Showing papers on "Cuneate nucleus published in 1994"

Descending projections from the caudal medulla oblongata to the superficial or deep dorsal horn of the rat spinal cord.

Abstract: The location of neurons in the caudal medulla oblongata that project to the superficial or deep dorsal horn was studied in the rat, by means of retrograde labelling from confined spinal injection sites. The tracer cholera toxin subunit B was injected into laminae I–III (fuve rats) or I–V (three rats) at C4–7 spinal segments. Neurons projecting to the superficial dorsal horn were located in the dorsomedial part of the dorsal reticular nucleus ipsilaterally, the subnucleus commissuralis of the nucleus tractus solitarius bilaterally, and a region occupying the lateralmost part of the ventrolateral reticular formation between the lateral reticular nucleus and the caudal pole of the spinal trigeminal nucleus, pars caudalis, bilaterally. Neurons projecting to the deep dorsal horn, which were only labelled when laminae I–V were filled by the tracer, occurred in the dorsomedial and ventrolateral parts of the dorsal reticular nucleus and in the ventral reticular nucleus bilaterally. A few cells were located in the above described lateralmost portion of the ventrolateral reticular formation bilaterally and in the ventral portion of the ipsilateral cuneate nucleus. In the light of previous data demonstrating that dorsal horn neurons project to the dorsal reticular nucleus, the ventrolateral reticular formation, and the nucleus tractus solitarius, and that neurons in these three medullary regions are involved in pain inhibition at the spinal level, the descending projections demonstrated here suggest the occurrence of spino-medullary-spinal loops mediating the analgesic actions elicited in each nucleus upon the arrival of nociceptive input from the dorsal horn.

Sensory Afferent Projections and Area 3b Somatotopy following Median Nerve Cut and Repair in Macaque Monkeys

Abstract: The fidelity of median nerve regeneration and the consequent effects of regeneration errors on cortical organization were determined in combined anatomical and electrophysiological studies. In three adult macaque monkeys, the median nerve was cut, sutured, and allowed to regenerate for 7-13 months. After regeneration, distributions of afferents to the dorsal horn of the spinal cord and the cuneate nucleus of the brainstem were determined by making injections of horseradish peroxidase conjugates into the distal phalanges of digit 1 or 2. While label from a single digit on the normal hand was confined to the appropriate locations in the median nerve territories of the dorsal horn and cuneate nucleus, label from the reinnervated digits spread out to cover most of the median nerve territories in those structures. These results are consistent with the interpretation that some proportion of primary sensory fibers normally innervating other digits and pads of median nerve skin erroneously reinnervated the skin of the injected digits. In the same monkeys, microelectrodes were used to record from an array of closely spaced sites across the representation of the hand in area 3b of somatosensory cortex. The reactivation pattern was abnormal, with neurons at many recording sites having more than one receptive field, larger than normal receptive fields, or receptive fields at abnormal skin locations. Thus, there is somatotopic disorder both in the regenerated median nerve and in reactivated cortex, indicating that primary somatosensory cortex does not reorganize to compensate fully for peripheral reinnervation errors in these adult primates. Nevertheless, the organization of receptive fields in area 3b suggests the existence of some central selection of synapses.

Synaptic transmission between single slowly adapting type I fibres and their cuneate target neurones in cat

Abstract: 1 The synaptic linkage between single, identified slowly adapting type I (SAI) fibres and their central target neurones of the cuneate nucleus was examined in pentobarbitone-anaesthetized cats Simultaneous extracellular recordings were made from individual cuneate neurones and from fine, intact fascicles of the lateral branch of the superficial radial nerve in which it was possible to identify and monitor the activity of each group II fibre Individual SAI fibres were activated by static displacement and by vibration delivered with a fine probe (025-2 mm diameter) to their associated touch domes in the hairy skin of the forelimb 2 Transmission properties across the synapse were analysed for nine SAI-cuneate pairs in which the single SAI fibre of each pair provided a suprathreshold input to the cuneate neurone Neither spatial nor temporal summation was required for effective impulse transmission, and often more than 80% of SAI impulses led to a response in the cuneate neurone Responses of the cuneate neurones to single SAI impulses occurred at a short, fixed latency (SD often 100-150 Hz despite 1:1 responses in their single SAI input fibres up to approximately 500 Hz 4 The reliable transmission of touch dome-associated SAI input across the cuneate nucleus indicates that transmission failure at this first relay is unlikely to be responsible for the reported failure of touch dome-SAI inputs to contribute to tactile perception 5 The transmission characteristics for the SAI fibres were very similar to those demonstrated previously for fibres associated with Pacinian corpuscles, which argues against any marked differential specialization in transmission characteristics for dorsal column nuclei neurones that receive input from different tactile fibre classes

Distribution of the postsynaptic dorsal column projection in the cuneate nucleus of monkeys.

Abstract: Cells in the spinal cord that are postsynaptic to primary afferent fibers project to the dorsal column nuclei in the postsynaptic dorsal column pathway. The projection of cells in the cervical spinal cord of monkeys to the cuneate nucleus has been reported to avoid pars rotunda of that nucleus, the part that contains the somatotopic representation of the ipsilateral hand. We used the sensitive anterograde tracer Phaseolus vularis leucoagglutinin to reexamine this projection. We made multiple iontophoretic injections into the cervical enlargements of three monkeys (two Macaca fascicularis and one Macaca mulatta). Control injections were made in the contralateral dorsal columns of one of these and in the dorsal roots of a fourth animal (M. fascicularis) to test for transport by fibers of passage. After 28–39 days, the animals were deeply anesthetized and perfused, and the tissue was processed for immunohistochemical detection of the label. In all cases (excluding control injections), labeled fibers and varicosities were distributed widely in the ipsilateral cuneate and external cuneate nuclei, including pars rotunda. The dorsal column nuclei ipsilateral to control injections contained no label or only very few poorly labeled fibers, indicating that labeling through fibers of passage did not contribute importantly to the results. This study indicates that the postsynaptic projection to the cuneate nucleus is widespread and includes pars rotunda. Such projections may contribute to transmission of information originating in nociceptors through the dorsal column-medial lemniscal system to the ventrobasal thalamus. © Wiley-Liss, Inc.

GABAergic boutons establish synaptic contacts with the soma and dendrites of cuneothalamic relay neurons in the rat cuneate nucleus

Abstract: This study investigates the synaptic relation between γ-aminobutyric acid-immunoreactive (GABA-IR) and cuneothalamic relay neurons (CTNs) in the rat cuneate nucleus. Retrograde transport of wheat germ agglutinin conjugated with horseradish peroxidase complex (WGA-HRP) was used to label CTNs while anti-GABA immunogold serum was used for the detection of GABA-IR boutons associated with CTNs. With these procedures, immunogold-labelled GABA-IR boutons were found to form axosomatic, axodendritic and axospinous synapses with the WGA-HRP-labelled but immunonegative CTNs. Quantitative estimation showed that the mean ratios of GABA-IR to GABA-immunonegative boutons making synaptic contacts with somata, proximal dendrites, and distal dendrites were 47.9%, 49.1% and 34.7%, respectively. Statistical analysis showed that the incidence of GABA-IR boutons on the somata and proximal dendrites of CTNs was significantly higher than on the distal dendrites. Our results indicate that GABA is the primary inhibitory neurotransmitter in the cuneate nucleus, thereby emphasizing the importance of postsynaptic inhibition on cuneothalamic relay neurons.

Ultrastructural and immunocytochemical characterization of primary afferent terminals in the rat cuneate nucleus

Abstract: The cuneate nucleus is a relay center for somatosensory information by receiving tactile and proprioceptive inputs from primary afferent fibers that ascend in the dorsal funiculus. The morphology, synaptic contacts, and neurochemical content of primary afferent terminals in the cuneate nucleus of rats were investigated by combining anterograde transport of horseradish peroxidase conjugated to wheat-germ agglutinin or to cholera toxin (injected in cervical dorsal root ganglia) with postembedding immunogold labeling for glutamate and GABA. Both tracers gave similar results. Two types of terminals were labeled: type I terminals were irregularly shaped, had a mean area of 4.0 μm2, synapsed on several dendrites, and were contacted by other terminals, some of which were GABA positive. Type II terminals were dome-shaped, had a mean area of 2.18 μm2, and made synaptic contact on a single dendrite. All the anterogradely labeled terminals (interpreted as endings of primary afferents) were enriched in glutamate but not in GABA. The finding that identified primary afferent terminals are enriched in glutamate with respect to other tissue profiles strongly suggests a neurotransmitter role for glutamate in this afferent pathway to the rat cuneate nucleus. © 1994 Wiley-Liss, Inc.

Regeneration of serotonergic immunoreactive fibers in the brain of 5,6-dihydroxytryptamine treated rat.

Abstract: After the intraventricular injection of 5,6-dihydroxytryptamine (5,6-DHT), the course of degeneration and regeneration of the serotonergic fibers in the rat brain was studied immunohistochemically by using serotonin antiserum. Three days after 5,6-DHT treatment, an extensive disappearance of serotonin immunoreactive fibers was observed throughout the brain. Degenerative serotonergic fibers characterized by droplet-like swelling and intense staining by serotonin antiserum were detected in the following discrete areas, e.g., medial forebrain bundle (MFB), cingulate cortex, septal nucleus, diagonal band of Broca (DBB), lateral preoptic area, bed nucleus of stria terminalis, perifornical area, stria-terminals, raphe nuclei, ventral tegmental area, periaqueductal gray lateral reticular nucleus and nucleus of the solitary tract. The swelling were regarded as the proximal stumps of the chemically injured serotonin fibers. Sprouting serotonin fibers emanating from these swellings were observed 5 days after injection. The swollen thick fibers were seen up to 3 months thereafter throughout the brain, although they gradually decreased in number until 1 month after injection. On the contrary, the sprouting fibers extended their terminal fields throughout the brain. Three types of reorganization pattern of regenerating serotonergic fibers were distinguished: hyperinnervation, normoinnervation (similar to the normal innervation) and hypoinnervation patterns. In the areas with hyperinnervation, the density of the serotonergic fibers gradually increased for 3 months. These hyperinnervation patterns of regenerative serotonergic fibers were observed in the MFB, cingulate cortex, diagonal band of Broca, perifornical area, raphe nuclei, ventral tegmental area, motor trigeminal nucleus, facial nucleus, lateral reticular nucleus, inferior olivary complex and hypoglossal nucleus. On the other hand, the hypoinnervation displayed by a few regenerating serotonergic fibers was observed in the periventricular part of the prosencephalon, the ventromedial part of the hypothalamus, the dorsal hippocampus, the neocortex, the superior and inferior colliculi, the cerebellum, the dorsal tegmental nucleus of Gudden, the vestibular nuclei, the gracile nucleus and the cuneate nucleus. These reorganization patterns were formed 3 months after injection, and continued for a long time (2 years). The mechanisms of serotonergic fiber reorganization are discussed.

Musculotopic Organization of Muscle Afferents in the External Cuneate Nucleus of the Gerbil as Revealed by Transganglionic Transport of Horseradish Peroxidase

Abstract: The projections of muscle afferents from six regions (hand, forearm, arm, thorax, shoulder and neck) to the external cuneate nucleus (ECN) of gerbils were investigated using transganglionic transport of horseradish peroxidase (HRP). These were chiefly ipsilateral projections which terminated in six discrete longitudinal columns in the ECN. A medial cell column confined to the caudal ECN received projections from the hand muscles, while the ventromedial and ventro-lateral cell columns in the posterior half of the ECN received projections from the forearm and arm muscles respectively. In the caudal ECN, the thoracic and shoulder muscles were represented by the dorsomedial and dorsolateral cell columns respectively. The last mentioned two columns extended anteriorly into the rostral ECN occupying a dorsal and intermediate portion leaving the ventral portion which represented the neck muscles. The latter also extended posteriorly into the middle 1/3 of ECN occupying a lateral portion. Serial sections and reconstruction studies showed that the ECN was located in the dorsal region of the upper medulla, approximately 0.3–1.8 mm rostral to the obex. The rostro-caudal extent of the six cell columns from hand proximally to neck were measured to be 0.5–0.8, 0.3–1.1, 0.3–1.3, 0.4–1.8, 0.4–1.8 and 0.8–1.8 mm rostral to the obex.

Distribution of calbindin D-28k-immunoreactivity in the cat brainstem.

Abstract: We studied the distribution of calbindin-immunoreactive fibers and cell bodies in the cat brainstem. The densest clusters of immunoreactive perikarya were found in the inferior and superior colliculi, the inferior olive, the periaqueductal gray, the central tegmental field and the substantia nigra, whereas the central linear nucleus, the locus coeruleus, the nucleus incertus, the dorsal and ventral nuclei of the lateral lemniscus, the cuneiform nucleus, the pontine gray, the Kolliker-Fuse nucleus, the dorsal motor nucleus of the vagus and the medial nucleus of the solitary tract had the lowest density. In the lateral tegmental field, the marginal nucleus of the brachium conjunctivum, the superior central nucleus, the nucleus sagulum, the dorsal nucleus of the raphe, the interpeduncular nucleus and the retrorubral nucleus the density of immunoreactive cell bodies was moderate. A high density of immunoreactive fibers was observed in the substantia nigra, the nucleus ruber, the superior and inferior colliculi, the periaqueductal gray, the interpeduncular nucleus, the central, magnocellular and lateral tegmental fields, the marginal nucleus of the brachium conjunctivum, the postpyramidal nucleus of the raphe, the inferior olive, the internal division of the lateral reticular nucleus and the medial and lateral nuclei of the superior olive. A moderate density of calbindin-immunoreactive fibers was found in the retrorubral nucleus, the central linear nucleus, the locus coeruleus, the nucleus sagulum, the dorsal nucleus of the raphe, the cuneiform nucleus, the ventral and dorsal nuclei of the lateral lemniscus, the medial nucleus of the solitary tract, the dorsal motor nucleus of the vagus, and the cuneate nucleus. Other brainstem regions such as the area postrema, the external division of the lateral reticular nucleus, the nucleus ambiguus, the nucleus intercalatus, the nucleus incertus, the pyramidal tract and the trapezoid body had the lowest density of immunoreactive fibers.

Ultrastructure of the cuneate nucleus in the streptozotocin-induced diabetic rat.

Abstract: This study describes the ultrastructural changes in the cuneate nucleus of the streptozotocin-induced diabetic rats at 3, 6, 9, and 12 months post-induction. At 3 and 6 months, post-diabetes, a marked atrophy was observed in the myelinated axons. The atrophic axons showed delamination of myelin sheath, tightly arranged lamellar whorls, vesicular elements and degenerating debris within the electron-lucent axoplasm. At 9 and 12 months post-diabetes, a variety of dystrophic and degenerating axonal profiles and dendrites were seen in neuropil. The dystrophic axonal profiles containing tubulovesicular elements, slit-like clefts, vacuoles, swollen mitochondria, membranous and multigranular bodies appeared to be hypertrophied. The degenerating axon terminals contained swollen mitochondria and clustered spherical agranular vesicles in their electron-dense granular axoplasm. The degenerating dendrites were identified by the presence of swollen mitochondria, dilated ER in the electron-dense cytoplasm and they often formed the synaptic glomeruli with central axon terminals. Macrophages containing lipid bodies and electron-dense elements in their cytoplasm were in the process of phagocytosis. In all the time intervals studied, the somata appeared to be normal and the number of dystrophic and degenerating axonal profiles in the cuneate nucleus of diabetic rats was significantly increased in comparison with age-matched saline injected control rats.

Influence of stimulation of movement-inhibiting areas of the pons on the activity of neurons of the medial region of the medulla oblongata.

Abstract: The reactions of 249 neurons located in the zones of gigantocellular reticular nucleus and the nucleus raphe magnus in response to electrical stimulation of areas of the cuneate nucleus of the midbrain, the medial parabrachial nucleus, and the central raphe nucleus, which inhibit movement, were analyzed in anesthetized white rats. Reactions to stimulation of these areas of the pons were lacking in 40 cells; 25 neurons were excited antidromically; 48 responded with solitary orthodromic action potentials; prolonged inhibition was observed in 72 neurons following the phase of activation; and 64 cells were tonically excited. The functional identification of the two last groups of neurons showed that the inhibition reactions are primarily recorded in cells receiving tactile and mechano- and nociceptive information, while the neurons which tonically discharge upon stimulation apparently participate in the inhibition of the motoneurons of the hind limbs.