Effects of succinylcholine and related substances administered into the medial preoptic area on the local EEG, body temperature, heart rate, galvanic skin resistance and biogenic amines.

Succinylcholine (Sch) which is a cholinergic neuromuscular blocker has been known to occasionally lead to episodes of malignant hyperthermia in swine and humans. In order to find whether it produces any hyperthermic effects through action on medial preoptic area, experiments were carried on by administering intracerebrally the chemical into the medial preoptic area through an in-dwelling cannula-cum-electrode in the free moving rat. The changes in body temperature and the local EEG were studied. For comparison purpose, the effects of carbachol, atropine and phenylephrine were also studied. Further, in the curarized state of no muscular activity, the effect of SCh on the preoptic area was again tested and also the changes in the other autonomic parameters of heart rate and galvanic skin resistance (GSR) were studied. It was observed that SCh given into preoptic area caused a clear hyperthermic effect. The effect was countered by prior administration of atropine into the site. After SCh the local EEG changed into a high amplitude slow wave format. The heart rate was not altered but the GSR increased by two-fold. Carbachol caused a rise in body temperature, heart rate and also GSR. SCh also caused a reduction in noradrenaline content of the hypothalamus by 23% while no change in dopamine and serotonin occurred. Serotonin increased by 28% in the brainstem with no change in the other amines. Septum showed an increase of noradrenaline and dopamine contents by 40% and 25% respectively. Keeping in view the monoaminergic connections and thermoregulatory role of the preoptic area, one may postulate that SCh could inhibit the warm sensors and the controls of the dual sympathetic mechanism which normally leads to an increase of sudomotor activity and a decrease of vasomotor activity, the inhibition resulting in rise of body temperature.