Author(s): Chao CC, Sharp BM, Pomeroy C, Filice GA, Peterson PK
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Abstract Opiates modulate a variety of immune responses. We investigated the effect of morphine on the pathogenesis of an acute Toxoplasma gondii infection. Repeated s.c. injections with morphine sulfate (300 mg/kg) every 36 hr addicted mice and increased markedly the mortality of mice infected with an avirulent strain of T. gondii (86\%) vs. 0\% mortality in addicted and control mice, respectively, P less than .001). However, a single challenge with morphine (300 mg/kg) also markedly (P less than .001) increased mortality (94\%) of infected mice when the morphine was administered at day 13 postinfection; susceptibility to the lethal effect was not observed until day 9 postinfection, a time when immune reactivity was evident (i.e., 3- to 4-fold splenic enlargement). This lethal effect was attenuated by pretreatment with naltrexone, suggesting involvement of an opiate receptor mechanism. Sulfadiazine treatment abrogated morphine-induced mortality, indicating a prerequisite of an active infectious state. These findings suggest that immune activation by T. gondii infection plays a critical role in morphine-induced mortality in this murine model.
This article was published in J Pharmacol Exp Ther
and referenced in Journal of Addiction Research & Therapy