WATER MAZE-LEARNING AND HIPPOCAMPAL SYNAPTIC PLASTICITY IN STREPTOZOTOCIN-DIABETIC RATS - EFFECTS OF INSULIN-TREATMENT

Streptozotocin-diabetic rats express deficits in water maze learning a nd hippocampal synaptic plasticity. The present study examined whether these deficits could be prevented and/or reversed with insulin treatm ent. In addition, the water maze learning deficit in diabetic rats was further characterized. Insulin treatment was commenced at the onset o f diabetes in a prevention experiment, and 10 weeks after diabetes ind uction in a reversal experiment. After 10 weeks of treatment, insulin- treated diabetic rats, untreated diabetic rats and non-diabetic contro ls were tested in a spatial version of the Morris water maze. Next, hi ppocampal long-term potentiation (LTP) was measured in vitro. To furth er characterize the effects of diabetes on water maze learning, a sepa rate group of rats was pre-trained in a non-spatial version of the maz e, prior to exposure to the spatial version. Both water maze learning and hippocampal LTP were impaired in diabetic rats. Insulin treatment commenced at the onset of diabetes prevented these impairments. In the reversal experiment, insulin treatment failed to reverse established deficits in maze learning and restored LTP only partially. Non-spatial pre-training abolished the performance deficit of diabetic rats in th e spatial version of the maze. It is concluded that insulin treatment may prevent but not reverse deficits in water maze learning and LTP in streptozotocin-diabetic rats. The pre-training experiment suggests th at the performance deficit of diabetic rats in the spatial version of the water maze is related to difficulties in learning the procedures o f the maze rather than to impairments of spatial learning. (C) 1998 El sevier Science B.V. All rights reserved.