding the MG. In contrast, injections in the ventromedial nucleus of the hypothalamus or the subparafascicular thalamic nucleus only produced labeling in the areas surrounding MG. Afferents to MG from the inferior colliculus were then identified. The central nucleus of the inferior colliculus, the main lemniscal acoustic relay nucleus in the midbrain, was found to project to the ventral and medial divisions of the MG. In contrast, the dorsal cortex and external nucleus of the inferior colliculus project to each division of the MG and to several additional nuclei in adjacent areas of the posterior thalamus. These data demonstrate that the medial division of MG, the suprageniculate nucleus, and immediately adjacent areas of the posterior thalamus provide a direct linkage between auditory neurons in the inferior colliculus and subcortical areas of the forebrain and thereby support the view that thalamic sensory nuclei relay afferent signals to subcortical as well as cortical areas.

Amygdala↗
PubMed1986

Single thalamic neurons project to both lateral suprasylvian visual cortex and area 17: a retrograde fluorescent double-labeling study.

Area 17 and the posteromedial lateral suprasylvian (PMLS) visual cortex receive inputs from three thalamic nuclei in common: the lateral division of the lateral posterior nucleus (LPl), the C-laminae of the lateral geniculate nucleus (LGNd), and the medial interlaminar nucleus (MIN). The present study determined whether these projections originate from the same cells via bifurcating axons or from separate populations of cells. Double-label retrograde transport techniques were used to label cells projecting to area 17 with one fluorescent dye and to label cells projecting to PMLS cortex with a different dye. The two dyes used were fast blue and Evans blue. Following injections into the two cortical areas, some cells were double labeled and some were single labeled in all three thalamic nuclei studied. However, the relative number of double- and single-labeled cells, as well as the relative number of cells single-labeled following injections into each cortical area, differed among the three thalamic nuclei. In both MIN and the C-laminae of the LGNd, the number of double-labeled cells was small. Similarly, the number of cells single labeled with the dye placed in PMLS cortex was small in these two nuclei. In contrast, a relatively large number of cells were single labeled with the dye placed in area 17, especially in the C-laminae of the LGNd. These results suggest that in both MIN and the C-laminae of the LGNd, few cells project to both area 17 and the PMLS cortex, few cells project only to PMLS cortex, and a relatively greater number of cells project only to area 17. In LPl, many cells were labeled after the cortical injections. In fact, when the areas of densest labeling for both dyes overlapped, almost every labeled cell in LPl was double labeled. This indicates that almost all LPl cells that project to one cortical area also project to the other via a bifurcating axon.

Animals↗
PubMed1986

Differential origin of brainstem serotoninergic projections to the midbrain periaqueductal gray and superior colliculus of the rat.

Previous studies have shown that both the midbrain periaqueductal gray (PAG) and the superior colliculus receive a significant serotoninergic (5-HT) innervation. In the present study the origins of these 5-HT projections to the rodent PAG and superior colliculus were analyzed by using a combined immunohistochemical-retrograde transport technique. Thirteen brainstem regions were found to contain double-labelled 5-HT-like immunoreactive neurons following HRP injections into the PAG while only four brainstem nuclei contained double-labelled neurons following superior collicular injections. After HRP deposits into the ventral PAG, the largest percentage of double-labelled neurons was identified in nucleus raphe magnus, pars alpha of the nucleus gigantocellularis, and the paragigantocellular nucleus. The dorsal PAG, on the other hand, received the largest percentage of its 5-HT projections from nuclei raphe dorsalis, raphe obscurus, raphe pontis, and raphe medianis. The 5-HT input to the superior colliculus was found to arise exclusively from nuclei raphe dorsalis, raphe medianis, and raphe pontis and from the contralateral periaqueductal gray. Raphe nuclei were found to contribute serotoninergic projections to both the PAG and the superior colliculus while reticular nuclei contributed 5-HT projections only to the PAG. Injections of the fluorescent retrograde tracers true blue and nuclear yellow were then made into the PAG and superior colliculus to ascertain if neurons located in raphe nuclei that projected to both structures provided axon collaterals to both areas. Generally, less than 10% of raphe neurons projecting to the superior colliculus were identified as providing axon collaterals to the PAG. The present results demonstrate major quantitative and qualitative differences in the origin of 5-HT projections to the ventral PAG and superior colliculus. The origin of 5-HT input to the dorsal PAG, on the other hand, showed many similarities to the origin of 5-HT innervation of the superior colliculus. These data also indicate that approximately 35% of raphe neurons provide nonserotoninergic projections to the PAG and superior colliculus.

Afferent Pathways↗
PubMed1987

Organization of central adrenergic pathways: I. Relationships of ventrolateral medullary projections to the hypothalamus and spinal cord.

We studied the organization of projections from the C1 adrenergic and A1 noradrenergic cell groups in the ventrolateral medulla (VLM) to the hypothalamus and the spinal cord by using a combination of retrograde transport of fluorescent tracers and immunocytochemistry. Three issues were addressed. Neurons in the VLM that stain immunohistochemically for phenylethanolamine N-methyltransferase (PNMT) have been assumed to be adrenergic. However, the presence of PNMT-immunoreactive neurons in the hypothalamus that do not stain for tyrosine hydroxylase (TH) prompted us to re-evaluate the VLM by an elution-restaining immunohistochemical procedure. We confirmed that nearly all of the rostral medullary PNMT-immunoreactive neurons also stained for TH. By contrast, in the caudal medulla, very few TH-positive neurons stained for PNMT. Neurons of the C1 group in the rostral VLM project both to the thoracic spinal cord and to the hypothalamus. To determine whether individual C1 neurons send collaterals to the hypothalamus and spinal cord, we injected different-colored fluorescent dyes (diamidino yellow or fast blue) into the thoracic spinal gray matter and either the median preoptic (MnPO) or paraventricular (PVH) nuclei of the hypothalamus. Very few double-labeled neurons were found in the VLM, indicating that hypothalamic and spinal cord projections arise from almost completely independent populations of cells. Approximately half of the neurons projecting to the spinal cord from rostral VLM were not immunoreactive for TH or PNMT, indicating that a substantial part of this projection is noncatecholaminergic. The MnPO and the PVH both receive extensive catecholaminergic inputs from the VLM. We also used fluorescent retrograde tracers to determine whether individual VLM neurons send collaterals to both hypothalamic sites. Approximately 20% of neurons projecting to the MnPO in the rostral two thirds of the VLM also sent collaterials to the PVH, nearly all of these neurons being TH-positive. The collateralization of the VLM catecholaminergic projection to the hypothalamus may provide an anatomical substrate for integration of fore-brain participation in cardiovascular regulation. In contrast, the adrenergic projection from the VLM to the intermediolateral column of the spinal cord arises from a separate population of neurons.

Adrenergic Fibers↗
PubMed1988

Organization of retinogeniculate projections in turtles of the genera Pseudemys and Chrysemys.

Organization of retinal projections to the dorsal lateral geniculate complex in turtles has been studied by means of light and electron microscopic axon tracing techniques. Orthograde degeneration studies with Fink-Heimer methods following restricted retinal lesions show the entire retina has a topologically organized projection to the contralateral dorsal lateral geniculate complex. The nasotemporal axis of the retina projects along the rostrocaudal axis of the geniculate complex; the dorsoventral axis of the retina projects along the dorsoventral axis of the geniculate complex. The projection to the ipsilateral dorsal lateral geniculate complex originates from the ventral, temporal and nasal edges of the retina. The nasotemporal axis of the ipsilateral retina projects along the rostrocaudal axis of the geniculate complex. It was not possible to determine the orientation of the dorsoventral axis of the ipsilateral retina on the geniculate complex. Light microscopic autoradiographic tracing experiments and electron microscopic degeneration experiments show the retinogeniculate projection has a laminar organization. Retinogeniculate terminals are found in both the neuropile and cell plate throughout all three subnuclei of the dorsal lateral geniculate complex but have a distinctive distribution in each subnucleus. In the subnucleus ovalis, they are frequent in both the neuropile and cell plate which forms the rostral pole of the complex. In the dorsal subnucleus, they are most prevalent in the outer part of the neuropile layer, less frequent in the inner part of the neuropile, and rare in the cell plate. In the ventral subnucleus, they are frequent in the outer part of the neuropile but are also common in the inner part of the neuropile and cell plate. These observations point to several principles of geniculate organization in turtles. First, the complex receives projections from the entire contralateral retina and a segment of the ipsilateral retina. It thus has monocular and binocular segments that together receive a topologically organized representation of the binocular visual space and the contralateral monocular visual space. Second, the three geniculate subnuclei receive information from different, specialized regions of the retina and visual space. Subnucleus ovalis receives information from the frontal binocular visual field. The ventral subnucleus receives information from the caudal binocular field. The dorsal subnucleus receives input from the contralateral monocular field. Third, there is a lamination of retinal inputs in the geniculate complex which differs in character within the three subnuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Plasticity in the developing chick visual system: topography and maintenance of experimentally induced ipsilateral projections.

The present work examines the topography of the contra- and ipsilateral centrifugal projections from the isthmooptic nuclei (IONs) to the remaining retina in monocular chick embryos. After removal of the left eyecup at embryonic day (E)1.5, the IONs were investigated at various embryonic stages by the retrograde transport of fluorescent dyes and horseradish perioxidase (HRP) injected into the remaining eye. The projection of the ipsilateral ION was consistently found at E13 and frequently disappeared by E18 to E19. Selective regional labeling of the remaining retina in monocular embryos with DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate) revealed that the retinotopic order of the enhanced projection from the ipsilateral ION corresponded precisely to the normal one from the contralateral ION. The formation of the projection from the retina to the ipsilateral tectum was also investigated at E18 to E19 by means of intravitreally injected HRP or rhodamine-B-isothiocyanate (RITC) in monocular embryos after early eyecup removal. In cases with persistent ION, the eye enucleations resulted in ipsilateral retinotectal projections consisting of varying numbers of retinofugal fibers. The data are consistent with the view that there is a certain degree of plasticity in the embryonic development of the chick visual system. If an ION projection to the ipsilateral retina is strongly developed, it is retinotopically organized and probably influences the maintenance of the ipsilateral retinotectal projection. The stabilization of the otherwise transiently formed ipsilateral retinotectal projection may be influenced by the tectal neurons which receive retinal input and are efferently connected with persisting ION neurons.

Animals↗
PubMed1989

Zonal organization of climbing fiber projections to the uvula in the cat.

Climbing fiber projections from the inferior olive to the uvula of the cerebellum were studied in the cat by using retrograde axonal transport of horseradish peroxidase. Following large and small injections into various parts of the uvula, the distribution of labeled cells in the inferior olive was investigated. The findings indicate six longitudinal zones extending throughout the dorsal and ventral uvula: the caudal part of the nucleus beta projects to a most medially located zone (caudal beta zone) with a width of about 0.4 mm; the rostral part of the nucleus beta projects to a zone located at about 0.6 mm from the midline (rostral beta zone); the caudal part of the medial accessory olive (MAO) projects to a zone (caudal MAO zone) located lateral to the rostral beta zone; the dorsomedial cell column projects to a zone (dorsomedial cell column zone) located in the intermediate part of the uvula at about 1.2 mm from the lateral edge of the uvula; the ventral lamella of the principal olive (PO) projects to a zone (ventral lamella of PO zone) about 0.7 mm from the lateral edge of the uvula; finally, the rostral part of the MAO projects to the most lateral zone (rostral MAO zone). These conclusions are in general agreement with those of earlier studies and also provide a more detailed zonal configuration of climbing fiber projections to the uvula.

Animals↗
PubMed1989

Descending projections from auditory brainstem nuclei to the cochlea and cochlear nucleus of the guinea pig.

Projections from auditory brainstem nuclei to the cochlea and cochlear nuclei in the guinea pig were studied by injection of two retrograde fluorescent neuronal tracers. For seven experiments fast blue was injected into the scala tympani of one cochlea and diamidino yellow was injected into dorsal or anteroventral cochlear nucleus of the same side. The results show that the efferent projections to the cochlea and cochlear nucleus generally form two separate neuronal systems even though they share many common nuclei of origin. The largest projections to the cochlear nucleus come bilaterally from the lateral and ventral nuclei of the trapezoid body. Other nuclei, the lateral superior olive, the ventral nucleus of the lateral lemniscus, the dorsomedial periolivary nuclei, and the medial nucleus of the trapezoid body showed an ipsilateral bias in their projections to the cochlear nucleus. An upper limit of 3.5% of the medial system olivocochlear efferent neurones projecting to the cochlea were labelled with both diamidino yellow and fast blue, suggesting that few efferent neurones projecting to the cochlea send collaterals to the cochlear nucleus in this species. However, the site of medial system olivocochlear efferent collateral terminations is the granule cell area for the cat, mouse, and gerbil. When diamidino yellow was injected in the superficial layers of the cochlear nucleus, including the superficial granule cell layer of the ventral cochlear nucleus, approximately 3.6% of medial system olivocochlear efferents projecting to the cochlea sent collaterals to the cochlear nucleus. In three animals fast blue was injected into the cochlear nucleus and diamidino yellow into the cochlea. These experiments revealed a greater proportion of the medial system olivocochlear efferents projecting to the cochlea sending collaterals to the cochlear nucleus, but this proportion was still less than 10%. These results were confirmed by the extracellular injection of horseradish peroxidase into the intraganglionic spiral bundle. Only three medial system olivocochlear efferents were observed to send collaterals to the cochlear nucleus. This number was less than 10% of all labelled medial system fibres. Although these experiments suggest that in the guinea pig the number of olivocochlear efferents sending collaterals to the cochlear nucleus is considerably smaller than is found for the cat, mouse, and gerbil, it is not possible with the current experimental procedures to conclude whether the results are due to species or methodological differences.

Animals↗
PubMed1989

Avian somatosensory system: II. Ascending projections of the dorsal column and external cuneate nuclei in the pigeon.

The ascending projections of the dorsal column and external cuneate nuclei (DCN/CuE) in the pigeon were investigated in anterograde tracing experiments by using autoradiography or wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). The results show that the majority of ascending projections decussate via internal arcuate fibers to form a contralateral medial lemniscus which ascends in a ventral position. In the brainstem, terminal fields were observed in the ventral lamella of the inferior olive (OI), the parabrachial nuclei (PB) of the dorsolateral pons, the intercollicular nucleus (ICo) of the midbrain, and the nucleus pretectalis diffusus (PD). In the diencephalon there were terminal fields in the strata cellulare externum and internum (SCE and SCI) of the caudal hypothalamus; in the intercalated (ICT), ventrolateral (VLT), and reticular nuclei of the ventral thalamus; in the nuclei principalis precommissuralis (PPC), spiriform medialis (SpM), and dorsolateralis posterior, pars caudalis (cDLP) of the caudal thalamus; and in the nuclei dorsalis intermedius ventralis anterior (DIVA), dorsolateralis posterior, pars rostralis (rDLP), dorsolateralis anterior (DLA), and dorsolateralis anterior, pars medialis (DLM) of the rostrodorsal thalamus. The origins of these projections within the DCN/CuE complex were verified in retrograde tracing experiments with WGA-HRP and were found to be partly differentiable with respect to their targets. The projections to DIVA, rDLP, DLA, DLM, cDLP, and SpM arise from all rostrocaudal levels of the DCN/CuE complex; those to ICo arise from caudomedial nuclear regions, while those to the hypothalamus and ventral thalamus arise from rostrolateral nuclear regions. Projections to PB arise from lamina I neurons of the dorsal horn of upper cervical spinal cord segments and from CuE. No evidence was found of a projection to the cerebellum. The distribution of the cells of origin of the medial lemniscus (ML) within the DCN/CuE complex was found to be largely coextensive with the areas of termination of primary spinal (Wild: J. Comp. Neurol. 240:377-395, '85) and some trigeminal (Dubbledam and Karten: J. Comp. Neurol. 180:661-678, '78) afferents. Furthermore, the areas of termination of the ML within the rostrodorsal and caudal thalamus are also either coextensive or closely associated with nuclei which provide a somatosensory projection to separate regions of the telencephalon (Wild: Brain Res. 412:205-223, '87). There are thus clear similarities in the overall pattern of somatosensory projections in the pigeon and in many mammalian species.

Amino Acids↗
PubMed1989

Crossed and uncrossed projections to cat sacrocaudal spinal cord: I. Axons from cutaneous receptors.

Intra-axonal recording and horseradish peroxidase staining techniques were used to map terminal fields of primary afferent fibers from cutaneous receptors within the cat sacrocaudal spinal cord. It was hypothesized that projection patterns of cutaneous afferent fibers mirror the known somatotopic organization of sacrocaudal dorsal horn cells. Forty-three primary afferent fibers, innervating either slowly adapting type I receptors, hair follicles, or slowly adapting type II receptors, all on the tail, were recovered. All collaterals (N = 372) branched from parent axons in the dorsal columns. Most collaterals coursed rostromedially to the ipsilateral gray matter, penetrated the medial dorsal horn, and arborized within laminae III, IV, and to a lesser extent, V. Ipsilateral projections to dorsal horn were as follows: axons with dorsal or dorsolateral receptive fields (RFs; n = 20) to the lateral portion, axons with lateral RFs (n = 4) to the central portion, and axons with ventral or ventro-lateral RFs (n = 19) to the medial portion. Most axons (16 of 20) with dorsal or dorsolateral RFs also had contralateral projections to lateral dorsal horn and most axons (15 of 19) with ventral or ventrolateral RFs also had contralateral projections to medial dorsal horn. No axons with lateral RFs had crossed projections. These data represent the first complete mapping of the somatotopic organization of primary afferent fiber projection patterns to a spinal cord level. The findings demonstrate that ipsilateral projection patterns of sacrocaudal primary afferent fibers are in register with the somatotopic organization of the dorsal horn. Our earlier suggestion that crossed projections of primary afferent fibers give rise to crossed components of dorsal horn RFs spanning the midline is supported by these results.

Action Potentials↗
PubMed1989

Topographical organization of the efferent projections of the medial prefrontal cortex in the rat: an anterograde tract-tracing study with Phaseolus vulgaris leucoagglutinin.

The purpose of the present investigation was to examine the topographical organization of efferent projections from the cytoarchitectonic divisions of the mPFC (the medial precentral, dorsal anterior cingulate and prelimbic cortices). We also sought to determine whether the efferents from different regions within the prelimbic division were organized topographically. Anterograde transport of Phaseolus vulgaris leucoagglutinin was used to examine the efferent projections from restricted injection sites within the mPFC. Major targets of the prelimbic area were found to include prefrontal, cingulate, and perirhinal cortical structures, the dorsomedial and ventral striatum, basal forebrain nuclei, basolateral amygdala, lateral hypothalamus, mediodorsal, midline and intralaminar thalamic nuclei, periaqueductal gray region, ventral midbrain tegmentum, laterodorsal tegmental nucleus, and raphe nuclei. Previously unreported projections of the prelimbic region were also observed, including efferents to the anterior olfactory nucleus, the piriform cortex, and the pedunculopontine tegmental-cuneiform region. A topographical organization governed the efferent projections from the prelimbic area, such that the position of terminal fields within target structures was determined by the rostrocaudal, dorsoventral, and mediolateral placement of the injection sites. Efferent projections from the medial precentral and dorsal anterior cingulate divisions (dorsomedial PFC) were organized in a similar topographical fashion and produced a pattern of anterograde labeling different from that seen with prelimbic injection sites. Target structures innervated primarily by the dorsomedial PFC included certain neocortical fields (the motor, somatosensory, and visual cortices), the dorsolateral striatum, superior colliculus, deep mesencephalic nucleus, and the pontine and medullary reticular formation. Previously unreported projections to the paraoculomotor central gray area and the mesencephalic trigeminal nucleus were observed following dorsomedial PFC injections. These results indicate that the efferent projections of the mPFC are topographically organized within and across the cytoarchitectonic divisions of the medial wall cortex. The significance of topographically organized and restricted projections of the rat mPFC is discussed in light of behavioral and physiological studies indicating functional heterogeneity of this region.

Animals↗
PubMed1990

Projections of the parabrachial nucleus in the pigeon (Columba livia).

The ascending and descending projections of the parabrachial nuclear complex in the pigeon have been charted with autoradiographic and histochemical (WGA-HRP) techniques. The ascending projections originate from a group of subnuclei surrounding various components of the brachium conjunctivum, namely, the superficial lateral, dorsolateral, dorsomedial, and ventromedial subnuclei. The projections are predominantly ipsilateral and travel in the quintofrontal tract. They are primarily to the medial and lateral hypothalamus (including the periventricular nucleus and the strata cellulare internum and externum), certain dorsal thalamic nuclei, the nucleus of the pallial commissure, the bed nucleus of the stria terminalis, the ventral paleostriatum, the olfactory tubercle, the nucleus accumbens, and a dorsolateral nucleus of the posterior archistriatum. There are weaker or more diffuse projections to the rostral locus coeruleus (cell group A8), the compact portion of the pedunculopontine tegmental nucleus, the central grey and intercollicular region, the ventral area of Tsai, the medial spiriform nucleus, the nucleus subrotundus, the anterior preoptic area, and the diagonal band of Broca. The parabrachial subnuclei have partially differential projections to these targets, some of which also receive projections from the nucleus of the solitary tract (Arends, Wild, and Zeigler: J. Comp. Neurol. 278:405-429, '88). Most of the targets, particularly those in the basal forebrain (viz., the periventricular nucleus and the strata cellulare internum and externum of the hypothalamus, the bed nucleus of the stria terminalis, and its lateral extension into the ventral paleostriatum, which may be comparable with the substantia innominata), have reciprocal connections with the parabrachial and solitary tract subnuclei and therefore may be said to compose parts of a "visceral forebrain system" analogous to that described in the rat (Van der Kooy et al: J. Comp. Neurol. 224:1-24, '84). The descending projections to the lower brainstem arise in large part from a ventrolateral subnucleus that may be comparable with the Kölliker-Fuse nucleus of mammals. They are mainly to the ventrolateral medulla, nucleus ambiguus, and massively to the hypoglossal nucleus, particularly its tracheosyringeal portion. These projections are therefore likely to be importantly involved in the control of vocalization and respiration (Wild and Arends: Brain Res. 407:191-194, '87). Some of these results have been presented in abstract form (Wild, Arends, and Zeigler: Soc. Neurosci. Abst. 13:308, '87).

Animals↗
PubMed1990

Vestibulo-ocular projections in the 11-day chicken embryo: pathway specificity.

The organization of vestibulo-ocular projections and their spatial relationship to vestibulo-spinal projections were ascertained in the 11-day chicken embryo through retrograde tracing experiments. An in vitro preparation of the brainstem facilitated precisely localized application of tracers. Unilateral labelling of the ascending medial longitudinal fascicle (MLF), just caudal to the trochlear nucleus, labelled coherent groups of vestibular neurons that had an asymmetrical distribution on the two sides of the brainstem. Axons originating from either side followed one of four trajectories, and the groups of neurons could therefore be identified on the basis of their position and their projection pathway. Labelling each side of the MLF with a different tracer showed that although neurons projecting in the ipsi- and contralateral MLF were intermingled in some areas, individual neurons projected on one side only. Labelling the ascending MLF and the high cervical spinal cord with different tracers showed that vestibulo-ocular neurons had a wider rostro-caudal distribution than vestibulospinal neurons. Some vestibulospinal and vestibulo-ocular groups were spatially segregated, others were intermingled. Very few (in most preparations no) neurons were found to project to both targets. Together with our previous study on vestibulospinal projections in the 11-day chicken embryo (Glover and Pétursdóttir, J. Comp. Neurol. 270:25-38, '88) the results show that vestibular neurons in different regions project in characteristic subsets of the available pathways.

Afferent Pathways↗