DOPAMINE RECEPTOR-MEDIATED REGULATION OF EXPRESSION OF FOS AND ITS RELATED ANTIGENS (FRA) IN SOMATOSTATIN NEURONS IN THE HYPOTHALAMIC PERIVENTRICULAR NUCLEUS

Somatostatin (SS)-containing perikarya located within the hypothalamic periventricular nucleus (PeVN) comprise a heterogenous population of neurons with both local intrahypothalamic and distant extrahypothalami c axonal projection sites. The close proximity of SS perikarya and the ir dendrites to dopaminergic (DA) neuronal processes in the PeVN sugge sts that these peptidergic neurons may be regulated by DA receptor-med iated mechanisms. To test this, the effects of the D-1 agonist SKF 383 93 and D-2/3 agonist quinelorane were examined on expression of the im mediate early gene products Fos and its related antigens (FRA) in SS-i mmunoreactive (IR) neurons in the PeVN. SS-IR neurons were located in the most medial portion of the PeVN bordered medially by the third ven tricle and laterally by tyrosine hydroxylase (TH)-IR neurons. In contr ol rats, 10-15% of all SS-IR neurons contained FRA-IR. Activation of D -1 receptors with SKF 38393 had no effect on either the total number o f SS-IR neurons or the number of SS-IR neurons containing FRA-IR. In c ontrast, activation of D-2/3 receptors with quinelorane decreased the number of SS-IR neurons containing FRA-IR, without affecting the total number of SS-IR neurons. The D-2/3 antagonist raclopride had no effec t per se, but prevented the quinelorane-induced decrease in the number of SS neurons expressing FRA-IR. These results reveal that activation of D-2/3 (but not D-1) receptors inhibits expression of the immediate early gene products FRA in SS-containing neurons in the PeVN, but exp ression of FRA in SS neurons is not tonically inhibited by dopamine ac ting on D-2/3 receptors. (C) 1997 Elsevier Science B.V.