Effects of forced exercise on object location memory and anxiety behaviour in morphine dependent ovariectomized rats

Previous findings from our laboratory indicated that exercise alleviates the deficits in cognitive and anxiety disorders in healthy female rats. But the effect of exercise on cognitive and anxiety disorders induced by chronic morphine in experimental monopose of rats (ovariectomized) not known. Aim of this study was to investigate the effects of mild and modorate forced exercise on anxiety-like behaviors, and object location memory in ovariectomized of morphine-dependent rats during spontaneous withdrawal period.

Sham or ovariectomized rats were injected with bi-daily doses (10 mg/kg, at 12 h intervals) of morphine or saline over a period of 10 days. Then the rats were trained under mild and moderate exercises for 30 minute in a session of five days per week for four weeks. Then object location memory, and anxiety profile in elevated plus maze (EPM) were examined.

Chronic morphine induced the anxiogenic-like behaviours (reductions in time spent, and entry into the EPM open arm) in intact, but not ovariectomized rats, which alleviated by both mild and moderate treadmill exercise. Also, both mild and moderate exercise produced anxiolytic behaviours in the non-morphine depedent intact and ovariectomized rats. Chronic morphine did not change object location memory in the intact and ovariectomized rats. Meanwhile, moderate exercise enhaced spatial location memory in non-morphine dependent, but not morphine dependent intact and ovarietomized rats.

In general, our findings demostrate that sex ovarian hormones modulate the effects of chronic morphine on congnitive function and anxiety behaviour. It seems the nature of this interaction is complex and needs further investigation.