Separation of the motivational and motor consequences of 6-hydroxydopamine lesions of the mesolimbic or nigrostriatal system in rats.

The effects of 6-hydroxydopamine (6-OHDA) lesions in the ventral tegmental area (VTA) or substantia nigra, pars compacta (SN/pC) on the behaviour of hungry rats were examined in a Columbia obstruction box test. The lesions of dopaminergic neurones in the VTA as well as in the SN/pC decreased the number of crossings of an electric obstruction for food. After the lesion in the VTA the reaction of rats became independent of the level of hunger--the number of their crossings was similar at different levels of hunger. In contrast, no effect of the lesion was found when the animals were trained and tested in the absence of shock. The 6-OHDA lesion in the SN/pC also decreased the number of crossings, but the animals remained sensitive to motivational hunger stimuli: they were still crossing the obstruction in a hunger-dependent manner. Lesions in neither the VTA nor the SN/pC significantly altered the spontaneous food intake and sensitivity to painful electric stimuli. In the Rotarod test only the SN/pC-lesioned rats showed a substantial motor impairment; lesions in the VTA had no effect in that test. The obtained results are discussed in terms of the role of the dopaminergic mesolimbic and nigrostriatal systems in mediation of the motivational arousal and motor performance of an instrumental food response.