Intergenerational consequences of adolescent morphine exposure on learning and memory

Drug addiction is a worldwide social and medical disorder. More than 50 percent of drug abusers start their substance abuse in adolescence between the ages of 15-19. Adolescence is a sensitive and crucial period for the development and maturity of the brain. Chronic exposure to morphine, particularly during this period, lead to long-lasting effects, including effects that extend to the next generation. The current study examined the intergenerational effects of paternal morphine exposure during adolescence on learning and memory. In this study, male Wistar rats were exposed to increasing doses of morphine (5-25 mg/kg, s.c.) or saline for 10 days at postnatal days (PND) 30-39 during adolescence. Following a 20-day drug-free period, the treated male rats were mated with naïve females. Adult male offspring (PND 60-80) were tested for working memory, novel object recognition memory, spatial memory, and passive avoidance memory using the Y-Maze, novel object recognition, Morris water maze, and shuttle box tests, respectively. The spontaneous alternation (as measured in the Y-Maze test) was significantly less in the morphine-sired group compared to the saline-sired one. The offspring showed significantly less discrimination index in the novel object recognition test when compared to the control group. Morphine-sired offspring tended to spend significantly more time in the target quadrant and less escape latency in the Morris water maze on probe day when compared to the saline-sired ones. The offspring showed significantly less step-through latency to enter the dark compartment compared to the control group when measured in the shuttle box test. Paternal exposure to morphine during adolescence impaired working, novel object recognition, and passive avoidance memory in male offspring. Spatial memory changed in the morphine-sired group compared to the saline-sired one.