Neurotransmitter Regulation of MAP Kinase Signaling in Striatal Neurons in Primary Culture

Glutamate and dopamine are important neurotransmitters in the basal ganglia. Dopamine can act via D1 receptors to activate adenylyl cyclase in striatal neurons, while glutamate stimulation of NMDA receptors leads to an increase in intracellular calcium. Increases in intracellular calcium or cAMP can induce immediate early gene expression in striatal neurons. In the present study, NMDA receptor stimulation or adenylyl cyclase activation resulted in the activation of MAP kinase in striatal neurons in primary culture. The effect of cAMP appeared to involve cAMP-dependent protein kinase, in addition to a tyrosine kinase and MEK. NMDA-induced MAP kinase activation was also dependent on a tyrosine kinase and MEK. The EGF receptor, which has been implicated in calcium- and G protein-induced MAP kinase activation, did not mediate the effects of NMDA or forskolin on MAP kinase. Furthermore, the src kinase inhibitor, herbimycin A, and the phosphoinositol-3-kinase inhibitor, wortmannin, did not prevent MAP kinase activation by these stimuli. However, the ability of both NMDA and forskolin to activate MAP kinase in striatal neurons was blocked by SB 203580, an inhibitor of p38 reactivating kinase. These results indicate that both NMDA receptor activation and elevations in cAMP can result in MEK-induced MAP kinase activation in striatal neurons. However, the signal transduction pathways mediating these responses appear to be distinct from those known to mediate MAP kinase activation by other stimuli.