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

Abstract

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.