Cyclic AMP and mitogen‐activated protein kinases are required for glutamate‐dependent cyclic AMP response element binding protein and Elk‐1 phosphorylation in the dorsal striatum in vivo

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Abstract
Dopaminergic and glutamatergic signalling cascades are integrated in striatal medium spiny neurones by cyclic AMP response‐element binding protein and Elk‐1 phosphorylation. Phosphorylated cyclic AMP response‐element binding protein and phosphorylated Elk‐1 contribute to c‐fos expression by binding to the calcium and cyclic AMP response‐element and the serum response element, respectively, in the c‐fos promoter. The role of cyclic AMP and mitogen‐activated protein kinase signalling cascades in glutamate‐induced cyclic AMP response‐element binding protein and Elk‐1 phosphorylation and Fos expression was investigated using semiquantitative immunocytochemistry in vivo. Intracerebroventricular infusion of the sodium channel blocker, tetrodotoxin, decreased the glutamate‐induced increase in phosphorylated cyclic AMP response‐element binding protein, phosphorylated Elk‐1, and Fos immunoreactivity. Intracerebroventricular infusion of the mitogen‐activated and extracellular signal‐regulated kinase inhibitor, PD98059, the p38 mitogen‐activated protein kinase inhibitor, SB203580, or the cyclic AMP inhibitor, Rp‐8‐Br‐cAMPS, decreased glutamate‐induced phosphorylated cyclic AMP response‐element binding protein, phosphorylated Elk‐1, and Fos immunoreactivity. Simultaneous infusion of glutamate and Sp‐8‐Br‐cAMPS, a cyclic AMP analogue, augmented induction of Fos immunoreactivity but not phosphorylated cyclic AMP response‐element binding protein or phosphorylated Elk‐1 immunoreactivity. These data indicate that cyclic AMP and mitogen‐activated protein kinase signalling cascades are necessary for glutamate to induce cyclic AMP response‐element binding protein and Elk‐1 phosphorylation and Fos expression in the striatum. Furthermore, neuronal activity plays an important role in glutamate‐induced signalling cascades in vivo.