CP 376395 is a potent and selective Corticotropin releasing factor 1 (CRF1) receptor antagonist. IC50 & Target: CRF1^[1] In Vitro: CP 376395 fully antagonizes oCRF-stimulated adenylate cyclase activity in rat cerebral cortex and at human CRF1 receptors with an apparent K_i value of 12 nM, indicating antagonist functional activity. It is highly selective for the human CRF1 receptor subtype; affinity for the CRF2 receptor is >10000 nM. It shows affinities greater than 1 µM against 40 neurotransmitter receptor and ion channels^[1]. In Vivo: In the CNS, systemically administered CP 376395 blocks the effects of both exogenous and endogenous CRF. Pretreatment with CP 376395 reverses the excitation of locus coeruleus neurons induced by icv CRF (3 µg) with an ID₅₀ of completely blocked the enhanced startle response induced by icv CRF (1 µg) at 17.8 mg/kg, p.o. and partially blocked at 10 mg/kg, p.o. without significantly altering baseline startle. The attenuation of fear-potentiated startle is statistically significant at lower doses (0.32-3.2 mg/kg, p.o., with 62-83% blockade) and completely reversed by CP 376395 at 10 mg/kg, p.o^[1].