Local administration of l-DOPA in the chicken ventromedial hypothalamus increases dopamine release in a dose-dependent manner

l-DOPA induced extracellular dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in the ventromedial hypothalamus (VMH) of chickens were measured by in vivo microdialysis. Several doses of 3,4-dihydroxy-l-phenylalanine (l-DOPA) were administered locally through the microdialysis probe into the VMH of chickens for 10 min. Local perfusion of l-DOPA increased the extracellular levels of DA. The increased DA was dose-related and was significantly higher compared to the baseline and control group. The maximal level of DA was 212% and 254%, respectively, of the baseline following administration of 1 and 2 μg/ml l-DOPA. There were no changes in NE and 5-HT levels from baseline after l-DOPA perfusion. l-DOPA (1 μg/ml) was mixed with Ca²⁺-free Ringer, tetrodotoxin (TTX) (2 μM) and high K⁺ and was perfused for 30 min into the chicken VMH. TTX and Ca²⁺-free Ringer's solution inhibited the effectiveness of l-DOPA in increasing DA release. The NE and 5-HT levels were significantly lower than the baseline. After administration of K⁺ a significant increase of DA, NE and 5-HT was observed. The microdialysis results are consistent with our objective that l-DOPA induced extracellular DA increases in the VMH in a dose-dependent manner and the released DA, NE and 5-HT within the dialysate were related to neuronal activity.     

Evidence for l-DOPA systems responsible for cardiovascular control in the nucleus tractus solitarii of the rat

Microinjections of l-DOPA (10–100 ng) into the medial area of the nucleus tractus solitarii (NTS) led to dose-dependent decreases in arterial blood pressure and heart rate in rats treated with i.p. 3-hydroxybenzylhydrazine, a central inhibitor of DOPA decarboxylase, or similarly with intraventricular 6-hydroxydopamine. d-DOPA, dopamine or noradrenaline (100 ng) produced no effect. l-DOPA methyl ester (1 μg), a competitive antagonist for l-DOPA, microinjected into NTS, blocked the depressor and bradycardic responses to l-DOPA. High K⁺ (40 mM) released endogenous DOPA in a Ca²⁺-dependent manner from slices of the rat dorsomedial medulla including NTS. These results support the hypothesis that there exist systems of l-DOPA itself responsible for cardiovascular regulation in NTS of rats. This regulatory action of l-DOPA seems to be postsynaptic in nature.     

l-DOPA treatment of parkinsonian rats changes the expression of Src,Lyn and PKC kinases

The dopamine (DA) precursor l-DOPA remains the most common treatment for Parkinson's disease (PD). However, long-term treatment with l-DOPA induces dyskinesia and motor disabilities in PD patients, indicating that this pharmacological agent is unable to fully compensate for the effects of DA denervation when used chronically. In this study, we examined the effect 6-hydroxydopamine (6-OHDA)-induced DA denervation of the striatum followed by either acute or chronic treatment with l-DOPA on gene expression of critical regulators of glutamate synaptic transmission. We found that administration of l-DOPA in rats with unilateral DA denervation resulted in a progressive increase of contraversive circling behavior and modulated the expression of Src, Lyn and PKC kinases. In particular, acute (3 days) and chronic (21 days) l-DOPA treatment were differentially able to rescue the effects of DA lesion, since only the acute treatment with l-DOPA corrected the decrease in Src, Lyn and PKC kinase expression induced by 6-OHDA lesion. Also, the reduced phosphorylation level of NR1 receptor subunit induced by 6-OHDA was only partially reversed by chronic l-DOPA treatment.     

Nitric oxide synthase inhibition attenuates l-DOPA-induced dyskinesias in a rodent model of Parkinson's disease

Chronic l-DOPA pharmacotherapy in Parkinson's disease is often accompanied by the development of abnormal and excessive movements known as l-DOPA-induced dyskinesia. Rats with 6-hydroxydopamine lesion of dopaminergic neurons chronically treated with l-DOPA develop a rodent analog of this dyskinesia characterized by severe axial, limb, locomotor and orofacial abnormal involuntary movements. While the mechanisms by which these effects occur are not clear, they may involve the nitric oxide system. In the present study we investigate if nitric oxide synthase inhibitors can prevent dyskinesias induced by repeated administration of l-DOPA in rats with unilateral 6-hydroxydopamine lesion. Chronic l-DOPA (high fixed dose, 100 mg/kg; low escalating dose, 10–30 mg/kg) treatment induced progressive dyskinesia changes. Two nitric oxide synthase inhibitors, 7-nitroindazole (1–30 mg/kg) and NG-nitro-l-arginine (50 mg/kg), given 30 min before l-DOPA, attenuate dyskinesia. 7-Nitroindazolee also improved motor performance of these animals in the rota-rod test. These results suggest the possibility that nitric oxide synthase inhibitors may be useful to treat l-DOPA-induced dyskinesia.     

Comparison of intrastriatal administration of noradrenaline and l-DOPA on dyskinetic movements: A bilateral reverse in vivo microdialysis study in 6-hydroxydopamine-lesioned rats

l-DOPA-induced dyskinesia is known as involuntary debilitating movement, which limits quality of life in patients suffering from Parkinson's disease. The present study focuses on the role of the neurotransmitter noradrenaline (NA) on dyskinetic movements in comparison to the effect of l-DOPA.     

Impaired transmethylation potential in Parkinson's disease patients treated with l-Dopa

Hyperhomocysteinaemia was reported in patients with Parkinson's disease (PD) treated with l-Dopa. The increase in plasma concentration of this sulfur compound arises from the massive methylation of the drug operated by the enzyme catechol-O-methyltransferase (COMT), which acts as a powerful sink of methyl groups. The contemporary occurrence of C677T polymorphism in homozygosity, leading to a temperature-labile variant of the MTHFR enzyme, induces an even more marked increase in tHcy. Here we show that l-Dopa administration in hyperhomocysteinemic PD patients is able to lower intracellular concentration of S-Adenosylmethionine (AdoMet) in erythrocytes (RBC), while the occurrence of hyperhomocysteinaemia causes a significant increase in S-Adenosylhomocysteine (AdoHcy) level. In patients with PD treated with l-Dopa and hyperhomocysteinemic, the remarkable decrease in AdoMet and the concurrent increase in AdoHcy concentration both contribute to significantly lower the transmethylation potential ([AdoMet]/[AdoHcy]), a useful index of the effectiveness of methyl group transfer by methyltransferases. This decrease could indeed contribute to partly attenuate, through a self-limiting kinetic mechanism, the tendency of developing drug resistance, partly mediated in these patients by COMT upregulation. Our results also support the conclusion that COMT inhibitors (entacapone or tolcapone), when administered in PD patients treated with l-Dopa, may potentiate the endogenous AdoHcy-dependent COMT inhibition mechanism already operative in a variable fashion.     

Conditioned flavor preference learning by intragastric administration of l-glutamate in rats

The preference for foods or fluids in rats is partly dependent on its postingestive consequences. Many studies have investigated postingestive effect of high caloric substances, such as carbohydrate or fat. In this study, we examined postingestive effect of l-glutamate at the preferable concentration using conditioned flavor preference paradigm. Adult male rats with chronic intragastric (IG) cannula were trained to drink a flavored solution (conditioned stimulus; CS+) paired with IG infusion of nutrient solution and another flavored solution (CS−) with IG distilled water infusion on alternate days. The nutrient solution was 60 mM monosodium l-glutamate, sodium chloride or glucose. Before and after conditioning, rats received 30 min two-bottle choice tests for CS+ and CS− solution. All groups exhibited no significant preference for CS+ in pre-test period. By the last half of conditioning period, intake of CS+ solution was significantly higher than that of CS− in MSG group, but not in NaCl and glucose groups. After conditioned, the MSG group showed significantly higher intake and preference for CS+ solution (69.9%), while the NaCl and glucose group did not show any significant intake and preference for CS+ solution (50.9%, 43.5%, respectively). These results indicate that the amino acid l-glutamate at a preferable concentration has a positive postingestive effect as demonstrated by its ability to condition a flavor preference. The mechanism(s) for this positive effect could be through a direct effect on gut Glu receptors rather than the provision of calories or glucose from metabolized Glu; Further studies are needed to test these hypotheses.     

Site-specific action of l-3,4-dihydroxyphenylalanine in the striatum but not globus pallidus and substantia nigra pars reticulata evokes dyskinetic movements in chronic l-3,4-dihydroxyphenylalanine-treated 6-hydroxydopamine-lesioned rats

Dyskinesia eventually develops in the majority of Parkinson's disease patients treated with l-3,4-dihydroxyphenylalanine (l-DOPA). We have investigated the effect of an acute and local administration of l-DOPA, GABA and glutamate to provoke dyskinetic movements in three basal ganglia structures (striatum, globus pallidus (GP) and substantia nigra pars reticulata (SNr)) of chronically l-DOPA-treated, unilaterally 6-hydroxydopamine-lesioned rats. We demonstrated that l-DOPA administration into the lesioned striatum using the technique of reverse in vivo microdialysis was an effective trigger to switch on dyskinesia. Notably, local l-DOPA perfusion at the same concentration in the ipsilateral GP and SNr did not provoke significant dyskinetic behaviour. Neither GABA nor glutamate triggered dyskinetic movements in the striatum, GP or SNr. We postulate a site-specific action of l-DOPA for the evocation of already established dyskinesia since l-DOPA in the striatum but not in the GP or SNr switched on dyskinetic behaviour.     

Inhalation of divalent and trivalent manganese mixture induces a Parkinson's disease model: immunocytochemical and behavioral evidences

The present study investigates the effects of divalent and trivalent manganese (Mn(2+)/Mn(3+)) mixture inhalation on mice to obtain a novel animal model of Parkinson disease (PD) inducing bilateral and progressive cell death in the substantia nigra compacta (SNc) and correlating these alterations with motor disturbances. CD-1 male mice inhaled a mixture of 0.04 M manganese chloride (MnCl(2)) and manganese acetate (Mn(OAc)(3)), 1 h twice a week for 5 months. Before Mn exposure, animals were trained to perform motor function tests and were evaluated each week after the exposure. By doing this, overall behavior was assessed by ratings and by videotaped analyses; by the end of Mn exposure period, animals were killed. The mesencephalon was processed for tyrosine hydroxylase (TH) immunocytochemistry. After 5 months of Mn mixture inhalation, mice developed evident deficits in their motor performance manifested as akinesia, postural instability and action tremor. SNc of the Mn-exposed animals showed an important decrease (67.58%) in the number of TH-immunopositive neurons. Our data provide evidence that MnCl(2) and Mn(OAc)(3) mixture inhalation produces similar morphological and behavioral alterations to those observed in PD providing a useful experimental model for the study of this neurodegenerative disease.     

Effects of intrahippocampal l-NAME treatment on the behavioral long-term potentiation in dentate gyrus

Using a combination of electrophysiological recordings, behavioral tests and local pharmacological administration in hippocampus, we investigated in the present study the effects of nitric oxide (NO) synthase inhibitor N-nitro-l-arginine methyl ester (l-NAME) on the behavioral long-term potentiation (LTP) and maze learning performance in freely moving rats. The results showed as follows: (1) intrahippocampal l-NAME administration led to a defect in maze learning performance of the animals; (2) l-NAME treatment also substantially impaired the induction of the behavioral LTP in perforant pathway to dentate gyrus (PP-DG) pathway induced by maze learning task, while it had no significant effects on basic synaptic transmission in PP-DG pathway; Collectively, these results indicate that NO synthesis may be critical for the behavioral LTP in PP-DG pathway and maze learning performance.     

dl-3-n-Butylphthalide prevents oxidative damage and reduces mitochondrial dysfunction in an MPP-induced cellular model of Parkinson's disease

The aim of the present study was to explore the neuroprotective effects and mechanisms of action of dl-3-n-butylphthalide (NBP) in a 1-methyl-4-phenylpyridiniumion (MPP⁺)-induced cellular model of Parkinson's disease (PD). NBP was extracted from seeds of Apium graveolens Linn. (Chinese celery). MPP⁺ treatment of PC12 cells caused reduced viability, formation of reactive oxygen, and disruption of mitochondrial membrane potential. Our results indicated that NBP reduced the cytotoxicity of MPP⁺ by suppressing the mitochondrial permeability transition, reducing oxidative stress, and increasing the cellular GSH content. NBP also reduced the accumulation of α-synuclein, the main component of Lewy bodies. Given that NBP is safe and currently used in clinical trials for stroke patients, NBP will likely be a promising chemical for the treatment of PD.     

l-theanine protects the APP (Swedish mutation) transgenic SH-SY5Y cell against glutamate-induced excitotoxicity via inhibition of the NMDA receptor pathway

As a natural analogue of glutamate, l-theanine is the unique amino acid derivative in green tea. Although its underlining mechanisms are not yet clear, it has been suggested that l-theanine treatment may prove beneficial to patients with neurodegenerative diseases. In this study, we investigated the neuroprotective effect and its mechanism of l-theanine in an in vitro model of Alzheimer's disease by using the human APP (Swedish mutation) transgenic SH-SY5Y cell. Amyloid beta (Aβ) neurotoxicity was triggered by l-glutamate in this cell line. Additionally, l-theanine significantly attenuated l-glutamate-induced apoptosis at similar levels to those seen with the NMDA receptor inhibitor MK-801 in the stably expressing APP Swedish mutation SH-SY5Y cells which over-generated Aβ. Meanwhile, the activation of c-Jun N-terminal kinase and caspase-3 induced by l-glutamate was suppressed by l-theanine. We also found that cells treated with l-theanine showed decreased production of nitric oxide resulting from the down-regulated protein levels of inducible nitric oxide synthase (iNOS) and neuronal nitric oxide synthase (nNOS). These results indicate that the inhibition of the NMDA subtype of glutamate receptors and its related pathways is the crucial point of the neuroprotective effect of l-theanine in the cell model. Thus, our present study supports the notion that l-theanine may provide effective prophylaxis and treatment for Alzheimer's disease.     

Hsp70 accumulation and ultrastructural features of lung and liver induced by ethanol treatment with and without l-carnitine protection in rats

This study examined Hsp70 accumulation and the subcellular characteristics of liver and lung when exposed to ethanol (EtOH), with and without L-carnitine protection. Female Sprague-Dawley rats, 150-200 g body weight, were randomized into four groups: Control (CON), Alcohol (ALC), L-carnitine (CAR) and Alcohol-L-carnitine (ALC-CAR). EtOH was administered per os at a dose of 4 g/kg body weight (1 ml) daily for 4 weeks. Before alcohol intake, an oral dose of 500 mg/kg body weight of L-carnitine was also administered to the ALC-CAR group. The liver and lung samples were subjected to Hsp70 Western blot and ultrastructural analysis. The Hsp70 accumulation was higher in the liver than in the lung samples. Hepatic Hsp70 accumulation was similar for all groups in contrast to lung, where the Hsp70 accumulation depends on the group studied. The ultrastructural results showed lung but not liver alterations, evidencing a stressful condition and subsequent cellular injury for lung tissue but not for liver. The ALC-CAR group showed less lung damage than the non-protected group and resembles the general appearance of the CON and CAR groups. EtOH intoxication induced differential cellular response in liver and lung in a dose and tissue dependent manner. L-carnitine seems to reduce lung EtOH-induced subcellular damage. The promotion of heat shock or stress proteins might represent one of the mechanisms involved that need to be further investigated.     

Effect of the N-methyl-d-aspartate receptor antagonist on locomotor activity and cholecystokinin-induced anorexigenic action in a goldfish model

We have previously identified that peripherally administered cholecystokinin (CCK) exerts an anorexigenic action via the vagal afferent, and subsequently the brain melanocortin- and corticotropin-releasing hormone-neuronal pathways in goldfish. N-Methyl-d-aspartate (NMDA) receptors have been shown to be involved in the regulations of locomotor activity and food intake in mammals. Although several neuropeptides and other factors exert similar effects in fish and mammals, the role of NMDA receptor in the control of locomotor activity and feeding behavior in fish is still unclear. In the present study, we examined the effect of the NMDA receptor antagonist, MK-801, on locomotor activity and food intake in the goldfish. Intraperitoneal (IP) injection of MK-801 at 0.15 nmol/g body weight (BW) increased locomotor activity, but did not affect food consumption. IP injection of MK-801 at same dose attenuated peripheral CCK (100 pmol/g BW)-induced anorexigenic, but not peripheral acyl ghrelin (10 pmol/g BW)-induced orexigenic actions. These data show for the first time that the NMDA receptor-signaling pathway is involved in the regulation of locomotor activity and feeding behavior through modulation of the peripheral CCK-induced satiety signal, but not the orexigenic effect of ghrelin.