PLCγ signaling underlies BDNF potentiation of Purkinje cell responses to GABA

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Abstract
Brain‐derived neurotrophic factor (BDNF) regulates neuronal survival, neurite outgrowth, and excitatory synaptic transmission. We reported recently that acute BDNF exposure decreased γ‐aminobutyric acid (GABA) responses in cultured mouse cerebellar granule cells through tyrosine receptor kinase B (TrkB) receptor‐mediated signaling. In the present study, we extend this work to investigate BDNF‐induced modulation of GABA responses and GABAA receptor‐mediated synaptic events in cerebellar slices. Thin (200 μm) parasagittal slices of cerebellum were prepared from postnatal Day 7 and 14 mice. Purkinje cells and granule cells, both of which express TrkB‐like immunoreactivity, were identified for whole‐cell recording. BDNF promptly enhanced GABA responses in Purkinje cells but, consistent with our previous finding in culture, attenuated those recorded in granule cells. In Purkinje cells, BDNF exposure shifted rightward the cumulative peak amplitude distribution for miniature inhibitory postsynaptic currents (mIPSCs) without changing the mIPSC frequency. BDNF‐induced potentiation of Purkinje cell responses to GABA was blocked by TrkB‐Fc (receptor body that sequesters BDNF), K252a (inhibitor of TrkB receptor autophosphorylation), U73122 (inhibitor of phospholipase‐Cγ [PLCγ]), KN62 (specific inhibitor of calcium/calmodulin‐dependent kinase), KT5720 (specific cyclic AMP‐dependent kinase inhibitor), and by intracellular dialysis of Rp‐cyclic AMP or BAPTA (1,2‐bis(o‐aminophenoxy)ethane‐N,N, N′,N′‐tetraacetic acid). Overall, our results indicate that BDNF acutely potentiates GABAA receptor function in cerebellar Purkinje cells via the TrkB receptor‐PLCγ signal transduction cascade. In addition, we propose that cyclic AMP‐mediated intracellular signaling mechanisms may facilitate manifestation of the BDNF‐induced modulatory outcome.