Parkinson disease (PD) is a progressive neurodegenerative disease that leads to a wide range of motor and non-motor deficits. Specifically, voice and swallow deficits manifest early, are devastating to quality of life, and are difficult to treat with standard medical therapies. The pathological hallmarks of PD include accumulation of the presynaptic protein alpha-synuclein as well as degeneration of substantia nigra dopaminergic neurons. However, there is no clear understanding of how or when this pathology contributes to voice and swallow dysfunction in PD. In the present study, we evaluated the effect of loss of function of the PTEN-induced putative kinase 1 gene in rats (PINK1 −/−), a model of autosomal recessive PD in humans, on vocalization, oromotor and limb function, and neurodegenerative pathologies. Behavioral measures included ultrasonic vocalizations, tongue force, biting, and gross motor performance that were assayed at 2, 4, 6, and 8 months of age. Aggregated alpha-synuclein and tyrosine hydroxylase immunoreactivity were measured at 8 months. We show that compared to wildtype controls PINK1 −/− rats develop (1) early and progressive vocalization and oromotor deficits; (2) reduced tyrosine hydroxylase immunoreactivity in the locus coeruleus that correlates with vocal loudness and tongue force; and (3) alpha-synuclein neuropathology in brain regions important for cranial sensorimotor control. This novel approach of characterizing a PINK1 −/− genetic model of PD provides the foundational work necessary to define behavioral biomarkers for the development of disease-modifying therapeutics for PD patients.

Parkinson disease (PD) compromises oropharyngeal swallowing, which negatively affects quality of life and contributes to aspiration pneumonia. Dysphagia often begins early in the disease process, and does not improve with standard therapies. As a result, swallowing deficits are undertreated in the PD population. The Pink1 −/− rat is used to model PD, and demonstrates widespread brainstem neuropathology in combination with early-onset sensorimotor dysfunction; however, to date, swallowing behaviors have not been evaluated. To test the hypothesis that Pink1 −/− rats demonstrate early-onset differences in swallowing, we analyzed within-subject oropharyngeal swallowing using videofluoroscopy. Pink1 −/− and wildtype (WT) controls at 4 (Pink1 −/− n = 16, WT = 16) and 8 (Pink1 −/− n = 12, WT = 12) months of age were tested. The average and maximum bolus size was significantly increased in Pink1 −/− rats at both 4 and 8 months. Bolus average velocity was increased at 8 months for all animals; yet, Pink1 −/− animals had significantly increased velocities compared to WT at 8 months. The data show a significant reduction in mastication rate for Pink1 −/− rats at 8 months suggesting the onset of oromotor dysfunction begins at this time point. Relationships among swallowing variables and neuropathological findings, such as increased alpha-synuclein protein in the nucleus ambiguus and reductions in noradrenergic cells in the locus coeruleus in the Pink1 −/− rats, were determined. The presence of early oropharyngeal swallowing deficits and relationships to brainstem pathology in Pink1−/− rat models of PD indicate that this may be a useful model of early swallowing deficits and their mechanisms. These findings suggest clinical implications for early detection and management of dysphagia in PD.

Parkinson disease (PD) is a progressive, neurological disease that affects millions of individuals worldwide. Although instability, rigidity, tremor, and bradykinesia are considered hallmark motor signs of the disease, these are not apparent until mid-to-late stage. In addition to limb motor impairment, individuals with PD also exhibit early-onset speech dysfunction and reduced vocal intelligibility as well as anhedonia and anxiety. Many of these clinical signs vary according to sex in humans with PD. In this study, a translational genetic rat model of early-onset PD (Pink1−/−) was used to address significant gaps in knowledge concerning sex-specific characteristics of limb sensorimotor deficits, vocal motor dysfunction, and changes in affective state. Traditional behavioral tests of limb function, ultrasonic vocalization, anxiety, and anhedonia in the Pink1−/− female rat and wildtype controls were used to test the hypothesis that behavioral performance would significantly differ between genotypes, and that these differences would increase with disease progression (age of the rat). Results demonstrate that Pink1−/− female rats do not exhibit limb sensorimotor deficits but do have significantly reduced intensity (loudness) of vocalizations, and present with anhedonia and anxiety by 8 months of age. Consistent with an early-disease model, Pink1−/− female rats do not exhibit significant decreases in nigrostriatal catecholamines/ metabolites, as measured by HPLC. These results are significant in expanding knowledge of earlyonset deficits in the female Pink1−/− genetic rat model of PD.

Objectives/Hypothesis: Voice disorders in Parkinson's disease (PD) are early-onset, manifest in the preclinical stages of the disease, and negatively impact quality of life. The complete loss of function in the PTEN-induced kinase 1 gene (Pink1) causes a genetic form of early-onset, autosomal recessive PD. Modeled after the human inherited mutation, the Pink1À/À rat demonstrates significant cranial sensorimotor dysfunction including declines in ultrasonic vocalizations. However, the underlying genetics of the vocal fold thyroarytenoid (TA) muscle that may contribute to vocal deficits has not been studied. The aim of this study was to identify differentially expressed genes in the TA muscle of 8-month-old male Pink1À/À rats compared to wildtype controls.Study Design: Animal experiment with control. Methods: High throughput RNA sequencing was used to examine TA muscle gene expression in adult male Pink1À/À rats and wildtype controls. Weighted Gene Co-expression Network Analysis was used to construct co-expression modules to identify biological networks, including where Pink1 was a central node. The ENRICHR tool was used to compare this gene set to existing human gene databases.Results: We identified 134 annotated differentially expressed genes (P < .05 cutoff) and observed enrichment in the following biological pathways: Parkinson's disease (Casp7, Pink1); Parkin-Ubiquitin proteasome degradation (Psmd12, Psmd7); MAPK signaling (Casp7, Ppm1b, Ppp3r1); and inflammatory TNF-α, Nf-κB Signaling (Casp7, Psmd12, Psmd7, Cdc34, Bcl7a, Peg3).Conclusions: Genes and pathways identified here may be useful for evaluating the specific mechanisms of peripheral dysfunction including within the laryngeal muscle and have potential to be used as experimental biomarkers for treatment development.

Background Parkinson’s disease (PD) is a complex neurodegenerative disease with vocal communication deficits that manifest early, progress, and are largely resistant to medical interventions; however, they do respond to exercise-based speech and voice therapies. Objective and Methods To study how exercise-based vocal treatment can affect the progression of communication deficits related to PD, we studied ultrasonic vocalizations (USVs) in rats with homozygous knockout (−/−) of PINK1, a gene mutation known to cause PD, under the manipulation of a behavioral vocal exercise paradigm that allows us to precisely control dose and timing of exercise in the prodromal (prior to diagnosis) stages. Results We show that intensive vocal-training rescues frequency range and intensity deficits as well as leads to an increase in call complexity and duration of calls compared to sham-training; however, over time this training regime loses significant effect as the disease progresses. We also show effects of frequent handling and conspecific (male-female) interaction in the sham-training group as they demonstrated significantly higher call rate, intensity, frequency range, and call complexity compared to rats without any form of training and consequently less handling/interaction. Further, we confirm that this model exhibits progressive gross motor deficits that indicate neurodegeneration. Discussion This study suggests that the evolving nature of vocal communication deficits requires an adjustment of therapy targets and more intensive training over the course of this progressive disease and demonstrates the importance of frequent social experiences.