Neostriatal dopamine and sensory inattention

Damage to the mesotelencephalic dopamine-containing projection of rats results in a sensory inattention, characterized by impairments in orientation toward somatosensory, visual, and olfactory stimuli. The present experiments were performed to establish which branch of this dopaminergic system is responsible for these sensorimotor deficits. Two approaches were used. In the first, individual dopamine-innervated forebrain sites were damaged by localized 6-hydroxydopamine injection into, or by electrolytic lesions of, these regions. In the second, rats were given tegmental 6-hydroxydopamine injections that damaged the entire mesotelencephalic projection and subsequently received intracerebral injections of the dopamine agonist apomorphine into specific forebrain sites in an attempt to reinstate orientation. The results demonstrate that dopaminergic terminals in the neostriatum are critical for orientation. Unilateral neostriatal 6-hydroxydopamine injections or electrolytic lesions reduced orientation to contralateral touch, whereas similar damage to other dopamine-innervated forebrain structures did not. Further, the results suggest that dopaminergic terminals in the anterior neostriatum are especially important for orientation to touch of the rostral body surface while those in the posterior neostriatum are most critical for orientation to caudal touch. After damage to all branches of the mesotelencephalic dopaminergic system, orientation to touch was reinstated by injection of apomorphine into the neostriatum but not by injection into the other dopamine-innervated forebrain regions tested.