THE substantia nigra has a key role in the control of posture and in the coordination of movements. This function is currently attributed to the dopaminergic neurones ascending from the pars compacta of the nigra to the neostriatum. In fact unilateral lesion of this pathway by intranigral injection of 6-hydroxydopamine (6OH-DA) produces a dramatic asymmetry consisting of a tendency of the animal to turn towards the side of the lesion (ipsilateral turning)1. But, unilateral electrolytic lesions of the substantia nigra, while similarly effective to 6OH-DA in destroying dopaminergic neurones, result in turning towards the intact side (contralateral turning)2,4. This has been taken to indicate the existence of non-dopaminergic neurones arising from or traversing the nigra, which control turning behaviour in a manner opposite to the nigro-neostriatal dopaminergic neurones2,4. We report here that unilateral intranigral injection of kainic acid5,6 produces a sustained contralateral turning independent from dopaminergic nigro-striatal function. Since kainic acid spares axons but produces neuronal loss in the pars reticulata of the nigra, our results indicate the existence of non-dopaminergic neurones originating in the pars reticulata which control turning behaviour and posture in a manner opposite to the nigrostriatal dopamine (DA) neurones.
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