BRAIN RESEARCH ELSEVIER Brain Research 692 (1995) 233-243 Research report Regional distribution of monoamine vesicular uptake sites in the mesencephalon of control subjects and patients with Parkinson's disease: a postmortem study using tritiated tetrabenazine F. Thibaut a, B.A. Faucheux a j. Marquez a j. Villares a, J.F. Menard b, y. Agid a, E.C. Hirsch "'* INSERM U289, Hbpital de la SalpOtri~re, 47 Blvd de l'Hhpital, F-75013 Paris, France b Laboratoire de Biophysique, H~pital Charles Nicolle, 1 rue de Germont, F-76031 Rouen, France Accepted 16 May 1995 Abstract The distribution of the vesicular monoamine transporter was investigated post mortem in the human ventral mesencephalon of control subjects (n = 7) and patients with Parkinson's disease (n = 4) using tritiated dihydrotetrabenazine binding and autoradiography. Tritiated dihydrotetrabenazine binding was characterized by a single class of sites with a K d of 7 nM and a Bmax of 180 fmol/mg of protein in the substantia nigra. Tritiated dihydrotetrabenazine binding sites were heterogeneously distributed in the mesencephalon of control subjects: the density of tritiated dihydrotetrabenazine binding sites was high in the substantia nigra pars compacta, locus coeruleus and nucleus raphe dorsalis, moderate in the ventral tegmental area and low in the substantia nigra pars reticulata and catecholaminergic cell group A8. Within the substantia nigra, a zone with maximal density of tritiated dihydrotetrabenazine binding, two times higher than the mean estimate for the whole substantia nigra pars compacta, was detected in the medial part of the structure. The anatomical organization of the human ventral mesencephalon was analyzed on adjacent sections stained for acetylcholinesterase histochemistry and tyrosine hydroxylase immunohistochemistry. Tritiated dihydrotetrabenazine binding displayed the same characteristic regional pattern of distribution as that observed with tyrosine hydroxylase immunohistochemistry except in the nucleus raphe dorsalis, where no tyrosine hydroxylase immunoreactivity was detected. In parkinsonian brains, the level of tritiated dihydrotetrabenazine binding was dramatically decreased in all regions of the ventral mesencephalon analyzed except in the substantia nigra pars reticulata. In the substantia nigra pars compacta, the reduction was by 55% for the whole structure and by 65% in its medial zone, where binding site density was maximal. In most nigral subsectors analyzed, the decrease in density of tritiated dihydrotetrabenazine binding sites reached the level expected given the loss of tyrosine hydroxylase-positive cells observed. By contrast, the ratio of [3H]dihydrotetrabenazine binding to the number of tyrosine hydroxylase positive neurons was significantly increased in the zone of high [3H]dihydrotetrabenazine binding sites. This relative sparing of tritiated dihydrotetrabenazine binding sites may be due either to the contribution of other monoaminergic neurons such as serotoninergic neurons or more likely to hyperactivity of the still surviving dopaminergic neurons. Keywords: Dopamine; Parkinson's disease; Substantia nigra; Human; Synaptic vesicle 1. Introduction Alterations of monoaminergic transmission in the cen- tral nervous system have been reported in several neurode- generative disorders [1,17,27]. Monoamines, their metabo- lites, biosynthetic enzymes and neuronal uptake systems are commonly used as markers of monoaminergic innerva- tion but have drawbacks in post-mortem studies [6,22,31]. * Corresponding author. Fax: (33) (1) 44 24 36 58 0006-8993/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0006-8993(95)00674-5 Monoamines are taken up into synaptic storage vesicles by an ATP-dependent process [5] which can be inhibited by dihydrotetrabenazine (TBZOH). Tritiated TBZOH ([3H]TBZOH) was recently introduced as a specific in vitro and in vivo high affinity ligand of the vesicular monoamine transporter in human brain studies [18,29] and has been used in human brain post mortem essentially as a presynaptic monoaminergic marker. Unlike for some other proteins, [3H]TBZOH binding sites are stable post mortem and the variability between individuals is only half of that for monoamines [29]. Thus, [3H]TBZOH autoradiography provides a reliable and precise method for anatomical