Figure 4. LTD is abolished in ventral striatum and PFC of fmr1^−/− mice.

(a) Summary graph showing whole-cell evoked EPSC amplitudes. Values are normalized to baseline before the induction of LTD and averaged per minute. Tetanic stimulation (10 min at 10 Hz starting at time 0) of PFC afferent fibres to medium spiny neurons in the ventral striatum induces a robust LTD in wild-type littermates (open symbols, n=4) but not fmr1^−/− mice (filled symbols, n=5). Here as in all physiology figures, n equals the number of animals. (b) Summary graph showing averaged time courses of the experiments in which the 10 min at 10-Hz protocol was given in control ACSF (open symbols, n=4) and after pre-treatment with tetrahydrolipstatin (THL, 10 μM, filled symbols, n=4), an inhibitor of the DGL-α. Graphs show EPSC amplitudes normalized to baseline before the induction of LTD and averaged per minute. (c) Direct pharmacological activation of mGlu_1/5 with 50 μM (S)-DHPG induces LTD in the ventral striatum of wild-type littermates (open symbols, n=16) but not fmr1^−/− mice (filled symbols, n=21). Summary graphs show excitatory postsynaptic field potentials (fEPSP) amplitudes. (d) Summary graph showing fEPSP amplitudes recorded in pyramidal neurons of the PFC. Values are normalized to baseline before the induction of LTD and averaged per minute. Tetanic stimulation (10 min at 10 Hz starting at time 0) of layers 2/3 to layers 5/6 pyramidal synapses induces a robust LTD in wild-type littermates (open symbols, n=8) but not fmr1^−/− mice (filled symbols, n=5). Statistical significance was determined using Mann–Whitney U-test. Error bars represent s.e.m.