Dopamine D1 vs D5 receptor-dependent induction of seizures in relation to DARPP-32, ERK1/2 and GluR1-AMPA signalling

Recent reports have shown that the selective dopamine D1-like agonist SKF 83822 [which stimulates adenylate cyclase, but not phospholipase C] induces prominent behavioral seizures in mice, whereas its benzazepine congener SKF 83959 [which stimulates phospholipase C, but not adenylate cyclase] does not. To investigate the relative involvement of D1 vs D5 receptors in mediating seizures, ethological behavioral topography and cortical EEGs were recorded in D1, D5 and DARPP-32 knockout mice in response to a convulsant dose of SKF 83822. SKF 83822-induced behavioral and EEG seizures were gene dose-dependently abolished in D1 knockouts. In both heterozygous and homozygous D5 knockouts, the latency to first seizure was significantly increased and total EEG seizures were reduced relative to wild-types. The majority (60%) of homozygous DARPP-32 knockouts did not have seizures; of those having seizures (40%), the latency to first seizure was significantly increased and the number of high amplitude, high frequency polyspike EEG events was reduced. In addition, immunoblotting was performed to investigate downstream intracellular signalling mechanisms at D1-like receptors following challenge with SKF 83822 and SKF 83959. In wild-types administered SKF 83822, levels of ERK1/2 and GluR1 AMPA receptor phosphorylation increased two-fold in both the striatum and hippocampus; in striatal slices DARPP-32 phosphorylation at Thr34 increased five-fold relative to vehicle-treated controls. These findings indicate that D1, and to a lesser extent D5, receptor coupling to DARPP-32, ERK1/2 and glutamatergic signalling is involved in mediating the convulsant effects of SKF 83822.