Effects Of Enriched Environment On Addictive Behavior, Behavioral Impairments Followed By Early Life Stress And Hippocampal Synaptic Plasticity In Rats

Part I Effects of Enriched Environment on Addictive Behavior and Hippocampal Synaptic Plasticity in RatsObjects: To study effects of enriched environment on spatial learning and memory and morphine induced conditioned place preference (CPP) of Wistar rats, to explore if enriched environment can affect hippocampal synaptic plasticity on normal and addicted rats.Materials and Methods: Male Wistar rats were raised from weaning (21 days old) to young adulthood (50-60 days old) in either an enriched or normal environment. All rats maintained in quiet rooms on a 12 h light/dark cycle with access to ad libitum chow and water. In the enriched environment (EE), rats were group-housed with various novel objects that were re-arranged daily. In the normal condition, rats were group housed without any objects. As adults, spatial learning and memory were tested in Morris water maze. In addition, a four-trial CPP test was used to assess reward produced by morphine (10 mg/kg). Furthermore, long term potentiation (LTP) and depression (LTD) were assessed in vitro from normal and addicted rats of different rearing conditions. Morphine addiction was produced by injecting morphine (10mg/kg b.i.d) to rats for at least 12 days. Statistical comparisons were made using ANOVA or Student's t-test.Results: EE increased spatial learning and memory significantly. Morphine-induced CPP was also enhanced in EE rats compared with normal environment rats, indicating that EE facilitate the rewarding effects of opioids. LTP and LTD were both enhanced in EE rats compared to normal controls. After chronic morphine treatment, LTP and LTD were impaired significantly. In contrast to the enhanced CPP effect, LTP and LTD impairments of addicted rats were attenuated in EE rats.Conclusion: EE enhanced morphine induced CPP, possibly due to the increased spatial learning and memory; and the synaptic plasticity impairments induced by morphine addiction can be attenuated by EE, suggest that EE may be helpful in protecting synaptic plasticity from opioids impairments. Partâ…¡Effects of Enriched Environment on the Spatial Learning and Memory, Depressive-like Behavior and Synaptic Plasticity Impairments Followed by Early Life StressObjects: To study effects of Stress in early life on cognitive and affective disorders, and hippocampal synaptic plasticity in young adult rats, and to study whether exposure to enriched environment (EE) can overcome these effects.Materials and Methods: Male Wistar rats were raised from born (2-21 days old) in either an normal environment or early life stress environment. Early life stress was induced by housing rats in limited nesting / bedding materials. And after then, rats were assigned to either enriched environment (EE) or normal environment randomly. All rats maintained in quiet rooms on a 12 h light/dark cycle with access to ad libitum chow and water. In the enriched environment, rats were group-housed with various novel objects that were re-arranged daily. In the normal condition, rats were group housed without any objects. As adults, spatial learning and memory were tested in Morris water maze. Depressive-like behavior was examined in forced swim test. Each rat was placed into a vertical Plexiglas cylindercontained water for 15 min. Twenty-four hours later, each rat was replaced into the cylinder for 5 min, and the total time when rats was not struggling for escape but remained minimal activity (head and forepaw) to keep respiration, passively floating in the water, was measured as immobility. Furthermore, long term potentiation (LTP) were assessed in vitro from normal and stressed rats of different rearing conditions. Statistical comparisons were made using ANOVA or Student's t-test.Results: We found that early life stress reduced body weigh gain, impaired spatial learning and memory of the Morris water maze and increased depressive-like behavior of the forced swim test in young adult rats. Early life stress also impaired long-term potentiation in hippocampal CA1 area of slices of young adult rats. Remarkably, EE experience had no effect on spatial learning / memory and depressive-like behavior, but significantly facilitated LTP in control rats, but completely overcame the effects of early life stress on young adult rats.Conclusion: Early life stress impaired spatial learning and memory of rats, enhanced depressive behavior and impaired hippocampal LTP, EE experience overcame these effects. These findings suggest that EE experience may be useful for clinical intervention in preventing cognitive and affective disorders during development.