Olfactory learning modifies predisposition for long-term potentiation and long-term depression induction in the rat piriform (Olfactory) cortex

Learning-related modifications in predisposition for long-term potentiation (LTP) and long-term depression (LTD) were studied in brain slices of the r at piriform cortex following olfactory learning. Rats were trained to discr iminate between pairs of odors until they demonstrated rule learning. We ha ve previously shown that such training is accompanied by enhanced neuronal excitability and increased synaptic transmission in the intrinsic synaptic pathway. Here we show that the susceptibility for further enhancing synapti c connectivity by inducing LTP in slices from trained rats is markedly redu ced after training, compared with slices from pseudo-trained and naive rats . Accordingly while 900 stimuli at 1 Hz did not induce LTD in slices from c ontrol rats, it induced significant LTD in shoes from trained rats. post-te tanic potentiation (PTP) was also reduced after training, indicating that s ynaptic release is enhanced after odor learning, as previously suggested. W e suggest that learning-related cellular modifications and activity-depende nt synaptic plasticity share a common mechanism in the primary olfactory co rtex. Our data also support the prediction generated according to the slidi ng modification threshold theory that learning should be accompanied by red uced capability of inducing LTP and increased susceptibility for LTD induct ion.