Cuneate nucleus

About: Cuneate nucleus is a research topic. Over the lifetime, 614 publications have been published within this topic receiving 24859 citations. The topic is also known as: cuneate nucleus of spinal cord.

The cerebral cortex modulates the cutaneous transmission through the dorsal column nuclei

Abstract: Summary. Introduction. The mechanisms used by the cerebral cortex to modulate the cutaneous information at prethalamic levelhave been scarcely studied. This article reviews experimental evidence leading to a better understanding of this issue at the levelof the cuneate nucleus (Burdach nucleus). Development. The primary afferents and the corticocuneate fibers make synapticcontact with cuneothalamic neurons and with inhibitory interneurons in the middle cuneate nucleus. By stimulating the skin atdifferent places while recording the cuneothalamic intracellular activity in anaesthetized animals with the cortex intact, withthe cortex pharmacologically inactivated, or in absence of a cerebral cortex it was possible to ascertain the functional role ofthe corticocuneate fibers. The primary afferents activated by stimulating a particular zone of the skin induce monosynapticexcitation on a group of cuneothalamic cells at the same time at which inhibit, through intranuclear interneurons, neighboringcuneothalamic cells with unmatched receptive fields. Similarly, the corticocuneate cells receiving information from the stimulated skinfurther increase the excitation of the cuneothalamic neurons with matched receptive fields while inhibiting others with unmatched fields.The cortex exaggerates an excited center surrounded by an inhibited periphery thus increasing the tactile discrimination both spatiallyand temporally which is essential for exploratory and manipulative purposes. [REV NEUROL 2001; 33: 448-54]

[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.

A study of the functional relationship between the dorsal column and spinocervical system of the cat

Abstract: Electrophysiological experiments have shown that stimulation of the ipsilateral DLF, caudal to a transection of the dorsal columns (at C4), inhibits cells in the dorsal column nuclei. The presence of such inhibition was shown both by focal potential, and single unit, recording. It was found that the amplitude of a volley, conducted down the dorsal columns in response to a shock applied to the cuneate nucleus and recorded from the killed ends of dorsal column fibres at the rostral and of a transection of the dorsal columns, was increased by a preceding tetanus applied to the ipsilateral DLF. This evidence of depolarisation of dorsal column fibre terminals suggests that presynaptic inhibition contributes to the inhibition produced by DLF stimulation. A contribution from postsynaptic inhibitory mechanisms was suggested by the observation, made on several occasions, that antidromic activation of a unit from the contralateral mid-brain could be prevented by a preceding shock applied to the ipsilateral DLF. In some oases inhibition of units was produced by squeezing one or more of the cat's paws; some of these units projected into the contralateral mid-brain. In addition to an inhibitory action from the ipsilateral DLF on the cells of the dorsal column nuclei, electrophysiological experiments have also demonstrated the presence of an excitatory action. The majority of the cells transynaptically activated stimulation of the DLF were found in the region andminus;3 to +2andnbsp;mm (the obex being aero); however this may have been because the majority of electrode penetrations were also made in this region. Many of the unite so excited were shown to project into the contralateral mid-brain, thereby demonstrating the existence of a genuine excitatory effect on the dorsal column nuclei. Approximately one third of the units excited by stimulation of the DLF were also excited by peripheral mechanical stimulation. In the majority of cases the effective stimulus was cutaneous stimulation. A number of units, deep in the cuneate nucleus, ware found to be excited by "noxious" mechanical stimulation; no such units wore found in the gracile nucleus. Only one of those tested was found to project into the contralateral mid-brain, suggesting that these units may be inhibitory interneurones. The excitation and inhibition, produced by stimulation of the ipsilateral DLF, were abolished by transection of the DLF. They were net affected by transection of the brain stem at a level immediately rostral to the dorsal column nuclei. None of the cells transynaptically activated by stimulation of the DLF were also activated by stimulation of the anterior lobe of the cerebellum; this suggests that dorsal column nuclei cells were not excited by collaterals of direct spinocerebellar tract fibres. The presence of direct connections between the dorsal column nuclei and the DLF was demonstrated electrophysiologically by the recording, in the dorsal column nuclei, of short constant latency responses with properties indicative of external recordings from fibres. Whether such fibres were afferent to, or efferent from, the cells of the dorsal column nuclei could not be established from such recordings. However, evidence for the existence of both such categories was found. Some cells in the dorsal column nuclei were antidromically activated by stimulation of the ipsilateral DLF. Some of these cells were orthodromically activated by afferents coursing in the DLF. The presence of such orthodromic activation of those cells led to the speculation that the cells with descending projections may synapse, directly or indirectly, with the cells of origin of the afferent pathway, and thereby form a feed-back circuit within this system. Anatomical experiments have demonstrated the existence of direct afferent fibre connections between the DLF and the dorsal column nuclei. Terminal degeneration was found, after lesions of the DLF, in the rostral parts of both cuneate and gracile nuclei. The terminal degeneration extended from 1andnbsp;mm caudal to the obex up to the rostral poles of both nuclei. Such anatomical evidence of a direct afferent pathway does not, of course, exclude the presence of indirect pathways; such pathways, if synapsing before reaching the dorsal column nuclei, would not be demonstrated by anatomical methods. It is not possible, from the results described, to determine whether the direct pathway is formed by collaterals from a tract already known, such as the spinocervical tract, or whether it exists as a separate entity.

Peripheral and Spinal Inputs to Physiologically Identified Thalamic and Nonthalamic Relay Neurons in Cat Cuneate Nucleus

Abstract: A single-unit population study of the feline cuneate nucleus was carried out to identify principal neuron types, their distribution within the nucleus, pattern of peripheral activation, and receptive field characteristics. Units were also tested for response to isolated dorsal column or dorsolateral funicular electrical stimulation. The nucleus was explored in a uniform pattern, and sample size was optimized by applying the search stimulus shocks to the dorsal spinal cord. Single units were defined as spinal afferents, cuneothalamic-relay (CTR) neurons, and non-cuneothalamic-relay (non-CTR) neurons. The following features were observed: (1) The distribution within the nucleus of specific cell types agreed with cytoarchitectural studies: Spinal afferent fibers were superficial and caudal; 22% of neurons were CTR neurons; CTR neurons were most dense in the middle of the nucleus and were largely separate from non-CTR neurons. (2) Of the 58 neurons tested for response to isolated dorsal column and dorsolatera...