Showing papers on "Cuneate nucleus published in 2003"

New Corticocuneate Cellular Mechanisms Underlying the Modulation of Cutaneous Ascending Transmission in Anesthetized Cats

Abstract: The ascending cutaneous transmission through the middle cuneate nucleus is subject to cortico-feedback modulation This work studied the intracuneate cellular mechanisms underlying the corticocunea

Somatosensory properties of cuneocerebellar neurones in the main cuneate nucleus of the rat

Abstract: Cells in the main cuneate nucleus (MCN) are known to provide a direct projection to the cerebellum, but the precise nature of the information these cells transmit to the cerebellum is unknown. The present study employed anatomical and electrophysiological procedures to determine the location of cuneocerebellar cells in the MCN, and their somatosensory properties in the rat. The location of neurones projecting to the cerebellum was determined with injections of the retrograde tracers, horseradish peroxidase or Fluoro-Gold in vermal and paravermal regions of the cerebellum. Topographically, the majority of retrogradely labelled cells in the MCN were found to lie primarily ventrolateral in the nucleus and rostral to the level of the obex. Single unit recordings from 69 well characterized MCN cells, identified as projection cells by antidromic activation from stimulation of the inferior cerebellar peduncle, were classified according to their responses to cutaneous stimulation and manipulation of joints and muscles. A slight majority of cells (37.7%) responded only to manipulation/stimulation of joints, and 30.4% of cells responded only to cutaneous stimulation. The remaining cells received convergent input from joint and cutaneous receptors. Cutaneous responsive cells all rapidly adapted to maintained stimuli, and had large receptive fields (RFs) that were generally located over the joints. These cells could be activated by passive movements of the forelimb that deformed the RF. They only discharged during movements and were silent during maintained limb positions. Cells responsive to punctate mechanical stimuli applied to the joint capsules, responded to passive movements of the forelimb, but typically only discharged towards the limits of joint movement, and adapted within a few seconds. Once adapted, small perturbations of joint position resulted in vigorous dynamic responses. The results indicate that the neurones in the MCN of the rat which project directly to the cerebellum are localized in the rostral half of the nucleus. They transmit predominantly dynamic information from joint and cutaneous receptors that are likely to be normally activated as a result of limb movements. These cells could signal information about evolving movements or disturbances of forelimb posture or stance.

Transmission security for single kinesthetic afferent fibers of joint origin and their target cuneate neurons in the cat.

Abstract: Transmission between single identified, kinesthetic afferent fibers of joint origin and their central target neurons of the cuneate nucleus was examined in anesthetized cats by means of paired electrophysiological recording. Fifty-three wrist joint afferent-cuneate neuron pairs were isolated in which the single joint afferent fiber exerted suprathreshold excitatory actions on the target cuneate neuron. For each pair, the minimum kinesthetic input, a single spike, was sufficient to generate cuneate spike output, often amplified as a pair or burst of spikes, particularly at input rates up to 50-100 impulses per second. The high security was confirmed quantitatively by construction of stimulus-response relationships and calculation of transmission security measures in response to both static and dynamic vibrokinesthetic disturbances applied to the joint capsule. Graded stimulus-response relationships demonstrated that the output for this synaptic connection between single joint afferents and cuneate neurons could provide a sensitive indicator of the strength of joint capsule stimuli. The transmission security measures, calculated as the proportion of joint afferent spikes that generated cuneate spike output, were high (>85-90%) even at afferent fiber discharge rates up to 100-200 impulses per second. Furthermore, tight phase locking in the cuneate responses to vibratory stimulation of the joint capsule demonstrated that the synaptic linkage preserved, with a high level of fidelity, the temporal information about dynamic kinesthetic perturbations that affected the joint. The present study establishes that single kinesthetic afferents of joint origin display a capacity similar to that of tactile afferent fibers for exerting potent synaptic actions on central target neurons of the major ascending kinesthetic sensory pathway.

An immunocytochemical mapping of methionine-enkephalin-Arg6-Gly7-Leu8 in the cat brainstem.

Abstract: The distribution of methionine-enkephalin-Arg6-Gly7-Leu8-immunoreactive cell bodies and fibres was studied in the brainstem of the cat using an indirect immunoperoxidase technique. In the mesencephalon, immunoreactive cell bodies were observed in the periaqueductal grey, the dorsal raphe nucleus, the central and pericentral nuclei of the inferior colliculus and the pericentral division of the dorsal tegmental nucleus. In the pons, immunoreactive cell bodies were observed in the dorsolateral division of the pontine nucleus; below the central division of the dorsal tegmental nucleus; above the dorsolateral division of the pontine nucleus, and close to the superior cerebellar peduncle. In the medulla oblongata, immunoreactive cell bodies were observed in the laminar spinal trigeminal nucleus and in the lateral tegmental field; the dorsal motor nucleus of the vagus; the prepositus hypoglossal nucleus; the medial nucleus of the solitary tract; the rostral division of the cuneate nucleus, and close to the parvocellular division of the alaminar spinal trigeminal nucleus. The highest (moderate) density of immunoreactive fibres was observed in the periaqueductal grey; the parvocellular and magnocellular divisions of the alaminar spinal trigeminal nucleus; the laminar spinal trigeminal nucleus; the rostral division of the cuneate nucleus; the dorsal motor nucleus of the vagus; the lateral nucleus of the solitary tract, and in the midline between the central divisions of the reticulotegmental pontine nucleus. The widespread distribution of methionine-enkephalin-Arg6-Gly7-Leu8 in the cat brainstem indicates that the peptide might be involved in several physiological functions.

Impulse propagation over tactile and kinaesthetic sensory axons to central target neurones of the cuneate nucleus in cat

Abstract: Paired, simultaneous recordings were made in anaesthetized cats from the peripheral and central axons of individual tactile and kinaesthetic sensory fibres. The aim was to determine whether failure of spike propagation occurred at any of the three major axonal branch points in the path to their cuneate target neurones, and whether propagation failure may contribute, along with synaptic transmission failures, to limitations in transmission security observed for the cuneate synaptic relay. No evidence for propagation failure was found at the two major axonal branch points prior to the cuneate nucleus, namely, the T-junction at the dorsal root ganglion, and the major branch point near the cord entry point, even for the highest impulse rates (∼400 impulses s−1) at which these fibres could be driven. However, at the highest impulse rates there was evidence at the central, intra-cuneate recording site of switching between two states in the terminal axonal spike configuration. This appears to reflect a sporadic propagation failure into one of the terminal branches of the sensory axon. In conclusion, it appears that central impulse propagation over group II sensory axons occurs with complete security through branch points within the dorsal root ganglion and at the spinal cord entry zone. However, at high rates of afferent drive, terminal axonal propagation failure may contribute to the observed decline in transmission security within the cuneate synaptic relay.

Sleep and wakefulness in the cuneate nucleus: a computational study

Abstract: The minimum-variance theory [12] was proposed to account for the eye and arm movement. However, we point out here that i) the input signals used in the the simulations are not Poisson processes; ii) when the input signal is a Poisson process, the solution of the minimumvariance is degenerate.

Research report C projections of sensory innervation of the rat superficial temporal artery

Abstract: Elucidating the central sensory projection pathways of extra- and intracranial vessels appears to be of fundamental importance for understanding the pathogenetic mechanisms of primary headaches. In this paper, two kinds of tracers, choleragenoid (cholera toxin subunit b, CTb) and wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP), were used to transganglionically label the central sensory projections of the innervation of the superficial temporal artery (STA). Following either of the tracers applied on the adventitia of the STA, labelled terminations were found mainly in the ipsilateral C1–C3 spinal dorsal horns. Sparse labelling was also found in the interpolar and caudal parts of the spinal trigeminal nucleus. In the spinal cord, CTb labelled profiles were mainly located in laminae III and IV, whereas WGA-HRP labelled profiles were mainly located in laminae I and II. In the medulla, CTb but not WGA-HRP labelled terminals were found in a small dorsolateral extension of the cuneate nucleus. The present results indicate that the primary sensory nervous center of the STA is located in the rostral cervical spinal dorsal horn. The caudal parts of the spinal trigeminal nucleus, which has been demonstrated as a center of pain and temperature sensations of the head and face, transmits limited information from the STA to higher nervous centers.  2002 Elsevier Science B.V. All rights reserved. Theme: Sensory systems Topic: Somatic and visceral afferents