Development of trigeminal motoneuron

哺乳动物的摄食行为在发育过程中从相对简单的吮吸行为向复杂的咀嚼行为转变。摄食行为的中枢神经机制的发展与口面部器官的发育相协调是非常重要的。三叉神经运动神经元在将中枢组织的咀嚼运动转化为颌骨运动中起着重要作用。本研究采用细胞内记录和膜片钳记录的方法，研究了大鼠三叉神经运动神经元生理特性在增龄过程中的发育变化。正如我们先前报道的，应用200μ的5-羟色胺抑制mAHP。应用25-200μ的M8-OH-DPAT、5-HT1a和GT和5-HT7受体激动剂可剂量依赖性地抑制mAHP。5-羟色胺受体拮抗剂吲哚洛尔不能阻断8-OH-DPAT对mAHP的抑制作用，而氯氮平、多巴胺D_2、5-羟色胺D_2、5-羟色胺受体拮抗剂和5-羟色胺7受体拮抗剂均能拮抗5-羟色胺和8-羟基-DPAT对mAHP的抑制作用。5-羟色胺受体激动剂α-甲基-5-羟色胺不能减弱8-羟色胺对mAHP的抑制作用，蛋白激酶A抑制剂H89也能拮抗8-羟色胺对mAHP的抑制作用。这些结果表明，5-HT7受体通过激活PKA介导了5-羟色胺对幼年大鼠mAHP的抑制作用。而在新生大鼠三叉神经运动神经元上应用10-100μ的5-羟色胺则调制低电压激活的钙电流。5-羟色胺可降低LVA电流的激活阈值，增加峰值幅度，缩短达峰时间和τ_m。8-OH-DPAT和5-HT7激动剂5-CT不能模拟5-羟色胺的作用。我们认为，三叉神经运动神经元受到不同年龄的5-羟色胺调制。

Feeding behavior of mammals changes from relatively simple sucking to complicated mastication during development. It should be very important that development of central neural mechanisms for feeding behavior is coordinated with the development of organs in oro-facial area. Trigeminal motoneurons play an important role in converting centrally organized masticatory drive to jaw movements. In the present study, we investigated developmental change of physiological properties of trigeminal motoneurons in rats age by using intracellular or patch clamp recordings. As we previously reported, application of 200 μM 5-HT suppressed the mAHP.Application of 25-200 μM 8-OH-DPAT, 5-HT_<1A> and 5-HT_7 receptor agonist, inhibited the mAHP dose-dependently. Application of pindolol, 5-HT_<1A> receptor antagonist failed to block 8-OH-DPAT-induced attenuation of the mAHP, whereas clozapine, dopamine D_2, 5-HT_<2A/2C> and 5-HT_7 receptor antagonist, antagonized both 5-HT- and 8-OH-DPAT-induced suppression of the mAHP.Ritanserin, 5-HT_<2A/2C> and 5-HT_7 receptor antagonist, also blocked 8-OH-DPAT-induced suppression of the mAHP.α-methyl-5-HT, 5-HT_<2A/2C> receptor agonist, did not attenuate the mAHP.The 8-OH-DPAT-induced suppression of the mAHP could be also antagonized by protein kinase A (PKA) inhibitor, H89. These results suggest that 5-HT-induced attenuation of the mAHP is mediated by 5-HT_7 receptors through activation of PKA in young adult rats. In contrast application of 10-100 μM 5-HT to trigeminal motoneurons of neonatal rats modulates low voltage activated (LVA) calcium currents. 5-HT lowered activation threshold, increases peak amplitude and decreases time to peak and τ_m of LVA currents. 8-OH-DPAT and 5-CT, a 5-HT_7 agonist, did not mimic the effects of 5-HT.We conclude that trigeminal motoneurons are modulated differently by 5-HT according to their age.