Chronic administration of d-galactose (d-gal) is widely used to mimic the process of brain aging; however, the neural mechanisms are still poorly understood. In this study, we investigated the effect of long-term d-gal treatment on the number of GABA-immunoreactive neurons in rat cerebral cortex and the behavioral correlates. After eight weeks of daily subcutaneous injection of d-gal (100mg/ml/kg), rats showed reduced exploratory activity and lower ambulation in the open field compared to controls. There was no significant reduction in total neurons in the cortex, but there was a marked decrease in the number of GABA-immunoreactive neurons in all cortical layers of d-gal-treated rats. The ratio of GABA-immunoreactive neurons to total neurons was significantly lower in all cortical layers of d-gal-treated rats, with greatest reductions in output layers III (39.9% reduction), V (46.3%), and VI (48.4%). Our study provides the first evidence that chronic d-gal treatment may decrease cortical GABAergic neurotransmission, especially in cerebral output layers. The reduction in GABA-immunoreactive cell number likely disrupts the intracortical excitatory/inhibitory balance and may contribute to the behavioral deficits observed in this aging model.
Keywords: Cerebral cortex; Rat; d-Galactose; γ-Aminobutyric acid.
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