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Abstract
Streptozotocin-diabetic rats express deficits in water maze learning and hippocampal
synaptic plasticity. The present study examined whether these deficits could be prevented
and/or reversed with insulin treatment. In addition, the water maze learning deficit
in diabetic rats was further characterized. Insulin treatment was commenced at the
onset of diabetes in a prevention experiment, and 10 weeks after diabetes induction
in a reversal experiment. After 10 weeks of treatment, insulin-treated diabetic rats,
untreated diabetic rats and non-diabetic controls were tested in a spatial version
of the Morris water maze. Next, hippocampal long-term potentiation (LTP) was measured
in vitro. To further characterize the effects of diabetes on water maze learning,
a separate group of rats was pre-trained in a non-spatial version of the maze, 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 the 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 that the performance deficit of diabetic rats in the spatial version of the
water maze is related to difficulties in learning the procedures of the maze rather
than to impairments of spatial learning.
Copyright 1998 Elsevier Science B.V. All rights reserved.