Effect of naloxone and housing conditions on shock-elicited reflexive fighting: Influence of immediate prior stress

Abstract

The effect of naloxone (4 mg!kg) on the defensive reaction of shock-elicited fighting was studied in male albino rats that were housed individually or in groups for 5 weeks. Naloxone consistently reduced the fighting reflex in both groups, but only when animals were exposed to the reflexive paradigm just prior to the naloxone injection and subsequently retested. Housing conditions also produced an effect on fighting independent of drug manipulation, in that individually housed animals exhibited decreased fighting compared with group-housed animals. Studies of pain sensitivity to shock in group-housed animals injected with naloxone exhibited a pattern similar to that of the fighting response. Naloxone increased pain sensitivity only when the animals were exposed to the shock just prior to drug administration and subsequently retested. Additional group-housed animals were tested with naloxone at lower shock intensities to examine the possibility of a positive linear relationship between pain sensitivity and shock-elicited reflexive fighting. Results did not support a positive relationship between pain sensitivity and fighting, but rather suggested that stress-related endorphin release will facilitate the fighting response. Data are discussed with respect to naloxone's effect on locomotor activity and the association of that activity with adaptive behavior. Recently it has been proposed that endogenous opioids, released under stress, should facilitate speciesspecific defense reactions (SSDRs). This facilitation is proposed to be mediated through the analgesic suppression of protective reflexes (Bolles & Fanselow, 1980). For the rat, these defense reactions would include freezing, fighting, or fleeing, the elicitation of which would be situation dependent (Bolles, 1970; Bolles & Collier, 1976). Support for this proposal can be generated from several areas. First, lesion studies have demonstrated the necessity of an intact midbrain central gray for the expression of SSDRs (Edwards & Adams, 1974; Hunsperger & Fernandez de Molina, 1%2), an area in which the localization and distribution studies of opioid peptides have consistently demonstrated significant quantities of opioids

The enhancement and reduction of defensive fighting by naloxone pretreatment

“…Despite several methodological differences, the present study replicated results from the prior work of both Fanselow et al (1980) and McGivern et al (1981). Like Fanselow et aI., the present study demonstrates that naloxone can enhance defensive fighting in hooded rats.…”

“…The effect of the drug on the defensive fighting exhibited by rats shocked in pairs is less clear. McGivern, Lobaugh, and Collier (1981) reported that naloxone produces a reduction in the incidence of defensive fighting, whereas Fanselow, Sigmundi, and Bolles (1980) found that naloxone enhanced this response. Although many methodological differences exist between the two sets of studies, the present paper concentrates on one difference which may be critical in determin ing the direction of naloxone's effect on this fighting behavior.…”