Regulation of Src Family Tyrosine Kinases in the Rat Striatum by Muscarinic Acetylcholine Receptors
Acetylcholine is an important neurotransmitter in the mammalian brain. This transmitter binds to muscarinic acetylcholine receptors (mAChR) to regulate activity of a variety of intracellular signaling molecules. Fyn and Src are two members of the Src family kinase (SFK). They are highly expressed in many brain regions, including the striatum, an area in the forebrain critical for cognitive, reward, mood, and movement. Since the striatum is also among brain regions showing a high level of mAChR expression, it is intriguing to investigate whether mAChRs regulate Fyn and Src. In this study, this topic was investigated by testing the effect of pharmacological blockade of mAChRs on phosphorylation of Fyn and Src at a specific tyrosine site, tyrosine 416 (Y416), a phosphorylation event leading to activation of Fyn and Src. A widely used mAChR antagonist scopolamine was used to block mAChRs and changes in phosphorylation of SFK Y416 were examined in the two subdivisions of the striatum, i.e., the caudate putamen (CPu) and nucleus accumbens (NAc), using Western blot with a phospho- and site-specific anti-Y416 antibody. We found that a single intraperitoneal injection of scopolamine at an effective dose (5 mg/kg) induced a significant increase in Y416 phosphorylation in the CPu. A similar increase in Y416 phosphorylation was also seen in the NAc following scopolamine administration. The scopolamine-stimulated Y416 phosphorylation was time-dependent. No significant change occurred to the amount of total Fyn and Src proteins in the two regions. These results indicate that mAChRs exert an inhibitory effect on basal phosphorylation of Fyn and Src in striatal neurons under normal conditions.