Postnatal Change of Glycinergic Synaptic Transmission from Supratrigeminal Region to Trigeminal Motoneurons

Summary

We have investigated excitatory synaptic transmission from the lateral part of the supratrigeminal region (lSuV) to the trigeminal motor nucleus (MoV) in neonatal and juvenile rat brain stem slice preparations by high-speed optical recording techniques and gramicidin perforated-patch recordings. Electrical stimulation of lSuV evoked optical responses in MoV. An antidromic response in lSuV was evoked by MoV stimulation while synaptic transmission was suppressed by substitution of external Ca²⁺ with Mn²⁺. Application of CNQX and APV to MoV reduced the optical responses in MoV evoked by ISuV stimulation in both neonatal and juvenile rats. Application of strychnine to MoV also suppressed the optical responses in MoV of neonatal rats. On the other hand, strychnine enhanced the optical responses in MoV of juveniles. Gramicidin perforated-patch recordings from trigeminal motoneurons (TMNs) revealed that glycinergic postsynaptic potentials evoked by lSuV stimulation were depolarizing in neonatal rats but become hyperpolarizing in juveniles. We conclude that inputs from lSuV excite TMNs through activation of glutamate or glycine receptors in neonatal rats, whereas glycine receptor activation in TMNs becomes inhibitory in juveniles. Such postnatal change of synaptic transmission from lSuV to MoV might be involved in the transition from suckling to mastication.