Graft-derived recovery from 6-OHDA lesions: specificity of ventral mesencephalic graft tissues

A series of experiments have been conducted to assess the specificity of recovery from motor asymmetries that is provided by dopamine-rich grafts in the neostriatum of rats with unilateral dopamine-depleting lesions produced by injection of 6-hydroxydopamine into the ascending nigrostriatal pathway. Grafts of embryonic tissue taken from the substantia nigra (rich in dopamine neurons could provide a complete recovery of methamphetamine-induced rotation and a partial recovery of apomorphine-induced rotation, whereas no recovery was seen in rats with grafts of tissue rich in another monoamine (serotonin, dissected from the mesencephalic raphe) or of tissue appropriate to the target (dissected from the striatal eminence). 6-Hydroxydopamine lesions of dopamine cells in the grafts of recovered animals reinstated the initial lesion-induced asymmetry. Dopamine-rich grafts implanted into the intact neostriatum did not induce any "supernormal" asymmetry in the rats, but did provide a "prophylactic" protection against subsequent lesions of the intrinsic ipsilateral dopamine nigrostriatal system. Post-mortem biochemical assays indicated that the extent of dopamine depletion in the neostriatum of lesioned rats correlated highly with both methamphetamine and apomorphine turning rates. Similarly, both drug rotation tests correlated significantly with the extent of dopamine restoration in the dorsal striatum of rats with dopamine-rich grafts, the correlation being significantly higher for the methamphetamine than for the apomorphine test.