GABAergic presynaptic inhibition of rat neostriatal afferents is mediated by Q-type Ca2+ channels

Population spikes associated with the paired pulse facilitation paradigm have been successfully used to measure presynaptic inhibition in several systems. In the present work, this paradigm was used to evaluate the action of baclofen on neostriatal glutamatergic transmission. Baclofen enhanced synaptic facilitation with an EC50 = 0.57 mu M and a maximal effect of 457%. Selective antagonists for N-, P- and Q-type Ca2+-channels enhanced paired pulse facilitation; suggesting that these channel types participate in the release of transmitter. Nevertheless, neither 1 mu M omega-conotoxin GVIA, nor 20 nM omega-agatoxinTK occluded the action of baclofen. Baclofen's action was occluded only by 400 nM w-agatoxinTK. These data suggest that Q-type Ca2+-channels mediate gamma-aminobutyric acids presynaptic inhibition of neostriatal afferents. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.