Effects of alpha-flupenthixol and naloxone on CRF-induced locomotor activation.

Corticotropin-releasing factor injected intracerebroventricularly in a dose of 1 microgram produced a prolonged locomotor activation (3 h) in rats previously habituated to the test cage environment. This activation was reversed by alpha-flupenthixol (intraperitoneally), a dopamine receptor antagonist, only at cataleptic doses and not at all by naloxone (subcutaneously) in doses of 0.02-5.0 mg/kg. The effective dose 50% (ED50) for the alpha-flupenthixol reversal of locomotor activity induced by corticotropin-releasing factor was 0.13 mg/kg; similar to the 0.14 mg/kg ED50 needed to reverse the locomotor activation produced by caffeine (10 mg/kg s.c.). The ED50 necessary to reverse amphetamine (0.75 mg/kg s.c.) locomotion with this drug was 0.07 mg/kg. The results suggest that the corticotropin-releasing factor acts independently of direct activation of the dopamine or opioid peptide systems.