Laminar difference in tetanus-induced increase of intracellular Ca2+ in visual cortex of young rats.
Changes in intracellular Ca2+ evoked by electrical stimulation of the white matter were observed by means of microfluorometry with a Ca2+ indicator, rhod-2, in slice preparations of the visual cortex obtained from 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 took place in a column-like manner from layer VI near the stimulation site to layer II/III of the cortex, although it spread horizontally in layer II/III. The magnitude of fluorescence rise was largest in layer II/III of the cortex. Since N-methyl-D-aspartate (NMDA) receptors are known to exist only on neurons, the following results are taken to indicate that the fluorescent signal is derived mostly from postsynaptic neurons: Application of NMDA in the presence of tetrodotoxin induced a marked fluorescence increase with the same laminar bias as tetanic stimulation did, and the fluorescence increase by single-shock stimulation in Mg(2+)-free medium was almost completely blocked by an antagonist for NMDA receptors. These results support the hypothesis that input-associated entry of Ca2+ into postsynaptic neurons triggers processes for induction of long-term potentiation of synaptic efficacy.
Takahashi
M P
MP
Department of Neurophysiology, Osaka University Medical School, Suita, Japan.
Sugiyama
M
M
Tsumoto
T
T
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D066298:In Vitro Techniques; D017774:Long-Term Potentiation / Q000502:physiology; D008274:Magnesium / Q000502:physiology; D008297:Male; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects; D013050:Spectrometry, Fluorescence; D013779:Tetrodotoxin / Q000494:pharmacology; D014793:Visual Cortex / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D016194:Receptors, N-Methyl-D-Aspartate; C068483:rhod-2; D013779:Tetrodotoxin; D008274:Magnesium; D002118:Calcium