D-2 INHIBITION OF STIMULATED FOS IMMUNOREACTIVITY IN CULTURED TYROSINE HYDROXYLASE-IR HYPOTHALAMIC NEURONS

We have previously demonstrated that Fos immunoreactivity can be stimu lated by KCl, forskolin or glutamate in cultured tyrosine hydroxylase- immunoreactive (TH-ir) hypothalamic neurons. The present study was per formed to determine whether agents that regulate dopaminergic activity , particularly D-1 and D-2 receptor agonists, modulate the intracellul ar cascade leading td Fos expression. Dissociated hypothalamic culture s were prepared from neonatal rats. The cultures were treated with D-1 - or D-2-specific agonists, followed by KCl, forskolin or glutamate. C ultures were fixed after 2 h and immunocytochemically stained for tyro sine hydroxylase and Fos. Pretreatment of the cultures with the D-2 ag onist LY163502 inhibited KCl- and forskolin-stimulated Fos-ir in TH-ir neurons in a saturable dose-dependent manner. The maximal effective d ose was 30 mu M LY163502, which decreased Fos-ir by 23% in cultures tr eated with 50 mM KCl and by 33% in those treated with 30 mu M forskoli n. The D-2 agonist had no effect on glutamate-stimulated Fos-ir. LY163 502 inhibition of Fos-ir was blocked by D-2 antagonist or Boudetella p ertussis toxin pretreatment which demonstrates that the effect is medi ated by D-2 receptor activation of an inhibitory G protein. Treatment of the cultures with the D-1 agonist SKF82526 had no effect on basal o r stimulated levels of Fos-ir. These results demonstrate that in neona tal TH-ir hypothalamic neurons the D-2 receptor system may regulate le vels of the immediate-early gene product Fos and, therefore, subsequen t genetic expression in these neurons.