Contribution of glutamate receptors to the maturation of central vestibular neurons in rats

Abstract

To investigate the role of ionotropic glutamate receptors (AMPAR and NMDAR) in the development of central vestibular neurons, whole-cell patch-clamp experiments were performed in spinal vestibular neurons of postnatal (P1-16) Sprague Dawley rats. The profiles of AMPAR- and NMDAR-mediated currents evoked by electrical stimulation of the ipsilateral vestibular nerve were studied. From P1 to P3, glutamatergic transmission is primarily mediated by NMDARs. The relative contribution of AMPARs versus NMDARs at vestibular afferent synapses increased during the first two weeks of life. To consider whether such an increase in AMPAR/NMDAR ratio could be due to an increase in synaptic AMPARs, we used strontium-evoked miniature EPSC to assess the quantal contribution of AMPAR-mediated transmission. A significant increase in the quantal amplitude of AMPAR was observed from P5 to P7. To further assess whether NMDAR-only synapses could also account for the change in AMPAR/NMDAR ratio, we compared synaptic responses at -80 mV and +40 mV using minimal stimulation paradigm. We found that silent NMDAR-only synapses were only present up to P5. The disappearance of NMDAR-only synapses towards the end of the first postnatal week coincides with the age-dependent increase of AMPARs. Taken together, our findings provide evidence that developmental shift in AMPAR and NMDAR component within glutamatergic synapses is important to the functional maturation of central vestibular neurons in postnatal rats.