Blockade of fast A-type and TEA-sensitive potassium channels provide an antiparkinsonian effect in a 6-OHDA animal model.

OBJECTIVE: To evaluate the effect of K+ channels inhibitors in treatment of parkinson`s disease (PD). METHODS: This prospective comparative study was conducted in the Qazvin University of Medical Sciences, Iran, from April 2015 to January 2016. Male rats (n=37) received intraperitoneal doses of TEA (2 and 5 mg/kg) or 4-AP (0.5 and 1 mg/kg) twice-daily, before a stereotactic injection of 6-hydroxydopamine (6-OHDA) for the following 7 days. The 6-OHDA was injected into right medial forebrain bundle (MFB) of the rat brains. Development and severity of PD were assessed using the apomorphine-induced rotational test, the elevated body swing test and rotarod tests. Concentration of malondialdehyde (MDA), a marker of oxidative stress, was measured in rat sera. RESULTS: Tetraethylammonium and 4-AP significantly reduced the number of apomorphine-induced rotations and improved motor learning in the rotarod test at both doses. Administration of 4-AP and TEA together was more effective than single administration of either agent. Malondialdehyde measurement showed that pretreatment with TEA could not prevent 6-OHDA-induced oxidative stress. CONCLUSION: Our results showed that pretreatment with TEA and 4-AP has a neuroprotective effect against 6-OHDA in dopaminergic neurons in the substantia nigra.

Pretreatment with potassium channel blockers of 4-aminopyridine and tetraethylammonium attenuates behavioural symptoms of Parkinsonism induced by intrastriatal injection of 6-hydroxydopamine; the role of lipid peroxidation.

OBJECTIVES: Potassium channels participate in cellular and molecular signalling pathways regulating the life and death of neurons. In this study, effect of pretreatment with potassium channel blockers of 4-aminopyridine (4-AP) and tetraethylammonium (TEA) on the behavioural symptoms of 6-hydroxydopamine (6-OHDA)-induced Parkinsonism was evaluated. METHODS: 6-OHDA was injected into right striatum of adult male Wistar rats using stereotaxic surgery. Severity of 6-OHDA-induced Parkinsonism was assessed by conventional behavioural tests. 4-AP and TEA were injected twice per day intraperitoneally, before 6-OHDA injection to 15 days after that. Also, malondialdehyde (MDA) concentration as a marker of oxidative stress was measured in rat sera. RESULTS: Pretreatment with 4-AP (0.5 and 1 mg/kg) and TEA (2 and 5 mg/kg) attenuated significantly behavioural symptoms of 6-OHDA-induced Parkinsonism. Application of both 4-AP and TEA together was more effective than the effect of each one of these blockers alone. 6-OHDA increased MDA concentration but pretreatment with 4-AP prevented of 6-OHDA-induced increase in MDA. On the other hand, pretreatment with TEA and combination of TEA and 4-AP could not prevent of 6-OHDA-induced oxidative stress. DISCUSSION: Since severity of behavioural symptoms of 6-OHDA-induced Parkinsonism is correlated to the degree of nigral dopaminergic cell death, we suggest that antiparkinsonism effect of TEA and 4-AP was mediated by their neuroprotective effect. Because, both Parkinsonism in rat and PD in human, the main pathophysiological hallmark, is neurodegeneration of dopaminergic neurons in substantia nigra, we suggest doing clinical trials for evaluation of effectiveness of 4-AP and TEA in slowing down of PD progress.

Intracerebral injection of low amounts of norharman induces moderate Parkinsonism-like behavioral symptoms in rat.

ß-Carbolines (BCs) are considered to be endogenous toxins and have been proposed as possible causative candidates inducing Parkinson's disease (PD). However, there is controversy about the effect and also effective dose of these compounds in the etiology of PD. This study was designed to further examine the effect of norharman (NH), a BC which in mammalian brain occurs at high levels in the substantia nigra, on the development of Parkinsonism-like behaviors in rats. A small amount (4µl) of NH solution at 2 or 200ng/ml was unilaterally injected into either striatum or substantia nigra (SN) by stereotaxic surgery. The development of Parkinsonism was assessed by three conventional behavioral tests, compared to the effects of unilateral 6-hydroxydopamine (6-OHDA) - induced lesions in the nigrostriatal pathway. An apomorphine-induced rotational test revealed no Parkinsonism-like behavior in the NH treated groups. However, rats that received the high concentration of NH into their SN showed significant biased swings in the elevated body swing test. In a rotarod test, NH treated groups showed relatively weak motor performance and their learning patterns were close to that of the 6-OHDA treated rats. Considering that the rotational test is only valid in animals with severe Parkinsonism, but time spent on the rotating rod correlates inversely with severity of Parkinsonism, our results indicate that a single exposure to low amounts of NH is effective in producing moderate Parkinsonism-like behavioral symptoms, possibly through a neurotoxic effect of this agent on the SN dopaminergic neurons.

Prolonged hyperoxia preconditioning attenuates behavioral symptoms of 6-hydroxydopamine-induced Parkinsonism.

OBJECTIVES: Several lines of evidences show that hyperoxia preconditioning provides neuronal protection against central nervous system ischemic damages. Common pathways including mitochondrial dysfunction, apoptosis, and caspase activation are involved in acute neurodegeneration (e.g. after cerebral ischemia) and chronic neurodegeneration (e.g. neuronal death in Parkinson's disease). The aim of the present research was to study the effect of hyperoxia preconditioning on 6-hydroxydopamine (6-OHDA)-induced Parkinsonism. METHODS: Male Wistar rats were first subjected to either air with high oxygen concentration (>90%) or atmospheric air for prolonged (24 hours) or intermittent (six consecutive days, 4 hours each day) periods and then 6-OHDA was injected into their left striatums by stereotaxic surgery. Development and severity of the 6-OHDA-induced Parkinsonism was assessed using apomorphine-induced rotational test, elevated body swing test, and rotarod test within 2-5 weeks after the surgery. RESULTS: Significant data obtained in rats treated with prolonged hyperoxia, but not the intermittent hyperoxia. In these rats, the number of apomorphine-induced rotations was ∼60% lower than that in control and sham groups. Rats belonging to the prolonged hyperoxia group also showed considerably better motor performance and learning pattern in rotarod test. These results were confirmed by the data obtained in the elevated body swing test. DISCUSSION: Our findings show that the prolonged hyperoxia preconditioning attenuates the behavioral symptoms of 6-OHDA-induced Parkinsonism. Considering the well-known correlation between dopaminergic neuronal death in the substantia nigra and the behavioral symptoms of 6-OHDA-induced Parkinsonism, it could be speculated that the prolonged hyperoxia preconditioning induces the mechanisms that provide dopaminergic neuroprotection against Parkinsonism-induced toxins.

High intake of folic acid or complex of B vitamins provides anti-Parkinsonism effect: no role for serum level of homocysteine.

Several lines of evidence show that homocysteine (Hcy) levels are increased in blood and CSF of patients with Parkinson's disease. B vitamins are necessary for Hcy metabolism and their deficiencies cause hyperhomocysteinemia and neurodegeneration. In present study, effect of B vitamin supplementation on the severity of 6-hydroxydopamine (6-OHDA)-induced Parkinsonism was investigated. Rats were nourished with B vitamin supplements from 1 month before of stereotaxic injection of 6-OHDA to the end of experiments. Total serum Hcy was measured at the end of experiments to identify its association with Parkinsonism. Both rotational and rotarod tests revealed that supplementation of folic acid, in a dose dependent manner, attenuates severity of Parkinsonism. Supplement of B complex also had beneficial effect and improved motor performance in rotarod test and decreased biased swings in elevated body swing test but had no effect on the apomorphine-induced rotational behavior. Supplement of B(6) attenuated rotational behavior but had no effect on the rotarod performance and swinging behavior. Supplement of B(12) or combination of folic acid with B(6) and B(12) had no effect on the behavioral symptoms of Parkinsonism. Except one group, the levels of Hcy in other vitamin B treated groups were near to that in control group. Surprisingly, Hcy in group of rats that received high intake of folic acid was significantly higher than that in control group. Our results indicate that high intake of folic acid or B complex provides anti-Parkinsonism effect but it is not mediated by lowering plasma Hcy.

Significant effects of 4-aminopyridine and tetraethylammonium in the treatment of 6-hydroxydopamine-induced Parkinson's disease.

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterizing by degeneration of dopaminergic neurons in the nigrostriatal pathway. The discovery of levodopa revolutionized the treatment of PD however, after several years of treatment most patients develop involuntary movements which significantly impair the quality of life. 4-Aminopyridine (4-AP) and tetraethylammonium (TEA) are wide-spectrum potassium channel blockers which based on the animal model studies and clinical trials have beneficial effects in treatment of several neurological disorders such as ataxia, Alzheimer disease and multiple sclerosis. Current study investigates effect of these blockers in the treatment of 6-hydroxydopamine (6-OHDA)-induced Parkinsonism. After surgical injection of 6-OHDA into medial forebrain bundle, behavioral tests were performed in the 2nd and 3rd weeks post-surgery. Only animals which showed more than 100 apomorphine-induced rotations/1h in the 3rd week were selected for evaluation of the blocker effects. Statistical analysis of results from rotational test shows that application of high dose of 4-AP (1mg/kg) and moderate dose of TEA (2mg/kg) attenuate behavioral symptoms of the Parkinsonism while high dose of TEA (5mg/kg) and application both 4-AP and TEA exacerbates these symptoms. Results from elevated body swing test confirmed the effects of TEA but not 4-AP on the rotational test. However, experiments performed on the partial Parkinsonian rats show that application of high dose of TEA attenuates apomorphine-induced rotational asymmetry significantly. Our findings indicating TEA and 4-AP could have significant effects in attenuation of PD symptoms but these effects are sensitive to dose and degree of severity of PD.

Long term exposure to norharman exacerbates 6-hydroxydopamine-induced parkinsonism: possible involvement of L-type Ca2+ channels.

beta-Carbolines (BCs) are considered as endogenous neurotoxins that may contribute to the pathogenesis of Parkinson's disease (PD). However, several lines of evidences show that these compounds have neuroprotective effect. This study was designed to assess effect of long term exposure to norharman, a BC compound which in mammalian brain occurs at high levels in the substantia nigra, on the progress of parkinsonism induced by 6-hydroxydopamine (6-OHDA). Animals were daily treated by norharman at doses 100, 200 and 1000microg/kg (i.p.) just before to four weeks after the intrastriatal injection of 6-OHDA. Statistical analysis of apomorphine-induced rotation tests demonstrates that treatment by norharman at doses 200 and 1000microg/kg for four weeks exacerbates significantly behavioral symptoms of the parkinsonism. To explore mechanisms by which norharman affects nigral dopaminergic cells, we studied the role of L-type Ca2+ channels. For this purpose, animals were daily treated with either L-type Ca2+ channel blocker of nifedipine at doses 2 and 5mg/kg (i.p.) or nifedipine together with norharman before to four weeks after the 6-OHDA injection. While treatment with nifedipine improved behavioral symptoms of the parkinsonism, treatment with both nifedipine and norharman had no affect on these symptoms. This data indicates that long term exposure to BCs promote nigral dopaminergic cell death possibly through L-type Ca2+ channels.