Mp. Takahashi et al., CONTRIBUTION OF NMDA RECEPTORS TO TETANUS-INDUCED INCREASE IN POSTSYNAPTIC CA2-CORTEX OF YOUNG-RATS( IN VISUAL), Neuroscience research, 17(3), 1993, pp. 229-239
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.