Spontaneous firing level distinguishes the effects of NMDA and non-NMDA receptor antagonists on the ganglion cells in the cat retina.
Different responses of retinal ganglion cells to iontophoretically applied NMDA receptor antagonists and non-NMDA receptor antagonists were studied in anaesthetized cats. Cells with normal range of spontaneous firing and those with abnormally high spontaneous firing levels showed a different response to these drugs. Both visually driven and spontaneous firing of cells with 'normal' spontaneous firing level were blocked by non-NMDA receptor antagonists, but not by NMDA receptor antagonists which often raised spontaneous firing. In contrast, the responses of cells with abnormally high spontaneous firing level were blocked effectively by NMDA antagonists including MK-801, an NMDA channel blocker, as well as by non-NMDA receptor antagonists. The results suggest that under normal physiological conditions, NMDA receptors which are not involved in synaptic transmission may play a role in reducing the resting discharge level of the retinal ganglion cells. NMDA receptors, however, appear to open ion channels in response to glutamate input when ganglion cells become abnormally depolarized.
Research Unit of Sherington School, UMDS, The Rayne Institute, St. Thomas' Hospital, London, U.K.
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Ikeda
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D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000596:Amino Acids / Q000037:antagonists & inhibitors; D000818:Animals; D002415:Cats; D016291:Dizocilpine Maleate / Q000494:pharmacology; D005074:Evoked Potentials, Visual / Q000187:drug effects; D005724:Ganglia / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007478:Iontophoresis; D007736:Kynurenic Acid / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D017459:Receptors, Amino Acid; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors*; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*; D012160:Retina / Q000166:cytology / Q000187:drug effects* / Q000502:physiology
D000596:Amino Acids; D010879:Piperazines; D017459:Receptors, Amino Acid; D011956:Receptors, Cell Surface; D016194:Receptors, N-Methyl-D-Aspartate; D016291:Dizocilpine Maleate; D015763:2-Amino-5-phosphonovalerate; C050592:3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid; D007736:Kynurenic Acid