The anatomical substrate of the turning behaviour seen after lesions in the nigrostriatal dopamine system.

Studies of the fibre connections of the substantia nigra suggest that the behavioural results of changes in the activity in the striatal dopamine-containing system are mediated by a pathway from the striatum to the substantia nigra and thence to the thalamus. Small discrete electrolytic lesions in the appropriate part of the crus cerebri interrupt the striatonigral axons without damage to the nigrostriatal system. Such lesions inhibit turning induced by activation of striatal dopamine receptors. Similarly, turning induced by apomorphine in rats lesioned with 6-hydroxydopamine is inhibited by damage to the ipsilateral ventromedial area of thalamus which receives fibres from the substantia nigra.