GHRL and major depressive disorder: Liu et al. [101] found that in a CUMS model of depression in rats, ghrelin and its receptor expression in the prefrontal cortex increased, accompanied by increased GSK-3β activity and NLRP3 expression; 4 weeks of moderate-intensity swimming exercise reversed these changes, suggesting that exercise may improve depressive behavior by regulating ghrelin and its receptor, GSK-3β activity, and NLRP3.