Finally, we found that, through their projection targets, CeA-Glp1R neuron activation by small-molecule GLP-1RAs inhibits dopamine release in response to rewarding food. This highlights a mechanism for reducing reward-driven eating and suggests potential for addiction treatment. 14/15

Remarkably, we observed increased calcium transients in these cells after injecting small-molecule GLP-1RAs. This response, expected from Gs-coupled receptors, confirms that small-molecule GLP-1RAs can directly access the brain when delivered peripherally. 13/15

Activation of CeA-Glp1R neurons by a small molecule GLP-1RA inhibited reward-driven food intake without affecting homeostatic feeding—remember, only neurons expressing the humanized receptor via viral vectors are sensitive to small-molecule GLP-1RAs in these assays. 11/15

We used conditional viral vectors to express the humanized receptor in cells naturally expressing mGlp1r in specific brain areas. This chemogenetic approach allowed selective activation by small-molecule GLP-1RAs, enabling precise dissection of brain region-specific mechanisms. 10/15

Using c-Fos, we observed that brain areas activated by peptide-based GLP-1RAs were also activated by small-molecule GLP-1RAs. We found a particularly intriguing response in the central amygdala (CeA). 9/15

Using this humanized mouse model, we confirmed that oral and peptide-based GLP-1RAs similarly suppress appetite. These drugs matched liraglutide in reducing both homeostatic and reward-driven (hedonic) food consumption. 8/15

To overcome this barrier, we used CRISPR-Cas9 to make a single amino acid substitution at position 33 of mouse Glp1R from S to W. This change conferred sensitivity to small-molecule GLP-1RAs, effectively humanizing the rodent model. 7/15

So, we set out to determine if the mechanisms regulating appetite are the same between peptide-based and small-molecule GLP-1RAs. However, many small molecules are human-specific and do not bind rodent models used to investigate brain circuits at needed resolution. 6/15