Differential effect of neurointermediate lobectomy on central oxytocin and vasopressin

Removal of the neurointermediate pituitary (NIL) affects the secretion of anterior pituitary (AP) hormones. It is not known if these effects are due to changes in central neuropeptide neurons. Two neuropeptides implicated in the neuroendocrine regulation of AP hormone secretion, and which are located in the NIL, are oxytocin and vasopressin. The present study evaluated whether removal of the NIL affected oxytocin and vasopressin concentrations in discrete brain areas containing cell bodies (paraventricular nucleus), fibers (arcuate nucleus), and/or terminals (median eminence) of these central neurons. Adult male rats underwent removal (NIL-X) or visualization (SHAM controls) of the NIL using a parapharyngeal approach. Oxytocin levels increased in the paraventricular nucleus and median eminence following NIL-X, whereas vasopressin concentrations were relatively unaffected by NIL-X. The data suggest that at least part of the influence of the NIL on AP hormone secretion may result from the ability of feedback from the NIL to differentially affect central neuropeptide neurons.