GABAB Receptor Activation Inhibits Neuronal Excitability and Spatial Learning in the Entorhinal Cortex by Activating TREK-2 K+ Channels

The entorhinal cortex (EC) is regarded as the gateway to the hippocampus and thus is essential for learning and memory. Whereas the EC expresses a high density of GABA(B) receptors, the functions of these receptors in this region remain unexplored. Here, we examined the effects of GABA(B) receptor activation on neuronal excitability in the EC and spatial learning. Application of baclofen, a specific GABA(B) receptor agonist, inhibited significantly neuronal excitability in the EC. GABA(B) receptor-mediated inhibition in the EC was mediated via activating TREK-2, a type of two-pore domain K+ channels, and required the functions of inhibitory G proteins and protein kinase A pathway. Depression of neuronal excitability in the EC underlies GABA(B) receptor.-mediated inhibition of spatial learning as assessed by Morris water maze. Our study indicates that GABA(B) receptors exert a tight control over spatial learning by modulating neuronal excitability in the EC.