Aim Energy deprivation causes neuronal death affecting the cognitive and memory ability of an individual. The kinetic parameters
of glutamate dehydrogenase (GDH), the enzyme involved in the production of glutamate, was studied in the cerebellum and liver
and the binding parameters of glutamate receptors in the cerebellum of insulin-induced hypoglycaemic and streptozotocin-induced
diabetic rats were studied to reveal the role of glutamate excitotoxicity.
Methods A single intrafemoral dose of streptozotocin was administered to induce diabetes. Hypoglycaemia was induced by appropriate
doses of insulin subcutaneously in control and diabetic rats. The kinetic parameters
V
max and
K
m of GDH were studied spectrophotometrically at different substrate concentrations of α-ketoglutarate. Glutamate receptor binding
assay was done with different concentrations of [
3H] Glutamate.
Results The GDH enzyme assay showed a significant increase (
P < 0.001) in the
V
max of the enzyme in the cerebellum of hypoglycaemic and diabetic rat groups when compared to control. The
V
max of hypoglycaemic groups was significantly increased (
P < 0.001) when compared to diabetic group. In the liver, the
V
max of GDH was significantly increased (
P < 0.001) in the diabetic and diabetic hypoglycaemia group when compared to control. The
V
max of GDH increased significantly (
P < 0.001) in the diabetic hypoglycaemic rats compared to diabetic group, whereas the control hypoglycaemic rats showed a significant
decrease in
V
max (
P < 0.001) when compared to diabetic and diabetic hypoglycaemic rats. The
K
m showed no significant change amongst the groups in cerebellum and liver. Scatchard analysis showed a significant increase
(
P < 0.001) in
B
max in the cerebellum of hypoglycaemic and diabetic rats when compared to control. The
B
max of hypoglycaemic rats significantly increased (
P < 0.001) when compared to diabetic group. In hypoglycaemic groups,
B
max of the control hypoglycaemic rats showed a significant increase (
P < 0.001) compared to diabetic hypoglycaemic rats. The
K
d of the diabetic group decreased significantly (
P < 0.01) when compared to control and control hypoglycaemic rats. There was a significant decrease (
P < 0.05) in the
K
d of diabetic hypoglycaemic group when compared to the control hypoglycaemic rats.
Conclusion Our studies demonstrated the increased enzyme activity in the hypoglycaemic rats with increased production of extracellular
glutamate. The present study also revealed increased binding parameters of glutamate receptors reflecting an increased receptor
number with increase in the affinity. This increased number of receptors and the increased glutamate production will lead
to glutamate excitotoxicity and neuronal degeneration which has an impact on the cognitive and memory ability. This has immense
clinical significance in the management of diabetes and insulin therapy.