Immunological evidence for thyroliberin (TRH) neurons in primary cultures of fetal mouse brain cells. Ontogenic aspects.

Primary cultures of dissociated cells were initiated from fetal mouse hypothalami and brain hemispheres, on the 13th and the 16th day of gestation (respectively 12-day and 15-day-old fetuses). After 10 days in vitro, the cultured cells were collected, pooled in an appropriate medium and thyroliberin (TRH) was assayed in the cell extracts using a specific radioimmunoassay. TRH was found in every type of culture. For hypothalami, higher levels of TRH were found when when starting from older embryos, while in brain hemisphere cultures the TRH content increased in culture of 12-day-old fetal cells only, whereas it decreased in cultures of 16-day-old fetal cells. Immunocytochemical staining allows visualization of TRH positive cells in all cultures except in hypothalamic cultures from 12-day-old embryos. This is consistent with the radioimmunoassay data. TRH was localized exclusively in some of the overlying cells, whereas the basal cells were always negative. Specificity of the staining was assessed by immunochemistry and radioimmunoassay. At the electron microscope level, the positive cells display neuronal features. The immunoprecipitate was found in both perikaryon and axons as well as in axonal dilatations.