Chronic morphine exposure and maternal separation induce impairments in cognition and locomotor activity of male adolescent rats

Abstract

Maternal morphine exposure reduces motivation for basic cognitive tasks, followed by executive function deficits in attention and accuracy. It also induces depression-like behaviors and has negative consequences for learning and memory in offspring. Interaction between mothers and pups has a crucial effect on the mammal's development. Maternal separation (MS) can originate behavioral and neuropsychiatric abnormalities later in life. It seems that adolescents are more susceptible to the effects of early-life stress; Therefore, this study aimed to evaluate the effects of chronic morphine consumption (21 days before and after mating and gestation) and MS (180 min/day from postnatal day [PND] 1-21) on the cognitive and behavioral performance of male offspring in mid-adolescence. Six groups, including control, MS, V (vehicle), morphine, V+MS, and morphine+MS, were tested for open field (OF), novel object recognition (NOR), and the Morris water maze (MWM). The results of the OF test showed that MS increased locomotor activity and movement velocity. Inner and outer zone durations did not differ among groups. The body stretching of the morphine+MS rats was significantly more than the MS rats. Moreover, the MS and morphine+MS groups showed significantly less sniffing behavior in the OF test. The MS group showed deficits in spatial learning in the MWM test, but recognition memory in the NOR and spatial memory in the MWM tests were not significantly different among groups. We concluded that MS could induce impairments in spatial learning and locomotor activity that could be worsened by maternal morphine exposure in adolescent male rats.