THALAMO-STRIATAL DEAFFERENTATION AFFECTS PREPROENKEPHALIN BUT NOT PREPROTACHYKININ GENE-EXPRESSION IN THE RAT STRIATUM

This study examined the effects of thalamo-striatal deafferentation on preprotachykinin and preproenkephalin mRNA expression in the rat neos triatum, using quantitative in situ hybridization histochemistry. Unil ateral ibotenate-induced intralaminar thalamic lesion produced a signi ficant decrease in preproenkephalin mRNA levels (-27%) restricted to t he ipsilateral striatum at 5 days post-lesion. At 12 days post-lesion, significant decreases in striatal preproenkephalin mRNA expression we re found on both brain sides. This post-lesional response was more pro nounced in the ipsilateral (-32%) than contralateral (-18%) striatum. All these changes were homogeneously distributed between the dorsolate ral and ventromedial parts of the striatum. In parallel, no significan t change in preprotachykinin mRNA expression was found at either 5 or 12 days after thalamic lesion, when considering the striatum as a whol e. However, at 5 days post-lesion, the regional analysis revealed a sl ight decrease (-17%)in preprotachykinin mRNA expression, confined to t he dorsolateral part of the ipsilateral striatum. These results show t hat thalamic lesion preferentially affects preproenkephalin vs. prepro tachykinin gene expression in the striatum, suggesting, at the first s ite, a predominant influence of thalamo-striatal inputs on the enkepha lin-containing striato-pallidal pathway. However, given that the thala mo-striatal projection is strictly ipsilateral, the bilateralization o f the down-regulation of preproenkephalin mRNA expression at 12 days p ost-lesion suggests an involvement of interhemispheric adaptive mechan isms via cortical networks. (C) 1998 Elsevier Science B.V. All rights reserved.