The nigrostriatal pathway: A correlative study based on neuroanatomical and neurochemical criteria in the cat and the monkey

Localized lesions of the corpus striatum result in a regional cell loss in the ipsilateral substantia nigra. Unilateral lesions of the ventromedial tegmental area (Tsaï) in the upper midbrain or caudal hypothalamus result in a complete cell loss in the corresponding substantia nigra and nucleus parabrachialis pigmentosus. The latter morphological changes are associated with a decreased concentration of dopamine in the ipsilateral corpus striatum. Lesions of the rostrolateral hypothalamus involving the region of the medial forebrain bundle (MFB) produce similar morphological and chemical changes. Caudolateral lesions of the substantia nigra result in a decreased concentration of dopamine in the laterocaudal part of the corpus striatum corresponding to the caudal putamen. The interruption of the striatonigral fibers does not produce any cell change in the substantia nigra. Lesions of the entopeduncular nucleus or of the ventral thalamus do not produce any cell change in the substantia nigra and are associated with a normal concentration of dopamine in the corpus striatum. These results suggest that the nigrostriatal fibers establish a topographical relationship between corresponding regions of the substantia nigra and the corpus striatum similar to that disclosed in the striatonigral pathway. This striato-nigro-striatal loop represents a peculiar mechanism involved in the synthesis of striatal dopamine.