The orexin-1 receptor antagonist SB-334867 attenuates anxiety in rats exposed to cat odor but not the elevated plus maze: an investigation of Trial 1 and Trial 2 effects.

The orexins are hypothalamic neuropeptides most well known for their roles in regulating feeding and sleeping behaviors. Recent findings suggest that orexin-A may also modulate anxiety, although how and when the orexin system is involved remains unclear. To address this, we investigated the dose-dependent effects of the orexin-1 receptor antagonist SB-334867 in two rodent models of anxiety: the cat odor avoidance model and the elevated plus maze. In both models we tested the effects of SB-334867 when anxiety is novel (Trial 1) and familiar (Trial 2). In the first experiment, Wistar rats were treated with vehicle or SB-334867 (5, 10 or 20mg/kg, i.p.) prior to their first or second exposure to cat odor. During Trial 1, rats treated with 10mg/kg of SB-334867 approached the cat odor stimulus more than vehicle-treated rats. During Trial 2 the effects were more marked, with 10mg/kg of SB-334867 increasing approach times, increasing the number of times rats exited the hide box to engage in exploratory behavior, and decreasing overall hide times. In addition, the 20mg/kg dose decreased general activity during Trial 2. In the second experiment, the effects of SB-334867 (10 and 20mg/kg) were tested in the elevated plus maze. There were no significant differences produced by drug treatment during either Trial 1 or Trial 2. Results suggest that SB-334867 decreases anxiety induced by some, but not all, stressors.