Effects of recurrent antecedent hypoglycaemia and chronic hyperglycaemia on brainstem extra-cellular glucose concentrations during acute hypoglycaemia in conscious diabetic BB rats

Abstract

Aims/hypothesis. Our aim was to determine whether the divergent effects of chronic exposure to hyperglycaemia or hypoglycaemia on the glycaemic threshold for auditory brainstem dysfunction are reflected in the extra-cellular fluid (ECF) concentrations of glucose in the inferior colliculus during hypoglycaemia in the diabetic BB rat. Methods. Microdialysis was used to measure inferior colliculus ECF glucose concentrations under basal and hyperinsulinaemic (20 mU/kg·min) hypoglycaemic conditions. Results. ECF glucose is increased under basal (hyperglycaemic) conditions and decreases during hypoglycaemia in both recurrently hypoglycaemic and chronically hyperglycaemic diabetic BB rats (to 0.5±0.1 and 0.8±0.2 mmol/L respectively), with no significant differences between groups. In both groups the plasma to ECF glucose ratio doubled during hypoglycaemia. Conclusion/interpretation. Prior exposure to recurrent hypoglycaemia does not lead to increased ECF glucose concentrations in the inferior colliculus of diabetic BB rats. The resistance to impaired brainstem function seen in recurrently hypoglycaemic rats during hypoglycaemia cannot simply be attributed to increased blood-brain barrier glucose transport within this brain region.