Abstract
Rationale
Drug exposure initiated in adolescence has been associated with more severe mental health outcomes related to substance abuse and anxiety disorders.Objectives
The aim of the present study was to compare the long-term effects of repeated heroin vapor inhalation during adolescence with similar heroin exposure in adulthood.Methods
Groups of female Wistar rats underwent twice daily 30-minute sessions of heroin or propylene glycol (control) vapor inhalation from postnatal days (PND) 36-45 (Adolescent-Exposed) or PND 85-94 (Adult-Exposed). Nociception was assessed after vapor inhalation sessions and forty days later. Anxiety-like behavior was assessed with an elevated plus-maze (EPM) on PND 93/142 and spatial learning was assessed with a Barnes maze from PND 105-116/154-165. Acute effects of naloxone (0.3 mg/kg, i.p.) and heroin (0.5 and 1.0 mg/kg, s.c.) on thermal nociception were determined on PND 140/189 and PND 149/198, respectively.Results
Repeated heroin vapor inhalation produced anti-nociceptive tolerance in both groups, with the Adolescent-Exposed rats exhibiting more complete tolerance. Heroin vapor inhalation produced anxiolytic effects 48 days after repeated exposure. There were no effects of heroin on spatial learning. Naloxone produced acute hyperalgesia in all but the Adolescent-Exposed heroin group, and heroin anti-nociception was blunted in the Adult-Exposed heroin group at the highest heroin dose.Conclusions
Repeated heroin vapor inhalation can produce lasting effects on nociception and anxiety-like behavior that persist for months after the exposure. Importantly, these findings suggest that adolescent exposure to heroin vapor produces specific effects on nociception that are not observed when exposure occurs in adulthood.