The inhibitory effect of diazepam on defensive burying: anxiolytic vs. analgesic effects

The hypothesis that analgesic mechanisms might account for the suppressive effect of diazepam on defensive burying was tested in four experiments. In the first experiment, 1 mg/kg of diazepam had no appreciable effect on rat's latency to escape from a painful heat stimulus, but reliably suppressed defensive burying behavior. There was no significant relationship between the diazepam-treated rats' latency to escape and their duration of burying. Rats in Experiment 2 were injected with diazepam during a delay between shock and testing, so that they could not be experiencing the putative analgesic effect of diazepam during the shock. In spite of this, diazepam produced a significant suppression of burying compared to saline control. In the next experiment, the effect of diazepam on defensive burying was assessed in the complete absence of painful stimulation by exposing the rats to a novel stimulus known to elicit burying behavior. Diazepam suppressed burying behavior to the novel stimulus in a dose-dependent fashion. Finally, the ability of 10 mg/kg of naloxone to reverse the suppressive effect of 1 mg/kg of diazepam was assessed in Experiment 4. Naloxone failed to reverse the suppressive effect of diazepam and had no significant effect on defensive burying by itself, suggesting that the modulating influence of diazepam on rats' defensive burying behavior did not depend upon endogenous opiate mechanisms. Taken together, the results of the four experiments did not support the view that benzodiazepines produce their anxiolytic effects through analgesic mechanisms.