Showing papers on "Cuneate nucleus published in 1980"

Termination in overlapping sagittal zones in cerebellar anterior lobe of mossy and climbing fiber paths activated from dorsal funiculus.

Abstract: The termination patterns in the cerebellar anterior lobe of one mossy fiber path, the exteroceptive component of the cuneocerebellar tract (E-CCT), and one climbing fiber system, the dorsal spino-olivocerebellar paths (DF-SOCPs), which both relay in the main cuneate nucleus, were compared in the cat. The E-CCT terminates in the ipsilateral half of the anterior lobe in five sagittal zones which overlap five of the eight zones activated from the DFSOCPs. In at least one zone the E-CCT projection has a somatotopical organization which is similar to and overlaps that of the DF-SOCP.

Patterns of responses of neurons in cuneate nucleus to controlled mechanical stimulation of cutaneous velocity receptors in the cat.

Abstract: 1. The responses of single cuneate neurons to controled mechanical stimulation of skin were recorded in cats lightly anesthetized with a nitrous oxide-halothane mixture. The discharge patterns and peripheral receptive-field characteristics were studied in neurons driven by sensitive cutaneous mechanoreceptors, including slowly adapting skin mechanoreceptors. Virtually all cuneate neurons display maximum discharge during the velocity component of displacement. 2. Among cuneate neurons encountered in this study, approximately 46% were driven by guard hair mechanoreceptors, 15% were driven by field receptors, and 13% were driven by slowly adapting skin receptors. Neurons responding to stimulation of deep tissues (including claws) were not studied with controlled mechanical stimulation and accounted for 19%. The rest of the neurons were driven by Pacinian corpuscles, received afferent inputs from several different first-order afferents, or were not definitely identified. There was no clear evidence of down hair or high-threshold mechanoreceptor representation. 3. The discharge pattern in response to a constant-velocity stimulus proved most valuable in describing submodality classes of neurons driven by hair and field receptors since sensitivity of these neurons to dynamic and to static phases of stimulation constitute respective continua and, thus, preclude sharp separation into distinct groups. 4. The majority of neurons displayed response properties and receptive fields similar to those of first-order afferents. A minority of cells had receptive fields that were larger than those of primary afferents, with nearly identical modality and velocity characteristics throughout the receptive field. 5. Approximately 2% of recorded neurons displayed convergent properties not encountered in first-order afferents, including neurons driven from receptors of different modalities or from discontinuous receptive fields. 6. Inhibition of neuronal firing generated from outside the receptive field was rarely seen, possibly due to anesthetic conditions. In a small number of neurons, irregularities in the discharge were observed that might indicate inhibitory influences originating from within the receptive field.

The projection of joint receptors to the cuneate nucleus in the cat.

Abstract: 1. Records were made from axons in the dorsal columns and cells in the cuneate nucleus which responded to stimulation of the wrist joint nerve. 2. A sample of twenty-five axons activated by the wrist joint nerve was recorded in the dorsal columns at the level of the third cervical segment. All twenty-five were post-synaptic fibres as judged by response latency, burst length, and maximum frequency of following. Nineteen of the twenty-five had convergent inputs from the wrist joint nerve and the cutaneous superficial radial nerve. 3. While no primary wrist joint afferent fibres were recorded in the dorsal columns, their presence was demonstrated by recording single units in the wrist joint nerve which were antidromically activated by microstimulation in the cuneate fasciculus. 4. The majority of cells recorded in the cuneate nucleus were activated not only by stimulation of joint afferents, but also by skin and muscle afferent fibres. 5. About half of the cells in the cuneate nucleus responded to wrist movement in animals with partially denervated forelimbs, where the intact wrist joint nerve was the only afferent channel providing information about natural, imposed wrist movements. The majority of the cells had phasic responses, which were weak and irregular in comparison with the responses of primary wrist joint afferents to the same movements. 6. Only two of thirty-four cells tested could be shown to project directly to the ventrobasal thalamus, using collision of antidromic and peripherally activated impulses as the criterion.

Experimental degeneration of motor and sensory cortical terminals in the cuneate nucleus of the monkey (Macaca fascicularis).

Abstract: A total of nine monkeys (Macaca fascicularis) of both sexes was used for the present study. Eight monkeys were used for either motor or sensory cortical lesions, and were allowed to survive for 1--7 days post-operatively. No degenerating nerve terminals were observed 1 day following either motor or sensory cortical lesions. After a motor cortical lesion, most degenerating terminals were seen on the third and only a few on the fifth day. Following a sensory cortical lesion, most degenerating terminals were seen on the fifth and fewer on the third and seventh days. Two types of degenerative changes were observed: granular and electron-dense. Granular change was more evident after the shorter survival periods, while the electron-dense type of degeneration was more commonly seen in animals which were allowed to survive longer after operation. The cortical axon terminals were small and contained either round or flattened synaptic vesicles. Most of those axons containing flattened vesicles originated from the sensory cortex, but a few came from the motor cortex. Vice versa, most of those axons containing round vesicles appeared to arise from the motor cortex and only a few from the sensory cortex. Cortical axon terminals containing round synaptic vesicles formed asymmetrical synapses with small to medium-sized dendrites poor in organelles. In a few instances such cortical terminals were observed to be postsynaptic to other axon terminals containing flattened vesicles. No cortical axon terminal was observed to terminate presynaptically on another axon terminal. Cortical terminals containing flattened vesicles formed symmetrical synapses with dendritic profiles of varying diameters, some of which were the proximal dendrites of Group II neurons. No cortical axon terminals containing flattened vesicles have been observed to form axo-axonal synapses in the cuneate neuropil.

Slow waves and unitary activity evoked by cutaneous stimulation from the rat cuneate nucleus.

Abstract: Depth profiles of averaged evoked potentials (AEPs) and simultaneously generated unitary activity have been recorded from the cuneate nucleus of the rat in response to controlled tactile stimulation of the ipsilateral forepaw.

On the functional significance of axonal triads in medial cuneate nucleus.

Abstract: Theoretical considerations are presented about the possible functional significance of special triadic synaptic arrangements in medial cuneate nucleus. Although they can not be regarded functionally equivalent to the dendritic triadic arrangements in the thalamic nuclei, the cuneate axonal triads are likely to participate not only in distance dependent stimulus discrimination, but also in movement perception.

Complex synapses in the medial cuneate nucleus of the cat.

Abstract: An electronmicroscopical study using an analysis of thin sections and experimental degeneration of the medial cuneate nucleus of the cat has revealed five types of axon terminals: (1) Relatively large axon terminals characterized by a population of large (45-60 nm) spheroid vesicles which are the terminals of the spinal afferents: (2) Small axon terminals - probably of local interneuronal source - containing characteristic flattened vesicles: (3) Small axon terminals, mostly of local source (probably relay cell axon collaterals or possibly interneurons) containing small spheroid vesicles. A few axon terminals with similar small spheroid vesicles are of (contralateral) cortical origin from the somatosensory area; (4) Medium size axon terminals containing pleomorphic (ovoid to round) vesicles and being of local source (probably from local or neighbouring interneurons); (5) Occasionally axon terminals containing large dense-core vesicles (100-120 nm) were also observed. While types (1), (2), (3) and (4) are presynaptic to dendrites and (less frequently) to cell bodies, type (2), (3) and (4) were observed to be presynaptic also (axo-axonally) to type (1). Section series revealed that such axo-axonal synapses are in fact always arranged in "triadic combination" having the general formula of: 1 leads to dendrite (or soma), 2 (or 3, or 4) leads to 1, and 2 (or 3 or 4) leads to dendrite (or soma); the arrow indicating the morphological polarity of the synapse. -Presynaptic dendrites forming dendritic synapses and occasionally engaged in reciprocal synapses were also found, but in view of their rarity are probably only of secondary significance.

[Projection of neck muscle afferents to the brain stem of the cats (author's transl)]

Abstract: In order to investigate the afferent projection of neck muscles biventer cervicis, splenius and occipitoscapularis, extremities were performed on cats anaesthetized with chloralose urethane. 246 neurons were found to respond to electrical stimulation of these muscle nerves and they were located mainly in the ipsilateral external cuneate nucleus (242; 98.3%) and the remaining 4 neurons were in the rostral tip of the main cuneate nucleus. It was found that 241 neurons responded to only one of these afferent nerves, 3 neurons received convergent inputs from biventer cervicis and occipitoscapularis nerve and one neuron from biventer cervicis and great auricural nerve. Out of 241 neurons studied, 97 neurons (40.3%) responded to biventer cervicis, 88 (36.5%) to splenius and 56 (23.2%) to occipitoscapularis. 40 out of the 97 biventer cervicis responded neurons showed the monosynaptic firing. 51 out of the biventer cervicis responded neurons, 35 out of the splenius and 34 out of the occipitoscapularis responded neurons fired the first spike response at stimulus strength below 1.7 times the threshold of the largest afferents of each nerves suggesting group I afferents are responsible for the discharges. The monosynaptically activated neurons showed somatotopic distribution in the nucleus; biventer cervicis responded neurons locate in the most lateral part, splenius locate in the middle and occipitoscapularis locate in the medial part of the external cuneate nucleus. Antidromic discharges were evoked in 43/143 (30.1%) of the external cuneate neurons by electrical stimulation of the ipsilateral inferior peduncle and anterior lobes IV and V of the cerebellum. No such and antidromic discharges could be evoked by electrical stimulation of the contralateral thalamus. It was concluded that the relay neurons of the external cuneate nucleus from biventer cervicis, splenius and occipitoscapularis neck muscles projected their axons to the ipsilateral cerebellum but not to ventral posterolateral (VPL) and ventral posteromedial (VPM) nucleus of the contralateral thalamus.