Synaptic plasticity in barrel cortex is occluded by classical conditioning training and depends on the activity of metalloproteinases
It is well established that classical conditioning paradigms induce plastic changes in the mouse barrel cortex. In particular, tactile whisker stimulation paired with a tail shock affects GABAergic currents in the layer IV in the cell-specific manner. It is thus expected that sensory learning might affect the neuronal networks in the “trained” barrel, possibly altering its ability to express the synaptic plasticity. To test this possibility, we have compared the long-term potentiation (LTP) induction in “trained” barrels in slices from animals which underwent classical conditioning to that in corresponding barrels in control (yoked, pseudoconditioned) mice. To induce LTP, classical pairing protocol was used (stimulation - layer IV, current-clamp whole-cell recordings - layer II/III). Interestingly, while in control mice, pairing resulted in a clear LTP (161% EPSP increase, 30 min after pairing), in trained animals the LTP induction was nearly absent. This result suggests that behavioral learning occludes the synaptic plasticity in the considered model. It has been demonstrated in other brain region (hippocampus) that synaptic plasticity as well as behavioural learning may critically depend on the activity of metalloproteases (MMPs). We were thus interested whether LTP in the barrel cortex depends on these enzymes. To address this issue, pairing protocol was used to induce LTP in the barrel cortex of control animals and MMPs were blocked by a broad spectrum MMP inhibitor (FN-439). We found that pre-treatment of slices with MMPs inhibitor practically abolished LTP indicating that these enzymes play a critical role in the LTP maintenance in this model. In conclusion, these data indicate that behavioural learning occludes the synaptic plasticity in the barrel cortex and that LTP maintenance in this preparation relies on the activity of MMPs. Supported by the Ministry of Science and Higher Education grants N401 028 32/0664 and NN401541540.
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