OPIOID INVOLVEMENT IN BEHAVIOR MODIFICATIONS OF MICE INFECTED WITH THE PARASITIC NEMATODE, NIPPOSTRONGYLUS-BRASILIENSIS

Several studies have documented the opiate effects of parasitic infect ion on experimental animals. The current study examined the relationsh ips between infection with the intestinal nematode, Nippostrongylus br asiliensis with analgesia and activity levels. Male white mice infecte d with N. brasiliensis displayed a significant increase in thermal lat ency thresholds that rose through the duration of infection and subsid ed with its termination. Analgesia first became apparent on day three- post infection but did not reach statistical significance (p < 0.05) u ntil day 7 post infection. The maximum analgesia was reached on day 8- post infection and gradually declined. By day 15 post infection, there was no significant difference in the latency times between control an d infected mice. The initial significant difference in latency roughly corresponded with the on set of egg production by the parasite. The p eak difference in latency times and their subsequent decline also para llels peak egg production and the decline in egg production as the inf ection subsided. Both naloxone and naltrindole significantly reduced t he latency times (p<0.05) of infected mice. There was also a significa nt difference in total ambulatory activity levels between infected and control mice. Activity levels began to decline on the second day post infection but did not reach a statistically significant difference (p < 0.05) from the controls until 9th day post infection. Infected mice that were injected with either naloxone or naltrindole had a signific antly higher activity level than the infected mice injected with salin e.