CONTRIBUTION OF NMDA RECEPTORS TO TETANUS-INDUCED INCREASE IN POSTSYNAPTIC CA2-CORTEX OF YOUNG-RATS( IN VISUAL)

Mechanisms underlying the Ca2+ increase during tetanic synaptic inputs in layer II/III of visual cortical slices of young rats were investig ated with microfluorometry using a Ca2+ indicator, rhod-2, and simulta neous recordings of field potentials evoked by,white matter stimulatio n. Application of an antagonist for N-methyl-D-aspartate (NMDA) recept ors, 2-amino-5-phosphonovalerate, did not significantly affect field p otentials but reduced the tetanus-induced fluorescence rise to 56%, on average, of the control values. Application of a broad-spectrum antag onist for both NMDA and non-NMDA receptors, kynurenate, completely abo lished the synaptically evoked component of field potentials and decre ased the tetanus-induced fluorescence rise to 42%. Application of a no n-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, in t he Mg2+-free medium diminished the field potentials but did not decrea se the tetanus-induced fluorescence increase. Nifedipine and diltiazem , L-type Ca2+ channel blockers, and Ni2+, a relatively selective block er for T-type Ca2+ channels, did not affect the tetanus-induced fluore scence rise. These results indicate that NMDA receptors play a signifi cant role in the increase of intracellular Ca2+ during tetanic synapti c inputs in the visual cortex of young rats.