Relationship between Long-Term Potentiation and the Initial Properties of CA3–CA1 Synapses: Importance of the Effects of External Factors on Hippocampal Synaptic Plasticity for Studies

  • I. V. KudryashovaEmail author

The phenomenon of long-term potentiation (LTP) is used for studies of the effects of various factors on the long-term plasticity of synapses in health and disease. One of the most important problems for these experiments is selection of a suitable stimulation protocol for comparing individual and group characteristics. Experiments on living hippocampal slices from Wistar rats aged 1–1.5 months addressed the individual features of the induction and maintenance of LTP (tetanization at 100 Hz for 1 sec) depending on the initial magnitude of the overall response of CA1 neurons to the stimulation of Schaffer collaterals used for tetanization and testing. The statistical relationship between the intensity of the synaptic input at the moment of tetanization and the magnitude of the post-tetanic increase after induction of LTP was assessed. Early potentiation was found to depend on the parameters of the test stimulation but not the amplitude of the response to the stimulation used for tetanization; the two factors acted independently. On testing with variable intensities, weak (near-threshold) responses were potentiated significantly more strongly than near-maximal responses. The saturation effect was found to limit mainly early LTP and only indirectly influenced the remaining potentiation. When differences in the level of early potentiation were excluded, late LTP depended on the intensity of tetanization but not the parameters of the test stimulation. The optimum tetanization of Schaffer collaterals for maintenance of LTP was the level inducing overall postsynaptic neuron responses of 1–2 mV, both weak and excessively strong activation on induction having negative impact on the efficiency with which LTP was maintained. This pattern may be due to a low level of depolarization, including in conditions of quite intense activation, due to the involvement of inhibitory interneurons in the response. These data provide evidence that all the study factors need to be considered for adequate comparison of groups of animals exposed to various environmental factors, including stress factors, particularly when the input characteristics of the connections of interest change.


hippocampus long-term plasticity early LTP consolidation maintenance synaptic input conditions on tetanization and testing 


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Authors and Affiliations

  1. 1.Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of SciencesMoscowRussia

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