GABAergic amd serotonergic modulation of calcium currents in rat trigeminal motoneurons

Abstract

We investigated the effects of a GABAB agonist baclofen, and serotonin, on the high voltage-activated Ca channel (HVACC) currents in trigeminal motoneurons. Immunohistochemical and reverse transcription-polymerization chain reaction (RT-PCR) studies demonstrated the expression of α1C, α1B, α1A, and α1E subunits in the trigeminal motoneurons, which form L-, N-, P/Q-, and R-type Ca channels, respectively. By use of specific Ca blockers, it was found that N-type (38%), P/Q-type (27%), L-type (16 %), and R-type Ca currents (19%) contribute to HVACC IBa. Baclofen inhibited HVACC IBa in the majority of trigeminal motoneurons tested (n=15 outof 16), whereas serotonin only did in a small population (n=5 outof 18). The IBa inhibition by baclofen and serotonin was associated with slowing of activation kinetics, relieved by strong prepulse, and prevented by N-ethylmaleimide (NEM), indicative of mediation of Gi/Go. These data provide evidence that GABAergic and serotonergic inputs to trigeminal motoneurons regulate neuronal activities through the inhibition of HVACC currents.