Effect of ethanol on DARPP-32 phosphorylation in transgenic mice that express human type VII adenylyl cyclase in brain

BACKGROUND: Dopamine and cyclic adenosine monophosphate-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32) is a bidirectional signaling protein found in dopaminergically innervated brain areas. The characteristics and direction of DARPP-32 effects are regulated by phosphorylation of this protein. Phosphorylation of DARPP-32 on threonine-34 (T34) is regulated through the activation of dopamine (D1) receptors and stimulation of adenylyl cyclase (AC) and protein kinase A activity and by calcineurin. Phosphorylation of DARPP-32 on threonine-75 (T75) is regulated by cyclin-dependent kinase 5 and protein phosphatase 2A. DARPP-32 has been implicated in the motivational effects of ethanol. METHODS: The authors characterized transgenic mice that overexpress an ethanol-sensitive isoform of AC (AC7) in brain by measuring basal and ethanol-modulated DARPP-32 phosphorylation. Phosphorylated and total DARPP-32 were measured by immunoblotting in brain areas associated with the motivational and anxiolytic effects of ethanol (nucleus accumbens, striatum, and amygdala). RESULTS: AC7 transgenic mice had higher basal levels of T34 DARPP-32 than wild-type mice in striatum and amygdala, whereas basal levels of T75 DARPP-32 did not differ between wild-type and transgenic mice. Ethanol administration increased T34 DARPP-32 in nucleus accumbens and amygdala (but not in the striatum) of wild-type and transgenic mice (with a greater effect in amygdala of transgenic mice than wild-type mice). Ethanol administration increased T75 DARPP-32 in amygdala of only the wild-type mice and in nucleus accumbens and striatum of both the transgenic and wild-type mice. CONCLUSIONS: The effect of ethanol on the balance of DARPP-32 phosphorylation, especially in amygdala of wild-type versus transgenic mice, may contribute to differential motivational effects of ethanol in these animals.