Somatosensory inattention after dopamine-depleting intracerebral 6-OHDA injections: spontaneous recovery and pharmacological control.

The unilateral injection of 6-hydroxydopamine into the area ventralis tegmenti of rats pretreated with desmethylimipramine resulted in an inattention to somatosensory stimuli impinging on the contralateral body surface. Three separate groups of rats could be identified, that varied in their behavioral deficit: (1) 7 rats showed no recovery of orientation to touch during 4 months postoperatively; (2) 8 showed a marked loss of orientation followed by recovery that was nearly complete within one month; (3) 11 showed a minimal deficit in orientation. Those rats that did recover showed a characteristic pattern: orientation began first to touch of rostral body points (e.g. snout) and only later to touch of caudal body regions. The administration of low doses of alpha-methyl-p-tyrosine or spiroperidol to rats that had spontaneously recovered from their somatosensory loss reinstated their contralateral inattention while not affecting their orientation to ipsilateral touch. As these drugs took effect, orientation was affected first at the caudal body points and only later at more rostral regions. As the drug effects dissipated, orientation was restored rostrocaudally. High correlations were observed between neostriatal DA and the extent of somatosensory orientation observed immediately after surgery (r = +0.76) or during the entire postoperative month (r = +0.66). While the results point clearly to the role of neostriatal DA loss in the somatosensory inattention syndrome, a loss of the DA-containing terminals in olfactory tubercles and nucleus accumbens septi may contribute to this impairment.