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 neostriatum, using quantitative in situ hybridization histochemistry. Unilateral ibotenate-induced intralaminar thalamic lesion produced a significant decrease in preproenkephalin mRNA levels (-27%) restricted to the ipsilateral striatum at 5 days post-lesion. At 12 days post-lesion, significant decreases in striatal preproenkephalin mRNA expression were found on both brain sides. This post-lesional response was more pronounced in the ipsilateral (-32%) than contralateral (-18%) striatum. All these changes were homogeneously distributed between the dorsolateral and ventromedial parts of the striatum. In parallel, no significant change in preprotachykinin mRNA expression was found at either 5 or 12 days after thalamic lesion, when considering the striatum as a whole. However, at 5 days post-lesion, the regional analysis revealed a slight decrease (-17%) in preprotachykinin mRNA expression, confined to the dorsolateral part of the ipsilateral striatum. These results show that thalamic lesion preferentially affects preproenkephalin vs. preprotachykinin gene expression in the striatum, suggesting, at the first site, a predominant influence of thalamo-striatal inputs on the enkephalin-containing striato-pallidal pathway. However, given that the thalamo-striatal projection is strictly ipsilateral, the bilateralization of the down-regulation of preproenkephalin mRNA expression at 12 days post-lesion suggests an involvement of interhemispheric adaptive mechanisms via cortical networks.