The selective, non-peptidergic corticotropin-releasing factor (CRF) 1 receptor antagonists, CP154,526 and DMP695, dose-dependently increased punished responses of rats in a Vogel conflict test and enhanced social interaction (SI) of rats in an unfamiliarCorticotropin-releasing factor (CRF) plays a crucial role in modulation of the release of adrenocorticotrophic hormone from the anterior pituitary (De Souza 1995). In addition, CRF is broadly distributed throughout the mammalian central nervous system (CNS), being concentrated in corticolimbic regions such as amygdala, hippocampus, and periaqueductal gray (PAG) and frontal cortex (FCX), as well as the locus coeruleus (LC) and dorsal raphe nucleus (DRN), the origin of ascending adrenergic and serotonergic projections, respectively (Sawchenko et al. 1993;Van Bockstaele et al. 1996;Price et al. 1998;Steckler and Holsboer 1999). In line with this organization, independently of the hypothalamocorticotrophic axis, cerebral CRF-containing neurones fulfill an important role in the control of emotional behavior (Adamec and McKay 1993;De Souza 1995;Mitchell 1998;Steckler and Holsboer 1999;Smagin and Dunn 2000), actions expressed via two principal subtypes of CRF receptor, both of which positively couple to adenyl cyclase (Grigoriadis et al. 1996). CRF 1 receptors bind CRF and a related neuropeptide, urocortin, with high affinity whereas CRF 2 receptors display a NO . 4 distinct preference for the latter (Donaldson et al. 1996;Grigoriadis et al. 1996). Of several splice variants of the latter, the CRF 2 ␣ subtype is found predominantly in the rodent CNS, notably in several corticolimbic regions enriched in CRF itself, such as the hippocampus, medial amygdala, septum, olfactory bulb, and raphe nuclei, although species differences in this regard should be pointed out (Chalmers et al. 1995;Sánchez et al. 1999). Studies of mRNA encoding CRF 1 receptors and of the corresponding peptide have established a contrasting pattern of distribution in rats with a predominance of CRF 1 over CRF 2 ␣ sites in anterior pituitary, FCX and basolateral amygdala, as well as high levels in the hippocampus and PAG (Potter et al. 1994;Chalmers et al. 1995;Sánchez et al. 1999;Chen et al. 2000).These observations provide a neuroanatomical substrate for a potential role of CRF 1 and/or CRF 2 receptors in the control of mood (Coplan et al. 1996;Steckler and Holsboer 1999), and, in this regard, there is a diversity of evidence implicating CRF 1 sites in the modulation of anxious states. First, several studies have reported anxiogenic actions of CRF (and urocortin) upon i.c.v. administration (see Steckler and Holsboer, 1999) and similar effects have been seen upon direct introduction into the dorsal PAG (Martins et al. 1997), basolateral amygdala (Sajdyk et al. 1999), and hippocampus (Radulovic et al. 1999), structures possessing a high density of CRF 1 receptors. Second, direct evidence for participation of CRF 1 receptors in anxiogenic actions is derived from studies of antisense probes for their ...