Mp. Takahashi et al., LAMINAR DIFFERENCE IN TETANUS-INDUCED INCREASE OF INTRACELLULAR CA2-CORTEX OF YOUNG-RATS( IN VISUAL), Neuroscience research, 17(3), 1993, pp. 217-228
Changes in intracellular Ca2+ evoked by electrical stimulation of the
white matter were observed by means of microfluorometry with a Ca2+ in
dicator, rhod-2, in slice preparations of the visual cortex obtained f
rom young rats. Tetanic stimulation at 5 Hz for 1 min induced a marked
fluorescence increase, while single-shock stimulation did not induce
a sizable increase in normal perfusate. The tetanus-induced increase t
ook place in a columnlike manner from layer VI near the stimulation si
te to layer II/III of the cortex, although it spread horizontally in l
ayer II/III. The magnitude of fluorescence rise was largest in layer I
I/III of the cortex. Since N-methyl-D-aspartate (NMDA) receptors are k
nown to exist only on neurons, the following results are taken to indi
cate that the fluorescent signal is derived mostly from postsynaptic n
eurons: Application of NMDA in the presence of tetrodotoxin induced a
marked fluorescence increase with the same laminar bias as tetanic sti
mulation did, and the fluorescence increase by single-shock stimulatio
n in Mg2+-free medium was almost completely blocked by an antagonist f
or NMDA receptors. These results support the hypothesis that input-ass
ociated entry of Ca2+ into postsynaptic neurons triggers processes for
induction of long-term potentiation of synaptic efficacy.