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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: We developed a rapid and sensitive radioimmunohistochemical method for the quantification of tyrosine hydroxylase (TH) at both the anatomical and cellular level. Coronal tissue sections from fresh-frozen rat brains were incubated in the presence of a TH monoclonal antibody. The reaction was revealed with a 35S-labeled secondary antibody. TH content was quantified in catecholaminergic brain areas by measuring optical density on autoradiographic films or silver grain density on autoradiographic emulsion-coated sections. Regional TH concentrations determined in the locus ceruleus (LC), substantia nigra pars compacta (SNC), and ventral tegmental area (VTA) were significantly increased by 45% after reserpine treatment in the LC but unchanged in the SNC and VTA. Microscopic examination of TH radioimmunolabeling showed a heavy accumulation of silver grains over catecholaminergic cell bodies. In the LC, grain density per cell was heterogeneous and higher in the ventral than in the dorsal part of the structure. After reserpine treatment, TH levels were significantly increased (57%) in the neurons of the LC but not in those of the SNC or VTA. The data support the validity of this radioimmunohistochemical method as a tool for quantifying TH protein at the cellular level and they confirm that TH protein content is differentially regulated in noradrenergic and dopaminergic neurons in response to reserpine.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Levels of tyrosine hydroxylase (TH) were quantified in discrete areas of unfixed rat brain tissue sections using a rapid and sensitive radioimmunohistochemical method. The immunological reaction with the TH monoclonal antibody was revealed by a 35S-labelled secondary antibody and thus permitted autoradiographic detection of the enzyme. Autoradiograms were generated by apposition of tissue sections to high-sensitivity films or by dipping into autoradiographic emulsion. A detailed analysis of antibody concentration, incubation time, tissue section thickness, and exposure time of the film was undertaken to determine optimal conditions to produce a linear radiolabelling intensity with respect to the amount of antigen. Quantification of the antigen at regional levels was assessed by computer-assisted image analysis. Autoradiographic optical density of radiolabelling in brain areas was converted to enzyme concentrations by interpolation with a constructed TH calibration curve processed in parallel with tissue sections. The specificity of the labelling and the validity and reproducibility of the quantification were investigated. The distribution of TH radiolabelling was comparable to that described using immunofluorescence histochemistry or measuring TH enzymatic activity on homogenates. Using a 35S-labelled antibody, the detection of TH could be performed at the cellular level.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The present study was undertaken to examine the adaptive changes occurring 1 and 6 months after moderate or severe unilateral 6-hydroxydopamine-induced lesions confined to the lateral part of the rat substantia nigra pars compacta (SNC). The expression of tyrosine hydroxylase (TH) enzyme was analyzed in the remaining dopaminergic nigral cell bodies and in the corresponding striatal nerve endings. In the cell bodies of the lesioned SNC, TH mRNA content was increased (+20 to +30%) 6 months after the lesion without changes in cellular TH protein amounts. The depletion of TH protein in the nerve terminal area was less severe than the percentage of cell loss observed in the SNC at 1- and 6-month postlesion intervals. Moreover, the decrease in TH protein in the ipsilateral striatum was less pronounced 6 months after lesion than 1 month after. That no corresponding change in TH protein content was observed in the cell bodies at a time when TH increased in nerve terminals suggests that the newly synthesized protein is probably rapidly transported to the striatal fibers. These results suggest the existence of a sequence of changes in TH expression between cell bodies and fibers, occurring spontaneously after partial denervation of the nigrostriatal pathway.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: In Parkinson’s disease, nigrostriatal denervation leads to an overactivity of the subthalamic nucleus and its target areas, which is responsible of the clinical manifestations of the disease. Because the subthalamic nucleus uses glutamate as neurotransmitter and is innervated by glutamatergic fibers, pharmacological blockade of glutamate transmission might be expected to restore the cascade of neurochemical changes induced by a dopaminergic denervation within the basal ganglia. To test this hypothesis, two types of glutamate antagonists, the NMDA receptor antagonist MK-801 and the α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor antagonist LY293558, were administered systemically, either alone or in combination with L-DOPA, in rats with a unilateral 6-hydroxydopamine lesion of the nigrostriatal dopamine pathway. The effect of treatment was assessed neurochemically by analyzing at the cellular level the functional activity of basal ganglia output structures and the subthalamic nucleus using the expression levels of the mRNAs coding for glutamic acid decarboxylase and cytochrome oxidase, respectively, as molecular markers of neuronal activity. The present study shows that treatment with glutamate antagonists, and particularly with AMPA antagonists, alone or in combination with L-DOPA, reverses the overactivity of the subthalamic nucleus and its target areas induced by nigrostriatal denervation. These results furnish the neurochemical basis for the potential use of glutamate antagonists as therapeutic agents in Parkinson’s disease.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The death of dopaminergic neurons that occurs spontaneously in mesencephalic cultures was prevented by depolarizing concentrations of K+ (20–50 mm). However, unlike that observed previously in other neuronal populations of the PNS or CNS, promotion of survival required concurrent blockade of either NMDA or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors by the specific antagonists, MK-801 and GYKI-52466, respectively. Rescued neurons appeared to be healthy and functional because the same treatment also dramatically enhanced their capacity to accumulate dopamine. The effects on survival and uptake were rather specific to dopaminergic neurons, rapidly reversible and still observed when treatment was delayed after plating. Glutamate release increased substantially in the presence of elevated concentrations of K+, and chronic treatment with glutamate induced a loss of dopaminergic neurons that was prevented by MK-801 or GYKI-52466 suggesting that an excitotoxic process interfered with survival when only the depolarizing treatment was applied. The effects of the depolarizing stimulus in the presence of MK-801 were mimicked by BAY K-8644 and abolished by nifedipine, suggesting that neuroprotection resulted from Ca2+ influx through L-type calcium channels. Measurement of intracellular calcium revealed that MK-801 or GYKI-52466 were required to maintain Ca2+ levels within a trophic range, thus preventing K+-induced excitotoxic stress and Ca2+ overload. Altogether, our results suggest that dopaminergic neurons may require a finely tuned interplay between glutamatergic receptors and calcium channels for their development and maturation.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The rat parkin cDNA sequence was characterized afterscreening a rat hypothalamus cDNA library with a 32P-labeled probe containing the entire open reading frame of the human parkin cDNA. This sequence encompasses 1,576 bp and contains a single open reading frame that encodes a 465-amino acid protein. The rat parkin amino acid sequence exhibits a very striking homology to the human and mouse parkin, with 85 and 95% identity, respectively. Both the N-terminal ubiquitin and the ring-IBR (in between ring)-ring finger domains appear to be highly conserved among rat, human, and mouse parkin. An affinity-purified polyclonal antibody (ASP5p) was generated with a synthetic peptide corresponding to amino acids 295-311 of the parkin sequence, which is identical in the three species. Western blotting revealed that ASP5p recognizes a single 52-kDa band, which corresponds to the molecular mass of the parkin protein. Immunostaining with ASP5p showed that parkin is principally located in the cytoplasm of neurons that are widely distributed in the rat brain. Parkin-immunoreactive neurons abound in structures that are specifically targeted in Parkinson's disease, e.g., subtantia nigra, but are also present in unaffected structures, e.g., cerebellum. Furthermore, parkin-enriched glial cells can be detected in various nuclei of the rat brain. Thus, the role of parkin may be much more global than previously thought on the basis of genetic findings gathered in cases of early-onset parkinsonism.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The role of dopamine in iron uptake into catecholaminergic neurons, and dopamine oxidation to aminochrome and its one-electron reduction in iron-mediated neurotoxicity, was studied in RCSN-3 cells, which express both tyrosine hydroxylase and monoamine transporters. The mean ± SD uptake of 100 µm59FeCl3 in RCSN-3 cells was 25 ± 4 pmol per min per mg, which increased to 28 ± 8 pmol per min per mg when complexed with dopamine (Fe(III)–dopamine). This uptake was inhibited by 2 µm nomifensine (43%p 〈 0.05), 100 µm imipramine (62%p 〈 0.01), 30 µm reboxetine (71%p 〈 0.01) and 2 mm dopamine (84%p 〈 0.01). The uptake of 59Fe–dopamine complex was Na+, Cl– and temperature dependent. No toxic effects in RCSN-3 cells were observed when the cells were incubated with 100 µm FeCl3 alone or complexed with dopamine. However, 100 µm Fe(III)–dopamine in the presence of 100 µm dicoumarol, an inhibitor of DT-diaphorase, induced toxicity (44% cell death; p 〈 0.001), which was inhibited by 2 µm nomifensine, 30 µm reboxetine and 2 mm norepinephrine. The neuroprotective action of norepinephrine can be explained by (1) its ability to form complexes with Fe3+, (2) the uptake of Fe–norepinephrine complex via the norepinephrine transporter and (3) lack of toxicity of the Fe–norepinephrine complex even when DT-diaphorase is inhibited. These results support the proposed neuroprotective role of DT-diaphorase and norepinephrine.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Levodopa, the major treatment for patients with Parkinson's disease, has been shown to induce a variety of compensatory effects, including facilitation of sprouting by dopaminergic neurons, in experimental animals with lesions leading to denervation of the striatum. To better understand the cellular and molecular environment where most of these compensatory changes take place, in particular elements that might contribute to the recovery of dopaminergic innervation, we have constructed a differential expression library enriched in transcripts from the striata of rats with lesions of the medial forebrain bundle treated with levodopa for 6 months. We have used this library to screen an expression array of rat genes representing the major cell functions, and have identified several that are involved in neurotrophic mechanisms and plasticity. We have confirmed the differential expression of selected transcripts by non-radioactive in situ hybridization, and report that the growth factor pleiotrophin, myelin basic protein and calmodulin are overexpressed in the denervated striatum of levodopa-treated rats.
    Type of Medium: Electronic Resource
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