title: Evidence for N-methyl-D-aspartic acid receptor-mediated modulation of the commissural input to central vestibular neurons of the frog.
abstract: We have investigated the role of N-methyl-D-aspartate (NMDA) receptors in the excitatory synaptic transmission to central vestibular neurons in the isolated superfused brainstem of the frog. In superfusate containing 1 mM Mg2+ field potentials in the vestibular nuclei evoked by electrical stimulation of either the ipsi- or the contralateral VIIIth nerve were not affected by bath-applied D-2-amino-5-phosphonovaleric acid (D-APV, 25-50 microM), a selective NMDA antagonist. In a low Mg2+ solution postsynaptic field potential components were larger than control but still unaffected by D-APV. Ipsi- and contralaterally evoked excitatory postsynaptic potentials (EPSPs) differed in their shape parameters as well as in their pharmacological sensitivity. Ipsilaterally evoked EPSPs were not affected by D-APV and has a rise time that was faster than that of contralaterally evoked EPSPs. The peak amplitude of hte latter was reduced by D-APV (25-50 microM) to about 65% of the control value in the presence of 1 mM Mg2+. During bath application of NMDA (100 microM) an increased input resistance and repetitive de- and hyperpolarizing membrane potential shifts were observed. Similar events were observed during a reduction of the Mg2+ concentration. Bath application of NMDA (0.1-1 microM) resulted in an enhanced size of the recorded EPSPs. Dendritic and somatic EPSPs were simulated on a computer with the assumption of a constant NMDA receptor activation and a pulse-like non-NMDA receptor activation. The results of these simulations are consistent with the hypothesis that the efficacy of non-NMDA-mediated vestibular commissural synaptic transmission is modulated through tonically activated NMDA receptors.
mesh_terms: D015763:2-Amino-5-phosphonovalerate; D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology; D001224:Aspartic Acid / Q000031:analogs & derivatives*; D001933:Brain Stem / Q000187:drug effects / Q000502:physiology*; D005071:Evoked Potentials; D007839:Functional Laterality; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology*; D011896:Rana temporaria; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000502:physiology*; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology; D014726:Vestibular Nuclei / Q000502:physiology
chemical_list: D000927:Anticonvulsants; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D001224:Aspartic Acid; D015763:2-Amino-5-phosphonovalerate; D014633:Valine; D008274:Magnesium