THE SUPRACHIASMATIC NUCLEUS IN STATIONARY ORGANOTYPIC CULTURE

Suprachiasmatic nuclei, derived from neonate rats, were maintained for several weeks in stationary organotypic culture. Hypothalamic slice e xplants, supported by Millicell filters and incubated in Petri dishes containing serum-based medium, flattened appreciably, yet preserved th e organization of the suprachiasmatic nucleus and the surrounding hypo thalamic tissue. After two to three weeks, cultures were fixed, and th ree neuronal sub-populations were identified as vasopressinergic, vaso active intestinal peptide-containing, or GABA-containing. The GABAergi c component of the cultured suprachiasmatic nucleus was particularly p rofuse, projecting extensively into the hypothalamic slice. Unilateral ablation of the nucleus in the explant dramatically reduced ipsilater al GABA-immunoreactivity in the slice. Explants in which an incision s eparated the bilateral suprachiasmatic nucleus from the paraventricula r nucleus, deprived the latter of its fine-caliber GABA-immunoreactive input. Extra- or intra-cellular electrophysiological recordings from the suprachiasmatic nucleus were obtained in 51 of 58 cultures. The el ectrical properties of the long-term cultured suprachiasmatic nucleus were similar to those recorded in acute slices from adult rats. In six cultures recordings were extended for up to 10-24 h. Within long-term stationary organotypic cultures of the suprachiasmatic nucleus, sub-p opulations of neurons, intrinsic to the nucleus in vivo, were identifi ed immunocytochemically. Lesion studies supported the observation that the main source of the GABAergic innervation within the entire hypoth alamic slice explant appeared to be the suprachiasmatic nucleus. Elect rophysiological studies confirmed the viability of the long-term cultu red nucleus and revealed changes in spontaneous electrical activity th at may indicate circadian fluctuation.