Pro- and anti-nociceptive effects of corticotropin-releasing factor (CRF) in central amygdala neurons are mediated through different receptors

Corticotropin-releasing factor ( CRF) is not only a stress hormone but also acts as a neuromodulator outside the hypothalamic-pituitary-adrenocortical axis, playing an important role in anxiety, depression, and pain modulation. The underlying mechanisms remain to be determined. A major site of extra- hypothalamic expression of CRF and its receptors is the amygdala, a key player in affect-related disorders such as anxiety. The latero-capsular division of the central nucleus of the amygdala ( CeLC) is also important for pain modulation and pain affect. This study analyzed the effects of CRF on nociceptive processing in CeLC neurons and the contribution of CRF1 and CRF2 receptors and protein kinases A and C. Extracellular single-unit recordings were made from CeLC neurons in anesthetized adult rats. All neurons responded more strongly to noxious than innocuous mechanical stimulation of the knee. Evoked responses and background activity were measured before and during administration of CRF into the CeLC by microdialysis. CRF was administered alone or together with receptor antagonists or protein kinase inhibitors. CRF (0.01-1 mu M; concentrations in microdialysis probe; 15 min) facilitated the evoked responses more strongly than background activity; a higher concentration ( 10 mu M) had inhibitory effects. Facilitation by CRF ( 0.1 mu M) was reversed by a selective CRF1 receptor antagonist ( NBI27914, 10 mu M) but not a CRF2 receptor antagonist ( astressin-2B, 100 mu M) and by a protein kinase A ( PKA) inhibitor ( KT5720, 100 mu M) but not a protein kinase C inhibitor ( GF109203X, 100 mu M). Inhibitory effects of CRF ( 10 mu M) were reversed by astressin-2B. These data suggest that CRF has dual effects on amygdala neurons: CRF1 receptor-mediated PKA-dependent facilitation and CRF2 receptor-mediated inhibition.