Anxiolytic-Like Effects of Antisauvagine-30 in Mice Are Not Mediated by CRF(2) Receptors

The role of brain corticotropin-releasing factor type 2 (CRF(2)) receptors in behavioral stress responses remains controversial. Conflicting findings suggest pro-stress, anti-stress or no effects of impeding CRF(2) signaling. Previous studies have used antisauvagine-30 as a selective CRF(2) antagonist. The present study tested the hypotheses that 1) potential anxiolytic-like actions of intracerebroventricular (i.c.v.) administration of antisauvagine-30 also are present in mice lacking CRF(2) receptors and 2) potential anxiolytic-like effects of antisauvagine-30 are not shared by the more selective CRF(2) antagonist astressin(2)-B. Cannulated, male CRF(2) receptor knockout (n = 22) and wildtype littermate mice (n = 21) backcrossed onto a C57BL/6J genetic background were tested in the marble burying, elevated plus-maze, and shock-induced freezing tests following pretreatment (i.c.v.) with vehicle, antisauvagine-30 or astressin(2)-B. Antisauvagine-30 reduced shock-induced freezing equally in wildtype and CRF(2) knockout mice. In contrast, neither astressin(2)-B nor CRF(2) genotype influenced shock-induced freezing. Neither CRF antagonist nor CRF(2) genotype influenced anxiety-like behavior in the plus-maze or marble burying tests. A literature review showed that the typical antisauvagine-30 concentration infused in previous intracranial studies (∼1 mM) was 3 orders greater than its IC(50) to block CRF(1)-mediated cAMP responses and 4 orders greater than its binding constants (K(d), K(i)) for CRF(1) receptors. Thus, increasing, previously used doses of antisauvagine-30 also exert non-CRF(2)-mediated effects, perhaps via CRF(1). The results do not support the hypothesis that brain CRF(2) receptors tonically promote anxiogenic-like behavior. Utilization of CRF(2) antagonists, such as astressin(2)-B, at doses that are more subtype-selective, can better clarify the significance of brain CRF(2) systems in stress-related behavior.