Influence of 6-hydroxydopamine injections in the substantia nigra on lateral hypothalamic reinforcement

Repeated unilateral injections of 6-hydroxydopamine (6-OHDA) into the substantia nigra of rats caused massive non-specific lesions and disrupted self-stimulation by lever-pressing equally from electrodes in the ipsilateral and contralateral hypothalamus. Repeated bilateral injections of 6-OHDA abolished self-stimulation when lever-pressing was the criteria, but not when simpler motor responses were used as operants. Hence, nigrostriatal dopamine is unlikely to be critically involved in operant learning and reward processes.