Electrical Discharge Patterns in Hypothalamic Neurosecretory Neurones Associated with Hormone Release

Abstract

There is a clearly defined nervous pathway connecting the neural lobe of the pituitary gland and the hypothalamus, and Harris (1955) showed that electrical stimulation of this hypothalamo-hypophysial tract would release oxytocin and vasopressin. It has been suggested, therefore, that an increase in the electrical activity, in the form of action potentials, of the neurones in the supraoptic and paraventricular nuclei is associated with neurohypophysial hormone release. Several attempts have been made to show that stimuli which release one or both these hormones also increase the electrical activity in the supraoptic and paraventricular nuclei (see Cross and Silver, 1966). However when recordings are made from neuronal units in the central nervous system it is difficult to be certain of the type of neurone from which the recordings are being made, even if the location of the recording electrode is known. To overcome this difficulty the technique of antidromic stimulation of the neural lobe was developed for the identification of supraoptic and paraventricular neurones in rats (Yagi, Azuma and Matsuda, 1966; Dyball, 1969b; Dyball and Koizumi, 1969). After neurosecretory units had been identified in this way their spontaneous discharge rate was monitored before and after intracarotid injections of hypertonic and isotonic NaCl solutions. The mean change in firing rate following the injections was then compared with the mean change in plasma ADH concentration at different time intervals after similar injections.

The author is much indebted to Professor B. A. Cross for his help in the preparation of the manuscript and to Miss P. Pountney for technical assistance. The work was supported by a grant from the Medical Research Council.