6-OHDA Rats Research Articles

Deep brain stimulation on the external segment of the globus pallidus improves the electrical activity of internal segment of globus pallidus in a rat model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the progressive degeneration of neurons in the substantia nigra pars compacta. Deep brain stimulation (DBS) is an effective treatment for PD cardinal motor symptoms. DBS of GPe has been recognized as an effective treatment option for motor symptoms of PD, but the mechanism is still essentially unknown. To investigate the impact of DBS in the external segment of globus pallidus (GPe) on the pathway of the basal ganglia (BG), we recorded the electrical activities of single neurons and local field potential (LFP) of the internal segment of globus pallidus (GPi). The results showed that the firing rate of GPi neurons in the 6-OHDA lesioned rats returned to the normal level after GPe-DBS for two weeks. Moreover, the CV value of GPi neurons is significantly lower than that in the PD group. The different frequency bands of GPi LFP in PD rats have improved correspondingly. These findings indicate that the improvement of the electrical activity of GPi by GPe-DBS in PD rats may be an important electrophysiological mechanism for treating PD.

A time-course study of urodynamic analyses in rat models with dopaminergic depletion induced through unilateral and bilateral 6-hydroxydopamine injections

Bladder dysfunction is a common non-motor disorder in Parkinson's disease (PD). This study attempted to determine the bladder dysfunction with disease progression in the PD rat model produced from unilateral/bilateral injections of 6-hydroxydopamine (6-OHDA). Cystometrographic (CMG) and external urethral sphincter electromyographic (EUS-EMG) measurements were scheduled in a time-course manner to determine the disease timing, onset, and severity. Animals were allotted into normal control, unilateral, bilateral 6-OHDA injected groups and subjected to scheduled CMG, EUS-EMG analyses at weeks 1, 2, and 4. The urodynamic results concluded that voiding efficiency (VE) was reduced in both unilateral and bilateral PD rats at all-time points. VE had decreased from 57±11% to 31±7% in unilateral PD rats and in bilateral PD rats, a decreased VE of 20±6% was observed compared to control and unilateral PD rats. The EMG results in unilateral PD rats indicated declines in bursting period (BP) (3.78-2.94s), active period (AP) (93.38-88.75ms), and silent period (SP) (161.62-114.30ms). A sudden reduction was noticed in BP (3.62-2.82s), AP (92.21-86.01ms), and SP (128.61-60.16ms) of bilateral PD rats than in control and unilateral PD rats. Histological evidence exhibited a progressive dopaminergic neurons (DA) depletion in the substantia nigra (SN) region in 6-OHDA lesioned rats. The experimental outcomes strongly implied that significant variations in bladder function and VE decline were due to the depletion of DA neurons in the SN region of the brain.

Inhibition of Spinal 5-HT3 Receptor and Spinal Dorsal Horn Neuronal Excitability Alleviates Hyperalgesia in a Rat Model of Parkinson's Disease.

Pain in Parkinson's disease (PD) is increasingly recognized as a major factor associated with poor life quality of PD patients. However, classic therapeutic drugs supplying dopamine have limited therapeutic effects on PD-related pain. This suggests that there is a mechanism outside the dopamine system that causes pain in PD. Our previous study demonstrated that 6-OHDA induced PD model manifested hyperalgesia to thermal and mechanical stimuli and decreased serotonin (5-hydroxytryptamine; 5-HT) in the spinal dorsal horn (SDH). Several 5-HT receptor subtypes have been confirmed to be associated with nociception in the spinal cord, such as 5-HT1A receptor, 5-HT1B receptor, 5-HT2 receptor, 5-HT3 receptor, and 5-HT7 receptor. Most research has shown that 5-HT1A receptor and 5-HT3 receptor play a key role in pain transmission in the spinal cord. We hypothesized that hyperalgesia of 6-OHDA rats may be related to increased excitability of SDH neurons, and functional change of 5-HT3 receptor may reverse the hyperalgesia of 6-OHDA lesioned rats and decrease cell excitability of SDH neurons. To test this hypothesis, we used whole-cell patch-clamp and pharmacological methods to evaluate the effect of 5-HT3 receptor and 5-HT1A receptor on the hyperalgesia of 6-OHDA rats. The results suggested that increased excitability in SDH neurons could be reversed by 5-HT3 receptor antagonist ondansetron (20μmol/L) and palosetron (10μmol/L), but not 5-HT3 receptor agonist m-CPBG (30μmol/L) and SR 57,727 (10μmol/L), 5-HT1A receptor agonist 8-OH DPAT (10μmol/L) and eptapirone (10μmol/L) and 5-HT1A receptor antagonist WAY-100635 (10μmol/L) and p-MPPI (10μmol/L). Intrathecal injection of ondansetron (0.1mg/kg) but not m-CPBG (0.1mg/kg), 8-OH DPAT (0.1mg/kg), and WAY-100635 (0.1mg/kg) significantly attenuated the mechanical hyperalgesia and thermal hyperalgesia in 6-OHDA lesioned rats. In conclusion, the present study suggests that inhibition of spinal 5-HT3 receptor and SDH neuronal excitability alleviates hyperalgesia in PD rats. Our study provides a novel mechanism or therapeutic strategy for pain in patients with PD.

Human Embryonic Stem Cell-Derived Dopaminergic Grafts Alleviate L-DOPA Induced Dyskinesia.

First-in-human studies to test the efficacy and safety of human embryonic stem cells (hESC)-derived dopaminergic cells in the treatment of Parkinson's disease (PD) are imminent. Pre-clinical studies using hESC-derived dopamine neuron transplants in rat models have indicated that the benefits parallel those shown with fetal tissue but have thus far failed to consider how ongoing L-DOPA administration might impact on the graft. To determine whether L-DOPA impacts on survival and functional recovery following grafting of hESC-derived dopaminergic neurons. Unilateral 6-OHDA lesioned rats were administered with either saline or L-DOPA prior to, and for 18 weeks following surgical implantation of dopaminergic neural progenitors derived from RC17 hESCs according to two distinct protocols in independent laboratories. Grafts from both protocols elicited reduction in amphetamine-induced rotations. Reduced L-DOPA-induced dyskinesia preceded the improvement in amphetamine-induced rotations. Furthermore, L-DOPA had no effect on overall survival (HuNu) or dopaminergic neuron content of the graft (TH positive cells) but did lead to an increase in the number of GIRK2 positive neurons. Critically, we found that L-DOPA was not detrimental to graft function, potentially enhancing graft maturation and promoting an A9 phenotype. Early improvement of L-DOPA-induced dyskinesia suggests that grafts may support the handling of exogenously supplied dopamine earlier than improvements in amphetamine-induced behaviours indicate. Given that one of the protocols will be employed in the production of cells for the European STEM-PD clinical trial, this is vital information for the management of patients and achieving optimal outcomes following transplantation of hESC-derived grafts for PD.

Therapeutic Potential of Low-Intensity Magnetic Field Stimulation in 6-Hydroxydopamine Rat Model of Parkinson's Disease: From Inflammation to Motor Function.

Parkinson's disease (PD) is a progressive neurodegenerative disorder that mainly affects the aged population. Transcranial magnetic field (MF) stimulation has shown to provide temporary motor recovery in neurological disorders. The aim of this study was to understand the cellular and molecular mechanism of low-intensity MF stimulation (17.96 µT; 50Hz; 2 h/day, four weeks) in a rat model of severe PD. A clinically relevant, bilateral striatal 6-hydroxydopamine (6-OHDA) lesioned rat model of severe PD was employed to test the efficacy of low-intensity MF stimulation in the management of motor symptoms. The mechanism of action of MF was dissected by assessing the microglial activation, tissue ultrastructure, and cerebrospinal fluid (CSF) metabolomics using microdialysis. We observed a significant improvement in the postural balance and gait after MF exposure with a significant reduction in the number of activated microglia. There was an improvement in striatal dopaminergic innervation and glutamate levels but it did not reach a level of statistical significance. MF stimulation helped ameliorate the motor deficits and reduced inflammation but was unable to provide a significant change in terms of dopaminergic innervation and metabolic profile in the severe 6-OHDA PD rat model.

A positive allosteric modulator of mGlu4 receptors restores striatal plasticity in an animal model of l-Dopa-induced dyskinesia

By decreasing glutamate transmission, mGlu4 receptor positive allosteric modulators (mGlu4-PAM), in combination with levodopa (l-DOPA) may restore the synergy between glutamatergic and dopaminergic transmissions, thus maximizing the improvement of motor function in Parkinson's disease (PD). This study aimed to clarify the effects of foliglurax, a selective mGlu4-PAM, on the loss of bidirectional synaptic plasticity associated with l-DOPA-induced dyskinesia (LID). Behavioral assessments compared dyskinesia intensity in 6-hydroxydopamine (6-OHDA)-lesioned rats treated with l-DOPA or l-DOPA plus foliglurax. In slices from the same rats, patch-clamp techniques were used to examine electrophysiological differences in glutamatergic synapses, evaluating the EPSCs mediated by NMDA and AMPA receptors in striatal spiny projection neurons. High-frequency stimulation of corticostriatal fibers was used as long-term potentiation (LTP)-inducing protocol. Conversely, 15 min of low-frequency stimulation was applied to depotentiate LTP. The density of dendritic spines was measured in striatal slices in the same experimental conditions. Our results show that, in corticostriatal slices, foliglurax decreased spontaneous glutamatergic transmission in both sham-operated and 6-OHDA lesioned rats. When co-administered with l-DOPA in 6-OHDA-lesioned rats, foliglurax fully restored dendritic spine density in a dose-dependent manner. Moreover, this co-treatment rescued striatal bidirectional plasticity and attenuated the intensity of l-DOPA-induced dyskinesia. This is the first demonstration in an animal model of PD and dyskinesia that a mGlu4 PAM can restore striatal synaptic plasticity.

Effects of mangiferin and its combination with nNOS inhibitor 7-nitro-indazole (7-NI) in 6-hydroxydopamine (6-OHDA) lesioned Parkinson's disease rats.

Nitric oxide (NO), generated by nitric oxide synthase enzymes (NOS), has an important role in maintaining synapse plasticity, neuro-modulation, and other physiological functions in the brain. NO thus generated also has a key role in formation of reactive oxygen and reactive nitrite species and subsequent neuronal damage due to sustained oxidative stress. Due to its property of ROS and RNOS generation, NO plays a significant role in Parkinson's disease (PD) pathogenesis. Therefore, we evaluated the effect of mangiferin alone and in combination with nNOS inhibitor 7-nitro-indazole (7-NI) in 6-OHDA lesioned rats. Male Wistar rats weighing 200-250 g (n = 8/group) were used in the study. Stereotactic surgeries of rats were done to induce 6-OHDA lesioning in rats. Then, treatment with mangiferin alone and in combination with 7-NI 10mg/kg was done from days 14 to 42 for 28 days. On day 42, rats were subjected to behavioral studies, and their brains were taken out after euthanasia to perform biochemical and molecular studies. Treatment with mangiferin and 7-NI significantly increases locomotor parameters in 6-OHDA lesioned rats. Treatment with mangiferin 45 μg and 7-NI 10mg/kg alone and in combination significantly reduces oxidative stress along with decrease in concentration of pro-inflammatory cytokines, cyclooxygenase 2, total nitrite (NOx) and FOS B concentration. Results of this study suggest that treatment with 7-NI 10mg/kg further enhances anti-inflammatory and anti-parkinsonism activity of mangiferin owing to its property of inhibiting nNOS mediated FOS B signaling and thereby inhibiting mRNA formation of TNF-α and IL-6.

Re-routing Metabolism by the Mitochondrial Pyruvate Carrier Inhibitor MSDC-0160 Attenuates Neurodegeneration in a Rat Model of Parkinson's Disease.

A growing body of evidence supports the idea that mitochondrial dysfunction might represent a key feature of Parkinson's disease (PD). Central regulators of energy production, mitochondria, are also involved in several other essential functions such as cell death pathways and neuroinflammation which make them a potential therapeutic target for PD management. Interestingly, recent studies related to PD have reported a neuroprotective effect of targeting mitochondrial pyruvate carrier (MPC) by the insulin sensitizer MSDC-0160. As the sole point of entry of pyruvate into the mitochondrial matrix, MPC plays a crucial role in energetic metabolism which is impacted in PD. This study therefore aimed at providing insights into the mechanisms underlying the neuroprotective effect of MSDC-0160. We investigated behavioral, cellular, and metabolic impact of chronic MSDC-0160 treatment in unilateral 6-OHDA PD rats. We evaluated mitochondrially related processes through the expression of pivotal mitochondrial enzymes in dorsal striatal biopsies and the level of metabolites in serum samples using nuclear magnetic resonance spectroscopy (NMR)-based metabolomics. MSDC-0160 treatment in unilateral 6-OHDA rats improved motor behavior, decreased dopaminergic denervation, and reduced mTOR activity and neuroinflammation. Concomitantly, MSDC-0160 administration strongly modified energy metabolism as revealed by increased ketogenesis, beta oxidation, and glutamate oxidation to satisfy energy needs and maintain energy homeostasis. MSDC-0160 exerts its neuroprotective effect through reorganization of multiple pathways connected to energy metabolism.

Changes in the expression of TRPV4 and TRPM8 channels in the colon of rats with 6-OHDA-induced Parkinson’s disease

Parkinson’s disease (PD) is neurodegenerative disease, which is accompanied by degeneration of dopaminergic neurons in subtantia nigra. Non-motor symptoms, in particular, disorders of the gastrointestinal (GI) tract are observed in 20-80% of patients some 15-20 years before clinically diagnosed PD and are not a least important feature of PD pathogenesis. The transient receptor potential (TRP) channels are expressed throughout the GI tract, where they play an important role in taste, thermoregulation, pain, mucosal function and homeostasis, control of interstitial motility etc. The aim of this study was to investigate the contribution of TRPV4 and TRPM8 channels in the GI motor function in the colon of rats with PD, incduced by injection of the 12 μg 6-hydroxydopamine (6-OHDA). The studies were performed on the 4th week and the 7th month after PD induction The rats were randomly divided into: I group – the sham-lesioned rats, 4 μl 0.9% NaCl, autopsy 4 weeks after injection (n = 5); II group – the 6-OHDA-PD rats, 4 μl 12 μg of 6-OHDA, autopsy 4 weeks after injection (n = 5); III group – the sham-lesioned rats, 4 μl 0.9% NaCl, autopsy 7 months after injection (n = 4); IV group – the 6-OHDA-PD rats, 4 μl 12 μg of 6-OHDA, autopsy 7 months after injection (n = 5). We evaluated the body weight of rats, GI transit time, the cecum weight index and immunohistochemical identification of tyrosine hydroxylase (TH) -positive cells, and TRPV4, TRPM8 expression in rat’s colon. We showed that on the 7th month of the experiment, the GI transit time doubles over time; the cecum weight index of 6-OHDA rats increased by 57%; the number of TH-positive cells in colon rats decreased 2-fold, while TRPM8 ion channels were downregulated in PD rats and TRPV4 ion channels were upregulated in the colon of rats with 6-OHDA-PD. It was concluded that TRPV4 and TRPM8 ion channels may be considered pharmacological targets in the progression of PD pathology.

Lateralization in hemi-parkinsonian rats is affected by deep brain stimulation or glutamatergic neurotransmission in the inferior colliculus.

After unilateral lesion of the medial forebrain bundle by 6-OHDA rats exhibit lateralized deficits in spontaneous behavior or apomorphine-induced rotations. We investigated whether such lateralization is attenuated by either deep brain stimulation (DBS) or glutamatergic neurotransmission in the inferior colliculus (IC) of Wistar rats. Intracollicular DBS did not affect spontaneous lateralization but attenuated apomorphine-induced rotations. Spontaneous lateralization disappeared after either the glutamatergic antagonist MK-801 or the agonist NMDA microinjections into the IC. Apomorphine-induced rotations were potentiated by MK-801 but were not affected by NMDA intracollicular microinjection. After injecting a bidirectional neural tract tracer into the IC, cell bodies and/or axonal fibers were found in the periaqueductal gray matter, superior colliculus, substantia nigra, cuneiform nucleus, and pedunculo-pontine tegmental nucleus, suggesting the involvement of these structures in the motor improvement after IC manipulation. Importantly, the side of the IC microinjection regarding the lesion (ipsilateral or contralateral) is particularly important, and this effect may not involve the neostriatum directly.

Effects of Bromelain on Noradrenaline Release During Anxiety-Like Behaviour Following Intra-Medial Forebrain Bundle 6-OHDA Injection in Rat Model of Parkinsonism

Introduction: Parkinson’s disease (PD) is characterized by emotional dysfunction which is a typical manifestation of non-motor symptoms. Non-motor symptoms may occur simultaneously with motor impairment in PD. Anxiety is a comorbidity in PD. This study therefore addresses the question of whether prior/post 6-OHDA lesion treatment with bromelain can show an effect on the behavioural signs of parkinsonism and damage to the CNS noradrenergic system in experimental rats. Methods: Open field and despair swim tests were used to assess certain psychomotor functions and emotional reactivity in the neurotoxin injected rats. The level of noradrenaline in certain regions of the brain as well as in the blood was further analyzed by enzyme linked immunosorbent assay. Findings: The results showed that unilateral injection of the neurotoxin into the rats’ medial forebrain bundle caused a decrease in the rearing time and a corresponding increase in the time spent grooming. There was a further indication that 6-OHDA injection resulted in the reduction of noradrenaline in the systemic environment. Also, the duration of immobility was increased by 6-OHDA injection but not statistically significant. Pretreatment with bromelain caused a change in the grooming behaviour not consistent with noradrenaline level. Conclusion: This finding suggests that bromelain treatment interferes with the regulation of mood and emotion during the early phase of parkinsonism in the 6-OHDA rat model of PD which was accompanied by changes in noradrenaline level.

The modulatory effect of 100 Hz electroacupuncture on striatal synaptic plasticity in unilateral lesioned 6-OHDA rats

Recent studied have reported that impaired striatal synaptic plasticity played a crucial role in Parkinson’s disease (PD). Previous studies have suggested that electroacupuncture (EA) alleviated the motor deficits in PD patients and animal models. However, the mechanisms underlying this protection need to be further elucidated. In this study, we found that EA-induced improvement of motor deficits in the 6-hydroxydopamine (6-OHDA) rat model doesn’t act through dopaminergic system. EA rescued the decreased striatal long-term potentiation (LTP) in 6-OHDA rats. In addition, the declined expression of N-methyl-D-aspartic acid receptor subunit 2B (NR2B) in the striatum was remarkably up-regulated by EA. The EA-induced improvement of LTP can be eliminated by NR2B-selective inhibitor. It is indicated that EA-induced recovery of striatal LTP was correlated with the up-regulation of NR2B subunit. EA was also found to rescue the decreased dendritic arborization and the spine density in the striatum of 6-OHDA rats. Meanwhile, EA suppressed striatal glutamate content and vesicular glutamate transporter 1 which is expressed in cortico-striatal glutamatergic projections. The decrease of striatal glutamate content induced by decortication, EA treatment or a combination of both reversed the loss of striatal spine density in 6-OHDA rats. It is indicated that EA-induced reduction of cortico-striatal glutamate transmission contributes to the recovery of striatal spine density. In conclusion, the therapeutic effect of EA on the motor deficits of 6-OHDA rats was mediated by rescuing cortico-striatal glutamate transmission and striatal synaptic plasticity.

High-Frequency Repetitive Transcranial Magnetic Stimulation Regulates Astrocyte Activation by Modulating the Endocannabinoid System in Parkinson’s Disease

Reactive astrogliosis and the over-production of proinflammatory factors are key pathogenetic processes in Parkinson's disease (PD). Repetitive transcranial magnetic stimulation (rTMS), a promising noninvasive technique in treating PD, has been shown to alleviate neuroinflammation. However, high-frequency (HF) and low-frequency (LF) rTMS, which one produces better therapeutic and anti-inflammatory effects, and the underlying mechanism have yet to be determined. The efficacies of HF, LF, and sham rTMS on the survival of dopaminergic (DA) neurons, improvement of motor function, and downregulation of proinflammatory factors were compared in 6-hydroxydopamine (6-OHDA) rat model. Then we investigated the role of endocannabinoid (eCB) system in the inhibition of astrocyte activation between HF vs LF rTMS. The results showed that HF rTMS daily for 4weeks produced stronger anti-inflammatory and neuroprotective effects. ECB receptor 2 (CB2R) but not receptor 1 (CB1R) expressions were substantially elevated in the GFAP-positive reactive astrocytes of the rat brains with 6-OHDA or LPS insults. Increased anandamide (AEA) and 2-arachidonoylglycerol (2-AG) were also observed. Interestingly, the elevated CB2R, AEA and 2-AG, and the increased GFAP expression could be all significantly suppressed by HF rTMS, but not by LF rTMS. This effect was also confirmed in cell culture. Of note, selective agonism of CB2R was able to reverse HF rTMS-mediated activation of extracellular regulated kinase1/2 (Erk1/2) and suppression of GFAP expression, while selective antagonism of CB2R sustained these effects. This study indicates that the modulation of eCB/CB2R is a potential mechanism for the greater effectiveness of HF rTMS on the inhibition of astrogliosis.

S-adenosyl methionine improves motor co-ordination with reduced oxidative stress, dopaminergic neuronal loss, and DNA methylation in the brain striatum of 6-hydroxydopamine-induced neurodegeneration in rats.

Parkinson's disease (PD) is the most common age-related neurodegenerative disease worldwide. S-adenosyl methionine (SAMe), a methyl donor that plays an important role in DNA methylation, could replenish the cellular antioxidant glutathione (GSH). Herein, we investigated the neuroprotective effects of SAMe in 6-hydroxydopamine (6-OHDA) rat models of PD and elucidated the underlying mechanism. PD model rats were developed by injecting 6-OHDA stereotaxically into the striatum. In Phase 1 of the study, we performed the neurobehavioral tests, GSH assay, and histopathology to evaluate the neuroprotective effects of SAMe. The animals were treated with SAMe (150 or 300 mg/kg body weight) orally for 28 days. The positive control group received selegiline (5mg/kg), whereas the disease control group received normal saline. In Phase 2, we evaluated the striatal dopamine levels and performed DNA methylation assay to uncover the mechanism of action of SAMe. In this phase, a higher dose of SAMe (300 mg/kg) was used. SAMe (300 mg/kg) treatment for 4 weeks significantly attenuated the abnormal circling behavior in PD rats (p < 0.05). Moreover, SAMe at both doses (150 and 300 mg/kg) enhanced the performance of PD rats in the open field test and stepping test (p < 0.05). SAMe treatment significantly increased the GSH levels, and at high dose, SAMe restricted neuronal loss in the striatum of PD-model rats (p < 0.05). Moreover, SAMe treatment led to a significant recovery in the dopamine levels and improved the DNA methylation status in the dopaminergic neurons (p < 0.05) of PD model rats. SAMe exhibits antioxidant activity and DNA methylation modulating effects in 6-OHDA model PD rats. Moreover, SAMe prevents neuronal loss in PD rats suggesting that SAMe has therapeutic potential in preventing PD development. The neuroprotective potential of SAMe is greater at high doses.

Modulatory role of 17α‐estradiol (non‐feminizing estrogen) on 6‐OHDA‐induced Parkinsonism in ovariectomized rats

BackgroundEpidemiological studies have reported that the incidence of Parkinson’s disease (PD) is 1.5 times more in men as compared to women. It suggests that gonadal hormones influence the development and progression of PD. Estrogen replacement therapies have a protective effect against dopaminergic toxins and can be protective in Parkinsonism. However, there are multiple unresolved issues regarding the safety of ERT. Thus, there is a essential need to find alternatives that would avoid these health risks.ObjectivesThus main objective of study was to assess effect of 17α‐estradiol, a non‐feminizing estrogen, in attenuating PD employing an animal model of surgical menopause.Methodology17α‐estradiol and 17β‐estradiol was injected 10 µg/kg/s.c. for 14 days in ovariectomized 6‐OHDA rats. After 14 days of drug administration behavioral parameters of Parkinsonism (sensorimotor activity, motor coordination, and locomotor activity) were performed. These behavioral parameters were further correlated with various biochemical and molecular markers in postmenopausal Parkinsonism. Uterine weight and serum estradiol levels were also assessed to determine estrogenic effect of both the drugs peripherally. Effect of both drugs on expression of ER‐α and ER‐β in striatum was also evaluated. Further the differential effect of 17α‐estradiol and 17β‐estradiol was evaluated in postmenopausal Parkinsonism.Results17α‐estradiol and 17β‐estradiol equally modulated behavioral changes and attenuated rise in oxidative stress markers, inflammatory markers, improving neurotrophic factors and modulation of striatal neuron morphology. 17β‐estradiol treatment restored the uterine weight and serum estradiol levels towards normal, however 17α‐estradiol did not show any effect on uterine horns and serum estradiol levels. No effect of 17α‐estradiol was observed on expression of ER‐α and ER‐β in the striatum, indicates receptor independent effect of 17α‐estradiolConclusionBoth 17α‐estradiol and 17β‐estradiol are equally effective in Parkinsonism, however, 17α‐estradiol may prove to be safer alternative of 17β‐estradiol in Parkinsonism due to lack of feminizing effect.

Modulation by Estradiol of L-Dopa-Induced Dyskinesia in a Rat Model of Post-Menopausal Hemiparkinsonism.

Treatment with levodopa (L-dopa) in Parkinson’s disease (PD) leads to involuntary movements termed L-dopa-induced dyskinesia (LID). There are contradictory data about the influence of hormone therapy in female PD patients with LID and of 17-β-estradiol (E2) on animal correlates of LID-abnormal involuntary movements (AIMs). Our aim was to characterize the influence of E2 on motor impairment and AIMs in ovariectomized 6-hydroxydopamine (6-OHDA) rat model of PD. Half of the rats received empty and the other half implants filled with E2. Following the 6-OHDA surgery, the rats received daily treatment with either L-dopa or saline for 16 days. They were assessed for AIMs, contralateral rotations, and FAS. In the L-dopa-treated rats, E2 intensified and prolonged AIMs and contralateral rotations. On the other hand, it had no effect on motor impairment. Postmortem tyrosine hydroxylase immunostaining revealed an almost complete unilateral lesion of nigrostriatal dopaminergic neurons. E2 partially prevented the upregulation of striatal ΔFosB caused by dopamine depletion. L-dopa potentiated the upregulation of ΔFosB within the dopamine-depleted striatum and this effect was further enhanced by E2. We speculate that the potentiating effects of E2 on AIMs and on contralateral rotations could be explained by the molecular adaptations within the striatal medium spiny neurons of the direct and indirect striatofugal pathways.

Impaired nitrergic relaxation in pyloric sphincter of the 6-OHDA Parkinson's disease rat.

Patients with Parkinson's disease (PD) often suffer from delayed gastric emptying, but the underlying mechanism remains unclear. We have shown previously that a PD rat model comprising bilateral substantia nigra destruction by 6-hydroxydopamine (6-OHDA rats) exhibits gastroparesis with alteration of neural nitric oxide synthase (nNOS) and acetylcholine in gastric corpus. However, changes in pyloric motility in the 6-OHDA rats have not been characterized. Solid gastric emptying test, immunofluorescence, Western blot, and in vitro pyloric motility recordings were used to assess pyloric motor function in the 6-OHDA rats. The 6-OHDA-treated rats displayed delayed solid gastric emptying and a lower basal pyloric motility index. In the 6-OHDA rats, high K+-induced transient contractions were weaker in pyloric sphincters. Electric field stimulation (EFS)-induced pyloric sphincter relaxation was lower in the 6-OHDA rats. NG-nitro-l-arginine methyl ester (l-NAME), a nonselective inhibitor of NOS, markedly inhibited the EFS-induced relaxation in both control and 6-OHDA rats. Pretreatment of tetrodotoxin abolished the effect of EFS on the pyloric motility. In addition, nNOS-positive neurons were extensively distributed in the pyloric myenteric plexus, whereas the number of nNOS-immunoreactive neurons and the protein expression of nNOS were significantly decreased in the pyloric muscularis of 6-OHDA rats. However, sodium nitroprusside-induced pyloric relaxations were similar between the control and 6-OHDA rats. These results indicate that the pyloric sphincters of 6-OHDA rats exhibit both weakened contraction and relaxation. The latter may be due to reduced nNOS in the pyloric myenteric plexus. The dysfunction of the pyloric sphincter might be involved in the delayed gastric emptying.NEW & NOTEWORTHY Reduced nitrergic neurons in pyloric myenteric plexus potently contributed to the attenuated relaxation in 6-hydroxydopamine (6-OHDA) rats, subsequently affecting gastric emptying. SNP could well improve the relaxation of pylori in 6-OHDA rats. The present study provides new insight into the diagnosis and treatment of delayed gastric emptying in patients with PD.

Peripheral administration of the Class-IIa HDAC inhibitor MC1568 partially protects against nigrostriatal neurodegeneration in the striatal 6-OHDA rat model of Parkinson’s disease

Parkinson’s disease (PD) is a neurodegenerative disorder characterised by nigrostriatal dopaminergic (DA) neurodegeneration. There is a critical need for neuroprotective therapies, particularly those that do not require direct intracranial administration. Small molecule inhibitors of histone deacetylases (HDIs) are neuroprotective in in vitro and in vivo models of PD, however it is unknown whether Class IIa-specific HDIs are neuroprotective when administered peripherally. Here we show that 6-hydroxydopamine (6-OHDA) treatment induces protein kinase C (PKC)-dependent nuclear accumulation of the Class IIa histone deacetylase (HDAC)5 in SH-SY5Y cells and cultured DA neurons in vitro. Treatment of these cultures with the Class IIa-specific HDI, MC1568, partially protected against 6-OHDA-induced cell death. In the intrastriatal 6-OHDA lesion in vivo rat model of PD, MC1568 treatment (0.5 mg/kg i.p.) for 7 days reduced forelimb akinesia and partially protected DA neurons in the substantia nigra and their striatal terminals from 6-OHDA-induced neurodegeneration. MC1568 treatment prevented 6-OHDA-induced increases in microglial activation in the striatum and substantia nigra. Furthermore, MC1568 treatment decreased 6-OHDA-induced increases in nuclear HDAC5 in nigral DA neurons. These data suggest that peripheral administration of Class IIa-specific HDIs may be a potential therapy for neuroprotective in PD.

Thymol protects against 6-hydroxydopamine-induced neurotoxicity in in vivo and in vitro model of Parkinson\u2019s disease via inhibiting oxidative stress

BackgroundParkinson’s disease (PD) is a multifactorial movement disorder with the progressive degeneration of the nigrostriatal system that impairs patients’ movement ability. Oxidative stress has been found to affect the etiology and pathogenesis of PD. Thymol, a monoterpenic phenol, is one of the most important dietary constituents in thyme species. It has been used in traditional medicine and possesses some properties including antioxidant, free radical scavenging, anti-inflammatory. In this study, in vitro and in vivo experiments were performed with the thymol in order to investigate its potential neuroprotective effects in models of PD.MethodsThe present study aimed to evaluate the therapeutic potential of thymol in 6-hydroxydopamine (6-OHDA)-induced cellular and animal models of PD. ResultsPost-treatment with thymol in vitro was found to protect PC12 cells from toxicity induced by 6-OHDA administration in a dose-dependent manner by (1) increasing cell viability and (2) reduction in intracellular reactive oxygen species, intracellular lipid peroxidation, and annexin-positive cells. In vivo, post-treatment with thymol was protective against neurodegenerative phenotypes associated with systemic administration of 6-OHDA. Results indicated that thymol improved the locomotor activity, catalepsy, akinesia, bradykinesia, and motor coordination and reduced the apomorphine-caused rotation in 6-OHDA-stimulated rats. Increased level of reduced glutathione content and a decreased level of MDA (malondialdehyde) in striatum were observed in the 6-OHDA rats post-treated with thymol.ConclusionsCollectively, our findings suggest that thymol exerts protective effects, possibly related to an anti-oxidation mechanism, in these in vitro and in vivo models of Parkinson’s disease.

Preventive Vitamin A Supplementation Improves Striatal Function in 6-Hydroxydopamine Hemiparkinsonian Rats.

BackgroundThe mechanisms leading to a loss of dopaminergic (DA) neurons from the substantia nigra pars compacta (SNc) in Parkinson's disease (PD) have multifactorial origins. In this context, nutrition is currently investigated as a modifiable environmental factor for the prevention of PD. In particular, initial studies revealed the deleterious consequences of vitamin A signaling failure on dopamine-related motor behaviors. However, the potential of vitamin A supplementation itself to prevent neurodegeneration has not been established yet.ObjectiveThe hypothesis tested in this study is that preventive vitamin A supplementation can protect DA neurons in a rat model of PD.MethodsThe impact of a 5-week preventive supplementation with vitamin A (20 IU/g of diet) was measured on motor and neurobiological alterations induced by 6-hydroxydopamine (6-OHDA) unilateral injections in the striatum of rats. Rotarod, step test and cylinder tests were performed up to 3 weeks after the lesion. Post-mortem analyses (retinol and monoamines dosages, western blots, immunofluorescence) were performed to investigate neurobiological processes.ResultsVitamin A supplementation improved voluntary movements in the cylinder test. In 6-OHDA lesioned rats, a marked decrease of dopamine levels in striatum homogenates was measured. Tyrosine hydroxylase labeling in the SNc and in the striatum was significantly decreased by 6-OHDA injection, without effect of vitamin A. By contrast, vitamin A supplementation increased striatal expression of D2 and RXR receptors in the striatum of 6-OHDA lesioned rats.ConclusionsVitamin A supplementation partially alleviates motor alterations and improved striatal function, revealing a possible beneficial preventive approach for PD.