Excitatory synaptic transmission in neostriatal neurons: regulation by cyclic AMP-dependent mechanisms

The purpose of the present study was to examine whether cAMP-dependent mechanisms regulated excitatory synaptic transmission in the neostriatum. A brain slice preparation was utilized for intracellular recordings of the excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation. Bath application of forskolin, an activator of adenylate cyclase, enhanced the EPSP amplitude and duration. This potentiation was dose dependent and did not occur with the inactive analog 1,9-dideoxyforskolin. Forskolin potentiation was unaltered by treatment with the GABAA receptor antagonist bicuculline. Furthermore, two inhibitors of cAMP-dependent protein kinase (PKA), Rp-cAMPS and IP20-amide, attenuated forskolin's enhancement of the EPSP. In addition, the PKA activator Sp-cAMPS enhanced excitatory synaptic transmission. Interestingly, treatment with PKA inhibitors alone depressed while the phosphatase inhibitor okadaic acid enhanced the synaptic response. These results suggest a role for tonic kinase and phosphatase activity in regulating excitatory synaptic transmission in the neostriatum. Finally, forskolin was found to enhance the responses of neostriatal neurons to glutamate receptor agonists. This potentiation, which occurred in the presence of tetrodotoxin, provides at leas part of the explanation for the cAMP/PKA-dependent regulation of the EPSP. Overall, these results suggest a role for the adenylate cyclase cascade in the regulation of excitatory synaptic transmission in the neostriatum.