Density Of Dopamine Uptake Sites Research Articles

Dopaminergic innervation of the human striatum in Parkinson's disease

In Parkinson's disease (PD), dopaminergic input to the caudate nucleus and a band of putaminal tissue abutting the external globus pallidus seems well preserved on immunohistochemical staining for the dopamine transporter. Counting of dopaminergic terminals showed that terminal density in these regions in PD was the same as that in controls, which indicates that input is truly preserved and not a consequence of a compensatory upregulation of metabolism in a reduced pool of surviving terminals. When the branching pattern of dopaminergic axons coursing through the globus pallidus was examined, we found no evidence for increased axonal sprouting in PD that might have contributed to preservation of dopaminergic input to the putamen or caudate nucleus. Although terminal counting indicated that anatomic input was preserved to parts of the striatum, dopamine uptake site density in these regions was reduced significantly. This suggests that the impact of disease in these areas is more profound than was thought previously.

Inhibiting BDNF expression by antisense oligonucleotide infusion causes loss of nigral dopaminergic neurons

Brain derived neurotrophic factor (BDNF) expression is significantly reduced in the Parkinson's disease substantia nigra. This neurotrophin has potent affects on dopaminergic neuron survival protecting them from the neurotoxins MPTP and 6-hydroxydopamine (6-OHDA) commonly used to create animal models of Parkinson's disease and also promoting dopaminergic axonal sprouting. In this study, we demonstrate that an antisense oligonucleotide infusion (200 nM for 28 days) to prevent BDNF production in the substantia nigra of rats mimics many features of the classical animal models of Parkinson's disease. 62% of antisense treated rats rotate ( P ≤ 0.05) in response to dopaminergic receptor stimulation by apomorphine. 40% of substantia nigra pars compacta tyrosine hydroxylase immunoreactive neurons are lost ( P ≤ 0.00001) and dopamine uptake site density measured by 3H-mazindol autoradiography is reduced by 34% ( P ≤ 0.005). Loss of haematoxylin and eosin stained nigral neurons is significant ( P ≤ 0.0001) but less extensive (34%). These observations indicate that loss of BDNF expression leads both to down regulation of the dopaminergic phenotype and to dopaminergic neuronal death. Therefore, reduced BDNF mRNA expression in Parkinson's disease substantia nigra may contribute directly to the death of nigral dopaminergic neurons and the development of Parkinson's disease.

Dopaminergic activities in the human striatum: rostrocaudal gradients of uptake sites and of D 1 and D 2 but not of D 3 receptor binding or dopamine

The human striatum, which receives dopaminergic innervation from the substantia nigra and ventral tegmental area (cell groups A8, A9 and A10), has structural and functional subdivisions both rostrocaudally and dorsoventrally. These relate to motor and non-motor origins of cortical projections and the specific areas of the substantia nigra and ventral tegmental area providing dopaminergic innervation. In the present study, we have evaluated the distribution of a number of dopaminergic parameters in the caudate, putamen and nucleus accumbens at separate coronal levels in a post mortem study in a series of elderly normal individuals aged 55–94 years, with analysis of the effect of post mortem variables. Dopamine D 1 receptor density displayed a rostrocaudally declining gradient in the putamen but not in the caudate, such that at levels posterior to the anterior commisure, there was significantly lower D 1 binding in the putamen compared to the caudate. The density of dopamine D 2 receptors was similar in the putamen and caudate, increasing rostrocaudally. The density of dopamine uptake sites exhibited an increasing rostrocaudal gradient in the caudate, especially ventrally, but not in the putamen, where binding was more constant. The dopamine D 3 receptor was concentrated in the ventral striatum, particularly the nucleus accumbens, although there was no evidence of a rostrocaudal gradient. With respect to striosome–matrix compartmentalization, there was no complete segregation, although D 1 and D 3 receptors were concentrated in striosomes, whereas D 2 receptors and uptake sites showed higher density in the matrix. Levels of dopamine were similar in the caudate and putamen, and were significantly elevated at levels including the nucleus accumbens and the anterior commisure. Homovanillic acid and the metabolic index (homovanillic acid/dopamine ratio) were significantly higher in the putamen compared to the caudate, especially at levels from and caudal to the anterior commisure. These distributions of dopamine receptors and metabolic indicators, reflecting the different functional domains of the striatum, are relevant to the interpretation of current in vivo imaging of the dopamine transporter and receptors in neurological and psychiatric disorders. They provide information to assist in the detection of perturbations in expression, in specific diseases, at particular points on rostrocaudal, lateromedial and dorsoventral axes, a level of resolution beyond current neuroimaging capability.

Upregulation of striatal D2 receptors in the MPTP-treated vervet monkey is reversed by grafts of fetal ventral mesencephalon: an autoradiographic study

Although neural transplantation holds promise as a treatment for Parkinson's disease, parkinsonian primates have generally exhibited inconsistent and incomplete recovery of motor functions following intrastriatal grafting of fetal ventral mesencephalon. One possible contributing factor to this variable response is lack of appropriate integration of donor neurons with host striatal circuitry with the result that there is insufficient dopamine release and postsynaptic dopamine receptor activation. This issue was examined by measuring the effect of transplanting fetal ventral mesencephalon to the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated (MPTP) monkeys on striatal D2 receptor binding. One year after receiving MPTP, D2 receptor binding was upregulated in the dorsal and ventral striatum of African green monkeys. Grafting of fetal ventral mesencephalon to the dorsal striatum of MPTP-treated monkeys 9 months before sacrifice, eliminated the D2 receptor upregulation in dorsal, but not ventral, region. Dopamine concentration in dorsal striatum of grafted MPTP-treated monkeys was significantly higher than in that region of MPTP-treated non-grafted monkeys. In addition, dopamine concentration was significantly higher in dorsal compared to ventral striatum of grafted MPTP-treated monkeys. These data, in addition to those from a previous autoradiographic study on dopamine uptake site density in these monkeys, strongly supports the hypothesis that ectopically placed ventral mesencephalon not only produces, but maintains the release of sufficient levels of dopamine to restore postsynaptic dopamine transmission in regions influenced by graft-derived dopamine.

Mesostriatal dopamine markers in aged Long-Evans rats with sensorimotor impairment

Changes in the mesostriatal dopamine system associated with normal aging are observed in both human and laboratory animals, but the specific behavioral consequences of these nonpathological changes are largely unexplored. The present study (a) assessed the effects of normal aging on markers for the mesostriatal dopamine system, and (b) examined the relationship of age-related changes in this system to decline in reaction time performance. Decreased levels of midbrain dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) were observed in the aged rats as compared to young, but there was no evidence for age-related changes in the density of D 1 or D 2 receptor binding or the density of dopamine uptake sites. Some differences were observed when the aged rats were grouped according to reaction time performance. Aged RT-unimpaired rats exhibited higher density of D 1 binding in rostrodorsal striatal patch areas, but lower overall levels of DA. In caudal striatum, aged RT-unimpaired rats exhibited lower DA and higher DOPAC levels.

Invariance of the density of dopamine uptake sites and dopamine metabolism in the rat brain after a chronic treatment with the dopamine uptake inhibitor GBR 12783.

A chronic treatment (10 mg/kg, twice daily during 9 days) with the dopamine uptake inhibitor GBR 12783 was performed in rats at a dose increasing their locomotor activity. Forty-eight hours after the last administration, animals were sacrificed and 3H mazindol binding was performed on brain slices. Autoradiographic analysis revealed no change in this binding relatively to control animals in regions with high dopamine contents: striatum, nucleus accumbens, olfactory tubercle, substantia nigra and ventral tegmentum area. The treatment did not either modify the levels of dopamine (DA) and metabolites (HVA, DOPAC) both in the striatum and the nucleus accumbens. Thus, early after the end of the treatment, the chronic blockade of the dopamine uptake complex regulates neither the dopamine uptake complex nor the dopamine metabolism.

Chronic antidepressant drug treatment attenuates motor-suppressant effectsof apomorphine without changing [ 3H]GBR 12935 binding

The effects of chronic administration (28 days s.c. via osmotic minipumps) of the antidepressants phenelzine sulphate, desipramine hydrochloride and clomipramine hydrochloride (each at 10 mg/kg per day) on dopamine function have been measured in rats. Both phenelzine and desipramine attenuated the suppression of locomotor activity induced by apomorphine hydrochloride (0.05 mg/kg s.c. 15 min). Clomipramine did not affect the behavioural response to apomorphine. Analyses of brain tissue from these animals using the radioligand [ 3H]GBR 12935 revealed that there were no changes in dopamine uptake site density or affinity following the administration of phenelzine, desipramine or clomipramine. Analyses of brain monoamine oxidase activity and tricyclic levels were used to confirm the efficacy of the drug administration protocol. These data indicate that changes in dopamine uptake site density do not mediate antidepressant-induced changes in behavioural responses to apomorphine.

Effect of Chronic Estradiol and Progesterone Treatments of Ovariectomized Rats on Brain Dopamine Uptake Sites

Dopamine released from brain nerve terminals is mainly removed from the synaptic cleft by an uptake mechanism. Despite their functional importance, modulation of the dopamine uptake sites is still not well known. Steroid hormones were shown to modulate brain dopamine transmission. The aim of this study was thus to investigate in ovariectomized rats the effects of 17 beta-estradiol and progesterone treatments on brain dopamine uptake sites. Treatments consisted of 17 beta-estradiol (10 micrograms/0.2 ml), progesterone (0.72 mg/0.2 ml), 17 beta-estradiol + progesterone, or the vehicle (0.3% gelatin in saline solution) twice daily for 2 weeks. The steroid treatments left the affinity of [3H]GBR 12935 binding to striatal homogenates unchanged (ovariectomized rats, 0.823 +/- 0.028 nM), whereas the density was increased by these steroids alone or in combination to a similar extent of 16-23%. Chronic treatment of ovariectomized rats with 17 beta-estradiol, progesterone, or their combination increased to the same extent and uniformly [3H]-GBR 12935 binding in the striatum as measured by autoradiography; the increase was similar in the substantia nigra pars compacta, whereas no steroid effect was observed in the nucleus accumbens and in the substantia nigra pars reticulata. In summary, chronic exposure to 17 beta-estradiol and/or progesterone increased dopamine uptake site density in the nigrostriatal dopaminergic system, whereas the nucleus accumbens and the substantia nigra pars reticulata were unaffected.

Mesostriatal and mesolimbic dopamine uptake binding sites are reduced in Parkinson's disease and progressive supranuclear palsy: A quantitative autoradiographic study using [ 3H]mazindol

It has been suggested that not only mesostriatal but also mesolimbic pathways are involved in the degeneration of dopaminergic neurons in Parkinson's disease. Using quantitative ligand autoradiography we have investigated dopamine transporter sites in basal ganglia of patients affected by Huntington's chorea, Parkinson's disease and progressive supranuclear palsy. [ 3H]Mazindol, a ligand for catecholamine uptake, was used in the presence of desipramine to block the binding to norepinephrine uptake sites. Schizophrenic cases were entered in the study to take into account the effects of neuroleptics, commonly administered also to Huntington's disease patients, on dopamine uptake sites. In control cases high densities of [ 3H]mazindol binding sites were found in the caudate nucleus, putamen and nucleus accumbens, whereas very low densities were present in substantia nigra and ventral tegmental area. In Huntington's chorea the density of [ 3H]mazindol binding sites was slightly decreased in the caudate nucleus, an area severely affected by the neurodegenerative process. In schizophrenic patients the density of dopamine uptake sites in the basal ganglia was slightly reduced, mainly in the middle third of putamen. Both Parkinson's disease and progressive supranuclear palsy populations were characterized by a marked loss of [ 3H]mazindol binding sites in the neostriatum (about 75%) and in the nucleus accumbens (about 65%). These results suggest that in Parkinson's disease and progressive supranuclear palsy severe decreases of dopamine uptake sites occur not only in the mesostriatal pathway but also in the mesolimbic tract.

In vivo labelling of the neuronal dopamine uptake complex in the mouse striatum by [ 3H]GBR 12783

Various characteristics of the in vivo striatal binding of [ 3H]GBR 12783 (1-[2-(diphenylmethoxy)-ethyl]-4-(3-phenyl-1[ 3H]-2- propenyl)piperazine), a specific ligand of the neuronal dopamine uptake complex, were determined in mice. Increasing doses of the ligand revealed the saturability of the binding at a single site with half-maximal saturation at a dose of approximately 7 ωmol/kg and an apparent maximal number of binding sites (B max) of 12.8 pmol/mg protein in striatum. Specific binding was prevented by various dopamine uptake blockers, pyrovalerone, GBR 13069, GBR 12783, N-[1-2-benzo(b)thiophenyl)cyclohexyl] piperidine, cocaine, methylphenidate and was inhibited in a stereoselective manner by the enantiomers of nomifensine. Other drugs which are not dopamine uptake blockers either did not modify [ 3H]GBR 12783 binding (the diphenylbutylpiperazine derivative flupenthixol) or increased it (the diphenylpiperazine derivative flunarizine or the chemically unrelated compounds fenfluramine and SKF 525A). A close correlation was found between occupancy of the striatal [ 3H]GBR 12783 binding site and the stimulant locomotor effect of the drug. A similar specific striatal binding of [ 3H]GBR 12783 was evidenced in both NMRI and CD1 strains. It was concluded that [ 3H]GBR 12783 administered in vivo provides a measure of the density of dopamine uptake sites in mouse striatum.

Postnatal development of striatal dopamine function. I. An examination of D 1 and D 2 receptors, adenylate cyclase regulation and presynaptic dopamine markers

We have characterized the postnatal development from 1 to 7 weeks after birth in rat striatal homogenates of D 1 and D 2 dopamine (DA) receptor sites, adenylate cyclase (AC) enzyme activity coupled to DA receptor function, guanine nucleotide binding sites and presynaptic markers of DA terminal function. D 1 receptor density, expressed per unit of membrane protein, does not increase over this developmental interval, while maximum DA-stimulated AC activity per mg membrane protein increases 50–100%. D 1 agonist affinity for D 1 receptor sites doubles by 7 weeks of age but is consistently reduced by guanine nucleotide during development. Guanine nucleotide stimulation of AC develops a biphasic dose-response curve after 3 weeks of age. Between 2 and 4 weeks postnatal age there is a rapid increase in AC catalytic component activity as manifested by the capacity of forskolin or manganese ion to stimulate AC in presence of guanine nucleotide and DA. Reversible [ 3H]GppNHp (guanyldiphosphonateimidophosphate) binding to striatal homogenates is dependent on Mg 2+, inhibited by Ca 2+ and GppNHp analogues, and occurs in about a 300-fold excess over D 1 sites. Presynaptic markers of dopaminergic function indicate a 7-fold increase in tissue DA levels, a 2-fold reduction in DA turnover and no apparent change in density of DA uptake sites, assayed by [ 3H]mazindol binding. Subcomponents of D 1 and D 2 DA receptors have distinct postnatal developmental profiles. Striatal D 1 sites do not change significantly during development, but D 2 receptors and GTP inhibition of AC increase and appear, respectively, at 3–4 weeks of age, at the same time as the massive matrix innervation of striatum by DA terminals.