CRF and urocortin decreased brain stimulation reward in the rat: reversal by a CRF receptor antagonist

Abstract

The present studies were designed to investigate the effects of corticotropin-releasing factor (CRF) receptor activation and antagonism on intracranial self-stimulation (ICSS) reward using a discrete-trial current-intensity threshold procedure. Bipolar electrodes were implanted in the lateral hypothalamus, and cannula guides were implanted above the lateral ventricle of male Wistar rats. Dose-effect functions were established for the effects on ICSS of the competitive CRF receptor agonist h/rCRF (0–5.0 μg, i.c.v.), the CRF receptor agonist urocortin (0–5.0 μg, i.c.v.), and the CRF receptor antagonist [ d-Phe 12, Nle 21,38, C α MeLeu 37] h/rCRF 12–41 (0–5.0 μg, i.c.v.). Administration of h/rCRF or urocortin dose-dependently elevated ICSS thresholds without altering performance measures (latencies to respond to stimulation, extra and time-out responses). CRF was more potent than urocortin in terms of threshold dose-effects on ICSS thresholds compared to vehicle. Despite these apparent potency differences, percent effect sizes on ICSS thresholds were comparable at the highest doses of both peptides. In contrast to the significant threshold elevation effects of CRF and urocortin, the competitive CRF antagonist d-Phe CRF 12–41 had no effect on ICSS thresholds or performance measures. To determine the neuropharmacological specificity of the effect of CRF on brain stimulation reward, d-Phe CRF 12–41 was used to antagonize CRF-induced threshold elevations. Pretreatment with either the 5.0- or 10.0-μg doses of d-Phe CRF 12–41 effectively blocked CRF-induced reward threshold elevations (3.0 μg) without affecting other ICSS performance measures. These results indicate that CRF neurotransmission can modulate ICSS reward processes.