ChR2 expression, as indicated by eYFP labeling in the HDB/MCPO, was almost exclusively found in cholinergic neurons (89% of the cells positive for eYFP were also ChAT+, 440 double+ cells from a total of 495 eYFP+ cells in coronal slices from four mice) with an infection rate of 34% (440 double+ cells from a total of 1305 ChAT+ cells). The gene discussed is CHAT; the disease is infection.