Showing papers on "Cuneate nucleus published in 2000"

Growth of new brainstem connections in adult monkeys with massive sensory loss.

Abstract: Somatotopic maps in the cortex and the thalamus of adult monkeys and humans reorganize in response to altered inputs. After loss of the sensory afferents from the forelimb in monkeys because of transection of the dorsal columns of the spinal cord, therapeutic amputation of an arm or transection of the dorsal roots of the peripheral nerves, the deprived portions of the hand and arm representations in primary somatosensory cortex (area 3b), become responsive to inputs from the face and any remaining afferents from the arm. Cortical and subcortical mechanisms that underlie this reorganization are uncertain and appear to be manifold. Here we show that the face afferents from the trigeminal nucleus of the brainstem sprout and grow into the cuneate nucleus in adult monkeys after lesions of the dorsal columns of the spinal cord or therapeutic amputation of an arm. This growth may underlie the large-scale expansion of the face representation into the hand region of somatosensory cortex that follows such deafferentations.

Comparative study on the distribution patterns of P2X1–P2X6 receptor immunoreactivity in the brainstem of the rat and the common marmoset (Callithrix jacchus): Association with catecholamine cell groups

Abstract: The present study investigated the topographical distribution of P2X(1)-P2X(6) receptor subtypes in the rat and common marmoset hindbrain by immunohistochemistry. In addition, double-labeling immunofluorescence was used to determine the extent of colocalization between catecholamine cell groups and the various P2X receptors. The data demonstrate a widespread distribution pattern for all six P2X receptors throughout both the rat hindbrain and the marmoset hindbrain, although distinctions between species, brain nuclei, and P2X receptor subtypes exist. In rat, dense staining for the P2X receptors was found in the nucleus of the solitary tract (NTS), medial vestibular nucleus, and medial and lateral parabrachial nuclei. Moderate staining was observed in the hypoglossal nucleus, cuneate nucleus, inferior olive, prepositus hypoglossi, rostral ventrolateral medulla (RVLM), and locus coeruleus. Staining was also observed in the gracile nucleus, the mesencephalic trigeminal nucleus, and the central pontine gray. In marmoset, prominent P2X receptor-like immunoreactivity occurred in the NTS, medial cuneate nucleus, prepositus hypoglossi, and medial vestibular nucleus. Moderate staining was observed in the area postrema, dorsal motor nucleus of the vagus, lateral cuneate, lateral reticular, spinal trigeminal nucleus, RVLM, and inferior olive. Immunofluorescent double labeling of tyrosine hydroxylase (TH)-containing cells revealed that all subtypes of P2X receptors show some degree of colocalization with TH. The highest proportion of TH and P2X receptor double labeling was in the A5 region (with the P2X(2) subunit), whereas the lowest proportion of double-labeled cells occurred in the C2 region of the NTS for the P2X(5) subunit. These findings support a role for extracellular adenosine 5'-triphosphate in fast synaptic neurotransmission within the brainstem.

Progressive transneuronal changes in the brainstem and thalamus after long-term dorsal rhizotomies in adult macaque monkeys.

Abstract: This study deals with a potential brainstem and thalamic substrate for the extensive reorganization of somatosensory cortical maps that occurs after chronic, large-scale loss of peripheral input. Transneuronal atrophy occurred in neurons of the dorsal column (DCN) and ventral posterior lateral thalamic (VPL) nuclei in monkeys subjected to cervical and upper thoracic dorsal rhizotomies for 13–21 years and that had shown extensive representational plasticity in somatosensory cortex and thalamus in other experiments. Volumes of DCN and VPL, number and sizes of neurons, and neuronal packing density were measured by unbiased stereological techniques. When compared with the opposite, unaffected, side, the ipsilateral cuneate nucleus (CN), external cuneate nucleus (ECN), and contralateral VPL showed reductions in volume: 44–51% in CN, 37–48% in ECN, and 32–38% in VPL. In the affected nuclei, neurons were progressively shrunken with increasing survival time, and their packing density increased, but there was relatively little loss of neurons (10–16%). There was evidence for loss of axons of atrophic CN cells in the medial lemniscus and in the thalamus, with accompanying severe disorganization of the parts of the ventral posterior nuclei representing the normally innervated face and the deafferented upper limb. Secondary transneuronal atrophy in VPL, associated with retraction of axons of CN neurons undergoing primary transneuronal atrophy, is likely to be associated with similar withdrawal of axons from the cerebral cortex and should be a powerful influence on reorganization of somatotopic maps in the somatosensory cortex.

Anatomic origin and clinical application of the widespread N18 potential in median nerve somatosensory evoked potentials.

Abstract: N18 is a broad negativity, with a duration of approximately 20 msec after positive far-field potentials and is recorded widely over the scalp using a noncephalic reference. Its origin has been controversial but its preservation after pontine or upper medullary lesion while loss after high cervical lesions suggested its medullary origin. Comparison with animal studies and direct recording studies in humans leads the authors to conclude that N18 is most likely generated at the cuneate nucleus by primary afferent depolarization. Namely, dorsal column afferents send collaterals to interneurons within the cuneate nucleus, which in turn synapse on presynaptic terminals of dorsal column fibers and depolarize them as a mechanism of presynaptic inhibition. In this way, an electrical sink is formed on presynaptic terminals, whereas their dorsocaudally situated axons serve as a source. The ventrorostral negative pole of the resultant dipolar potential must correspond to N18. The authors obtained a measure to evaluate medullary function objectively, and therefore N18 may be useful as a diagnostic tool for brain death. Usage of a C2S reference is essential for the accurate estimation of N18. Origins of other somatosensory evoked potential components related to the cuneate nucleus are also discussed.

Cuneothalamic relay neurons are postsynaptic to glycine-immunoreactive terminals in the rat cuneate nucleus.

Abstract: This study was aimed to clarify whether the cuneothalamic relay neurons (CTNs) in the rat cuneate nucleus contained glycine or whether the neurons were modulated directly by presynaptic glycine-IR terminals. For this purpose, retrograde transport of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) and immunoperoxidase labelling for glycine have been used to ascertain if the CTNs in the rat are glycine-immunoreactive (glycine-IR). Our results have shown that the WGA-HRP-labelled CTNs (mean area = 318 +/- 6.5 microm(2)) were not reactive for glycine. Glycine immunoreactivity, however, was localized in some small-sized neurons (mean area = 210 +/- 6.2 microm(2)) and axon terminals associated with the CTNs. The synaptic organization between the glycine-IR terminals and CTNs was further analyzed using anti-glycine postembedding immunogold labelling. By electron microscopy, the immunogold-labelled glycine-IR terminals containing pleomorphic synaptic vesicles formed symmetrical synaptic contacts with the dendrites, dendritic spines, and somata of CTNs. Quantitative estimation showed that the mean ratios of glycine-IR terminals to total terminals associated with the soma, proximal dendrites and distal dendrites of the CTN were 49.5, 45.2, and 45.8%, respectively. The higher incidence of glycine-IR terminals on the soma, however, was not significantly different from that of the proximal and distal dendrites. Notwithstanding the above, this study has shown a large number of glycine-IR terminals making direct synaptic contacts with CTNs, suggesting that glycine is one of the important neurotransmitters involved in postsynaptic inhibition on the cuneothalamic relay neurons to modulate incoming somatosensory information from forelimb areas in the rat.

Transganglionic gracile response following limb amputation in man.

Abstract: Gracile neuroaxonal dystrophy (NAD) is an distinctive morphological alteration of central projecting axon terminals of dorsal root ganglion neurons. Experimentally, lower limb amputation has been shown to accelerate the formation of gracile NAD, suggesting that the transganglionic response to peripheral axotomy may play a role in its development. To determine if a similar response occurs in the human sensory nervous system following peripheral nerve injury, we have performed postmortem histopathological examinations of the dorsal column nuclei of three patients (aged 15, 55, and 77 years old); all of whom had undergone accidental or therapeutic unilateral limb amputation (1 year, 38 years, and 1 year 8 months prior to death, respectively). In a 15-year-old man who underwent therapeutic leg amputation, the gracile nuclei on the transected side revealed reactive gliosis and many small axonal spheroids. The spheroids and fine neurites were immunolabelled with antibodies for growth-associated protein-43, ubiquitin and neuropeptide Y (NPY). Neither routine histological nor immunohistochemical methods demonstrated comparable changes in the contralateral gracile nucleus. In a 77-year-old man who underwent leg amputation, the gracile nucleus on the amputated side was gliotic and showed several NPY and ubiquitin-immunoreactive spheroids, which were not seen in the contralateral non-transected side. A 55-year-old man with a history of accidental arm amputation showed well-developed NAD in the cuneate nucleus only on the transected side. This study clearly demonstrates the occurrence of transganglionic response to limb amputation in human dorsal column nuclei. The extent of the regenerative and/or degenerative responses may vary depending on the age of the patient and the time interval following the peripheral axotomy.