Reduction of Stress-Induced Behavior by Antagonism of Corticotropin-Releasing Hormone 2 (CRH2) Receptors in Lateral Septum or CRH1Receptors in Amygdala

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Abstract
Although corticotropin-releasing hormone (CRH), a regulator of stress responses, acts through two receptors (CRH1 and CRH2), the role of CRH2 in stress responses remains unclear. Knock-out mice without the CRH2gene exhibit increased stress-like behaviors. This profile could result either directly from the absence of CRH2 receptors or indirectly from developmental adaptations. In the present study, CRH2 receptors were acutely blocked by α-helical CRH (αhCRH, CRH1/CRH2 antagonist; 0, 30, 100, and 300 ng) infusion into the lateral septum (LS), which abundantly expresses CRH2 but not CRH1receptors. Freezing, locomotor activity, and analgesia were tested after infusion. Intra-LS αhCRH blocked shock-induced freezing without affecting activity or pain responses; infusions into lateral ventricle or nucleus of the diagonal band had no effects. The same behavioral profile was obtained with d-Phe-CRH(12–41)(100 ng), another CRH1/CRH2 antagonist. A selective CRH1 antagonist (NBI27914), in doses that reduced freezing on intra-amygdala (central nucleus) infusion (0, 0.2, and 1.0 μg), did not affect freezing when infused into the LS.Ex vivo autoradiography revealed that binding of [125I]sauvagine, a mixed CRH1/CRH2 agonist, was prevented in the LS by previous intra-LS infusion of αhCRH but not NBI27914. In vitro studies demonstrated that [125I]sauvagine binding in the LS could be inhibited by a CRH1/CRH2 antagonist but not by the selective CRH1 receptor antagonist, confirming that in the LS, αhCRH antagonized exclusively CRH2receptors. Acute antagonism of CRH2 receptors in the LS thus produces a behaviorally, anatomically, and pharmacologically specific reduction in stress-induced behavior, in contrast to results of recent knock-out studies, which induced congenital and permanent CRH2 removal. CRH2 receptors may thus represent a potential target for the development of novel CRH system anxiolytics.