Abstract

This study investigated the effects of diazepam(1mg/kg) on the conditional freezing and analgesic responses in 96 Sparague-Dawley female rats, using 2-trial conditioned fear test. On the first training day, each rat was placed in the observation chamber, and 3 min later recieved shock three times(0.75s, 1mA) at a 20-s intershock interval. During the second testing day, the animal`s behavior was observed according to a time-sampling procedure in the same preshocked chamber. Results showed that diazepam, administered before the 1st trial, caused an decrease in freezing observed 24hr later(exp 1). The duration of activity burst that occurred following shock in testing period was decreased when diazepam given was before testing(exp 2). In formalin test, diazepam given before training decreased freezing response but increased formalin-induced recuperative behavior, i. e blocked conditioned analgesia(exp 3). The finding that diazepam given before training attenuate both conditional responses suggested that the freezing and analgesia are mediated by a common underlying process. It was also argued that diazepam's effect on the modulation of conditioned fear is attributed to the interference of the processing of novel contextual cue rather than the decreasing of perceived shock intensity.