Showing papers on "Cuneate nucleus published in 1998"

Organization of diencephalic projections from the medullary subnucleus reticularis dorsalis and the adjacent cuneate nucleus: a retrograde and anterograde tracer study in the rat.

Abstract: The distribution and organization of diencephalic projections from the subnucleus reticularis dorsalis (SRD) and the neighbouring cuneate nucleus (Cu) were studied in the rat by using microinjections of Phaseolus vulgaris leucoagglutinin in SRD and Cu and wheat germ agglutinin-apo horseradish peroxidase-gold in some selected thalamic areas. As previously reported, the efferent projections from the Cu were essentially contralateral and terminated mainly in the ventroposterolateral thalamic nucleus. Less dense terminals from the Cu were also observed in the posterior thalamic group, the ventral aspect of the zona incerta and the caudal and dorsal portion of the reuniens area. Retrograde tracer injections in the medial ventroposterolateral thalamic nucleus labeled numerous cells in the contralateral Cu, with a smaller number in the gracile nucleus. From the SRD, terminals were observed in the lateral aspect of the ventromedial thalamic nucleus, the lateral parafascicular area and, to a lesser extent, in the ventral aspect of the zona incerta and the core of the reuniens area. Retrograde tracer injections in the lateral part of the ventromedial thalamic nucleus labeled cells in the caudal medulla, many of which were located in the dorsal-most aspect of the SRD throughout its caudo-rostral extent. The existence of SRD-thalamic connections reinforces the idea that the caudal reticular formation is an important nociceptive relay to the thalamus. Our data shed new light on old hypotheses suggesting that, in addition to spino-thalamic pathways, spino-reticulo-thalamic pathways may play an important role in distributing pain signals to the forebrain.

Organization of ascending pathways to the forelimb area of the dorsal accessory olive in the cat.

Abstract: The purpose of these experiments was to define the topography of cuneate and spinal projections to the forelimb representation in the rostral dorsal accessory olive (rDAO). We were interested in determining whether the spinal and cuneate inputs constitute a homogeneous afferent source, and whether there is evidence that they serve different functional roles. We were also interested in determining whether the somatotopy of rDAO is the result of a point-to-point projection from its afferent sources, or whether the projection suggests a reorganization of afferents at the olive. Single unit recording was used to identify specific regions of rDAO, and the topography of inputs to the identified regions was determined by using wheat germ agglutinin-horseradish peroxidase (WGA-HRP) as a tracer. The results from retrograde tracing were confirmed by using WGA-HRP as an anterograde tracer from input sources. The cuneate and spinal neurons providing input to rDAO constitute two distinct neural populations. One consists of cells in the caudal cuneate nucleus and lamina VI of the rostral two cervical segments, the other consists of cells in the rostral cuneate nucleus. The cells in the caudal cuneate nucleus and the rostral cervical segments are large, multipolar neurons that form a single column of rDAO input cells. The column of cells projects to the contralateral rDAO in a topographic fashion with rostral regions of the column projecting to rostral rDAO, which contains cells that respond to somatosensory stimulation of the contralateral shoulder, trunk, and proximal forelimb. Caudal regions of the column project to caudal rDAO, which contains cells that respond to stimulation of the distal forelimb. Despite this topography, there is a large degree of overlap in the terminations from neighboring regions of the input column, indicating that a major reorganization occurs at the rDAO. The projection from the rostral cuneate nucleus arises from small neurons that project bilaterally to rDAO, and the input from the rostral cuneate nucleus lacks a clear topography. We propose that input from the cell column is responsible for the somatosensory sensitivity of rDAO neurons, whereas input from rostral cuneate is most likely modulatory, probably inhibitory, in nature. J. Comp. Neurol. 392:115–133, 1998. © 1998 Wiley-Liss, Inc.

Effect of transcutaneous electrical nerve stimulation (TENS) on central nervous system amplification of somatosensory input

Abstract: The effect of transcutaneous electrical nerve stimulation (TENS) on the central nervous system amplification process was investigated focusing on the dorsal column-medial lemniscal pathway, because the dorsal column nucleus was recently shown to receive multiple sources of sensory information, including pain. Short latency somatosensory evoked potentials (SSEPs) were recorded in ten healthy normal volunteers. Amplitude changes in each SSEP component (the N9 brachial plexus potential, the P14 potential that originates from the cervicomedullary junction, spinal N13/P13 generated by the cervical dorsal horn and the cortical N20/P25 potential) were studied at stimulus strenghts ranging from the threshold (40% maximum stimulus) to 2.5 times the threshold (maximum). The findings suggest that sensory amplification begins at the P14 generator source near the cuneate nucleus. There was no statistically significant difference in sensory amplification between P14 and cortical N20/P25, indicating that the cuneate nucleus is the main site of the central amplifying process. When TENS was applied to the palm distal to the median nerve stimulation used for SSEP, cortical N20/P25 amplification disappeared, evidence that TENS suppresses the central amplification phenomenon, most probably at the level of the cuneate nucleus.

A developmental study of novH gene expression in human central nervous system.

Abstract: The expression pattern of the human nephroblastoma overexpressed (novH) gene in the fetal human central nervous system was examined by in situ hybridization using digoxigenin-labeled novH-specific riboprobes. In the spinal cord, the nov-expressing neurons were first detected both in the ventral region at 16 weeks of gestation (G16W) and in the dorsal region at G38W. In the medulla, nov-expressing neurons were detected in the principal nucleus of the inferior olive, the hypoglossal nucleus and the dorsal motor nucleus of vagus at G16W. Nov-positive neurons were detected at G28W in the nucleus of the spinal tract of the trigeminal and cuneate nucleus, and at G38W in the abducens nucleus of pons, the red nucleus and the substantia nigra of the midbrain, the ventral posterolateral and the mediodorsal thalamic nucleus. A strong labeling was also detected in the striatum of the cerebrum and the cerebral cortex of the parietal lobe. These data established that novH is mainly expressed in somato-motor neurons in the lower central nervous system at early developmental stages and in the higher central nervous system at later stages, suggesting that nov may play an important role in neuronal differentiation.

Signalling of static and dynamic features of muscle spindle input by cuneate neurones in the cat

Abstract: The present experiments examined the capacity of external cuneate nucleus (ECN) neurones in the anaesthetized cat to respond to static and vibrotactile stretch of forearm extensor muscles. The aim was to compare their signalling capacities with the known properties of main cuneate neurones in order to determine whether there is differential processing of muscle spindle inputs at these parallel relay sites. Static stretch (≤ 2 mm in amplitude) and sinusoidal vibration were applied longitudinally to individual muscle tendons and responses recorded from single ECN neurones. The muscle-related ECN neurones that were sampled displayed a high sensitivity to both static and dynamic components of stretch, including muscle vibration at frequencies of 50-800 Hz, consistent with their dominant input being derived from primary spindle afferent fibres. In response to ramp-and-hold muscle stretch, ECN neurones resembled their main cuneate counterparts in the pattern of their responses and in quantitative response measures. Their coefficients of variation in interspike intervals during steady stretch ranged from ≈0.3 to 0.7, as they do in main cuneate responses, and their stimulus-response relations were graded as a function of stretch magnitude with low variability in responses at a fixed stretch amplitude. In response to muscle vibration, ECN activity was tightly phase locked to the vibration waveform, in particular at frequencies of ≤ 150 Hz, where vector strength measures (R) were high (R≥ 0.8) before declining as a function of frequency, with R values of ≈0.6 at 300 Hz and ≤ 0.4 at 800 Hz. Both the qualitative and quantitative aspects of ECN responsiveness to the vibro-stretch disturbances were indistinguishable from those of the main cuneate neurones. The results demonstrate a high transmission fidelity for muscle signals across the ECN and no evidence for differential synaptic transmission across the parallel main and external cuneate nuclei. Earlier limitations observed in the capacity of cerebellar Purkinje cells to respond to primary spindle inputs must therefore be imposed at synapses within the cerebellum. Inputs arising from a particular class of receptor may be directed to multiple targets within the central nervous system and utilized for a variety of processing tasks at the different sites. In the case of muscle receptors, the inputs are conveyed over segmental pathways at the spinal cord level for the reflex regulation of posture and movement. However, these muscle inputs are also directed over ascending pathways for processing at hierarchically higher levels of the nervous system, including the cerebral cortex, where they contribute to kinaesthetic sensation (McCloskey, 1978), and the cerebellum where they are presumably utilized for the regulation and control of voluntary movements (e.g. Cooke et al. 1971). Muscle inputs from the forelimb project to the cuneate and external cuneate nuclei which form parallel synaptic relays in these ascending pathways to the cerebral cortex and cerebellum, respectively (Cooke et al. 1971). The input to these parallel relay nuclei from muscle spindle afferents is known to contain precise information about both static and dynamic aspects of muscle length changes. Furthermore, the responses, in particular of primary spindle afferent fibres, to controlled forms of muscle vibration reveal their capacity for signalling, with great precision, information about high-frequency, low-amplitude perturbations in muscle length (e.g. Bianconi & Van der Meulen, 1963; Brown et al. 1967; Mackie et al. 1998). However, it is uncertain whether equivalent information is extracted from the muscle afferent inputs by neurones within the main and external cuneate nuclei, arranged as they are, in parallel, for conveying information rostrally, predominantly for the purpose of kinaesthesia in the case of the main cuneate nucleus and for motor control in the case of the external cuneate nucleus. Some of the early studies on neurones of both nuclei left some doubt over their capacities to retain the precision of impulse patterning evident in the responses of their spindle afferent inputs. Neurones of both the cuneate and external cuneate nuclei of the macaque monkey displayed responses to brief trains (2-8 cycles) of muscle vibration that were phase locked at frequencies up to 50-100 Hz, although contributions to these responses from other mechanoreceptors, including Pacinian corpuscles and joint receptors, could not be excluded (Hummelsheim & Wiesendanger, 1985). Both cuneate and external cuneate neurones in the cat were shown by Rosen & Sjolund (1973a) to respond with high discharge rates to muscle vibration but no assessment was made of how precisely the pattern of discharge could reflect the temporal detail in the vibratory stretch disturbance. However, our recent quantitative analysis of cat main cuneate responses to muscle vibration revealed that these neurones signal, with great precision, the temporal features of vibro-stretch perturbations up to frequencies of 400-500 Hz and display an overall bandwidth of vibration sensitivity that extends to ∼800 Hz (Mackie et al. 1998). These attributes enable the cuneate neurones to contribute accurate temporal information for kinaesthetic sensation in circumstances involving dynamic length changes in skeletal muscle. In the present study, in part reported in preliminary abstract form (Mackie et al. 1994), we have examined quantitatively the capacity of external cuneate neurones in the cat to respond to the same forms of static and vibrational stretch of forearm extensor muscles. The aim was to determine whether the information signalled by these neurones to the cerebellum for the purposes of motor control provides evidence for differential processing of muscle spindle inputs at the parallel synaptic relays of the main cuneate and external cuneate nuclei.