Showing papers on "Cuneate nucleus published in 1979"

Sources of subcortical projections to the superior colliculus in the cat.

Abstract: A comprehensive search for subcortical projections to the cat superior colliculus was conducted using the retrograde horseradish peroxidase (HRP) method. Over 40 different subcortical structures project to the superior colliculus. The more notable among these are grouped under the following categories. Visual structures: ventral lateral geniculate nucleus, parabigeminal nucleus, pretectal area (nucleus of the optic tract, posterior pretectal nucleus, nuclei of the posterior commissure). Auditory structures: inferior colliculus (external and pericentral nuclei), dorsomedial periolivary nucleus, nuclei of the trapezoid body, ventral nucleus of the lateral lemniscus. Somatosensory structures: sensory trigeminal complex (all divisions, but mainly the γ division of nucleus oralis), dorsal column nuclei (mostly cuneate nucleus), and the lateral cervical nucleus. Catecholamine nuclei: locus coeruleus, raphe dorsalis, and the parabrachial nuclei. Cerebellum: medial, interposed, and lateral nuclei, and the perihypoglossal nuclei. Reticular areas: zona incerta, substantia nigra, midbrain tegmentum, nucleus paragigantocellularis lateralis, and the hypothalamus. Evidence is presented that only the parabigeminal nucleus, the nucleus of the optic tract, and the posterior pretectal nucleus project to the superficial collicular layers (striatum griseum superficiale and stratum opticum), while all other afferents terminate in the deeper layers of the colliculus. Also presented is information concerning the rostrocaudal distribution of some of these afferent connections. These findings stress the multiplicity and diversity of inputs to the deeper collicular layers, and more specifically, identify multiple sources of the physiologically well-known representations of the somatic and auditory modalities in the colliculus.

An autoradiographic examination of the central distribution of the trigeminal, facial, glossopharyngeal, and vagal nerves in the monkey.

Abstract: The central distributions of primary afferent axons in cranial nerves V, VII, IX, and X have been re-examined autoradiographically after 3H-proline injections into their peripheral ganglia. Fiber-labeling after subtotal injections of the trigeminal ganglion, besides confirming earlier classical descriptions, suggests that trigeminal fibers of the ophthalmic and mandibular (but not maxillary) branches enter the ventrolateral part of the nucleus of the solitary tract (NST). Injection of VII's geniculate ganglion labels fibers which both ascend and descend upon reaching NST. The ascending fibers distribute in a compact and circumscribed zone immediately dorsal to the spinal V nucleus as far rostral as the caudal pole of the principal trigeminal nucleus. The descending fibers distribute to the lateral NST rostral to the level at which X joins the solitary tract. For a short distance caudal to this level, sparse label is confined to a small part of lateral NST ventral to the solitary tract, which corresponds to the zone receiving direct trigeminal afferents. Fiber-labeling after injections of the ganglia of nerves IX and X suggest the following. Although, upon reaching NST, a few fibers of either IX or X ascend as far rostrally as had those of VII, both have a much larger descending component which distributes to more caudal levels of NST. Most of IX's axons appear to end in the lateral NST; only a few travel as far as the obex. Fibers of X, on the other hand, are abundant in the medial and commissural parts of NST. Moreover, only X appears to have a crossed projection in the commissural nucleus and caudal portion of the contralateral NST. A few fibers of vagal origin also appear to enter the area postrema. Whereas fibers of X appear to constitute the solitary tract, few if any fibers of VII or IX travel within that fascicle. A significant descending components of labeled fibers appears in the spinal V tract when the superior ganglion of either IX or X is injected. These fibers distribute mainly in the pars caudalis of the spinal V nucleus and, to a lesser degree, the cuneate nucleus.

Organization of trigeminothalamic tracts and other thalamic afferent systems of the brainstem in the rat: Presence of gelatinosa neurons with thalamic connections†

Abstract: Thalamic projections from trigeminal and certain other nuclei of the brainstem of the rat have been investigated using the technique of retrograde transport of horseradish peroxidase (HRP). The pattern of trigeminothalamic projections is very specifically related to the individual subnuclei of the complex. The Main Sensory Nucleus (MSN) provides profuse cross connections to the ventrobasal thalamus (VB); these arise exclusively from medium and small-sized neurons, but never from the large cells. In addition to these crossed connections, a small ipsilateral dorsal trigeminothalamic tract arises from the dorsal third of the most rostral part of the MSN; this is the only ipsilateral connection to VB found in the trigeminal complex. Subnucleus Oralis has no projections to the thalamus; it is suggested that it may be concerned primarily with reflex activation of the facial nucleus, with which it is co-extensive in the rostro-caudal axis. Subnucleus Interpolaris has a well-defined crossed projection of moderate size which arises from the large, medium and some of the small neurons. Subnucleus Caudalis has a sparse output to the thalamus and differs in its projections from rostral to caudal. At the most rostral level, all layers (marginal, transitional gelatinosa and magnocellularis) contain neurons which project to the thalamus; particularly conspicuous in this respect are the marginal neurons, most of which are strongly labelled. The presence of gelatinosa neurons projecting to the thalamus emphasizes a point made in earlier reports, that these neurons do not form an homogeneous population. At caudal levels, the marginal neurons are the major source of thalamic projections, while connections to the thalamus form deeper lying neurons are infrequent. With a single exception, the medullary reticular nuclei contained no neurons with thalamic connections; a small number of reticulo-thalamic neurons were found in the ventral pontine area. Marked labelling of the medial cuneate nucleus and moderate labelling of the gracilis and lateral cuneate nuclei occurred contralaterally to the injection site. A small numebr of medial cuneate and gracile neurons project to the ipsilateral thalamus. Projections from the solitary nucleus were always ipsialteral. The boundaries of individual subnuclei of the lateral sensory trigeminal complex in the rat have been redefined on the basis of cytological criteria; these are in good accord with the corresponding thalamic projection patterns.

Dorsal column nuclei and ascending spinal afferents in macaques.

Abstract: Cell populations and thalamic projections of the dorsal column nuclei in macaques have been investigated in the medullae of normal animals and of animals with injections of horseradish peroxidase in the nucleus ventralis posterolateralis. In the same species, the course, distribution and origin of ascending non-primary pathways to the dorsal column nuclei have been demonstrated with the aid of degeneration methods, 3H-amino acid autoradiography and retrograde axonal transport of horseradish peroxidase. Non-primary afferents to the gracile and cuneate nuclei ascend mainly in the dorsal columns and, to a lesser extent, in the dorsal part of the lateral funiculus. Afferents originating from lumbar segments and ascending in the lateral funiculus terminate mainly in the rostral part of the gracile nucleus while those ascending in the dorsal columns distribute throughout most of the rostrocaudal extent of the same nucleus. Afferents from brachial levels terminate mainly in the cuneate nucleus and in the external cuneate nucleus. Degeneration and autoradiographic material concurrently demonstrate that non-primary afferents to the cuneate nucleus terminate preferentially within certain cytoarchitectonic subdivisions of this nucleus. Ascending spinal afferents to the dorsal column nuclei originate mainly from the ipsilateral dorsal horn, particularly from its medial part at upper cervical levels and from a band of gray, throughout the cord, largely corresponding to lamina IV and adjacent laminae. Large neurons along the lateral border of the ventral horn at lumbar levels may also contribute non-primary afferents to the ipsilateral dorsal column nuclei. These anatomical results provide some cues to a revised view of the organization of the dorsal column nuclei in monkeys and, taken together with recent electrophysiological and clinical data, contribute to a re-evaluation of some functional aspects of the dorsal column-medial lemniscal system of primates.

Projections of the cerebellar and dorsal column nuclei upon the inferior olive in the rhesus monkey: an autoradiographic study.

Abstract: Projections from the cerebellar and dorsal column nuclei to the inferior olive of the rhesus monkey were traced with anterograde autoradiographic methods. The cerebellar nuclei give rise to a massive projection which reaches the contralateral inferior olivary complex by way of the descending limb of the superior cerebellar peduncle. Dentato-olivary fibers project exclusively upon the principal olivary nucleus (PO) and observe a strict topography. The dorsal, lateral, and ventral dentate project respectively to the dorsal, lateral, and ventral lamellae of the PO. Within the lamellae, the dentato-olivary fibers are related point for point in the medio-lateral axis. By contrast, the rostro-caudal topography is reversed so that the rostral pole of the dentate projects to the caudal PO and the caudal dentate to the rostral PO. These connections are predominantly crossed but a small ipsilateral component recrosses the midline at the olivary commissure and mirrors the topography on the opposite side. The anterior interpositus projects only to the medial half of the DAO and the posterior interpositus projects only to the rostral two thirds of the MAO. The ipsilateral component is minor in comparison with the contralateral projection, but appears to be more substantial than the ipsilateral projection to the PO arising from the dentate nucleus. The fastigial nucleus does not project upon the olivary complex. The dorsal column nuclei project topographically upon the contralateral accessory nuclei with the gracile nucleus sending fibers primarily to the lateal half of the DAO and the cuneate nucleus projecting to rostral cell groups of the MAO. The present results when compared with other olivary connections described by previous studies in a veriety of species suggest that regions of the MAO and DAO receiving sensory information from the periphery may lie outside the influence of cerebellar feedback loops.

Neck muscle and trigeminal input to the upper cervical cord and lower medulla of the cat

Abstract: Experiments on chloralose-anaesthetized cats have shown that low-threshold neck muscle afferents project to laminae IV and V in the dorsal horn of the upper cervical cord, to lamina VI including the region which encompasses the central cervical nucleus, as well as to extensive regions of the ventral horn. At posterior medullary levels projections also exist to laminae IV, V, and VI of the spinal nucleus of V (although those to lamina IV are circumscribed), to the deep layers and lateral margin of the cuneate nucleus, and to the inferior olive. These projections are both from low- and high-threshold afferents. Evidence of a functional relationship between the trigeminal and neck muscle afferent system was found both in the upper cervical cord and lower medulla. About 40% of units in both regions receive a convergent input and when convergence could not be demonstrated, prior stimulation of one modality in some instances affected the responsiveness of the unit to the other modality. A motor role was found for some trigeminal afferent projections to the upper cervical cord. Trigeminal afferents consistently activated antidromically identified motoneurons of splenius, biventer cervicis, and complexus.

Differential projections of cortical sensorimotor areas upon the dorsal column nuclei of cats

Abstract: Cortical projections to the dorsal column nuclei (DCN) of cats arise from layer V pyramids throughout the sensorimotor cortex and also from the second somatosensory cortical area (SII). In this study, the relative contribution from various cortical areas to different portions within the DCN-complex has been investigated in cats with restricted cortical lesions and using the Fink-Heimer technique. The sensorimotor cortex (areas 4, 3, 1, and 2) projects throughout most of the rostro-caudal extent of the gracile nucleus. Densest projections arise from the upper bank of the cruciate sulcus containing mainly the hindlimb region (area 4), from the medial wall of the posterior sigmoid gyrus (mainly area 3a) and terminate in the rostral as well as in the clusters regions of the gracile nucleus. The contribution of cortico-gracile projections from the hindlimb regions of areas 3b, 1 and 2 are much less conspicuous and terminate mainly in the rostral region of the nucleus. The nucleus z, the medullary relay for Ia fibers from the hindlimb, receives exceedingly sparse cortical projections. Dense projections to the cuneate n. arise from the cortical forelimb representation in the posterior sigmoid gyrus (areas 3a and 4) and laterally in the upper bank of the cruciate sulcus (area 4). The distribution pattern of cortical projections within the cuneate nucleus is however different from that within the gracile n. since (a) none of the lesioned cortical areas in the forelimb representation project to the clusters region, and (b) cortical projections terminate most densely in the base of the cuneate n., a medullary relay for Ia fibers from the forelimb. Sparse projections to the rostral region of the cuneate n. arise uniformly from all cytoarchitectonic areas of the forelimb representation. Cortical projections from SII are sparse and confined to the base and rostral region of the cuneate n. The results provide further evidence for the origin of descending projections upon the DCN mainly from cortical regions related to movement control. Further, it is suggested that cortico-DCN control is biased toward nuclear subdivisions related to cutaneous afferents from the hindlimb within the gracile n.-nucleus Z complex but toward nuclear subdivisions related to deep and muscle afferents from the forelimb within the cuneate nucleus.

Experimental degeneration of primary afferent terminals in the cuneate nucleus of the monkey (Macaca fascicularis).

Abstract: Six monkeys (Macaca fascicularis) were used for the present study. In animals which survived for 2-6 days after section of C5 to T1 dorsal roots, at least four types of degenerating afferent terminal were observed - electron-dense, electron-lucent, neurofilamentous and flocculent. The electron-dense degeneration was the most common and was seen as early as 2 days after rhizotomy. The neurofilamentous type was the second commonest and was found predominantly in the 3 days' survival material. The electron-lucent and flocculent types were less commonly encountered. Since the profiles exhibiting neurofilamentous hyperplasia showed varying degrees of electron density it is suggested that this type of degeneration progresses to the electron-dense type with time. The present study also showed that the primary afferent terminals in the cuneate nucleus of the monkey are mostly large and that they contain round vesicles. They are commonly found within synaptic complexes in which they are presynaptic to dendrites of various sizes, and are themselves postsynaptic to smaller axon terminals containing flattened vesicles. Degenerating terminals forming isolated synapses were less commonly seen. No dorsal root axon terminals formed axosomatic synapses.