Intra-BLA alteration of interneurons' modulation of activity in rats, reveals a dissociation between effects on anxiety symptoms and extinction learning.

The basolateral amygdala (BLA) is a dynamic brain region involved in emotional experiences and subject to long-term plasticity. The BLA also modulates activity, plasticity, and related behaviors associated with other brain regions, including the mPFC and hippocampus. Accordingly, intra-BLA plasticity can be expected to alter both BLA-dependent behaviors and behaviors mediated by other brain regions. Lasting intra-BLA plasticity may be considered a form of metaplasticity, since it will affect subsequent plasticity and response to challenges later on. Activity within the BLA is tightly modulated by GABAergic interneurons, and thus inducing lasting alteration of GABAergic modulation of principal neurons may have an impactful metaplastic effect on BLA functioning. Previously, we demonstrated that intra-BLA knockdown (KD) of neurofascin (NF) reduced GABAergic synapses exclusively at the axon initial segment (AIS). Here, by reducing the expression of the tyrosine kinase receptor ephrin A7 (EphA7), we selectively impaired the modulatory function of a different subpopulation of interneurons, specifically targeting the soma and proximal dendrites of principal neurons. This perturbation induced an expected reduction in the spontaneous inhibitory synaptic input and an increase in the excitatory spontaneous synaptic activity, most probably due to the reduction of inhibitory tone. Moreover, this increased synaptic activity was followed by a reduction in intrinsic excitability. While intra-BLA NF-KD resulted in impaired extinction learning, without increased symptoms of anxiety, intra-BLA reduction of EphA7 expression resulted in increased symptoms of anxiety, as measured in the elevated plus maze, but without affecting fear conditioning or extinction learning. These results confirm the role of the BLA and intra-BLA metaplasticity in stress-induced increased anxiety symptoms and in impaired fear extinction learning but reveals a difference in intra-BLA mechanisms involved. The results also confirm the contribution of GABAergic interneurons to these effects but indicate selective roles for different subpopulations of intra-BLA interneurons.