ALTERATION OF ACTIVITY OF SINGLE NEURONS IN THE NUCLEUS CENTRUM MEDIANUM FOLLOWING STIMULATION OF THE PERIPHERAL NERVE AND APPLICATION OF NOXIOUS STIMULI

Abstract

Using unanesthetized cats, investigation of the perception of the sensory information in the CM-neuron was conducted by microelectrodical recording of the spontaneous discharge of the neuron, the driven unitary discharge following stimulation of the peripheral nerve and the action potential of the neuron in response to noxious stimuli. The prerequisite for the CM-neuron was to establish that convergence of the splanchnic and sciatic transmissions existed in the neuron and that the neuron responded to noxious stimuli. The present authors have analysed 82 units of the CM-neuron which fulfilled the prerequisites.The results were summarized in the following way.
The spontaneous discharge of the CM-neuron had a frequency of 5 to 25 per second. The average interval showed 34.1 msec with a standard deviation of 13.8 msec. The deviation was relatively large. The spontaneous discharge did not show a burst-like volley as far as the animal was in an unanesthetic condition. The interval of the spontaneous firing became shortened as the frequency increased in stimulation of the peripheral nerve. When stimulation of 1 cps was applied to the peripheral nerve, the spontaneous discharge of the CM neuron succeeding from the driven unitary discharge increased in firing rate and was facilitated for 550 msec. When stimulation of 10 cps was applied to the peripheral nerve, the driven unitary discharge of the CMneuron did not follow an individual stimulus but the spontaneous unitary discharge was extremely facilitated. The spontaneous firing of the CM-neuron was facilitated in various modes following tetanic stimulation of the splanchnic nerve. The neurons in 59% showed a marked continuous facilitation of the spontaneous firing and some of these neurons showed a facilitation of the spontaneous firing in close relation to the spindle burst of the slow potential.And the neurons in 25% showed a marked inhibition of the spontaneous unitary discharge followed by a phasic facilitation.
The receptive field of the CM-neuron responding to noxious stimuli was very large and covered the part on both sides of the body, extending to more than two limbs. The firing rate of action potential and the duration of after-discharge were different according to the site of the receptive field. The reactability of the CM-neuron to noxious stimuli was augmented to increase the frequency of action potential and to prolong the duration of of terdischarge, following brief train stimulation of the MRF or contralateral CM by 10 cps or 100 cps.
The perception of noxious stimuli was mostly related to the spontaneous discharge of the CM-neuron and supported by excitation in the polysynaptic central core conduction.