Modulatory inputs to trigeminal motoneurons in rat slice preparation

在大鼠闭口运动神经元(JCMIN)的脑片标本上进行细胞内记录，观察5-羟色胺(5-HT)对尖峰后中时程后超极化(MAHP)的影响及蛋白激酶的参与。应用50 mU的5-HT可引起多数细胞的膜去极化和输入阻力增加，而较大剂量的5-HT(100或200 um)不仅引起膜去极化和输入阻力的增加，而且还抑制mAHP的幅度。另一方面，当mAHP幅度随[Ca^&lt；2+1&GT；].从2 mM到6 mM，5-羟色胺引起的mAHP幅度衰减增强，甚至50 mM 5-羟色胺也使mAHP幅度降低，这种抑制作用可被膜通透性cAMP类似物8-溴-cAMP、cAMP特异性磷酸二酯酶抑制剂Ro 20-1724增强和蛋白激酶A(PKA)抑制剂H89拮抗。另一方面，PKC激动剂佛波酯12-肉豆蔻酸13-乙酸酯对mAHP的抑制作用几乎完全被H89阻断，提示PKC对mAHP的作用需要PKA的激活。我们得出结论：5-羟色胺通过cAMP依赖的PKA激活诱导mAHP幅度的剂量依赖性衰减，PKC依赖的PKA激活也可能参与升高[Ca&^lt；2+&gt；]下5-羟色胺诱导的mAHP的减弱。我们还检测了细胞内钙离子浓度([Ca^&lt；2+&gt；])的变化。[Ca^&lt；2+&gt；]随着运动神经元活动的变化而增加。

Intracellular recordings were obtained from rat jaw-closing motoneurons (JCMINs) in slice preparations to investigate the effects of serotonin (5-HT) on the post-spike medium-duration afterhyperpolarization (mAHP) and an involvement of protein kinases in the effects.Application of 50 muM 5-HT caused membrane depolarization and increased input resistance in the most cells without affecting the mAHP, whereas not only membrane depolarization and an increase in input resistance, but also the suppression of the mAHP amplitude was induced by higher dose of 5-HT (100 or 200 muM).On the other hand, when the mAHP amplitude was increased by raising [Ca ^<2+1>]。 from 2 to 6 mM, 5-HT-induced attenuation of the mAHP amplitude was enhanced and even 50 muM 5-HT reduced the mAHP amplitude.This 5-HT-induced suppression of the mAHP could be mimicked by application of membrane-permeable cAMP analog 8-Br- cAMP, potentiated by the cAMP-specific phosphodiesterase inhibitor Ro 20-1724 and antagonized by protein kinase A (PKA) inhibitor H89.The enhancement of the mAHP attenuation induced by 50 muM 5-HT under raised [Ca ^<2+>]。 was blocked by a protein kinase C (PKC) inhibitor chelerythrine, suggesting an involvement of PKC in this enhancement.On the other hand, the attenuation of the mAHP induced by PKC activator phorbol 12-myristate 13-acetate was almost completely blocked by H89, suggesting that the PKC action on the mAHP requires PKA activation.We conclude that 5-HT induces dose-dependent attenuation of the mAHP amplitude through cAMP-dependent activation of PKA, and that PKC-dependent PKA activation is also likely to be involved in the enhancement of 5-HT-induced attenuation of the mAHP under raised [Ca^<2+>]。We also examied alteration of intracellular calcium concentration ([Ca^<2+>]). [Ca^<2+>] increased when burst firing was eliced by current injection.It is suggested that [Ca^<2+>] changes according to motoneuronal activity.