SYNAPTIC RECRUITMENT DURING LONG-TERM POTENTIATION AT SYNAPSES OF THEMEDIAL PERFORANT PATHWAY IN THE DENTATE GYRUS OF THE RAT-BRAIN

Long-term potentiation (LTP) in synapses of the medial perforant pathw ay of the rat dentate gyrus has been studied using the whole-cell volt age clamp technique and a standard hippocampal slice preparation. The rate of LTP induction by 2-4 brief trains of stimuli at 100 Hz, paired with postsynaptic depolarization to -20 mV, in individual granule neu rons was only 42% but the average magnitude was large. In a representa tive series of nine experiments the average potentiation was 339% (s.d . 255%). The variable magnitude of LTP appeared to be related to the r elative size of the NMDA receptor dependent current in individual neur ons. LTP was further characterized by the selective enhancement of the AMPA (but not the NMDA) component in the excitatory synaptic response s. This selective enhancement of the AMPA component and a graphical va riance analysis suggest that the large magnitude of LTP in dentate gyr us can be best explained by recruitment of previously silent synapses by a combination of pre- and post-synaptic mechanisms. (C) 1996 Wiley- Liss, Inc.