This is the first immunohistochemical report on the distribution of the vasopressin (VP) and oxytocin (OT) producing neurons and their processes in the central nervous system of the gerbil. These neurons are primarily associated with the paraventricular, supraoptic and accessory neurosecretory nuclei. Two types of immunoreacted neurons, large multipolar (magnocellular) and small fusiform (parvocellular), coexist in some of these nuclei. The distribution of VP neurons is broader than that 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 the ventromedial nucleus within the hypothalamus. VP neurons in these nuclei where OT neurons do not coexist are all parvocellular type. By contrast, 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 neuropeptidergic fibers terminate in the neurohypophysis and median eminence. Extrahypophyseal projections have also been observed. The distribution of VP neurons and their fibers are more extensive in the gerbil than in other mammals. VP neurons distributed within the internal capsule, dorsal 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 reflected by its excellent water reservation ability.
Immunohistochemistry, Vasopressin, Oxytocin
