BED NUCLEUS OF STRIA TERMINALIS ENKEPHALIN NEURONS CONTRIBUTE TO DEPLETION-INDUCED SALT APPETITE

Sodium is an essential dietary component. Terrestrial mammals have evolved salt appetite behaviour to seek and consume sodium-containing salts that is controlled by highly conserved brain pathways. However, maladaptive recruitment of these pathways driving salt overconsumption contributes to numerous detrimental health effects. Thus, it is imperative to improve our understanding of the neural mechanisms underpinning salt appetite.
Endogenous opioid signalling can modulate neuronal pathways to influence salt intake. We investigated the previously underexplored role of neurons in the bed nucleus of the stria terminalis that express the endogenous opioid, enkephalin, (BNST^ENK) in salt appetite and their connectivity with other brain regions.
Mice expressing Cre recombinase in preproenkephalin gene-expressing cells (Penk-Cre) were used to selectively target BNST^ENK neurons. Bilateral chemogenetic inhibition of BNST^ENK neurons reduced salt appetite in sodium-depleted Penk-Cre mice without affecting salt consumption in a sodium-replete state, or water or food intake following deprivation. This suggests a specific role for BNST^ENK neurons in driving salt consumption to restore a sodium debt.
Retrograde trans-synaptic rabies virus tracing revealed strong inputs onto BNST^ENK neurons from subregions of the extended amygdala, thalamus and hypothalamus. Anterograde adeno-associated virus tracing identified major outputs of BNST^ENK neurons within the extended amygdala, hypothalamus, and parabrachial nucleus of the pons.
In conclusion, we demonstrate a functional role for BNST^ENK neurons in needs-based salt consumption following sodium depletion. Further, we characterised the upstream and downstream connectivity of BNST^ENK neurons to provide a roadmap for future investigations into the broader circuitry regulating salt appetite.