Abstract
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 JCMNs 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. [J Physiol Sci. 2007;57 Suppl:S23]
