Reduction of [125I]Bolton Hunter CCK8 and [3H]MK-329 (devazepide) binding to CCK receptors in the substantia nigra/VTA complex and its forebrain projection areas following MPTP-induced hemi-parkinsonism in the monkey.

Cholecystokinin (CCK) receptors were visualized autoradiographically using [125I]Bolton Hunter CCK8 ([125I]BHCCK8) in the fore- and midbrain of 3 monkeys rendered hemi-parkinsonian by unilateral intra-carotid infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). More specifically, CCK-A receptors were detected using [3H]MK-329 (devazepide), a peripheral-type (CCK-A) receptor antagonist. In the substantia nigra pars compacta, ipsilateral to the toxin infusion, where dopamine D2 receptors (labelled with [3H]sulpiride) were lost, there was a decrease in the binding of both [125I]BHCCK8 and [3H]MK-329. Binding of the two CCK ligands was also reduced in the ipsilateral nucleus accumbens and most medial part of the caudate nucleus, whereas 3H-sulpiride binding was increased in the lateral caudate nucleus and putamen. These results indicate that CCK-A receptors may be located on dopaminergic cells within the substantia nigra, which are lost in the parkinsonian brain, and may also be present on dopaminergic terminals within restricted regions of nigral/ventral tegmental area projection sites.