Temporal spacing of synaptic stimulation critically modulates the dependence of LTP on cyclic AMP-dependent protein kinase.

Genetic and electrophysiological experiments have defined an important role for cAMP-dependent protein kinase (PKA) in certain forms of long-term potentiation (LTP). However, the characteristics of stimulation that are critical for regulating the PKA-dependence of LTP have not been clearly defined. In the present study, we have used PKA mutant mice (R(AB) transgenic mice), which have reduced PKA activity in neurons within the hippocampus, to explore the role of temporal spacing of synaptic stimulation in regulating the PKA-dependence of LTP. The time interval between successive bursts of electrical stimulation was varied while keeping constant the total number of stimulus pulses. LTP induced by temporally spaced tetraburst synaptic stimulation was impaired in the Schaeffer collateral pathway of hippocampal slices from R(AB) mutant mice. In contrast, LTP induced by temporally compressed tetraburst stimulation was normal in slices from R(AB) mutants, and its long-term maintenance was not significantly affected by bath application of KT-5720, an inhibitor of catalytic subunits of PKA. In slices from wildtype mice, LTP induced by spaced tetraburst stimulation was significantly attenuated by KT-5720. These genetic and pharmacological experiments show that LTP induced by these compressed patterns of stimulation does not require PKA activation. Thus, altering the temporal spacing of synaptic stimulation per se critically modulates the PKA-dependence of hippocampal LTP. PKA-dependent LTP is selectively recruited by temporally spaced, multiburst synaptic stimulation.