STIMULUS-SECRETION COUPLING IN THE NEUROHYPOPHYSIS OF THE JERBOA JACULUS-ORIENTALIS

1. In many mammals, severe dehydration is known to cause exhaustion of the vasopressin content of the neural lobe. Here, we have examined th e physiological state of the neurohypophysis of the jerboa Jaculus ori entalis, a rodent inhabitant of a semi-desert climate. 2. Isolated neu rohypophyses and neurosecretory nerve endings were perfused in vitro a nd vasopressin and oxytocin release were determined by radioimmunoassa y. 3. Electrical stimulation of the neurohypophysis with bursts of pul ses mimicking the activity of hypersecreting neuroendocrine neurones i nduced similar increases of secretion in both control animals and anim als dehydrated for up to 2 months. Neurohormone release was greatly po tentiated when the bursts of pulses were separated by silent intervals . 4. Prolonged stimulation of neurohypophyses from both control and de hydrated animals induced a sustained increase of vasopressin release; in contrast, oxytocin release under similar conditions showed a biphas ic secretory pattern consisting of a transient increase that subsequen tly decreased to a steady level whose amplitude was similar to that fo r vasopressin. 5. K+-induced secretion was largely inhibited by the Ca 2+ channel blockers nicardipine and omega-conotoxin, suggesting that i n this neurosecretory system both L- and N-type calcium channels play a major role in stimulus-secretion coupling. Depolarization of isolate d nerve endings using a fast-flow perifusion system showed that there was no difference in the amplitude and the time course of the secretor y response in dehydrated and hydrated animals. 6. The results demonstr ate that, despite the climatic conditions in which the jerboas live, t heir neural lobes retain the capacity to release, upon depolarization of the plasma membrane of the nerve endings, large amounts of neurohor mone. It is concluded that the neurohypophyseal peptidergic release sy stem in the dehydrated jerboa functions adequately even under extreme environmental stress.