Oxytocin- and vasopressin-immunoreactive nerve fibers in the pineal gland of the hedgehog, Erinaceus europaeus L.

Oxytocin- and vasopressin-immunoreactive nerve fibers, apparently originating from a dorsal subunit of the paraventricular nucleus, were demonstrated in the pineal gland of the hedgehog. The majority of these fibers (pinealopetal projections) is intimately related to the capillaries of the pineal organ, whereas only a few elements are scattered throughout the pineal parenchyma. The number of peptidergic elements observed in the central portion of the pineal organ exceeds that of fibers located at the periphery. In relation to the functional state of the animals, the amount of immunoreactive material in these pinealopetal nerve fibers exhibits conspicuous variations. In hibernating hedgehogs (group 1), these nerve fibers were considerably richer in oxytocin than in non-hibernating or arousing winter animals (group 2 and 3). In contrast, only weak immunoreactivity for vasopressin was found in intrapineal nerve fibers of hibernating hedgehogs (group 1), whereas the fibers of arousing or non-hibernating hedgehogs (group 2 and 3) contained slightly larger amounts of vasopressin. In the pineal organ of animals sacrificed during the summer period (group 4), no immunoreactivity for both neuropeptides was found. The functional significance of the connection between the hypothalamic paraventricular nucleus and the pineal organ is discussed with special reference to the vascular terminals of the pinealopetal peptidergic nerve fibers.