Abstract
Cholinergic presynaptic inhibition was investigated on neostriatal glutamatergic transmission. Paired pulse facilitation (PPF) of orthodromic population spikes (PS) were used to construct a concentration-response relationship for muscarine on presynaptic inhibition. Muscarine had an effect proportional to its extracellular concentration with an EC 50 (mean ± standard estimation error) of: 2.5 ± 1.5 nM, and a maximal effect (saturation) of 245 ± 16 %. Several peptidic toxins against some voltage-gated Ca 2+-channels increased PPF indicating that the Ca 2+-channels they block participate in transmitter release. However, neither 1 μM ω-conotoxin GVIA, a specific blocker of N-type Ca 2+-channels, nor 10–30 nM ω-agatoxinTK, a selective blocker of P-type Ca 2+-channels, were able to occlude muscarine’s effect on presynaptic inhibition. Nevertheless, 100–400 nM ω-agatoxinTK occluded muscarine’s action on PPF in a dose-dependent manner. These results are consistent with Q-type Ca 2+-channels mediating muscarinic presynaptic inhibition of neostriatal afferents.
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