Brain-derived neurotrophic factor inhibits GABA uptake by the rat hippocampal nerve terminals

The lifespan of the predominant inhibitory neurotransmitter in the central nervous system, gamma-aminobutyric acid (GABA), is determined by its uptake into neurons and glia, through high-affinity Na(+)/Cl(-) dependent transporters (GATs). We now evaluated how the uptake of GABA by nerve endings, which is mostly mediated by the GAT-1 subtype, is modulated by brain-derived neurotrophic factor (BDNF). BDNF (10-200 ng/ml) decreased GAT-1-mediated GABA uptake by isolated hippocampal rat nerve terminals (synaptosomes), an effect that occurred within 1 min of incubation with BDNF and blocked by the tyrosine kinase inhibitor K252a (100 nM) as well as by the PLC inhibitor, U73122 (3 microM). Maximum inhibition was attained with 100 ng/ml BDNF. In contrast with what has been observed for other synaptic actions of BDNF, the inhibition of GABA transport by BDNF does not require tonic activation of adenosine A(2A) receptors since it was not blocked by the A(2A) receptor antagonist SCH 58261 (50 nM). However, in synaptosomes previously depleted of extracellular endogenous adenosine by incubation with adenosine deaminase (1 U/ml), activation of A(2A) receptors with the A(2A) receptor agonist, CGS 21680 (30 nM), enhanced the inhibitory effect of BDNF upon GABA transport, an action prevented by the A(2A) receptor antagonist, SCH 58261 (50 nM). It is concluded that BDNF, through TrkB and PLCgamma signalling inhibits GAT-1-mediated GABA transport by nerve endings and that this action is not dependent on, but can be enhanced by, TrkB/A(2A) receptor cross talk.