The neurophysin-containing innervation of the forebrain of the mouse

Abstract The oxytocinergic and vasopressinergic innervation of the forebrain of normal mice was studied immunocytochemically by use of a set of mouse monoclonal anti-neurophysins applied to serial vibratome sections. The extensive hypothalamic and extra-hypothalamic location of these neuropeptides was revealed, with, or without colchicine pretreatment. Magnocellular perikarya immunoreactive for either oxytocin-neurophysin or vasopressin-neurophysin were concentrated mainly: in the anterior commissural nucleus; in various subdivisions of the paraventricular nucleus; in a profuse array in the periventricular region; in the supraoptic nucleus including its retrochiasmatic division; in various accessory nuclei; and as a number of cells scattered throughout the preoptic and hypothalamic regions. Extensive groups of parvocellular neurons, containing only vasopressin-neurophysin, were located in the suprachiasmatic nucleus including a ventromedian division, in the bed nucleus of the stria terminalis, and in the medial amygdaloid nucleus. Perikarya in the magnocellular nuclei were of generally similar size distribution and there was no evidence that distinct populations of magnocellular and parvicellular neurons, separable on the basis of size, had been labelled within these nuclei. Within the paraventricular nucleus, however, neurons in the posterior part were smaller than those located more anteriorly, and the cells containing oxytocinneurophysin were slightly smaller than those containing vasopressin-neurophysin. Within the generally similar size distribution, magnocellular neurons of the anterior commissural nucleus were the largest. During processing, shrinkage of the tissue and immunolabelled cells had occurred. The immunocytochemical procedure delineated neuronal processes, in particular dendrites, very effectively. The dendrites were shown to project for far greater distances than is generally recognized, some were of a characteristic corkscrew-like morphology, and most were oriented in a well-defined pattern. Many dendrites of paraventricular neurons passed medially then caudally towards and then along the third ventricle. Most dendrites of supraoptic neurons, in particular those containing vasopressinneurophysin, had an extensive anteroposterior course beneath the pia of the base of the brain. The axons containing oxytocin- and vasopressin-neurophysin were shown to take rather different paths from the paraventricular nucleus towards the median eminence. Other well-delineated immunoreactive processes and putative terminal plexi were found throughout the preoptic area, the septum, hypothalamus, subthalamus, thalamus, habenula, amygdala and ventral hippocampus; scattered fibres were also seen in the cortex. In general the bundles of fibres containing vasopressin-neurophysin were more dense, more extensive and of wider distribution than those containing oxytocin-neurophysin, although individual fibres were in the same calibre range. Distinguishing features of the forebrain of mice include a large population of neurophysinimmunoreactive perikarya throughout the subependymal periventricular region of the rostral third ventricle, an extensive anterior commissural nucleus containing both oxytocin- and vasopressinneurophysin, a distinctive bilateral accessory nucleus in the medioventral hypothalamus, a rostromedian division of the suprachiasmatic nucleus, a prominent posterior division of the paraventricular nucleus, and conspicuous neurophysin-immunoreactive plexi in the subthalamus.