Naloxone, preshock, and defensive burying.

Abstract

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.

Effect of naloxone on conditioned suppression in rats.

“…Nevertheless, our results indicate that conditioned suppression increases with both shock intensity and naloxone treatment. This finding can be added to the growing list of aversively motivated behaviors that increase with shock intensity and naloxone treatment, such as freezing (Fanselow & Bolles, 1979b), defensive burying (Whiteside & Devenport, 1985), shock-elicited aggression (Fanselow, Sigmundi, & Bolles, 1980), and suppressive effects of shock punishment (Young, 1980). Collectively, these experiments provide growing support for the hypothesis that aversive stimuli can activate an endogenous analgesic system along with species-specific-defensive behaviors.…”

Species-specific danger signals, endogenous opioid analgesia, and defensive behavior.

“…For example, animals that receive a priming footshock tend to increase freezing relative to animals that receive a single footshock, and naloxone pretreatment results in a further enhancement of freezing in the primed animals (Fanselow & Bolles, 1979a, Experiment 3). When defensive burying (Whiteside & Devenport, 1985) is examined, a priming shock tends to produce a very small decrease in burying, but naloxone produces an enhancement of burying in the primed animals, so that they show substantially more burying than primed-saline or nonprimed rats (either saline or naloxone). The pattern of results with defensive burying is directly analagous to the results of Experiments 2 and 3 of this report.…”

“…The pattern of results with defensive burying is directly analagous to the results of Experiments 2 and 3 of this report. As Whiteside & Devenport (1985) have pointed out, this pattern presents a bit of a paradox: Naloxone's rather pronounced effect on defensive behavior is interpreted in terms of an antianalgesic effect of the drug, but the analgesic effect of the priming stimulus on the defensive response appears to be minimal.…”

“…Prior work with this assay has led to one line of evidence that endogenous opioid analgesic mechanisms are under stimulus control. The evidence is based on the finding that naloxone enhances postshock freezing if the rat receives multiple shocks but not if it receives a single shock (e.g., Fanselow, 1981; Fanselow & Bolles, 1979a, 1979b; see Whiteside & Devenport, 1985, for a similar example with defensive burying). Such results suggest that opioid analgesic mechanisms are not tonically active but that the first shock in a series, by activating them, serves to prime the postshock freezing paradigm.…”