Immunohistochemical detection of cholinergic neurons in formalin-fixed floated cryostat sections from the basal forebrain of the rat. Choline acetyltransferase immunoreactivity was detected with the rabbit polyclonal ChAT antiserum (R-043-100; 1:20,000), using the biotinylated secondary antibody-ABC method and nickel-diaminobenzidine chromogen. Photo courtesy of Dr. Erik Hrabovszky, Hungarian Academy of Sciences, Budapest, Hungary.