Long-term suspension culture of isolated hypothalamic nuclei of the rat: morphological differentiation and release of substances influencing corticotropin and growth hormone secretion

Individual hypothalamic nuclei were removed from 17-day-old rat embryos with 300 microns punches and maintained in suspension culture. Suspension culture of isolated nuclei appears to be suitable for studying morphological and functional differentiation of neural tissue and release of bioactivity influencing corticotropin and growth hormone release. During the 4 weeks in culture, neurons and glial cells differentiated well in each nucleus studied. The fine structure of the arcuate, periventricular, ventromedial and dorsomedial nuclei resembled that of the adult nuclei with many mature synapses; in contrast, in the neuropil of cultured preoptic, paraventricular and posterior hypothalamic nuclei mature synapses were very few or absent. The release of substances influencing corticotropin and growth hormone secretion by the cultured nuclei was tested in bioassays using anterior pituitary cell cultures and radioimmunoassay of hormones released into the medium. Corticotropin-releasing bioactivity was tested at weekly intervals. Cultured preoptic and paraventricular nuclei released corticotropin-releasing activity for up to 4 weeks whereas arcuate nuclei released corticotropin-releasing activity at 1 week only. The ventromedial and dorsomedial nuclei did not release corticotropin-releasing activity. The release of substances influencing growth hormone secretion was studied between 3 and 11 days in culture. After 3 days the medium of some hypothalamic nuclei stimulated growth hormone secretion, but after 7 and 11 days all cultured nuclei strongly inhibited it. The present findings demonstrate that hypothalamic nuclei can be cultured separately and suggest that neurons capable of releasing corticotropin-releasing activity(ies) are present in the preoptic and paraventricular nuclei of the rat whereas all hypothalamic nuclei studied contain intrinsic neurons capable of synthesizing and secreting somatostatin-like bioactivity.