Anxiety-like behavior during the first week after chronic cocaine exposure in rats
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Elevated levels of anxiety-like behaviors appearing during abstinence from chronic cocaine exposure are thought to be important "withdrawal" symptoms that contribute to relapse. This study was designed to determine the temporal pattern of the emergence of anxiety-like behavior in a rat model of cocaine dependence. Rats were administered an escalating cocaine dose regimen (5 mg/kg to 30 mg/kg, I.P.) or its vehicle (saline) for 21 days and tested for the presence of anxiety-like behavior on one day during the first week after cocaine exposure. A conditioned defensive burying test was used to measure anxiety-like behaviors, in which rats were administered a mild shock (1 mA) through an electrified prod (a novel object for them), removed to a holding room for 35 minutes and then reintroduced to the shock testing apparatus and observed for ten minutes in the presence of a de-electrified prod. Measurements of the latency to initiate burying, time spent burying the de-electrified prod and the height of bedding material accumulated around the prod during the test were used as measures of anxiety-like behaviors. No significant increase in anxiety-like behavior was found in cocaine -treated rats on any test day during the first drug-free week after the last cocaine exposure. These results do not support previous findings that report an increase in anxiety-like behavior as a consequence of withdrawal from cocaine use. Additional analyses conducted as a matter of course to evaluate certain methodological constraints found that the burying responses of cagemates were independent, but that the order of cagemate testing on a particular day, among control rats only, influenced the burying response in a reliable way.