INS and diabetes mellitus: All five muscarinic receptors are expressed by striatal neurones, with M1 and M4 receptors as the predominant subtypes, conforming together nearly 80% of the receptor population in the rat as shown by immunodetection [15,16] The main objective of the present study was to determine whether uncontrolled hyperglycemia, as a consequence of diabetes, altered the acetylcholine esterase enzyme activity, total and muscarinic M1 receptor binding parameters and muscarinic M1 receptor gene expression and the regulatory role of insulin in the rat corpus striatum.