Metformin produces anxiolytic-like effects in rats by facilitating GABA receptor trafficking to membrane.

Background And Purpose: Altered function or expression of GABA receptors contributes to anxiety disorders. Benzodiazepines are widely prescribed for the treatment of anxiety. However, the long-term use of benzodiazepines increases the risk of developing drug dependence and tolerance. Thus, it is urgent to explore new therapeutic approaches. Metformin is widely used to treat Type 2 diabetes and other metabolic syndromes. However, the role of metformin in psychiatric disorders, especially anxiety, remains largely unknown.

Experimental Approach: We examined the effects of metformin on anxiety-like behaviour of rats in open field test and elevated plus maze test. We also observed the effect of metformin (10 μM, in vitro; 100 mg·kg , in vivo) on the trafficking of GABA receptors, as mechanisms underlying the anxiolytic effects of metformin.

Key Results: Metformin (100 mg·kg , i.p. 30 min) displayed a robust and rapid anxiolytic effect, without tolerance. Metformin up-regulated the surface expression of GABA receptors and increased miniature inhibitory postsynaptic currents (mIPSCs). AMP-activated protein kinase (AMPK) activated by metformin-induced stimulation of forkhead box O3a (FoxO3a) transcriptional activity, followed by increased expression of GABA receptor-associated protein (GABARAP) and its binding to GABA receptors finally resulted in the membrane insertion of GABA receptors.

Conclusions And Implications: Metformin increased mIPSCs by up-regulating the membrane insertion of GABA receptors, via a pathway involving AMPK, FoxO3a, and the GABA receptor-associated protein. Thus metformin has a potential new use in the treatment of anxiety disorders.