Differential Activation States of Direct Pathway Striatal Output Neurons during l-DOPA-Induced Dyskinesia Development.

l-DOPA-induced dyskinesia (LID) is a debilitating motor side effect arising from chronic dopamine (DA) replacement therapy with l-DOPA for the treatment of Parkinson's disease. LID is associated with supersensitivity of striatal dopaminergic signaling and fluctuations in synaptic DA following each l-DOPA dose, shrinking the therapeutic window. The heterogeneous composition of the striatum, including subpopulations of medium spiny output neurons (MSNs), interneurons, and supporting cells, complicates the identification of cell(s) underlying LID. We used single-nucleus RNA sequencing (snRNA-seq) to establish a comprehensive striatal transcriptional profile during LID development. Male hemiparkinsonian mice were treated with vehicle or l-DOPA for 1, 5, or 10 d, and striatal nuclei were processed for snRNA-seq. Analyses indicated a limited population of DA D1 receptor-expressing MSNs (D1-MSNs) formed three subclusters in response to l-DOPA treatment and expressed cellular markers of activation. These activated D1-MSNs display similar transcriptional changes previously associated with LID; however, their prevalence and transcriptional behavior were differentially influenced by l-DOPA experience. Differentially expressed genes indicated acute upregulation of plasticity-related transcription factors and mitogen-activated protein kinase signaling, while repeated l-DOPA-induced synaptic remodeling, learning and memory, and transforming growth factor-ß (TGF-ß) signaling genes. Notably, repeated l-DOPA sensitized Inhba, an activin subunit of the TGF-ß superfamily, in activated D1-MSNs, and its pharmacological inhibition impaired LID development, suggesting that activin signaling may play an essential role in LID. These data suggest distinct subsets of D1-MSNs become differentially l-DOPA-responsive due to aberrant induction of molecular mechanisms necessary for neuronal entrainment, similar to processes underlying hippocampal learning and memory.

The Therapeutic Frequency Profile of Subthalamic Nucleus Deep Brain Stimulation in Rats Is Shaped by Antidromic Spike Failure.

The therapeutic mechanisms of subthalamic nucleus (STN) deep brain stimulation (DBS) may depend on antidromic activation of cortex via the hyperdirect pathway. However, hyperdirect pathway neurons cannot reliably follow high-stimulation frequencies, and the spike failure rate appears to correlate with symptom relief as a function of stimulation frequency. We hypothesized that antidromic spike failure contributes to the cortical desynchronization caused by DBS. We measured in vivo evoked cortical activity in female Sprague Dawley rats and developed a computational model of cortical activation from STN DBS. We modeled stochastic antidromic spike failure to determine how spike failure affected the desynchronization of pathophysiological oscillatory activity in cortex. We found that high-frequency STN DBS desynchronized pathologic oscillations via the masking of intrinsic spiking through a combination of spike collision, refractoriness, and synaptic depletion. Antidromic spike failure shaped the parabolic relationship between DBS frequency and cortical desynchronization, with maximum desynchronization at ∼130 Hz. These findings reveal that antidromic spike failure plays a critical role in mediating the dependency of symptom relief on stimulation frequency.SIGNIFICANCE STATEMENT Deep brain stimulation (DBS) is a highly effective neuromodulation therapy, yet it remains uncertain why conventionally used stimulation frequencies (e.g., ∼130 Hz) are optimal. In this study, we demonstrate a potential explanation for the stimulation frequency dependency of DBS through a combination of in vivo experimental measurements and computational modeling. We show that high-frequency stimulation can desynchronize pathologic firing patterns in populations of neurons by inducing an informational lesion. However, sporadic spike failure at these high frequencies limits the efficacy of the informational lesion, yielding a parabolic profile with optimal effects at ∼130 Hz. This work provides a potential explanation for the therapeutic mechanism of DBS, and highlights the importance of considering spike failure in mechanistic models of DBS.

Byrsonima sericea Ethanol Extract Protected PC12 Cells from the Oxidative Stress and Apoptosis Induced by 6-Hydroxydopamine.

Parkinson's disease is characterized by the progressive loss of dopaminergic neurons in the nigrostriatal pathway and oxidative stress is one of the main mechanisms that lead to neuronal death in this disease. Previous studies have shown antioxidant activity from the leaves of Byrsonima sericea, a plant of the Malpighiaceae family. This study aimed to evaluate the cytoprotective activity of the B. sericea ethanolic extract (BSEE) against the cytotoxicity induced by 6-hydroxydopamine (6-OHDA) in PC12 cells, an in vitro model of parkinsonism. The identification of phenolic compounds in the extract by HPLC-DAD revealed the presence of geraniin, rutin, isoquercetin, kaempferol 3-O-ß-rutinoside, and quercetin. The BSEE (75-300 µg/mL) protected PC12 cells from toxicity induced by 6-OHDA (25 µg/mL), protected cell membrane integrity and showed antioxidant activity. BSEE was able to decrease nitrite levels, glutathione depletion, and protect cells from 6-OHDA-induced apoptosis. Thus, we suggest that the BSEE can be explored as a possible cytoprotective agent for Parkinson's disease due to its high antioxidant capacity and anti-apoptotic action.

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 10 µg 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-1ß), 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.

GPR40 agonist ameliorates neurodegeneration and motor impairment by regulating NLRP3 inflammasome in Parkinson's disease animal models.

Parkinson's disease (PD) is characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra (SN) and accumulation of intracellular α-synuclein (ɑ-syn) aggregates known as Lewy bodies and Lewy neurites. Levels of polyunsaturated fatty acids (PUFAs) have previously been shown to be reduced in the SN of PD patients. G protein-coupled receptor 40 (GPR40) serves as a receptor for PUFAs, playing a role in neurodevelopment and neurogenesis. Additionally, GPR40 has been implicated in several neuropathological conditions, such as apoptosis and inflammation, suggesting its potential as a therapeutic target in PD. In this study, we investigated the neuroprotective effects of the GPR40 agonist, TUG469 in PD models. Our results demonstrated that TUG469 reduces the neurotoxicity induced by 6-OHDA in SH-SY5Y cells. In 6-OHDA-induced PD model mice, TUG469 treatment improved motor impairment, preserved dopaminergic fibers and cell bodies in the striatum (ST) or SN, and attenuated 6-OHDA-induced microgliosis and astrogliosis in the brain. Furthermore, in a PD model involving the injection of mouse ɑ-syn fibrils into the brain (mPFFs-PD model), TUG469 treatment reduced the levels of pSer129 ɑ-syn, and decreased microgliosis and astrogliosis. Our investigation also revealed that TUG469 modulates inflammasome activation, apoptosis, and autophagy in the 6-OHDA-PD model, as evidenced by the results of RNA-seq and western blotting analyses. In summary, our findings highlight the neuroprotective effects of GPR40 agonists on dopaminergic neurons and their potential as therapeutic agents for PD. These results underscore the importance of targeting GPR40 in PD treatment, particularly in mitigating neuroinflammation and preserving neuronal integrity.

Selenoprotein T, a potential treatment of attention-deficit/hyperactivity disorder and comorbid pain in neonatal 6-OHDA lesioned mice.

pathological pain and Attention-deficit/hyperactivity disorder (ADHD) are two complex multifactorial syndromes. The comorbidity of ADHD and altered pain perception is well documented in children, adolescents, and adults. According to pathophysiological investigations, the dopaminergic system's dysfunction provides a common basis for ADHD and comorbid pain. Growing evidence suggests that oxidative stress may be crucial in both pathologies. Recent studies revealed that a small peptide encompassing the redox-active site of selenoprotein T (PSELT), protects dopaminergic neurons and fibers as well as lesioned nerves in animal models. The current study aims to examine the effects of PSELT treatment on ADHD-like symptoms and pain sensitivity, as well as the role of catecholaminergic systems in these effects. Our results demonstrated that intranasal administration of PSELT reduced the hyperactivity in the open field, decreased the impulsivity displayed by 6-OHDA-lesioned male mice in the 5-choice serial reaction time task test and improved attentional performance. In addition, PSELT treatment significantly increased the nociception threshold in both normal and inflammatory conditions. Furthermore, anti-hyperalgesic activity was antagonized with sulpiride pre-treatment, but not by phentolamine, or propranolol pre-treatments. The present study suggests that PSELT reduces the severity of ADHD symptoms in mice and possesses potent antinociceptive effects which could be related to the involvement of D2/D3 dopaminergic receptors.

[3H]-NFPS binding to the glycine transporter 1 in the hemi-parkinsonian rat brain.

L-3,4-dihydroxyphenylalanine (L-DOPA) is the main treatment for Parkinson's disease (PD) but with long term administration, motor complications such as dyskinesia are induced. Glycine transporter 1 (GlyT1) inhibition was shown to produce an anti-dyskinetic effect in parkinsonian rats and primates, coupled with an improvement in the anti-parkinsonian action of L-DOPA. The expression of GlyT1 in the brain in the dyskinetic state remains to be investigated. Here, we quantified the levels of GlyT1 across different brain regions using [3H]-NFPS in the presence of Org-25,935. Brain sections were chosen from sham-lesioned rats, L-DOPA-naïve 6-hydroxydopamine (6-OHDA)-lesioned rats and 6-OHDA-lesioned rats exhibiting mild or severe abnormal involuntary movements (AIMs). [3H]-NFPS binding decreased in the ipsilateral and contralateral thalamus, by 28% and 41%, in 6-OHDA-lesioned rats with severe AIMs compared to sham-lesioned animals (P < 0.01 and 0.001). [3H]-NFPS binding increased by 21% in the ipsilateral substantia nigra of 6-OHDA-lesioned rats with severe AIMs compared to 6-OHDA-lesioned rats with mild AIMs (P < 0.05). [3H]-NFPS binding was lower by 19% in the contralateral primary motor cortex and by 20% in the contralateral subthalamic nucleus of 6-OHDA-lesioned rats with mild AIMs animals compared to rats with severe AIMs (both P < 0.05). The severity of AIMs scores positively correlated with [3H]-NFPS binding in the ipsilateral substantia nigra (P < 0.05), ipsilateral entopeduncular nucleus (P < 0.05) and contralateral primary motor cortex (P < 0.05). These data provide an anatomical basis to explain the efficacy of GlyT1 inhibitors in dyskinesia in PD.

Fumaria vaillantii extract protects PC12 cells against neurotoxicity induced by 6-OHDA.

BACKGROUND: Parkinson's disease is a neurological disorder caused by the loss of dopaminergic neurons in the midbrain. Various mechanisms are involved in the incidence of the disease including oxidative stress. Several herbs and natural products may interfere with the oxidative-stress pathway due to their antioxidant effects. OBJECTIVE: Herein, we aimed to investigate the neuroprotective role of F. vaillantii extract on Parkinson's in vitro and in vivo model owing to the presence of the bioactive agents with antioxidant properties. METHODS: In vitro experments showed that 6-hydroxydopamine could induce toxicity in PC12 cells. The impact of F. vaillantii extract on cell viability was measured by using MTT assay. Nuclear morphological changes were qualitatively evaluated employing Hoechst staining. The antioxidant activity of the extract was determined by ROS and lipid peroxidation assays. Tyrosine hydroxylase protein expression was measured by western blotting in PC12 cells. For in vivo study, movement parameters were evaluated. RESULTS: The results indicated that 75 µΜ of 6-OHDA induced 50% toxicity in PC12 cells for 24 h. Following post-treatment with F. vaillantii extract (0.1 mg/ml) for 72 h, we observed that the extract effectively prevented cell toxicity induced by 6-OHDA and reduced the apoptotic cell population. Furthermore, the extract attenuated the ROS level, lipid peroxidation and increased protein expression of TH after 72 h of treatment. In addition, oral administration of 300 mg/kg of F. vaillantii extract for 14 days improved locomotor activity, catalepsy, bradykinesia, motor coordination and reduced the apomorphine-caused rotation in 6-OHDA- induced Parkinson's disease-like symptoms in male rats. CONCLUSION: The present study suggests a protective role for the extract of F. vaillantii against oxidative stress-induced cell damage in the PC12 cells exposed to neurotoxin 6-OHDA which was verified in in vivo model by reducing the motor defects induced by 6-OHDA. This extract could be a promising therapeutic agent for the prevention of PD progression.

No Effects of Decanoic Acid on Locomotor Activity and Antioxidant Defences in an Experimental Animal Model of Attention-Deficit/Hyperactivity Disorder.

BACKGROUND: Medium-chain triglycerides such as decanoic acid (C10), which is one of the fatty acids that constitute dietary fats, are of substantial interest for their potential therapeutic effects on neuropsychiatric disorders. However, the effects of C10 on attention-deficit/hyperactivity disorder (ADHD) remain to be studied. We explored the effects of C10 on behavioural activity and antioxidant defences in an experimental animal model of ADHD. METHODS: To establish an experimental animal model of ADHD, neonatal rats were subjected to unilateral striatal lesions using 6-hydroxydopamine (6-OHDA). The rats sequentially underwent open-field and Y-maze tests before treatment [postnatal day 25 (PN25)]. After the subcutaneous administration of either vehicle or C10 solution (250 mg/kg) for 14 days, the behavioural tests were repeated on PN39. Next, we examined the effects of C10 on the expression of the constitutive antioxidant enzymes catalase and glutathione peroxidase-1/2 and the phase II transcription factor nuclear factor erythroid 2-related factor 2 in four different regions of the rat brain. RESULTS: Injection of 6-OHDA unilaterally into the striatum resulted in elevated locomotor activity on PN39. The administration of C10 for a period of 14 days did not alter the locomotor hyperactivity. Moreover, the administration of C10 had no significant effects on the expression of proteins related to antioxidant defences in the hippocampus, prefrontal cortex, striatum or cerebellum of both control and lesioned rats. CONCLUSIONS: The lack of significant effects of C10 in our study may depend on the dose and duration of C10 administration. Further exhaustive studies are needed to verify the efficacy and effects of different doses and treatment durations of C10 and to explore the underlying mechanisms.

On-Off and Proportional Closed-Loop Adaptive Deep Brain Stimulation Reduces Motor Symptoms in Freely Moving Hemiparkinsonian Rats.

OBJECTIVES: Closed-loop adaptive deep brain stimulation (aDBS) continuously adjusts stimulation parameters, with the potential to improve efficacy and reduce side effects of deep brain stimulation (DBS) for Parkinson's disease (PD). Rodent models can provide an effective platform for testing aDBS algorithms and establishing efficacy before clinical investigation. In this study, we compare two aDBS algorithms, on-off and proportional modulation of DBS amplitude, with conventional DBS in hemiparkinsonian rats. MATERIALS AND METHODS: DBS of the subthalamic nucleus (STN) was delivered wirelessly in freely moving male and female hemiparkinsonian (N = 7) and sham (N = 3) Wistar rats. On-off and proportional aDBS, based on STN local field potential beta power, were compared with conventional DBS and three control stimulation algorithms. Behavior was assessed during cylinder tests (CT) and stepping tests (ST). Successful model creation was confirmed via apomorphine-induced rotation test and Tyrosine Hydroxylase-immunocytochemistry. Electrode location was histologically confirmed. Data were analyzed using linear mixed models. RESULTS: Contralateral paw use in parkinsonian rats was reduced to 20% and 25% in CT and ST, respectively. Conventional, on-off, and proportional aDBS significantly improved motor function, restoring contralateral paw use to approximately 45% in both tests. No improvement in motor behavior was observed with either randomly applied on-off or low-amplitude continuous stimulation. Relative STN beta power was suppressed during DBS. Relative power in the alpha and gamma bands decreased and increased, respectively. Therapeutically effective adaptive DBS used approximately 40% less energy than did conventional DBS. CONCLUSIONS: Adaptive DBS, using both on-off and proportional control schemes, is as effective as conventional DBS in reducing motor symptoms of PD in parkinsonian rats. Both aDBS algorithms yield substantial reductions in stimulation power. These findings support using hemiparkinsonian rats as a viable model for testing aDBS based on beta power and provide a path to investigate more complex closed-loop algorithms in freely behaving animals.

Transient Increases in Neural Oscillations and Motor Deficits in a Mouse Model of Parkinson's Disease.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor symptoms like tremors and bradykinesia. PD's pathology involves the aggregation of α-synuclein and loss of dopaminergic neurons, leading to altered neural oscillations in the cortico-basal ganglia-thalamic network. Despite extensive research, the relationship between the motor symptoms of PD and transient changes in brain oscillations before and after motor tasks in different brain regions remain unclear. This study aimed to investigate neural oscillations in both healthy and PD model mice using local field potential (LFP) recordings from multiple brain regions during rest and locomotion. The histological evaluation confirmed the significant dopaminergic neuron loss in the injection side in 6-OHDA lesioned mice. Behavioral tests showed motor deficits in these mice, including impaired coordination and increased forelimb asymmetry. The LFP analysis revealed increased delta, theta, alpha, beta, and gamma band activity in 6-OHDA lesioned mice during movement, with significant increases in multiple brain regions, including the primary motor cortex (M1), caudate-putamen (CPu), subthalamic nucleus (STN), substantia nigra pars compacta (SNc), and pedunculopontine nucleus (PPN). Taken together, these results show that the motor symptoms of PD are accompanied by significant transient increases in brain oscillations, especially in the gamma band. This study provides potential biomarkers for early diagnosis and therapeutic evaluation by elucidating the relationship between specific neural oscillations and motor deficits in PD.

IRE1/JNK Is the Leading UPR Pathway in 6-OHDA-Induced Degeneration of Differentiated SH-SY5Y Cells.

Parkinson's disease (PD) is a neurodegenerative disorder which affects dopaminergic neurons of the midbrain. Accumulation of α-synuclein or exposure to neurotoxins like 6-hydroxydopamine (6-OHDA) induces endoplasmic reticulum (ER) stress along with the unfolded protein response (UPR), which executes apoptosis via activation of PERK/CHOP or IRE1/JNK signaling. The present study aimed to determine which of these pathways is a major contributor to neurodegeneration in an 6-OHDA-induced in vitro model of PD. For this purpose, we have applied pharmacological PERK and JNK inhibitors (AMG44 and JNK V) in differentiated SH-SY5Y cells exposed to 6-OHDA. Inhibition of PERK and JNK significantly decreased genotoxicity and improved mitochondrial respiration, but only JNK inhibition significantly increased cell viability. Gene expression analysis revealed that the effect of JNK inhibition was dependent on a decrease in MAPK10 and XBP1 mRNA levels, whereas inhibition of either PERK or JNK significantly reduced the expression of DDIT3 mRNA. Western blot has shown that JNK inhibition strongly induced the XBP1s protein, and inhibition of each pathway attenuated the phosphorylation of eIF2α and JNK, as well as the expression of CHOP. Collectively, our data suggests that targeting the IRE1/JNK pathway of the UPR is a more effective option for PD treatment as it simultaneously affects more than one pro-apoptotic pathway.

Impact of Serotonergic 5HT1A and 5HT2A Receptor Activation on the Respiratory Response to Hypercapnia in a Rat Model of Parkinson's Disease.

In Parkinson's disease (PD), along with typical motor dysfunction, abnormal breathing is present; the cause of which is not well understood. The study aimed to analyze the effects of stimulation of the serotonergic system with 5-HT1A and 5-HT2A agonists in a model of PD induced by injection of 6-hydroxydopamine (6-OHDA). To model PD, bilateral injection of 6-OHDA into both striata was performed in male Wistar rats. Respiratory disturbances in response to 7% hypercapnia (CO2 in O2) in the plethysmographic chamber before and after stimulation of the serotonergic system and the incidence of apnea were studied in awake rats 5 weeks after 6-OHDA or vehicle injection. Administration of 6-OHDA reduced the concentration of serotonin (5-HT), dopamine (DA) and norepinephrine (NA) in the striatum and the level of 5-HT in the brainstem of treated rats, which have been associated with decreased basal ventilation, impaired respiratory response to 7% CO2 and increased incidence of apnea compared to Sham-operated rats. Intraperitoneal (i.p.) injection of the 5-HT1AR agonist 8-OH-DPAT and 5-HT2AR agonist NBOH-2C-CN increased breathing during normocapnia and hypercapnia in both groups of rats. However, it restored reactivity to hypercapnia in 6-OHDA group to the level present in Sham rats. Another 5-HT2AR agonist TCB-2 was only effective in increasing normocapnic ventilation in 6-OHDA rats. Both the serotonergic agonists 8-OH-DPAT and NBOH-2C-CN had stronger stimulatory effects on respiration in PD rats, compensating for deficits in basal ventilation and hypercapnic respiration. We conclude that serotonergic stimulation may have a positive effect on respiratory impairments that occur in PD.

Neuroprotection of Truncated Peptide IIAVE from Isochrysis zhanjiangensis: Quantum Chemical, Molecular Docking, and Bioactivity Studies.

Parkinson's disease (PD) is a progressive neurodegenerative disorder of the elderly for which there is no cure or disease-modifying therapy. Mitochondrial dysfunction and oxidative stress play a central role in dopaminergic neurodegeneration in PD. Therefore, antioxidants are considered a promising neuroprotective approach. In in vivo activity studies, 6-OHDA-induced oxidative stress in SH-SY5Y cells was established as a model of PD for cellular experiments. IIAVE (Ile-Ile-Ala-Val-Glu) was derived from Isochrysis zhanjiangensis octapeptide (IIAVEAGC), which has a small molecular weight. The structure and antioxidant activity of IIAVE were tested in a previous study and proved to have good antioxidant potential. In this study, the chemical properties of IIAVE were calculated using quantum chemical methods, including frontier molecular orbital (FMO), molecular electrostatic potential (MEP), natural population analysis (NPA), and global reactivity properties. The interaction of IIAVE with Bcl-2 and DJ-1 was investigated using the molecular docking method. The results showed that IIAVE promoted the activation of the Keap1/Nrf2 pathway and up-regulated the expression of the superoxide dismutase 1 (SOD-1) protein by inhibiting the level of reactive oxygen species (ROS) in cells. In addition, IIAVE inhibits ROS production and prevents 6-OHDA-induced oxidative damage by restoring mitochondrial membrane potential. Furthermore, IIAVE inhibited cell apoptosis by increasing the Bcl-2/Bax ratio and inhibiting the activation of Caspase-9 and Caspase-3. Thus, IIAVE may become a potential drug for the treatment and prevention of PD.

The Effect of Chronic Treatment with the Inhibitor of Phosphodiesterase 5 (PDE5), Sildenafil, in Combination with L-DOPA on Asymmetric Behavior and Monoamine Catabolism in the Striatum and Substantia Nigra of Unilaterally 6-OHDA-Lesioned Rats.

The use of phosphodiesterase inhibitors in the treatment of Parkinson's disease is currently widely discussed. The study aimed to investigate the impact of acute and chronic treatment with the phosphodiesterase 5 inhibitor, sildenafil, at low and moderate doses of 2 mg/kg and 6 mg/kg, and L-DOPA (12.5 mg/kg), alone or in combination, on asymmetric behavior and dopamine (DA) and serotonin metabolism in the striatum and substantia nigra of unilaterally 6-OHDA-lesioned rats. Acute administration of sildenafil at both tested doses jointly with L-DOPA significantly increased the number of contralateral rotations during a 2 h measurement compared to L-DOPA alone. The effect of a lower dose of sildenafil combined with L-DOPA was much greater in the second hour of measurement. However, the acute combined administration of a higher dose of sildenafil with L-DOPA resulted in an immediate and much stronger increase in the number of contralateral rotations compared to L-DOPA alone, already visible in the first hour of measurement. Interestingly, the chronic combined administration of 2 mg/kg of sildenafil and L-DOPA significantly reduced the number of contralateral rotations, especially during the first hour of measurement, compared to the long-term treatment with L-DOPA alone. Such an effect was not observed after the long-term combined treatment of a higher dose of sildenafil and L-DOPA compared to L-DOPA alone. The concentration of DA in the ipsilateral striatum and substantia nigra after the last combined chronic dose of sildenafil (2 or 6 mg/kg) and L-DOPA (12.5 mg/kg) was significantly higher than after L-DOPA alone. In spite of much stronger increases in the DA concentration in the ipsilateral striatum and substantia nigra, the number of contralateral rotations was reduced in the group of rats treated with the combination of 2 mg/kg sildenafil and L-DOPA compared to the group receiving L-DOPA alone. Moreover, the combined treatment with a low dose of sildenafil and L-DOPA had an opposite effect on DA catabolism, as assessed by DOPAC/DA and HVA/DA indexes, and these indexes were reduced in the ipsilateral striatum but increased in the contralateral striatum and substantia nigra compared to the treatment with L-DOPA alone. The results of the present study show that the addition of a low dose of a PDE5 inhibitor to the standard L-DOPA therapy differently modulates rotational behavior, the tissue DA concentration and its catabolism in the striatum and substantia nigra.

Cannabidiol improves non-motor symptoms, attenuates neuroinflammation, and favours hippocampal newborn neuronal maturation in a rat model of Parkinsonism.

OBJECTIVE: To investigate the effects of cannabidiol (CBD) on emotional and cognitive symptoms in rats with intra-nigral 6-hydroxydopamine (6-OHDA) lesions. METHODS: Adult male Wistar rats received bilateral intranigral 6-OHDA infusions and were tested in a battery of behavioural paradigms to evaluate non-motor symptoms. The brains were obtained to evaluate the effects of CBD on hippocampal neurogenesis. RESULTS: 6-OHDA-lesioned rats exhibited memory impairments and despair-like behaviour in the novelty-suppressed feeding test and forced swim test, respectively. The animals also exhibited dopaminergic neuronal loss in the substantia nigra pars compacta (SNpc), striatum, and ventral tegmental area and a reduction of hippocampal neurogenesis. CBD decreased dopaminergic neuronal loss in the SNpc, reduced the mortality rate and decreased neuroinflammation in 6-OHDA-lesioned rats. In parallel, CBD prevented memory impairments and attenuated despair-like behaviour that were induced by bilateral intranigral 6-OHDA lesions. Repeated treatment with CBD favoured the neuronal maturation of newborn neurons in the hippocampus in Parkinsonian rats. CONCLUSION: The present findings suggest a potential beneficial effect of CBD on non-motor symptoms induced by intra-nigral 6-OHDA infusion in rats.

BDNF/TrkB pathway activation in D1 receptor-expressing striatal projection neurons plays a protective role against L-DOPA-induced dyskinesia.

L-DOPA-induced dyskinesia (LID) is a frequent adverse side effect of L-DOPA treatment in Parkinson's disease (PD). Understanding the mechanisms underlying the development of these motor disorders is needed to reduce or prevent them. We investigated the role of TrkB receptor in LID, in hemiparkinsonian mice treated by chronic L-DOPA administration. Repeated L-DOPA treatment for 10 days specifically increased full-length TrkB receptor mRNA and protein levels in the dopamine-depleted dorsal striatum (DS) compared to the contralateral non-lesioned DS or to the DS of sham-operated animals. Dopamine depletion alone or acute L-DOPA treatment did not significantly increase TrkB protein levels. In addition to increasing TrkB protein levels, chronic L-DOPA treatment activated the TrkB receptor as evidenced by its increased tyrosine phosphorylation. Using specific agonists for the D1 or D2 receptors, we found that TrkB increase is D1 receptor-dependent. To determine the consequences of these effects, the TrkB gene was selectively deleted in striatal neurons expressing the D1 receptor. Mice with TrkB floxed gene were injected with Cre-expressing adeno-associated viruses or crossed with Drd1-Cre transgenic mice. After unilateral lesion of dopamine neurons in these mice, we found an aggravation of axial LID compared to the control groups. In contrast, no change was found when TrkB deletion was induced in the indirect pathway D2 receptor-expressing neurons. Our study suggests that BDNF/TrkB signaling plays a protective role against the development of LID and that agonists specifically activating TrkB could reduce the severity of LID.

Evoked responses to single pulse electrical stimulation reveal impaired striatal excitability in a rat model of Parkinson's disease.

BACKGROUND: Sensorimotor beta oscillations are increased in Parkinson's disease (PD) due to the alteration of dopaminergic transmission. This electrophysiological read-out is reported both in patients and in animal models such as the 6-OHDA rat model obtained with unilateral nigral injection of 6-hydroxydopamine (6-OHDA). Current treatments, based on dopaminergic replacement, transiently normalize this pathological beta activity and improve patients' quality of life. OBJECTIVES: We wanted to assess in vivo whether the abnormal beta oscillations can be correlated with impaired striatal or cortical excitability of the sensorimotor system and modulated by the pharmacological manipulation of the dopaminergic system. METHODS: In the unilateral 6-OHDA rat model and control animals, we used intra-striatal and intra-cortical single-pulse electrical stimulation (SPES) and concurrent local field potentials (LFP) recordings. In the two groups, we quantified basal cortico-striatal excitability from time-resolved spectral analyses of LFP evoked responses induced remotely by intracerebral stimulations. The temporal dependance of cortico-striatal excitability to dopaminergic transmission was further tested using electrophysiological recordings combined with levodopa injection. RESULTS: LFP evoked responses after striatal stimulation showed a transient reduction of power in a large time-frequency domain in the 6-OHDA group compared to the sham group. This result was specific to the striatum, as no significant difference was observed in cortical LFP evoked responses between the two groups. This impaired striatal excitability in the 6-OHDA group was observed in the striatum at least during the first 3 months after the initial lesion. In addition, the striatum responses to SPES during a levodopa challenge showed a transient potentiation of the decrease of responsiveness in frequencies below 40 Hz. CONCLUSION: The spectral properties of striatal responses to SPES show high sensitivity to dopaminergic transmission in the unilateral 6-OHDA rat model. We thus propose that this approach could be used in preclinical models as a time-resolved biomarker of impaired dopaminergic transmission capable of monitoring progressive neurodegeneration and/or challenges to drug intake.

Acyl-Ghrelin Attenuates Neurochemical and Motor Deficits in the 6-OHDA Model of Parkinson's Disease.

The feeding-related hormone, acyl-ghrelin, protects dopamine neurones in murine 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-based models of experimental Parkinson's disease (PD). However, the potential protective effect of acyl-ghrelin on substantia nigra pars compacta (SNpc) dopaminergic neurones and consequent behavioural correlates in the more widely used 6-hydroxydopamine (6-OHDA) rat medial forebrain bundle (MFB) lesion model of PD are unknown. To address this question, acyl-ghrelin levels were raised directly by mini-pump infusion for 7 days prior to unilateral injection of 6-OHDA into the MFB with assessment of amphetamine-induced rotations on days 27 and 35, and immunohistochemical analysis of dopaminergic neurone survival. Whilst acyl-ghrelin treatment was insufficient to elevate food intake or body weight, it attenuated amphetamine-induced circling behaviour and SNpc dopamine neurone loss induced by 6-OHDA. These data support the notion that elevating circulating acyl-ghrelin may be a valuable approach to slow or impair progression of neurone loss in PD.

MicroRNA-124-3p-enriched small extracellular vesicles as a therapeutic approach for Parkinson's disease.

Parkinson's disease is a neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra with no effective cure available. MicroRNA-124 has been regarded as a promising therapeutic entity for Parkinson's disease due to its pro-neurogenic and neuroprotective roles. However, its efficient delivery to the brain remains challenging. Here, we used umbilical cord blood mononuclear cell-derived extracellular vesicles as a biological vehicle to deliver microRNA (miR)-124-3p and evaluate its therapeutic effects in a mouse model of Parkinson's disease. In vitro, miR-124-3p-loaded small extracellular vesicles induced neuronal differentiation in subventricular zone neural stem cell cultures and protected N27 dopaminergic cells against 6-hydroxydopamine-induced toxicity. In vivo, intracerebroventricularly administered small extracellular vesicles were detected in the subventricular zone lining the lateral ventricles and in the striatum and substantia nigra, the brain regions most affected by the disease. Most importantly, although miR-124-3p-loaded small extracellular vesicles did not increase the number of new neurons in the 6-hydroxydopamine-lesioned striatum, the formulation protected dopaminergic neurons in the substantia nigra and striatal fibers, which fully counteracted motor behavior symptoms. Our findings reveal a novel promising therapeutic application of small extracellular vesicles as delivery agents for miR-124-3p in the context of Parkinson's disease.