Histaminergic nerve fibers in the median eminence and hypophysis of rats demonstrated immunocytochemically with antibodies against histidine decarboxylase and histamine.

Histaminergic fibers in the median eminence and hypophysis of rats were examined immunocytochemically with antibodies against histidine decarboxylase (HDC), the sole histamine-synthesizing enzyme, and against histamine itself. A similar distribution of immunoreactive fibers was observed with these two antibodies. In the median eminence, immunoreactive fibers were mainly located in the internal layer and could be traced to the posterior lobe of the hypophysis. A few fibers were detected in the external layer of the median eminence, but none in the anterior or intermediate lobe of the hypophysis. These observations suggest that neuronal histamine may take part in regulation of the hypothalamo-neurohypophysial neuroendocrine system in rats.