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PubMed1979

Spinal projections from the mesencephalic and pontine reticular formation in the North American Opossum: a study using axonal transport techniques.

The results from several experimental approaches lead to the following conclusions. The nucleus cuneiformis projects to at least lumbar levels of the spinal cord. Its axons course through the ipsilateral sulcomarginal and ventral funiculi to distribute within lamina VIII and adjacent portions of lamina VII. Neurons within the nucleus reticularis pontis (RP), particularly within more medial parts of the nucleus, project through comparable routes to the same laminae. In addition, however, neurons within the lateral and dorsolateral RP relay through the lateral and dorsolateral funiculi, ipsilaterally, and the dorsolateral funiculus, contralaterally. Axons could be traced from the dorsolateral tracts to laminae IV through VII, lamina X and, in some instances, to laminae I and II. Injections of the dorsolateral pons also label the intermediolateral cell column and an area presumed to be the sacral parasympathetic nucleus. Many of the neurons which contribute to the contralateral bundle are located adjacent to the ventral nucleus of the lateral lemniscus. The nucleus reticularis gigantocellularis projects mainly via the sulcomarginal, ventral and lateral funiculi to laminae VIII and adjacent portions of lamina VII. The nucleus reticularis gigantocellularis pars ventralis innervates the same laminae; but, in addition, projects heavily to laminae I and II, to lateral portions of laminae IV through VII; to laminae IX and X and to the intermediolateral cell column. Axons destined for laminae I and II, as well as IV through VII and X, traverse the dorsolateral funiculi as described for the cat by Basbaum et al. ('78). Neurons within the nucleus reticularis parvocellularis project to cervical levels, mainly through the ventral funiculi. In general our results show that reticulospinal projections are more complex than suggested by degeneration methods and that laminae I, II. lateral parts of laminae IV-VII, laminae IX and X, as well as the intermediolateral cell column and sacral parasympathetic nucleus are targets of axons from specific areas.

Animals↗
PubMed1980

Ascending projections from the lateral descending and common sensory trigeminal nuclei in python.

The primary sensory trigeminal system of Python is characterized by the presence of an additional nucleus which is involved in processing data obtained by infrared sensors. This so-called lateral descending nucleus (LTTD) is strictly separated from the nuclei of the common sensory trigeminal system. The present study was undertaken in order to establish the relation between the two sensory trigeminal systems and higher brainstem structures. Further we studied whether the projections of these two systems remain separated at higher brainstem levels. It is shown that the organization of particularly the thalamus is characterized by the presence of specific projection areas of each of the two trigeminal systems: a) the ability of infrared preception is reflected particularly in the presence of an unique thalamic nucleus: the nucleus pararotundus and probably also in the enlargement of nucleus rotundus; and b) distinct subnuclei in the thalamic ventral nuclear complex are related to the various nuclei of the common sensory trigeminal system. The main ascending projection of LTTD runs via a distinct tract to the central gray layer (SGC) of the contralateral tectum mesencephali and the nucleus pararotundus (PR). Rostrally, numerous fibres decussate again via the tectal commissure and terminate ipsilaterally in the rostral part of SGC and in PR. The ascending projections of the common sensory trigeminal nuclei resemble those of mammals by gaining thalamic nuclei (ventral nuclear complex). No projections of the tectum nor to the striatum (like in birds) were observed. The two sensory trigeminal systems remain separately organised, in their projections as well as in their structure. No major connection between the two trigeminal system is present.

Animals↗
PubMed1980

Projections of the nucleus of the basal optic root in the pigeon: an autoradiographic and horseradish peroxidase study.

The efferent projections of the nBOR complex, have been studied with both anterograde autoradiographic and retrograde horseradish peroxidase (HRP) techniques. The nBOR complex includes three distinct subdivisions: the nucleus of the basal optic root (nBOR), the nBOR pars dorsalis (nBORd) and the nBOR pars lateralis (nBOR1). Unilateral injections of 3H-leucine or 3H-proline/3H-leucine mixtures into the nBOR complex have demonstrated prominent bilateral projections upon (1) the vestibulocerebellum, (2) the inferior olivary complex, (3) the oculomotor nuclear complex, (4) the nucleus interstitialis, contralateral projections upon (5) the contralateral nBOR complex and ipsilateral projections upon (6) a pretectal nucleus, the nucleus lentiformis mesencephali, pars magnocellularis. Unilateral injections of HRP confined to folia IXc,d and paraflocculus of the cerebellum, the contralateral nBOR complex or the nucleus lentiformis mesencephali resulted in retrograde labeling of predominantly medium and large size cells within the entire nBOR complex. Unilateral injections of HRP within the inferior olive resulted in retrograde labeling of small, spindle-shaped cells within nBOR and nBORd. Unilateral injections of the oculomotor complex which included the trochlear nucleus resulted in retrograde labeling of small cells within the ipsilateral nBORd and predominantly medium and large cells in the contralateral nBOR. The displaced ganglion cells of the retina give rise to a prominent and distinct projection upon the nBOR complex (Karten et al., '77). The nBOR complex in turn projects upon the oculomotor nuclear complex, the nucleus interstitialis and the vestibulocerebellum, regions which have been implicated in oculomotor function. These findings strongly suggest that the displaced ganglion cells and the accessory optic system have a major influence upon oculomotor reflexes including eye and head movements.

Animals↗
PubMed1980

The efferent projections of the central nucleus and the pericentral nucleus of the inferior colliculus in the cat.

The efferent projections of the central nucleus of the inferior colliculus (ICC) and the pericentral nucleus of the inferior colliculus (ICP) were examined by placing restricted injections of anterograde tracers at electrophysiologically defined loci in the inferior colliculus (IC) of the cat. It was found that single loci in the ICC projected bilaterally onto the ventral division of the medial geniculate body (MGB) in the form of caudorostrally oriented sheets of terminals. The ICC loci also projected bilaterally onto the MGB in the form of caudorostrally oriented columns of terminals; these columns had their caudal aspects located in the medial and their rostral aspects located in the deep dorsal nucleus of the dorsal division. The caudal aspect of the sheets of terminals in the ventral division was folded and passed through both pars lateralis and pars ovoidea of the ventral division. Every component of the ICC-to-MGB projection was cochleotopically ordered. Periodic discontinuities of two types were noted in the projections of ICC onto pars lateralis (VI) of the ventral division. The one type of periodic discontinuity sometimes approximated bands oriented caudorostrally in the caudal aspect of VI. The second type of discontinuity was of very thin parallel columns of more intense labeling oriented rough dorsoventrally and oblique or normal to the first type of discontinuity. Injections in the ICP produced autoradiographic labeling in the caudal dorsal nucleus (Dc) of the dorsal division of the MGB. Thus the ICC-to-MGB and ICP-to-MGB projections are segregated. The efferent connections of the IC with other brainstem auditory structures were noted.

Animals↗
PubMed1981

Morphology of the giant interneurons and cercal nerve projections of the American cockroach.

We have investigated the morphology of the giant interneurons (GIs) and the main sensory projections to these interneurons in the American cockroach. These neurons are thought to mediate the animal's escape behavior. We describe here the dendritic branching pattern of each of the 14 GIs (7 bilateral pairs) in the terminal ganglion, the pattern of projection of the cercal sensory nerve, and the overlap of the cercal projections with the dendrites of the GIs. Visualization of the GIs and cercal nerve projection was accomplished by single cell injection and axonal backfilling with cobalt. Comparisons of the same identified GI in different animals show the position of the soma and the locations and orientations of the major processes are characteristic for each GI. The axons of the cercal nerve project to a well-defined ipsilateral region of the terminal ganglion. After entering the terminal ganglion, the cercal afferents split into lateral and medial tracts. The projections of the lateral cercal tract overlap extensively with the dendritic fields of the GIs. In contrast, the medial tract does not overlap the dendritic fields of the GIs in the posterior portion of the ganglion and shows only a small degree of overlap in the anterior portion. Correlations between physiological properties of the GIs and cercal afferents are discussed in relation to our anatomical findings.

Afferent Pathways↗
PubMed1981

Direct retinal projections to the hypothalamus, piriform cortex, and accessory optic nuclei in the golden hamster as demonstrated by a sensitive anterograde horseradish peroxidase technique.

The central projections of the retinal ganglion cells of the golden hamster were examined using horseradish peroxidase (HRP) as the anterograde tracer molecule. Following monocular injections of HRP into the vitreous, retinofugal fibers were histochemically demonstrated using the chromagen tetramethylbenzidine. This procedure, being more sensitive than the 3H-amino acid radioautographic technique, provided a clear demonstration of previously controversial retinal projections, clearer definition of established projections, and the discovery of new retinal pathways. An inferior accessory optic system was shown to be unequivocally present in this species and to consist of both crossed and uncrossed components. A direct retinal projection to the suprachiasmatic nucleus (SCN) of the hypothalamus was confirmed in this study. But the distribution of terminals as seen by this procedure was substantially different than previously reported; both rostrocaudal and mediolateral asymmetries in the distribution of label between the ipsilateral and contralateral SCN were observed. Substantial differences in the retinal projection to the SCN in the hamster and the rat were also noted. It is suggested that these differences may reflect the different effects photic input has on the neuro-endocrine-gonadal axis in these two species. Finally, labeled retinal axons were followed leaving the optic tract and coursing anteriorly through the plexiform layer of the piriform cortex; other labeled fibers were seen to enter the septal region. The physiological significance of these previously undescribed retinal projections is not known.

Animals↗
PubMed1981

Descending projections from the spinal and mesencephalic nuclei of the trigeminal nerve to the spinal cord in the cat. A study with the horseradish peroxidase technique.

Descending projections from the spinal (Vsp) and the mesencephalic nuclei (Vme) of the trigeminal nerve to the spinal cord were studied by means of the retrograde horseradish peroxidase technique in the cat. The number of labeled neurons was largest in the case of high cervical injections and decreased as the injections were placed caudally. Small laminae III and IV neurons of the nucleus caudalis (Vc) were labeled ipsilaterally following injections placed as caudally as the middle cervical segments (C4-C5). Lamina I (marginal) neurons of the Vc were labeled ipsilaterally after injections at the middle thoracic level (T6) but those of C1 were labeled after lumbar injections (L3). Lamina V neurons of C1 and the medullary counterparts were labeled bilaterally after injections placed caudally to thoracic segments. A few small neurons were labeled in the ipsilateral nucleus interpolaris (Vi) after injections placed as caudally as the middle cervical segments (C6). Among the subdivisions of the Vsp, the labeled neurons were most numerous in the nucleus oralis (Vo). They were medium-sized and large, and appeared bilaterally, with an ipsilateral predominance at the level of the superior olive. The great majority projected to the cervical segments but a few also projected to the lower cervical to the thoracic segments (C8-T9). Neurons of the Vme projected ipsilaterally to the upper cervical segments (C1-C3). No projections were found from the principal sensory nucleus. The present study suggests that the trigeminospinal projections of the Vsp and the Vme are composed of various cells of origin and thereby subserve not only the trigeminospinal reflex but other unknown functions.

Animals↗
PubMed1981

Spinal projections from the medullary reticular formation of the North American opossum: heterogeneity.

Retrograde and orthograde transport techniques show that the nucleus reticularis gigantocellularis pars ventralis and the nucleus reticularis gigantocellularis project the entire length of the spinal cord. Double-labelling methods show that some of the neurons in each area innervate both cervical and lumbar levels. There is evidence, however, that neurons in the lateral part of the nucleus reticularis gigantocellularis pars ventralis and the dorsal extreme of the nucleus reticularis gigantocellularis project mainly to cervical and thoracic levels. The autoradiographic method shows that the above nuclei supply direct innervation to somatic and autonomic motor columns as well as to laminae V-VIII and X. The nucleus reticularis gigantocellularis pars ventralis provides additional projections to lamina I and the outer part of lamina II. Several areas of the medullary reticular formation project mainly, and in some cases exclusively, to cervical and thoracic levels. These areas include the nucleus reticularis parvocellularis, the nucleus reticularis lateralis, the nucleus retrofacialis, the nucleus ambiguus, the nucleus lateralis reticularis, caudal parts of the nuclei reticularis medullae oblongatae dorsalis and ventralis, and the nucleus supraspinalis. Autoradiographic experiments reveal that neurons in the ventrolateral medulla, particularly rostrally (the nucleus reticularis lateralis and neurons related to the nucleus lateralis reticularis), innervate sympathetic nuclei. Our results indicate that spinal projections from bulbar areas of the reticular formation are more complicated than previously supposed. Axons from separate areas project to different spinal levels and in some cases to different nuclear targets. These data are in conformity with the evolving concept of reticular heterogeneity.

Animals↗
PubMed1981

Retinal projections in the goldfish: a study using cobaltous-lysine.

Cobaltous lysine applied to the distal stump of a severed optic nerve was used to study the retinal projections of normal adult goldfish. Both the termination areas of optic axons and the pathways they traveled were established. Contrary to previous descriptions of the goldfish visual system, the optic nerves do not decussate completely at the optic chiasm. Fascicles that entered the ipsilateral optic tract innervated targets in the ipsilateral thalamus and optic tectum. Other optic fibers crossed the posterior commissure from the contralateral side of the brain and also innervated the ipsilateral tectum and thalamus. In addition, optic fibers bilaterally innervated a hypothalamic target in close proximity to the infundibulum that may correspond to the nucleus tuberis lateralis. The contralateral preoptic region contained two discrete areas of innervation, each served by separate fascicles. The ipsilateral preoptic region was similarly innervated, but more sparsely. Fibers that entered the controlateral ventral thalamus originated from three fascicles and terminated in three distinct targets. In contrast, three targets in the contralateral dorsal thalamus were served by one fascicle, and fibers passed from one nucleus to the other two. Innervation of the ipsilateral thalamus was similar to that seen contralaterally. Each main optic tract divided into three tracts, two of which entered the optic tectum, while the other innervated several pretectal areas. Other fibers innervated an accessory optic nucleus located near nucleus glomerulosus. The contralateral tectum contained numerous radially oriented optic fascicles. These fascicles represented optic fibers that left thalamic and pretectal targets to enter the optic tectum from beneath the stratum periventriculare. Optic fibers were also observed in the transverse commissure, tractus rotundus, horizontal commissure, tectobulbar tract, and fasciculus retroflexus. Therefore, it appears that many of the anomalous projections seen after tectal ablation or after optic nerve crush are not in fact aberrant. Such projections probably reflect the presence of unusually large numbers of optic fibers in tracts that normally contain optic axons, as well as increased innervation of areas that normally receive sparse retinal projections. Filled tectal cells that could represent cells projecting to the retina were not observed in either tectal lobe. The ipsilateral retinal projections could not be attributed to cobaltous-lysine being transneuronally transported in readily detectable amounts.

Animals↗
PubMed1982

Immunohistochemical identification of neurons in the paraventricular nucleus of the hypothalamus that project to the medulla or to the spinal cord in the rat.

A method that allows the concurrent localization of an antigen and a retrogradely transported fluorescent dye (true blue) was used to identify, immunohistochemically, cells in the paraventricular nucleus of the hypothalamus (PVH) that project to autonomic centers in the brainstem or in the spinal cord of the adult albino rat. After placing injections of true blue in the dorsal vagal complex or in upper thoracic segments of the spinal cord, series of evenly spaced sections through the PVH were stained with antisera directed against oxytocin, vasopressin, somatostatin, methionine-enkephalin, or leucine-encephalin. The results indicate that both oxytocin- and vasopressin-stained cells in the PVH project to the spinal cord and (or) to the dorsal vagal complex, although about three times as many oxytocin-stained cells were doubly labeled after injections centered in either terminal field. The oxytocin- and vasopressin-stained cells that give rise to these long descending projections were found primarily in caudal part of the parvocellular division of the PVH, where immunoreactive cells were shown to be significantly smaller than oxytocin- and vasopressin-stained cells in parts of the nucleus that project to the posterior pituitary. Small populations of cells in the PVH that cross-react with antisera against somatostatin, leucine-enkephalin, or methionine-enkephalin were also shown to project directly to the region of the dorsal vagal complex and to the spinal cord, and to have a unique distribution within the PVH. Collectively, the total number of doubly labeled cells that were identified in these experiments accounts for only about one-fourth of the total number of PVH neurons with long descending projections, thus suggesting that additional neuroactive substances are contained within these pathways.

Animals↗
PubMed1982

Spinocerebellar projections to lobules III to V of the anterior lobe in the cat, as studied by retrograde transport of horseradish peroxidase.

Spinocerebellar tract (SCT) neurons projecting to lobules III to V of the cerebellar anterior lobe were identified by the retrograde horseradish peroxidase technique. SCT neurons projecting to lobule III with crossed ascending axons were located mainly in the central cervical nucleus (CCN), the medial part of lamina VII of L6 to the caudal segments, and the dorsal horn (lamina V) and ventral horn (lamina VIII) of the sacral-caudal segments. Spinal border cells with crossed ascending axons also projected to lobule III. SCT neurons projecting to this lobule with uncrossed ascending axons were located in the medial part of lamina VI of the cervical segments and the middle part of lamina VII of C6 to T1, lamina V of the lower cervical, thoracic and the lumbar segments, Clarke's column including marginal neurons, and the medial part of lamina VI of L5 and L6. These neuronal groups also projected to lobule IV, except for those present caudal to L6 (in the medial part of lamina VII, and laminae V and VIII of the sacral-caudal segments). A far smaller number of similar neurons projected to lobule V. Injections of HRP restricted to the vermal region labeled mainly neurons in the CCN and Clarke's column while restricted injections to the intermediate-lateral regions labeled ipsilaterally spinal border cells, lamina V neurons, and Clarke column neurons, especially of the lumbar segments as well as marginal neurons of this column.

Afferent Pathways↗
PubMed1982

Projections of the dorsal lateral geniculate and lateral posterior nuclei to visual cortex in the rabbit.

The origin and terminations of thalamic inputs to the striate cortex and the occipital cortex of the rabbit were studied using both anterograde autoradiographic techniques and retrograde transport of horseradish peroxidase (HRP). After injections of [3H]-leucine into the dorsal lateral geniculate nucleus (DLGN) the transport of radiolabeled material was demonstrated in separate loci in both the striate and the occipital cortex. In both these cortical areas, the principal site of geniculocortical termination was in lamina IV with some diminished input spreading into laminae II-III and a light termination in layer I overlying the lamina IV termination. Layer VI of striate cortex received a substantial projection from DLGN while infragranular laminae of occipital cortex received a similar although lighter and more diffuse projection. The lateral posterior nucleus (LPN) was similarly demonstrated to project to both striate and occipital cortices, the projection terminating principally in lamina IV of occipital cortex, lamina V of striate cortex, and layer I over a large, continuous area of the posterior pole of the cortex. Moreover, a projection from LPN to the retrosplenial cortex medial to the striate area was consistently seen. The autoradiographic demonstration of a projection from DLGN and LPN to both striate cortex and occipital cortex was corroborated by the retrograde studies. Following the injection of HRP into either the striate or occipital cortex, columns of retrogradely filled somata were identified in both the DLGN and LPN. The location of the column of labeled neurons within each nucleus varied predictably with the location of the injection in either the striate or the occipital cortex.

Animals↗
PubMed1982

Modification of visual callosal projections in rats.

The effects of a variety of developmental manipulations on the distribution of the callosal pathway to visual cortex were examined by using the Fink Heimer technique in adult rats. First, the callosal projections in albino and pigmented rats were compared and found to be similar. The callosal pathway was limited in area 17 to a region adjoining its lateral border with area 18a. Second, dark-reared rats were found to have normal callosal projections. Third, rats bilaterally enucleated at birth and expanded callosal inputs within area 17. Fourth, monocular enucleation at birth produced an expanded callosal pathway to area 17 contralateral to the enucleation and normal callosal projections to the opposite hemisphere. The expanded callosal inputs after enucleation showed a patchy distribution and usually avoided the most medial part of area 17. Fifth, a reduction in the callosal projections to the area 17/18a border was found after neonatal unilateral optic tract lesions. Sixth, expanded callosal inputs to area 17 were found following unilateral thalamic lesions at birth. The abnormal projection occupied mainly layers IV and III. The results of the different experiments indicate that the detailed distribution of the visual callosal projection within area 17 depends heavily on the organization of the retinogeniculocortical pathways to each hemisphere.

Animals↗
PubMed1983

Retinal ganglion cell size groups projecting to the superior colliculus and the dorsal lateral geniculate nucleus in the North American opossum.

The retinal ganglion cells projecting to the superior colliculus (SC) and dorsal lateral geniculate nucleus (LGNd) of the North American opossum (Didelphis virginiana) were studied by using the retrograde transport of horseradish peroxidase (HRP). The four ganglion cell size groups recognized previously were found to project in systematically different ways. After injections of HRP into the superior colliculus, labeled cells were seen in nasal retina contralateral to the injection and in temporal retina both ipsilateral and contralateral to the injection. In contralateral nasal retina cells of all size classes were labeled, while in contralateral temporal retina small (8-14 micrometers diameter), small-medium (15-19 micrometers diameter), and large (greater than 24 micrometers diameter) cells were labeled but few, if any, large-medium (20-24 micrometers diameter) cells were labeled. In ipsilateral temporal retina, soma size groups labeled included small-medium, large-medium, and large cells, but very few small cells. A nasal-temporal difference in the soma size of ganglion cells projecting to the SC was found: Labeled cells in temporal retina were 1.7-4.2 micrometers larger than their counterparts in nasal retina. Following injection of HRP into the LGNd, label was seen in contralateral nasal and ipsilateral temporal retina with no label seen in contralateral temporal retina. The labeled cells were small-medium, large-medium, and large. No small ganglion cells were labeled from the LGNd. A small nasal-temporal soma size difference in retinal ganglion cells projecting to the LGNd was seen: labeled cells in temporal retina were 1.0-2.1 micrometers larger than in nasal. It is concluded that all four ganglion cell size groups in the opossum project to the SC, but that only the three largest project to the LGNd.

Animals↗
PubMed1983

A cobalt study of medullary sensory projections from lateral line nerves, associated cutaneous nerves, and the VIIIth nerve in adult Xenopus.

The medullary projections of the anterior lateral line nerve, dorsal branch (Alln.d), the posterior lateral line nerve, dorsal branch (PLLn.d), associated cutaneous nerves, and the VIIIth nerve in Xenopus laevis have been delineated by axonal infusion of cobalt chloride and silver intensification. The peripheral innervation of the posterior lateral line sense organs has also been traced. From wholemount and sectioned preparations, we describe three central projections, extending the length of the ipsilateral medulla but occupying distinct zones: lateral line afferents dorsomedially, stato-acoustic dorsolaterally, and cutaneous ventrolaterally. Arborizations of ALLn.d and PLLn.d afferents are morphologically similar, intermingling throughout the lateral line lobe. Each divides into ascending and descending limbs bearing collaterals, which terminate in the lateral line neuropile and nucleus. Evidence is presented for directional and positional mapping in the branching of individual PLLn.d afferents and for topography in the ALLn.d projection. Second-order neurones have been identified by transneuronal staining and their axons traced into the contralateral torus semicircularis. The morphology of efferent neurones is also described. Rostral branches of PLLn.d also contain cutaneous afferents which run through the medulla into the spinal cord, similar to the nerve V (cutaneous) projection. In nerve VIII preparations, the projection to the compact cochlear nucleus and the massive vestibular projection are identified. Cutaneous and vestibular but not lateral line afferents extend into the cerebellum. The separation of VIIIth nerve and lateral line afferents in Xenopus medulla is considered as evidence against the validity of the acousticolateralis concept. Information processing in the lateral line lobe is discussed in relation to connectivity patterns between first- and second-order neurones.

Afferent Pathways↗
PubMed1983

Projections of nucleus caudalis and spinal cord to brainstem and diencephalon in the hedgehog (Erinaceus europaeus and Paraechinus aethiopicus): a degeneration study.

In the light of hypotheses related to the evolution of pain-carrying systems in mammals, terminal projection fields in brainstem and diencephalon of efferents of nucleus caudalis (NC) of the spinal trigeminal complex and spinal cord were determined in hedgehog by using Nauta-Gygax and Fink-Heimer silver techniques for degeneration. Unilateral NC lesions resulted in medullary degeneration in the ventral portion of NC contralaterally and bilaterally in cuneate nucleus (CU) and reticular formation. Pontine degeneration was noted ipsilaterally in medial (PBM) and lateral (PBL) parabrachial, facial motor (VII), and interpolar, oral, and main sensory trigeminal nuclei; degeneration in reticular formation was bilateral. Midbrain degeneration was seen bilaterally in caudal superior colliculus (SC), inferior colliculus (IC), periaqueductal gray, and tegmentum. In thalamus, projections to ventroposterior nucleus (VP) were contralateral and concentrated in a crescent extending along the lateral one-third-to-one-half and ventral border of the nucleus. Bilateral degeneration fields were noted in a dorsomedial sector of the "ventral nuclear field," posterior complex (PO), and mediodorsal nucleus (MD), the degeneration always heavier contralaterally in these nuclei. Sparse degeneration was noted in the medial most portions of the medial geniculate nuclei bordering PO and VP. In rostral diencephalon, bilateral degeneration was traced from the inferior thalamic peduncle to the lateral hypothalamic area (LH). Unilateral spinal cord lesions made between C7 and T1 vertebrae resulted in medullary degeneration in NC contralaterally, ipsilaterally in CU and lateral cuneate nucleus, and bilaterally in gracile nucleus, inferior olivary complex, and reticular formation. Pontine degeneration was limited to ipsilateral PBL and bilaterally to VII. Midbrain degeneration was found bilaterally in IC, SC, nucleus sagulum, and tegmentum; a minor projection was noted in interpeduncular nucleus. In thalamus, projections were confined to ipsilateral PO and zona incerta. In rostral diencephalon bilateral fields were noted in LH. NC terminations in PO and VP parallel results of research in hedgehogs on thalamic projections of the dorsal column nuclei (Jane and Schroeder, '71), and particularly the location in VP of most cells responsive to stimulation of the face (Erickson et al., '67). This suggests that somatic input from NC, some of which may be pain-specific, reaches thalamic areas, a portion of whose neurons are characterized as polymodal and at least partially convergent for somatotopy. These results are consistent with the thesis that specific sensory thalamic nuclei evolved from a diffuse sensory region. Response properties of neurons in the dorsomedial portion of the ventral nuclear field, an area which are also received NC efferents, are not known. Last, NC projections to MD and LH implicate the role of "limbic" aspects of nociception.

Animals↗
PubMed1983

Cytoarchitecture and topographic projections of the gustatory centers in a teleost, Carassius carassius.

The neuronal connections in the central gustatory system of the crucian carp were examined by means of degeneration and HRP methods. Cell morphology in the primary gustatory lobes was studied in Golgi-impregnated material. Medium-sized neurons of the facial lobe emit axons which project to the secondary gustatory nucleus. The nucleus intermedius facialis of Herrick ('05) projects bilaterally. Large neurons send axons through the spinal trigeminal tract to terminate in the spinal trigeminal nucleus and in the medial funicular nucleus. In the vagal lobe, second-order neurons for the ascending projections are located in the superficial part of the sensory zone. These neurons project exclusively to the ipsilateral secondary gustatory nucleus. Neurons located in the deeper part of the sensory zone send axons to the motor zone and to the brainstem reticular formation to form short reflex arcs. The glossopharyngeal lobe has similar neuronal connections to the vagal sensory zone. Both facial and vagal lobes receive afferent projections from the following central structures: nucleus posterioris thalami, nucleus diffusus lobi inferioris, optic tectum, motor nucleus of the trigeminal nerve, medullary reticular formation, and the gray matter of the upper spinal cord. The facial lobe has an additional afferent from the mesencephalic reticular formation. The major sources to the medullary gustatory lobes are the nucleus posterioris thalami and nucleus diffusus lobi inferioris. Each type of neuron classified by morphology and location in the facial, glossopharyngeal, and vagal lobes was correlated with its particular destination. Topographic projections were demonstrated in the secondary and tertiary gustatory centers.

Afferent Pathways↗
PubMed1983

Thalamocortical projections in the reeler mutant mouse.

The normal radial distribution of the different neocortical cell classes is inverted in the reeler mutant mouse. The organization of the thalamocortical projection in adult reelers has been investigated by using anterograde degeneration techniques. Thalamocortical axons follow anomalous trajectories to their target cytoarchitectonic fields in the mutant. After leaving the internal capsule, the axons ascend in sigmoid-shaped fascicles to enter a fiber stratum near the cortical surface. The axons course through this superficial stratum until they reach their target fields and then descend to terminate in deeper cortical planes. In the normal animal, by contrast, the axons course tangentially at the interface of the cortex with the subcortical white matter; upon reaching their target fields, they ascend to terminate more superficially in the cortex. Thus, in both genotypes the tangential portions of the axon trajectories pass through the polymorphic cell population. Both with respect to degree of divergence and the radial distribution of terminals within the different cytoarchitectonic fields, the thalamocortical projection in reeler, like that in the normal animal, appears to be composed of two distinct axon classes. The "class I" axons, the less-divergent system which terminates densely in two or three tiers within the cortex, are the subject of the present analysis. The "class I" projections form an orderly cortical representation of the thalamus: Despite distortions in the topography of the reeler thalamus and cortex, both the nucleus to field relationships and the detailed topologic organization of the projection appear to be normal. The terminals of class I projections are distributed in radially segregated tiers that resemble the tiered pattern of termination as in normal mice, and there are field-specific variations in the tiers that, like those of normal mice, are systematically related to variations of cortical cytoarchitecture. Thus, similar mechanisms, which may depend in part on the interaction of ingrowing axons with specific postsynaptic cell surfaces, must determine the restricted radial distribution of thalamocortical projections in both genotypes. However, there is an abnormal mix of somata and dendrites at all radial levels of the mutant cortex, suggesting that the spatial domain of termination of thalamocortical axons may be governed to some extent by factors other than the distribution of specific prospective postsynaptic cell surfaces. The reeler mutation alters the radial but not the tangential structure of the neocortex, suggesting that these two aspects of cortical organization develop under the control of independent mechanisms. The present results suggest that despite the anomalies of radial position, normal relationships between thalamocortical afferents and distinct classes of postsynaptic elements with characteristic radial distributions are largely conserved in reeler. Certain types of aberrant connections are highly probable, however.

Animals↗