Brain-derived neurotrophic factor upregulates and maintains AMPA receptor currents in neocortical GABAergic neurons

The regulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors is implicated in synaptic plasticity. Although we have found that brain-derived neurotrophic factor (BDNF) triggers surface translocation of AMPA receptor proteins, the physiological significance of the BDNF effect remained to be determined. The present immunohistochemical studies revealed that cortical GABAergic neurons exhibited the most striking response to BDNF. Accordingly, we monitored AMPA-triggered currents through GABAergic neurons: Chronic BDNF treatment increased the AMPA-triggered currents but not NMDA-triggered currents in culture. In parallel, the amplitude, but not frequency, of spontaneous miniature excitatory postsynaptic currents (mEPSCs) was elevated in GABAergic neurons. In agreement, BDNF enhanced GABA release triggered by AMPA compared to the amount triggered by high potassium. Conversely, there was a significant decrease in the mEPSC amplitude of GABAergic neurons in heterozygous BDNF-knockout mice. These findings indicate that the neurotrophin enhances the input sensitivity of GABAergic neurons to facilitate their inhibitory function in the neocortex.