6-OHDA Injection Research Articles

Neuroprotective action and mechanistic evaluation of protodioscin against rat model of Parkinson's disease.

Parkinson's disease (PD) is the most widespread motor-affecting disease affecting majorly middle- and late age population. Thus, in the current study, we intended to explore the neuroprotective effect of protodioscin (Proto) against 6-hydroxydopamine (6-OHDA)-induced PD rat model. After induction of PD with the injection of 6-OHDA, the different dose of Proto was administered for the duration of experimental protocol (2 months). We have scrutinized the consequence of Proto on the cognitive behaviours via Moris water maze (MWM), and recognition of novel objects and its location tasks. The effect of Proto was also investigated on the expression of Nrf2 in human neuroblastoma SHSY5Y cells via western blot analysis. The results showed significant decrease in travelled distance as compared by the lesion treated group. Further significant difference was revealed in the latency time to detect the platform that is visible and it confirmed that, there were no noteworthy dissimilarity was observed in the visual and motor function ability. The result also suggests that, the activation of Nrf2 is the possible mechanism of neuroprotection of Proto against PD. As a concluding remark, the present study confirmed the neuroprotective role of Proto against PD both in in vitro and in vivo models.

An altered blood–brain barrier contributes to brain iron accumulation and neuroinflammation in the 6-OHDA rat model of Parkinson’s disease

Brain iron accumulation is a common feature shared by several neurodegenerative disorders including Parkinson’s disease. However, what produces this accumulation of iron is still unknown. In this study, the 6-hydroxydopamine (6-OHDA) hemi-parkinsonian rat model was used to investigate abnormal iron accumulation in substantia nigra. We investigated three possible causes of iron accumulation; a compromised blood–brain barrier (BBB), abnormal expression of ferritin, and neuroinflammation. We identified alterations in the BBB subsequent to the injection of 6-OHDA using gadolinium-enhanced magnetic resonance imaging (MRI). Moreover, detection of extravasated IgG suggested that peripheral components are able to enter the brain through a leaky BBB. Presence of iron following dopamine cell degeneration was studied by MRI, which revealed hypointense signals in the substantia nigra. The presence of iron deposits was further validated in histological evaluations. Furthermore, iron inclusions were closely associated with active microglia and with increased levels of L-ferritin indicating a putative role for microglia and L-ferritin in brain iron accumulation and dopamine neurodegeneration.

Treadmill Exercise Prevents Increase of Neuroinflammation Markers Involved in the Dopaminergic Damage of the 6-OHDA Parkinson's Disease Model.

Parkinson's disease (PD) involves loss of dopaminergic neurons in the substantia nigra (SN), which can be correlated to neuroinflammatory changes with the aging of the nervous system. On the other hand, exercise can reduce the deleterious effects promoted by age, but the mechanism involved is still unclear. This study investigated the preventive exercise-induced changes on neuroinflammatory processes in a rat model of PD induced by unilateral striatal injections of 6-hydroxydopamine (6-OHDA). Adult male Wistar rats were divided into two groups: (1) sedentary (SED) or (2) exercised (EX), animals that did treadmill exercise three times per week, every other day, for 4weeks prior to 6-OHDA or saline injection. The rats were then divided into four sub-groups: (1) sedentary saline (SED), (2) sedentary 6-OHDA (SED + 6-OHDA), (3) exercised saline (EX), and (4) exercised 6-OHDA (EX + 6-OHDA). Seven and 30days after surgery, brains were collected for immunohistochemistry and immunoblotting for dopaminergic and neuroinflammatory markers into SN and striatum. The SED + 6-OHDA animals presented an increase in the astrocyte, microglial, and oxidative species activation. On the other hand, EX + 6-OHDA animals did not present neuroinflammatory responses and performed better apormorphine test. Our data suggest that treadmill exercise throughout life can markedly reduce the chances of dopamine decrease, reinforcing studies that showed a lower incidence of Parkinson's disease in patients who were active during life.

Effect of Intrastriatal 6-OHDA Lesions on Extrastriatal Brain Structures in the Mouse.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive loss of midbrain dopaminergic neurons, resulting in motor and non-motor symptoms. The underlying pathology of non-motor symptoms is poorly understood. Discussed are pathological changes of extrastriatal brain structures. In this study, we characterized histopathological alterations of extrastriatal brain structures in the 6-hydroxydopamine (6-OHDA) PD animal model. Lesions were induced by unilateral stereotactic injections of 6-OHDA into the striatum or medial forebrain bundle of adult male mice. Loss of tyrosine hydroxylase positive (TH+) fibers as well as glia activation was quantified following stereological principles. Loss of dopaminergic innervation was further investigated by western-blotting. As expected, 6-OHDA injection into the nigrostriatal route induced retrograde degeneration of dopaminergic neurons within the substantia nigra pars compacta (SNpc), less so within the ventral tegmental area. Furthermore, we observed a region-specific drop of TH+ projection fiber density in distinct cortical regions. This pathology was most pronounced in the cingulate- and motor cortex, whereas the piriform cortex was just modestly affected. Loss of cortical TH+ fibers was not paralleled by microglia or astrocyte activation. Our results demonstrate that the loss of dopaminergic neurons within the substantia nigra pars compacta is paralleled by a cortical dopaminergic denervation in the 6-OHDA model. This model serves as a valuable tool to investigate mechanisms operant during cortical pathology in PD patients. Further studies are needed to understand why cortical dopaminergic innervation is lost in this model, and what functional consequence is associated with the observed denervation.

Altered adenosine 2A and dopamine D2 receptor availability in the 6-hydroxydopamine-treated rats with and without levodopa-induced dyskinesia

Several lines of evidence imply alterations in adenosine signaling in Parkinson's disease (PD). Here, we investigated cerebral changes in adenosine 2A receptor (A2AR) availability in 6-hydroxydopamine (6-OHDA)-lesioned rats with and without levodopa-induced dyskinesia (LID) using positron-emission tomography (PET) with [11C]preladenant. In parallel dopamine type 2 receptor (D2R) imaging with [11C]raclopride PET and behavioral tests for motor and cognitive function were performed. MethodsParametric A2AR and D2R binding potential (BPND) images were reconstructed using reference tissue models with midbrain and cerebellum as reference tissue, respectively. All images were anatomically standardized to Paxinos space and analyzed using volume-of-interest (VOI) and voxel-based approaches. The behavioral alternations were assessed with the open field test, Y-maze, novel object recognition test, cylinder test, and abnormal involuntary movement (AIM) score. In total, 28 female Wistar rats were included. ResultsOn the behavioral level, 6-OHDA-lesioned rats showed asymmetry in forepaw use and deficits in spatial memory and explorative behavior as compared to the sham-operated animals. 15-Days of levodopa (L-DOPA) treatment induced dyskinesia but did not alleviate motor deficits in PD rats. Intranigral 6-OHDA injection significantly increased D2R binding in the lesioned striatum (BPND: 2.69 ± 0.40 6-OHDA vs. 2.31 ± 0.18 sham, + 16.6%; p = 0.03), whereas L-DOPA treatment did not affect the D2R binding in the ipsilateral striatum of the PD rats. In addition, intranigral 6-OHDA injection tended to decrease the A2AR availability in the lesioned striatum. The decrease became significant when data were normalized to the non-affected side (BPND: 4.32 ± 0.41 6-OHDA vs. 4.58 ± 0.89 sham; NS, ratio: 0.94 ± 0.03 6-OHDA vs. 1.00 ± 0.02 sham; − 6.1%; p = 0.01). L-DOPA treatment significantly increased A2AR binding in the affected striatum (BPND: 6.02 ± 0.91 L-DOPA vs. 4.90 ± 0.76 saline; + 23.4%; p = 0.02). In PD rats with LID, positive correlations were found between D2R and A2AR BPND values in the ipsilateral striatum (r = 0.88, ppeak = 8.56.10−4 uncorr), and between AIM score and the D2R BPND in the contralateral striatum (r = 0.98; ppeak = 9.55.10−5 uncorr). ConclusionA2AR availability changed in drug-naïve and in L-DOPA-treated PD rats. The observed correlations of striatal D2R availability with A2AR availability and with AIM score may provide new knowledge on striatal physiology and new possibilities to further unravel the functions of these targets in the pathophysiology of PD.

Influence of Estrogen Modulation on Glia Activation in a Murine Model of Parkinson's Disease.

Epidemiological data suggest a sexual dimorphism in Parkinson disease (PD), with women showing lower risk of developing PD. Vulnerability of the nigrostriatal pathway may be influenced by exposure to estrogenic stimulation throughout fertile life. To further address this issue, we analyzed the progression of nigrostriatal damage, microglia and astrocyte activation and microglia polarization triggered by intrastriatal injection of dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) in male, female and ovariectomized (OVX) mice, as well as in OVX mice supplemented with 17βestradiol (OVX+E). Animals were sacrificed at different time points following 6-OHDA injection and brain sections containing striatum and substantia nigra pars compacta (SNc) underwent immunohistochemistry for tyrosine hydroxylase (TH) (dopaminergic marker), immunofluorescence for IBA1 and GFAP (markers of microglia and astrocyte activation, respectively) and triple immunoflorescent to identify polarization of microglia toward the cytotoxic M1 (DAPI/IBA1/TNFα) or cytoprotective M2 (DAPI/IBA1/CD206) phenotype. SNc damage induced by 6-OHDA was significantly higher in OVX mice, as compared to all other experimental groups, at 7 and 14 days after surgery. Astrocyte activation was higher in OVX mice with respect the other experimental groups, at all time points. Microglial activation in the SNc was detected at earlier time points in male, female and OVX+E, while in OVX mice was detected at all time-points. Microglia polarization toward the M2, but not the M1, phenotype was detected in female and OVX+E mice, while the M1 phenotype was observed only in male and OVX mice. Our results support the protective effects of estrogens against nigrostriatal degeneration, suggesting that such effects may be mediated by an interaction with microglia, which tend to polarize preferentially toward an M2, cytoprotective phenotype in the presence of intense estrogenic stimulation.

4R-Cembranoid Improves Outcomes after 6-Hydroxydopamine Challenge in Both In vitro and In vivo Models of Parkinson's Disease.

(1S, 2E, 4R, 6R,-7E, 11E)-2, 7, 11-cembratriene-4, 6-diol (4R) is one of the cembranoids found in tobacco leaves. Previous studies have found that 4R protected acute rat hippocampal slices against neurotoxicity induced by N-methyl-D-aspartate (NMDA) and against the toxic organophosphorus compounds paraoxon and diisopropylfluorophosphate (DFP). Furthermore, in vivo, 4R reduced the infarct size in a rodent ischemic stroke model and neurodegeneration caused by DFP. The present study expanded our previous study by focusing on the effect of 4R in Parkinson's disease (PD) and elucidating its underlying mechanisms using 6-hydroxydopamine (6-OHDA)-induced injury models. We found that 4R exhibited significant neuroprotective activity in the rat unilateral 6-OHDA-induced PD model in vivo. The therapeutic effect was evident both at morphological and behavioral levels. 4R (6 and 12 mg/kg) treatments significantly improved outcomes of 6-OHDA-induced PD in vivo as indicated by reducing forelimb asymmetry scores and corner test scores 4 weeks after injection of 6-OHDA (p < 0.05). The therapeutic effect of 4R was also reflected by decreased depletion of tyrosine hydroxylase (TH) in the striatum and substantia nigra (SN) on the side injected with 6-OHDA. TH expression was 70.3 and 62.8% of the contralateral side in striatum and SN, respectively, after 6 mg/kg 4R treatment; furthermore, it was 80.1 and 79.3% after treatment with 12 mg/kg of 4R. In the control group, it was 51.9 and 23.6% of the contralateral striatum and SN (p < 0.05). Moreover, 4R also protected differentiated neuro-2a cells from 6-OHDA-induced cytotoxicity in vitro. The activation of p-AKT and HAX-1, and inhibition of caspase-3 and endothelial inflammation, were involved in 4R-mediated protection against 6-OHDA-induced injury. In conclusion, the present study indicates that 4R shows a therapeutic effect in the rat 6-OHDA-induced PD model in vivo and in 6-OHDA-challenged neuro-2a cells in vitro.

Effects of L-DOPA/benserazide co-treatment on colonic excitatory cholinergic motility and enteric inflammation following dopaminergic nigrostriatal neurodegeneration

IntroductionThe mainstay therapy for Parkinson's disease (PD) relies on L-3,4-dihydroxyphenylalanine (L-DOPA) plus a DOPA-decarboxylase inhibitor. However, their effects on colonic dysmotility and inflammation observed in PD are undetermined. This study examined the effects of L-DOPA plus benserazide (BE) on colonic motility and inflammation in rats with central nigrostriatal dopaminergic denervation. MethodsNeurodegeneration was induced by 6-hydroxydopamine (6-OHDA) injection into the medial forebrain bundle (MFB). 6-OHDA animals were treated orally with L-DOPA/BE for 28 days, starting 28 days after 6-OHDA injection. At the end of treatment, in vivo colonic transit was evaluated by a radiologic assay. Electrically stimulated (ES) cholinergic contractions were recorded in vitro from colonic preparations, while acetylcholine release was measured in the incubation medium. Choline acetyltransferase (ChAT) and glial fibrillary acidic protein (GFAP) expression as well as eosinophil and mast cell density were examined in the colonic wall by immunohistochemistry. Colonic TNF and IL-1β levels were also assayed. Results6-OHDA animals displayed: 1) decrease in in vivo colonic transit; 2) impairment of ES-stimulated cholinergic contractions; 3) decreased acetylcholine release from myenteric nerves; 4) decrease in ChAT and increase in GFAP myenteric immunopositivity; 5) increase in eosinophil and mast cell density; 6) increase in TNF and IL-1β levels. Treatment with L-DOPA/BE elicited an improvement of in vivo and in vitro colonic motor activity, a normalization of acetylcholine release, ChAT immunopositivity, as well as pro-inflammatory cytokine patterns, ganglionic GFAP levels, eosinophil and mast cell density. ConclusionUnder dopaminergic nigrostriatal denervation, treatment with L-DOPA/BE ameliorated colonic motility through a normalization of myenteric cholinergic neurotransmission, along with an improvement of colonic inflammation.

Cerium oxide nanoparticles could ameliorate behavioral and neurochemical impairments in 6-hydroxydopamine induced Parkinson's disease in rats

BackgroundCerium oxide nanoparticles (CeO2NPs) showed promising effects in neurodegenerative diseases including some animal models of Parkinsonism. However, the implication of CeO2NPs in 6-hydroxydopamine (6-OHDA) induced Parkinsonism remains to be investigated. AimThis study was designed to assess whether CeO2NPs treatment could alleviate neurobehavioral and neurobiochemical deficits in 6-OHDA induced neurotoxicity in rats. Material and methods50 rats received left intrastriatal (IS) injection of either saline (control, n = 10) or 6-OHDA (n = 40). At the third week post-lesion, motor dysfunction was verified using neurobehavioral tests. Then diseased rats received intraperitoneal injection of 0.1, 0.5 or 1 mg/kg of CeO2NPs or vehicle (10 rats each) for 3 weeks. Rats were subjected to behavioral assessments and then sacrificed for biochemical analyses of the striatum. Striatal dopamine levels, oxidative stress markers including total antioxidant capacity (TAC) and malondialdehyde (MDA), and caspase 3 activity as an apoptotic marker were assessed. ResultsDifferent doses of CeO2NPs variably improved motor dysfunctions induced by 6-OHDA injection in open field, Rota Rod and stepping tests. In addition, the neurobiochemical derangements were almost reversed by the 0.5 mg/kg dose of CeO2NPs, while 0.1 mg/kg dose was not sufficient to alter biochemical measurements in the striatum. Administration of 1 mg/kg of CeO2NPs partially ameliorated striatal dopamine and decreased apoptosis without significant effect on oxidative stress. ConclusionThe present study showed a putative therapeutic role of CeO2NPs in the treatment of 6-OHDA-induced Parkinsonian rats, and suggested their antioxidant and antiapoptotic effects as possible mechanisms for elevated striatal dopamine level and improved motor performance.

Role of the locus coeruleus catecholaminergic neurons in the chemosensory control of breathing in a Parkinson's disease model

A previous study has demonstrated that in the 6-hydroxydopamine (6-OHDA)-model of Parkinson's disease (PD) there is a reduction in the number of Phox2b neurons in the retrotrapezoid nucleus (RTN) and a decrease in the respiratory response to hypercapnia 40days after PD-induction. The functional deficiency is restored 60days after 6-OHDA injection and here we tested the hypothesis that the locus coeruleus (LC) could be a candidate to restore the breathing deficiency. Minute Ventilation (VE) in response to hypercapnia (7% CO2) was assessed one day before, and then 40 and 60days after bilateral 6-OHDA (24μg/μL) or vehicle injections into the LC in control or PD-induced male Wistar rats. Bilateral injections of 6-OHDA decreased catecholaminergic neurons by 86% and 83% in the substantia nigra pars compacta (SNpc) and LC, respectively. As already described, in animals with lesions to the SNpc (N=6/group), the reduction in the ventilatory response to hypercapnia was restored 60days after PD (1257±81 vs. vehicle: 1185±49mL/kg/min). However, in animals with PD and lesion in the LC, the ventilation was blunted (674±39mL/kg/min). In another group of PD rats, we observed a reduction in the number of hypercapnia-induced-fos+ cells in the RTN region (40days: 38±3 and 60days: 8.5±0.9 vs. vehicle 78±3 cells) and an increase in the LC (40days: 46±4 and 60days: 94±22 vs. vehicle 1±1 cells). Our data suggest that LC catecholaminergic neurons can be a candidate structure mediating chemoreceptor function in a model of PD.

Impact of the Chronic Omega-3 Fatty Acids Supplementation in Hemiparkinsonism Model Induced by 6-Hydroxydopamine in Rats.

Parkinson's disease (PD) is characterized by a progressive degeneration of dopaminergic neurons in the substantia nigra. The neuronal degeneration may result from the convergence of a number of different pathogenic factors, including apoptosis, excitotoxicity and oxidative stress. Many studies emphasize the importance of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) in vital processes such as maintenance of the properties of cell membranes and the participation in signal transduction and biodynamic activity of neuronal membranes. In this study, the protective effect of ω-3 PUFA administration on the 6-hydroxydopamine (6-OHDA) model of PD in rats was investigated. ω-3 PUFA (1.5 and 3.0 g/kg) was orally administered by gavage during 28 consecutive days to male Wistar rats. On the 4th day, hemiparkinsonism was induced through intrastriatal injection of 6-OHDA. On the 25th day, the animals were submitted to behavioural analysis. On the 28th day, after euthanasia, the brain areas were collected for neurochemical evaluation. ω-3 PUFAs (1.5 and 3.0 g/kg) restored monoamine and amino acid levels on the striatum from hemiparkinsonian rats, followed by reduction in the number of apomorphine-induced rotations and promotion of a partial locomotor recovery. In addition, ω-3 PUFAs (1.5 and 3.0 g/kg) decreased the lipid peroxidation levels and nitrite levels in the brain areas from hemiparkinsonian rats. Thus, this study suggests that supplementation with ω-3 PUFAs prevents behavioural and neurochemical disturbances induced by 6-OHDA, presenting a potential neuroprotective action.

Brilliant Blue G, but not Fenofibrate, Treatment Reverts Hemiparkinsonian Behavior and Restores Dopamine Levels in an Animal Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder, characterized by the loss of dopaminergic neurons in the substantia nigra and their projections to the striatum. Several processes have been described as potential inducers of the dopaminergic neuron death, such as inflammation, oxidative stress, and mitochondrial dysfunction. However, the death of dopaminergic neurons seems to be multifactorial, and its cause remains unclear. ATP-activating purinergic receptors influence various physiological functions in the CNS, including neurotransmission. Purinergic signaling is also involved in pathological scenarios, where ATP is extensively released and promotes sustained purinergic P2X7 receptor (P2X7R) activation and consequent induction of cell death. This effect occurs, among other factors, by oxidative stress and during the inflammatory response. On the other hand, peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) is involved in energy metabolism and mitochondrial biogenesis. Expression and activity upregulation of this protein has been related with reduction of oxidative stress and neuroprotection. Therefore, P2X7R and PGC-1α are potential targets in the treatment of PD. Here hemiparkinsonism was induced by unilateral stereotactic injection of 6-OHDA in a rat model. After 7 days, the establishment of PD was confirmed and followed by treatment with the P2X7R antagonist Brilliant Blue G (BBG) or PGC-1α agonist fenofibrate. BBG, but not fenofibrate, reverted hemiparkinsonian behavior accompanied by an increase in tyrosine hydroxylase immunoreactivity in the substantia nigra. Our results suggest that the P2X7R may be a therapeutic target in Parkinson's disease.

Serotonergic system in hypoxic ventilatory response in unilateral rat model of Parkinson\u2019s disease

BackgroundMalfunctioning of the serotonergic system in Parkinson’s disease may contribute to non-motor symptoms such as respiratory complications. Thus the aim of our study was to investigate the role of serotonin 5-HT2 receptors in the modulation of normoxic breathing and the hypoxic ventilatory response (HVR) in rat model of Parkinson’s disease.MethodsWistar rats were lesioned unilaterally with double 6-hydroxydopamine (6-OHDA) injection to the right medial forebrain bundle (MFB). Before lesion and two weeks later animals were put in whole body plethysmography chamber and exposed to hypoxia (8% O2). Before hypoxic tests animals received intraperitoneal injections of DOI and ketanserin. Efficacy of lesion was confirmed by cylinder test, assessing limb use asymmetry.ResultsDegeneration of the nigrostriatal pathway augmented response of tidal volume and minute ventilation to hypoxia. DOI administration in control and lesion state caused a significant rise in normoxic respiratory rate and minute ventilation. Yet, ventilatory response of these parameters to hypoxia was attenuated. Post-DOI magnitude of HVR in lesioned state was decreased in compare to pre-lesion control. Subsequent ketanserin injection reverted DOI-induced respiratory effects. We demonstrated that 6-OHDA treatment decreased the content of serotonin in the injured striatum and on both sides of the brainstem, leaving the concentration of noradrenaline on unchanged level.ConclusionsThese observations showed that damage of the nigrostriatal system initiates changes in the serotonergic system, confirmed by reduced concentration of serotonin in the striatum and brainstem, which affects the magnitude of respiratory response to hypoxia after activation of 5-HT2 receptors.

In vivo bioluminescence imaging of neurogenesis - the role of the blood brain barrier in an experimental model of Parkinson's disease.

Bioluminescence imaging in transgenic mice expressing firefly luciferase in Doublecortin+ (Dcx) neuroblasts might serve as a powerful tool to study the role of neurogenesis in models of brain injury and neurodegeneration using non-invasive, longitudinal invivo imaging. Therefore, we aimed to use BLI in B6(Cg)-Tyrc-2J/J Dcx-Luc (Doublecortin-Luciferase, Dcx-Luc) mice to investigate its suitability to assess neurogenesis in a unilateral injection model of Parkinson's disease. We further aimed to assess the blood brain barrier leakage associated with the intranigral 6-OHDA injection to evaluate its impact on substrate delivery and bioluminescence signal intensity. Two weeks after lesion, we observed an increase in bioluminescence signal in the ipsilateral hippocampal region in both, 6-OHDA and vehicle injected Dcx-Luc mice. At the same time, no corresponding increase in Dcx+ neuroblast numbers could be observed in the dentate gyrus of C57Bl6 mice. Blood brain barrier leakage was observed in the hippocampal region and in the degenerating substantia nigra of C57Bl6 mice invivo using T1 weighted Magnetic Resonance Imaging with Gadovist® and exvivo using Evans Blue Fluorescence Reflectance Imaging and mouse Immunoglobulin G staining. Our data suggests a BLI signal dependency on blood brain barrier permeability, underlining a major pitfall of substrate/tracer dependent imaging in invasive disease models.

Bilateral distribution of enkephalinase activity in the medial prefrontal cortex differs between WKY and SHR rats unilaterally lesioned with 6-hydroxydopamine

Changes in the basal brain bilateral morphologic, neurochemical and/or functional patterns may be partly responsible for some brain disorders such as those involving mood. WKY and SHR strains as well as 6-hydroxydopamine (6-OHDA)-lesioned animals are validated models for the study of mood disorders. Because dopamine and enkephalins are involved in anxiety-related behaviors, the aim of our study was to analyze enkephalinase activity, assayed as aminopeptidase M activity, in the left and right medial prefrontal cortex (mPFC) of WKY and SHR treated with saline (sham group) or following left or right intrastriatal injections of the neurotoxic 6-OHDA. Sham left and sham right WKY exhibited a significant left predominance. Left 6-OHDA-lesioned rats inverted the left predominance of sham to right predominance. In right 6-OHDA-lesioned rats, the left predominance in sham right rats disappeared. Sham left as well as sham right SHR did not show any bilateral differences. In contrast, while the left lesion demonstrated a highly significant left predominance, the right lesion showed a slight but significant right predominance. A significant negative correlation between enkephalinase activity of the right mPFC and blood pressure and heart rate was observed only in left-lesioned SHR. Our results demonstrate that unilateral nigrostriatal injections of 6-OHDA influence the bilateral distribution of enkephalinase activity depending on both the side of the lesion and the strain analyzed. These results support the hypothesis that DA pathways may interact asymmetrically with enkephalins in the mPFC and that enkephalinase activity may play a role in the regulatory mechanisms underlying this interaction.

Neurosteroid allopregnanolone attenuates motor disability and prevents the changes of neurexin 1 and postsynaptic density protein 95 expression in the striatum of 6-OHDA-induced rats’ model of Parkinson’s disease

Abstract Background The striatum is an important brain structure for the learning and memory as well as motor and cognitive skills. Abnormalities in subcellular localization and synaptic cell surface proteins occur within the striatum in Parkinson’s disease (PD). In this study; we tested the effects of neurosteroid allopregnanolone (Allo) in the restoration of the nigrostriatal pathway output in 6-OHDA-lesioned rats. Methods To simulate PD, 6-hydroxydopamine (6-OHDA) was injected into the rat’s substantia nigra. Allo (5 and 20 mg/kg, orally) was administered on the day after the 6-OHDA injection and continued every other day for 8 weeks. Motor-skill learning and motor behaviors were assessed by the apomorphine-induced rotation, accelerating rotarod, beam-balance (BB) and beam-walk (BW), and bar tests. The levels of striatal postsynaptic density protein 95 (PSD-95) and neurexin 1 as well as cyclooxygenase-2 (COX-2) and caspase-3 proteins were determined by immunoblotting. Results The data indicated that Allo significantly improved the 6-OHDA-induced motor impairment which revealed by the increase in the ability to remain on a rotating rod and the increase in balancing and crossing on beam and also with decrease in the degree of catalepsy in bar test. Furthermore, PSD-95 and neurexin 1 levels were significantly decreased, while COX-2 and activated caspase-3 were increased in the striatum of 6-OHDA-treated animals. The mentioned molecular changes were attenuated by Allo treatment. Conclusions The data demonstrated that Allo has protective effect in 6-OHDA-treated rats and inhibits striatal inflammation and apoptosis and preserves pre- and post-synaptic proteins and maybe the synaptic integrity in nigrostriatal pathway.

Effects of Postnatal Enriched Environment in a Model of Parkinson's Disease in Adult Rats.

Environmental enrichment is a widespread neuroprotective strategy during development and also in the mature nervous system. Several research groups have described that enriched environment in adult rats has an impact on the progression of Parkinson’s disease (PD). The aim of our present study was to examine the effects of early, postnatal environmental enrichment after 6-hydroxydopamine-induced (6-OHDA) lesion of the substantia nigra in adulthood. Newborn Wistar rats were divided into control and enriched groups according to their environmental conditions. For environmental enrichment, during the first five postnatal weeks animals were placed in larger cages and exposed to intensive complex stimuli. Dopaminergic cell loss, and hypokinetic and asymmetrical signs were evaluated after inducing PD with unilateral injections of 6-OHDA in three-month-old animals. Treatment with 6-OHDA led to a significant cell loss in the substantia nigra of control animals, however, postnatal enriched circumstances could rescue the dopaminergic cells. Although there was no significant difference in the percentage of surviving cells between 6-OHDA-treated control and enriched groups, the slightly less dopaminergic cell loss in the enriched group compared to control animals resulted in less severe hypokinesia. Our investigation is the first to provide evidence for the neuroprotective effect of postnatal enriched environment in PD later in life.

Iron accumulation and microglia activation contribute to substantia nigra hyperechogenicity in the 6-OHDA-induced rat model of Parkinson's disease

IntroductionThis study aims to explain the mechanisms for the formation of sonographic features of Parkinson's disease (PD) using a 6-hydroxydopamine (6-OHDA) rat model of PD. The iron chelator deferiprone (DFP) was used in the PD model rat to examine the relationship between iron and the echo signal. MethodsRat models were created using stereotactic injections of 6-OHDA. DFP was administered intragastrically. Transcranial sonography (TCS) was performed to observe the substantia nigra (SN) echo signal of the brain. Immunofluorescence and iron staining were performed to observe the histological characteristics of the hyperechogenic area. The imaging findings were compared with the histopathological findings. ResultsThe PD model rat presented a large area of hyperechogenicity in the SN. Ferric ion accumulation and microglia proliferation occurred in the hyperechogenic area. DFP inhibited dopaminergic (DA) neuron necrosis, ferric ion accumulation and microglia proliferation and reduced the hyperechogenic area of the SN. ConclusionsBoth iron aggregation and gliosis contribute to the formation of substantia nigra hyperechogenicity (SNH) in PD. DFP exhibits a neuroprotective effect by inhibiting SNH. Iron deposit and the SNH are correlated with DA neuron necrosis.

Evidence for an Additive Neurorestorative Effect of Simultaneously Administered CDNF and GDNF in Hemiparkinsonian Rats: Implications for Different Mechanism of Action.

Parkinson’s disease (PD) is a neurodegenerative disorder associated with a progressive loss of dopaminergic (DAergic) neurons of the substantia nigra (SN) and the accumulation of intracellular inclusions containing α-synuclein. Current therapies do not stop the progression of the disease, and the efficacy of these treatments wanes over time. Neurotrophic factors (NTFs) are naturally occurring proteins promoting the survival and differentiation of neurons and the maintenance of neuronal contacts. CDNF (cerebral dopamine NTF) and GDNF (glial cell line-derived NTF) are able to protect DAergic neurons against toxin-induced degeneration in experimental models of PD. Here, we report an additive neurorestorative effect of coadministration of CDNF and GDNF in the unilateral 6-hydroxydopamine (6-OHDA) lesion model of PD in rats. NTFs were given into the striatum four weeks after unilateral intrastriatal injection of 6-OHDA (20 µg). Amphetamine-induced (2.5 mg/kg, i.p.) rotational behavior was measured every two weeks. Number of tyrosine hydroxylase (TH)-positive cells from SN pars compacta (SNpc) and density of TH-positive fibers in the striatum were analyzed at 12 weeks after lesion. CDNF and GDNF alone restored the DAergic function, and one specific dose combination had an additive effect: CDNF (2.5µg) and GDNF (1µg) coadministration led to a stronger trophic effect relative to either of the single treatments alone. The additive effect may indicate different mechanism of action for the NTFs. Indeed, both NTFs activated the survival promoting PI3 kinase (PI3K)-Akt signaling pathway, but only CDNF decreased the expression level of tested endoplasmatic reticulum (ER) stress markers ATF6, glucose-regulated protein 78 (GRP78), and phosphorylation of eukaryotic initiation factor 2α subunit (eIF2α).

The Treadmill Exercise Protects against Dopaminergic Neuron Loss and Brain Oxidative Stress in Parkinsonian Rats.

Parkinson's disease (PD), a progressive neurological pathology, presents motor and nonmotor impairments. The objectives were to support data on exercise benefits to PD. Male Wistar rats were distributed into sham-operated (SO) and 6-OHDA-lesioned, both groups without and with exercise. The animals were subjected to treadmill exercises (14 days), 24 h after the stereotaxic surgery and striatal 6-OHDA injection. Those from no-exercise groups stayed on the treadmill for the same period and, afterwards, were subjected to behavioral tests and euthanized for neurochemical and immunohistochemical assays. The data, analyzed by ANOVA and Tukey post hoc test, were considered significant for p < 0.05. The results showed behavioral change improvements in the 6-OHDA group, after the treadmill exercise, evaluated by apomorphine rotational behavior, open field, and rota rod tests. The exercise reduced striatal dopaminergic neuronal loss and decreased the oxidative stress. In addition, significant increases in BDNF contents and in immunoreactive cells to TH and DAT were also observed, in striata of the 6-OHDA group with exercise, relatively to those with no exercise. We conclude that exercise improves behavior and dopaminergic neurotransmission in 6-OHDA-lesioned animals. The increased oxidative stress and decreased BDNF contents were also reversed, emphasizing the importance of exercise for the PD management.