Rapid regulation of GAD67 mRNA and protein level in cortical neurons after sensory learning.

Cortical representations of different modalities can be modified by sensory learning. Our previous studies in the barrel cortex showed that expansion of the cortical representation of a row of vibrissae could be induced by pairing stimulation of a row of vibrissae with a tail shock. The plastic change in cortical reactivity to the input used during the training was accompanied by increased density of GABA immunoreactive neurons in the involved row of cortical barrels. Using the same paradigm, the present study examined the pathway of GABA synthesis-expression of GAD67 mRNA and immunoreactivity of GAD67 isoenzyme in the barrel cortex of mice after sensory learning. In situ hybridization revealed that the GAD67 mRNA level was elevated in one row of barrels in the trained group as well as in controls receiving vibrissae stimulation alone. In contrast, elevation of immunoreactivity of the GAD67 protein occurred only in the trained group. The density of GABA-immunoreactive neurons in the hollows of barrels representing the row of vibrissae activated during the training was increased by 50%. These data indicated that sensory stimulation alone affected expression of the 67 kDa glutamate decarboxylase isoenzyme synthesis pathway, whereas the processes involved in cortical plasticity induced by associative learning modified this pathway additionally at the level of translation.