GABAB receptors in the hippocampal dentate gyrus are involved in spatial learning and memory impairment in a rat model of vascular dementia

The roles of γ-aminobutyric acid (GABA) and GABAB receptors of the hippocampal dentate gyrus (DG) in spatial learning and memory impairment were investigated in a rat model of vascular dementia (VaD) established by permanent bilateral carotid occlusion. The extracellular concentration of GABA in the DG was determined by in vivo microdialysis and HPLC, and spatial learning and memory were assessed by the Morris water maze (MWM) test. Next, the possible involvement of GABAB receptors in spatial learning and memory impairments of VaD rats was examined by microinjection of its antagonist into the DG region. In VaD group rats, the extracellular concentration of GABA in the DG was significantly increased, and during MWM test, the escape latency was increased in place navigation trial and the percentage of time spent in target quadrant and the number of platform crossings were decreased in spatial probe trial, compared with the sham group. In sham-operated rats, the extracellular concentrations of glutamate (Glu) and glycine (Gly) in the DG were significantly increased during place navigation trial of MWM test, and these responses were inhibited in VaD rats. Saclofen (an antagonist of GABAB receptor) significantly attenuated the spatial learning and memory impairment in VaD rats, and partly reversed the inhibitory effects of VaD in responses of Glu and Gly in the DG during MWM test. Our results suggest that GABA and GABAB receptors in the hippocampal DG are involved in spatial learning and memory impairment in VaD rats, in part by attenuating the responses of Glu and Gly during spatial learning.