To be or not to be pink(1): contradictory findings in an animal model for Parkinson's disease

Ideal animal models according to multifaceted mechanisms and peculiarities in neurological disorders: present and challenges

Neurological disorders, encompassing conditions such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS), pose a significant global health challenge, affecting millions worldwide. With an aging population and increased life expectancy, the prevalence of these disorders is escalating rapidly, leading to substantial economic burdens exceeding trillions of dollars annually. Animal models play a crucial role in understanding the underlying mechanisms of these disorders and developing effective treatments. Various species, including rodents, non-human primates, and fruit flies, are utilized to replicate specific aspects of human neurological conditions. However, selecting the ideal animal model requires careful consideration of its proximity to human disease conditions and its ability to mimic disease pathobiology and pharmacological responses. An Animal Model Quality Assessment (AMQA) tool has been developed to facilitate this selection process, focusing on assessing models based on their similarity to human conditions and disease pathobiology. Therefore, integrating intrinsic and extrinsic factors linked to the disease into the study's objectives aids in constructing a biological information matrix for comparing disease progression between the animal model and human disease. Ultimately, selecting an ideal animal disease model depends on its predictive, face, and construct validity, ensuring relevance and reliability in translational research efforts.

The BE (2)-M17 neuroblastoma cell line: revealing its potential as a cellular model for Parkinson's disease

Parkinson's disease is a pathology with a wide range of in vivo and in vitro models available. Among these, the SH-SY5Y neuroblastoma cell line is one of the most employed. This model expresses catecholaminergic markers and can differentiate and acquire various neuronal phenotypes. However, challenges persist, primarily concerning the variability of growth media, expression of dopaminergic markers, and a wide variety of differentiation protocols have been reported in the literature without direct comparison between them. This lack of standardized differentiation conditions impacts result reproducibility and it makes it very difficult to compare the results obtained from different research groups. An alternative cellular model is the neuroblastoma BE (2)-M17 which exhibits a high basal expression of numerous dopaminergic markers such as tyrosine hydroxylase (TH), vesicular monoamine transporter 2 (VMAT2), and dopamine transporter (DAT). The BE (2)-M17 cells show neuronal properties, grows rapidly in conventional media, and can easily be differentiated to increase their dopaminergic phenotype. In this review, we will thoroughly explore the properties of the BE (2)-M17 cell line and discuss its potential as an excellent model for studying Parkinson's disease.

Cerebellar activity in PINK1 knockout rats during volitional gait

Preclinical models of Parkinson's disease are imperative to gain insight into the neural circuits that contribute to gait dysfunction in advanced stages of the disease. A PTEN-induced putative kinase 1 knockout early-onset model of Parkinson's disease may be a useful rodent model to study the effects of neurotransmitter degeneration caused by a loss of PTEN-induced putative kinase 1 function on brain activity during volitional gait. The goal of this study was to measure changes in neural activity at the cerebellar vermis at 8 months of age. It was found that gait deficits, except run speed, were not significantly different from age-matched wild-type controls, as previously reported. PTEN-induced putative kinase 1 knockout (n = 4) and wild-type (n = 4) rats were implanted with a micro-electrocorticographic array placed over cerebellar vermis Lobules VI (a-c) and VII. Local field potential recordings were obtained during volitional gait across a runway. Power spectral analysis and coherence analysis were used to quantify network oscillatory activity in frequency bands of interest. Cerebellar vermis power was hypoactive in the beta (VIb, VIc and VII) and alpha (VII) bands at cerebellar vermis Lobules VIb, VIc and VII in PTEN-induced putative kinase 1 knockout rats compared with wild-type controls during gait (P < 0.05). These results suggest that gait improvement in PTEN-induced putative kinase 1 knockout rats at 8 months may be a compensatory mechanism attributed to movement corrections caused by a decreased inhibition of the alpha band of cerebellar vermis Lobule VII and beta band of Lobules VIb, VIc and VII. The PTEN-induced putative kinase 1 knockout model may be a valuable tool for understanding the circuit mechanisms underlying gait dysfunction in patients with early-onset Parkinson's disease with a functional loss of PTEN-induced putative kinase 1. Future studies investigating the cerebellar vermis as a potential biomarker and therapeutic target for the treatment of gait dysfunction in Parkinson's disease are warranted.

Pink1/Parkin deficiency alters circulating lymphocyte populations and increases platelet-T cell aggregates in rats

Parkinson's disease (PD) is the most common progressive neurodegenerative movement disorder and results from the selective loss of dopaminergic neurons in the substantia nigra pars compacta. Pink1 and Parkin are proteins that function together in mitochondrial quality control, and when they carry loss-of-function mutations lead to familial forms of PD. While much research has focused on central nervous system alterations in PD, peripheral contributions to PD pathogenesis are increasingly appreciated. We report Pink1/Parkin regulate glycolytic and mitochondrial oxidative metabolism in peripheral blood mononuclear cells (PBMCs) from rats. Pink1/Parkin deficiency induces changes in the circulating lymphocyte populations, namely increased CD4 + T cells and decreased CD8 + T cells and B cells. Loss of Pink1/Parkin leads to elevated platelet counts in the blood and increased platelet-T cell aggregation. Platelet-lymphocyte aggregates are associated with increased thrombosis risk suggesting targeting the Pink1/Parkin pathway in the periphery might have therapeutic potential.

Pink1/Parkin deficiency alters circulating lymphocyte populations and increases platelet-T cell aggregates in rats

Parkinson's disease (PD) is the most common progressive neurodegenerative movement disorder and results from the selective loss of dopaminergic neurons in the substantia nigra pars compacta. Pink1 and Parkin are proteins that function together in mitochondrial quality control, and when they carry loss-of-function mutations lead to familial forms of PD. While much research has focused on central nervous system alterations in PD, peripheral contributions to PD pathogenesis are increasingly appreciated. We report Pink1/Parkin regulate glycolytic and mitochondrial oxidative metabolism in peripheral blood mononuclear cells (PBMCs) from rats. Pink1/Parkin deficiency induces changes in the circulating lymphocyte populations, namely increased CD4 + T cells and decreased CD8 + T cells and B cells. Loss of Pink1/Parkin leads to elevated platelet counts in the blood and increased platelet-T cell aggregation. Platelet-lymphocyte aggregates are associated with increased thrombosis risk, and venous thrombosis is a cause of sudden death in PD, suggesting targeting the Pink1/Parkin pathway in the periphery has therapeutic potential.

PINK1 knockout rats show premotor cognitive deficits measured through a complex maze

Cognitive decline in Parkinson's disease (PD) is a critical premotor sign that may occur in approximately 40% of PD patients up to 10 years prior to clinical recognition and diagnosis. Delineating the mechanisms and specific behavioral signs of cognitive decline associated with PD prior to motor impairment is a critical unmet need. Rodent PD models that have an impairment in a cognitive phenotype for a time period sufficiently long enough prior to motor decline can be useful to establish viable candidate mechanisms. Arguably, the methods used to evaluate cognitive decline in rodent models should emulate methods used in the assessment of humans to optimize translation. Premotor cognitive decline in human PD can potentially be examined in the genetically altered PINK1-/- rat model, which exhibits a protracted onset of motor decline in most studies. To increase translation to cognitive assessment in human PD, we used a modified non-water multiple T-maze, which assesses attention, cognitive flexibility, and working memory similarly to the Trail Making Test (TMT) in humans. Similar to the deficiencies revealed in TMT test outcomes in human PD, 4-month-old PINK1-/- rats made more errors and took longer to complete the maze, despite a hyperkinetic phenotype, compared to wild-type rats. Thus, we have identified a potential methodological tool with cross-species translation to evaluate executive functioning in an established PD rat model.

Prodromal Parkinson disease signs are predicted by a whole-blood inflammatory transcriptional signature in young Pink1-/- rats

BACKGROUND

Parkinson disease (PD) is the fastest growing neurodegenerative disease. The molecular pathology of PD in the prodromal phase is poorly understood; as such, there are no specific prognostic or diagnostic tests. A validated Pink1 genetic knockout rat was used to model early-onset and progressive PD. Male Pink1-/- rats exhibit progressive declines in ultrasonic vocalizations as well as hindlimb and forelimb motor deficits by mid-to-late adulthood. Previous RNA-sequencing work identified upregulation of genes involved in disease pathways and inflammation within the brainstem and vocal fold muscle. The purpose of this study was to identify gene pathways within the whole blood of young Pink1-/- rats (3 months of age) and to link gene expression to early acoustical changes. To accomplish this, limb motor testing (open field and cylinder tests) and ultrasonic vocalization data were collected, immediately followed by the collection of whole blood and RNA extraction. Illumina® Total RNA-Seq TruSeq platform was used to profile differential expression of genes. Statistically significant genes were identified and Weighted Gene Co-expression Network Analysis was used to construct co-expression networks and modules from the whole blood gene expression dataset as well as the open field, cylinder, and USV acoustical dataset. ENRICHR was used to identify the top up-regulated biological pathways.

RESULTS

The data suggest that inflammation and interferon signaling upregulation in the whole blood is present during early PD. We also identified genes involved in the dysregulation of ribosomal protein and RNA processing gene expression as well as prion protein gene expression.

CONCLUSIONS

These data identified several potential blood biomarkers and pathways that may be linked to anxiety and vocalization acoustic parameters and are key candidates for future drug-repurposing work and comparison to human datasets.

Aging hastens locomotor decline in PINK1 knockout rats in association with decreased nigral, but not striatal, dopamine and tyrosine hydroxylase expression

Parkinson's disease (PD) rodent models provide insight into the relationship between nigrostriatal dopamine (DA) signaling and locomotor function. Although toxin-based rat models produce frank nigrostriatal neuron loss and eventual motor decline characteristic of PD, the rapid nature of neuronal loss may not adequately translate premotor traits, such as cognitive decline. Unfortunately, rodent genetic PD models, like the Pink1 knockout (KO) rat, often fail to replicate the differential severity of striatal DA and tyrosine hydroxylase (TH) loss, and a bradykinetic phenotype, reminiscent of human PD. To elucidate this inconsistency, we evaluated aging as a progression factor in the timing of motor and non-motor cognitive impairments. Male PINK1 KO and age-matched wild type (WT) rats were evaluated in a longitudinal study from 3 to 16 months old in one cohort, and in a cross-sectional study of young adult (6-7 months) and aged (18-19 months) in another cohort. Young adult PINK1 KO rats exhibited hyperkinetic behavior associated with elevated DA and TH in the substantia nigra (SN), which decreased therein, but not striatum, in the aged KO rats. Additionally, norepinephrine levels decreased in aged KO rats in the prefrontal cortex (PFC), paired with a higher DA content in young and aged KO. Although a younger age of onset characterizes familial forms of PD, our results underscore the critical need to consider age-related factors. Moreover, the results indicate that compensatory mechanisms may exist to preserve locomotor function, evidenced by increased DA in the SN early in the lifespan, in response to deficient PINK1 function, which declines with aging and the onset of motor impairment.

PINK1 knockout rats show premotor cognitive deficits measured through a complex maze

Cognitive decline in Parkinson's disease (PD) emerges up to 10 years before clinical recognition. Neurobiological mechanisms underlying premotor cognitive impairment in PD can potentially be examined in the PINK1 -/- rat, which exhibits a protracted motor onset. To enhance translation to human PD cognitive assessments, we tested a modified multiple T-maze, which measures cognitive flexibility similarly to the Trail-Making Test in humans. Like human PD outcomes, PINK1 -/- rats made more errors and took longer to complete the maze than wild types. Thus, we have identified a potential tool for assessing cross-species translation of cognitive functioning in an established PD animal model.

Parkinson's disease relevant pathological features are manifested in male Pink1/Parkin deficient rats

Animal disease models are important for neuroscience experimentation and in the study of neurodegenerative disorders. The major neurodegenerative disorder leading to motor impairments is Parkinson's disease (PD). The identification of hereditary forms of PD uncovered gene mutations and variants, such as loss-of-function mutations in PTEN-induced putative kinase 1 (Pink1) and the E3 ubiquitin ligase Parkin, two proteins involved in mitochondrial quality control, that could be harnessed to create animal models. However, to date, such models have not reproducibly recapitulated major aspects of the disease. Here, we describe the generation and phenotypic characterization of a combined Pink1/Parkin double knockout (dKO) rat, which reproducibly exhibits PD-relevant abnormalities, particularly in male animals. Motor dysfunction in Pink1/Parkin dKO rats was characterized by gait abnormalities and decreased rearing frequency, the latter of which was responsive to levodopa treatment. Pink1/Parkin dKO rats exhibited elevated plasma levels of neurofilament light chain and significant loss of tyrosine hydroxylase expression in the substantia nigra pars compacta (SNpc). Glial cell activation was also observed in the SNpc. Pink1/Parkin dKO rats showed elevated plasma and reduced cerebrospinal levels of alpha-synuclein as well as the presence of alpha-synuclein aggregates in the striatum. Further, the profile of circulating lymphocytes was altered, as elevated CD3⁺CD4⁺ T cells and reduced CD3⁺CD8⁺ T cells in Pink1/Parkin dKO rats were found. This coincided with mitochondrial dysfunction and infiltration of CD3⁺ T cells in the striatum. Altogether, the Pink1/Parkin dKO rats exhibited phenotypes similar to what is seen with PD patients, thus highlighting the suitability of this model for mechanistic studies of the role of Pink1 and Parkin in PD pathogenesis and as therapeutic targets.

PINK1-PRKN mediated mitophagy: differences between in vitro and in vivo models

Mitophagy is a key intracellular process that selectively removes damaged mitochondria to prevent their accumulation that can cause neuronal degeneration. During mitophagy, PINK1 (PTEN induced kinase 1), a serine/threonine kinase, works with PRKN/parkin, an E3 ubiquitin ligase, to target damaged mitochondria to the lysosome for degradation. Mutations in the PINK1 and PRKN genes cause early-onset Parkinson disease that is also associated with mitochondrial dysfunction. There are a large number of reports indicating the critical role of PINK1 in mitophagy. However, most of these findings were obtained from in vitro experiments with exogenous PINK1 expression and acute damage of mitochondria by toxins. Recent studies using novel animal models suggest that PINK1-PRKN can also function independent of mitochondria. In this review, we highlight the major differences between in vitro and in vivo models for investigating PINK1 and discuss the potential mechanisms underlying these differences with the aim of understanding how PINK1 functions under different circumstances.Abbreviations: AAV: adeno-associated viruses;AD: Alzheimer disease; CCCP: carbonyl cyanidem-chlorophenyl hydrazone; HD: Huntington disease; MPTP: 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; MTS: mitochondrial targeting sequence; PD: Parkinson diseases; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; ROS: reactive oxygen species; UIM, ubiquitin interacting motif.

Role of rodent models in advancing precision medicine for Parkinson's disease

With a current lack of disease-modifying treatments, an initiative toward implementing a precision medicine approach for treating Parkinson's disease (PD) has emerged. However, challenges remain in how to define and apply precision medicine in PD. To accomplish the goal of optimally targeted and timed treatment for each patient, preclinical research in a diverse population of rodent models will continue to be an essential part of the translational path to identify novel biomarkers for patient diagnosis and subgrouping, understand PD disease mechanisms, identify new therapeutic targets, and screen therapeutics prior to clinical testing. This review highlights the most common rodent models of PD and discusses how these models can contribute to defining and implementing precision medicine for the treatment of PD.

Brain sciences and the R words

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Spontaneous Object Exploration in a Recessive Gene Knockout Model of Parkinson's Disease: Development and Progression of Object Recognition Memory Deficits in Male Pink1-/- Rats

Cognitive impairments appear at or before motor signs in about one third of patients with Parkinson's disease (PD) and have a cumulative prevalence of roughly 80% overall. These deficits exact an unrelenting toll on patients' quality and activities of daily life due in part to a lack of available treatments to ameliorate them. This study used three well-validated novel object recognition-based paradigms to explore the suitability of rats with knockout of the PTEN-induced putative kinase1 gene (Pink1) for investigating factors that induce cognitive decline in PD and for testing new ways to mitigate them. Longitudinal testing of rats from 3-9 months of age revealed significant impairments in male Pink1-/- rats compared to wild type controls in Novel Object Recognition, Novel Object Location and Object-in-Place tasks. Task-specific differences in the progression of object discrimination/memory deficits across age were also seen. Finally, testing using an elevated plus maze, a tapered balance beam and a grip strength gauge showed that in all cases recognition memory deficits preceded potentially confounding impacts of gene knockout on affect or motor function. Taken together, these findings suggest that knockout of the Pink1 gene negatively impacts the brain circuits and/or neurochemical systems that support performance in object recognition tasks. Further investigations using Pink1-/- rats and object recognition memory tasks should provide new insights into the neural underpinnings of the visual recognition memory and visuospatial information processing deficits that are often seen in PD patients and accelerate the pace of discovery of better ways to treat them.

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Oxidative stress and synaptic dysfunction in rodent models of Parkinson's disease

Parkinson's disease (PD) is a multifactorial disorder involving a complex interplay between a variety of genetic and environmental factors. In this scenario, mitochondrial impairment and oxidative stress are widely accepted as crucial neuropathogenic mechanisms, as also evidenced by the identification of PD-associated genes that are directly involved in mitochondrial function. The concept of mitochondrial dysfunction is closely linked to that of synaptic dysfunction. Indeed, compelling evidence supports the role of mitochondria in synaptic transmission and plasticity, although many aspects have not yet been fully elucidated. Here, we will provide a brief overview of the most relevant evidence obtained in different neurotoxin-based and genetic rodent models of PD, focusing on mitochondrial impairment and synaptopathy, an early central event preceding overt nigrostriatal neurodegeneration. The identification of early deficits occurring in PD pathogenesis is crucial in view of the development of potential disease-modifying therapeutic strategies.

Mitochondrial-Dependent and Independent Functions of PINK1

PINK1 has been characterized as a mitochondrial kinase that can target to damaged mitochondria to initiate mitophagy, a process to remove unhealthy mitochondria for protecting neuronal cells. Mutations of the human PINK1 gene are also found to cause early onset Parkinson’s disease, a neurodegenerative disorder with the pathological feature of mitochondrial dysfunction. Despite compelling evidence from in vitro studies to support the role of PINK1 in regulation of mitochondrial function, there is still lack of strong in vivo evidence to validate PINK1-mediated mitophagy in the brain. In addition, growing evidence indicates that PINK1 also executes function independent of mitochondria. In this review, we discuss the mitochondrial dependent and independent functions of PINK1, aiming at elucidating how PINK1 functions differentially under different circumstances.

Dopaminergic but not cholinergic neurodegeneration is correlated with gait disturbances in PINK1 knockout rats

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by gait dysfunction in later stages of the disease. PD hallmarks include a decrease in stride length, run speed, and swing time; an increase in stride time, stance time, and base of support; dopaminergic degeneration in the basal ganglia; and cholinergic degeneration in the pedunculopontine nucleus (PPN). A progressive animal model of PD is needed to identify treatments for gait dysfunction. The goal of this study was to quantify progressive gait degeneration in PTEN-induced putative kinase 1 knockout (P1KO) rats and investigate neurodegeneration as potential underlying mechanisms. Gait analysis was performed in male P1KO and wild-type rats at 5 and 8 months of age and immunohistochemical analysis at 8 months. Multiple parameters of volitional gait were measured using a runway system. P1KO rats exhibited significant gait deficits at 5 months, but not 8 months. Gait abnormalities improved over time suggesting compensation during behavioral testing. At 8 months a 15% loss of tyrosine hydroxylase (TH) in the striatum, a 27% loss of TH-positive cells in the substantia nigra pars compacta, and no significant loss of choline acetyltransferase-positive cells in the PPN was found. Dopaminergic cell loss may contribute to gait deficits in the P1KO model, but not cholinergic cell loss. The P1KO rat with the greatest dopamine loss exhibited the most pronounced PD-like gait deficits, highlighting variability within the model. Further analysis is required to determine the suitability of the P1KO rat as a progressive model of gait abnormalities in PD.

Intraperitoneal Administration of Forskolin Reverses Motor Symptoms and Loss of Midbrain Dopamine Neurons in PINK1 Knockout Rats

BACKGROUND

Parkinson's disease (PD) is a relentless, chronic neurodegenerative disease characterized by the progressive loss of substantia nigra (SN) neurons that leads to the onset of motor and non-motor symptoms. Standard of care for PD consists of replenishing the loss of dopamine through oral administration of Levodopa; however, this treatment is not disease-modifying and often induces intolerable side effects. While the etiology that contributes to PD is largely unknown, emerging evidence in animal models suggests that a significant reduction in neuroprotective Protein Kinase A (PKA) signaling in the SN contributes to PD pathogenesis, suggesting that restoring PKA signaling in the midbrain may be a new anti-PD therapeutic alternative.

OBJECTIVE

We surmised that pharmacological activation of PKA via intraperitoneal administration of Forskolin exerts anti-PD effects in symptomatic PTEN-induced kinase 1 knockout (PINK1-KO), a bona fide in vivo model of PD.

METHODS

By using a beam balance and a grip strength analyzer, we show that Forskolin reverses motor symptoms and loss of hindlimb strength with long-lasting therapeutic effects (> 5 weeks) following the last dose.

RESULTS

In comparison, intraperitoneal treatment with Levodopa temporarily (24 h) reduces motor symptoms but unable to restore hindlimb strength in PINK1-KO rats. By using immunohistochemistry and an XF24e BioAnalyzer, Forskolin treatment reverses SN neurons loss, elevates brain energy production and restores PKA activity in SN in symptomatic PINK1-KO rats.

CONCLUSION

Overall, our collective in vivo data suggest that Forskolin is a promising disease-modifying therapeutic alternative for PD and is superior to Levodopa because it confers long-lasting therapeutic effects.

Establishing Equivalent Aerobic Exercise Parameters Between Early-Stage Parkinson's Disease and Pink1 Knockout Rats

BACKGROUND

Rodent Parkinson's disease (PD) models are valuable to interrogate neurobiological mechanisms of exercise that mitigate motor impairment. Translating these mechanisms to human PD must account for physical capabilities of the patient.

OBJECTIVE

To establish cardiovascular parameters as a common metric for cross-species translation of aerobic exercise impact.

METHOD

We evaluated aerobic exercise impact on heart rate (HR) in 21 early-stage PD subjects (Hoehn Yahr ≤1.5) exercising in non-contact boxing training for ≥3 months, ≥3x/week. In 4-month-old Pink1 knockout (KO) rats exercising in a progressively-increased treadmill speed regimen, we determined a specific treadmill speed that increased HR to an extent similar in human subjects.

RESULTS

After completing aerobic exercise for ∼30 min, PD subjects had increased HR∼35% above baseline (∼63% maximum HR). Motor and cognitive test results indicated the exercising subjects completed the timed up and go (TUG) and trail-making test (TMT-A) in significantly less time versus exercise-naïve PD subjects. In KO and age-matched wild-type (WT) rats, treadmill speeds of 8-10 m/min increased HR up to 25% above baseline (∼67% maximum HR), with no further increases up to 16 m/min. Exercised KO, but not WT, rats showed increased locomotor activity compared to an age-matched exercise-naïve cohort at 5 months old.

CONCLUSION

These proof-of-concept results indicate HR is a cross-species translation parameter to evaluate aerobic exercise impact on specific motor or cognitive functions in human subjects and rat PD models. Moreover, a moderate intensity exercise regimen is within the physical abilities of early-stage PD patients and is therefore applicable for interrogating neurobiological mechanisms in rat PD models.

PINK1 kinase dysfunction triggers neurodegeneration in the primate brain without impacting mitochondrial homeostasis

In vitro studies have established the prevalent theory that the mitochondrial kinase PINK1 protects neurodegeneration by removing damaged mitochondria in Parkinson's disease (PD). However, difficulty in detecting endogenous PINK1 protein in rodent brains and cell lines has prevented the rigorous investigation of the in vivo role of PINK1. Here we report that PINK1 kinase form is selectively expressed in the human and monkey brains. CRISPR/Cas9-mediated deficiency of PINK1 causes similar neurodegeneration in the brains of fetal and adult monkeys as well as cultured monkey neurons without affecting mitochondrial protein expression and morphology. Importantly, PINK1 mutations in the primate brain and human cells reduce protein phosphorylation that is important for neuronal function and survival. Our findings suggest that PINK1 kinase activity rather than its mitochondrial function is essential for the neuronal survival in the primate brains and that its kinase dysfunction could be involved in the pathogenesis of PD.

Rat Models of Vocal Deficits in Parkinson's Disease

Parkinson's disease (PD) is a progressive, degenerative disorder that affects 10 million people worldwide. More than 90% of individuals with PD develop hypokinetic dysarthria, a motor speech disorder that impairs vocal communication and quality of life. Despite the prevalence of vocal deficits in this population, very little is known about the pathological mechanisms underlying this aspect of disease. As such, effective treatment options are limited. Rat models have provided unique insights into the disease-specific mechanisms of vocal deficits in PD. This review summarizes recent studies investigating vocal deficits in 6-hydroxydopamine (6-OHDA), alpha-synuclein overexpression, DJ1-/-, and Pink1-/- rat models of PD. Model-specific changes to rat ultrasonic vocalization (USV), and the effects of exercise and pharmacologic interventions on USV production in these models are discussed.

Distribution of alpha-synuclein in the rat cranial sensory ganglia, and oro-cervical regions

BACKGROUND

Alpha-synuclein (Syn), an unfolded soluble cytosolic protein, is known as a disease-associated protein in the brain. However, little is known about distribution of this protein in the peripheral nervous system. In this study, expression of Syn was investigated in the sensory ganglia of the cranial nerves V, IX and X.

METHODS

To analyze distribution of Syn and its co-expression with calcitonin gene-related peptide (CGRP) or the transient receptor potential cation channel subfamily V member 1 (TRPV1), immunohistochemical techniques were used in the rat cranial sensory ganglia and their peripheral tissues.

RESULTS

Syn-immunoreactive (-ir) neurons were abundant in the sensory ganglia of the petrosal (56.7%), jugular (28.3%) and nodose ganglia (82.5%). These neurons had small to medium-sized cell bodies (petrosal, mean ± S.D. = 667.4 ± 310.8 μ m²; jugular, 625.1 ± 318.4 μ m²; nodose, 708.3 ± 248.3 μ m²), and were distributed throughout the ganglia. However, the trigeminal ganglion was mostly free of Syn-ir neurons. By double and triple immunofluorescence staining, Syn-ir neurons co-expressed CGRP and TRPV1 in the petrosal and jugular ganglia. Syn-immunoreactivity was expressed by nerve fibers in the epithelium and taste bud of oral and cervical viscerae. These nerve fibers were abundant in the naso-pharynx, epiglottis and laryngeal vestibule. Some taste bud cells were also immunoreactive for Syn. In addition, Syn-ir nerve fibers were detected in the vicinity of macrophages, dendritic cells and Langerhans cells.

CONCLUSIONS

Syn was abundant in the visceral sensory neurons but not in somatic sensory neurons. This protein may play a role in nociceptive and chemosensory transduction in the glossopharyngeal and vagal sensory ganglia. It is possible that Syn has a function about the immune mechanism of the upper air way.

Fidelity of the PINK1 knockout rat to oxidative stress and other characteristics of Parkinson disease

Parkinson disease (PD) is the second most common age-related neurodegenerative disease in the world, and PD significantly impacts the quality of life, especially as in general people are living longer. Because of the numerous and complex features of sporadic PD that progressively develops, it is difficult to build an ideal animal model for PD research. Genetically modified PD rodent animal models are considered as a major tool with which to study the mechanisms and potential therapeutic targets for PD. Up to now, none of the rodent animal models displays all PD characteristics. The Michael J. Fox Foundation for Parkinson's Research (MJFF) funded SAGE Laboratories to generate a PTEN-induced putative kinase-1 (PINK1) knockout (KO) rat model for familial PD using zinc finger nuclease (ZFN) technology. In the current paper, we review all papers from PubMed that report studies with PINK1 KO rats, presenting the research results, and discussing the fidelity of this rat model to PD according to its phenotypes studied by several laboratories. This review will serve as a critical reference for future studies with this rodent model, providing a better understanding of PD etiology, pathology, and potential treatment strategies.

Increased glutamate transmission onto dorsal striatum spiny projection neurons in Pink1 knockout rats

Loss-of-function PTEN Induced Kinase 1 (PINK1) mutations cause early-onset familial Parkinson's disease (PD) with similar clinical and neuropathological characteristics as idiopathic PD. While Pink1 knockout (KO) rats have mitochondrial dysfunction, locomotor deficits, and α-synuclein aggregates in several brain regions such as cerebral cortex, dorsal striatum, and substantia nigra, the functional ramifications on synaptic circuits are unknown. Using whole cell patch clamp recordings, we found a significant increase in the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) onto striatal spiny projection neurons (SPNs) in Pink1 KO rats at ages 4 and 6 months compared to wild-type (WT) littermates, suggesting increased excitability of presynaptic neurons. While sEPSC amplitudes were also increased at 2 and 4 months, no changes were observed in AMPAR/NMDAR ratio or receptor expression. Further analysis revealed increased glutamate release probability and decreased recovery of the synaptic vesicle pool following a train of stimulation in Pink1 KO rats. Ultrastructural analysis revealed increased excitatory and inhibitory synapse number and increased levels of presynaptic α-synuclein, while the number and structure of striatal mitochondria appeared normal. Lastly, we found that Pink1 KO rats have altered striatal dopamine tone, which together with the abnormal α- synuclein distribution and dysfunctional mitochondria, could contribute to the increase in excitatory transmission. Together, these studies show that PINK1 is necessary for normal glutamatergic transmission onto striatal SPNs and reveal possible mechanisms underlying striatal circuit dysfunction in PD.