Morphological adaptability at neurosecretory axonal endings on the neurovascular contact zone of the rat neurohypophysis.

To compare the effects of a variety of acute and chronic stimuli that bring about or terminate hormone release the ultrastructure of nerve terminal contact at the basal lamina of the neurohypophysial neurovascular contact zone was examined quantitatively in young adult rats of the following treatment groups: untreated virgin females, untreated male rats, prepartum (day 21 of gestation), postpartum (on the day of parturition), lactating (14 days of suckling), mothers 10 days after their pups were weaned, 48 h water-deprived males, males given 2% saline solution (dehydrated) for 10 days, males given 2% saline as described then given tap water to rehydrate for 2 or 5 weeks. Morphometric analysis of electron micrographs revealed that all stimuli leading to increased hormone release were accompanied by both increased occupation of the basal lamina by nerve terminals as well as decreased enclosure of neurosecretory processes by pituicyte cytoplasm. Neural occupation of the basal lamina remained significantly elevated 10 days post-weaning and at 2 weeks (but not 5 weeks) of rehydration following 10 days of dehydration. Pituicyte enclosure of neurosecretory axons had returned to control values in the postweaning and 5 week (but not 2 week) rehydrated animals. The mean length of individual nerve terminal contact with the basal lamina was found to increase under some, but not all, conditions associated with increased hormone release (i.e. parturition, acute and chronic dehydration, but not during lactation) and to decrease below control values in prepartum females and after 5 weeks of rehydration.(ABSTRACT TRUNCATED AT 250 WORDS)