Dopamine facilitates striatal EPSPs through an L-type Ca2+ conductance

WHEN synaptic activity is evoked from relatively depolarized membrane potentials, D-1 receptor agonists enhance the depolarization level and slow the decay of synaptic responses recorded from neostriatal spiny neurons. The population spikes' amplitude is also increased. These D-1 actions facilitate firing and are evident in the presence oi bath NMDA and GABA selective blockers. us, dopaminergic D-1 receptor activation facilitates the AMPA-mediated EPSP in these conditions. This facilitatory effect could be suppressed by L-type Ca2+ channel antagonists (200 nM calciseptine and 5 mu M nicardipine), suggesting that it is mediated by an increase in L-current. D-1-receptor activation thus mediates orthodromic facilitation of neostriatal neurons when evoked from depolarized membrane potentials. This reinforces the dopamine facilitation mediated through NMDA responses.