Effect of acute changes in glucose concentration on neuronal activity and plasticity in the rat hippocampus

Diabetes mellitus is a major public health concern in many regions of the world, including the Caribbean. Diabetes is associated with multi-system pathology and central nervous system complications have been receiving increasing attention (dementia, cognitive decline and memory loss). While such pathology has been shown to be associated with long term derangement in glucose metabolism, less is known about the effects of acute changes in glucose concentration on neuronal function. This study assesses the effects of acute changes in glucose concentration upon neuronal transmission and neuronal plasticity.

We made use of extracellular recordings from hippocampal slices of young adult rats and exposed them to changes in glucose concentration for 60 minutes before assessing synaptic plasticity. Experiments were carried out at both 30 degrees C and 35 degrees C.

At 30 degrees C, glucose concentrations of 30 mM and 4 mM had little effect upon population spike potentials (PSP). However reducing glucose concentration to 2 mM, 1 mM and 0 mM respectively resulted in a progressive decrease in the size of PSP until they were completely abolished. Similar results were observed at 35 degrees C except that 30 mM caused a significant increase in PSP size. Changes in glucose concentration had no effect upon synaptic plasticity at either 30 degrees C or 35 degrees C except below 2 mM glucose.

Acute changes in glucose concentration have a limited impact on neuronal transmission unless concentrations drop below 2 mM. However there seems to be little impairment of synaptic plasticity even at very low concentrations of glucose. We suggest that short term acute changes in glucose concentrations may not contribute directly to the cognitive decline associated with diabetes unless extremely severe.