Rats were treated chronically with atropine (14 days, 20 mg/kg/day, s.c.) and corticotropin-releasing factor (CRF) receptors and CRF-mediated adenylate cyclase activity were measured in discrete brain regions. Chronic atropine treatment produced significant increases in muscarinic cholinergic receptors in the frontoparietal cortex (30% increase) and hippocampus (20% increase). No significant changes in the concentration of [125I]Tyr0-rat CRF binding sites were observed in olfactory bulb, cerebellum, striatum and hippocampus. In contrast, there was a significant and selective increase (35%) in CRF receptors in the frontoparietal cortex of atropine-treated rats. However, no significant corresponding changes in the Vmax or EC50 of CRF-stimulated adenylate cyclase activity accompanied the upregulation of CRF receptors in the cerebral cortex. These results demonstrate that CRF receptors in rat brain are subject to receptor regulation, the upregulation of CRF receptors occurs as a consequence of chronic muscarinic cholinergic receptor blockade, and this interaction between acetylcholine and CRF may be limited to the cerebral cortex.