Temporal patterns of vasopressin release following electrical stimulation of the amygdala and the neuroendocrine pathway in the monkey.

To evaluate a possible role of the amygdala (Amyg) in the neural control of arginine vasopressin (AVP) release, adult female monkeys (Macaca mulatta) with electrodes chronically implanted in the Amyg, hypothalamus and pituitary gland were given 5% dextrose and water infusions and were stimulated electrically at these sites. Immediately before and after, and at 5, 10, 15 and 30 min intervals following electrical stimulation, blood samples were withdrawn from unanesthetized monkeys, through implanted cardiac cannulae, for radioimmunoassay (RIA) of plasma AVP and for plasma osmolality determination. In the Amyg-stimulated monkeys, plasma AVP rose rapidly to peak values at the end of stimulation followed by an abrupt post-stimulation fall to control levels in 30 min. A small yet significant rise in plasma osmolality was also observed. Electrical stimulation of the hypothalamus and the pituitary gland yielded a temporal pattern of plasma AVP rise and fall identical to that seen following Amyg stimulation. Blood sampling, precisely timed to the onset and end of the stimulus train, was important in capturing the rise and fall in plasma AVP. Stimulus intensity determined the magnitude of plasma AVP elevation at each of these sites, with the highest current densities yielding the highest levels of plasma AVP. It is suggested that the Amyg may be involved in the neural triggering of AVP release from the neurohypophysis.