In vitro differentiation of hypothalamic magnocellular neurons of guinea pigs.

The development of neurophysin-oxytocin and neurophysin-vasopressin containing neurons of the guinea pig was studied in vitro. Supraoptic (SO) and paraventricular (PV) nuclei were explanted from guinea pig foetuses at the 40th day of gestation and cultured in Maximov slides for nearly fifty days. The cultures were observed daily under a phase-contrast microscope. Explants were fixed every five days for observation with the electron microscope. At the time of explantation, magnocellular neurons were still immature. They acquired the morphologic characteristics of mature neurons, with axosomatic synapses, after about 10 days in vitro. After 15-20 days in vitro, they contained in addition neurosecretory granules (NSG), first in the Golgi region, then also dispersed in the cytoplasm. In the oldest culture (45-50 days), signs of granulolysis were regularly found. It appears that magnocellular neurosecretory neurons are able to differentiate in vitro from a primitive state in the absence of specific stimulation.