The autoradiographic distribution of [³H]arginine vasopressin, [³H]spiperone, [³H]GABA, [³H]dihydroalprenolol and the peripheral-type benzodiazepine ligand [³H]Ro5-4864 were examined in the rat pituitary before and after pituitary stalk transection. Stalk transection produced dramatic changes in the cellular architecture of the pars nervosa. Glial fibrillary acidic protein, an astrocyte marker reported in pituicytes, increased after stalk transection, whereas neurofilament, a marker for neuronal innervation, was lost. These structural changes demonstrated a successful stalk transection, permitting interpretation of changes in the densities of several [³H]-ligands over the three lobes. [³H]Ro5-4864 binding was markedly increased, suggesting that this site was located on the pituicytes. Conversely [³H]spiperone and [³H]arginine vasopressin binding density over the pars nervosa decreased. In the mutant diabetes insipidus rat (Brattleboro), which lacks pituitary vasopressin, [³H]arginine vasopressin binding was undetectable in the pars nervosa. [³H]dihydroalprenolol and [³H]GABA binding sites were unchanged by the lesion. These results are discussed in terms of the occurrence of functional acceptors on pituicytes and their possible role in neurohydrophyseal secretions.

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Astrocyte-enriched monolayer cultures were obtained by growing cells dissociated from 8-day-old rat cerebella pretreated with hydroxyurea. After 7 days in vitro a carpet of flat polygonal cells was obtained. The identity of these flat cells was established and their numbers quantified using immunological markers for astrocytes, fibroblasts and endothelial cells (antisera against fibrillary acidic protein and Thy-1, and Chagasic sera respectively). A combination of [³H] thymidine autoradiography and immunocytochemistry showed extensive replication of astrocytes, the number of which rose from about 20 to 80% of the total cells during the 1st week in vitro: 80% of these cells were labelled at 7 days after exposure to thymidine on the 1st day in culture. The culture conditions chosen did not support the survival of nerve cells, and fibroblasts constituted 5–7% of the cells at 7–14 DIV, whilst the total cell number remained roughly constant. On the other hand, staining with a new specific marker for endothelial cells revealed that these cells divided actively, ultimately accounting for the majority of the non-astrocytic cells.