CHAT and Down syndrome: Notably, there are also studies showing that 17β-estradiol increased the number of ChAT-immunoreactive (IR) neurons in the medial septum (MS) and the vertical diagonal band (VDB) of the basal forebrain in young Ovx rats [288,289], and increased the number and size of MS ChAT-IR neurons in middle-aged Ts65Dn mice, a mouse model of Down syndrome [290].