Postnatal development of the local neural circuit controlling jaw movement

哺乳动物的摄食行为在出生后的发育过程中从哺乳到咀嚼发生变化。为了研究控制口面部结构摄食运动的神经元回路的生后发育，我们在脑干切片和麻醉成年大鼠上观察了三叉神经运动神经元(TMN)兴奋性运动前神经元的定位，以及这些运动前神经元向TMN的输入在出生后的变化。电刺激脑干脑片三叉神经上区(SUV)和面神经核背侧网状结构(RdVII)可诱发闭合和张口运动神经元兴奋性突触后电流(EPSCs)。电刺激和化学刺激RdVII也可引起麻醉大鼠合口肌的兴奋性反应。细胞内生物细胞素染色示与TMN有突触联系。应用CNQX和APV可抑制由SUV或RDVII刺激的新生和幼年脑片JCMN和JOMN中的EPSCs。士的宁和GABA也抑制新生JCMN和JOMN的EPSCs，而士的宁增强幼年JCMN和JOMN的EPSCs。我们的结论是，位于SUV和RDVII的神经元最有可能兴奋TMN。在新生大鼠，SUV对TMN的兴奋性传入是通过激活谷氨酸、GABA和甘氨酸受体介导的，而在幼年大鼠则是通过激活TMN的甘氨酸受体而实现的。这种出生后从SUV到TMN的突触传递的变化可能参与了从哺乳到咀嚼的转变。

Feeding behavior in mammals changes from suckling to mastication during postnatal development. In order to investigate the postnatal development in the neuronal circuits controlling feeding movements of orofacial structures, we have examined the location of excitatory premotor neurons for trigeminal motoneurons (TMNs), and postnatal changes of inputs from these premotor neurons to TMNs in brain stem slice preparations and anesthetized adult rats. Electrical stimulation of the supratrigeminal region (SupV) and the reticular formation dorsal to the facial nucleus (RdVII) in the brainstem slices evoked excitatory postsynaptic currents (EPSCs) in jaw-closing (JCMNs) and jaw-opening (JOMNs) motoneurons. Electrical and chemical stimulation of RdVII also induced excitatory responses in jaw-closing muscles of anesthetized rats. Intracellular staining of SupV neurons by biocytin revealed synaptic contacts with TMNs. Application of CNQX and APV inhibited EPSCs induced by stimulation of SupV or RdVII in both JCMNs and JOMNs of neonatal and juvenile slices. Strychnine and GABA also inhibited EPSCs in neonatal JCMNs and JOMNs, whereas strychnine enhanced EPSCs in juvenile JCMNs and JOMNs. We conclude that neurons located in SupV and RdVII most likely excite TMNs. It is also suggested that excitatory inputs from SupV to TMNs are mediated by activation of glutamate, GABA and glycine receptors in neonatal rats, whereas glycine receptor activation in TMNs becomes inhibitory in juveniles. Such postnatal change of synaptic transmission from SupV to TMNs might be involved in the transition from suckling to mastication.