Evidence for extensive inter-connections within the zona incerta in rats

We have examined whether there is an extensive system of inter-connections between the functionally distinct sectors of the zona incerta (ZI) of the thalamus. Unilateral injections of biotinylated dextran were made into each of the different incertal sectors (rostral, dorsal, ventral and caudal) of Sprague–Dawley rats by using stereotaxic coordinates. Our results show that after separate injections limited to each of the incertal sectors, many labelled terminals and cells were seen across the different sectors of the ipsilateral, as well as the contralateral side, with the heaviest labelling being on the side ipsilateral to the injection. Thus, these results suggest that the ZI is in a position to integrate an extensive array of afferents from many functionally diverse neural centres of the brain.