Menthol, a cyclic monoterpene found in mint leaves and stems, in LPS-induced PD rats, attenuates IBA-1 expression, inhibits the activation of microglia, and via the MAPK/AKT/NF-κB pathway, reduces IL-1β, IL-6, TNF-α, iNOS, and COX-2 levels. The gene discussed is TNF; the disease is Parkinson disease.