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Abstract Adenosine A1 receptors are widely expressed in the mammalian brain. Through interacting with Gαi/o‐coupled A1 receptors, the neuromodulator adenosine modulates a variety of cellular and synaptic activities. To determine the linkage from A1 receptors to a key intracellular signaling pathway, we investigated the impact of blocking A1 receptors on a subfamily of nonreceptor tyrosine kinases, that is, the Src family kinase (SFK), in different rat brain regions in vivo. We found that pharmacological blockade of A1 receptors by a single systemic injection of the A1 selective antagonist 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX) induced an increase in autophosphorylation of SFKs at a consensus activation site, tyrosine 416 (Y416), in the two subdivisions of the striatum, the caudate putamen and nucleus accumbens. DPCPX also increased SFK Y416 phosphorylation in the medial prefrontal cortex (mPFC) but not the hippocampus. The DPCPX‐induced Y416 phosphorylation was time dependent and reversible. In immunopurified Fyn and Src proteins from the striatum, DPCPX elevated SFK Y416 phosphorylation and tyrosine kinase activity in Fyn but not in Src proteins. In the mPFC, DPCPX enhanced Y416 phosphorylation and tyrosine kinase activity in both Fyn and Src immunoprecipitates. DPCPX had no effect on expression of total Fyn and Src proteins in the striatum, mPFC, and hippocampus. These results demonstrate a tonic inhibitory linkage from A1 receptors to SFKs in the striatum and mPFC. Blocking this inhibitory tone could significantly enhance constitutive SFK Y416 phosphorylation in the rat brain in a region‐ and time‐dependent manner.

Abstract Objective The adenosine A1 receptor is a Gαi/o protein‐coupled receptor and inhibits upon activation cAMP formation and protein kinase A (PKA) activity. As a widely expressed receptor in the mammalian brain, A1 receptors are implicated in the modulation of a variety of neuronal and synaptic activities. In this study, we investigated the role of A1 receptors in the regulation of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors in the adult rat brain in vivo. Methods Adult male Wistar rats were used in this study. After a systemic injection of the A1 antagonist DPCPX, rats were sacrificed and several forebrain regions were collected for assessing changes in phosphorylation of AMPA receptors using Western blots. Results A systemic injection of the A1 antagonist DPCPX induced an increase in phosphorylation of AMPA receptor GluA1 subunits at a PKA‐dependent site, serine 845 (S845), in the two subdivisions of the striatum, the caudate putamen, and nucleus accumbens. DPCPX also increased S845 phosphorylation in the medial prefrontal cortex (mPFC) and hippocampus. The DPCPX‐stimulated S845 phosphorylation was a transient and reversible event. Blockade of Gαs/olf‐coupled dopamine D1 receptors with a D1 antagonist SCH23390 abolished the responses of S845 phosphorylation to DPCPX in the striatum, mPFC, and hippocampus. DPCPX had no significant impact on phosphorylation of GluA1 at serine 831 and on expression of total GluA1 proteins in all forebrain regions surveyed. Conclusion These data demonstrate that adenosine A1 receptors maintain an inhibitory tone on GluA1 S845 phosphorylation under normal conditions. Blocking this inhibitory tone leads to the upregulation of GluA1 S845 phosphorylation in the striatum, mPFC, and hippocampus via a D1‐dependent manner.