Analysis of neural network responsible for matication in slice preparation

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To know the phy siological and pharmacological mechanisms responsible for generation of spike discharge pattern of trigeminal motoneurons (TMNs), we examined afterpotentials of TMNs and effects of serotonin on TMNs by using intracellular recording in the rat brain stem slice preparation.In most neurons afterhyperpolarization (AHP) was separated the fast (fAHP) from slow afterhyperpolarization (mAHP). Replacement of extracellular Ca^<2+> with calcium channel blocker Mn^<2+> or Co^<2+> reduced the mAHP amplitudes. Increasing extracellular Ca^<2+> concentration from 2 to 6mM enhanced the mAHP amplitudes. Furthermore, application of SK type Ca^<2+> dependent K^+ channel blocker apamin almost abolished the mAHP amplitudes. Regarding ADP,Increasing extracellular Ca^<2+> concentration did not enhance the ADP amplitude of all the neurons tested. When extracellular Ca^<2+> was elevated in combination with apamin application, the ADP amplitude was enhanced. Bath application of serotonin (20-100 muM) caused depolarization and increased input resistance in the most cells tested. Time-dependent inward rectification was enhanced by serotonin. These effects persisted in the presence of tetrodotoxin (1 muM). Serotonin also increased firing frequency response to injected current in every cell tested.These results suggested mAHP may be due to activation of SK type Ca^<2+> dependent K^+ channel and Ca^<2+> influx play an important role of activation of ADP in the rat trigeminal motoneurons. It was also suggested that serotonin facilitates trigeminal motoneuron excitability.