Electropharmacological Consideration on Action Mechanism of Analgesics in Central Nervous System.

Abstract

Electropharmacological studies have been done by many investigators in order to determine the site of action of anesthetics and analgesics in central nervous system. Cortical action potential i. e. reverberating response, recruiting response, local cortical response and also spinal action potential in afferent as well as efferent pathways were used in these experiments as indicator of activity of central nervous system. On the other hand, electromyographic experiments on reflex activtity of spinal cord with unanesthetized rabbits have in past few years been carried out in our laboratory and the influences of these drugs on nociceptively and proprioceptively induced reflex pattern of hind limb were investigated in reference to the central action of these drugs.
The results reported in the papers were picked up and discussed.
(1) In barbiturate anesthetized animal, morphine blocked splanchnic afferent synapses in spinal cord and depressed intracortical neurone activity. Conduction of repetitive impulses through N. ventralis posterolateralis of thalamus was suppressed by morphine as well as aminopyrine.
(2) The activity of ascending activating system was depressed by barbiturate and ether but aminopyrine might be probably stimulating on this system.
(3) Barbiturate depressed significantly nociceptively induced muscle-after-discharge in spinal and midbrain rabbit and proprioceptively induced muscle-discharge in spinal rabbit. It was suggestive that barbitutrate also affected on central motor regulatory system.
Morphine depressed these muscle-discharges in the same degree in spinal lebel, and in nociceptive muscle-discharges, the one originated in higher center was more susceptible to morphine than the others. Aminopyrine suppressed spinal interneuronce-interneurone synapses.
(4) It was discussed that morphine exerted the strong action at higher center as well as spinal cord and aminopyrine at spinal cord and that morphine or barbiturate had both direct and indirect action on the central nervous system.