Infundibular localization of vasopressin, oxytocin and neurophysins in the rat; its relationships with corticotrope function.

The distribution of vasopressin (VP), oxytocin (OXY) and neurophysins 1 and 2 (N1, N2) has been studied in the median eminence (ME) of normal, heterozygous (HDI) and Brattleboro (DI) rats. Numerous thin periportal VP and N2 fibres exist in the normal and HD1 rats; they have never been observed in the DI rats. N1 and OXY fibres in the external layer of the median eminence are rare. Adrenalectomy increases periportal VP and N2 loading in normal and HDI rats; it does not modify the appearance of the DI median eminence. Dexamethasone prevents external VP and N2 overloading in adrenalectomized rats injected during the whole postoperative period. Injections of vasopressin indicated that it had a negative feedback effect during a short time (3 days) but not during a longer period (7 days). The suprachiasmatic neurons are stained only by anti-VP and anti-N2 antibodies. Their overstaining induced by adrenalectomy disappears with dexamethasone, aldosterone or vasopressin treatment. This central effect of hormones is not necessarily associated with disappearance of overloading in the external layer of the ME. The hypothalamo-infundibular tract carrying VP and N2 is involved in regulatory mechanisms of the corticotrope axis. Its relationships with suprachiasmatic neurons are discussed.