CHRNA4 and Parkinson disease: Moreover, it has been reported that thymol at concentrations of 10–100 ppm, in combination with gamma-terpinene or para-cymene, attenuated cholinergic dysfunction, which is manifested in a plethora of neurodegenerative and psychiatric disorders, such as Alzheimer’s, Parkinson’s, and Huntington’s diseases, by enhancing the synaptic levels of acetylcholine (ACh) and the responsiveness of the nicotinic acetylcholine receptor (nAChR) in a Caenorhabditis elegans model [183].