Glycine binding site of the synaptic NMDA receptor in subpostremal NTS neurons.
The nucleus of the tractus solitarius (NTS) plays an important role in the control of several autonomic reflex functions and has glutamate and GABA as main neurotransmitters. In this work, we used patch-clamp recordings in transverse slice preparations from rats to study whether the glycine binding site of the N-methyl-D-aspartate (NMDA) receptor is saturated or not in neurons of the subpostremal NTS. Except at hyperpolarized voltages and close to the reversal potential, glycine potentiated the NMDA responses in a concentration-dependent manner. The total charge transferred by glutamatergic currents was enhanced by glycine (500 microM; from 28 +/- 13 to 42 +/- 18 pC at +50 mV, n = 7, P < 0.05). Glycine increased the conductance of the postsynaptic membrane, without altering its reversal potential, both in the presence (from 2.4 +/- 0.06 to 3.4 +/- 0.09 nS; n = 7) and absence (from 3.1 +/- 0.06 to 4.4 +/- 0.10 nS; n = 8) of Mg2+ in the bathing solution. d-serine, in the presence of strychnine, also increased the amplitude of the NMDA component (by 68 +/- 19%, P < 0.05, n = 5). The membrane potential was hyperpolarized (16 +/- 6 mV, n = 8) by glycine, suggesting the presence of inhibitory glycinergic receptors. Our results indicate that the glycine site of the NMDA receptor in neurons of the subpostremal NTS is not saturated and that glycine may act as a modulator of the NMDA transmission in this nucleus.
Baptista
Vander
V
Department of Physiology, School of Medicine of Ribeirão Preto/University of São Paolo, Av. Bandeirantes 3900, 14049-900 Ribeirão Preto/SP, Brazil.
Varanda
Wamberto Antonio
WA
D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation / Q000379:methods; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D005998:Glycine / Q000378:metabolism*; D018684:Glycine Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D012694:Serine / Q000494:pharmacology; D017552:Solitary Nucleus / Q000166:cytology*; D013331:Strychnine / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*
D000634:Aminoquinolines; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018684:Glycine Agents; D016194:Receptors, N-Methyl-D-Aspartate; C074617:4-trans-2-carboxy-5,7-dichloro-4-phenylaminocarbonylamino-1,2,3,4-tetrahydroquinoline; D012694:Serine; D016202:N-Methylaspartate; D013331:Strychnine; D005998:Glycine