Neurochemical and behavioral effects of corticotropin-releasing factor in the ventral tegmental area of the rat

Corticotropin-releasing factor (CRF) is thought to have a neurotransmitter function in the mammalian central nervous system. The release of CRF into the hypothalamic-hypophyseal portal system in response to stress is known, and it has been suggested that CRF may function elsewhere in the central nervous system to promote stress-induced physiological and behavioral changes. Acute stress has been shown to activate dopamine (DA) neurons in the ventral tegmental area (VTA) that project to the prefrontal cortex. To determine whether CRF may act in the VTA to activate the mesocortical or mesolimbic DA systems, it was injected into the VTA of rats, and changes in spontaneous motor behavior and DA metabolism were measured. Intra-VTA injection of CRF produced a dose-dependent increase in horizontal and vertical photocell counts with a minimal effective dose of 0.01 and 0.1 nmol, respectively. In contrast, the minimal effective dose for CRF-stimulated motor behavior after injection into the lateral ventricles was 0.3 nmol for horizontal activity. Furthermore, in the open field, the behavioral profile of CRF (0.3 nmol) given intra-VTA differed from that observed after intraventricular injection. The motor stimulant effect of intra-VTA CRF was not blocked by pretreatment with the DA receptor antagonist haloperidol. After intra-VTA injection, CRF produced a dose-dependent decrease in DA metabolism in the prefrontal cortex. The decrease in DA metabolism in the prefrontal cortex was present at 30 and 60 min but not at 120 min after injection, and in the nucleus accumbens DA metabolism was increased only at 60 min after injection.(ABSTRACT TRUNCATED AT 250 WORDS)