| dc.description | Rat pups emit ultrasonic vocalizations (UVs) when separated from the dam and littermates. Some investigators have suggested that isolation-induced UVs signify a behavioural manifestation of distress or anxiety. Many compounds that possess anxiolytic properties reduce isolation-induced UVs, whereas anxiogenic drugs increase UVs. The CCK tetrapeptide fragment (CCK-4) induces panic in humans, and individuals diagnosed with panic disorder exhibit a heightened sensitivity to the anxiogenic effects of CCK-4. However, the effects of CCK in traditional animal models of anxiety have been variable, and data examining the effects of CCK on isolation-induced UVs is limited. Previous studies have demonstrated an anxioselective effect for CCK-8s in 11-day-old rats (Weller & Blass, 1988), although negative results have been reported with younger pups (Rex, Barth, Voight, Domeney, & Fink, 1994; Weller & Dubson, 1998). CCK-4 has been shown to increase UV rates (Rex et al., 1994) in 5-day-old rats. The current series of experiments was designed to assess the effects of various CCK fragments and antagonists on isolation-induced UVs, motor activity, and body temperature in 12-day-old, Long Evans hooded rats. It was hypothesized that CCK-4 would increase, whereas CCK-8s would decrease, UV rates. In Experiments 1--4, subjects were treated with BOC-CCK-4 (which acts on CCK-2 receptors) or CCK-8s (which acts on CCK-1 and CCK-2 receptors), and UVs, motor activity, and body temperature were examined 15 or 30 minutes following drug pre-treatment. Contrary to expectations, BOC-CCK-4 failed to exert any significant effects on UVs (Experiments 1 and 2), and CCK-8s, administered 15 minutes prior to testing, was also without effect on call rates (Experiment 3). In Experiment 4, CCK-8s (30 minutes post-treatment) reduced UV rates at each of the doses tested (0.5, 1.0, 2.0 and 4.0 mug/kg). This effect on UVs was specific in that motor activity and body temperature were unaffected. In Experiments 5 and 6, pups were pre-treated with vehicle, devazepide (a CCK-1 receptor antagonist), or L-365,260 (a CCK-2 receptor antagonist), respectively, 45 minutes prior to testing. (Abstract shortened by UMI.) | en_US |
