T. Tsumoto et H. Yasuda, A SWITCHING ROLE OF POSTSYNAPTIC CALCIUM IN THE INDUCTION OF LONG-TERM POTENTIATION OR LONG-TERM DEPRESSION IN VISUAL-CORTEX, Seminars in the neurosciences, 8(5), 1996, pp. 311-319
Long-term potentiation (LTP) and depression. (LTD) are considered to b
e an initial step in processes governing experience-dependent changes
in neuronal function in cerebral neocortex. As a mechanism for the ind
uction of LTP and LTD, it is hypothesized that an input-associated ris
e of Ca2+ beyond a certain threshold at postsynaptic sites leads to LT
P while a lower rise below the threshold leads to LTD. To test this Ca
2+-switching hypothesis, the method of microscopic fluorometry with Ca
2+ indicators such as fura-2 has been employed. In this review, proble
ms with this fura-2 method are described, and results obtained with ot
her indicators having weaker Ca2+-chelating action are mentioned brief
ly. Experimental results indicating the involvement of Ca2+/calmodulin
-dependent protein kinase II (CaMKII) and protein phosphatase (calcine
urin) are also reviews, and a model that includes the spatiotemporal d
ynamics of Ca2+ and the intracellular location of both enzymes as vari
ables ils proposed as a modification of the Ca2+-switching hypothesis.