THE DISTRIBUTION OF VASOPRESSINERGIC AND OXYTOCINERGIC NEURONS IN THECNS OF THE GERBIL

This is the first immunohistochemical report on the distribution of th e vasopressin (VP) and oxytocin (OT) producing neurons and their proce sses in the central nervous system of the gerbil. These neurons are pr imarily associated with the paraventricular, supraoptic and accessory neurosecretory nuclei. Two types of immunoreacted neurons, large multi polar (magnocellular) and small fusiform (parvocellular), coexist in s ome of these nuclei. The distribution of VP neurons is broader than th at of OT neurons. Only VP neurons are observed in the suprachiasmatic nucleus, internal capsule, medial amygdala, dorsal hypothalamic area, dorsomedial nucleus, lateral hypothalamic area and dorsal capsule of t he ventromedial nucleus within the hypothalamus. VP neurons in these n uclei where OT neurons do not coexist are all parvocellular type. By c ontrast, only OT neurons were detected in the medial preoptic area. VP and OT containing fibers were observed throughout the central nervous system of the gerbil. Most of the projections of these two neuropepti dergic fibers terminate in the neurohypophysis and median eminence. Ex trahypophyseal projections have also been observed. The distribution o f VP neurons and their fibers are more extensive in the gerbil than in other mammals. VP neurons distributed within the internal capsule, do rsal hypothalamic area and dorsal capsule of the ventromedial nucleus of the gerbil have not yet been described in other mammals. Moreover, the diffuse VP fiber distribution in the mammillary body of the gerbil is seldom observed in that of other mammals. Due to the antidiuretic role of VP, the well-developed VP system of the gerbil may be reflecte d by its excellent water reservation ability.