Adolescent morphine exposure does not alter low-dose lipopolysaccharide-induced sickness behavior in adult mice

Adolescent opioid use in the United States commands attention: millions of twelve- to nineteen-year-olds are exposed to opioids each year by prescription and misuse. Recent findings show that opioids bind not only to canonical opioid receptors but also interact with receptors on immune cells within both the central and peripheral nervous systems. The potential for early life opioid exposure to induce long-term changes in the neuroimmune system is not fully understood, particularly given the adolescent brains high susceptibility to neuroplastic changes. The goal of this study was to investigate the hypothesis that adolescent opioid use potentiates physiological and behavioral responses to pathogen-induced sickness later in life. To achieve this, we treated adolescent mice (PND 35-42) with bi-daily escalating doses of morphine to model dependence and then administered a low dose of lipopolysaccharide (LPS, 0.1 mg/kg) in adulthood (PND 60-76) to induce an immune response. In contrast to our hypotheses, we found that adolescent morphine exposure had no additive effect on low-dose LPS-induced sickness measures when assessed in adulthood. These data suggest that adolescent opioid exposure may have minimal effects on future immune challenges, although further research is needed to confirm this.