Showing papers on "Cuneate nucleus published in 1972"

Extracellular K + activity and slow potential changes in spinal cord and medulla.

Abstract: In cats under Dial, repetitive stimulation of primary afferent fibers evokes a negative potential change in the cuneate nucleus or the dorsal horn of the lumbar spinal cord, which is associated with a clear increase in extracellular K+ activity, recorded by K+ selective microelectrodes.

Effect of cooling on synaptic transmission through the cuneate nucleus.

Abstract: The synaptic transmission through the cuneate nucleus was studied during local cooling of the dorsal column region. Field potentials, recorded from the surface as well as inside the nucleus, were greatly increased during moderate cooling (to 30–25o C) but diminished rapidly if the cuneate temperature fell below about 20o C. The increase was most evident for the afferent fibre volley potentials, but large changes of synaptic potentials (N-wave) were regularly seen as well. The increase (up to several hundred per cent) was partly rate-dependent since fast cooling gave larger increases than slower cooling did. In spite of the greatly increased N-wave, the transmission through the nucleus was always reduced. This was tested in various ways: measurement of the latency and probability of firing of single units, “killed end”–recording from lemniscal fibres as a measure of number of discharging cuneate neurones, and measurement of the size of thalamic and cortical field potential produced by impulses relayed through the cuneate nucleus. The reduced transmission was most likely due to a greatly increased synaptic delay, with slowing of conduction along the terminal branches of the afferent fibres as a contributing factor. On severe cooling blocking of conduction in these branches occurred. During moderate cooling the probability of firing of most relay cells remained strikingly high.

Effects of cooling on inhibitory processes in the cuneate nucleus.

Abstract: Inhibitory mechanisms in the dorsal column nuclei have been studied during local cooling. The inhibition of transmission of a cutaneous volley across the cuneate nucleus caused by a preceding volley to the same or a neighbouring cutaneous nerve was prolonged and slightly increased by a moderate (25–30o C) reduction of the cuneate temperature. The excitability of presynaptic fibres and of the postsynaptic cell membrane both decreased progressively with decreasing temperature. Presynaptic depolarization increased during moderate cooling (25–30o C) but disappeared when the temperature was reduced to about 20o C. One type of interneurone in the cuneate nucleus showed a progressive disruption of the normal pattern of firing with a gradual increase in the initial latency. An other type showed an increase of the rate and duration of the discharges to a single afferent volley on cooling. The latter type was susceptible to stimulation at 10 per s or higher. The behaviour of the latter interneurones matched the increased and prolonged presynaptic depolarization. These cells may be interneurones in a presynaptic inhibitory pathway. The prolonged and moderately increased inhibition caused by local cooling is probably due to activation of such cells causing increased presynaptic depolarization.