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The course of retrogradely labeled spinocerebellar fibers in the ventral and lateral funiculi of the spinal cord was studied following injections of wheat germ agglutinin-conjugated horseradish peroxidase into the posterior spinocerebellar termination area in the cat. Fibers labeled from unilateral injections into the paramedian lobule were found on the same side in the dorsal part of the lateral funiculus (DLF), corresponding to the dorsal spinocerebellar tract (DSCT), but contralaterally in the ventral part of the lateral funiculus (VLF) and in the ventral funiculus (VF), corresponding to the ventral spinocerebellar tract (VSCT). Following injections into the posterior vermis, labeled fibers were less numerous. Most of them were found in the DSCT and only very few in the VSCT. Previously identified cells of origin of these spinocerebellar tracts were labeled in these experiments and counted. They correlated well with the extents and the locations of the injections that had been made into the two termination sites. These results represent novel detailed information on the location of axons projecting to the two main posterior spinocerebellar termination sites in the spinal white matter in the cat. [ABSTRACT FROM AUTHOR]

This study investigated the synaptic interactions between hypoglossal motoneurons that project to the genioglossus muscle and substance P (SP) containing immunoreactive nerve terminals. Cholera toxin B conjugated to horseradish peroxidase (CTB-HRP) was injected into the right half of the genioglossus muscle in four anesthetized cats. Two days later, the animals were perfused with acrolein fixative. Tetramethylbenzidine (TMB) was the chromogen used to detect retrogradely labeled cells containing CTB-HRP. The tissues were then processed for immunocytochemisty using an antiserum raised against SP with diaminobenzidine (DAB) as the chromogen. At the light microscopic level, labeled cells were observed primarily ipsilaterally in ventral and ventrolateral subdivisions of the hypoglossal nucleus. The majority of these labeled cells were observed at the level of the area postrema. At the electron microscopic level, SP-like immunoreactive nerve terminals formed synaptic contacts with retrogradely labeled dendrites and perikarya. Nineteen percent of the terminals that contacted retrogradely labeled cells contained SP. These are the first ultrastructural studies demonstrating synaptic interactions between protruder hypoglossal motoneurons and SP terminals. These studies demonstrate that hypoglossal motoneurons which innervate the major protruder muscle of the tongue, the genioglossus muscle, may be modulated by SP. Thus, SP may play a role in the control of protrusive movements of the tongue acting via neurokinin receptors. [ABSTRACT FROM AUTHOR]

The fluorescent dye diamidino yellow was injected into parts of the developing visual and auditory systems in the rat. The dye was retrogradely transported by projecting neurones and was found to stain pyknotic profiles within the labelled cell populations. It is thus possible to visualize directly the death of neurones which project axons to specific and identified target regions within the nervous system. [ABSTRACT FROM AUTHOR]

The ventral medulla oblongata of rats was analyzed with a double-labelling immunofiuorescence technique using guinea pig antibodies directed against serotonin (5-HT) and rabbit antisera directed against enkephalin (ENK). Numerous cells in the region of nucleus raphe obscurus, nucleus raphe pallidus and nucleus raphe magnus showed immuno-staining for either 5-HT or ENK. A substantial number of cells showed positive immunostaining for both 5-HT and ENK. 5-HT/ENK double-labelled cells were most frequently encountered in an area that extended from the rostral aspect of the inferior olivary nucleus to the pontomedullary border. This region corresponds anatomically to nucleus raphe magnus/nucleus paragigantocellularis. In addition, a number of the 5-HT/ENK-containing cells were retrogradely labelled with Fluoro-Gold dye that had been injected into the thoracic spinal cord several days prior to perfusion. Schematic drawings showing the anatomical distribution of 5-HT/ENK colocalization are provided. [ABSTRACT FROM AUTHOR]

By means of the retrograde transport of fluorescent tracers (Fast Blue, True Blue, Fluorogold and Diamidino Yellow), the cortico-cortical connections of prelimbic, insular, anterior and posterior cingulate (retrosplenial) areas have been studied. Our results demonstrate that there are, in the cortex of the adult rat, a few cells which have branched axons with connections in the ipsilateral hemisphere (associational neurons) or in the contralateral hemisphere (callosal neurons). The callosal neurons could be separated into two categories: 'double callosal' neurons which project both axon collaterals to two cortical areas of the contralateral hemisphere, and 'associational-callosal' neurons which send axon collaterals to both hemispheres. [ABSTRACT FROM AUTHOR]

In an attempt to identify cholinergic neurons of the brain stem which project to the forebrain, retrograde labeling of neurons in the brain stem was examined by autoradiography following injections of 20 μCi [H]choline into the thalamus, hypothalamus, basal forebrain and frontal cortex. After injections into the thalamus, retrogradely labeled neurons were evident within the lateral caudal mesencephalic and dorsolateral oral pontine tegmentum (particularly in the laterodorsal and pedunculopontine tegmental nuclei) and in smaller number within the latero-medial caudal pontine (Reticularis pontis caudalis, Rpc) and medullary (Reticularis gigantocellularis, Rgc) reticular formation. Following [H]choline injections into the lateral hypothalamus and into the basal forebrain, retrogradely labeled neurons were localized in the dorsolateral caudal midbrain and oral pontine tegmentum and in smaller number in the medial medullary reticular formation (Rgc), as well as in the midbrain, pontine and medullary raphe nuclei. After injections into the anterior medial frontal cortex, a small number of retrogradely labeled cells were found in the brain stem within the laterodorsal tegmental nucleus and the dorsal raphe nucleus. In a parallel immunohistochemical study, choline acetyltransferase (ChAT)-positive neurons were found to be located in most of the regions of the reticular formation where cells were retrogradely labeled from the forebrain following [H]choline injections. These results suggest that multiple cholinergic neurons within the lateral caudal midbrain and dorsolateral oral pontine tegmentum and a few within the caudal pontine and medullary reticular formation project to the thalamus, hypothalamus and basal forebrain and that a limited number of pontine cholinergic neurons project to the frontal cortex. [ABSTRACT FROM AUTHOR]

The location of bulbar neurones with axons projecting to the ipsi- and contralateral trigeminal motor nucleus were investigated in cats anaesthetized with sodium pentobarbital. Wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) was injected in amounts of 5-24 nl. A volume-calibrated microelectrode was used for recording of evoked potentials and pressure injection of WGA-HRP. The injection site was guided by the position where a maximal antidromic response was evoked by electrical stimulation of the masseteric nerve. The survival time was 19-22 h. In preparations with the depot located in the masseteric subnucleus retrogradely stained neurones were found bilaterally in the borderzone of the trigeminal motor nucleus. Dense populations of stained neurones were observed ipsi- and contralaterally in the dorsal division of the main sensory trigeminal nucleus and the subnucleus-γ of the oral nucleus of the spinal trigeminal tract. Clusters of WGA-HRP-neurones were observed bilaterally in the lateral tegmental field at the level of the subnucleus-β of the oral nucleus of the spinal trigeminal tract, bilaterally dorsal to the facial nucleus and contralaterally adjacent to the hypoglossal nucleus. No stained neurones were found in the gigantocellular reticular nucleus. A group of stained neurones was located in the marginal nucleus of brachium conjunctivum and some were found in the raphé nuclei near obex. Cell profiles were of two types: medium-sized neurones with a triangular profile and 30-40 μm diameter, and fusiform neurones 10×50-70 μm. Convergence of descending cortical and trigeminal afferent inputs on interneurones located in the lateral borderzone of the trigeminal motor nucleus, i.e. the intertrigeminal area, is reported in the preceding paper. [ABSTRACT FROM AUTHOR]

Following large injections of horseradish peroxidase - wheat germ agglutinin in the pontine nuclei, corticopontine neurons in areas 18 and 19 were quantitatively mapped and flat maps showing the distribution of retrogradely labeled cells were constructed. The areal borders were defined either cyto- and myeloarchitectonically or from standard retinotopic maps presented in frontal sections (Tusa et al. 1981). Maps of the retinotopic organization in areas 18 and 19 (Tusa et al. 1979) were transferred to the present flat maps. Thus, the number and distribution of pontine projecting cells could be correlated with the retinotopic organization. The cell density (number of labeled cells per mm cortex) is in both areas highest in the cortex representing the lower and upper visual periphery and decreases towards the representation of the retinal central area. However, since in both areas 18 and 19 the visual field representation is twisted and portions of the visual field are magnified, the actual number of cells is higher in the cortex representing the central area and the lower medial visual field than in other parts. The cortex representing the lower hemifield contains approximately 2/3 (mean, N = 4) of the corticopontine cells in both areas. The average density of corticopontine cells increases from area 17 through 18 to 19, but the total number of cells within each of the areas is about the same (area 17∶ 18000 cells, area 18∶ 13400 cells, area 19∶ 17200 cells; mean, N = 4; data on area 17 from Bjaalie and Brodal, 1983). In conclusion, areas 17, 18 and 19 contribute about equally in quantitative terms to the pontine nuclei. Furthermore, assuming that the corticopontine neurons transmit spatially relevant information, there is a moderate overrepresentation of central vision and the lower medial visual field in the pontine projection from areas 18 and 19. This visual field representation is remarkably similar to that found in the corticopontine projection from area 17 (Bjaalie and Brodal 1983). [ABSTRACT FROM AUTHOR]

Retrograde transport of the fluorescent dyes Evans blue and 4,6-diamidino-2-phenyl indole (DAPI) has been used to study projections from the medullary raphe nuclei to the trigeminal nucleus caudalis and to the dorsolateral quadrant of the thoracolumbar cord in the rat. The majority of projecting neurones were found in n. raphe magnus (NRM) and its ventrolateral extensions over the pyramids and inferior olive. Double labelling experiments showed that 94% of raphe-trigeminal neurones sent a collateral branch to the nucleus in the contralateral brainstem. Similarly, 92% of raphetrigeminal neurones branched to supply the thoracolumbar cord. It is suggested that the widespread nature of the analgesia produced by electrical stimulation in NRM in conscious animals may be due to activation of a population of raphe neurones which inhibit the responses of neurones in the trigeminal nucleus and dorsal horn via an extensive system of collateral projections to these structures. [ABSTRACT FROM AUTHOR]

The projections from the brain stem reticular formation to the inferior olive have been studied in cats in which microinjections of horseradish peroxidase have been made into the inferior olive from a ventral approach. Retrogradely labelled cells were observed within the reticular formation proper of the medulla, pons and mesencephalon (within the nucleus reticularis parvicellularis, reticularis ventralis, reticularis gigantocellularis, reticularis lateralis, reticularis pontis caudalis, reticularis pontis oralis, cuneiformis and subcuneiformis). Labelled cells were also found within the lateral reticular nucleus (the nucleus of the lateral funiculus), the paramedian reticular and the perihypoglossal nuclei. The connections are bilateral (the projection from the lateral reticular nucleus is only contralateral). The observations demonstrate a more widespread origin for the reticulo-olivary fibres than has previously been shown and indicate that the medullary reticular formation is the area with the highest number of cells projecting to the olivary complex. [ABSTRACT FROM AUTHOR]

In tracing the macaque's ascending spinal connections by anterograde axonal flow, perikaryal labelling was also observed within the n. ruber pars magnocellularis as well as in the sensorimotor cortex. While neuropil labelling was demonstrated after single injections of leucine or proline, labelling of perikarya was only evident following proline injections. Perikaryal labelling is most likely to be due to uptake of label by axons and/or axons terminals within the injection field and subsequent retrograde axonal transport of radioactive compound to the parent cell bodies. Advantages and disadvantages of the uptake of label by axon terminals are discussed in relation to the use of H-proline for tracing neuronal connections. The selectivity of this event and its relationship to the suggested inhibitory functional role of proline and its metabolites is not clear and needs further investigation. [ABSTRACT FROM AUTHOR]

This study has investigated the synaptic interactions between hypoglossal motoneurons and substance P (SP)-immunoreactive terminals. Cholera toxin B conjugated to horseradish peroxidase was injected into the tip of the tongue on the right side of six ketamine-anesthetized cats. Two to five days later, the animals were killed. Cells containing HRP were labeled with a histochemical reaction utilizing tetramethylbenzidine (TMB) as the chromogen. TMB forms crystalline reaction products that are very distinct at the electron microscopic level. The tissues were then processed for immunocytochemisty using an antiserum against SP. The chromogen used in this case, di-aminobenzidine, yields amorphous reaction products. At the light microscopic level, labeled cells were observed primarily ipsilaterally in both intermediate and ventrolateral subdivisions of the hypoglossal nucleus. The majority of these labeled cells were seen at the level of obex. At the electron microscopic level, both asymmetric and symmetric synapses were observed. SP-immunoreactive nerve terminals formed asymmetric synapses with labeled dendrites and symmetric synapses with labeled perikarya. SP-labeled terminals also synapsed on unlabeled dendrites and somata. These are the first ultrastructural studies demonstrating synaptic interactions between hypoglossal motoneurons and SP terminals. These studies demonstrate that hypoglossal motoneurons that innervate intrinsic tongue muscles are modulated by SP and that SP may play a role in the control of fine movements of the tongue. [ABSTRACT FROM AUTHOR]

The localization and the transmitter phenotype of subparafascicular thalamic nucleus (Spf) neurons projecting to the inferior colliculus (IC) and to the spinal cord (Sp) were studied by using a retrograde fluorescent double labeling technique, and a combined technique of retrograde tracing and immunohistochemistry for tyrosine hydroxylase (TH) and glutamate decarboxylase (GAD). The cell population of Spf-IC neurons was totally differentiated from that of Spf-Sp neurons which have been reported to be dopaminergic. The former were densely distributed, small to medium sized cells and localized in the central portion of the Spf, while the latter were sparsely distributed, large cells and localized in the marginal portion of the Spf. Spf-IC neurons were completely devoid of TH immunoreactivity and, instead, approximately half of them showed GAD immunoreactivity. From these findings, it is concluded that the Spf is distinctly compartmentalized by the presence at least two separate neuronal subpopulations, which are distinguishable in terms of their cell size, distribution patterns, transmitter phenotypes and trajectories. [ABSTRACT FROM AUTHOR]