Effects of ovine CRF injections into the dorsomedial, dorsolateral and lateral columns of the periaqueductal gray: A functional role for the dorsomedial column Karina G. Borelli, Marcus L. Brandão ⁎ Instituto de Neurociências & Comportamento-INeC, Campus USP, 14040-901, Ribeirão Preto, SP, Brazil Laboratório de Psicobiologia, FFCLRP, Campus USP, Avenida Bandeirantes 3900, 14049-901, Ribeirão Preto, SP, Brazil Received 26 June 2007; revised 16 August 2007; accepted 17 August 2007 Available online 7 September 2007 Abstract Corticotropin-releasing factor (CRF) and its receptor subtypes have been implicated in the regulation of endocrine, behavioral and autonomic responses to stress, fear and anxiety. Ovine CRF (oCRF) is a nonspecific CRF receptor agonist that produces anxiogenic-like effects when injected locally into the dorsal aspects of the periaqueductal gray (PAG). This structure is subdivided into four distinct longitudinal columns but their exact functional role is not fully understood. The purpose of the present study was to characterize the effects of oCRF (0.25, 0.5 and 1 μg/0.2 μL) injections into the dorsomedial (dmPAG), dorsolateral (dlPAG) and lateral (lPAG) columns of the PAG using an analysis of the exploratory behavior of rats in the elevated plus-maze (EPM) test. The results showed that microinjections of oCRF intra-dmPAG reduced entries and time spent in the open arms and decreased end-arm exploration and head-dipping. In contrast, oCRF intra-dlPAG or lPAG did not affect the exploratory behavior of the animals in the EPM. These findings point to a columnar specificity for the oCRF effects in the PAG, that is, it increased spatial avoidance measures of the EPM test only in the dmPAG. The proaversive effects of oCRF in the dmPAG gain further relevance when combined with previous immunohistochemical studies showing that CRF-containing projections from the periventricular hypothalamic system arch dorsomedially to the PAG, which could function as an important relay station in the midbrain tectum for avoidance behaviors. © 2007 Elsevier Inc. All rights reserved. Keywords: Anxiety; Fear; oCRF; Elevated plus-maze; Dorsomedial column of the PAG Introduction Many reports indicate that the dorsal periaqueductal gray (dPAG) is one of the main structures involved in the inte- gration of defensive behavior in the brain (Blanchard et al., 1981, 1993; Behbehani, 1995; Brandão et al., 1999). Indeed, its electrical or chemical stimulation produces several behavioral and somatic responses characteristic of high fear states, similar to that observed in animals confronted by predators or dangerous environmental cues (for reviews see Brandão et al., 1999, 2005). A brain aversion system essentially composed of the amygdala, medial hypothalamus and dPAG seems to be responsible for the organization of fear and anxiety-like behaviors (Graeff et al., 1997, Graeff, 2004; Blanchard et al., 2005; Brandão et al., 1999, 2005). The amygdala and the medial hypothalamus act downstream, through descending projections to brainstem regions, particularly the PAG (Canteras et al., 1997; Canteras and Goto, 1999; Risold and Swanson, 1997). The superior and inferior colliculi have also been proposed to integrate this system (Brandão et al., 1988, 1999, 2005). Thus, the midbrain tectum has been proposed as part of the neural substrates responsible for the expression of defensive behaviors. After a long series of studies carried out since the beginning of the 80s, it is well established that a variety of neurotransmit- ters mediate the defense-related behavior in the brain aversion system, that include γ-amino-butyric-acid (GABA; Brandão et al., 1982, 1988; Melo et al., 1992; Coimbra and Brandão, 1993), serotonin (Brandão et al., 1993; Melo and Brandão, 1995; Castilho and Brandão, 2001; Graeff, 2004; Coimbra et al., Available online at www.sciencedirect.com Hormones and Behavior 53 (2008) 40 – 50 www.elsevier.com/locate/yhbeh ⁎ Corresponding author. Fax: +55 16 3602 4830. E-mail address: mbrandao@usp.br (M.L. Brandão). 0018-506X/$ - see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2007.08.013