Increased neural activity in the bed nucleus of the stria terminalis of uninfected canaries after observation of infected conspecifics

Recent evidence suggests that the immune system may be upregulated in anticipation of pathogen exposure, yet the neural mechanisms that respond to and signal impending infection risk remain poorly understood. We investigated neural responses to infection risk in uninfected hosts observing infected conspecifics, using the canary (Serinus canaria domestica)—Mycoplasma gallisepticum host–parasite system. We focused on five brain regions of interest, comprising three nodes of the social decision-making network—preoptic area, bed nucleus of the stria terminalis (BNST) and hippocampus—a stress modulatory region (paraventricular nucleus) and a visual processing region (nucleus rotundus). After 1 h of observing infected canaries, healthy canaries had elevated neuronal activity, indicated by an increase in immunoreactive cells labelled for phospho-S6, in the BNST relative to birds observing sham-treated canaries. These results suggest that the BNST could have a role in processing infection-related stimuli.