Specific long-lasting potentiation of synaptic transmission in hippocampal slices

Abstract

SHORT bursts of tetanic stimulation (10–50 Hz for 10–15 s) give rise to long-lasting potentiation (LLP) of synaptic transmission in the intact hippocampal formation¹ and in hippocampal slices². The potentiation may last several hours. Because of the time course and the small number of conditioning impulses required, the process may have general interest as a model for long-term plasticity in the nervous system. Studies of the mechanisms underlying LLP have been hampered, however, by lack of control with the size of the input volley and of data on membrane potential changes of the participating cells. Further, it is not known whether the potentiation is specific for the tetanised input. Schwartzkroin and Wester² found an unchanged antidromic field potential, and concluded that there were no general postsynaptic changes. Lynch et al.³, however, found a reduction in glutamate sensitivity during the potentiated stage, and suggested that a reduction in excitability had taken place. We report here experiments on transverse hippocampal slices⁴ of guinea pigs in which we have monitored the size of two independent afferent inputs, one of which is tetanised to produce LLP, leaving the other as a control line to check for non-specific changes in excitability. Furthermore, intracellular recordings support our suggestion that LLP is caused by a specific augmentation of transmitter release.