Contribution of NMDA receptors to tetanus-induced increase in postsynaptic Ca2+ in visual cortex of young rats.
Mechanisms underlying the Ca2+ increase during tetanic synaptic inputs in layer II/III of visual cortical slices of young rats were investigated with microfluorometry using a Ca2+ indicator, rhod-2, and simultaneous recordings of field potentials evoked by white matter stimulation. Application of an antagonist for N-methyl-D-aspartate (NMDA) receptors, 2-amino-5-phosphonovalerate, did not significantly affect field potentials but reduced the tetanus-induced fluorescence rise to 56%, on average, of the control values. Application of a broad-spectrum antagonist for both NMDA and non-NMDA receptors, kynurenate, completely abolished the synaptically evoked component of field potentials and decreased the tetanus-induced fluorescence rise to 42%. Application of a non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, in the Mg(2+)-free medium diminished the field potentials but did not decrease the tetanus-induced fluorescence increase. Nifedipine and diltiazem, L-type Ca2+ channel blockers, and Ni2+, a relatively selective blocker for T-type Ca2+ channels, did not affect the tetanus-induced fluorescence rise. These results indicate that NMDA receptors play a significant role in the increase of intracellular Ca2+ during tetanic synaptic inputs in the visual cortex of young rats.
Takahashi
M P
MP
Department of Neurophysiology, Osaka University Medical School, Suita, Japan.
Sugiyama
M
M
Tsumoto
T
T
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D066298:In Vitro Techniques; D007736:Kynurenic Acid / Q000494:pharmacology; D017774:Long-Term Potentiation / Q000187:drug effects; D008297:Male; D008856:Microscopy, Fluorescence; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013569:Synapses / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D014793:Visual Cortex / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D011810:Quinoxalines; D016194:Receptors, N-Methyl-D-Aspartate; C068483:rhod-2; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D007736:Kynurenic Acid; D002118:Calcium