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 NMD A and GABA selective blockers. us, dopaminergic D-1 receptor activatio n facilitates the AMPA-mediated EPSP in these conditions. This facilit atory effect could be suppressed by L-type Ca2+ channel antagonists (2 00 nM calciseptine and 5 mu M nicardipine), suggesting that it is medi ated by an increase in L-current. D-1-receptor activation thus mediate s orthodromic facilitation of neostriatal neurons when evoked from dep olarized membrane potentials. This reinforces the dopamine facilitatio n mediated through NMDA responses.