"In vivo" visualization by positron emission tomography of the progressive striatal dopamine receptor damage occurring in MPTP-intoxicated non-human primates.

Intravenous administration of 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP) leads to the progressive development of a model of Parkinson's disease in the primate. The development of damage occurring in the striatal area during MPTP-treatment was followed "in vivo" in a baboon by positron emission tomography (PET). Spiperone labelled with a positron emitter 76Br (76Br-BSP) was used for the quantitative "in vivo" imaging of D2 dopamine receptors. The decrease in the striatal binding of 76Br-BSP measured "in vivo", after three series of MPTP injections, paralleled the increase in the severity of behavioral symptoms seen immediately after administration of the neurotoxin. At the end of the MPTP-treatment when neurological symptoms were the most important, a 36% decrease in the 76Br-BSP specific binding was measured. Between the series of MPTP injections a partial recovery in the quantitative measurement of the 76Br-BSP specific binding occurring in the striatum was well correlated with the disappearance of the neurological syndrome. Post-mortem histological and biochemical studies in nigro-striatal anatomical structures of MPTP-intoxicated primates compared with control animals showed a 80% loss of neuronal cell bodies in the substantia nigra compacta and a 42% decrease in the density (Bmax) of D2 receptors (in vitro 3H-spiperone binding). All these results showed that the use of PET and 76Br-BSP allow to follow in a noninvasive way both the degenerative processes and the subsequent partial recovery which occur in dopaminergic striatal receptor function during MPTP-treatment.