Electromyographic studies of effects of chlorpromazine on nociceptively and proprioceptively induced reflex pattern of rabbits hindlimb.

Numerous reports including Courvoisier et al. (1) have been made of the pharmacolo gical studies on chlorpromazine. The action of chlorpromazine on the central nervous system has been studied in reference to electroencephalography and evoked potentials from the brain of animal. Although the action mechanism of the drug has been well explained, much seems still left unclarified. The most conspicuous characteristics of the drug so far reported is a tranquilizing effect which, on the animal experimental basis, has been confirmed by Das et al. (2), Hendley et al. (3), and Preston (4). However, the locus of the action in the central nervous system does not seem to have been agreed upon. Evoked potentials from brain or spinal cord have been regarded to be a favorable medium through which the action of a drug on the central nervous system is to be investigated. This application seems very signi ficant in studying chlorpromazine. It is, however, not without a drawback in that the test animal must be previously anesthetized with the central depressant, as was regarded by Takeuchi (5). Since chlorpromazine has been suggested by many investigators to have a comparatively weak suppressive action to the central nervous system, it does not appear reasonable to study the drug using an anesthetized animal. It must be admitted that in animal experiments it is not always safe to define that an apparent recovery from anesthesia is a proof of return to a normal function of central nervous system. Accordingly it seems necessary to use unanesthetized animals in order to accurately study the central action mechanism of a drug. Thus the author took up as indicator Electromyo gram (EMG) evoked by adequate stimuli in unanesthetized rabbits in an attempt to clarify the central action mechanism of chlorpromazine.