Synaptic transmission changes in the pyramidal cells of the hippocampus in streptozotocin-induced diabetes mellitus in rats.

The central nervous system complications of diabetes mellitus (DM) include defects in hippocampal synaptic plasticity induction and difficulties in learning and memory. DM was induced by streptozotocin (STZ) injection in rats. After 12 weeks of DM duration, the rats were decapitated, and hippocampal slices were prepared for in vitro study. Field excitatory postsynaptic potentials (fEPSP) were recorded after repeated stimulations with 50 impulses given either in 10 or 20 Hz. The responses were significantly smaller in the diabetic animals than in the age-matched control rats. The summation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) responses was tested in both groups by stimulating the synapses with five consecutive stimuli given in 50-Hz frequency. Intracellular recording from the pyramidal hippocampal cells of the AMPA summation responses from diabetic and aged-matched control animals revealed a significant lower summation in the diabetic animals compared to the control. It is concluded that responses evoked by high-frequency stimulation (HFS) were significantly higher in the control animals. The defects in diabetic slices could be related to pre- as well as postsynaptic changes, and these defects play an important role in the synaptic plasticity changes seen in STZ-induced diabetic animals.