Naloxone, preshock, and defensive burying.

Rats were injected with naloxone hydrochloride (3 mg/kg) or saline and subjected to preshock or no preshock prior to receiving a test shock that elicited defensive burying. Preshock was administered in a context different from, or the same as, that in which the test shock was delivered. The combination of naloxone and preshock led to more defensive burying than did saline and preshock. This was the case regardless of preshock context, a result suggesting that fear and/or analgesia may not always be critical ingredients in the preshock-naloxone interaction. Interpretative matters notwithstanding, the pattern of results for defensive burying was in basic agreement with that of other research on naloxone and defensive behavior and represents an extension of the literature to a new species-specific defense reaction.