Rapid regulation of GAD67 mRNA and protein level in cortical neurons aftersensory learning

Cortical representations of different modalities can he modified by sensory learning. Our previous studios in the barrel cortex showed that expansion of the cortical representation of a row of vibrissae could be induced by pa iring stimulation of a row of vibrissae with a tail shock. The plastic chan ge in cortical reactivity to the input used during the training was accompa nied by increased density of GABA immunoreactive neurons in the involved ro w 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 vibris sae stimulation alone. In contrast, elevation of immunoreactivity of the GA D67 protein occurred only in the trained group. The density of GABA-immunor eactive neurons in the hollows of barrels representing the row of vibrissae activated during the training was increased by 50%. These data indicated t hat sensory stimulation alone affected expression of the 67 kDa glutamate d ecarboxylase isoenzyme synthesis pathway, whereas the processes involved in cortical plasticity induced by associative learning modified this pathway additionally at the level of translation.