卞丝肼对6-OHDA损毁大鼠纹状体AADC活性的影响

目的观察卞丝肼对6-羟多巴胺（6-OHDA）所致帕金森病模型大鼠纹状体芳香L-氨基酸脱羧酶（AADC）活性的影响。方法采用6-OHDA建立帕金森病大鼠模型（黑质纹状体去神经支配）,用生理盐水制作假损毁大鼠作为对照;注射卞丝肼60分钟后,处死大鼠,迅速摘除大脑,并取出纹状体,进行匀浆处理。取匀浆上清液加入到培养基中培养后用高效液相色谱柱（HPLC）进行DA含量测试。结果在假损毁大鼠中,10 mg/kg卞丝肼和50 mg/kg卞丝肼可以使纹状体AADC活性明显降低（P〈0.01）。在6-OHDA损毁大鼠纹状体中,10 mg/kg卞丝肼和50 mg/kg卞丝肼明显降低AADC活性,分别为对照物组的25%和12%（P〈0.01）。然而,10 mg/kg卞丝肼和50 mg/kg卞丝肼组之间无统计学差异。结论卞丝肼降低6-OHDA损毁大鼠黑质纹状体AADC活性,影响L-DOPA代谢。     

Tyrosine hydroxylase containing neurons lacking aromatic amino acid decarboxylase in the hamster brain

We have recently described populations of tyrosine hydroxylase-immunoreactive neurons in the hamster brain in regions not known to contain catecholamine cell bodies. In the present study, the nature of the tyrosine hydroxylase immunoreactivity in the hamster brain was determined. In addition, these tyrosine hydroxylase-immunoreactive cell groups were examined for their ability to express aromatic amino acid decarboxylase. Immunohistochemistry with two different antibodies to tyrosine hydroxylase identified immunoreactive cell bodies in regions known to contain catecholamine neurons, including the substantia nigra and locus ceruleus. In addition, tyrosine hydroxylase-immunoreactive neurons were observed in other regions, including the basal forebrain, inferior colliculus, lateral parabrachial nucleus, and dorsal motor nucleus of the vagus. Western blotting indicated that hamster brain contained only one immunoreactive molecule, very similar in size to rat tyrosine hydroxylase. Thus it is likely that the immunohistochemical studies stained authentic hamster tyrosine hydroxylase. Indeed, in situ hybridization studies using a synthetic oligonucleotide probe against tyrosine hydroxylase mRNA resulted in specific and heavy labelling of these novel tyrosine hydroxylase-immunoreactive neurons. When adjacent sections were stained with antibodies to aromatic amino acid decarboxylase, known catecholamine cell groups were stained. However, the novel tyrosine hydroxylase cell groups did not display any aromatic amino acid decarboxylase immunoreactivity. These results suggest that neurons are present in the hamster brain that are able to hydroxylate tyrosine to L-DOPA, but that lack the ability to decarboxylate aromatic amino acids to produce dopamine or other catecholamines.     

Effects of intracerebroventricular L-DOPA on caudate unit firing

Single units were recorded bilaterally from the caudate nuclei of cats before and after 50 μl injections of either Merlis solution or L-DOPA (200 μg) dissolved in Merlis into the left lateral cerebral ventricle. After injection of L-DOPA, but not Merlis solution, there was a period of unit silence in both caudates with an onset of about 10 min and a duration of 30–50 min. This period of caudate silence was coincident with a significant reduction of systolic blood pressure and heart rate. Upon resumption of unit firing in caudate, it was found that the interspike intervals on the contralateral side were markedly increased from 30 min-2 hr postinjection while there was no change on the side of injection. The similarity of this response to that following lesions which interrupt the caudate to thalamus pathway unilaterally was discussed. It is suggested that L-DOPA injection may produce this lesion-like effect by altering the firing of caudate output neurons.     

Noradrenaline synthesis from L-DOPA in rodents and its relationship to motor activity

Evidence has been obtained for an increase in noradrenaline (NA) turnover after administration of I-DOPA to rodents. Normal mice, and those pre-treated with either reserpine or α-methyl-p-tyrosine (AMPT) were given L-DOPA (200 mg/kg) plus MK 486 (α-methyldopahydrazine; 25 mg/kg). In all cases L-DOPA produced a rise in cerebral dopamine (DA) levels. Cerebral NA levels were increased by L-DOPA in reserpinised and AMPT-treated mice. The same dose of L-DOPA produced no change in NA in normal mice, although pre-treatment with the monoamine oxidase inhibitor pargyline (200 mg/kg) resulted in a greater rise in NA 1 hr after L-DOPA compared to animals receiving pargyline alone. This evidence suggests that NA is synthesized from L-DOPA in all these situations. But whole brain 3-methoxy-4-hydroxyphenylglcol sulphate (MOPEG-SO4), a major metabolite of NA, measured after administration of the same dose of L-DOPA plus MK 486, was unaltered in normal and AMPT-treated rats, and was significantly decreased in reserpinised rats. However, an elevation of whole brain MOPEG-SO4 was found in reserpinised and AMPT-treated rats after a lower dose of L-DOPA (50 mg/kg). This discrepancy may be explained by high doses of L-DOPA causing inhibition of catechol-O-methyl transferase (COMT), which is suggested by the observation that the forebrain homovanillic acid (HVA): 3,4-dihydroxyphenylacetic acid (DOPAC) ratio was significantly lower after the high dose of L-DOPA than in untreated mice. Such an inhibition would prevent formation of MOPEG-SO4. Pretreatment with the dopamine-β-hydroxylase inhibitor FLA (63(bis-(1-methyl-4-monopiperazinyl-thiocarbonyl)disulphide) prevented the increase in NA and MOPEG-SO4 formation observed following L-DOPA induced motor activity in these groups of animals suggesting the involvement of NA in the production of such behaviour.     

Modification of avoidance behavior in 6-hydroxydopamine-treated rats by stimulation of central noradrenergic and dopaminergic receptors.

Rats showing reliable decrements in conditioned avoidance behavior after the intraventricular administration of 6-hydroxdopamine (6-HD) with pargyline pretreatment were given various dopaminergic and noradrenergic agonists. Intraventricular injections of DA or L-NE or intraperitoneal injections of apomorphine or L-DOPA reversed the avoidance decrements, often restoring performance to pre-6-HD-treatment levels. Furthermore, these agonists all produced behavior characteristic of activity in dopaminergic neurons. Clonidine, a noradrenergic agonist, also reversed avoidance decrements, but did not produce behavior characteristic of stimulation of dopaminergic neurons in the brain. Pretreatment with spiroperidol, a dopaminergic receptor blocker, prevented the recovery induced by all agonists, although clonidine-induced recovery was affected least. The results are discussed in terms of possible separate roles for dopaminergic and noradrenergic neurons in the brain in avoidance behavior.     

6-Hydroxydopamine lesion of locus coeruleus and the antiparkinsonian potential of NMDA-receptor antagonists in rats

Summary Behavioral and neurochemical effects after bilateral 6-hydroxy-dopamine locus coeruleus- (LC) lesion were examined in rats and compared to sham-lesioned controls. Behavior after treatment with the antiakinetic drugs dizocilpine, amantadine, memantine or L-DOPA as well as joint treatment of these drugs with haloperidol were tested in an open field with holeboard and in an experimental chamber. Under saline spontaneous activity (open field with holeboard) and sniffing (experimental chamber) were reduced after lesion. Injection of the proparkinsonian drug haloperidol decreased sniffing in all rats but to a greater extent in LC-lesioned rats. In combination with haloperidol none of the tested drugs could completely compensate for the motor deficits induced by the lesion. Neurochemical data revealed a reduced content of noradrenaline in the prefrontal cortex and in the posterior striatum of LC-lesioned rats. These results indicate that loss of LC neurons intensifies parkinsonian symptoms induced by blockade of dopamine D2-receptors, and lowers the antiakinetic potential of dizocilpine, amantadine, memantine or L-DOPA.     

Glia protect fetal midbrain dopamine neurons in culture from L-DOPA toxicity through multiple mechanisms

Summary Mesencephalic glia produce soluble factors that protect dopamine neurons from L-DOPA toxicity. The chemical composition of these soluble factors is unknown. We investigated the protective effect against L-DOPA neurotoxicity in midbrain dopamine neurons of fractions of different molecular size of glia conditioned medium and candidate neuroprotective agents produced by glia including neurotrophic factors and antioxidants. Protective effects were evaluated according to the number of tyrosine hydroxylase immunoreactive cells, high affinity dopamine uptake and levels of quinones. Both fractions of glia conditioned medium, smaller and larger than 10kD, protected against L-DOPA, but the fraction of smaller molecular size, that contains small free radical scanvenger molecules, was more effective than the fraction of larger molecular size, that contains large neurotrophic peptides. Among the neurotrophic factors GDNF and BDNF totally prevented L-DOPA neurotoxicity, while NGF and bFGF were less effective. However, only NGF significantly reduced the elevation of quinones induced by L-DOPA. Ascorbic acid, at the concentration found in glia conditioned medium, provided partial protective effect against L-DOPA toxicity. Glutathione, had neurotrophic effects on untreated midbrain dopamine neurons and prevented the effect of L-DOPA. In conclusion, the protective effect against L-DOPA neurotoxicity by glia conditioned medium is mediated by several compounds including neurotrophic factors and small antioxidants.     

Morphine-induced muscular rigidity in rats

Morphine in doses of 7.5 to 17.5 mg/kg, i.p. induced dose-dependent, electromyographically recorded muscular activity (rigidity), which could be inhibited by the morphine antagonist, naloxone and by drugs increasing central dopaminergic activity, L-DOPA and apomorphine. The results suggest that the rigidity was morphine specific and was due to a functional dopamine deficiency in the striata. There was a good parallelism between catalepsy and rigidity. Since both effects were easily reversed by L-DOPA, it is suggested that in our system studied the primary action of morphine was a presynaptic effect in the nigrostriatal neurons and not blockade of striatal dopamine receptors. The results could be explained by ‘diversion’ of newly synthetized dopamine from storage sites to sites of catabolism resulting in a lack of dopamine at striatal receptor sites which might lead to a subsequent compensatory increase of dopamine utilization.     

Changes in taste under L-DOPA therapy

Summary Changes in taste is a side-effect of L-DOPA therapy. This side-effect is about five times less frequent when L-DOPA is administered with a decarboxylase inhibitor; in the absence of a decarboxylase inhibitor higher dose of L-DOPA must be given. The data suggest that the cause of changes in taste due to L-DOPA is extracerebral rather than intracerebral.

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Zusammenfassung Störungen des Geschmackssinnes gehören zu den Nebenwirkungen der L-DOPA-Therapie. Diese Erscheinung ist etwa fünfmal weniger häufig wenn L-DOPA zusammen mit einem Dekarboxylasehemmer gegeben wird. Die eigenen Untersuchungen lassen darauf schließen, daß die Geschmackstörungen bei L-DOPA-Therapie einen extracerebralen und nicht einen intracerebralen Angriffspunkt haben.

     

L-DOPA inhibits depolarization-induced [3H]GABA release in the dopamine-denervated globus pallidus of the rat: the effect is dopamine independent and mediated by D2-like receptors

Summary. The effect of L-DOPA on [³H]GABA release in slices of globus pallidus from 6-OHDA-lesioned rats was studied. Release was evoked by high (15 mM) K⁺. The lesion reduced dopamine content and dopamine synthesized from L-DOPA. The inhibition of DOPA decarboxylase blocked dopamine synthesis. Endogenous dopamine released by high K⁺ inhibited [³H]GABA release in normal but not in lesioned slices. L-DOPA inhibited (IC₅₀ = 0.44 μM) evoked [³H]GABA release. The inhibition was via D2-like receptors but not mediated by dopamine. The turning behavior induced by L-DOPA methyl ester (25 mg/kg, i.p.) was not abolished by the DOPA decarboxylase inhibitor 3-hydroxybenzylhydrazine but in this condition it was abolished by sulpiride. Results suggest that L-DOPA acting as D2-like agonist inhibits GABA release in the rat globus pallidus and induces turning behavior in rats with unilateral lesions of the dopamine innervation. L-DOPA could control Parkinson’s disease symptoms acting not only as dopamine precursor but also by itself.