Unilateral Injection Of 6-OHDA Research Articles

AdipoRon improves mitochondrial homeostasis and protects dopaminergic neurons through activation of the AMPK signaling pathway in the 6-OHDA-lesioned rats

The progressive decline of dopaminergic neurons in Parkinson's disease (PD) has been linked to an imbalance in energy and the failure of mitochondrial function. AMP-activated protein kinase (AMPK), the major intracellular energy sensor, regulates energy balance, and damage to nigral dopaminergic neurons induced by 6-hydroxydopamine (6-OHDA) is exacerbated in the absence of AMPK activity. This study aimed to examine the potential therapeutic advantages of AdipoRon, an AMPK activator, on motor function and mitochondrial homeostasis in a 6-OHDA-induced PD model. Male Wistar rats were subjected to unilateral injection of 6-OHDA (10 μg) into the left medial forebrain bundle at two points, and after 7 days, they were treated with intranasal AdipoRon (0.1, 1, and 10 μg) or Levodopa (10 mg/kg, p. o.) for 21 successive days. Following the last treatment day, motor behavior was evaluated through the Murprogo's test, bar test, beam walking test, and apomorphine-induced rotation test. After euthanasia, the left substantia nigra (SN) was separated for evaluation of ATP, mitochondrial membrane potential (MMP), and protein expressions of AMPK, p-AMPK, and mitochondrial dynamics markers (Mfn-2 and Drp-1). Moreover, the number of tyrosine hydroxylase-positive (TH+) cells was quantified in the left substantia nigra. Intranasal AdipoRon effectively reversed muscle rigidity, akinesia, bradykinesia, and rotation caused by 6-OHDA. Moreover, AdipoRon increased the phospho-AMPK/AMPK ratio, mitigated mitochondrial dysfunction, and improved mitochondrial dynamics in the SN. Furthermore, AdipoRon increased the number of TH+ cells in the SN of PD animals. These findings suggest that AdipoRon could protect dopaminergic neurons by activating the AMPK pathway and improving mitochondrial dysfunction.

Intranasal AdipoRon Mitigated Anxiety and Depression-Like Behaviors in 6-OHDA-Induced Parkinson 's Disease Rat Model: Going Beyond Motor Symptoms.

Depression and anxiety are prevalent neuropsychiatric conditions among patients with Parkinson's disease (PD), which may manifest prior to motor symptoms. As levodopa, a prominent treatment for PD motor symptoms, provides few benefits for mood-related abnormalities, tackling non-motor symptoms is particularly important. AdipoRon (Ad), an adiponectin agonist, has demonstrated neuroprotective effects by suppressing neuroinflammatory responses and activating the AMPK/Sirt-1 signaling pathway. This study looked at the potential advantages and underlying mechanisms of intranasal Ad in a rat model of PD induced by 6-hydroxydopamine (6-OHDA). We found that Ad at doses of 1 and 10µg for 21 days exhibited anxiolytic- and antidepressant effects in the open field (OF) test, elevated plus maze (EPM), sucrose splash test, and forced swimming test in a PD model caused by a unilateral 6-OHDA injection into the medial forebrain bundle (MFB). The Ad also lowered the levels of corticosterone in the blood, decreased inflammasome components (NLRP3, caspase 1, and IL-1β), and increased Sirt-1 protein levels in the prefrontal cortex (PFC) of PD rats. We conclude that Ad ameliorates anxious and depressive-like behaviors in the PD rat model through stimulating the AMPK/Sirt-1 signaling and blocking the NLRP3 inflammasome pathways in the PFC.

The effect of growth hormone on motor findings and dendrite morphology in an experimental Parkinson's disease model.

Approaches for the induction of neurogenesis and neuronal recovery through several modalities are gaining popularity in Parkinson's disease (PD). Growth hormone (GH) seems to have a role in the reversal of neural function following brain injury as well as in normal brain development and function; therefore, the use of GH may represent a feasible strategy in the management of PD. This experimental study aimed to evaluate the effect of growth hormone on motor function and dendrite morphology in rats with 6-hydroxydopamine (6-OHDA)-induced PD model. Thirty-six Sprague Dawley rats were included and randomly allocated into one of the six study groups: two controls and four treatment groups that received daily subcutaneous growth hormone injections for 21days, 1, 2, and 3months. PD model was induced through unilateral 6-OHDA injection to the nigrostriatal pathway. The following assessments were made: apomorphine rotation test, stepping test, and tissue examinations for tyrosine hydroxylase and dendrite morphology. The apomorphine rotation test and the stepping test confirmed the presence of PD. These tests as well as dendritic spine density/number and length assessments showed improvement in PD findings over time with GH administration. Findings of this study suggest that GH administration may improve dendrite morphology and motor function in the PD model, which may translate into symptom relief and quality of life improvement in patients with PD. Such potential benefits should be tested in robust clinical studies.

Inspiratory Neural Network Complexity Quantified by Approximate Entropy (ApEn) Analysis in SN 6-OHDA-induced Rat Model of Parkinson’s Disease

Parkinson’s disease (PD) is a multifaceted chronic and progressive neurodegenerative disease that includes a broad range of motor and non-motor symptoms (NMS). Breathing abnormalities are a common NMS in PD, and despite respiratory dysfunction being a major problem in PD as well as respiratory complications being the most common cause of death in PD patients, this NMS receives little attention. Over the last decade, a number of preclinical experimental rat models of PD generated by nigrostriatal site-targeted administration of the neurotoxin 6-hydroxydopamine (6-OHDA) have been used to evaluate various aspects of ventilatory control in PD. While all of these models have been shown to exhibit basal and chemical control of breathing abnormalities that are consistent with those in clinical reports, no studies have assessed the complex intrinsic dynamics that are associated with the central inspiratory neural network in PD. Since preclinical rat models of PD have also been shown exhibit neuroanatomical changes in brainstem regions involved in ventilatory control, it is likely that changes in inspiratory neural network dynamics, which can be assessed using nonlinear dynamical analysis methods, are also present in PD. To begin to assess this possibility, we quantified the complexity of 20 consecutive inspiratory (diaphragm EMG) bursts recorded during basal breathing in urethane-anesthetized spontaneously breathing adult female rats at 4-weeks after unilateral injection of 6-OHDA (n=18) or vehicle (VEH; n=14) directly into the substantia nigra (SN). For these analyses, we calculated approximate entropy (ApEn), which provides a statistical measure of regularity (orderliness) of a signal in the time domain, with values for the embedding dimension m and the tolerance r set to m=3 and r=0.44 SD. ApEn values were significantly higher in 6-OHDA-injected rats compared to VEH-injected rats (0.6169±0.0069 vs 0.5894±0.0087; P=0.017) albeit TI and Tpeak/TI were similar in both groups (TI: 305.8±9.5 vs 300.0±12.7 ms, P=0.713; Tpeak/TI: 51.0±1.3 vs 51.3±1.1%, P=0.904). Other significant differences in temporal features included higher breathing frequencies (93.4±2.4 vs 82.0±3.2 bpm; P=0.007), reduced TE (in ms: 334.7±12.7 vs 445.5±27.4; P=0.001), and decreased inspiratory duty cycle (in %: 47.2±1.1 vs 40.8±2.0; P=0.006) in 6-OHDA (compared to VEH)-injected rats. These observations suggest that respiratory dysfunction in PD is also accompanied by reorganization of the central inspiratory neural network that is associated with greater irregularity or less system order. Additional experiments are needed to identify the precise neural mechanisms underlying this higher system complexity. NIH NS101737; Thomas Hartman Center for Parkinson's Disease Research at Stony Brook University. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Analysis of Targeted Therapy of Parkinson’s Disease with Coloaded Nanoparticles

The key to the treatment of Parkinson’s disease (PD) is delivering an effective amount of drugs into the brain to work, and supplementing the missing dopamine (Dop) in the brain is still the most effective treatment currently. In this research, borneol (Bor) was utilized to promote the drug to enter the brain through the nasal cavity, and lactoferrin (Lf) was utilized as the targeting molecule to modify the nanoparticles (NPs) so that they entered the brain and focused on the lesion site of PD to achieve targeting. They were then evaluated in vivo and in vitro, thus providing the basis for the development of the Lac-Bor/Dop NPs in PD therapy. In the experiment, the particle size of Lac-Bor/Dop NPs prepared by the optimal prescription process was 163.7±15.6 nm, the Dop drug loading was (7.86±1.68) %, and the Zeta potential was (−21.36±3.34) mV. The in vitro release confirmed that the Lac-Bor/Dop NPs had good sustained release characteristics in PBS medium. The cytotoxicity and uptake experiments confirmed that the cytotoxicity of Dop encapsulated in NPs was markedly inferior to that of free Dop (P <0.05). For SH-SY5Y cells and 16HBE cells, Bor and Lf co-modified NPs can promote cell uptake. In vivo animal imaging counts confirmed that the coloaded NPs were capable of synergistic nasal drug delivery to the brain for better brain targeting. Furthermore, a PD model induced by dopaminergic neuron injury induced by unilateral striatal injection of 6-OHDA was constructed in rats and assigned into various groups to demonstrate the therapeutic effect of NPs on PD rats. The results revealed that relative to other groups, the contralateral rotations of rats in the Lac-Bor/Dop NP group were decreased drastically after 20 days of administration (P <0.01), and the levels of Dop and dihydroxyphenylacetic acid (DOPAC) in the injured striatum were increased markedly (P <0.01), demonstrating that the delivery system could achieve excellent PD therapy effects after nasal administration.

Pioglitazone enhances brain mitochondrial biogenesis and phase II detoxification capacity in neonatal rats with 6-OHDA-induced unilateral striatal lesions.

The psychostimulant methylphenidate (MPH) is the first-line pharmacological treatment for attention-deficit/hyperactivity disorder (ADHD), but has numerous adverse side effects. The PPARγ receptor agonist pioglitazone (PIO) is known to improve mitochondrial bioenergetics and antioxidant capacity, both of which may be deficient in ADHD, suggesting utility as an adjunct therapy. Here, we assessed the effects of PIO on ADHD-like symptoms, mitochondrial biogenesis and antioxidant pathways in multiple brain regions of neonate rats with unilateral striatal lesions induced by 6-hydroxydopamine (6-OHDA) as an experimental ADHD model. Unilateral striatal injection of 6-OHDA reduced ipsilateral dopaminergic innervation by 33% and increased locomotor activity. This locomotor hyperactivity was not altered by PIO treatment for 14 days. However, PIO increased the expression of proteins contributing to mitochondrial biogenesis in the striatum, hippocampus, cerebellum and prefrontal cortex of 6-OHDA-lesioned rats. In addition, PIO treatment enhanced the expression of the phase II transcription factor Nrf2 in the striatum, prefrontal cortex and cerebellum. In contrast, no change in the antioxidant enzyme catalase was observed in any of the brain regions analyzed. Thus, PIO may improve mitochondrial biogenesis and phase 2 detoxification in the ADHD brain. Further studies are required to determine if different dose regimens can exert more comprehensive therapeutic effects against ADHD neuropathology and behavior.

Activation and polarization of striatal microglia and astrocytes are involved in bradykinesia and allodynia in early-stage parkinsonian mice

In addition to the cardinal motor symptoms, pain is a major non-motor symptom of Parkinson's disease (PD). Neuroinflammation in the substantia nigra pars compacta and dorsal striatum is involved in neurodegeneration in PD. But the polarization of microglia and astrocytes in the dorsal striatum and their contribution to motor deficits and hyperalgesia in PD have not been characterized. In the present study, we observed that hemiparkinsonian mice established by unilateral 6-OHDA injection in the medial forebrain bundle exhibited motor deficits and mechanical allodynia. In these mice, both microglia and astrocytes in the dorsal striatum were activated and polarized to M1/M2 microglia and A1/A2 astrocytes as genes specific to these cells were upregulated. These effects peaked 7 days after 6-OHDA injection. Meanwhile, striatal astrocytes in parkinsonian mice also displayed hyperpolarized membrane potentials, enhanced voltage-gated potassium currents, and dysfunction in inwardly rectifying potassium channels and glutamate transporters. Systemic administration of minocycline, a microglia inhibitor, attenuated the expression of genes specific to M1 microglia and A1 astrocytes in the dorsal striatum (but not those specific to M2 microglia and A2 astrocytes), attenuated the damage in the nigrostriatal dopaminergic system, and alleviated the motor deficits and mechanical allodynia in parkinsonian mice. By contrast, local administration of minocycline into the dorsal striatum of parkinsonian mice mitigated only hyperalgesia. This study suggests that M1 microglia and A1 astrocytes in the dorsal striatum may play important roles in the development of pathophysiology underlying hyperalgesia in the early stages of PD.

Treadmill exercise modulates nigral and hippocampal cannabinoid receptor type 1 in the 6-OHDA model of Parkinson’s disease

Physical exercise benefits Parkinson’s disease (PD) patients but the mechanism is unclear. Cannabinoid receptor type 1 (CB1R) is known to be reduced in PD patients and animal models. We test the hypothesis that binding of the CB1R inverse agonist, [3H]SR141716A, is normalized by treadmill exercise in the toxin-induced 6-hydroxydopamine (6-OHDA) model of PD. Male rats had unilateral striatal injections of 6-OHDA or saline. After 15 days, half were submitted to treadmill exercise and half remained sedentary. [3H]SR141716A autoradiography was performed in postmortem tissue from striatum, substantia nigra (SN) and hippocampus. There was a 41% decrease of [3H]SR141716A specific binding in the ipsilateral SN of 6-OHDA-injected sedentary animals which was attenuated to 15% by exercise, when compared to saline-injected animals. No striatal differences were observed. A 30% bilateral hippocampal increase was observed in both healthy and 6-OHDA exercised groups. In addition, a positive correlation between nigral [3H]SR141716A binding and nociceptive threshold was observed in PD-exercised animals (p = 0.0008), suggesting a beneficial effect of exercise in the pain associated with the model. Chronic exercise can reduce the detrimental effects of PD on nigral [3H]SR141716A binding, similar to the reported reduction after dopamine replacement therapy, so should be considered as an adjunct therapy for PD.

Subthalamic neurons interact with nigral dopaminergic neurons to regulate movement in mice.

This study aims to address the role of the interaction between subthalamic (STN) neurons and substantia nigra pars compacta (SNc) dopaminergic (DA) neurons in movement control. Fiber photometry and optogenetic/chemogenetic techniques were utilized to monitor and manipulate neuronal activity, respectively. Locomotion in mice was recorded in an open field arena and on a head-fixed apparatus. A hemiparkinsonian mouse model was established by unilateral injection of 6-OHDA in the medial forebrain bundle. Whole-cell patch-clamp techniques were applied to record electrophysiological signals in STN neurons and SNc DA neurons. c-Fos-immunostaining was used to label activated neurons. A rabies virus-based retrograde tracing system was used to visualize STN neurons projecting to SNc DA neurons. The activity of STN neurons was enhanced upon locomotion in an open field arena and on a head-fixed apparatus, and the enhancement was significantly attenuated in parkinsonian mice. Optogenetic stimulation of STN neurons enhanced locomotion, increased activity of SNc DA neurons, meanwhile, reduced latency to movement initiation. Combining optogenetics with patch-clamp recordings, we confirmed that STN neurons innervated SNc DA neurons through glutamatergic monosynaptic connections. Moreover, STN neurons projecting to SNc DA neurons were evenly distributed in the STN. Either 6-OHDA-lesion or chemogenetic inhibition of SNc DA neurons attenuated the enhancement of locomotion by STN stimulation. SNc DA neurons not only affect the response of STN neurons to movement, but also contribute to the enhancement of movement by STN stimulation. This study demonstrates the role of STN-SNc interaction in movement control.

Longitudinal assessment of motor function following the unilateral intrastriatal 6-hydroxydopamine lesion model in mice.

Despite the widespread use of the unilateral striatal 6-hydroxydopamine (6-OHDA) lesion model in mice in recent years, the stability of behavioral deficits in the 6-OHDA striatal mouse model over time is not yet clear, raising concerns about using this model to evaluate a compound's long-term therapeutic effects. In the current study, mice were tested at regular intervals in the cylinder test and gait analysis beginning 3 days after 6-OHDA injection of 4 and 8 μg and lasting until 56 days post-lesion. Apomorphine-induced rotational test and rotarod test were also performed on Day 23 and 43 post-lesion, respectively. Immunohistochemistry for dopaminergic neurons stained by tyrosine hydroxylase (TH) was also performed. Our results showed that both the 4 and 8 μg 6-OHDA lesion groups exhibited forelimb use asymmetry with a preference for the ipsilateral (injection) side on Day 3 and until Day 21 post-lesion, but did not show forelimb asymmetry on Day 28 to 56 post-lesion. The 8 μg 6-OHDA lesion group still exhibited forelimb asymmetry on Day 28 and 42 post-lesion, but not on Day 56. The gait analysis showed that the contralateral front and hind step cycles increased from Day 3 to 42 post-lesion and recovered on Day 56 post-lesion. In addition, our results displayed a dose-dependent reduction in TH+ cells and TH+ fibers, as well as dose-dependent apomorphine-induced rotations. In the rotarod test, the 8 μg 6-OHDA lesion group, but not the 4 μg group, decreased the latency to fall on the rotarod on Day 43 post-lesion. In summary, unilateral striatal 6-OHDA injections of 4 and 8 μg induced spontaneous motor impairment in mice, which partially recovered starting on Day 28 post-lesion. Forced motor deficits were observed in the 8 g 6-OHDA lesion group, which remained stable on Day 43 post-lesion. In addition, the rotarod test and apomorphine-induced rotational test can distinguish between lesions of different extents and are useful tools for the assessment of functional recovery in studies screening novel potential therapies.

Chronic Cerebral Hypoperfusion Aggravates Parkinson's Disease Dementia-Like Symptoms and Pathology in 6-OHDA-Lesioned Rat through Interfering with Sphingolipid Metabolism.

Chronic cerebral hypoperfusion (CCH) is a cardinal risk factor for Parkinson's disease dementia (PDD), but this potential causality lacks mechanistic evidence. We selected bilateral common carotid artery occlusion (BCCAO) to simulate chronic cerebral hypoperfusion in the rat model of PD induced by typical neurotoxin 6-hydroxy dopamine (6-OHDA). Four weeks after unilateral injection of 6-OHDA into the medial forebrain bundle, rats underwent BCCAO. Male Sprague-Dawley rats were divided into five groups of ten, including sham, PD+BCCAO 2 weeks, PD+BCCAO 1 week, PD, and BCCAO 2 weeks. Then, open field test (OFT) and Morris water maze test (MWM) were used to assess the PDD-like symptoms in rats. Also, the pathological manifestations and mechanisms of BCCAO impairing cognitive functions have been explored via hematoxylin-eosin staining, Nissl staining, immunohistochemistry, immunofluorescence, RNA sequencing analysis, lipidomics, and quantitative real-time polymerase chain reaction. In this study, we found that CCH could aggravate PDD-like cognitive symptoms (i.e., learning memory and spatial cognition) and PDD-like pathology (higher expression of α-Syn and Aβ in prefrontal cortex and striatum). Moreover, a potential relationship between differentially expressed mRNAs and lipid metabolism was revealed by RNA sequencing analysis. Lipidomics showed that CCH could affect the intensity of 5 lipids, including sphingomyelin (SM 9:0;2O/26:2; SM 8:1;2O/25:0; and SM 8:0;2O/28:4), cardiolipin, lysophosphatidylcholine, cholesteryl ester, and triacylglycerol. Interestingly, the KEGG pathway analysis of both RNA sequencing analysis and lipidomics suggested that CCH leaded to learning impairment by affecting sphingolipid metabolism. Finally, we found that CCH disrupts the sphingolipid metabolism by affecting the mRNA expression of SMPD1 and SMS2, leading to the accumulation of sphingomyelin in the prefrontal cortex. In summary, CCH, an independent exacerbating reason for impairment in learning and memory within the pathopoiesis of PD, aggravates Parkinson's disease dementia-like symptoms and pathology in 6-OHDA-lesioned rat through interfering with sphingolipid metabolism.

Basal and Hypoxic Respiratory Behaviors in Aged 6‐OHDA‐Induced SN Lesion PD Rat Model: Effects of the 5‐HT1A Receptor Agonist Buspirone

Parkinson’s disease (PD) is progressive neurodegenerative disease, with the diagnosis of idiopathic PD occurring in humans at ~60 years of age. Most studies, however, use young adult (≤3 month old) rats to investigate PD‐related abnormalities in various physiological systems, with the most commonly used experimental rat PD model being generated by unilateral injection of the neurotoxin 6‐hydroxydopamine (6‐OHDA) into specific regions of the nigrostriatal pathway. While this model results in the loss of dopaminergic neurons and the subsequent changes in downstream neurotransmitter signaling that are characteristic of PD, it does not consider potential contributions of physical changes to the brain and neurotransmitter signaling that are part of normal aging on the progression of PD. To better understand age‐related influences and potential contributions of PD‐related abnormalities in serotonergic (5‐HT) neurotransmission on respiratory dysfunction (which is a common non‐motor symptom) in PD, we investigated basal and hypoxic (12% O2; 90s) respiratory behaviors before and after acute administration of the frequently prescribed anxiolytic 5‐HT1A receptor agonist buspirone (BUS; 0.5 mg/kg, iv) in an aged (~9 month old) female Sprague‐Dawley PD rat model produced by unilateral 6‐OHDA injection into the substantia nigra (SN). For these experiments, diaphragm EMG activity was recorded and quantified from spontaneously breathing urethane‐anesthetized rats at 2‐weeks after SN 6‐OHDA or vehicle (control) injections. We found that 6‐OHDA‐injected rats have a lower basal breathing frequency (P<0.05) due to shorter expiratory duration (TE; P<0.05) than vehicle‐injected rats, but both 6‐OHDA‐ and vehicle‐injected rats exhibit significant increases in breathing frequency (P≤0.001) and EMG amplitude (P≤0.023) during hypoxia; the magnitude of the peak frequency increase in 6‐OHDA‐injected rats was slightly greater (P=0.083). Both 6‐OHDA‐ and vehicle‐injected rats also showed similar post‐hypoxic frequency decline (P≤0.003), but only vehicle‐injected rats displayed a slight and sustained post‐hypoxic amplitude depression (P<0.1). In vehicle‐injected rats, acute BUS injection produced a progressive decrease in basal EMG amplitude (P=0.066) and a persistent increase in breathing frequency (P=0.064) by decreasing inspiratory duration (TI; P<0.001) while in 6‐OHDA‐injected rats, a transient initial increase in EMG amplitude (P=0.043) and a persistent decrease in TI (P=0.005) and TE (P=0.089) were noted. In both 6‐OHDA‐ and vehicle‐injected rats, BUS injection also slightly exaggerated the initial hypoxic frequency increase, but blunted the amplitude increase with amplitude progressively declining to near pre‐hypoxic levels before the end of the hypoxic exposure. BUS injection also shortened the duration of post‐hypoxic EMG amplitude depression in vehicle‐injected rats. These data demonstrate that some differences in basal and hypoxic respiratory behaviors exist between older 6‐OHDA‐ and vehicle‐injected rats, and that some respiratory behaviors of these rat models are differentially impacted by BUS‐induced effects on respiratory control. We suggest that this older PD rat model be further evaluated.

Reaching Task in Rats: Quantitative Evaluation and Effects of 6-OHDA into the Striatum

In this study, we developed an evaluation method using image analysis for reaching tasks. Using this method, we studied forearm function during the reaching task in rats that received a unilateral injection of 6-OHDA into the striatum. The success ratio of the reaching task reduced to 40.5% seven days after the injection. In addition, significant changes were observed in the pronation angle of the forearm, posture control, and targeting (i.e., the distance between all fingertips and the center of the target pellet). Thus, unilateral injection of 6-OHDA reduces dopaminergic function in the brain and causes deterioration of forearm function and posture control in the reaching task.

Severity Assessment of Complex and Repeated Intracranial Surgery in Rats

Introduction: Evidence-based grading of the impact of intracranial surgery on rat’s well-being is important for ethical and legal reasons. We assessed the severity of complex and repeated intracranial surgery in a 6-hydroxydopamine (6-OHDA) Parkinson’s rat model with subsequent intracranial electrode implantation and in an intracranial tumor model with subsequent resection. Methods: Stereotactic surgery was performed in adult male rats with the same general anesthesia and perioperative pain management. In Parkinson’s model, Sprague Dawley rats received unilateral injection of 6-OHDA (n = 11) or vehicle (n = 7) into the medial forebrain bundle as first operation (1st OP). After four weeks, neural electrodes were implanted in all rats as second operation (2nd OP). For tumor formation, BDIX/UlmHanZtm rats (n = 8) received frontocortical injection of BT4Ca cells as 1st OP, followed by tumor resection as 2nd OP after one week. Multiple measures severity assessment was done two days before and four days after surgery in all rats, comprising clinical scoring, body weight, and detailed behavioral screening. To include a condition with a known burden, rats with intracranial tumors were additionally assessed up to a predefined humane endpoint that has previously been classified as “moderate”. Results: After the 1st OP, only 6-OHDA injection resulted in transient elevated clinical scores, a mild long-lasting weight reduction, and motor disturbances. After the second surgery, body weight was transiently reduced in all groups. All other parameters showed variable results. Principal component analysis showed a separation from the preoperative state driven by motor-related parameters after 6-OHDA injection, while separation after electrode implantation and more clearly after tumor resection was driven by pain-related parameters, although not reaching the level of the humane endpoint of our tumor model. Conclusion: Overall, cranial surgery of different complexity only transiently and rather mildly affects rat’s well-being. Multiple measures assessment allows the differentiation of model-related motor disturbances in Parkinson’s model from potentially pain-related conditions after tumor resection and electrode implantation.

Role of toll-like receptor 4 and sex in 6-hydroxydopamine–induced behavioral impairments and neurodegeneration in mice

Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive loss of the nigrostriatal dopaminergic neurons that are associated with motor alterations and non-motor manifestations (such as depression). Neuroinflammation is a process with a critical role in the pathogenesis of PD. In this regard, toll-like receptor 4 (TLR4) is a central mediator of immune response in PD. Moreover, there are gender-related differences in the incidence, prevalence, and clinical features of PD. Therefore, we aimed to elucidate the role of TLR4 in the sex-dependent response to dopaminergic denervation induced by 6-hydroxydopamine (6-OHDA) in mice. Female and male adult wildtype (WT) and TLR4 knockout (TLR4−/−) mice were administered with unilateral injection of 6-OHDA in the dorsal striatum, and non-motor and motor impairments were evaluated for 30 days, followed by biochemistry analysis in the substantia nigra pars compacta (SNc), dorsal striatum, and dorsoventral cortex. Early non-motor impairments (i.e., depressive-like behavior and spatial learning deficits) induced by 6-OHDA were observed in the male WT mice but not in male TLR4−/− or female mice. Motor alterations were observed after administration of 6-OHDA in both strains, and the lack of TLR4 was also related to motor commitment. Moreover, ablation of TLR4 prevented 6-OHDA–induced dopaminergic denervation and microgliosis in the SNc, selectively in female mice. These results reinforced the existence of sex-biased alterations in PD and indicated TLR4 as a promising therapeutic target for the motor and non-motor symptoms of PD, which will help counteract the neuroinflammatory and neurodegenerative processes.

Antinociceptive effect of melatonin in the animal model of Parkinson’s Disease

Several animal experimental and clinical studies have shown the effectiveness of melatonin in the treatment of some symptoms of Parkinson's disease (PD). However, the antinociceptive effect of melatonin against pain associated to PD has not been fully investigated. Thus, the present study investigated the possible antiallodynic and antinociceptive effects of acute and chronic melatonin treatments in Parkinsonian model of rats. This model was created by unilateral injection of 6-hydroxydopamine (6-OHDA) into the left medial forebrain bundle (MFB). The electronic von Frey test was used to analyze the antiallodynic effect of melatonin on this PD animal model. In addition, c-Fos immunostaining was also used as a marker of nociception to evaluate the neuronal activity related to the nociception processing. The results showed that unilateral injection of 6-OHDA induced a significant decrease in paw withdrawal threshold in both ipsilateral and contralateral paws, which indicate mechanical allodynia induction. This allodynia was transitorily reversed by apomorphine as a dopamine agonist. Melatonin treatment significantly increased threshold of allodynia. Melatonin administration of both acutely or chronically significantly downregulated the c-Fos expression of neurons in 6-OHDA treated animals. In conclusion, 6-OHDA treatment can induces a bilateral mechanical hypernociception in rats while melatonin treatment produces profound antinociceptive effect. This finding paves the way to use melatonin as an antinociceptive agent for PD clinically.

Neuroprotective Effect of Intrastriatal Caffeic Acid Phenethyl Ester Treatment in 6-OH Dopamine Model of Parkinson's Disease in Rats.

Parkinson's disease (PD) is the second most common neurodegenerative disorder, and the main cause of PD is still not known. Until now, no cure for Parkinson's disease is yet in sight. Caffeic acid phenethyl ester (CAPE) is a polyphenolic component of the propolis, which can be derived from honeybee hive propolis. We aimed to determine the effect of intrastriatal CAPE administration as a neuroprotective agent on 6-hydroxydopamine (6-OHDA)-induced PD model. Adult male Wistar rats weighing 280–320 g were used. The PD model was induced with unilateral intrastriatal 6-OHDA injection. Treatment groups received 20 μmol/5 μL/4 day and 80 μmol/5 μL/4 day CAPE 24 h after 6-OHDA injection. Eight days after 6-OHDA application, behavioral studies (adhesive tape removal test, open-field test, cylinder test, and apomorphine-induced asymmetric rotational behavior) were performed once more to compare the effects of CAPE on behavior tests. Striatal histological verifications, immunohistochemistry, and stereological quantitation were performed. Our results for the first time showed that, besides improving the motor performance, CAPE treatment also prevents 6-OHDA-induced loss of TH-positive neurons. From our results, CAPE may be a promising clinical agent in the treatment of PD.

Study of the Effect of Concurrent Therapy of Spironolactone With Levodopa on Depression Disorder in Male Rats

Background: Depression has a high prevalence and high mortality and a tremendous negative impact on people’s quality of life. This study was considered to examine the effect of levodopa and spironolactone (SPIR) in 6-hydroxydopamine (6-OHDA)-induced depression-like behavior. Methods: Parkinson was induced by the unilateral intra-nigral injection of 6-OHDA (8 µg/2 µL/rat) in the central region of the substantia nigra pars compacta (SNc). In the levodopa treatment group, 21 days after the injection of 6-OHDA, the rats were treated with (i.p.) injections of levodopa (15 mg/kg) for 14 consecutive days. In the other group, only SPIR (25 mg/kg) was added to levodopa (15 mg/kg) as a concurrent therapy according to the treatment protocol. Anxiety and depression-like behavior were assessed by behavioral tests such as passive avoidance task (PAT), open field test (OFT), tail suspension test (TST), and forced swimming test (FST). Results: Intra-nigral injection of 6-OHDA in the SNc increased anxiety and depression-like behavior. Our results showed that the use of levodopa (15 mg/kg) treatment significantly attenuated depression-like behavior induced by 6-OHDA in FST (P<0.001) and TST (P<0.001) in rats. Moreover, levodopa (15 mg/kg) + SPIR (25 mg/kg) significantly reduced the symptoms of depression-like behavior induced by 6-OHDA in OFT (P<0.05), FST (P<0.001), and TST (P<0.001) tests in rats. Conclusion: Based on the findings, the intra-nigral injection of 6-OHDA into rats could cause anxiety and depression-like behavior in the fourth week onwards. Treatment with levodopa was able to attenuate stress and depressive symptoms. Additionally, our results revealed that SPIR could improve the effect of levodopa on depression-like behavior. Base on the results of this study, it is suggested that levodopa and SPIR could have some improving effects on 6-OHDA-induced depression-like behavior in parkinsonian rats.

Scorpion venom heat-resistant synthesized peptide ameliorates 6-OHDA-induced neurotoxicity and neuroinflammation: likely role of Nav 1.6 inhibition in microglia.

Microglia-related inflammation is associated with the pathology of Parkinson's disease. Functional voltage-gated sodium channels (VGSCs) are involved in regulating microglial function. Here, we aim to investigate the effects of scorpion venom heat-resistant synthesized peptide (SVHRSP) on 6-hydroxydopamine (6-OHDA)-induced Parkinson's disease-like mouse model and reveal its underlying mechanism. Unilateral brain injection of 6-OHDA was performed to establish Parkinson's disease mouse model. After behaviour test, brain tissues were collected for morphological analysis and protein/gene expression examination. Primary microglia culture was used to investigate the role of sodium channel Nav 1.6 in the regulation of microglia inflammation by SVHRSP. SVHRSP treatment attenuated motor deficits, dopamine neuron degeneration, activation of glial cells and expression of pro-inflammatory cytokines induced by 6-OHDA lesion. Primary microglia activation and the production of pro-inflammatory cytokines induced by lipopolysaccharide (LPS) were also suppressed by SVHRSP treatment. In addition, SVHRSP could inhibit mitogen-activated protein kinases (MAPKs) pathway, which plays pivotal roles in the pro-inflammatory response. Notably, SVHRSP treatment suppressed the overexpression of microglial Nav 1.6 induced by 6-OHDA and LPS. Finally, it was shown that the anti-inflammatory effect of SVHRSP in microglia was Nav 1.6 dependent and was related to suppression of sodium current and probably the consequent Na+ /Ca2+ exchange. SVHRSP might inhibit neuroinflammation and protect dopamine neurons via down-regulating microglial Nav 1.6 and subsequently suppressing intracellular Ca2+ accumulation to attenuate the activation of MAPKs signalling pathway in microglia.

Fluoxetine tunes the abnormal hippocampal oscillations in association with cognitive impairments in 6-OHDA lesioned rats

Cognitive decline is a common clinical symptom in Parkinson’s disease (PD) patients. Fluoxetine (FLU), a selective serotonin reuptake inhibitor, can improve cognitive deficits in demented patients. The present study investigated the effects of FLU on spatial learning and memory cognitions in 6-OHDA lesioned rats. Morris water maze (MWM) test showed that FLU significantly improved spatial cognitive deficits in rats with unilateral 6-OHDA injection at 4 and 7 weeks after 6-OHDA injection. Electrophysiological recordings demonstrated that the number and duration of high voltage spindles(HVSs)in the ipsilateral hippocampus of 6-OHDA lesioned rats were decreased by the administration of FLU. Furthermore, the spectral analysis of per frequency revealed increases in δ and θ rhythm power and decreases in α, β and γ rhythm power in the ipsilateral hippocampus of 6-OHDA lesioned rats in contrast to the saline-treated rats. Acute FLU treatment can reduce δ and θ rhythm power, and enhance α, β and γ rhythm power in the ipsilateral hippocampus of 6-OHDA lesioned rats. These findings suggest that FLU improves impaired cognition by tuning oscillatory activities in the hippocampus of 6-OHDA lesioned rats.