Impact of Chronic BDNF Depletion on GABAergic Synaptic Transmission in the Lateral Amygdala

Brain-derived neurotrophic factor (BDNF) has previously been shown to play an important role in glutamatergic synaptic plasticity in the amygdala, correlating with cued fear learning. While glutamatergic neurotransmission is facilitated by BDNF signaling in the amygdala, its mechanism of action at inhibitory synapses in this nucleus is far less understood. We therefore analyzed the impact of chronic BDNF depletion on GABA_A-mediated synaptic transmission in BDNF heterozygous knockout mice (BDNF^+/-). Analysis of miniature and evoked inhibitory postsynaptic currents (IPSCs) in the lateral amygdala (LA) revealed neither pre- nor postsynaptic differences in BDNF^+/- mice compared to wild-type littermates. In addition, long-term potentiation (LTP) of IPSCs was similar in both genotypes. In contrast, facilitation of spontaneous IPSCs (sIPSCs) by norepinephrine (NE) was significantly reduced in BDNF^+/- mice. These results argue against a generally impaired efficacy and plasticity at GABAergic synapses due to a chronic BDNF deficit. Importantly, the increase in GABAergic tone mediated by NE is reduced in BDNF^+/- mice. As release of NE is elevated during aversive behavioral states in the amygdala, effects of a chronic BDNF deficit on GABAergic inhibition may become evident in response to states of high arousal, leading to amygdala hyper-excitability and impaired amygdala function.