We found activation c-fos protein in the NO synthase-containing neurons within the islands of Calleja (96.46 +/- 16.03 fos-immunoreactive nuclei per 50 mm section) in control and suppression of this activation after unilateral 6-hydroxydopamine lesions of dopaminergic mesostriatal system of brain (14.31 +/- 4.59 nuclei per section). Since the neuronal activity in the islands of Calleja is associated with the blood supply changes in the basal ganglia we propose that the suppression of c-fos protein expression in this structure after lesions of dopaminergic mesostriatal system reflects the disorders its blood supply.