An Increased Basal Calcium Hypothesis for Long-Term Potentiation of Transmitter Release in Bullfrog Sympathetic Ganglia
Long-term potentiation (LTP) of synaptic transmission, a basis for learning and memory (cf. Tsukahara, 1981), occurs in response to conditioning stimuli in various neuronal elements at both central and peripheral synapses. In bullfrog sympathetic ganglia, there are two types of long-term potentiation of transmitter release, one induced by conditional tetanic stimulation of the preganglionic nerve through a Ca2+ -dependent mechanism (presynaptic LTP, pre-LTP; Koyano et al., 1985), and the other generated by the action of epinephrine through a cAMP-dependent mechanism (epinephrine-induced LTP, adrLTP; Kuba et al., 1981; Kuba and Kumamoto, 1986). We describe here novel mechanisms of these LTPs in which a rise in the basal level of the intracellular free Ca2+ ([Ca2+]i) in the presynaptic terminal plays an important role.
KeywordsTransmitter Release Presynaptic Terminal Quantal Content Dibutyryl cAMP Synaptic Delay
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