The origin of the vasopressinergic and oxytocinergic fibres of the external region of the median eminence of the rat hypophysis.

The origin of the vasopressinergic and oxytocinergic nerve fibres of the external region of the rat median eminence was investigated by means of hypothalamic lesions, adrenalectomy and immunocytochemistry. The results obtained in bilaterally adrenalectomized animals with complete, or incomplete, destruction of the suprachiasmatic nuclei showed that, at least, the great majority of the vasopressinergic and oxytocinergic nerve fibres of the external region of the rat median eminence do not originate from the suprachiasmatic nuclei. From the observations obtained in bilaterally adrenalectomized animals with total or subtotal destruction of both paraventricular hypothalamic nuclei, it appears that the paraventricular nuclei must be the origin of (nearly) all the vasopressinergic and oxytocinergic nerve fibres of the external region of the rat median eminence. The results strongly suggest that both types of fibres originate from all parts of the paraventricular nuclei.