Increased binding of calcium in the hippocampal slice during long-term potentiation.

Long-term potentiation (LTP) of CA1 pyramidal neurons was induced by tetanic stimulation in the stratum radiatum of hippocampal slices from guinea pigs. Unstimulated and stimulated slices were treated using a histochemical procedure enabling the electron microscopic (EM) visualization of Ca binding sites. Electron-dense, Ca-containing deposits were found in low numbers in unstimulated slices on pre- and postsynaptic sites. In the stratum radiatum of tetanized slices the overall number of deposits as well as the number of deposits in dendrites was clearly increased. The results support the hypothesis that Ca-dependent postsynaptic mechanisms are important for the generation of LTP.