Figure 2.

OR training and test cause an intrinsic decrease in synaptic strength. (a) Stable baseline recording was obtained when only test-pulses were applied to the Schaffer collateral—CA1 stratum radiatum synapses in the freely moving mice (n = 10). When test-pulse stimulation was coupled with OR training (OR A–B), a progressive decrease in synaptic strength that stabilized at ∼45 min and lasted for at least 24 h was observed. A similar trend was also observed during the test phase (OR A–C). The decrease in the training and the test phases were both significant compared with test-pulse only (ANOVA, P < 0.0001). (b) Analog traces illustrate the Schaffer collateral—CA1 field potentials at pretask, 5 min and 24 h (1440 min). Vertical scale bar corresponds to 2 mV and horizontal scale bar corresponds to 5 ms. (c) Behavioral analysis showed that the mice performed the OR task successfully with a delay period of 24 h between phases. The mice explored both objects A and B equally during the training phase but explored the novel object C to a significantly greater extent during the test phase. *t-test, P < 0.0001. (d) Analysis of the discrimination ratio revealed that the mice showed no preference for either object during the training phase but a strong preference for the novel object during the test phase (ANOVA, P < 0.0001).