The analgesic effect of corticotropin-releasing factor given into the periaqueductal gray matter of the midbrain

Corticotropin-releasing factor (CRF) is involved in regulating stress-induced analgesia. One of the key structures of the brain's antinociceptive system is the periaqueductal gray matter of the midbrain (PAGM). The aim of the present work was to study the effects of CRF given into the PAGM on pain sensitivity in conscious rats and the contribution of opioid mechanisms to mediating these effects. Somatic pain sensitivity was tested in terms of the latent period of the tail flick reaction in rats in response to thermal stimulation of the tail. The contribution of opioid mechanisms was studied by blockade of opioid receptors with the antagonist naltrexone, given both systemically and centrally into the PAGM. Administration of CRF (0.7 μg/rat into the PAGM induced an analgesic effect. Both systemic and central administration of naltrexone led to elimination of the analgesic effect of CRF, more quickly after central administration. The data obtained here provide evidence that one of the central mechanisms of the analgesic action of CRF on somatic pain sensitivity may be mediated by PAGM neurons with the involvement of opioid mechanisms. © 2013 Springer Science+Business Media New York.