Modeling Parkinson's disease in rats: an evaluation of 6-OHDA lesions of the nigrostriatal pathway

Involvement of the basolateral amygdaloid nucleus anterior part 5-HT7 receptors in the regulation of anxiety-like behaviors in hemiparkinsonian rats

Anxiety is a common non-motor symptom of Parkinson's disease (PD), but its neurobiological mechanism is obscure. 5-hydroxytryptamine7 (5-HT7) receptor is associated with anxiety and is widely distributed in brain regions related to emotion regulation, including anterior part of basolateral amygdaloid nucleus (BLA), and monosynaptic glutamatergic BLA to ventral hippocampus (vHPC) (BLAGlu-vHPC) pathway modulates anxiety-related behaviors. Measurable pathological and pathophysiological changes within the amygdala and hippocampus have also been reported in PD patients and parkinsonian animals. Thus, we hypothesized that BLA 5-HT7 receptors might regulate PD-related anxiety through BLAGlu-vHPC pathway. In this study, we found that down-regulation of BLA 5-HT7 receptors by RNA interference produced anxiolytic effects in sham and 6-hydroxydopamine-lesioned rats. And intra-BLA injection of 5-HT7 receptor agonist AS19 and antagonist SB269970 induced anxiogenic and anxiolytic responses in the two groups of rats. Further, intra-BLA injection of AS19 and SB269970 increased and decreased the mean firing rate of BLA glutamatergic neurons and vHPC extracellular glutamate levels in sham and the lesioned rats, respectively. Compared to sham rats, the effects of AS19 and SB269970 on the anxiety-related behaviors, firing activity and transmitter levels were decreased in the lesioned rats, which are associated with decreased expression of 5-HT7 receptors on BLAGlu-vHPC pathway after substantia nigra pars compacta lesion. Collectively, these results suggest that activation and blockade of 5-HT7 receptors on the BLAGlu-vHPC pathway are involved in the regulation of PD-related anxiety, and dopaminergic lesion decreases the expression of 5-HT7 receptors on this neural pathway.

Bright-light treatment ameliorates motor and non-motor deficits through distinct visual circuits in a mouse model of Parkinson's disease

Light has a profound impact on non-visual functions, and clinical evidence suggests bright-light therapy's effectiveness in alleviating motor and non-motor symptoms of Parkinson's disease (PD). However, the neural mechanisms underlying these effects remain unclear. Here, we demonstrate that bright-light treatment alleviates PD symptoms in mice via distinct visual circuits. Specifically, bright-light signals transmitted by the ventral lateral geniculate nucleus alleviate non-motor symptoms, such as depressive-like behaviors and spatial memory deficits. Conversely, the improvement in motor symptoms with bright-light treatment depends on a separate, disynaptic visual pathway that connects the superficial layers of the superior colliculus to the substantia nigra pars compacta (SNc). Notably, in this pathway, bright-light signals enhance the bursting activity of SNc dopaminergic neurons by upregulating HCN2 expression, a mechanism essential for motor improvements. These findings provide valuable insights into the neural mechanisms by which bright-light therapy benefits PD.

Impulsive-compulsive behaviours and striatal neuroactivity in mildly parkinsonian rats under D2/3 agonist and L-DOPA treatment

Dopamine replacement therapy for Parkinson's disease can induce impulsive-compulsive behaviours (ICBs). Here we compare the D2/3 agonist ropinirole and L-DOPA, given alone or combined, with regard to their potential to induce ICBs in rats sustaining bilateral striatal injections of 6-hydroxydopamine. Daily treatment with ropinirole (2.5 mg/kg), L-DOPA (24.0 mg/kg), or their combination was given for six weeks while animals were examined using tests of compulsive checking and motor stereotypies not previously used in the ICB literature. Independently of L-DOPA cotreatment, ropinirole induced a stereotyped hyperactivity pattern, compulsive checking, and maladaptive choices in the rat version of the Iowa gambling task. Compared to both L-DOPA and vehicle, ropinirole elicited a distinct pattern of striatal neuroactivity, shifting the expression of a cellular activity marker from dorsolateral to centro-medial regions. Our results reveal quite distinct profiles of ICBs and striatal activation upon treatment with ropinirole or L-DOPA, providing clues of therapeutic relevance to Parkinson's ICBs.

Activation or blockade of prelimbic 5-HT4 receptors improves working memory in hemiparkinsonian rats

Working memory deficits commonly occur in Parkinson's disease. 5-hydroxytryptamine4 (5-HT4) receptors are widely distributed in the prelimbic cortex (PrL) and involved in cognition. Here we tested the effects of activation and blockade of PrL 5-HT4 receptors on working memories by T-maze rewarded alternation and Morris water maze tests in rats with unilateral 6-hydroxydopamine (6-OHDA) lesion of the medial forebrain bundle. The lesion induced working memory deficits, decreased dopamine levels in the limbic-related brain regions, changed normalized δ, high θ, α, β, low and high γ power of the PrL, and upregulated expression of PrL 5-HT4 receptor. Intra-PrL injection of 5-HT4 receptor agonist BIMU8 or antagonist GR113808 did not impact working memories in sham rats, but improved working memory deficits in the lesioned rats. Intra-PrL injection of BIMU8 or GR113808 had no effect on monoamine levels in the limbic-related brain regions or normalized low and high γ power of the PrL in sham rats. However, in the lesioned rats, intra-PrL injection of BIMU8 significantly increased dopamine and 5-HT levels in the medial prefrontal cortex, amygdala and dorsal hippocampus, while intra-PrL injection of GR113808 significantly increased dopamine levels in these brain regions and increased normalized low and high γ power of the PrL. These results suggest that 6-OHDA lesion in rats induces working memory deficits, while activation or blockade of PrL 5-HT4 receptors improves the deficits in the lesioned rats, which possibly due to the changes of monoamine levels in the limbic-related brain regions and network activity of neurons in the PrL.

JM-20 administration to animals with lesion of the nigrostriatal dopamine pathway induced by 6-hydroxydopamine, partially reverses motor damage and oxidative stress

INTRODUCTION

Previous studies have shown that JM-20, a new chemical hybrid molecule, protects against rotenone and 6-hydroxydopamine (6-OHDA) neurotoxicity. Also, we demonstrated that JM-20 inhibit the formation of toxic alpha-synuclein aggregated species and aminochrome cytotoxicity.

OBJECTIVE

The present study sought to determine the neuroprotective property of JM-20 in animals with a partial lesion of the nigrostriatal dopamine pathway induced by 6-OHDA.

METHODS

For in vivo studies, adult male Wistar rats were lesioned in the right substantia nigra pars compacta (SNpc) with a 6-OHDA administration. Fifteen days after surgery, the animal's asymmetry levels were assessed. Those with asymmetry values higher than 50% were divided into two groups: animals that did not receive any treatment and those that were administered with JM-20 (40 mg/kg, intragastric via gavage) for 27 days. Every 7 days, the asymmetry values of the animals were analyzed until day 42 after the surgery. At the end of the experiment, the animals were euthanized, and the SNpc and striatum were taken out for the analysis of oxidative stress.

RESULTS

Our results reveal a behavioral function progressively recovered in the JM-20-treated animals, diminishing the percentage of motor asymmetry. Also, it improves some oxidative stress markers in the SNpc and the striatum of these animals.

CONCLUSION

Our study provides the preclinical evidence to support the long-term neuroprotective potential of JM-20 in 6-OHDA hemiparkinson rat model, pointing out to its possible use as a disease-modifying agent in PD.

Blockade of mGluR1 and mGluR5 in the lateral habenula produces the opposite effects in the regulation of depressive-like behaviors in the hemiparkinsonian rats

Depression is one of the most common non-motor symptoms in Parkinson's disease (PD) and the hyperactivity of the lateral habenula (LHb) may contribute to depression. The present study was performed to investigate the effects and mechanisms of group I metabotropic glutamate receptors (mGluRs) in the LHb on PD-related depressive-like behaviors. Unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc) were used to establish the PD rat model. The group I mGluRs agonist and antagonists for mGluR1 and mGluR5 were microinjected into the LHb to observe their effects on PD-related depressive-like behaviors, electrical activities of the LHb, release of monoamines in the medial prefrontal cortex (mPFC) in sham and the lesioned rats. Lesions of the SNc induced depressive-like behaviors and hyperactivity of LHb neurons. Activation of group I mGluRs by 3,5-DHPG induced or enhanced depressive-like behaviors, increased the firing rate of the LHb neurons, and decreased dopamine (DA) and serotonin (5-HT) levels in the mPFC in the two groups of rats. Blockade of mGluR1 by YM298198 also produced similar effects with 3,5-DHPG, however, blockade of mGluR5 by MTEP produced opposite effects. Western blotting data showed that lesions of the SNc in rats down-regulated the expression of mGluR1 and mGluR5 in the LHb. These results suggest that mGluR1 and mGluR5 in the LHb induce opposite effects on depressive-like behaviors, which may attribute to the changed firing rate of LHb neurons by the presynaptic and postsynaptic mechanisms, and the changes in the monoamine levels.

Uncaria rhynchophylla alkaloid extract exerts neuroprotective activity against Parkinson's disease via activating mitophagy with the involvement of UCHL1

ETHNOPHARMACOLOGICAL RELEVANCE

Uncaria rhynchophylla (Miq.) Miq. ex Havil. (UR), a traditional Chinese medicinal plant, plays an active role in neuroprotection. Clinical medication and modern pharmacological studies have proved the efficacy of UR against Parkinson's disease (PD), with alkaloids being recognized as the main bioactive components. But the therapeutic effect and mechanism of U. rhynchophylla alkaloid extract (URA) against PD need further exploration.

AIM OF STUDY

The study aimed to investigate the therapeutic effect and potential mechanism of URA on PD.

MATERIALS AND METHODS

LC-MS methodology was used to evaluate the chemical constituents of URA. The anti-PD activity of URA in vivo was measured on the mouse and rat models of PD. Neuroprotective effect of URA on PC12 cells was measured by MTT assay. Dopamine (DA) and its metabolites were detected by LC-MS for probing the protection ability on dopaminergic neurons. The differentially expressed proteins between model group and URA administrated group were analyzed by proteomics, suggesting oxidative phosphorylation as possible pathway of URA. Considering the critical role of mitochondria in oxidative phosphorylation, JC-1 staining, MitoSOX staining, transmission electron microscopy (TEM) observation and adenosine triphosphate (ATP) levels detection were used to analyze the effects of URA on mitochondrial morphology and function. Biolayer interferometry (BLI) was used to search for the possible UCHL1-bonding compounds in URA.

RESULTS

URA significantly mitigated the behavioural defects by improving coordination, shortening the time to climb down the whole pole (T-LA) and increasing the forelimbs' muscle strength of MPTP-induced PD mice and 6-OHDA-induced PD rats. In addition, URA improved tyrosine hydroxylase expression in dopaminergic neurons by immunohistochemistry (IHC) staining, and thus increased the neurotransmitter levels of DA and relevant metabolites. Furthermore, URA promoted mitophagy as reflected by a significant decrease in reactive oxygen species (ROS) generation, an increase in ATP levels and clearance of damaged mitochondria. Subsequently, Ubiquitin C-terminal hydrolase 1 (UCHL1), which is associated with the mitochondrial dysfunction in PD, is suggested to be a promising target based on the proteomics result, and proved by the blocked protective effects of URA by UCHL1 inhibitor. Furthermore, hirsuteine (HTE) was identified as a potential active compound of URA binding to UCHL1 by BLI, and the binding capacity and site were verified by surface plasmon resonance (SPR) and molecular docking.

CONCLUSION

This work demonstrates that URA exerts effective neuroprotective activity against PD via activation of mitophagy with the involvement of UCHL1, and HTE may be a potential active compound of URA.

Challenges and Opportunities in Exploring Non-Motor Symptoms in 6-Hydroxydopamine Models of Parkinson's Disease: A Systematic Review

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive loss of midbrain dopaminergic neurons, leading to motor symptoms such as tremors, rigidity, and bradykinesia. Non-motor symptoms, including depression, hyposmia, and sleep disturbances, often emerge in the early stages of PD, but their mechanisms remain poorly understood. The 6-hydroxydopamine (6-OHDA) rodent model is a well-established tool for preclinical research, replicating key motor and non-motor symptoms of PD. In this review, we systematically analyzed 135 studies that used 6-OHDA rodent models of PD to investigate non-motor symptoms. The review process adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Our analysis highlights the growing use of 6-OHDA PD models for experimental research of non-motor symptoms. It also reveals significant variability in methodologies, including choices of brain target, toxin dosage, lesion verification strategies, and behavioral assessment reporting. Factors that hinder reproducibility and comparability of findings across studies. We highlight the need for standardization in 6-OHDA-based models with particular emphasis on consistent evaluation of lesion extent and reporting of the co-occurrence of non-motor symptoms. By fostering methodological coherence, this framework aims to enhance the reproducibility, reliability, and translational value of 6-OHDA models in PD non-motor symptom research.

Acute Intermittent Theta-Burst Stimulation Produces Antidepressant-Like Effects by Modulating Neuronal Oscillations and Serotonin Levels of the Medial Prefrontal Cortex in Experimental Parkinson's Disease

Parkinson's disease (PD)-related depression is associated with aberrant neuronal oscillations and 5-hydroxytryptamine (5-HT) neurotransmission in the medial prefrontal cortex (mPFC). Intermittent theta-burst stimulation (iTBS), an updated pattern of high-frequency repetitive transcranial magnetic stimulation, has possible efficacy in PD-related depression. However, whether iTBS alleviates PD-related depression through modulating neuronal oscillations and 5-HT levels in the mPFC has not been determined. In this study, male Sprague-Dawley rats were used to establish a unilateral 6-hydroxydopamine-induced PD model. Then, acute iTBS was applied to the parkinsonian rats, and behavioral, neurochemical, and electrophysiological experiments were performed. We found that the parkinsonian rats exhibited increased immobility time and decreased sucrose preference accompanied by an increase of δ power and a decrease of θ power in the mPFC compared to sham-operated rats. One block of iTBS (1 block-iTBS, 300 stimuli) alleviated depressive-like behaviors in parkinsonian rats and elevated 5-HT levels in the mPFC compared to sham-iTBS. Additionally, it altered neuronal oscillations in the mPFC in the opposite fashion by suppressing the δ rhythm and enhancing the θ and β rhythms compared to sham-iTBS, suggesting that acute iTBS induces hyperactivity in the mPFC. With this iTBS paradigm, we also observed decreased parvalbumin expression in the mPFC, reflecting reduced cortical inhibition. Finally, correlation analyses showed strong correlation between immobility time and θ power after 1 block-iTBS. These findings suggest that the application of acute iTBS in parkinsonian rats produces antidepressant-like effects, which may be associated with elevated 5-HT levels and normalized neuronal oscillations in the mPFC.

Cortical VIP neurons as a critical node for dopamine actions

Dopamine modulates a wide range of cognitive processes in the prefrontal cortex, but the underlying mechanisms remain unclear. Here, we examined the roles of prefrontal vasoactive intestinal polypeptide (VIP)-expressing neurons and their D1 receptors (D1Rs) in working memory using a delayed match-to-sample task in mice. VIP neurons conveyed robust working-memory signals, and their inactivation impaired behavioral performance. Moreover, selective knockdown of D1Rs in VIP neurons also resulted in impaired performance, indicating the critical role of VIP neurons and their D1Rs in supporting working memory. Additionally, we found that dopamine release dynamics during the delay period varied depending on the target location. Furthermore, dopaminergic terminal stimulation induced a contralateral response bias and enhanced neuronal target selectivity in a laterality-dependent manner. These results suggest that prefrontal dopamine modulates behavioral responses and delay-period activity based on laterality. Overall, these findings shed light on dopamine-modulated prefrontal neural processes underlying higher-order cognitive functions.

Parkinson's disease models and death signaling: what do we know until now?

Parkinson's disease (PD) is the second neurodegenerative disorder most prevalent in the world, characterized by the loss of dopaminergic neurons in the Substantia Nigra (SN). It is well known for its motor and non-motor symptoms including bradykinesia, resting tremor, psychiatric, cardiorespiratory, and other dysfunctions. Pathological apoptosis contributes to a wide variety of diseases including PD. Various insults and/or cellular phenotypes have been shown to trigger distinct signaling events leading to cell death in neurons affected by PD. The intrinsic or mitochondrial pathway, inflammatory or oxidative stress-induced extrinsic pathways are the main events associated with apoptosis in PD-related neuronal loss. Although SN is the main brain area studied so far, other brain nuclei are also affected by the disease leading to non-classical motor symptoms as well as non-motor symptoms. Among these, the respiratory symptoms are often overlooked, yet they can cause discomfort and may contribute to patients shortened lifespan after disease diagnosis. While animal and in vitro models are frequently used to investigate the mechanisms involved in the pathogenesis of PD in both the SN and other brain regions, these models provide only a limited understanding of the disease's actual progression. This review offers a comprehensive overview of some of the most studied forms of cell death, including recent research on potential treatment targets for these pathways. It highlights key findings and milestones in the field, shedding light on the potential role of understanding cell death in the prevention and treatment of the PD. Therefore, unraveling the connection between these pathways and the notable pathological mechanisms observed during PD progression could enhance our comprehension of the disease's origin and provide valuable insights into potential molecular targets for the developing therapeutic interventions.

Phosphodiesterase inhibition and Gucy2C activation enhance tyrosine hydroxylase Ser40 phosphorylation and improve 6-hydroxydopamine-induced motor deficits

BACKGROUND

Parkinson's disease is characterized by a progressive loss of dopaminergic neurons in the nigrostriatal pathway, leading to dopamine deficiency and motor impairments. Current treatments, such as L-DOPA, provide symptomatic relief but result in off-target effects and diminished efficacy over time. This study explores an alternative approach by investigating the activation of tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Specifically, we explore the effects of phosphodiesterase (PDE) inhibition and guanylate cyclase-C (GUCY2C) activation on tyrosine hydroxylase Ser40 phosphorylation and their impact on motor behavior in a 6-hydroxydopamine (6-OHDA) Parkinson's disease model.

RESULTS

Our findings demonstrate that increasing cyclic nucleotide levels through PDE inhibition and GUCY2C activation significantly enhances tyrosine hydroxylase Ser40 phosphorylation. In a Pitx3-deficient mouse model, which mimics the loss of dopaminergic neurons seen in Parkinson's disease, Ser40 phosphorylation remained manipulable despite reduced tyrosine hydroxylase protein levels. Moreover, we observed no evidence of tyrosine hydroxylase degradation due to Ser40 phosphorylation, challenging previous reports. Furthermore, both PDE inhibition and GUCY2C activation resulted in improved motor behavior in the 6-OHDA Parkinson's disease mouse model, highlighting the potential therapeutic benefits of these approaches.

CONCLUSIONS

This study underscores the therapeutic potential of enhancing tyrosine hydroxylase Ser40 phosphorylation to improve motor function in Parkinson's disease. Both PDE inhibition and GUCY2C activation represent promising non-invasive strategies to modulate endogenous dopamine biosynthesis and address motor deficits. These findings suggest that targeting cyclic nucleotide pathways could lead to novel therapeutic approaches, either as standalone treatments or in combination with existing therapies like L-DOPA, aiming to provide more durable symptom relief and potentially mitigate neurodegeneration in Parkinson's disease.

Experimental models of Parkinson's disease: Challenges and Opportunities

Parkinson's disease (PD) is a widespread neurodegenerative disorder occurs due to the degradation of dopaminergic neurons present in the substantia nigra pars compacta (SNpc). Millions of people are affected by this devastating disorder globally, and the frequency of the condition increases with the increase in the elderly population. A significant amount of progress has been made in acquiring more knowledge about the etiology and the pathogenesis of PD over the past decades. Animal models have been regarded to be a vital tool for the exploration of complex molecular mechanisms involved in PD. Various animals used as models for disease monitoring include vertebrates (zebrafish, rats, mice, guinea pigs, rabbits and monkeys) and invertebrate models (Drosophila, Caenorhabditis elegans). The animal models most relevant for study of PD are neurotoxin induction-based models (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 6-Hydroxydopamine (6-OHDA) and agricultural pesticides (rotenone, paraquat), pharmacological models (reserpine or haloperidol treated rats), genetic models (α-synuclein, Leucine-rich repeat kinase 2 (LRRK2), DJ-1, PINK-1 and Parkin). Several non-mammalian genetic models such as zebrafish, Drosophila and Caenorhabditis elegance have also gained popularity in recent years due to easy genetic manipulation, presence of genes homologous to human PD, and rapid screening of novel therapeutic molecules. In addition, in vitro models (SH-SY5Y, PC12, Lund human mesencephalic (LUHMES) cells, Human induced pluripotent stem cell (iPSC), Neural organoids, organ-on-chip) are also currently in trend providing edge in investigating molecular mechanisms involved in PD as they are derived from PD patients. In this review, we explain the current situation and merits and demerits of the various animal models.

Clinical correlates of dopamine transporter availability in cross-sectional and longitudinal studies with [18F]FE-PE2I PET: independent validation with new insights

[18F]FE-PE2I PET is a promising alternative to single positron emission computed tomography-based dopamine transporter (DAT) imaging in Parkinson's disease. While the excellent discriminative power of [18F]FE-PE2I PET has been established, so far only one study has reported meaningful associations between motor severity scores and DAT availability. In this study, we use high-resolution (∼3 mm isotropic) PET to provide an independent validation for the clinical correlates of [18F]FE-PE2I imaging in separate cross-sectional (28 participants with Parkinson's disease, Hoehn-Yahr: 2 and 14 healthy individuals) and longitudinal (initial results from 6 participants with Parkinson's disease with 2-year follow-up) cohorts. In the cross-sectional cohort, DAT availability in the putamen and substantia nigra of patients with Parkinson's disease showed a significant negative association with total motor severity (r = -0.59, P = 0.002 for putamen; r = -0.46, P = 0.018 for substantia nigra), but not tremor severity. To our knowledge, this is the first observed association between motor severity in Parkinson's disease and DAT availability in the substantia nigra. The associations with motor severity in most nigrostriatal regions improved if tremor scores were excluded from motor scores. Further, we found significant asymmetry in DAT availability in the putamen (∼28% lower DAT availability within the more-affected side of the putamen), and DAT-based asymmetry index for the putamen was correlated with asymmetry in motor severity (r = -0.60, P = 0.001). In the longitudinal study, [18F]FE-PE2I PET detected significant annual percentage reduction of DAT availability at the individual level in the putamen (9.7 ± 2.6%), caudate (10.5 ± 3.8%) and ventral striatum (5.5 ± 2.7%), but not the substantia nigra. Longitudinal per cent reduction in DAT availability within the putamen was strongly associated with increase in motor severity (r = 0.91, P = 0.011) at follow-up, demonstrating the high sensitivity of [18F]FE-PE2I PET in tracking longitudinal changes. These results provide further evidence for the utility of [18F]FE-PE2I as an important in vivo PET biomarker in future clinical trials of Parkinson's disease.

Applying the area fraction fractionator (AFF) probe for total volume estimations of somatic, dendritic and axonal domains of the nigrostriatal dopaminergic system in a murine model

BACKGROUND

The Cavalieri estimator is used for volume measurement of brain and brain regions. Derived from this estimator is the Area Fraction Fractionator (AFF), used for efficient area and number estimations of small 2D elements, such as axons in cross-sectioned nerves. However, to our knowledge, the AFF has not been combined with serial sectioning analysis to measure the volume of small-size nervous structures.

NEW METHOD

Using the nigrostriatal dopaminergic system as an illustrative case, we describe a protocol based on Cavalieri's principle and AFF to estimate the volume of its somatic, nuclear, dendritic, axonal and axon terminal cellular compartments in the adult mouse. The protocol consists of (1) systematic random sampling of sites within and across sections in regions of interest (substantia nigra, the nigrostriatal tract, caudate-putamen), (2) confocal image acquisition of sites, (3) marking of cellular domains using Cavalieri's 2D point-counting grids, and 4) determination of compartments' total volume using the estimated area of each compartment, and between-sections distance.

RESULTS

The volume of the nigrostriatal system per hemisphere is ∼0.38 mm3, with ∼5 % corresponding to perikarya and cell nuclei, ∼10 % to neuropil/dendrites, and ∼85 % to axons and varicosities.

COMPARISON WITH EXISTING METHODS

In contrast to other methods to measure volume of discrete objects, such as the optical nucleator or 3D reconstructions, it stands out for its versatility and ease of use.

CONCLUSIONS

The use of a simple quantitative, unbiased approach to assess the global state of a system may allow quantification of compartment-specific changes that may accompany neurodegenerative processes.

Targeting ferroptosis with the lipoxygenase inhibitor PTC-041 as a therapeutic strategy for the treatment of Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disorder, affecting nearly 10 million people worldwide. Ferroptosis, a recently identified form of regulated cell death characterized by 15-lipoxygenase-mediated hydroperoxidation of membrane lipids, has been implicated in neurodegenerative disorders including amyotrophic lateral sclerosis and Parkinson's disease. Pharmacological inhibition of 15 -lipoxygenase to prevent iron- and lipid peroxidation-associated ferroptotic cell death is a rational strategy for the treatment of Parkinson's disease. We report here the characterization of PTC-041 as an anti-ferroptotic reductive lipoxygenase inhibitor developed for the treatment of Parkinson's disease. In these studies, PTC-041 potently protects primary human Parkinson's disease patient-derived fibroblasts from lipid peroxidation and subsequent ferroptotic cell death and prevents ferroptosis-related neuronal loss and astrogliosis in primary rat neuronal cultures. Additionally, PTC-041 prevents ferroptotic-mediated α-synuclein protein aggregation and nitrosylation in vitro, suggesting a potential role for anti-ferroptotic lipoxygenase inhibitors in mitigating pathogenic aspects of synucleinopathies such as Parkinson's disease. We further found that PTC-041 protects against synucleinopathy in vivo, demonstrating that PTC-041 treatment of Line 61 transgenic mice protects against α-synuclein aggregation and phosphorylation as well as prevents associated neuronal and non-neuronal cell death. Finally, we show that. PTC-041 protects against 6-hydroxydopamine-induced motor deficits in a hemiparkinsonian rat model, further validating the potential therapeutic benefits of lipoxygenase inhibitors in the treatment of Parkinson's disease.

Advances in animal models of Parkinson's disease

Parkinson's disease is a complex neurodegenerative disease characterized by progressive movement impairments. Predominant symptoms encompass resting tremor, bradykinesia, limb rigidity, and postural instability. In addition, it also includes a series of non-motor symptoms such as sleep disorders, hyposmia, gastrointestinal dysfunction, autonomic dysfunction and cognitive impairment. Pathologically, the disease manifests through dopaminergic neuronal loss and the presence of Lewy bodies. At present, no significant breakthrough has been achieved in clinical Parkinson's disease treatment. Exploring treatment modalities necessitate the establishment of scientifically sound animal models. In recent years, researchers have focused on replicating the symptoms of human Parkinson's disease, resulting in the establishment of various experimental animal models primarily through drugs and transgenic methods to mimic relevant pathologies and identify more effective treatments. This review examines traditional neurotoxin and transgenic animal models as well as α-synuclein pre-formed fibrils models, non-human primate models and non-mammalian specie models. Additionally, it introduces emerging models, including models based on optogenetics, induced pluripotent stem cells, and gene editing, aiming to provide a reference for the utilization of experimental animal models and clinical research for researchers in this field.

A2AR antagonists triggered the AMPK/m-TOR autophagic pathway to reverse the calcium-dependent cell damage in 6-OHDA induced model of PD

Calcium dyshomeostasis, oxidative stress, autophagy and apoptosis are the pathogenesis of selective dopaminergic neuronal loss in Parkinson's disease (PD). Earlier, we reported that A2A R modulates IP3-dependent intracellular Ca2+ signalling via PKA. Moreover, A2A R antagonist has been reported to reduce oxidative stress and apoptosis in PD models, however intracellular Ca2+ ([Ca2+]i) dependent autophagy regulation in the 6-OHDA model of PD has not been explored. In the present study, we investigated the A2A R antagonists mediated neuroprotective effects in 6-OHDA-induced primary midbrain neuronal (PMN) cells and unilateral lesioned rat model of PD. 6-OHDA-induced oxidative stress (ROS and superoxide) and [Ca2+]i was measured using Fluo4AM, DCFDA and DHE dye respectively. Furthermore, autophagy was assessed by Western blot of p-m-TOR/mTOR, p-AMPK/AMPK, LC3I/II, Beclin and β-actin. Apoptosis was measured by Annexin V-APC-PI detection and Western blot of Bcl2, Bax, caspase3 and β-actin. Dopamine levels were measured by Dopamine ELISA kit and Western blot of tyrosine hydroxylase. Our results suggest that 6-OHDA-induced PMN cell death occurred due to the interruption of [Ca2+]i homeostasis, accompanied by activation of autophagy and apoptosis. A2A R antagonists prevented 6-OHDA-induced neuronal cell death by decreasing [Ca2+]i overload and oxidative stress. In addition, we found that A2A R antagonists upregulated mTOR phosphorylation and downregulated AMPK phosphorylation thereby reducing autophagy and apoptosis both in 6-OHDA induced PMN cells and 6-OHDA unilateral lesioned rat model. In conclusion, A2A R antagonists alleviated 6-OHDA toxicity by modulating [Ca2+]i signalling to inhibit autophagy mediated by the AMPK/mTOR pathway.

Cerebellar Metabolic Connectivity during Treadmill Walking before and after Unilateral Dopamine Depletion in Rats

Compensatory changes in brain connectivity keep motor symptoms mild in prodromal Parkinson's disease. Studying compensation in patients is hampered by the steady progression of the disease and a lack of individual baseline controls. Furthermore, combining fMRI with walking is intricate. We therefore used a seed-based metabolic connectivity analysis based on 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) uptake in a unilateral 6-OHDA rat model. At baseline and in the chronic phase 6-7 months after lesion, rats received an intraperitoneal injection of [18F]FDG and spent 50 min walking on a horizontal treadmill, followed by a brain PET-scan under anesthesia. High activity was found in the cerebellar anterior vermis in both conditions. At baseline, the anterior vermis showed hardly any stable connections to the rest of the brain. The (future) ipsilesional cerebellar hemisphere was not particularly active during walking but was extensively connected to many brain areas. After unilateral dopamine depletion, rats still walked normally without obvious impairments. The ipsilesional cerebellar hemisphere increased its activity, but narrowed its connections down to the vestibulocerebellum, probably aiding lateral stability. The anterior vermis established a network involving the motor cortex, hippocampus and thalamus. Adding those regions to the vermis network of (previously) automatic control of locomotion suggests that after unilateral dopamine depletion considerable conscious and cognitive effort has to be provided to achieve stable walking.

Lateral habenula 5-HT1B receptors are involved in regulation of anxiety-like behaviors in parkinsonian rats

Although the output of the lateral habenula (LHb) controls the activity of midbrain dopaminergic and serotonergic systems, which are implicated in the pathophysiology of anxiety, it is not clear the role of LHb 5-HT1B receptors in regulation of anxiety-like behaviors, particularly in Parkinson's disease-related anxiety. In this study, unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta in rats induced anxiety-like behaviors, led to decreased normalized δ power and increased normalized θ power in the LHb, and decreased dopamine (DA) level in the prelimbic cortex (PrL) compared with sham rats. Down-regulation of LHb 5-HT1B receptors by RNA interference produced anxiety-like effects, decreased normalized δ power and increased normalized θ power in the LHb in both sham and lesioned rats. Further, intra-LHb injection of 5-HT1B receptor agonist CP93129 induced anxiolytic-like responses, increased normalized δ power and decreased normalized θ power in the LHb, and increased DA and serotonin (5-HT) release in the PrL; conversely, 5-HT1B receptor antagonist SB216641 produced anxiety-like effects, decreased normalized δ power and increased normalized θ power in the LHb, and decreased DA and 5-HT release in the PrL in sham and lesioned rats. Additionally, effects of CP93129 and SB216641 on the behaviors, normalized δ and θ power in the LHb, and DA and 5-HT release in the PrL were decreased in lesioned rats, which were consistent with down-regulation of LHb 5-HT1B receptors after DA depletion. Collectively, these findings suggest that 5-HT1B receptors in the LHb are involved in the regulation of anxiety-like behaviors.

Alpha-Synuclein Gene Alterations Modulate Tyrosine Hydroxylase in Human iPSC-Derived Neurons in a Parkinson's Disease Animal Model

Parkinson's disease (PD) caused by SNCA gene triplication (3XSNCA) leads to early onset, rapid progression, and often dementia. Understanding the impact of 3XSNCA and its absence is crucial. This study investigates the differentiation of human induced pluripotent stem cell (hiPSC)-derived floor-plate progenitors into dopaminergic neurons. Three different genotypes were evaluated in this study: patient-derived hiPSCs with 3XSNCA, a gene-edited isogenic line with a frame-shift mutation on all SNCA alleles (SNCA 4KO), and a normal wild-type control. Our aim was to assess how the substantia nigra pars compacta (SNpc) microenvironment, damaged by 6-hydroxydopamine (6-OHDA), influences tyrosine hydroxylase-positive (Th+) neuron differentiation in these genetic variations. This study confirms successful in vitro differentiation into neuronal lineage in all cell lines. However, the SNCA 4KO line showed unusual LIM homeobox transcription factor 1 alpha (Lmx1a) extranuclear distribution. Crucially, both 3XSNCA and SNCA 4KO lines had reduced Th+ neuron expression, despite initial successful neuronal differentiation after two months post-transplantation. This indicates that while the SNpc environment supports early neuronal survival, SNCA gene alterations-either amplification or knock-out-negatively impact Th+ dopaminergic neuron maturation. These findings highlight SNCA's critical role in PD and underscore the value of hiPSC models in studying neurodegenerative diseases.

Thymoquinone ameliorates symptoms of Parkinson's disease in a 6-OHDA rat model by downregulation of miR-204-3p

microRNAs (miRNAs) play a significant role in the pathophysiology of Parkinson's disease. In this study, we evaluated the neuroprotective effect of thymoquinone on the expression profiles of miRNA and cognitive functions in the 6-hydroxydopamine (6-OHDA)-induced Parkinson's model. Male adult Wistar albino rats (200-230 g, n  = 36) were randomly assigned to six groups: Sham, thymoquinone (10 mg/kg, p.o.), 6-OHDA, 6-OHDA + thymoquinone (10 mg/kg), 6-OHDA + thymoquinone (20 mg/kg), and 6-OHDA + thymoquinone (50 mg/kg). Behavioral changes were detected using the open field and the elevated plus maze tests. The mature 728 miRNA expressions were evaluated by miRNA microarray (GeneChip miRNA 4.0). Ten miRNAs were selected (rno-miR-212-5p, rno-miR-146b-5p, rno-miR-150-5p, rno-miR-29b-2-5p, rno-miR-126a-3p, rno-miR-187-3p, rno-miR-34a-5p, rno-miR-181d-5p, rno-miR-204-3p, and rno-miR-30c-2-3p) and confirmed by real-time PCR. Striatum samples were stained with hematoxylin-eosin to determine the effect of dopaminergic lesions. One-way ANOVA test and independent sample t -test were used for statistical analyses. rno-miR-204-3p was upregulated at 6-OHDA and downregulated at the 50 mg/kg dose of thymoquinone. In conclusion, thymoquinone at a dose of 50 mg/kg ameliorates symptoms of Parkinson's disease in a 6-OHDA rat model by downregulation of miR-204-3p. Also, the results showed that thymoquinone can improve locomotor activity and willing exploration and decreased anxiety. Therefore, thymoquinone can be used as a therapeutic agent.

Sleep deprivation induces late deleterious effects in a pharmacological model of Parkinsonism

Parkinson's disease is a degenerative, chronic and progressive disease, characterized by motor dysfunctions. Patients also exhibit non-motor symptoms, such as affective and sleep disorders. Sleep disorders can potentiate clinical and neuropathological features and lead to worse prognosis. The goal of this study was to evaluate the effects of sleep deprivation (SD) in mice submitted to a progressive pharmacological model of Parkinsonism (chronic administration with a low dose of reserpine). Male Swiss mice received 20 injections of reserpine (0.1 mg/kg) or vehicle, on alternate days. SD was applied before or during reserpine treatment and was performed by gentle handling for 6 h per day for 10 consecutive days. Animals were submitted to motor and non-motor behavioral assessments and neurochemical evaluations. Locomotion was increased by SD and decreased by reserpine treatment. SD during treatment delayed the onset of catalepsy, but SD prior to treatment potentiated reserpine-induced catalepsy. Thus, although SD induced an apparent beneficial effect on motor parameters, a delayed deleterious effect on alterations induced by reserpine was found. In the object recognition test, both SD and reserpine treatment produced cognitive deficits. In addition, the association between SD and reserpine induced anhedonic-like behavior. Finally, an increase in oxidative stress was found in hippocampus of mice subjected to SD, and tyrosine hydroxylase immunoreactivity was reduced in substantia nigra of reserpine-treated animals. Results point to a possible late effect of SD, aggravating the deficits in mice submitted to the reserpine progressive model of PD.

Alpha-pine self-emulsifying nano formulation attenuates rotenone and trichloroethylene-induced dopaminergic loss

AIM

The current investigation's goals are to pharmacologically evaluate the neurotherapeutic role of the bioactive compound Alpha Pinene (ALP)-loaded Self-emulsifying nano-formulation (SENF) in neurotoxin (Rotenone and the Industrial Solvent Trichloroethylene)- induced dopaminergic loss. It is believed that these models simulate important aspects of the molecular pathogenesis of Parkinson's disease.

MATERIAL AND METHODS

The ALP-nano-formulation's anti-Parkinson's activity was compared to ALP suspension in Wistar rats after rotenone and trichloro ethylene-induced dopaminergic loss. Neurobehavioral and motor performances were measured on the 14th, 21st, and 28th day in the rotenone model. However, in the trichloroethylene model, it was measured from the 4th to the 8th week.

RESULTS

Significant neurobehavioral improvement has been found in ALP-SENF treated animals then untreated and animals treated with plain ALP suspension. Furthermore, biochemical tests reveal marked expression of catalase, glutathione, and superoxide dismutase, which significantly combat the (Oxidative stress) OS-induced neurodegeneration.

CONCLUSION

The antioxidant effect of ALP-SENF likely includes free radicals neutralization and the activation of enzymes associated with antioxidant activity, leading to the enhancement of neurobehavioral abnormalities caused by rotenone and trichloroethylene.

Dopamine across timescales and cell types: Relevance for phenotypes in Parkinson's disease progression

Dopamine neurons in the substantia nigra pars compacta (SNc) synthesize and release dopamine, a critical neurotransmitter for movement and learning. SNc dopamine neurons degenerate in Parkinson's Disease (PD), causing a host of motor and non-motor symptoms. Here, we review recent conceptual advances in our basic understanding of the dopamine system - including our rapidly advancing knowledge of dopamine neuron heterogeneity - with special attention to their importance for understanding PD. In PD patients, dopamine neuron degeneration progresses from lateral SNc to medial SNc, suggesting clinically relevant heterogeneity in dopamine neurons. With technical advances in dopamine system interrogation, we can understand the relevance of this heterogeneity for PD progression and harness it to develop new treatments.

The neurobiological effects of senescence on dopaminergic system: A comprehensive review

Over time, the body undergoes a natural, multifactorial, and ongoing process named senescence, which induces changes at the molecular, cellular, and micro-anatomical levels in many body systems. The brain, being a highly complex organ, is particularly affected by this process, potentially impairing its numerous functions. The brain relies on chemical messengers known as neurotransmitters to function properly, with dopamine being one of the most crucial. This catecholamine is responsible for a broad range of critical roles in the central nervous system, including movement, learning, cognition, motivation, emotion, reward, hormonal release, memory consolidation, visual performance, sexual drive, modulation of circadian rhythms, and brain development. In the present review, we thoroughly examine the impact of senescence on the dopaminergic system, with a primary focus on the classic delimitations of the dopaminergic nuclei from A8 to A17. We provide in-depth information about their anatomy and function, particularly addressing how senescence affects each of these nuclei.

Deep brain stimulation of the subthalamic nucleus restores spatial reversal learning in patients with Parkinson's disease

Spatial learning and navigation are supported by distinct memory systems in the human brain such as the hippocampus-based navigational system and the striatum-cortex-based system involved in motor sequence, habit and reversal learning. Here, we studied the role of subthalamic circuits in hippocampus-associated spatial memory and striatal-associated spatial reversal learning formation in patients with Parkinson's disease, who underwent a deep brain stimulation of the subthalamic nucleus. Deep brain stimulation patients (Parkinson's disease-subthalamic nucleus: n = 26) and healthy subjects (n = 15) were tested in a novel experimental spatial memory task based on the Morris water maze that assesses both hippocampal place memory as well as spatial reversal learning. All subjects were trained to navigate to a distinct spatial location hidden within the virtual environment during 16 learning trials in a subthalamic nucleus Stim-On condition. Patients were then randomized into two groups with either a deep brain stimulation On or Off condition. Four hours later, subjects were retested in a delayed recall and reversal learning condition. The reversal learning was realized with a new hidden location that should be memorized during six consecutive trials. The performance was measured by means of an index indicating the improvement during the reversal learning. In the delayed recall condition, neither patients, healthy subjects nor the deep brain stimulation On- versus Off groups showed a difference in place memory performance of the former trained location. In the reversal learning condition, healthy subjects (reversal index 2.0) and patients in the deep brain stimulation On condition (reversal index 1.6) showed a significant improvement. However, patients in the deep brain stimulation Off condition (reversal index 1.1) performed significantly worse and did not improve. There were no differences between all groups in a final visual guided navigation task with a visible target. These results suggest that deep brain stimulation of subthalamic nucleus restores spatial reversal learning in a virtual navigation task in patients with Parkinson's disease and gives insight into the neuromodulation effects on cognition of subthalamic circuits in Parkinson's disease.

VGF modifications related to nigrostriatal dopaminergic neurodegeneration induced by the pesticide fipronil in adult male rats

BACKGROUND

Dopamine is reduced in the brain of rats treated with fipronil, a broad-spectrum insecticide. VGF (no acronym) is a neurotrophin-inducible protein expressed as the 75 kDa form (precursor or pro-VGF) or its truncated peptides. VGF immunostaining has been revealed using an antibody against the C-terminal nonapeptide of the rat pro-VGF in the nerve terminals of the rat substantia nigra, where it was reduced after 6-hydroxydopamine treatment. It is unknown whether pro-VGF and/or its shortened peptides are present in these neurons. Therefore, the aim of this study was first to determine which types of VGF are expressed in the normal substantia nigra (and striatum) and then to determine VGF modulations and whether they occur in parallel with locomotor changes after fipronil injection.

METHODS

Rats were divided into two groups that received a unilateral intranigral infusion of either fipronil (25 µg) diluted in dimethyl sulfoxide (DMSO) or DMSO alone, and then were tested for locomotor activity. An untreated group of rats (n=4) was used for identification of the VGF fragments using high performance liquid chromatography-mass spectrometry and western blot, while changes in treated groups (fipronil vs DMSO, each n=6) were investigated by immunohistochemistry using an antibody against the rat pro-VGF C-terminal nonapeptide in parallel with the anti-tyrosine hydroxylase antibody.

RESULTS

In untreated rats, the VGF C-terminal antibody identified mostly a 75 kDa band in the substantia nigra and striatum, supporting the finding of high-resolution mass spectrometry, which revealed fragments covering the majority of the pro-VGF sequence. Furthermore, several shortened VGF C-terminal forms (varying from 10 to 55 kDa) were also found by western blot, while high-resolution mass spectrometry revealed a C-terminal peptide overlapping the immunogen used to create the VGF antibody in both substantia nigra and striatum. In the substantia nigra of fipronil-treated rats, immunostaining for tyrosine hydroxylase and VGF was reduced compared to DMSO-treated rat group, and this was related with significant changes in locomotor activity.

CONCLUSION

Fipronil has the ability to modulate the production of pro-VGF and/or its C-terminal truncated peptides in the nigrostriatal system indicating its intimate interaction with the dopaminergic neurotransmission and implying a potential function in modulating locomotor activity.

Nanoscale Magneto-mechanical-genetics of Deep Brain Neurons Reversing Motor Deficits in Parkinsonian Mice

Here, we introduce the magneto-mechanical-genetic (MMG)-driven wireless deep brain stimulation (DBS) using magnetic nanostructures for therapeutic benefits in the mouse model of Parkinson's disease (PD). Electrical DBS of the subthalamic nucleus (STN) is an effective therapy for mitigating Parkinson's motor symptoms. However, its broader application is hampered by the requirement for implanted electrodes and the lack of anatomical and cellular specificity. Using the nanoscale magnetic force actuators (m-Torquer), which deliver torque force under rotating magnetic fields to activate pre-encoded Piezo1 ion channels on target neurons, our system enables wireless and STN-specific DBS without implants, addressing key unmet challenges in the DBS field. In both late- and early-stage PD mice, MMG-DBS significantly improved locomotor activity and motor balance by 2-fold compared to untreated PD mice. Moreover, MMG-DBS enabled sustained therapeutic effects. This approach provides a non-invasive and implant-free DBS with cellular targeting capability for the effective treatment of Parkinsonian symptoms.

Transcranial direct current stimulation of the prefrontal cortex improves depression-like behaviors in rats with Parkinson's disease

Depression associated with Parkinson's disease (PD) seriously affects patients, and there is a lack of effective treatments. Transcranial direct current stimulation (tDCS) is increasingly used as a new non-invasive neuromodulation technique in the treatment of neuropsychiatric diseases. However, there is a paucity of research on tDCS for PD-related depression. Our study used PD model rats established with unilateral destruction of the medial forebrain bundle (MFB) to observe the modulatory effects of tDCS acting on the mPFC on depression-like behaviors. We found that tDCS acting on the mPFC improved depression-like behaviors in PD model rats by increasing sucrose intake in sucrose preference test (n = 7-10 rats/group) and shortening immobility time in forced swimming test (n = 7-8 rats/group). Meanwhile, tDCS decreased the expression of c-Fos protein (n = 8-11 rats/group) and the excitation of glutamatergic neurons (n = 6-8 rats/group) in the PrL and LHb of PD model rats. Western blots showed that tDCS decreased the overexpression of serine 845 phosphorylation site of AMPA receptor GluR1 (p-GluR1-S845) in the PrL and LHb of PD model rats (n = 8-11 rats/group), and the overexpression of p-GluR1-S831 in the LHb (n = 8-11 rats/group). The results of this study show that tDCS acting on the mPFC helps to improve PD-related depression, which involves the modulation of excitability and AMPA receptor phosphorylation on the PrL and LHb neurons.

Executive dysfunction and cognitive decline, a non-motor symptom of Parkinson's disease captured in animal models

The non-motor symptoms of Parkinson's disease (PD) have gained increasing attention in recent years due to their significant impact on patients' quality of life. Among these non-motor symptoms, cognitive dysfunction has emerged as an area of particular interest where the clinical aspects are covered in Chapter 2 of this volume. This chapter explores the rationale for investigating the underlying neurobiology of cognitive dysfunction by utilising translational animal models of PD, from rodents to non-human primates. The objective of this chapter is to review the various animal models of cognition that have explored the dysfunction in animal models of Parkinson's disease. Some of the more advanced pharmacological studies aimed at restoring these cognitive deficits are reviewed, although this chapter highlights the lack of systematic approaches in dealing with this non-motor symptom at the pre-clinical stages.

Hydroxychloroquine attenuated motor impairment and oxidative stress in a rat 6-hydroxydopamine model of Parkinson's disease

PURPOSE

Parkinson's disease (PD) is associated with the destruction of dopaminergic neurons in the substantia nigra (SN). Hydroxychloroquine (HCQ) has the capability to cross the blood-brain barrier and promote a neuroprotective potential. This study evaluated the effects of HCQ on the 6-hydroxydopamine (6-OHDA)-induced PD model in rats.

METHODS

Wistar rats were randomly divided into sham, PD, PD + levodopa and PD + HCQ groups. The PD model was induced by a stereotactic administration of 6-OHDA into the left SN pars compacta (SNpc) and confirmed by rotation and the Murprogo's tests. HCQ (100 mg/kg, p.o.) and levodopa (12 mg/kg, p.o.) were administered once a day for 21 days. Three weeks after surgery, the behavioral tests were performed. Brain lipid peroxidation index (MDA), glutathione peroxidase activity (GPx), total antioxidant capacity (TAC) levels and α-synuclein protein expression in the SN were also measured.

RESULTS

The behavioral tests demonstrated that induction of PD increased the muscle rigidity and the number of rotations, which were reversed by HCQ treatment. Also, induction of PD was associated with an increase in α-synuclein protein levels and MDA and decreased TAC levels and GPx activity. However, HCQ decreased α-synuclein and MDA levels while increased TAC levels and GPx activity. In addition, histopathological data showed that HCQ protects dopaminergic neurons against 6-OHDA-induced toxicity.

CONCLUSION

According to the results, HCQ has a beneficial effect in improving PD-related pathophysiology, in part, by mitigating oxidative stress and protecting the dopaminergic neurons in the SN.

Animal models of Parkinson's disease: bridging the gap between disease hallmarks and research questions

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by motor and non-motor symptoms. More than 200 years after its first clinical description, PD remains a serious affliction that affects a growing proportion of the population. Prevailing treatments only alleviate symptoms; there is still neither a cure that targets the neurodegenerative processes nor therapies that modify the course of the disease. Over the past decades, several animal models have been developed to study PD. Although no model precisely recapitulates the pathology, they still provide valuable information that contributes to our understanding of the disease and the limitations of our treatment options. This review comprehensively summarizes the different animal models available for Parkinson's research, with a focus on those induced by drugs, neurotoxins, pesticides, genetic alterations, α-synuclein inoculation, and viral vector injections. We highlight their characteristics and ability to reproduce PD-like phenotypes. It is essential to realize that the strengths and weaknesses of each model and the induction technique at our disposal are determined by the research question being asked. Our review, therefore, seeks to better aid researchers by ensuring a concrete discernment of classical and novel animal models in PD research.

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.

N-Acetylcysteine Treatment May Compensate Motor Impairments through Dopaminergic Transmission Modulation in a Striatal 6-Hydroxydopamine Parkinson's Disease Rat Model

Preventing degeneration and the loss of dopaminergic neurons (DAn) in the brain while mitigating motor symptoms remains a challenge in Parkinson's Disease (PD) treatment development. In light of this, developing or repositioning potential disease-modifying approaches is imperative to achieve meaningful translational gains in PD research. Under this concept, N-acetylcysteine (NAC) has revealed promising perspectives in preserving the dopaminergic system capability and modulating PD mechanisms. Although NAC has been shown to act as an antioxidant and (neuro)protector of the brain, it has yet to be acknowledged how this repurposed drug can improve motor symptomatology and provide disease-modifying properties in PD. Therefore, in the present work, we assessed the impact of NAC on motor and histological deficits in a striatal 6-hydroxydopamine (6-OHDA) rat model of PD. The results revealed that NAC enhanced DAn viability, as we found that it could restore dopamine transporter (DAT) levels compared to the untreated 6-OHDA group. Such findings were positively correlated with a significant amelioration in the motor outcomes of the 6-OHDA-treated animals, demonstrating that NAC may, somehow, be a modulator of PD degenerative mechanisms. Overall, we postulated a proof-of-concept milestone concerning the therapeutic application of NAC. Nevertheless, it is extremely important to understand the complexity of this drug and how its therapeutical properties interact with the cellular and molecular PD mechanisms.

Ginkgo Biloba and Long COVID: In Vivo and In Vitro Models for the Evaluation of Nanotherapeutic Efficacy

Coronavirus infections are neuroinvasive and can provoke injury to the central nervous system (CNS) and long-term illness consequences. They may be associated with inflammatory processes due to cellular oxidative stress and an imbalanced antioxidant system. The ability of phytochemicals with antioxidant and anti-inflammatory activities, such as Ginkgo biloba, to alleviate neurological complications and brain tissue damage has attracted strong ongoing interest in the neurotherapeutic management of long COVID. Ginkgo biloba leaf extract (EGb) contains several bioactive ingredients, e.g., bilobalide, quercetin, ginkgolides A-C, kaempferol, isorhamnetin, and luteolin. They have various pharmacological and medicinal effects, including memory and cognitive improvement. Ginkgo biloba, through its anti-apoptotic, antioxidant, and anti-inflammatory activities, impacts cognitive function and other illness conditions like those in long COVID. While preclinical research on the antioxidant therapies for neuroprotection has shown promising results, clinical translation remains slow due to several challenges (e.g., low drug bioavailability, limited half-life, instability, restricted delivery to target tissues, and poor antioxidant capacity). This review emphasizes the advantages of nanotherapies using nanoparticle drug delivery approaches to overcome these challenges. Various experimental techniques shed light on the molecular mechanisms underlying the oxidative stress response in the nervous system and help comprehend the pathophysiology of the neurological sequelae of SARS-CoV-2 infection. To develop novel therapeutic agents and drug delivery systems, several methods for mimicking oxidative stress conditions have been used (e.g., lipid peroxidation products, mitochondrial respiratory chain inhibitors, and models of ischemic brain damage). We hypothesize the beneficial effects of EGb in the neurotherapeutic management of long-term COVID-19 symptoms, evaluated using either in vitro cellular or in vivo animal models of oxidative stress.

Escalating Bi-Directional Feedback Loops between Proinflammatory Microglia and Mitochondria in Ageing and Post-Diagnosis of Parkinson's Disease

Parkinson's disease (PD) is a chronic and progressive age-related neurodegenerative disease affecting up to 3% of the global population over 65 years of age. Currently, the underlying physiological aetiology of PD is unknown. However, the diagnosed disorder shares many common non-motor symptoms associated with ageing-related neurodegenerative disease progression, such as neuroinflammation, microglial activation, neuronal mitochondrial impairment, and chronic autonomic nervous system dysfunction. Clinical PD has been linked to many interrelated biological and molecular processes, such as escalating proinflammatory immune responses, mitochondrial impairment, lower adenosine triphosphate (ATP) availability, increasing release of neurotoxic reactive oxygen species (ROS), impaired blood brain barrier integrity, chronic activation of microglia, and damage to dopaminergic neurons consistently associated with motor and cognitive decline. Prodromal PD has also been associated with orthostatic hypotension and many other age-related impairments, such as sleep disruption, impaired gut microbiome, and constipation. Thus, this review aimed to present evidence linking mitochondrial dysfunction, including elevated oxidative stress, ROS, and impaired cellular energy production, with the overactivation and escalation of a microglial-mediated proinflammatory immune response as naturally occurring and damaging interlinked bidirectional and self-perpetuating cycles that share common pathological processes in ageing and PD. We propose that both chronic inflammation, microglial activation, and neuronal mitochondrial impairment should be considered as concurrently influencing each other along a continuum rather than as separate and isolated linear metabolic events that affect specific aspects of neural processing and brain function.

Neuroprotective effects of a novel peptide from Lignosus rhinocerotis against 6-hydroxydopamine-induced apoptosis in PC12 cells by inhibiting NF-κB activation

According to previous studies, oxidative stress is a leading cause of dopaminergic neuron death and may contribute to the pathogenesis of Parkinson's disease (PD). In the current study, we used chromatography of gel filtration to identify a novel peptide (Lignosus rhinocerotis peptide [LRP]) from the sclerotium of Lignosus rhinocerotis (Cooke) Ryvarden. Its neuroprotective effect was evaluated using an in vitro PD model constructed by 6-hydroxydopamine (6-OHDA)-stimulated to apoptosis in PC12 cells. The molecular weight of LRP is determined as 1532 Da and the secondary structure is irregular. The simple amino acid sequence of LRP is Thr-Leu-Ala-Pro-Thr-Phe-Leu-Ser-Ser-Leu-Gly-Pro-Cys-Leu-Leu. Notably, LRP has the ability to significantly boost the viability of PC12 cells after exposure to 6-OHDA, as well as enhance the cellular activity of antioxidative enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px). LRP also lowers the level of malondialdehyde (MDA), decreases the activation performance of Caspase-3, and reduces 6-OHDA-induced apoptosis via inhibition of nuclear factor-kappa B (NF-κB) activation. These data indicate that LRP may have the potential to act as a neuroprotective agent.

Design, synthesis, and SAR study of novel flavone 1,2,4-oxadiazole derivatives with anti-inflammatory activities for the treatment of Parkinson's disease

Inflammation is one of a major feature of Parkinson's disease (PD) which poses a threat to people's health in the world. It has been reported that antioxidation and anti-inflammation have significant effects on the treatment of PD. 1,2,4-oxadiazole and flavone derivatives have remarkable antioxidant and anti-inflammatory activities. In order to find highly effective drugs for PD treatment, based on the remarkable anti-inflammatory and antioxidant activities of the 1,2,4-oxadiazole pharmacophore and the flavonoid pharmacophore, we designed and synthesized a novel series of 3-methyl-8-(3-methyl-1,2,4-oxadiazol-5-yl)-2-phenyl-4H-chromen-4-one derivatives by pharmacophore combination, and evaluated their anti-inflammatory and antioxidation activities for PD treatment. Preliminary structure-activity relationship (SAR) analysis was conducted by their inhibitory activities against reactive oxygen species (ROS) and NO release in LPS-induced BV2 Microglia cells, and the optimal compound Flo8 exhibited the most potent anti-inflammatory and antioxidant activities. Both in vivo and in vitro results showed that Flo8 inhibited neuronal apoptosis by inhibiting inflammatory and apoptotic signaling pathways. In vivo studies also showed that the compound Flo8 ameliorated motor and behavioral deficits and increased serum dopamine levels in MPTP-induced PD model mice. Taken together, this study demonstrated the compound Flo8 could be a promising agent for the treatment of PD.

Lactiplantibacillus plantarum PS128 Alleviates Exaggerated Cortical Beta Oscillations and Motor Deficits in the 6-Hydroxydopamine Rat Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by midbrain dopaminergic neuronal loss and subsequent physical impairments. Levodopa manages symptoms best, while deep brain stimulation (DBS) is effective for advanced PD patients; however, side effects occur with the diminishing therapeutic window. Recently, Lactiplantibacillus plantarum PS128 (PS128) was found to elevate dopamine levels in rodent brains, suggesting its potential to prevent PD. Here, the therapeutic efficacy of PS128 was examined in the 6-hydroxydopamine rat PD model. Suppression of the power spectral density of beta oscillations (beta PSD) in the primary motor cortex (M1) was recorded as the indicator of disease progression. We found that 6 weeks of daily PS128 supplementation suppressed M1 beta PSD as well as did levodopa and DBS. Long-term normalization of M1 beta PSD was found in PS128-fed rats, whereas levodopa and DBS showed only temporal effects. PS128 + levodopa and PS128 + DBS exhibited better therapeutic effects than did levodopa + DBS or either alone. Significantly improved motor functions in PS128-fed rats were correlated with normalization of M1 beta PSD. Brain tissue analyses further demonstrated the role of PS128 in dopaminergic neuroprotection and the enhanced availability of neurotransmitters. These findings suggest that psychobiotic PS128 might be used alongside conventional therapies to treat PD patients.

The assessment of executive functions to test the integrity of the nigrostriatal network: A pilot study

Background

Parkinson’s disease (PD) is a chronic neurodegenerative disorder characterized by motor and non-motor symptoms. The latter mainly include affective, sleep, and cognitive deficits. Non-demented PD patients often demonstrate impairments in several executive domains following neuropsychological evaluation. The current pilot study aims at assessing the discriminatory power of the Frontal Assessment Battery-15 (FAB15) in differentiating (i) non-demented PD patients and healthy controls and (ii) PD patients with more and less pronounced motor symptoms.

Methods

Thirty-nine non-demented early-stage PD patients in the “on” dopamine state (26 females, mean age = 64.51 years, SD = 6.47, mean disease duration = 5.49 years, SD = 2.28) and 39 healthy participants (24 females, mean age = 62.60 years, SD = 5.51) were included in the study. All participants completed the FAB15. Motor symptoms of PD patients were quantified via the Unified Parkinson’s Disease Rating Scale-Part III (UPDRS-Part III) and Hoehn and Yahr staging scale (H&Y).

Results

The FAB15 score, adjusted according to normative data for sex, age, and education, proved to be sufficiently able to discriminate PD patients from healthy controls (AUC = 0.69 [95% CI 0.60–0.75], SE = 0.06, p = 0.04, optimal cutoff = 11.29). Conversely, the battery lacked sufficient discriminative capability to differentiate PD patients based on the severity of motor symptoms.

Conclusion

The FAB15 may be a valid tool for distinguishing PD patients from healthy controls. However, it might be less sensitive in identifying clinical phenotypes characterized by visuospatial impairments resulting from posteroparietal and/or temporal dysfunctions. In line with previous evidence, the battery demonstrated to be not expendable in the clinical practice for monitoring the severity of PD-related motor symptoms.

Association of Cognitive Deficit with Glutamate and Insulin Signaling in a Rat Model of Parkinson's Disease

Cognitive deficit is a frequent non-motor symptom in Parkinson's disease (PD) with an unclear pathogenesis. Recent research indicates possible involvement of insulin resistance and glutamate excitotoxicity in PD development. We investigated cognitive performance and the brain glutamate and insulin signaling in a rat model of PD induced by bilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA). Cognitive functions were assessed with Passive Avoidance (PA) and Morris Water Maze (MWM) tests. The expression of tyrosine hydroxylase (TH) and proteins involved in insulin (insulin receptor - IR, phosphoinositide 3 kinase - pI3K, extracellular signal-regulated kinases-ERK) and glutamate receptor (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptos-AMPAR, N-methyl-D-aspartate receptor - NMDAR) signaling was assessed in the hippocampus (HPC), hypothalamus (HPT) and striatum (S) by immunofluorescence, Western blot and enzyme-linked immunosorbent assay (ELISA). Three months after 6-OHDA treatment, cognitive deficit was accompanied by decreased AMPAR activity and TH levels (HPC, S), while levels of the proteins involved in insulin signaling remained largely unchanged. Spearman's rank correlation revealed a strong positive correlation for pAMPAR-PA (S), pNMDAR-pI3K (HPC) and pNMDAR-IR (all regions). Additionally, a positive correlation was found for TH-ERK and TH-pI3K, and a negative one for TH-MWM/errors and pI3K-MWM/time (S). These results suggest a possible association between brain glutamate (but not insulin) signaling dysfunction and cognitive deficit in a rat PD model, detected three months after 6-OHDA treatment.

Embryoid Body Cells from Human Embryonic Stem Cells Overexpressing Dopaminergic Transcription Factors Survive and Initiate Neurogenesis via Neural Rosettes in the Substantia Nigra

Transplantation of immature dopaminergic neurons or neural precursors derived from embryonic stem cells (ESCs) into the substantia nigra pars compacta (SNpc) is a potential therapeutic approach for functional restitution of the nigrostriatal pathway in Parkinson's disease (PD). However, further studies are needed to understand the effects of the local microenvironment on the transplanted cells to improve survival and specific differentiation in situ. We have previously reported that the adult SNpc sustains a neurogenic microenvironment. Non-neuralized embryoid body cells (EBCs) from mouse ESCs (mESCs) overexpressing the dopaminergic transcription factor Lmx1a gave rise to many tyrosine hydroxylase (Th⁺) cells in the intact and damaged adult SNpc, although only for a short-term period. Here, we extended our study by transplanting EBCs from genetically engineered naive human ESC (hESC), overexpressing the dopaminergic transcription factors LMX1A, FOXA2, and OTX2 (hESC-LFO), in the SNpc. Unexpectedly, no graft survival was observed in wild-type hESC EBCs transplants, whereas hESC-LFO EBCs showed viability in the SNpc. Interestingly, neural rosettes, a developmental hallmark of neuroepithelial tissue, emerged at 7- and 15-days post-transplantation (dpt) from the hESC-LFO EBCs. Neural rosettes expressed specification dopaminergic markers (Lmx1a, Otx2), which gave rise to several Th⁺ cells at 30 dpt. Our results suggest that the SNpc enables the robust initiation of neural differentiation of transplanted human EBCs prompted to differentiate toward the midbrain dopaminergic phenotype.

Potential of Nano-Antioxidants and Nanomedicine for Recovery from Neurological Disorders Linked to Long COVID Syndrome

Long-term neurological complications, persisting in patients who cannot fully recover several months after severe SARS-CoV-2 coronavirus infection, are referred to as neurological sequelae of the long COVID syndrome. Among the numerous clinical post-acute COVID-19 symptoms, neurological and psychiatric manifestations comprise prolonged fatigue, "brain fog", memory deficits, headache, ageusia, anosmia, myalgias, cognitive impairments, anxiety, and depression lasting several months. Considering that neurons are highly vulnerable to inflammatory and oxidative stress damages following the overproduction of reactive oxygen species (ROS), neuroinflammation and oxidative stress have been suggested to dominate the pathophysiological mechanisms of the long COVID syndrome. It is emphasized that mitochondrial dysfunction and oxidative stress damages are crucial for the pathogenesis of neurodegenerative disorders. Importantly, antioxidant therapies have the potential to slow down and prevent disease progression. However, many antioxidant compounds display low bioavailability, instability, and transport to targeted tissues, limiting their clinical applications. Various nanocarrier types, e.g., liposomes, cubosomes, solid lipid nanoparticles, micelles, dendrimers, carbon-based nanostructures, nanoceria, and other inorganic nanoparticles, can be employed to enhance antioxidant bioavailability. Here, we highlight the potential of phytochemical antioxidants and other neuroprotective agents (curcumin, quercetin, vitamins C, E and D, melatonin, rosmarinic acid, N-acetylcysteine, and Ginkgo Biloba derivatives) in therapeutic strategies for neuroregeneration. A particular focus is given to the beneficial role of nanoparticle-mediated drug-delivery systems in addressing the challenges of antioxidants for managing and preventing neurological disorders as factors of long COVID sequelae.

Detection of Brain Abnormalities in Parkinson's Rats by Combining Deep Learning and Motion Tracking

Parkinson's disease (PD) is a chronic neurodegenerative disease that affects the central nervous system. PD mainly affects the motor nervous system and may cause cognitive and behavioral problems. One of the best tools to investigate the pathogenesis of PD is animal models, among which the 6-OHDA-treated rat is a widely employed rodent model. In this research, three-dimensional motion capture technology was employed to obtain real-time three-dimensional coordinate information about sick and healthy rats freely moving in an open field. This research also proposes an end-to-end deep learning model of CNN-BGRU to extract spatiotemporal information from 3D coordinate information and perform classification. The experimental results show that the model proposed in this research can effectively distinguish sick rats from healthy rats with a classification accuracy of 98.73%, providing a new and effective method for the clinical detection of Parkinson's syndrome.

5-(4-Hydroxy-3-dimethoxybenzylidene)-thiazolidinone improves motor functions and exerts antioxidant potential in hemiparkinsonian rats

Our previous study demonstrated that 5-(4-hydroxy-3-dimethoxybenzylidene)-thiazolidinone (RD-1), one of rhodamine derivatives, significantly improves motor function in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mice model and could minimize mitochondrial impairment, which is a potential therapeutic target to slow down the dopaminergic neurodegeneration in Parkinson's disease. To further evaluate its therapeutic and antioxidative potential in Parkinson's disease, the current study was designed to explore the effect of RD-1 on hemiparkinsonian rats following unilateral 6-hydroxydopamine lesions. Motor functional behavioral tests, including apomorphine-induced rotational analysis and beam walking tests, were assessed. Our results showed that oral RD-1 administration for 2 weeks alleviated beam walking disability, but not the rotational behavior. Furthermore, compared to the sham group, tyrosine hydroxylase- (TH-) positive neurons in the substantia nigra pars compacta and fibers in the striatum were significantly preserved in the RD-1 treatment group. The abnormal activities of superoxide dismutase, catalase, and glutathione peroxidase and contents of MDA were evidently ameliorated by RD-1, at least partly. We conclude that RD-1 could improve motor functions and alleviate the loss of dopaminergic expression in the nigrostriatal pathway of Parkinson's disease rats, and the protective mechanism of RD-1 against neurodegeneration was possibly via its modulation of antioxidation.

Lipid profiles in the cerebrospinal fluid of rats with 6-hydroxydopamine-induced lesions as a model of Parkinson's disease

Background

Parkinson's disease (PD) is a progressive neurodegenerative disease with characteristic pathological abnormalities, including the loss of dopaminergic (DA) neurons, a dopamine-depleted striatum, and microglial activation. Lipid accumulation exhibits a close relationship with these pathologies in PD.

Methods

Here, 6-hydroxydopamine (6-OHDA) was used to construct a rat model of PD, and the lipid profile in cerebrospinal fluid (CSF) obtained from model rats was analyzed using lipidomic approaches.

Results

Establishment of this PD model was confirmed by apomorphine-induced rotation behaviors, loss of DA neurons, depletion of dopamine in the striatum, and microglial activation after 6-OHDA-induced lesion generation. Unsupervised and supervised methods were employed for lipid analysis. A total of 172 lipid species were identified in CSF and subsequently classified into 18 lipid families. Lipid families, including eicosanoids, triglyceride (TG), cholesterol ester (CE), and free fatty acid (FFA), and 11 lipid species exhibited significantly altered profiles 2 weeks after 6-OHDA administration, and significant changes in eicosanoids, TG, CE, CAR, and three lipid species were noted 5 weeks after 6-OHDA administration. During the period of 6-OHDA-induced lesion formation, the lipid families and species showed concentration fluctuations related to the recovery of behavior and nigrostriatal abnormalities. Correlation analysis showed that the levels of eicosanoids, CE, TG families, and TG (16:0_20:0_18:1) exhibited positive relationships with apomorphine-induced rotation behaviors and negative relationships with tyrosine hydroxylase (TH) expression in the midbrain.

Conclusion

These results revealed that non-progressive nigrostriatal degeneration induced by 6-OHDA promotes the expression of an impairment-related lipidomic signature in CSF, and the level of eicosanoids, CE, TG families, and TG (16:0_20:0_18:1) in CSF may reveal pathological changes in the midbrain after 6-OHDA insult.

Distribution of Cleaved SNAP-25 in the Rat Brain, following Unilateral Injection of Botulinum Neurotoxin-A into the Striatum

In Parkinson's disease, hypercholinism in the striatum occurs, with the consequence of disturbed motor functions. Direct application of Botulinum neurotoxin-A in the striatum of hemi-Parkinsonian rats might be a promising anticholinergic therapeutic option. Here, we aimed to determine the spread of intrastriatally injected BoNT-A in the brain as well as the duration of its action based on the distribution of cleaved SNAP-25. Rats were injected with 1 ng of BoNT-A into the right striatum and the brains were examined at different times up to one year after treatment. In brain sections immunohistochemically stained for BoNT-A, cleaved SNAP-25 area-specific densitometric analyses were performed. Increased immunoreactivity for cleaved SNAP-25 was found in brain regions other than the unilaterally injected striatum. Most cleaved SNAP-25-ir was found in widespread areas ipsilateral to the BoNT-A injection, in some regions, however, immunoreactivity was also measured in the contralateral hemisphere. There was a linear relationship between the distance of a special area from the injected striatum and the time until its maximum averaged immunoreactivity was reached. Moreover, we observed a positive relationship for the area-specific distance from the injected striatum and its maximum immunoreactivity as well as for the connection density with the striatum and its maximum immunoreactivity. The results speak for a bidirectional axonal transport of BoNT-A after its application into the striatum to its widespread connected parts of the brain. Even one year after BoNT-A injection, cleaved SNAP-25 could still be detected.

Characterizing the relationship between L-DOPA-induced-dyskinesia and psychosis-like behaviors in a bilateral rat model of Parkinson's disease

Parkinson's disease associated psychosis (PDAP) is a prevalent non-motor symptom (NMS) that significantly erodes patients' and caregivers' quality of life yet remains vastly understudied. One potential source of PDAP in late-stage Parkinson's disease (PD) is the common dopamine (DA) replacement therapy for motor symptoms, Levodopa (L-DOPA). Given the high incidence of L-DOPA-induced dyskinesia (LID) in later phases of PD, this study sought to characterize the relationship between PDAP and LID in a bilateral medial forebrain bundle 6-hydroxydopamine hydrobromide (6-OHDA) lesion rat model. To assess PDAP in this model, prepulse inhibition (PPI), a well-validated assay of sensorimotor gating, was employed. First, we tested whether a bilateral lesion alone or after chronic L-DOPA treatment was sufficient to induce PPI dysfunction. Rats were also monitored for LID development, using the abnormal involuntary movements (AIMs) test, to examine PPI and LID associations. In experiment 2, Vilazodone (VZD), a serotonin transporter (SERT) blocker and 1A receptor (5-HT_1A) partial agonist was administered to test its potential efficacy in reducing LID and PPI dysfunction. Once testing was complete, tissue was collected for high performance liquid chromatography (HPLC) to examine the monoamine levels in motor and non-motor circuits. Results indicate that bilateral DA lesions produced motor deficits and that chronic L-DOPA induced moderate AIMs; importantly, rats that developed more severe AIMs were more likely to display sensorimotor gating dysfunction. In addition, VZD treatment dose-dependently reduced L-DOPA-induced AIMs without impairing L-DOPA efficacy, although VZD's effects on PPI were limited. Altogether, this project established the bilateral 6-OHDA lesion model accurately portrayed LID and PDAP-like behaviors, uncovered their potential relationship, and finally, demonstrated the utility of VZD for reducing LID.

The Evolving Role of Animal Models in the Discovery and Development of Novel Treatments for Psychiatric Disorders

Historically, animal models have been routinely used in the characterization of novel chemical entities (NCEs) for various psychiatric disorders. Animal models have been essential in the in vivo validation of novel drug targets, establishment of lead compound pharmacokinetic to pharmacodynamic relationships, optimization of lead compounds through preclinical candidate selection, and development of translational measures of target occupancy and functional target engagement. Yet, with decades of multiple NCE failures in Phase II and III efficacy trials for different psychiatric disorders, the utility and value of animal models in the drug discovery process have come under intense scrutiny along with the widespread withdrawal of the pharmaceutical industry from psychiatric drug discovery. More recently, the development and utilization of animal models for the discovery of psychiatric NCEs has undergone a dynamic evolution with the application of the Research Domain Criteria (RDoC) framework for better design of preclinical to clinical translational studies combined with innovative genetic, neural circuitry-based, and automated testing technologies. In this chapter, the authors will discuss this evolving role of animal models for improving the different stages of the discovery and development in the identification of next generation treatments for psychiatric disorders.