CGRP Reception Potentiates Anxiety in an Influenza A Derived Immune Engram

Abstract

Immune stimulus can form an “immune engram” encoding aspects of the organism’s response, but little is known about the function and mechanisms underlying these engrams. Here I investigate an immune engram arising from respiratory infection with influenza A virus, demonstrating a molecular mechanism with differential influence over behavioral and immunological aspects of the engram. I first define a cellular response to acute non-neurotropic influenza A/Puerto Rico/8/1934 (PR8) infection in the central nervous system by mapping cFos+ cells and microglia morphology across brain regions. In the posterior insula, this response peaks early at 3 days post infection. Using a cre-dependent excitatory chemogenetic system in TRAP2 mice, I then capture an engram at this same region and infection timepoint. Activation of this “PR8 engram” results in anxiety behavior and increased transcriptional expression of cytokines in lung tissue but not spleen tissue. I further explore how pulmonary signals contribute to this PR8 engram. Using tissue-specific, cre-dependent expression of diphtheria toxin fragment in Calcacre mice, I ablate calca-expressing cells including pulmonary neuroendocrine cells in respiratory tissue. Loss of calca-expressing cells prevents changes in synaptic engulfment by microglia in the insula during PR8 infection without altering the cellular response to infection in pulmonary tissue. Signaling of CGRP, a peptide encoded by calca, can be blocked with the small molecule CGRP receptor antagonist rimegepant. Using rimegepant during acute PR8 infection I again demonstrate that loss of calca signaling prevents the cellular response to PR8 infection in the insula. Finally, returning to the chemogenetic system in TRAP2 mice I show that rimegepant administration prior to engram capture prevents anxiety behavior but not gene expression changes resulting from PR8 engram activation.