Transgenic brain-derived neurotrophic factor modulates a developing cerebellar inhibitory synapse.

Brain-derived neurotrophic factor (BDNF) has been shown to promote synapse formation and maturation in neurons of many brain regions, including inhibitory synapses. In the cerebellum, the Golgi cell-granule cell GABAergic synaptic responses undergo developmental transition from slow-decaying to fast-decaying kinetics, which parallels a developmental increase of GABA(A) receptor alpha6 subunit expression in the cerebellar granule cells. In culture, BDNF accelerates the expression of GABA(A) receptor alpha6 subunit expression in granule cells. Here we examined synaptic GABA(A) response kinetics in BDNF transgenic mice. The mutant mouse, which carries a BDNF transgene driven by a beta-actin promoter, overexpresses BDNF (two- to fivefold increase compared with wild types) in all brain regions. Recordings of the spontaneous GABA(A) responses indicate that the decay time constant of the GABAergic responses decreases during early postnatal development; this transition is accelerated in the BDNF transgenic mouse. The amplitude of the spontaneous GABA(A) responses was also larger in the transgenic mouse than in the wild-type mouse. However, the frequency of the spontaneous GABA(A) responses were not different between the two groups. Our results suggest that BDNF may modulate GABAergic synapse maturation in the cerebellum.