6-OHDA Injection Research Articles

Changes in Day/Night Activity in the 6-OHDA-Induced Experimental Model of Parkinson's Disease: Exploring Prodromal Biomarkers.

The search for experimental models mimicking an early stage of Parkinson’s disease (PD) before motor manifestations is fundamental in order to explore early signs and get a better prognosis. Interestingly, our previous studies have indicated that 6-hydroxydopamine (6-OHDA) is a suitable model to induce an early degeneration of the nigrostriatal system without any gross motor impairment. Considering our previous findings, we aim to implement a novel system to monitor rats after intrastriatal injection of 6-OHDA to detect and analyze physiological changes underlying prodromal PD. Twenty male Sprague-Dawley rats were unilaterally injected with 6-OHDA (n = 10) or saline solution (n = 10) into the right striatum and placed in enriched environment cages where the activity was monitored. After 2 weeks, the amphetamine test was performed before the sacrifice. Immunohistochemistry was developed for the morphological evaluation and western blot analysis to assess molecular changes. Home-cage monitoring revealed behavioral changes in response to 6-OHDA administration including significant hyperactivity and hypoactivity during the light and dark phase, respectively, turning out in a change of the circadian timing. A preclinical stage of PD was functionally confirmed with the amphetamine test. Moreover, the loss of tyrosine hydroxylase expression was significantly correlated with the motor results, and 6-OHDA induced early proapoptotic events. Our findings provide evidence for a novel prodromal 6-OHDA model following a customized monitoring system that could give insights to detect non-motor deficits and molecular targets to test neuroprotective/neurorestorative agents.

Both Intracranial and Intravenous Administration of Functionalized Carbon Nanotubes Protect Dopaminergic Neuronal Death from 6-Hydroxydopamine.

PurposeAlthough single-walled nanotubes (SWNTs) with functional groups have been suggested as a potential nanomedicine to treat neuronal disorders, effective routes to administer SWNTs have not been compared thus far. The blood–brain barrier is a considerable challenge for the development of brain-targeting drugs, and therefore functionalized SWNT routes of administration have been needed for testing Parkinson’s disease (PD) treatment. Here, effective administration routes of functionalized SWNTs were evaluated in PD mouse model.MethodsThree different administration routes were tested in PD mouse model. Functionalized SWNTs were injected directly into the lateral ventricle three days before (Method 1) or after (Method 2) 6-hydroxydopamine (6-OHDA) injection to compare the protective effects of SWNTs against dopaminergic neuronal death or functionalized SWNTs were injected intravenously at three and four days after 6-OHDA injection (Method 3). Asymmetric behaviors and histological assessment from all animals were performed at two weeks after 6-OHDA injection.ResultsVentricular injections of SWNTs both before or after 6-OHDA exposure protected dopaminergic neurons both in the substantia nigra and striatum and alleviated rotational asymmetry behavior in PD mice. Moreover, intravenous administration of SWNTs three and four days after 6-OHDA injection also prevented neuronal death and PD mice behavioral impairment without apparent cytotoxicity after six months post-treatment.ConclusionOur study demonstrates that functionalized SWNTs could effectively protect dopaminergic neurons through all administration routes examined herein. Therefore, SWNTs are promising nanomedicine agents by themselves or as therapeutic carriers to treat neuronal disorders such as PD.

Transplanted Wharton’s jelly mesenchymal stem cells improve memory and brain hippocampal electrophysiology in rat model of Parkinson’s disease

BackgroundExperimental findings have shown that stem cell transplantation is a therapeutic procedure for Parkinson’s disease (PD). In this study, effects of human Wharton's jelly-derived mesenchymal stem cells (hWJ-MSCs), alone and combined with l-dopa, were examined for repairing memory impairment in a rat model of PD. MethodsFifty adult male Wistar rats were randomly divided into five groups: 1) sham, 2) PD, 3) PD + C, 4) PD + C+D, and 5) PD + D. PD was induced by 6-OHDA injection (16 μg/2 μl) into medial forebrain bundle (MFB) and was confirmed 14 days later by contralateral rotation using apomorphine injection. The rats received hWJ-MSCs (1 × 106 cells, i.v.) twice on the 14th and 28th days post PD induction. Treated PD rats received hWJ-MSCs alone or combined with l-Dopa and Carbidopa (10/30 mg/kg, i.p.). Four months later, memory, hippocampal long-term potentiation (hLTP), histological changes, and the levels of BDNF and NGF in striatum were evaluated. ResultsPD caused both cell loss with small dark stained nuclei in granular zone as well as significant decrement of BDNF and NGF (P < 0.001) in striatum. These pathological alterations were associated with memory and hLTP deficits (P < 0.001 respectively). Treating PD rats with hWJ-MSCs, alone (P < 0.05 and P < 0.001) and combined with l-Dopa (P < 0.001), significantly restored the levels of both of the neurotrophins followed by improving cognition and hLTP (P < 0.001). ConclusionCurrent findings showed that chronic treatment of PD rats with hWJ-MSCs, alone and in combination with l-Dopa, could restore memory and hLTP by reconstructing dopaminergic neurons and elevating the BDNF and NGF factors.

Exercise-Induced Neuroprotection in the 6-Hydroxydopamine Parkinson's Disease Model.

Exercise exerts helpful effects in Parkinson's disease. In this study, the 6-hydroxydopamine (6-OHDA) injection was used to investigate the effect of exercise on apomorphine-induced rotation and neurorestoration. Rats (n = 32) were divided into four groups: (1) Saline+Noexercise (Sham); (2) 6-OHDA+Noexercise (6-OHDA); (3) Saline+Exercise (S+EXE), and (4) 6-OHDA+Exercise (6-OHDA+EXE). The rats were administered 8μg 6-OHDA by injection into the right medial forebrain bundle. After 2weeks, the exercise group was run (14 consecutive days, 30min per day). One month after the surgery, following the injection of apomorphine, the 6-OHDA group displayed a significant increase in rotation and the 6-OHDA+EXE group showed a significant reduction of rotational asymmetry (P<0.001). 6-OHDA injection reduced the mRNA and protein expression of the AMP-activated protein kinase, brain-derived neurotropic factor, and tyrosine hydroxylase in relation to the Sham group and exercise increased these levels. Expression of the silent information regulator 2 homolog 1 and peroxisome proliferator-activated receptor gamma coactivator 1-alpha was unexpectedly enhanced in the 6-OHDA groups in relation to the Sham group. These findings suggest that the 6-OHDA injection increased the neurodegeneration and mitochondrial and behavioral dysfunctions and the treadmill running attenuated these disorders in the ipsilateral striatum of the 6-OHDA+EXE group.

Dopamine transporter neuroimaging accurately assesses the maturation of dopamine neurons in a preclinical model of Parkinson\u2019s disease

BackgroundSignificant developments in stem cell therapy for Parkinson’s disease (PD) have already been achieved; however, methods for reliable assessment of dopamine neuron maturation in vivo are lacking. Establishing the efficacy of new cellular therapies using non-invasive methodologies will be critical for future regulatory approval and application. The current study examines the utility of neuroimaging to characterise the in vivo maturation, innervation and functional dopamine release of transplanted human embryonic stem cell-derived midbrain dopaminergic neurons (hESC-mDAs) in a preclinical model of PD.MethodsFemale NIH RNu rats received a unilateral stereotaxic injection of 6-OHDA into the left medial forebrain bundle to create the PD lesion. hESC-mDA cell and sham transplantations were carried out 1 month post-lesion, with treated animals receiving approximately 4 × 105 cells per transplantation. Behavioural analysis, [18F]FBCTT and [18F]fallypride microPET/CT, was conducted at 1, 3 and 6 months post-transplantation and compared with histological characterisation at 6 months.ResultsPET imaging revealed transplant survival and maturation into functional dopaminergic neurons. [18F]FBCTT-PET/CT dopamine transporter (DAT) imaging demonstrated pre-synaptic restoration and [18F]fallypride-PET/CT indicated functional dopamine release, whilst amphetamine-induced rotation showed significant behavioural recovery. Moreover, histology revealed that the grafted cells matured differently in vivo producing high- and low-tyrosine hydroxylase (TH) expressing cohorts, and only [18F]FBCTT uptake was well correlated with differentiation.ConclusionsThis study provides further evidence for the value of in vivo functional imaging for the assessment of cell therapies and highlights the utility of DAT imaging for the determination of early post-transplant cell maturation and differentiation of hESC-mDAs.

Intranasal insulin ameliorates cognitive impairment in a rat model of Parkinson's disease through Akt/GSK3β signaling pathway

AimsParkinson's disease dementia (PDD) is one of the most common non-motor symptoms of advanced Parkinson's disease (PD). This study aimed to determine whether intranasal insulin has protective effects on cognition in the rat PD model induced by 6-hydroxylase dopamine (6-OHDA) through the insulin signaling pathway. Materials and methodsThe rats were given intranasal insulin administration for six weeks after unilateral medial forebrain bundle (MFB) injection of 6-OHDA. Then a series of cognitive-behavioral tests, immunofluorescence, and immunoblotting was performed on the rats. Key findingsThe results demonstrated that the injection of 6-OHDA in the unilateral MFB damaged working memory and long-term habituation of rats in the T-maze rewarded alternation test and hole-board test. Besides, rats with unilateral 6-OHDA injury performed poorly in terms of escape latency and average speed during the hidden platform training phase rather than in the probe trial of the Morris Water Maze (MWM) test. Immunofluorescence results showed that unilateral 6-OHDA injury in MFB led to the massive death of ipsilateral-substantia nigra (SN) tyrosine hydroxylase (TH)-positive neurons. Western blot results further indicated that 6-OHDA-induced necrosis of ipsilateral-SN dopaminergic neurons reduced the levels of p-Akt (Ser473) and p-GSK3β (Ser9) in the ipsilateral-hippocampus. SignificanceThese findings provide a solid evidence base for the relationship between PD cognitive impairment and insulin signaling pathways.

Role of Prefrontal Cortex on Recognition Memory Deficits in Rats following 6-OHDA-Induced Locus Coeruleus Lesion.

Degeneration of the locus coeruleus (LC), the main source of cerebral noradrenaline (NA), has been reported in diverse neurodegenerative diseases, including Parkinson's diseases (PD). There is increasing evidence indicating the role of NA deficiency in the prefrontal cortex (PFC) and the development of early cognitive impairments in PD. Here, we evaluated whether a selective noradrenergic lesion of LC caused by 6-hydroxydopamine (6-OHDA) may induce memory deficits and neurochemical alterations in the PFC. Adult male Wistar rats received stereotaxic bilateral injections of 6-OHDA (5 μg/2 μl) into the LC, and two stainless-steel guide cannulas were implanted in the PFC. The SHAM group received just vehicle. To induce a selective noradrenergic lesion, animals received nomifensine (10 mg/kg), a dopamine transporter blocker, one hour before surgery. 6-OHDA-lesioned rats displayed impairments of the short- and long-term object recognition memory associated to reduced content of tyrosine hydroxylase in the LC. Neurochemical analysis revealed an altered mitochondrial membrane potential in LC. Regarding the PFC, an increased ROS production, cell membrane damage, and mitochondrial membrane potential disruption were observed. Remarkably, bilateral NA (1 μg/0.2 μl) infusion into the PFC restored the recognition memory deficits in LC-lesioned rats. These findings indicate that a selective noradrenergic LC lesion induced by 6-OHDA deregulates a noradrenergic network in the PFC, which could be involved in the early memory impairments observed in nondemented PD patients.

Classical Model of 6-Hydroxydopamine-Induced Parkinsonism in Rats Is Characterized by Unilateral Lesion of Brain Mesolimbic System

Abstract—Localizing lesions in the brain of rodents after administration of neurotoxic 6-hydroxidopamine (6-OHDA) is important for understanding the mechanisms of progression of parkinsonism. The present study provides the results of behavioral tests, immunohistochemistry, and measurements of dopamine (DA) level in different areas of the striatum 25 days after unilateral intranigral injection of 6-OHDA to rats. Neuronal death was observed in the both pars compacta of the substantia nigra and the lateral nucleus of the ventral tegmental area (VTA). Detailed analysis of DA levels showed a 90% decrease in the dorsal striatum and a 73% decrease in the ventral striatum only at the side ipsilateral to toxin injection. The changes discovered in VTA are similar to the results of morphological post mortem studies of Parkinson’s disease. Previously described emotional disturbances in rats with 6-OHDA-induced Parkinson’s disease may be related to the damage in VTA shown in our study.

Hesperidin Ameliorates Anxiety-Depressive-Like Behavior in 6-OHDA Model of Parkinson's Disease by Regulating Striatal Cytokine and Neurotrophic Factors Levels and Dopaminergic Innervation Loss in the Striatum of Mice.

The mechanisms underlying the neuroprotective effects of hesperidin in a murine model of PD are not fully elucidated. The current study was carried out to investigate the ability of hesperidin in modulating proinflammatory cytokines, neurotrophic factors, and neuronal recovery in 6-hydroxydopamine (6-OHDA)-induced nigral dopaminergic neuronal loss. Adult male C57BL/6 mice were randomly assigned into four groups: (I) sham/vehicle, (II) sham/hesperidin, (III) 6-OHDA/vehicle, and (IV) 6-OHDA/hesperidin. Mice received a unilateral intrastriatal injection of 6-OHDA and treated with hesperidin (50mg/kg; per oral) for 28days. After hesperidin treatment, mice were submitted to behavioral tests and had the striatum removed for neurochemical assays. Our results demonstrated that oral treatment with hesperidin ameliorated the anxiety-related and depressive-like behaviors in 6-OHDA-lesioned mice (p < 0.05). It also attenuated the striatal levels of proinflammatory cytokines tumor necrosis factor-α, interferon-gamma, interleukin-1β, interleukin-2, and interleukin-6 and increased the levels of neurotrophic factors, including neurotrophin-3, brain-derived neurotrophic factor, and nerve growth factor in the striatum of 6-OHDA mice (p < 0.05). Hesperidin treatment was also capable to increase striatal levels of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid and protects against the impairment of dopaminergic neurons in the substantia nigra pars compacta (SNpc) (p < 0.05). In conclusion, this study indicated that hesperidin exerts anxiolytic-like and antidepressant-like effect against 6-OHDA-induced neurotoxicity through the modulation of cytokine production, neurotrophic factors levels, and dopaminergic innervation in the striatum.

Impact of Aging on the 6-OHDA-Induced Rat Model of Parkinson's Disease.

Parkinson’s disease (PD) is the second most common age-related neurodegenerative disorder. The neurodegeneration leading to incapacitating motor abnormalities mainly occurs in the nigrostriatal pathway due to the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Several animal models have been developed not only to better understand the mechanisms underlying neurodegeneration but also to test the potential of emerging disease-modifying therapies. However, despite aging being the main risk factor for developing idiopathic PD, most of the studies do not use aged animals. Therefore, this study aimed at assessing the effect of aging in the unilateral 6-hydroxydopamine (6-OHDA)-induced animal model of PD. For this, female young adult and aged rats received a unilateral injection of 6-OHDA into the medial forebrain bundle. Subsequently, the impact of aging on 6-OHDA-induced effects on animal welfare, motor performance, and nigrostriatal integrity were assessed. The results showed that aging had a negative impact on animal welfare after surgery. Furthermore, 6-OHDA-induced impairments on skilled motor function were significantly higher in aged rats when compared with their younger counterparts. Nigrostriatal histological analysis further revealed an increased 6-OHDA-induced dopaminergic cell loss in the SNpc of aged animals when compared to young animals. Overall, our results demonstrate a higher susceptibility of aged animals to 6-OHDA toxic insult.

Comparison between Tail Suspension Swing Test and Standard Rotation Test in Revealing Early Motor Behavioral Changes and Neurodegeneration in 6-OHDA Hemiparkinsonian Rats

The unilateral 6-hydroxydopamine (6-OHDA) model of Parkinson’s disease (PD) is one of the most commonly used in rodents. The anatomical, metabolic, and behavioral changes that occur after severe and stable 6-OHDA lesions have been extensively studied. Here, we investigated whether early motor behavioral deficits can be observed in the first week after the injection of 6-OHDA into the right substantia nigra pars compacta (SNc), and if they were indicative of the severity of the dopaminergic (DAergic) lesion in the SNc and the striatum at different time-points (day 1, 3, 5, 7, 14, 21). With this aim, we used our newly modified tail suspension swing test (TSST), the standard rotation test (RT), and immunohistochemical staining for tyrosine hydroxylase (TH). The TSST, but not the standard RT, revealed a spontaneous motor bias for the 6-OHDA-lesioned rats from the day 1 post-surgery. Both tests detected the motor asymmetry induced by (single and repeated) apomorphine (APO) challenges that correlated, in the first week, with the DAergic neuronal degeneration. The described TSST is fast and easy to perform, and in the drug-free condition is useful for the functional assessment of early motor asymmetry appearing after the 6-OHDA-lesion in the SNc, without the confounding effect of APO challenges.

Neuroprotective effect of regular swimming exercise on calretinin-positive striatal neurons of Parkinsonian rats.

In Parkinson's disease (PD), physical therapy is one of the mainstays of supportive treatment modalities. This study focused on the neuroprotective effect of regular exercise on striatal calretinin positive interneurons in a rat model of PD. 6-hydroxydopamine (6-OHDA) was injected unilaterally into the medial forebrain bundle of Wistar rats. 6-OHDA lesioned (Parkinsonian) and unlesioned (control) rats were divided into sedentary and exercise groups. Exercise groups had daily swimming sessions for 30min for 6 weeks. After 6-OHDA injections, an apomorphine-induced rotation test was performed (0.05mg/kg, subcutaneous) at the 3rd and 6th weeks. At the end of the 6th week, brains were removed following transcardiac perfusion. The brain sections were stained immunohistochemically for tyrosine hydroxylase and calretinin reactivity. The number of rotations was significantly lower in Parkinsonian exercise group compared to Parkinsonian sedentary group at the 6th week (p = 0.024) and there was significant difference between Parkisonian sedentary groups at the 3rd and 6th weeks (p < 0.002). The calretinin positive interneurons significantly increased in the Parkinsonian exercise group compared to Parkinsonian sedentary group (p = 0.0003) and control exercise group (p < 0.0001). To conclude, the swimming exercise led to a striking increment of calretinin positive interneurons in the striatum of Parkinsonian rat. These findings indicated that the neuroprotective mechanism of exercise increased the number of striatal calretinin positive interneurons that might generate new approaches for the mechanism of neuroprotection. We concluded that striatal calretinin positive interneurons have an important role in the neuroprotective mechanisms of exercise in PD.

Increased GABAergic transmission in neuropeptide Y-expressing neurons in the dopamine-depleted murine striatum.

As the main input nucleus of the basal ganglia, the striatum plays a central role in planning, control, and execution of movement and motor skill learning. More than 90% of striatal neurons, so-called medium spiny neurons (MSN), are GABAergic projection neurons, innervating primarily the substantia nigra pars reticulata or the globus pallidus internus. The remaining neurons are GABAergic and cholinergic interneurons, synchronizing and controlling striatal output by reciprocal connections with MSN. Besides prominent local cholinergic influence, striatal function is globally regulated by dopamine (DA) from the nigrostriatal pathway. Little is known about whether DA depletion, as occurs in Parkinson's disease, affects the activity of striatal interneurons. Here we focused on neuropeptide Y (NPY)-expressing interneurons, which are among the major subgroups of GABAergic interneurons in the striatum. We investigated the effects of striatal DA depletion on GABAergic transmission in NPY interneurons by electrophysiologically recording GABAergic spontaneous (s) and miniature (m) inhibitory postsynaptic currents (IPSCs) in identified NPY interneurons in slices from 6-hydroxydopamine (6-OHDA)- and vehicle-injected transgenic NPY-humanized Renilla green fluorescent protein (hrGFP) mice with the whole cell patch-clamp technique. We report a significant increase in sIPSC and mIPSC frequency as well as the occurrence of giant synaptic and burst sIPSCs in the 6-OHDA group, suggesting changes in GABAergic circuit activity and synaptic transmission. IPSC kinetics remained unchanged, pointing to mainly presynaptic changes in GABAergic transmission. These results show that chronic DA depletion following 6-OHDA injection causes activity-dependent and -independent increase of synaptic GABAergic inhibition onto striatal NPY interneurons, confirming their involvement in the functional impairments of the DA-depleted striatum.NEW & NOTEWORTHY Neuropeptide Y (NPY) interneurons regulate the function of striatal projection neurons and are upregulated upon dopamine depletion in the striatum. Here we investigated how dopamine depletion affects NPY circuits and show electrophysiologically that it leads to the occurrence of giant synaptic and burst GABAergic spontaneous inhibitory postsynaptic currents (IPSCs) and to an activity-independent increase in GABAergic miniature IPSC frequency in NPY neurons. We suggest that degeneration of dopaminergic terminals in the striatum causes functional changes in striatal GABAergic function.

Respiratory pattern and phrenic and hypoglossal nerve activity during normoxia and hypoxia in 6-OHDA-induced bilateral model of Parkinson\u2019s disease

Respiratory disturbances present in Parkinson’s disease (PD) are not well understood. Thus, studies in animal models aimed to link brain dopamine (DA) deficits with respiratory impairment are needed. Adult Wistar rats were lesioned with injection of 6-hydroxydopamine (6-OHDA) into the third cerebral ventricle. Two weeks after hypoxic test was performed in whole-body plethysmography chamber, phrenic (PHR) and hypoglossal (HG) nerve activities were recorded in normoxic and hypoxic conditions in anesthetized, vagotomized, paralyzed and mechanically ventilated rats. The effects of activation and blockade of dopaminergic carotid body receptors were investigated during normoxia in anesthetized spontaneously breathing rats. 6-OHDA injection affected resting respiratory pattern in awake animals: an increase in tidal volume and a decrease in respiratory rate had no effect on minute ventilation. Hypoxia magnified the amplitude and minute activity of the PHR and HG nerve of 6-OHDA rats. The ratio of pre-inspiratory to inspiratory HG burst amplitude was reduced in normoxic breathing. Yet, the ratio of pre-inspiratory time to total time of the respiratory cycle was increased during normoxia. 6-OHDA lesion had no impact on DA and domperidone effects on the respiratory pattern, which indicate that peripheral DA receptors are not affected in this model. Analysis of monoamines confirmed substantial striatal depletion of dopamine, serotonin and noradrenaline (NA) and reduction of NA content in the brainstem. In bilateral 6-OHDA model changes in activity of both nerves: HG (linked with increased apnea episodes) and PHR are present. Demonstrated respiratory effects could be related to specific depletion of DA and NA.

Assessment of vitamin D and inflammatory markers profile in cardiac tissue on Parkinson disease animal model.

Cardiovascular dysfunctions are common non-motor symptoms in patients with Parkinson's disease (PD) that can result in reduced quality of life and even death. Research in animal models designed to characterize the pathological association between PD and cardiovascular abnormalities is still in its infancy. This study assessed the early impact of the nigrostriatal dopaminergic damage on cardiological features in the unilateral 6-OHDA rat model of PD. Male Wistar rats received unilateral intrastriatal injections of 6-OHDA and sham rats were injected with saline. Animals were studied 15days later. Immunohistochemistry was used for visualization of tyrosine hydroxylase (TH)-positive neurons in the nigrostriatal system. Electrocardiogram recordings of heart rate were performed in conscious rats. Heart levels of vitamin D, inflammatory cytokines and C-reactive protein were assessed through electrochemiluminescence immunoassay, quantitative reverse transcription PCR and turbidimetric method, respectively. We found a post-injury reduction of TH-immunoreactivity of approximately 45% in the substantia nigra pars compacta and 20% in the striatum. Heart rate reduction was found in 6-OHDA-lesioned rats as compared with sham counterparts. Reduced levels of vitamin D and increased levels of inflammatory factors (C-reactive protein, IL-6, TNF-α and TGF-β) were detected in the heart tissue of PD rats in comparison with sham. Our findings suggest a link between cardiac tissue changes and cardiac functional changes early after the central dopaminergic damage induced by 6-OHDA. Knowledge of the cardiac abnormalities in the 6-OHDA model is critical in identifying future therapeutic targets and disease-modifying approaches for PD non-motor features.

Pathological remodelling of colonic wall following dopaminergic nigrostriatal neurodegeneration

Background and aimPatients with Parkinson's disease (PD) are often characterized by functional gastrointestinal disorders. Such disturbances can occur at all stages of PD and precede the typical motor symptoms of the disease by many years. However, the morphological alterations associated with intestinal disturbances in PD are undetermined. This study examined the remodelling of colonic wall in 6-hydroxydopamine (6-OHDA)-induced PD rats. Methods8 weeks after 6-OHDA injection animals were sacrificed. Inflammatory infiltrates, collagen deposition and remodelling of intestinal epithelial barrier and tunica muscularis in the colonic wall were assessed by histochemistry, immunohistochemistry, immunofluorescence and western blot analysis. Results6-OHDA rats displayed significant alterations of colonic tissues as compared with controls. Signs of mild inflammation (eosinophil infiltration) and a transmural deposition of collagen fibres were observed. Superficial colonic layers were characterized by severe morphological alterations. In particular, lining epithelial cells displayed a reduced claudin-1 and transmembrane 16A/Anoctamin 1 (TMEM16A/ANO1) expression; goblet cells increased their mucin expression; colonic crypts were characterized by an increase in proliferating epithelial cells; the density of S100-positive glial cells and vimentin-positive fibroblast-like cells was increased as well. Several changes were found in the tunica muscularis: downregulation of α-smooth muscle actin/desmin expression and increased proliferation of smooth muscle cells; increased vimentin expression and proliferative phenotype in myenteric ganglia; reduction of interstitial cells of Cajal (ICCs) density. ConclusionsA pathological remodelling occurs in the colon of 6-OHDA rats. The main changes include: enhanced fibrotic deposition; alterations of the epithelial barrier; activation of mucosal defense; reduction of ICCs. These results indicate that central nigrostriatal denervation is associated with histological changes in the large bowel at mucosal, submucosal and muscular level. These alterations might represent morphological correlates of digestive symptoms in PD.

Attenuated baroreflex in a Parkinson's disease animal model coincides with impaired activation of non-C1 neurons.

Orthostatic hypotension is one of the most common symptoms observed in Parkinson's disease (PD), a neurodegenerative disease caused by death of dopaminergic neurons in the substantia nigra pars compacta (SNc), and it is associated with denervation of the heart and impairment of the baroreflex. Here, we aimed to investigate if the impaired baroreflex was associated with lower activation of cardiovascular brainstem areas in a 6-hydroxydopamine (6-OHDA) animal model of PD. The PD model was generated with male Wistar rats by injection of 6-OHDA or vehicle into the striatum. After 20 or 60days, the femoral vein and artery were cannulated to assess cardiovascular parameters during injection of sodium nitroprusside (SNP) or phenylephrine (Phe). Brainstem slices were submitted to immunohistochemistry and immunofluorescence. After 6-OHDA injection, 75% of the dopaminergic neurons in the SNc were absent, confirming establishment of the PD model. Intravenous (iv) injection of SNP generated reduced hypotension and tachycardia response, and the noncatecholaminergic (nonC1) neurons of the rostral ventrolateral medulla (RVLM) were less activated. Additionally, iv injection of Phe increased blood pressure and bradycardia to the same extent and activated equivalent numbers of neurons in the nucleus of the solitary tract and the caudal ventrolateral medulla as well as cholinergic neurons of the dorsal motor nucleus of the vagus and the nucleus ambiguus between control and PD animals. In summary, these data showed that in the PD model, impairment of cardiovascular autonomic control was observed only during deactivation of the baroreflex, which could be related to reduced activation of non-C1 neurons within the RVLM.

The Dopamine D5 receptor contributes to activation of cholinergic interneurons during L-DOPA induced dyskinesia

The dopamine D5 receptor (D5R) is a Gαs-coupled dopamine receptor belonging to the dopamine D1-like receptor family. Together with the dopamine D2 receptor it is highly expressed in striatal cholinergic interneurons and therefore is poised to be a positive regulator of cholinergic activity in response to L-DOPA in the dopamine-depleted parkinsonian brain. Tonically active cholinergic interneurons become dysregulated during chronic L-DOPA administration and participate in the expression of L-DOPA induced dyskinesia. The molecular mechanisms involved in this process have not been elucidated, however a correlation between dyskinesia severity and pERK expression in cholinergic cells has been described. To better understand the function of the D5 receptor and how it affects cholinergic interneurons in L-DOPA induced dyskinesia, we used D5R knockout mice that were rendered parkinsonian by unilateral 6-OHDA injection. In the KO mice, expression of pERK was strongly reduced indicating that activation of these cells is at least in part driven by the D5 receptor. Similarly, pS6, another marker for the activity status of cholinergic interneurons was also reduced. However, mice lacking D5R exhibited slightly worsened locomotor performance in response to L-DOPA and enhanced LID scores. Our findings suggest that D5R can modulate L-DOPA induced dyskinesia and is a critical activator of CINs via pERK and pS6.

Unilateral 6-Hydroxydopamine-Lesioned Rat as Relevant Model to Study the Pain Related to Parkinson’s Disease

The present study was conducted to test the use of the hemiparkinsonian rat, obtained by the unilateral injection of 6-hydroxydopamine (6-OHDA) in the substantia nigra pars compacta (SNc), as a suitable model for the study of pain associated to Parkinson’s disease (PD). For this purpose, 14 days after unilateral injection of saline or 6-OHDA, rats were assessed for behavioral function in the cylinder test, and apomorphine-induced circling test. Thereafter, at 21st day after injection, mechanical nociceptive threshold was compared between 6-OHD-lesioned and sham-operated animals using electronic von Frey test. Our results showed that injection of 6-OHDA in the SNc induced alterations of behavioral motor as ascertained by predominant use of the ipsilateral forepaw in cylinder test and by the expression of contralateral turnings after subcutaneous injection of apomorphine. The mechanical nociceptive threshold was significantly decreased in 6-OHDA-lesioned rats compared to that of sham-operated rats (p &lt;0.05). This response was reversed by apomorphine treatment. In conclusion, hemiparkinsonian rat, obtained by the unilateral injection of the 6-OHDA in the SNc, can be used to investigate pain symptoms and central pain processing mechanisms related to PD.

The Effect of Focused Transcranial Magnetic Stimulation on Behavioral Profiles and Motor Cortex Signals in the Animal Model of Parkinsonism

Background: Non-invasive magnetic stimulation therapies have become a widespread neuromodulation method utilized in the treatment of mood disorders. Although these methods have shown efficacy in the treatment of psychiatric disorders such as bipolar affective disorder and depression, a few studies have been done on Parkinson's disease (PD). Objective: This study was executed to demonstrate the effectiveness of focused transcranial magnetic stimulation (fTMS) for the treatment of PD. For this aim, a new stimulation coil design with the semi-hexagonal core was used to concentrate magnetic flux in the particular innervation nucleus. Several TMS protocols were tested to stimulate the STN region of 6-OHDA lesioned rats to determine the most effective treatment. Results: The progress of treatment was investigated by recording and analyzing the neurophysiological activity of the primary motor cortex and locomotor behaviors. After 6-OHDA injection, sharp increases in the energy and power spectral density of beta and low- gamma band were caused. Also, the motor activities of rats reduced, and the degree of catalepsy increased significantly. By completing the proposed 1Hz r-TMS treatment, the amount of energy and power density in these bands diminished and came close to the baseline. Furthermore, debilitating motor fluctuations were reverted considerably. Conclusion: Experimental results reveal that after 40 days of the non-invasive procedure, both oscillatory activity and the locomotor behavior produce remarkable changes. The 1Hz r-TMS showed acceptable performance in a reduction of symptoms in the PD. The outcomes of the animal trials have raised some hopes to employ the findings of this study in human clinical research.