LTP inhibition and reduced synaptic burst responses in anaesthetized TG rats. (a) Both STP and LTP were strongly impaired in 3.5-4 month-old urethane anesthetized TG rats compared with age-matched WT rats. Standard 200 Hz conditioning stimulation (arrow) induced robust LTP in the controls but not in the TG rats. Time-course graphs are shown in the left hand panel. Insets show representative EPSP traces at the times indicated. Vertical, 1.0 mV; horizontal, 10 ms. (b) The peak amplitude of the HFS-evoked field potential (expressed as a % of the pre-HFS baseline EPSP amplitude) was significantly reduced in TG rats compared with WT littermates. Insets show representative EPSPs triggered by a single test pulse (i, left hand trace) and the average of 10 trains of 200 Hz burst of 20 stimuli (ii, right hand trace) in WT and TG rats. (c) The NMDA receptor antagonist D-AP5 reduced the peak amplitude of the HFS-evoked field potential in WT animals. Injection i.c.v. with 100 nmol D-AP5 10 min prior to HFS significantly reduced the burst response. Calibration bars: Vertical, 1.0 mV; horizontal, 20 ms. Values are the mean ± S.E.M. % pre-HFS baseline EPSP amplitude. Summary statistics are shown in the right hand panels. *P < 0.05 compared with WT littermates.