In vitro and in vivo studies on development and regeneration of vasopressin neurons.

The present paper reviews recent work conducted in our laboratory on vasopressin neurons either grown in culture or transplanted into vasopressin deficient rats. The in vitro model of reaggregated cell culture used the anterior hypothalamus, including vasopressin neurons of the SON from normal timed-pregnant LE rats of similar ages used in our in vivo model. Various cells were co-cultured with their known target tissue, the posterior pituitary to analyze further the influence of the target tissue on hormone production. At a designated end point, cultured cells were fixed and stained immunocytochemically for vasopressin and neurophysin. Radioimmunoassay of the samples was performed for vasopressin quantification. Hypothalamic cells from all ages produced vasopressin (VP). The co-culturing of hypothalamus with posterior pituitary produced a significant increase in VP. Correlative transplantation studies were conducted using timed-pregnant Long-Evans (LE) rats at various days post coitus (dpc) and neonatal tissue from 0- and 5-day old rat pups. Animals survived about 40 days then were perfused and their brains processed for vasopressin and neurophysin thick-section immunocytochemistry. The results showed that the capability for survival of younger grafts was much greater than that of older tissue. With this paper, we have shown that the reaggregation of anterior hypothalamic cells in a culture system can be used for microassay of neurosecretory activity. These data suggest a close correlation between the ability of a neuron to survive transplantation and its stage of development. With the present studies, we have shown that neurons not fully differentiated maintain a greater degree of plasticity than older tissue and are better able to survive the rigors of transplantation and that various manipulations of environmental factors have an effect on brain development at critical times.