Ex Vivo Modulation of the BNST by Parabrachial CGRP Projections Is Decreased After a History of Stress-Induced Anxiety.

Activity in the parabrachial calcitonin gene-related peptide to bed nucleus of the stria terminalis (PBN[CGRP] → BNST) circuit associates with anxiety-like behavior. To test whether previous stress-induced anxiety is associated with neuronal adaptations in the PBN (CGRP) → BNST circuit, C57 mice were exposed to 4 days of daily forced swim stress (FSS). The novelty-suppressed feeding test (NSFT) demonstrated repeated FSS increased anxiety-like behavior. To assess if repeated FSS potentiates anxiety-like behavior in mice with dysregulated affect, mice received chronic intermittent ethanol vapor followed by FSS in abstinence. Anxiety-like behavior measured by NSFT was potentiated by repeated FSS in alcohol-abstinence. To measure neuroadaptations associated with a history of stress, Calca(CRE) mice, with the Cre-dependent hM3D(Gq) DREADDs, in the PBN and the GFP-based Ca2+ sensor GCaMP7f in the bed nucleus of the stria terminalis (BNST), were exposed to repeated FSS and anxiety-like behavior measured with the NSFT. Weeks later, neurotransmission was measured by recording GCaMP7f fluorescence in ex vivo BNST slices. hM3D(Gq) DREADDs in PBN (CGRP) projections were activated via bath application of clozapine-n-oxide. PBN (CGRP) projections increased GCaMP7f spike frequency in the BNST in naïve conditions but not after a history of repeated FSS. Post-activation of PBN (CGRP) projections decreased GCaMP frequency and amplitude in the BNST, which was potentiated by a history of repeated FSS. These findings extend the anxiogenic role of PBN (CGRP) neurons by demonstrating neurotransmission in the PBN (CGRP) → BNST circuit is dysregulated after a stress-induced anxiogenic state. Given the potential of CGRP-related therapies, future studies will investigate the role of CGRP within the PBN → BNST circuit in inducing anxiety-related neuroadaptations.