Decreased muscarinic M1 receptor gene expression in the hypothalamus, brainstem, and pancreatic islets of streptozotocin-induced diabetic rats.

The brain neurotransmitters' receptor activity and hormonal pathways control many physiological functions in the body. Acetylcholine (ACh), a major neurotransmitter from autonomic nervous system, regulates the cholinergic stimulation of insulin secretion, through interactions with muscarinic receptors. The objective of the present study was to investigate the changes in the total muscarinic and muscarinic M1 receptor ([3H]quinuclidinyl benzilate; QNB) binding and gene expression in the hypothalamus, brainstem, and pancreatic islets of streptozotocin (STZ)-induced diabetic and insulin-treated diabetic rats. In the hypothalamus and brainstem, total muscarinic receptor numbers were increased in diabetic rats with increase in affinity. Hypothalamic and brainstem muscarinic M1 receptors number were decreased in STZ diabetic rats with increase in affinity. In the pancreatic islets, muscarinic M1 receptors of diabetic rats were decreased, with a decrease in affinity. In all cases, the binding parameters were reversed to near control by the treatment of diabetic rats with insulin. Real-time PCR data also showed a decrease in muscarinic M1 receptor gene expression and a similar reversal with insulin treatment. Thus our results suggest that insulin modulates binding parameters and gene expression of total and muscarinic M1 receptors. © 2007 Wiley-Liss, Inc.