In the analysis of several brain tissue samples, CHRM3 expression was associated with the expression of three other genes related to neuropsychiatric traits, GABRG2, CHRNA4, and HRH3. GABRG2 was co-expressed with CHRM3 across eight brain tissues and the same co-expression pattern was observed for its mouse homologous Chrm3 with Gabrg2 in six GABAergic single neurons. GABRG2 encodes a γ-aminobutyric acid receptor subunit; the receptor has chloride channel activity. Mutations in GABRG2 have been associated with epilepsy and febrile seizures28. Meanwhile, CHRNA4 and HRH3 are co-expressed with CHRM3 in specific brain tissues (particularly in THAL) and the same pattern is observed for the mouse homologs Chrna4 and Hrh3 with different GABAergic neurons. CHRNA4 encodes CHRNA4 (the α4 nicotinic ACh receptor), which belongs to a superfamily of ligand-gated ion channels that play a role in fast synaptic signal transmission. CHRNA4 interacts with CHRNB2 (the β2 nicotinic ACh receptor), which are critical for dopamine-dependent locomotor activation after repeated nicotine administration29. Mutations in CHRNA4 cause nocturnal frontal lobe epilepsy type 130 and polymorphisms of CHRNA4 have been reported in association with nicotine dependence31–33. HRH3
