Effects of Cooling on Inhibitory Processes in the Cuneate Nucleus

Abstract

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 (25–30 o 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 (25–30 o C) but disappeared when the temperature was reduced to about 20 o 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.