Place field specific spiking activity of dentate gyrus granule cells triggers long-term potentiation of mossy fiber synaptic responses in vitro.
(A) Presentation of spike train 1 (indicated by grey area) led to potentiation of mossy fiber fEPSP amplitudes in this examplary recording. Constant stimulation frequency before and after delivery of spike train was 0.05 Hz. Application of DCGIV at the end of experiment blocked mossy fiber synaptic transmission. Upper traces show averages of 10 sweeps under control condition and 30 min after presentation of spike train 1. (B) Summary of n = 5 such experiments. Presentation of spike train led to reliable long-term potentiation of fEPSP amplitudes to ∼130% of control values 25 min after spike train 1. (C) Time-resolved plot of another place field specific spike episode (spike train 2, up) and continuous recording of mossy fiber fEPSP response to single presentation of this spike train (lower part). Stimulus artifacts are cut for visual clarity. Please note different timescale compared to spike train 1. (D) Examplary mossy fiber synaptic fEPSP recording, where a single presentation of spike train 2 (grey bar, not drawn to scale) leads to long-term potentiation of fEPSP responses. Arrow points to frequency facilitation paradigm (switch of stimulation frequency from 0.05 Hz to 1 Hz for 20 stimuli). Application of DCGIV (1 µM) at the end of experiment blocked mossy fiber fEPSPs. Upper traces show averages of 10 sweeps each under control condition and 25 minutes after presentation of spike train. Constant stimulation frequency was 0.05 Hz. (E) Repetitive presentation of spike train 2 (5x with 30 s pauses inbetween) resulted in pronounced long-term potentiation of mossy fiber fEPSP amplitudes in this examplary experiment. Upper traces show averages of 10 sweeps each under control condition and 25 minutes after repetitive presentation of spike train. (F) Summary of n = 6 experiments with single presentation of spike train (open circles) and n = 7 experiments with repetitive presentation (filled circles). Both paradigms led to significant long-term potentiation of response amplitudes to ∼150% and ∼230% of control values, respectively. Data shows mean ± sem. Upper dashed lines in subpanels indicate basal response amplitudes to constant stimulation at 0.05 Hz.