Distribution of cortical cells projecting to the main sensory trigeminal nucleus in the cat: A study with the horseradish peroxidase technique

The distribution of cortical cells projecting to the dorsal (Sd) or the ventral (Sv) part of the main sensory trigeminal nucleus of the cat was examined after injection of horseradish peroxidase into each nucleus. In both cases, labeled cells were densely distributed bilaterally in the face areas of the cortex. Comparing the extent of the distribution of labeled cells between these two cases, differences were seen in the bilateral presylvian sulcus and the dorsal part of the coronal gyrus on the contralateral side. In the presylvian sulcus, in the Sd case the distribution was seen throughout the dorsoventral extent of the lateral wall bilaterally and ipsilaterally in the dorsal part of the medial wall, whereas in the Sv case, most labeled cells were confined to the most ventral part of the lateral wall bilaterally, and on the contralateral side, labeled cells were confined to its rostral part. In the dorsal part of the coronal gyrus on the contralateral side, in the Sd case a few labeled cells were scattered only in its ventral portion, whereas in the Sv case, many labeled cells were distributed throughout the dorsoventral extent of the gyrus. In addition, in both cases a region devoid of labeling was found in the most ventral part of the coronal gyrus on the contralateral side; the ipsilateral counterpart was filled with dense labeling. All cortical labeled cells were pyramidal cells of various sizes in layer V.     

Soma size comparison of the trigeminal ganglion cells giving rise to the ascending and descending tracts: a horseradish peroxidase study in the cat

Soma size was compared between the trigeminal ganglion cells projecting to the main sensory trigeminal nucleus (Vs) and those projecting to the nucleus caudalis (Vc) of the spinal trigeminal nucleus in the cat after injection of horseradish peroxidase (HRP) into each nucleus. The results showed that the cells projecting to the Vc (Vc cells) contained by far a greater percentage of small cells than do those projecting to the Vs (Vs cells). In the Vc case, about one-half the total number of measured labeled cells were the smallest with a diameter less than 36 microns, whereas in the Vs cases, only a small proportion of the total number of measured labeled cells were that small. In addition, the results also made it clear that the Vs cells in the ophthalmic and maxillary divisions contained a higher percentage of larger cells than those in the mandibular division.     

Parabrachial nucleus neurons projecting to the lower brain stem and the spinal cord. A study in the cat by the Fink-Heimer and the horseradish peroxidase methods

Direct projections from the parabrachial nucleus (PBN) to the lower brain stem and the spinal cord were examined in the cat by the Fink-Heimer and the horseradish peroxidase (HRP) methods. After placing lesions in the PBN, many fine degenerated fibers were seen contralaterally in the ventromedial portions of the caudal pontine reticular formation, and ipsilaterally in the lateral portions of the facial nucleus, the regions around the hypoglossal nucleus, and the regions around the ambiguus nucleus; some degenerated fibers were traced ipsilaterally down to the spinal cord. Subsequently, HRP injections were attempted into these regions where many fine degenerated fibers were observed. In cats injected with HRP into the lateral portions of the facial nucleus, the regions around the hypoglossal nucleus, the regions around the ambiguus nucleus, or the first cervical cord segment, many HRP-labeled neurons were seen in the ventral portions of the PBN. The mean of the average soma diameters of the PBN neurons labeled with HRP injected into the regions around the hypoglossal nucleus or the first cervical cord segment was significantly larger than that of the PBN neurons labeled with HRP injected into the lateral portions of the facial nucleus or the regions around the ambiguus nucleus.     

The corticotrigeminal projection in the cat. A study of the organization of cortical projections to the spinal trigeminal nucleus

The projection from the cerebral cortex to the spinal trigeminal nucleus has been studied light microscopically in adult cats. Both orthograde degeneration and orthograde intra-axonal labeling techniques have been applied. Our results indicate that the projection from the coronal gyrus (face area of primary somatosensory cortex) to the spinal trigeminal complex is somatotopically organized. In subnucleus caudalis this somatotopy is organized dorsoventrally and appears to match the somatotopic distribution of the divisional trigeminal afferents. Hence cortical fibers originating from the posterior coronal gyrus (upper representation) project ventrolaterally into caudalis where division I trigeminal afferents terminate. Likewise cortical fibers from the anterior coronal gyrus (jaw and tongue representation) terminate dorsomedially in caudalis to overlap with division III trigeminal afferents. In contrast, the distribution of corticofugal afferents to the rostral spinal trigeminal subnuclei (pars interpolaris and oralis) is organized mediolaterally. Therefore in these subnuclei the cortical projection does not appear to overlap the dorsoventral lamination of the divisional trigeminal afferents. In addition, our results suggest that the cortical projection to subnucleus caudalis includes fibers which terminate in the marginal zone (lamina I) and its extensions into the spinal trigeminal tract (the interstitial cells of Cajal). We have been unable to document a projection from the proreate gyrus to the spinal trigeminal complex.     

Cortical neurons projecting to the cervical and lumbar enlargements of the spinal cord in young and adult rhesus monkeys

Cortical neurons projecting to cervical and lumbar segments of the spinal cord in five young and one adult monkeys were identified using the retrograde transport method following multiple unilateral injections of horseradish peroxidase (HRP) into the anterior horn at cervical and lumbar levels of the spinal cord. Somatotopically organized labeled neurons were found in the precentral and postcentral gyri, the rostral half of both the medial and dorsal aspects of area 5, the cingulate sulcus within the medial aspect of area 6, and the second somatosensory area within the lateral sulcus. All HRP-positive neurons were confined to cortical layer V or to a depth corresponding to the fifth layer in regions where delineation of cortical layers was obscured due to freezing or sectioning artifacts. Although cross-sectional areas of labeled neurons varied widely within each field, more large labeled neurons were present in the leg than in the arm subdivision of the precentral gyrus. HRP-positive neurons in the first and second somatosensory areas as well as those in the medial aspect of area 5 were of medium size, and those in the primary and supplementary motor areas as well as those within the dorsal aspect of area 5 were of medium or larger size.     

Fluorescent compounds as retrograde tracers compared with horseradish peroxidase (HRP). II. A parametric study in the peripheral motor system of the cat

Fluorescent compounds which are currently used as retrograde tracers were tested in the cat peripheral motor system and compared with horseradish peroxidase (HRP). The tracers were either injected into forelimb muscles or applied to the proximal end of transected forelimb nerves. The remaining muscles of the limb has been carefully denervated. Following intramuscular injection all fluorescent compounds labeled spinal cord motoneurons, the DAPI compounds labeled endothelial cells in addition. In the nerve application mode tracer positive motoneurons were only observed when propidium iodide (PI) and the DAPI compounds were used, whereas bisbenzimide (BB), nuclear yellow (NY) and primuline did not label any cells. The fluorescence of BB labeled motoneurons were predominantly located in the cytoplasma. NY positive motoneurons showed a different localization of the fluorescent label between the different neurons of the same motornucleus: in some neurons it was exclusively located in the nucleus, in others predominantly in the cytoplasma, in the majority in both compartments. The intracellular distribution of the BB and the NY label was independent of the pH of the fixation fluid. The fluorescent tracers labeled the motoneuronal cell columns in their complete rostrocaudal extent and in a position identical to the one obtained with HRP. However, some substances (PI, fast blue) labeled less motoneurons of a motornucleus than did HRP, none of the fluorescent tracers labeled more. The results are discussed under several aspects: use of the investigated fluorescent compounds as single tracers; use of several tracers in the same animal to map collateral projections of one and the same neuron; use of several tracers in the same animal to establish the topographical relation between several independent neuronal populations.     

A study of the origin of brain stem projections to monkey spinal cord using the retrograde transport method.

We identified brain stem neurons projecting to cervical and lumbar levels of the spinal cord in young rhesus monkeys using the retrograde transport method. The somatotopic organizations of the red nucleus and lateral vestibular nucleus were clarified. In addition, the presence of bulbospinal neurons in the medial vestibular nucleus; the nucleus of the tractus solitarius; the medial and lateral reticular formations; the raphe nuclei magnus, obscurus, and pallidus; the hypothalamus; and the nuclei of the locus ceruleus and subceruleus was confirmed.     

Distinct patterns of neuronal inputs and outputs of the juxtaparaventricular and suprafornical regions of the lateral hypothalamic area in the male rat

We have analyzed at high resolution the neuroanatomical connections of the juxtaparaventricular region of the lateral hypothalamic area (LHAjp); as a control and in comparison to this, we also performed a preliminary analysis of a nearby LHA region that is dorsal to the fornix, namely the LHA suprafornical region (LHAs). The connections of these LHA regions were revealed with a coinjection tract-tracing technique involving a retrograde (cholera toxin B subunit) and anterograde (Phaseolus vulgaris leucoagglutinin) tracer. The LHAjp and LHAs together connect with almost every major division of the cerebrum and cerebrospinal trunk, but their connection profiles are markedly different and distinct. In simple terms, the connections of the LHAjp indicate a possible primary role in the modulation of defensive behavior; for the LHAs, a role in the modulation of ingestive behavior is suggested. However, the relation of the LHAjp and LHAs to potential modulation of these behaviors, as indicated by their neuroanatomical connections, appears to be highly integrative as it includes each of the major functional divisions of the nervous system that together determine behavior, i.e., cognitive, state, sensory, and motor. Furthermore, although a primary role is indicated for each region with respect to a particular mode of behavior, intermode modulation of behavior is also indicated. In summary, the extrinsic connections of the LHAjp and LHAs (so far as we have described them) suggest that these regions have a profoundly integrative role in which they may participate in the orchestrated modulation of elaborate behavioral repertoires.