INVOLVEMENT OF CORTICOTROPIN-RELEASING FACTOR RECEPTORS TYPE 2, LOCATED IN PERIAQUADUCTAL GRAY MATTER, IN CENTRAL AND PERIPHERAL CRF-INDUCED ANALGESIC EFFECT ON SOMATIC PAIN SENSITIVITY IN RATS

Corticotropin-releasing factor (CRF) is involved in the regulation of pain sensitivity and can induce an analgesic effect in animals and humans. The periaqueductal gray matter (PAGM) of the midbrain is one of the key structures of the antinociceptive system. The aim of the study was to investigate the involvement of CRF receptor type 2 (CRF-R2 receptors), localized in the PAGM, in the analgesic effect caused by central or systemic CRF on somatic pain sensitivity in conscious rats. Somatic pain sensitivity was tested by a tail flick test (measuring tail flick latency induced by tail's thermal stimulation). The involvement of CRF-R2 receptors was studied by administering the selective antagonist astressin(2)-B into the PAGM. Both peripheral and central CRF administration caused an increase in tail flick latencies (analgesic effect). Administration of astressin2-B into the PAGM attenuated the analgesic effect induced by the central as well as systemic CRF administration. The results suggest that one of the mechanisms of the CRF-induced analgesic effect may be mediated by CRF-R2 receptors located in PAGM.