Reduced numbers of cortical GABA-immunoreactive neurons in the chronic D-galactose treatment model of brain aging

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 (100 mg/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. Crown Copyright (C) 2013 Published by Elsevier Ireland Ltd. All rights reserved.