Evidence for Multiple Muscarinic Receptor Subtypes in Human Brain

Abstract
Pirenzepine, a compound with selective anti-muscarinic activity, was used to distinguish muscarinic acetylcholine receptor subtypes in normal human brain. Hill coefficients and IC50 values derived from the inhibition of specific [3H]l-quinuclidinyl benzilate receptor binding suggest the presence of two muscarinic binding sites, differing both in affinity for pirenzepine and in tissue distribution.