Brain-derived neurotrophic factor attenuates mouse cerebellar granule cell GABAA receptor-mediated responses via postsynaptic mechanisms

In addition to exerting long-term neurotrophic influences on developmental process such as neuronal survival and neuritic outgrowth, brain-derived neurotrophic factor (BDNF) has been reported to modulate synaptic transmission in the short-term. Considerable evidence indicates that BDNF acutely modulates NMDA receptor-mediated synaptic activity. However, whether BDNF modulates inhibitory synaptic transmission remains to be firmly established. In the present study, we examined the effect of acute BDNF exposure on GABA-evoked whole-cell responses as well as GABAergic synaptic activity in cultured mouse cerebellar granule cells. GABA-evoked responses were reduced by 39.5 +/- 4.7 % upon acute and focal application of BDNF (100 ng ml(-1)). The reduction of the GABA response recovered only partially even minutes after removal of BDNF. TrkB-IgG and K252a, but not K252b, prevented the BDNF-induced attenuation of the GABA response. BDNF exposure shifted the cumulative peak amplitude distribution leftward for both spontaneous IPSCs (sIPSCs) and miniature IPSCs (mIPSCs) without affecting the rise time and decay time constants. Acute exposure to BDNF also resulted in internalization of GABA(A) receptors in cultured cerebellar granule cells, as reflected by diminished immunostaining with an antibody against the GABA(A) receptor beta(2/3) subunit. Although the BDNF-induced GABA(A) receptor internalization was sensitive to K252a, it did not become manifest until 5 min after exposure to BDNF. Therefore, receptor internalization alone cannot account for the prompt BDNF-induced attenuation of GABA-mediated activity. We conclude that BDNF modulates GABA(A) receptor-mediated activity through TrkB receptor signalling that triggers a kinase-dependent short latency effect and a delayed longer latency effect hallmarked by receptor internalization.