raclopride and Nerve-Degeneration

Huntington's disease (HD) is a progressive neurodegenerative disorder, which is characterised by prominent neuronal cell loss in the basal ganglia with motor and cognitive disturbances. One of the most well-studied pharmacological models of HD is produced by local injection in the rat brain striatum of the excitotoxin quinolinic acid (QA), which produces many of the distinctive features of this human neurodegenerative disorder. Here, we report a detailed analysis, obtained both in vivo and in vitro of this pharmacological model of HD.. By combining emission tomography (PET) with autoradiographic and immunocytochemical confocal laser techniques, we quantified in the QA-injected striatum the temporal behavior (from 1 to 60 days from the excitotoxic insult) of neuronal cell density and receptor availability (adenosine A(2A) and dopamine D(2) receptors) together with the degree of microglia activation.. Both approaches showed a loss of adenosine A(2A) and dopamine D(2) receptors paralleled by an increase of microglial activation.. This combined longitudinal analysis of the disease progression, which suggested an impairment of neurotransmission, neuronal integrity and a reversible activation of brain inflammatory processes, might represent a more quantitative approach to compare the differential effects of treatments in slowing down or reversing HD in rodent models with potential applications to human patients.

Topics: Animals; Carbon Radioisotopes; Corpus Striatum; Isoquinolines; Kinetics; Microglia; Nerve Degeneration; Quinolinic Acid; Raclopride; Radioisotope Dilution Technique; Rats; Rats, Wistar; Receptors, Dopamine D2; Receptors, Purinergic P1; Reference Values; Stereotaxic Techniques

Degeneration of dopaminergic neurons of the substantia nigra pars compacta is a cardinal feature of Parkinson's disease (PD). Although uncertain, the pathology has been suggested to derive from a malfunction of the complex interaction between dopaminergic and metabotropic glutamate receptors (mGluRs). To further address this issue, we investigated the imaging profile and expression of dopamine D(2) receptors and mGluRs in a classic parkinsonian rodent model induced by the toxin 6-hydroxydopamine.. Adult male Sprague-Dawley rats (250-300 g) received a stereotaxic injection of 8 mug/2 muL of 6-hydroxydopamine (n = 6) or saline solution (n = 4) in the right medial forebrain bundle. Small-animal PET was performed on all rats 4 wk after the surgical procedure to assess dopamine transporter (DAT) status using (11)C-2beta-carbomethoxy-3beta-(4-fluorophenyl)-tropane (CFT), as well as dopamine D(2) receptor and mGluR(5) modulation using (11)C-raclopride and 2-(11)C-methyl-6-(2-phenylethynyl)-pyridine ((11)C-MPEP), respectively. Behavioral studies were also conducted 6 wk after lesioning by d-amphetamine challenge. Immunohistochemistry and Western blotting were carried out at 8 wk after lesioning to confirm dopamine fiber, neuronal loss, and level of striatal mGluR(5) expression.. PET images showed decreased (11)C-CFT binding on the lesioned side, including the structures of the striatum, hippocampus, and cortex, compared with the contralateral intact side. Interestingly, dopamine D(2) receptors and mGluR(5) upregulation were observed in the right striatum, hippocampus, and cortex, using (11)C-raclopride and (11)C-MPEP, respectively. A negative correlation was also found between the percentage change in mGluR(5) expression and DAT function. Finally, tyrosine hydroxylase immunoreactivity confirmed both dopamine fiber loss (t test, P < 0.01) and neuronal loss (t test, P < 0.01) on the lesioned side. These changes were accompanied by a strongly enhanced mGluR(5) expression in the right striatum of the lesioned side analyzed by Western plot.. These findings support the existence of compensatory mechanisms in nigrostriatal dopamine degeneration and provide new insights that help further dissect some of the pathways underlying neurodegeneration. In addition, these results reconfirm that PET is a valuable tool for multilevel receptor studies, significantly contributing to the understanding of pathogenic mechanisms and ultimately opening new avenues in the study of neuroprotective approaches toward PD.

Topics: Animals; Carbon Radioisotopes; Cocaine; Corpus Striatum; Dopamine Plasma Membrane Transport Proteins; Hippocampus; Immunohistochemistry; Male; Nerve Degeneration; Neurons; Oxidopamine; Parkinsonian Disorders; Positron-Emission Tomography; Pyridines; Raclopride; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Dopamine D2; Receptors, Metabotropic Glutamate; Substantia Nigra; Tyrosine 3-Monooxygenase

Among 27 preclinical carriers of the Huntington disease mutation (PMC), the authors found normal striatal values for MRI volumetry in 88% and for fluorodesoxyglucose PET metabolic index in 67%. Raclopride PET binding potential (RAC-BP) was decreased in 50% and correlated with increases in the product of age and CAG repeat length (p < 0.0005). Dopamine D2 receptor availability measured by RAC-BP seems the most sensitive indicator of early neuronal impairment in PMC.

Topics: Adult; Binding, Competitive; Biomarkers; Corpus Striatum; Disease Progression; DNA Mutational Analysis; Dopamine; Dopamine Antagonists; Female; Fluorodeoxyglucose F18; Glucose; Humans; Huntingtin Protein; Huntington Disease; Magnetic Resonance Imaging; Male; Middle Aged; Mutation; Nerve Degeneration; Nerve Tissue Proteins; Nuclear Proteins; Positron-Emission Tomography; Predictive Value of Tests; Raclopride; Receptors, Dopamine D2; Trinucleotide Repeat Expansion

Common marmosets (Callithrix jacchus) with near-complete unilateral 6-hydroxydopamine denervation of the dopaminergic input received a single injection of saline or L-DOPA (15mg/kg plus 6.25mg/kg benserazide). Using in situ hybridization, the effects of these treatments on c-fos messenger RNA expression in the cerebral cortex, the striatal complex and the external layer of the pallidum were studied. Moreover, receptor autoradiography was used to determine the levels of dopamine D(1) and D(2) receptors in these areas. In the cerebral cortex, animals treated with L-DOPA displayed a high expression of c-fos messenger RNA restricted to the dopamine-denervated hemisphere. No changes in the levels of cortical D(1) and D(2) receptors were found in the dopamine-denervated hemisphere. L-DOPA treatment also induced a strong expression of c-fos messenger RNA in the striatal complex in the dopamine-denervated hemisphere. The levels of striatal D(2), but not D(1), receptors were increased in the dopamine-denervated hemisphere. In the external pallidum, the major terminal region for D(2) dopamine receptor-containing striatal projection neurons, L-DOPA treatment induced c-fos messenger RNA expression in both the intact and the dopamine-denervated hemispheres.Thus, using c-fos messenger RNA as a biochemical marker of postsynaptic neuronal activation, these results provide evidence that near-complete dopamine depletion causes a profound supersensitization to L-DOPA treatment in the cerebral cortex and in the striatal complex, but not in the external layer of the pallidum, of the primate brain. The cortical response may be unique to the primate brain, but c-fos messenger RNA activation within the striatum has also been reported in the rodent. The effects of L-DOPA probably depend both on a direct activation of supersensitized dopamine receptors by dopamine produced in the few remaining, but hyperactive, dopaminergic nerve terminals and in serotonergic nerve terminals, as well as on indirect actions of L-DOPA related to activation of circuitries connecting cerebral cortex and basal ganglia structures. These results provide novel information on the mechanisms underlying L-DOPA's action in the cerebral cortex, striatum and external pallidum in a primate model of Parkinson's disease.

Topics: Animals; Benzazepines; Blotting, Western; Callithrix; Cerebral Cortex; Corpus Striatum; Denervation; Disease Models, Animal; Dopamine; Dopamine Agents; Dopamine Antagonists; Enkephalins; Gene Expression; Genes, Immediate-Early; Levodopa; Nerve Degeneration; Oxidopamine; Parkinson Disease; Protein Precursors; Proto-Oncogene Proteins c-fos; Raclopride; Radioligand Assay; Receptors, Dopamine D1; Receptors, Dopamine D2; RNA, Messenger; Substance P; Substantia Nigra; Sympatholytics; Tritium

We studied sequential changes in muscarinic cholinergic receptors, high-affinity choline uptake sites and dopamine D2 receptors in the brain after 6-hydroxydopamine lesions of the medial forebrain bundle in rats. The animals were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks postlesion. [3H]Quinuclidinylbenzilate (QNB), [3H]hemicholinum-3 (HC-3) and [3H]raclopride were used to label muscarinic cholinergic receptors, high-affinity choline uptake sites and dopamine D2 receptors, respectively. The degeneration of nigrostriatal pathway produced a transient decrease in [3H]QNB binding in the parietal cortex of both ipsilateral and contralateral sides at 2 and 8 weeks postlesion. [3H]QNB binding also showed a mild but insignificant decrease in the ipsilateral striatum throughout the postlesion periods. No significant change was observed in the substantia nigra (SN) of both ipsilateral and contralateral sides throughout the postlesion periods. In contrast, [3H]HC-3 binding showed no significant change in the parietal cortex of both ipsilateral and contralateral sides during the postlesion. However, [3H]HC-3 binding was upregulated in the ipsilateral dorsolateral striatum throughout the postlesion periods. The ventromedial striatum also showed a significant increase in [3H]HC-3 binding at 1 week and 2 weeks postlesion. On the other hand, no significant change in [3H]raclopride binding was found in the parietal cortex of both ipsilateral and contralateral sides during the postlesion. [3H]Raclopride binding showed a conspicuous increase in the ipsilateral striatum (35-52% of the sham-operated values in the lateral part and 39-54% in the medial part) throughout the postlesion periods. In the contralateral side, a mild increase in [3H]raclopride binding was also found in the striatum (10-15% of the sham-operated values in the lateral part and 22% in the medial part) after lesioning. However, a significant decline in [3H]raclopride binding was observed in the ipsilateral SN and ventral tegmental area during the postlesion. The present study indicates that 6-hydroxydopamine injection of medial forebrain bundle in rats can cause functional changes in high-affinity choline uptake site in the striatum, as compared with muscarinic cholinergic receptors. Furthermore, our studies demonstrate an upregulation in dopamine D2 receptors in the striatum and a decrease in the receptors in the SN and ventral tegmental area a

Topics: Animals; Autoradiography; Choline; Cholinergic Agents; Corpus Striatum; Dopamine Antagonists; Hemicholinium 3; Male; Medial Forebrain Bundle; Muscarinic Agonists; Nerve Degeneration; Oxidopamine; Quinuclidinyl Benzilate; Raclopride; Radioligand Assay; Rats; Rats, Wistar; Receptors, Cholinergic; Receptors, Dopamine D2; Substantia Nigra; Sympatholytics; Tritium

This study investigates the rate of age-related dopamine D2 receptor loss as determined by positron emission tomography (PET) and 11C-raclopride and compares it with D2 loss previously estimated with 18F-N-methylspiroperidol (NMS). Dopamine D2 receptors were measured with 11C-raclopride in 24 healthy volunteers (24-73 years of age) using the ratio of the distribution volume in striatum to that in cerebellum (Bmax/Kd + 1). The results were compared with those obtained in 20 healthy male volunteers (20-49 years of age) in whom D2 receptors were measured with NMS using the ratio index (slope of the striatum-to-cerebellum ratio as a function of time). Findings of correlational analysis between age and dopamine D2 receptor availability were significant for both ligands. Estimates of dopamine D2 receptor loss per decade corresponded to 7.9% for the 11C-raclopride study and 7.8% for the NMS study. Both ligands documented significant age-related decreases in dopamine D2 receptors that occurred relatively early in life (40 years of age).

Topics: Adult; Age Factors; Aged; Aging; Cerebellum; Corpus Striatum; Dopamine Agonists; Female; Humans; Ligands; Male; Middle Aged; Nerve Degeneration; Raclopride; Receptors, Dopamine D2; Salicylamides; Spiperone; Tomography, Emission-Computed

Equilibrium striatal: cerebellar 11C-raclopride (RAC) uptake ratios reflect the density of striatal dopamine D2 binding sites. Using positron emission tomographic scanning we have measured striatal RAC uptake in 6 untreated patients with Parkinson's disease (PD), 5 chronically treated patients with PD and a fluctuating response to L-dopa, 10 patients with striatonigral degeneration (SND), and 9 patients with progressive supranuclear palsy (PSP). Regional cerebral blood flow was determined also, with C15O2. Mean striatal: cerebellar RAC uptake was not significantly different from normal in untreated patients with PD, though 2 of these 6 patients showed significantly increased putamen tracer binding. Mean caudate and putamen: cerebellar RAC uptake ratios of the group with PD and a fluctuating response to L-dopa were significantly reduced by 30% and 18%, respectively. The patients with SND had lesser, but significant, 10% and 11% decreases in mean caudate and putamen: cerebellar RAC uptake ratios, respectively, whereas patients with PSP showed 24% and 9% reductions in caudate and putamen: cerebellar RAC binding. Striatal and frontal blood flow were significantly reduced in patients with PSP, but not in patients with PD or SND. In conclusion, striatal D2 binding potential is normal or raised in untreated patients with PD, but reduced in patients with PD and a fluctuating response to L-dopa. Patients with SND and PSP show a decrease in striatal RAC binding, but to a lesser extent than patients with PD and a fluctuating response to treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adult; Aged; Caudate Nucleus; Corpus Striatum; Humans; Levodopa; Middle Aged; Nerve Degeneration; Parkinson Disease; Putamen; Raclopride; Receptors, Dopamine; Salicylamides; Substantia Nigra; Supranuclear Palsy, Progressive; Tomography, Emission-Computed