Electrical and electrochemical stimulation of the hypothalamo-adenohypophysial system with stainless steel electrodes.

Abstract

Characteristics of electrical and DC electrochemical stimulation with stainless steel electrodes have been studied in vitro in an agar medium and in vivo in proestrous female rats. The transparent agar medium contained salts to display the Prussian Blue reaction if Fe+++ was deposited by the electric current. It was found that, to avoid Fe+++ deposition (which converts electrical to electrochemical stimulation), the stimulating tip of the bipolar concentric electrode should be made the cathode and the outer barrel the anode; to maintain this relationship the wave form should be monophasic; individual pulses should be of short duration, usually 0.5 msec or less, and the intensity of the stimulating current should generally be kept under 500 μA. Observing these criteria, we were able to induce the release of an ovulating quantum of pituitary gonadotrophin by electrical stimulation of either the arcuate nucleus-median eminence area or the medial preoptic region in the pentobarbital-blocked proestrous rat. Electrochemical stimulation was also effective in both regions and, with either type of stimulus, the threshold in the medial preoptic region was considerably less than in the median eminence. Within the limits of the parameters employed, the septum and nucleus accumbens responded readily to the DC electrochemical stimulus but not to electrical stimulation. The low thresholds in the medial preoptic region have led to the proposal that this area serves as a multisynaptic amplifier of afferent signals concerned with ovulation, in much the same manner as the reticular formation acts to amplify certain visceral afferent mechanisms. (Endocrinology84: 918, 1969)