Bladder, bowel, and sexual dysfunction in Parkinson's disease

Diagnosis and treatment of autonomic failure, pain and sleep disturbances in Parkinson's disease: guideline "Parkinson's disease" of the German Society of Neurology

BACKGROUND AND OBJECTIVE

Non-motor symptoms frequently develop throughout the disease course of Parkinson's disease (PD), and pose affected individuals at risk of complications, more rapid disease progression and poorer quality of life. Addressing such symptom burden, the 2023 revised "Parkinson's disease" guideline of the German Society of Neurology aimed at providing evidence-based recommendations for managing PD non-motor symptoms, including autonomic failure, pain and sleep disturbances.

METHODS

Key PICO (Patient, Intervention, Comparison, Outcome) questions were formulated by the steering committee and refined by the assigned authors. Recommendations were drafted based on relevant studies, systematic reviews, meta-analyses and high-quality guidelines identified by the literature search. They were subsequently reviewed, revised, and voted by the Guideline Group in online consensus conferences. Consensus was achieved in case of > 75% agreement among the group members. The consensus was considered strong, if agreement was > 95%.

RESULTS

The guideline entails: (i) 10 PICOs and 23 recommendations on the diagnosis and treatment of urogenital, cardiovascular and gastrointestinal autonomic failure; (ii) four PICOs and four recommendations on the possible types of pain in PD individuals, their diagnosis and treatment; (iii) 11 PICOs and 11 recommendations on the screening, diagnosis and treatment of sleep disturbances and excessive daytime sleepiness in PD individuals, as well as on their prognostic implications. Thirty-one out of 38 recommendations achieved a strong consensus.

CONCLUSION

The current German PD guideline provides a practice-oriented and etiology-driven stepwise approach to the diagnosis and treatment of autonomic failure, pain and sleep disturbances in PD individuals.

Effect of deep brain stimulation on sexual dysfunction among patients who had Parkinson's disease: a systematic review and meta-analysis

BACKGROUND

Patients who have Parkinson's disease (PD) present several non-motor issues, such as sexual dysfunction. Deep brain stimulation (DBS) is a great treatment for PD and could affect both motor and non-motor symptoms of patients.

AIM

The main goal of the current study is to evaluate the impact of DBS on the sexual dysfunction among patients with PD.

METHODS

Five databases (PubMed, Scopus, Embase, Web of Science, and Cochrane Library) were searched for records. Studies that measured the effect of DBS sexual function were included. The risk of bias assessment tool of non-randomized studies of interventions (ROBINS-I) was used to assess the quality of the included studies. The before and after data extraction and statistical analysis were performed using the Comprehensive Meta-analysis software (CMA) version 3.0.

RESULT

Ten studies were included in the systematic review; six of them were eligible to perform a meta-analysis with a total sample size of 532 participants and a mean age of 62.21 ± 1.59 years. All participants performed STN-DBS. The sexual function of participants after STN-DBS implantation significantly increased (SMD = -0.124, 95% CI: -0.209 to -0.038, P-value = 0.005). It also did not have any publication bias. Additionally, their quality of life mounts significantly (SMD = -0.712, 95% CI: -1.002 to -0.422, p-value <0.001).

CONCLUSION

Our systematic review highlights the potential effect of STN-DBS on reducing the sexual dysfunction of patients with PD and boosting their quality of life.

The Effect of Cervical and Lumbar Decompression Surgery for Spinal Stenosis on Erectile Dysfunction

STUDY DESIGN

Observational study.

OBJECTIVES

To evaluate the prevalence of erectile dysfunction and evaluate the effects of decompressive surgery on erectile dysfunction in cervical spinal stenosis and lumbar canal stenosis patients.

METHODS

This observational, prospective analysis enrolled patients aged 18-80 with cervical spinal stenosis and/or lumbar canal stenosis that underwent respective decompressive surgery. The IIEF-5 questionnaire was administered preoperatively, and at 6- and 12-months postoperatively to assess erectile dysfunction severity. The EPIC database was queried to determine any postoperative complications and document prominent erectile dysfunction risk factors.

RESULTS

Of 79 patients included in the analysis, 42 (53.2%) completed the IIEF-5 at 6 months, and 62 (78.5%) completed it at 12 months. Eighteen had cervical stenosis only, 54 had lumbar stenosis only, and 7 had both. 72% (18/25) of cervical stenosis patients and 83.6% (51/61) of lumbar stenosis patients had erectile dysfunction preoperatively according to IIEF-5 responses. The average preoperative IIEF-5 score indicated significant presence of erectile dysfunction for both the cervical and lumbar stenosis groups. No significant differences were identified in IIEF-5 score deltas from pre- to both postoperative periods. The presence of erectile dysfunction in both the cervical and lumbar stenosis groups was not significantly associated with the presence of any documented risk factors.

CONCLUSIONS

Our results suggest no significant improvement in overall erectile function postoperatively for patients with preoperative erectile dysfunction. This is important to address during patient counseling for decompression surgery candidates with cervical spinal stenosis and/or lumbar canal stenosis to manage expectations.

[Bladder dysfunction in patients with stages I-III of Parkinson's disease]

OBJECTIVE

To evaluate bladder dysfunction (BD) and its relationship with Parkinson's disease (PD) symptoms and dopaminergic therapy.

MATERIAL AND METHODS

One hundred and thirteen patients with PD of I-III H&Y stages were examined using the following scales: IPSS, including irritative and obstructive symptom indices, UPDRS I-IV, Sch&En, PDQ-39, BDI, STAI, PFS-16, GDSS, GSRS, MMSE, FAB and NMSQ.

RESULTS

Most of the patients (89.4%) had BD according to IPSS (Me=6.0 [3.0-13.0]), all of them showed irritative disorders, which were combined with obstructive ones in 61%. BD did not depend on sex, stage and duration of PD. IPSS scores correlated with age (rS=0.307), Sch&En (rS=-0.210) and PDQ-39 (rS=0.460), total UPDRS score (rS=0.296) and subscales I-IV scores, postural stability, and non-motor disorders (depression, anxiety, fatigue, frontal dysfunction, and gastrointestinal and orthostatic symptoms). No significant effect of dopaminergic therapy on BD severity was found. BD occurrence predictors according to regression analysis are (R2=0.420) BDI, FAB and male sex. An analysis of obstructive symptoms index in the general group and separately for women showed many correlations with motor PD symptoms (hypokinesia, rigidity, and off-periods) meanwhile the irritative index had practically no such correlations.

CONCLUSIONS

BD is present in the majority of PD patients and significantly reduces the quality of life already in the early stages of PD; BD predictors are depression, frontal dysfunction and male sex. Both obstructive and evacuation dysfunctions are detected in men and women. The obstructive dysfunction relations with a wide range of motor and non-motor PD symptoms indicate that neurodegenerative process is involved in its development.

Sexual dysfunction among patients with Parkinson's disease: A systematic review and meta-analysis

BACKGROUND

Previous studies have reported a higher prevalence of sexual dysfunction (SD) in patients with Parkinson's disease (PD). In the current study, we aimed to conduct a systematic review and meta-analysis to investigate the role of PD as a potential risk factor for SD in both genders.

METHODS

We performed a comprehensive search on PubMed, Embase, Scopus, and Web of Science. All observational studies comparing the prevalence of SD in PD with the general population were included.

RESULTS

After screening 22 studies were included in our qualitative and statistical analysis. We included 13 studies that reported odds ratio (OR) and found a significant association between PD and SD (pooled OR = 3.5, 95% CI = 2.19-5.58). Five studies included only male patients and reported an OR of 3.34 (95% CI = 1.34-8.35; heterogeneity I2 = 81%, Tau2 = 0.79, p < 0.00), while seven studies included both sexes and reported an OR of 3.55 (95% CI = 1.89-6.66; heterogeneity I2 = 78%, Tau2 = 0.53, p < 0.00).

CONCLUSION

In conclusion, our study suggests a strong association between PD and SD in both men and women. Our analysis of 22 observational studies reveals that the prevalence of sexual dysfunction is significantly higher in patients with PD compared to the general population. These findings highlight the importance of addressing SD as part of the comprehensive management of patients with PD.

Non-pharmacological and drug treatment of autonomic dysfunction in multiple system atrophy: current status and future directions

Multiple system atrophy (MSA) is a sporadic, fatal, and rapidly progressive neurodegenerative disease of unknown etiology that is clinically characterized by autonomic failure, parkinsonism, cerebellar ataxia, and pyramidal signs in any combination. Early onset and extensive autonomic dysfunction, including cardiovascular dysfunction characterized by orthostatic hypotension (OH) and supine hypertension, urinary dysfunction characterized by overactive bladder and incomplete bladder emptying, sexual dysfunction characterized by sexual desire deficiency and erectile dysfunction, and gastrointestinal dysfunction characterized by delayed gastric emptying and constipation, are the main features of MSA. Autonomic dysfunction greatly reduces quality of life and increases mortality. Therefore, early diagnosis and intervention are urgently needed to benefit MSA patients. In this review, we aim to discuss the systematic treatment of autonomic dysfunction in MSA, and focus on the current methods, starting from non-pharmacological methods, such as patient education, psychotherapy, diet change, surgery, and neuromodulation, to various drug treatments targeting autonomic nerve and its projection fibers. In addition, we also draw attention to the interactions among various treatments, and introduce novel methods proposed in recent years, such as gene therapy, stem cell therapy, and neural prosthesis implantation. Furthermore, we elaborate on the specific targets and mechanisms of action of various drugs. We would like to call for large-scale research to determine the efficacy of these methods in the future. Finally, we point out that studies on the pathogenesis of MSA and pathophysiological mechanisms of various autonomic dysfunction would also contribute to the development of new promising treatments and concepts.

6-OHDA-Induced Changes in Colonic Segment Contractility in the Rat Model of Parkinson's Disease

Background

Gastrointestinal dysfunction is one of the most common non-motor symptoms in Parkinson's disease (PD). The exact mechanisms behind these symptoms are not clearly understood. Studies in the well-established 6-hydroxydopamine (6-OHDA) lesioned rats of PD have shown altered contractility in isolated circular and longitudinal smooth muscle strips of distal colon. Contractile changes in proximal colon and distal ileum are nevertheless poorly studied. Moreover, segments may serve as better tissue preparations to understand the interplay between circular and longitudinal smooth muscle. This study aimed to compare changes in contractility between isolated full-thickness distal colon muscle strips and segments, and extend the investigation to proximal colon and distal ileum in the 6-OHDA rat model.

Methods

Spontaneous contractions and contractions induced by electrical field stimulation (EFS) and by the non-selective muscarinic agonist methacholine were investigated in strip and/or segment preparations of smooth muscle tissue from distal and proximal colon and distal ileum in an in vitro organ bath comparing 6-OHDA-lesioned rats with Sham-operated animals. Key Results. Our data showed increased contractility evoked by EFS and methacholine in segments, but not in circular and longitudinal tissue strips of distal colon after central 6-OHDA-induced dopamine denervation. Changes in proximal colon segments were also displayed in high K⁺ Krebs-induced contractility and spontaneous contractions.

Conclusions

This study further confirms changes in smooth muscle contractility in distal colon and to some extent in proximal colon, but not in distal ileum in the 6-OHDA rat model of PD. However, the changes depended on tissue preparation.

Sexual dysfunction precedes motor defects, dopaminergic neuronal degeneration, and impaired dopamine metabolism: Insights from Drosophila model of Parkinson's disease

Sexual dysfunction (SD) is one of the most common non-motor symptoms of Parkinson's disease (PD) and remains the most neglected, under-reported, and under-recognized aspect of PD. Studies have shown that Dopamine (DA) in the hypothalamus plays a role in regulating sexual behavior. But the detailed mechanism of SD in PD is not known. Drosophila melanogaster shares several genes and signaling pathways with humans which makes it an ideal model for the study of a neurodegenerative disorder such as PD. Courtship behavior of Drosophila is one such behavior that is closely related to human sexual behavior and so plays an important role in understanding sexual behavior in diseased conditions as well. In the present study, a sporadic SD model of PD using Drosophila was developed and SD phenotype was observed based on abnormalities in courtship behavior markers. The Drosophila SD model was developed in such a way that at the window of neurotoxin paraquat (PQ) treatment [PQ is considered a crucial risk factor for PD due to its structural similarity with 1-methyl-4-phenyl pyridinium (MPP+), the active form of PD-inducing agent, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)], it does not exhibit mobility defects but shows SD. The whole brain tyrosine hydroxylase immunostaining showed no observable dopaminergic (DAergic) degeneration (number of DA neurons and fluorescence intensity of fluorescently labeled secondary antibodies that target anti-TH primary antibody) of the SD model. Similarly, there was no significant depletion of brain DA and its metabolite levels (HVA and DOPAC) as determined using HPLC-ECD (High-Performance Liquid Chromatography using Electrochemical Detector). The present study illustrates that the traits associated with courtship and sexual activity provide sensitive markers at the earlier stage of PD onset. This PQ-induced SD fly model throws an opportunity to decipher the molecular basis of SD under PD conditions and to screen nutraceuticals/potential therapeutic molecules to rescue SD phenotype and further to DAergic neuroprotection.

Sleep and circadian rhythms in Parkinson's disease and preclinical models

The use of animals as models of human physiology is, and has been for many years, an indispensable tool for understanding the mechanisms of human disease. In Parkinson's disease, various mouse models form the cornerstone of these investigations. Early models were developed to reflect the traditional histological features and motor symptoms of Parkinson's disease. However, it is important that models accurately encompass important facets of the disease to allow for comprehensive mechanistic understanding and translational significance. Circadian rhythm and sleep issues are tightly correlated to Parkinson's disease, and often arise prior to the presentation of typical motor deficits. It is essential that models used to understand Parkinson's disease reflect these dysfunctions in circadian rhythms and sleep, both to facilitate investigations into mechanistic interplay between sleep and disease, and to assist in the development of circadian rhythm-facing therapeutic treatments. This review describes the extent to which various genetically- and neurotoxically-induced murine models of Parkinson's reflect the sleep and circadian abnormalities of Parkinson's disease observed in the clinic.

Urodynamic Evaluation in Multiple System Atrophy: A Retrospective Cohort Study

Background

Urological dysfunction in patients with multiple system atrophy (MSA) is one of the main manifestations of autonomic failure. Urodynamic examination is clinically relevant since underlying pathophysiology of lower urinary tract (LUT) dysfunction can be variable.

Objective

Evaluation of the pathophysiology of urological symptoms and exploration of differences in urodynamic patterns of LUT dysfunction between MSA-P and MSA-C.

Methods

Retrospective study of patients with possible and probable MSA who were referred for urodynamic studies between 2004 and 2019. Demographic data, medical history, physical examination and urodynamic studies assessing storage and voiding dysfunction were obtained.

Results

Seventy-four patients were included in this study (MSA-P 64.9% n = 48; median age 62.5 (IQR 56.8-70) years). Detrusor overactivity during filling phase was noted in 58.1% (n = 43) of the patients. In the voiding phase, detrusor sphincter dyssynergia and detrusor underactivity were observed in 24.6% (n = 17) and in 62.1% (n = 41) of the patients, respectively. A postmicturition residual volume of over 100 ml was present in 71.4% (n = 50) of the patients. Comparison of MSA subtypes showed weaker detrusor contractility in MSA-P compared to MSA-C [pdetQmax 26.2 vs. 34.4 cmH20, P = 0.04]. In 56.2% (n = 41) of patients pathophysiology of LUT dysfunction was deemed to be neurogenic and consistent with the diagnosis of MSA. In 35.6% (n = 26) urodynamic pattern suggested other urological co-morbidities.

Conclusion

Urodynamic evaluation is an important tool to analyze the pattern of LUT dysfunction in MSA. Impaired detrusor contractility was seen more in MSA-P which needs to be investigated in further studies.

Does Depression Contribute to the Bladder and Bowel Complaint in Parkinson's Disease Patients?

Background

The question of whether depression contributes to the bladder and bowel complaint in Parkinson's disease (PD) has not been addressed.

Objectives

We studied bladder, bowel and sexual symptoms in PD patients with/without depression.

Methods

We had 267 referred PD patients: age 68.3 ± 7.7 years, 150 men, 117 women. We divided them into those with/without depression and performed the pelvic function questionnaires including bladder, bowel and sexual items; for example, OABSS, IPSS, and a pelvic organ questionnaire).

Results

The patient age, sex ratio, disease duration, Hoehn-Yahr motor grade, and cognitive score were not significantly different between the PD with depression (n = 35, 13.1%) and PD without depression (n = 232, 86.9%) groups. Regarding bladder, bowel and sexual complaints, significant difference was noted in constipation (P = 0.000854) and sensation of residual urine (P = 0.04820) items.

Conclusions

Our PD patients with depression showed significantly more common constipation and sensation of residual urine compared to the patients with PD alone, suggesting that depression contributes to the bladder and bowel complaint in PD patients.

SURINPARK: Safinamide for Urinary Symptoms in Parkinson's Disease

BACKGROUND

Urinary symptoms are common, disabling and generally unresponsive to treatment in Parkinson´s disease (PD). Safinamide is approved as an add-on therapy to levodopa to improve fluctuations.

METHODS

Retrospective analysis of electronic records of nondemented PD patients seen consecutively in a Movement Disorders Unit (November 2018-February 2019). All were assessed with Scale for Outcomes in Parkinson's disease for Autonomic Symptoms-Urinary subscale (SCOPA-AUT-U) by the attending neurologist, and a month afterwards by an independent researcher blinded to treatment and clinical records in a routine clinical practice setting. Clinical variables were compared among patients who were prescribed safinamide (SA+) for the treatment of motor fluctuations and those with different treatment regimes (SA-).

RESULTS

From 169 patients screened initially, 54 were excluded due to severe incontinence, absence of urinary symptoms or previous safinamide treatment. Thirty-five patients were included in SA+ and 79 in SA-. Both groups were comparable in terms of clinical variables, except in basal urinary symptoms, with more severity in the SA+ group. In the follow-up assessment, total SCOPA-AUT-U, as well as urgency, incontinence, frequency and nocturia subscales improved significantly in the SA+ group, while the SA- group remained unchanged.

CONCLUSIONS

Safinamide could be helpful in the improvement of urinary symptoms in PD.

Erectile dysfunction in common neurological conditions: A narrative review

Neurogenic erectile dysfunction (NED) can be defined as the inability to achieve or maintain an erection due to central or peripheral neurologic disease. Neurologic diseases can also affect the physical ability and psychological status of the patient. All these factors may lead to a primary or secondary NED. Medication history plays an important role since there are many drugs commonly used in neurologic patients that can lead to ED. The assessment of NED in these patients is generally evolving with the application of evoked potentials technology in the test of somatic and autonomic nerves, and functional magnetic resonance imaging. With the electrophysiological examinations, neurogenic causes can be determined. These tools allow to categorize neurologic lesion and assess the patient prognosis. The first-line treatment for NED is phosphodiesterase inhibitors. Second-line treatments include intracavernous and intraurethral vasoactive injections. Third-line treatments are penile prostheses. The efficacy and safety of each treatment modality depend on the specific neurologic condition. This review discusses the physiology, pathophysiology, diagnosis, and treatment of ED in multiple peripheral and central neurologic conditions, as well as for future research.

Autonomic failure in Parkinson's disease is associated with striatal dopamine deficiencies

Autonomic dysfunction is a common non-motor symptom in Parkinson's disease (PD). Dopamine and serotonin are known to play a role in autonomic regulation, and, therefore, PD-related degeneration of serotonergic and dopaminergic neurons in these regions may be associated with autonomic dysfunction. We sought to clarify the association between extrastriatal serotonergic and striatal dopaminergic degeneration and the severity of autonomic symptoms, including gastrointestinal, pupillomotor, thermoregulatory, cardiovascular, and urinary dysfunction. We performed hierarchical multiple regression analyses to determine the relationships between (extra)striatal serotonergic and dopaminergic degeneration and autonomic dysfunction in 310 patients with PD. We used [¹²³I]FP-CIT SPECT binding to presynaptic serotonin (SERT) and dopamine (DAT) transporters as a measure of the integrity of these neurotransmitter systems, and the SCOPA-AUT (Scales for Outcomes in Parkinson's Disease-Autonomic) questionnaire to evaluate the perceived severity of autonomic dysfunction. Motor symptom severity, medication status, and sex were added to the model as covariates. Additional analyses were also performed using five subdomains of the SCOPA-AUT: cardiovascular, gastrointestinal, urinary, thermoregulatory, and pupillomotor symptoms. We found that autonomic symptoms were most significantly related to lower [¹²³I]FP-CIT binding ratios in the right caudate nucleus and were mainly driven by gastrointestinal and cardiovascular dysfunction. These results provide a first look into the modest role of dopaminergic projections towards the caudate nucleus in the pathophysiology of autonomic dysfunction in PD, but the underlying mechanism warrants further investigation.

Executive Function Is Related to the Urinary Urgency in Non-demented Patients With Parkinson's Disease

Introduction: Evidence suggests urinary urgency is associated with cognitive impairment in a subtype of Parkinson’s disease (PD) patients. This study investigates if cognitive impairment independently predicts the presence of urinary dysfunction.

Methods: We report data of 189 idiopathic PD patients, excluding those with concomitant diseases or medication interacting with bladder function. A standardized questionnaire was used to define the presence of urinary urgency. All patients underwent a comprehensive motor, cognitive non-motor and health-related quality of life (HRQoL) assessment. Multivariable linear regression analysis was performed to identify independent variables characterizing urinary urgency in PD (PD-UU), which were assigned as discriminant features to estimate their individual contribution to the phenotype of the PD-UU group.

Results: Of 189 PD patients, 115 (60.8%) reported PD-UU. The linear regression analysis showed that among cognitive domains, executive function (EF; p = 0.04) had a significant negative association with PD-UU. In a second model, scores of the Montreal Cognitive Assessment (MoCA) significantly differentiated between study groups (p = 0.007) and also non-motor symptom (NMS) burden (p < 0.001). The third model consisted of reports of HRQoL, of which stigma was the only subscale of the Parkinson’s Disease Questionnaire (PDQ-39) differentiating between patients with and without PD-UU (p = 0.02). The linear discriminant analysis provided evidence that the combination of EF, NMS burden, nocturia, and stigma discriminated between groups with 72.4% accuracy.

Conclusion: In our large, non-demented PD cohort, urinary urgency was associated with executive dysfunction (EF), supporting a possible causative link between both symptoms. A combination of neuropsychological and non-motor aspects identified patients with PD-UU with high discriminative accuracy.

Stimulation of the tibial nerve: a protocol for a multicentred randomised controlled trial for urinary problems associated with Parkinson's disease-STARTUP

INTRODUCTION

Parkinson's disease is the second most common chronic neurodegenerative condition with bladder dysfunction affecting up to 71%. Symptoms affect quality of life and include urgency, frequency, hesitancy, nocturia and incontinence. Addressing urinary dysfunction is one of the top 10 priority research areas identified by the James Lind Alliance and Parkinson's UK.

OBJECTIVES

Conduct a randomised controlled trial (RCT) targeting people with Parkinson's disease (PwP) who have self-reported problematic lower urinary tract symptoms, investigating the effectiveness of transcutaneous tibial nerve stimulation (TTNS) compared with sham TTNS. Implement a standardised training approach and package for the correct application of TTNS. Conduct a cost-effectiveness analysis of TTNS compared with sham TTNS.

METHODS AND ANALYSIS

An RCT of 6 weeks with twice weekly TTNS or sham TTNS. Participants will be recruited in 12 National Health Service neurology/movement disorder services, using a web-based randomisation system, and will be shown how to apply TTNS or sham TTNS. Participants will receive a weekly telephone call from the researchers during the intervention period. The trial has two coprimary outcome measures: International Consultation on Incontinence Questionnaire-Urinary Incontinence Short Form and the International Prostate Symptom Score. Secondary outcomes include a 3-day bladder diary, quality of life, acceptability and fidelity and health economic evaluation. Outcomes will be measured at 0, 6 and 12 weeks.A sample size of 208 randomised in equal numbers to the two arms will provide 90% power to detect a clinically important difference of 2.52 points on the Internatioanl Consultation on Incontinence Questionnaire - Short Form (ICIQ-SF) and of 3 points in the International Prostate Symptom Score total score at 12 weeks at 5% significance level, based on an SD of 4.7 in each arm and 20% attrition at 6 weeks. Analysis will be by intention to treat and pre defined in a statistical analysis plan ETHICS AND DISSEMINATION: East of Scotland Research Ethics Service (EoSRES), 18/ES00042, obtained on 10 May 2018. The trial will allow us to determine effectiveness, safety, cost and acceptability of TTNS for bladder dysfunction in PWP. Results will be published in open access journals; lay reports will be posted to all participants and presented at conferences.

TRIAL REGISTRATION NUMBER

ISRCTN12437878; Pre-results.

Frequency and Dynamics of Non-motor Symptoms Presentation in Hispanic Patients With Parkinson Disease

The clinical phenotype of Parkinson's disease (PD) encompasses a wide range of non-motor symptoms (NMS) compromising the quality of life of affected patients. Currently, information about NMS in PD is scarce among Hispanic populations. Furthermore, few studies have reported the temporal pattern of NMS presentation. We conducted a cross-sectional study aimed to describe the frequency and time of NMS occurrence in Hispanic patients with PD using the self-completed NMS questionnaire (NMSQuest). Participants were interrogated about the time of each NMS presentation respect to the onset of motor symptoms. The frequency of NMS was described according to gender, age at disease onset, disease duration and Hoehn and Yahr (H&Y) stage. We enrolled 120 patients, 73.33% males and 26.66% females, with a mean age of 63.33 ± 8.60 years. All the participants presented at least 1 NMS. The median number of NMS per patient was 12. The most frequent NMS domains were miscellaneous, urinary tract, sleep/fatigue, and gastrointestinal tract symptoms, with no significant gender differences. The most frequent individual NMS were nocturia, urinary urgency, feeling sadness, and constipation. Any patient reported NMS before the onset of motor manifestations. The pattern of occurrence of NMS domains in our population was as follows: attention/memory, cardiovascular, gastrointestinal tract, perceptual problems/hallucinations, mood/cognition, urinary, miscellaneous, sleep/fatigue, and sexual function. Nausea/vomiting was the earliest symptom observed in all patients, whereas sexual dysfunction and changes in interest for sex were the last symptoms to occur. We found no differences in the total number and frequency of NMS between participants grouped according to their age at disease onset. Conversely, patients with a duration of disease >10 years reported a higher frequency of NMS compared to participants with a duration of disease < 10 years. The total number of NMS per patient increased as the HY stage progressed. The proportion of patients presenting symptoms of the gastrointestinal tract, urinary tract, mood/cognition, cardiovascular, and sexual function domains was higher in the HY 4–5 group. Our study provides relevant data to improve our understanding of NMS in PD, which may contribute to anticipate and plan diagnostic and therapeutic strategies among Hispanic PD patients.

Urinary Symptoms in Patients with Parkinson's Disease and Progressive Supranuclear Palsy: Urodynamic Findings and Management of Bladder Dysfunction

OBJECTIVE

The objective of this study is to observe urinary symptoms in patients with Parkinson's disease (PD) and progressive supranuclear palsy (PSP) and advice bladder dysfunction management based on urodynamic study (UDS) findings.

PATIENTS AND METHODS

Twenty-two patients (12 males) with PD and PSP (15 and 7, respectively) with urinary symptoms were included in this study. All patients except one were on levodopa and carbidopa medication. UDS was performed, and bladder management determined.

RESULTS

Mean age was 60.4 years (range 41-73 years, standard deviation [SD] 8.4). Mean illness duration was 31.9 months (range 9-146 months, SD 31.0) and mean duration of urinary symptoms was 14.8 months (range 1-61 months, SD 15.8). Eighteen patients reported nocturia and 16 patients had urgency with or without urge incontinence. Three patients had retention and straining to void and 3 had mixed urinary complaints. Twelve out of 22 patients had absence of voluntary anal contraction on per-rectal examination. UDS was suggestive of 12 patients with neurogenic detrusor overactivity with or without sphincter dyssynergy. Six patients had normal detrusor pressure, and four patients were found to have contractile detrusor. Ten patients had significant postvoid residual. Bladder management included pharmacotherapy, supportive, and behavioral management as appropriate.

CONCLUSIONS

Patients with PD/PSP are known to develop urinary symptoms during illness. Clinical complaints and UDS findings do not necessarily match. UDS is required to manage urinary symptoms. Most of the patients respond to oral antimuscarinic medications along with behavioral and supportive therapy.

Multiple Beneficial Effects of Ghrelin Agonist, HM01 on Homeostasis Alterations in 6-Hydroxydopamine Model of Parkinson's Disease in Male Rats

Background and objective: Developing therapy for non-motor symptoms of Parkinson’s disease (PD) is important for improving patients’ quality of life. Previously, we reported that the ghrelin receptor agonist, HM01 normalized the decreased 4-h fecal output and levodopa-inhibited gastric emptying in 6-OHDA rats, and activated selective areas in brain and spinal cord. In this study, we evaluated whether chronic HM01 treatment influences motor functions and/or has beneficial effects on non-motor symptoms including alterations of body weight and composition, defecation, feeding and water intake in 6-OHDA rats.

Methods: Male rats were microinjected unilaterally into the medial forebrain bundle with either vehicle or 6-OHDA. Three weeks later, we assessed basal body weight, and 24-h fecal output (pellets, weight, dry weight and water content), water intake and food intake (ingested and spillage). Then, HM01 (3 mg/kg) or vehicle was given per gavage daily for 10–12 days and the same parameters were re-assessed daily. Motor behavior (stepping and rotations tests), body composition were monitored before and after the HM01 treatment.

Results: 6-OHDA rats showed motor deficits in rotation test induced by apomorphine and stepping test. They also displayed a significant reduction in body weight, water consumption, fecal weight and water content and an increase in food spillage compared to vehicle microinjected rats. Daily oral treatment of HM01 did not modify motor alterations compared to vehicle but significantly increased the body weight, fat mass, and 24-h fecal weight, fecal water content, food and water intake in 6-OHDA rats, while HM01 had no significant effect in vehicle microinjected rats. Fecal weight and water content were both correlated with water intake, but not with food intake. Fat mass, but not body weight, was correlated with food intake. HM01 effects were significant after 24 h and remained similar during the treatment.

Conclusions: Chronic treatment with ghrelin agonist, HM01 improved several non-motor symptoms in the rat PD model induced by 6-OHDA lesion including the decrease in body weight, water consumption, fecal weight and water content, and increased food intake while not improving the motor deficits. These findings provide pre-clinical evidence of potential benefits of ghrelin agonists to alleviate non-motor symptoms in PD patients.

Lower urinary tract symptoms and sexual dysfunction in men with multiple sclerosis

OBJECTIVES

To assess the prevalence and interrelationship between lower urinary tract symptoms and sexual dysfunction in men with multiple sclerosis (MS).

METHODS

In a cross-sectional study, we evaluated 41 men (mean age 41.1±9.9 years) with MS from February 2011 to March 2013, who were invited to participate irrespective of the presence of lower urinary tract symptoms or sexual dysfunction. Neurological impairment was assessed with the Expanded Disability Status Scale; lower urinary tract symptoms were evaluated with the International Continence Society male short-form questionnaire, and sexual dysfunction was evaluated with the International Index of Erectile Function. All patients underwent transabdominal urinary tract sonography and urine culture.

RESULTS

The mean disease duration was 10.5±7.3 years. Neurological evaluation showed a median Expanded Disability Status Scale score of 3 [2-6]. The median International Continence Society male short-form questionnaire score was 17 [10-25]. The median International Index of Erectile Function score was 29 [15-46]. Twenty-nine patients (74.4%) had sexual dysfunction as defined by an International Index of Erectile Function score <45. Voiding dysfunction and sexual dysfunction increased with the degree of neurological impairment (r=0.02 [0.02 to 0.36] p=0.03 and r=-0.41 [-0.65 to -0.11] p=0.008, respectively). Lower urinary tract symptoms and sexual dysfunction also displayed a significant correlation (r=-0.31 [-0.56 to -0.01] p=0.04).

CONCLUSIONS

Most male patients with MS have lower urinary tract symptoms and sexual dysfunction. The severity of the neurological disease is a predictive factor for the occurrence of voiding and sexual dysfunctions.

Lewy body constipation

We systematically reviewed literature regarding “Lewy body constipation”, i.e., constipation due to Lewy body diseases (LBD), with minimal neurologic symptoms. Epidemiology and pathology studies showed that LBD can start with constipation alone, mostly due to neuronal loss and appearance of Lewy bodies in the myenteric plexus. Because LBD significantly increases with age, “Lewy body constipation” may also increase with age. Neuroimaging methods such as metaiodobenzylguanidine (MIBG) scintigraphy and dopamine transporter (DAT) scan provide a way to detect “Lewy body constipation.” Key for “Lewy body constipation” includes minimal non-motor features such as REM sleep behavior disorder (night talking). Add-on therapy may be required to ameliorate constipation in patients. Diagnosis is not always easy; therefore, collaboration of gastroenterologists and neurologists is highly recommended to maximize patients' quality of life. In conclusion, “Lewy body constipation” might become a distinct category among geriatric constipation, regarding patients' follow-up and their management.

The Gut and Nonmotor Symptoms in Parkinson's Disease

Gastrointestinal (GI) symptoms are one of the most common nonmotor symptoms (NMS) in patients with Parkinson's disease (PD) involving the whole GI tract (GIT) and being evident throughout the whole course of the disease. Furthermore, constipation serves as a risk factor for PD as well as an early prodromal NMS of PD. The gut as gateway to the environment with its enteric nervous system (ENS) plays a crucial role in the neurodegenerative process that leads to PD. Alpha-synucleinopathy as the pathological hallmark of PD could be found within the whole GIT in a rostrocaudal gradient interacting with the ENS, the gut microbiome, and enteric glial cells. Bidirectional interactions between the ENS and the central nervous system (CNS) via a brain-gut-enteric microbiota axis have been reported. As well as there is evidence out of animal, autopsy, and epidemiological studies that α-synuclein spreads via rostrocranial transmission by transsynaptic cell-to-cell transfer via the sympathetic and parasympathetic nervous system to the CNS causing the typical neuropathological changes of PD. Recognition of GI NMS as prodromal markers of PD as well as a better understanding of the brain-gut connection offers new insights in the pathophysiology of PD and might provide the opportunity of PD diagnosis before CNS involvement. Hereby the opportunity for development of neuroprotective and disease-modifying therapeutics, respectively, seem to be promising. This chapter covers the variety of GI NMS and its consequences in PD as well as the important role of the gut as part of the pathological process in PD.

Gastrointestinal Dysfunctions in Parkinson's Disease: Symptoms and Treatments

A diagnosis of Parkinson's disease is classically established after the manifestation of motor symptoms such as rigidity, bradykinesia, and tremor. However, a growing body of evidence supports the hypothesis that nonmotor symptoms, especially gastrointestinal dysfunctions, could be considered as early biomarkers since they are ubiquitously found among confirmed patients and occur much earlier than their motor manifestations. According to Braak's hypothesis, the disease is postulated to originate in the intestine and then spread to the brain via the vagus nerve, a phenomenon that would involve other neuronal types than the well-established dopaminergic population. It has therefore been proposed that peripheral nondopaminergic impairments might precede the alteration of dopaminergic neurons in the central nervous system and, ultimately, the emergence of motor symptoms. Considering the growing interest in the gut-brain axis in Parkinson's disease, this review aims at providing a comprehensive picture of the multiple gastrointestinal features of the disease, along with the therapeutic approaches used to reduce their burden. Moreover, we highlight the importance of gastrointestinal symptoms with respect to the patients' responses towards medical treatments and discuss the various possible adverse interactions that can potentially occur, which are still poorly understood.

Treatment Options for Urogenital Dysfunction in Parkinson's Disease

Urogenital dysfunction is commonly reported in Parkinson’s disease (PD), and history taking and a bladder diary form the cornerstone of evaluation. The assessment of lower urinary tract (LUT) symptoms include urinalysis, ultrasonography, and urodynamic studies and help to evaluate concomitant urological pathologies such as benign prostate enlargement. Antimuscarinic medications are the first line treatment for overactive bladder (OAB) symptoms and solifenacin has been specifically studied in PD. Antimuscarininc drugs may exacerbate PD-related constipation and xerostomia, and caution is advised when using these medications in individuals where cognitive impairment is suspected. Desmopressin is effective for the management of nocturnal polyuria which has been reported to be common in PD. Intradetrusor injections of botulinum toxin have been shown to be effective for detrusor overactivity, however, are associated with the risk of urinary retention. Neuromodulation is a promising, minimally invasive treatment for PD-related OAB symptoms. Erectile dysfunction is commonly reported and first line treatments include phosphodiesterase-5 inhibitors. A patient-tailored approach is required for the optimal management of urogenital dysfunction in PD.

The clinical symptoms of Parkinson's disease

In this review, the clinical features of Parkinson's disease, both motor and non-motor, are described in the context of the progression of the disease. Also briefly discussed are the major treatment strategies and their complications. Parkinson's disease is a slowly progressing neurodegenerative disorder, causing impaired motor function with slow movements, tremor and gait and balance disturbances. A variety of non-motor symptoms are common in Parkinson's disease. They include disturbed autonomic function with orthostatic hypotension, constipation and urinary disturbances, a variety of sleep disorders and a spectrum of neuropsychiatric symptoms. This article describes the different clinical symptoms that may occur and the clinical course of the disease. This article is part of a special issue on Parkinson disease.

Stimulation of dopamine D2-like receptors in the lumbosacral defaecation centre causes propulsive colorectal contractions in rats

KEY POINTS

The pathophysiological roles of the CNS in bowel dysfunction in patients with irritable bowel syndrome and Parkinson's disease remain obscure. In the present study, we demonstrate that dopamine in the lumbosacral defaecation centre causes strong propulsive motility of the colorectum. The effect of dopamine is a result of activation of sacral parasympathetic preganglionic neurons via D2-like dopamine receptors. Considering that dopamine is a neurotransmitter of descending pain inhibitory pathways, our results highlight the novel concept that descending pain inhibitory pathways control not only pain, but also the defaecation reflex. In addition, severe constipation in patients with Parkinson's disease can be explained by reduced parasympathetic outflow as a result of a loss of the effect of dopaminergic neurons.

ABSTRACT

We have recently demonstrated that intrathecally injected noradrenaline caused propulsive contractions of the colorectum. We hypothesized that descending pain inhibitory pathways control not only pain, but also the defaecation reflex. Because dopamine is one of the major neurotransmitters of descending pain inhibitory pathways in the spinal cord, we examined the effects of the intrathecal application of dopamine to the spinal defaecation centre on colorectal motility. Colorectal intraluminal pressure and expelled volume were recorded in vivo in anaesthetized rats. Slice patch clamp and immunohistochemistry were used to confirm the existence of dopamine-sensitive neurons in the sacral parasympathetic nuclei. Intrathecal application of dopamine into the L6-S1 spinal cord, where the lumbosacral defaecation centre is located, caused propulsive contractions of the colorectum. Inactivation of spinal neurons using TTX blocked the effect of dopamine. Although thoracic spinal transection had no effect on the enhancement of colorectal motility by intrathecal dopamine, the severing of the pelvic nerves abolished the enhanced motility. Pharmacological experiments revealed that the effect of dopamine is mediated primarily by D2-like dopamine receptors. Neurons labelled with retrograde dye injected at the colorectum showed an inward current in response to dopamine in slice patch clamp recordings. Furthermore, immunohistochemical analysis revealed that neurons immunoreactive to choline acetyltransferase express D2-like dopamine receptors. Taken together, our findings demonstrate that dopamine activates sacral parasympathetic preganglionic neurons via D2-like dopamine receptors and causes propulsive motility of the colorectum in rats. The present study supports the hypothesis that descending pain inhibitory pathways regulate defaecation reflexes.

Dopamine is produced in the rat spinal cord and regulates micturition reflex after spinal cord injury

Dopamine (DA) neurons in the mammalian central nervous system are thought to be restricted to the brain. DA-mediated regulation of urinary activity is considered to occur through an interaction between midbrain DA neurons and the pontine micturition center. Here we show that DA is produced in the rat spinal cord and modulates the bladder reflex. We observed numerous tyrosine hydroxylase (TH)⁺ neurons in the autonomic nuclei and superficial dorsal horn in L6-S3 spinal segments. These neurons are dopamine-β-hydroxylase (DBH)^- and some contain detectable dopamine decarboxylase (DDC), suggesting their capacity to produce DA. Interestingly, following a complete thoracic spinal cord injury (SCI) to interrupt supraspinal projections, more TH⁺ neurons emerged in the lumbosacral spinal cord, coincident with a sustained, low level of DA expression there and a partially recovered micturition reflex. Non-selective blockade of spinal DA receptors reduced bladder activity whereas activation of spinal D₂-like receptors increased bladder activity and facilitated voiding. Additionally, depletion of lumbosacral TH⁺ neurons with 6-hydroxydopamine (6-OHDA) decreased bladder non-voiding contractions and voiding efficiency. Furthermore, injecting the transsynaptic neuronal tracer pseudorabies virus (PRV) into the bladder detrusor labeled TH⁺ cells in the lumbosacral cord, confirming their involvement in spinal micturition reflex circuits. These results illustrate that DA is synthesized in the rat spinal cord; plasticity of lumbosacral TH⁺ neurons following SCI may contribute to DA expression and modulate the spinal bladder reflex. Thus, spinally-derived DA and receptors could be a novel therapeutic target to improve micturition recovery after SCI.

Brain-gut-microbiota axis in Parkinson's disease

Parkinson’s disease (PD) is characterized by alpha-synucleinopathy that affects all levels of the brain-gut axis including the central, autonomic, and enteric nervous systems. Recently, it has been recognized that the brain-gut axis interactions are significantly modulated by the gut microbiota via immunological, neuroendocrine, and direct neural mechanisms. Dysregulation of the brain-gut-microbiota axis in PD may be associated with gastrointestinal manifestations frequently preceding motor symptoms, as well as with the pathogenesis of PD itself, supporting the hypothesis that the pathological process is spread from the gut to the brain. Excessive stimulation of the innate immune system resulting from gut dysbiosis and/or small intestinal bacterial overgrowth and increased intestinal permeability may induce systemic inflammation, while activation of enteric neurons and enteric glial cells may contribute to the initiation of alpha-synuclein misfolding. Additionally, the adaptive immune system may be disturbed by bacterial proteins cross-reacting with human antigens. A better understanding of the brain-gut-microbiota axis interactions should bring a new insight in the pathophysiology of PD and permit an earlier diagnosis with a focus on peripheral biomarkers within the enteric nervous system. Novel therapeutic options aimed at modifying the gut microbiota composition and enhancing the intestinal epithelial barrier integrity in PD patients could influence the initial step of the following cascade of neurodegeneration in PD.

New ghrelin agonist, HM01 alleviates constipation and L-dopa-delayed gastric emptying in 6-hydroxydopamine rat model of Parkinson's disease

BACKGROUND

Constipation and L-dopa-induced gastric dysmotility are common gastrointestinal (GI) symptoms in Parkinson's disease (PD). We investigated the novel ghrelin agonist, HM01 influence on GI motor dysfunctions in 6-hydroxydopamine (6-OHDA) rats.

METHODS

HM01 pharmacological profiles were determined in vitro and in vivo in rats. We assessed changes in fecal output and water content, and gastric emptying (GE) in 6-OHDA rats treated with orogastric (og) HM01 and L-dopa/carbidopa (LD/CD, 20/2 mg/kg). Fos immunoreactivity (ir) cells in specific brain and lumbosacral spinal cord were quantified.

KEY RESULTS

HM01 displayed a high binding affinity to ghrelin receptor (Ki: 1.42 ± 0.36 nM), 4.3 ± 1.0 h half-life and high brain/plasma ratio. 6-OHDA rats had reduced daily fecal output (22%) and water intake (23%) compared to controls. HM01 (3 and 10 mg/kg) similarly reversed the decreased 4-h fecal weight and water content in 6-OHDA rats. Basal GE was not modified in 6-OHDA rats, however, LD/CD (once or daily for 8 days) delayed GE in 6-OHDA and control rats that was prevented by HM01 (3 mg/kg acute or daily before LD/CD). HM01 increased Fos-ir cell number in the area postrema, arcuate nucleus, nucleus tractus solitarius, and lumbosacral intermediolateral column of 6-OHDA rats where 6-OHDA had a lowering effect compared to controls.

CONCLUSIONS & INFERENCES

6-OHDA rats display constipation- and adipsia-like features of PD and L-dopa-inhibited GE. The new orally active ghrelin agonist, HM01 crosses the blood-brain barrier and alleviates these alterations suggesting a potential benefit for PD with GI disorders.

Bladder dysfunction in presymptomatic gene carriers and patients with Huntington's disease

The objective of this study was to report bladder dysfunction and cystometric findings in a systematically studied cohort of Huntington's disease (HD) patients. In HD patients and asymptomatic HD gene carriers a urinary function questionnaire, neurologic assessment using the Unified Huntington's Disease Rating Scale, and postvoid residual volume measurement were applied. All patients were also invited to cystometric studies. Urinary function data were compared to control men and women. The most common symptoms in 54 HD patients (24 men) were those of bladder overactivity (men/women 54%/40%), followed by urinary incontinence (29%/43%) and symptoms of disturbed bladder emptying (25%/40%). Using urinary function questionnaires severe bladder dysfunction was found in 4%/0%, moderate in 21%/23%, and mild in 25%/30% of HD men/women. Urinary symptoms interfered with daily life in 21%/37% and sexual life in 21%/33% of sexually active HD men/women. In 5 HD men and 1 woman, increased postvoid residual volume (>100 ml) was found. Compared to 49/55 control men/women urinary incontinence, and urgency were more common in HD men, but not in HD women (urinary incontinence reported 10%/38% of control men/women). Cystometry, performed in 12 HD patients and 1 of 10 asymptomatic HD gene carriers, demonstrated detrusor-sphincter dyssynergia in 5 (42%), detrusor overactivity in 2 (17%), and reduced detrusor capacity in 2 (17%) HD patients. Our study demonstrated significant urinary symptoms in HD patients, which reduced their quality of life. Physicians helping HD patients should also consider this largely neglected aspect of the disease.

Erectile dysfunction in the elderly: an old widespread issue with novel treatment perspectives

Erectile dysfunction (ED) is one of the most common chronic diseases affecting men and its prevalence increases with aging. It is also the most frequently diagnosed sexual dysfunction in the older male population. A number of different diseases potentially worsening sexual function may occur in elderly people, together with polypharmacy. Related causes of ED are variable and can include arterial, neurogenic, hormonal, cavernosal, iatrogenic, and psychogenic causes. The aim of the present review was to examine the main aspects of erectile dysfunction going through epidemiology and pathophysiology and revise most of ED in elderly disabled men and in those affected with psychiatric disorders. Lastly we tried to focus on the main aspects of nonpharmacological and pharmacological treatments of ED and the recreational use in the elderly. Phosphodiesterase-5 inhibitors (PDE5-I) are commonly used for on-demand or chronic treatment of ED. It is widely known that PDE5-I have lower response rates in older men than in younger patients, but they have the advantages of ease of use and excellent safety profile, also in the elderly. The old and new PDE5-I as well as the alternative treatments for ED are extensively discussed.

Functional role of Barrington's nucleus in the micturition reflex: relevance in the surgical treatment of Parkinson's disease

The pontine micturition center or Barrington's nucleus (BN) - besides regulating micturition - co-regulates the activity of other pelvic viscera such as the colon and genitals. At present, this issue is gaining particular importance due to: (i) recent findings of α-synuclein in BN, (ii) known urinary dysfunction in parkinsonian patients (part of the so-called non-motor symptoms), other patients with dementia and as in very old individuals; and (iii) its proximity to the pedunculopontine nucleus, a surgical target in deep brain stimulation for Parkinson's disease (PD). The structural and functional organization of the micturition reflex comprises a coordinating action of somatic motor activity with both divisions of the autonomic nervous system, modulated by trunk encephalic and cortical centers that involve the BN as locus coeruleus and periaqueductal gray matter, among other trunk encephalic structures. The involvement of dopaminergic activity (physiologic inhibition of the micturition reflex mediated by dopaminergic D1 activity) that diminishes in Parkinsonism and leads to overactivity of the micturition reflex is also well known. In this review, the integrating role of the BN in the context of vesical and gastrointestinal behavior is revisited, and the principal morpho-functional findings that associate dysfunction with the urinary disorders that appear during the pre-motor stages of PD are summarized.

Animal models of Parkinson's disease: a gateway to therapeutics?

Parkinson's disease (PD) is a progressive, neurodegenerative disorder of unknown etiology, although a complex interaction between environmental and genetic factors has been implicated as a pathogenic mechanism of selected neuronal loss. A better understanding of the etiology, pathogenesis, and molecular mechanisms underlying the disease process may be gained from research on animal models. While cell and tissue models are helpful in unraveling involved molecular pathways, animal models are much better suited to study the pathogenesis and potential treatment strategies. The animal models most relevant to PD include those generated by neurotoxic chemicals that selectively disrupt the catecholaminergic system such as 6-hydroxydopamine; 1-methyl-1,2,3,6-tetrahydropiridine; agricultural pesticide toxins, such as rotenone and paraquat; the ubiquitin proteasome system inhibitors; inflammatory modulators; and several genetically manipulated models, such as α-synuclein, DJ-1, PINK1, Parkin, and leucine-rich repeat kinase 2 transgenic or knock-out animals. Genetic and nongenetic animal models have their own unique advantages and limitations, which must be considered when they are employed in the study of pathogenesis or treatment approaches. This review provides a summary and a critical review of our current knowledge about various in vivo models of PD used to test novel therapeutic strategies.

Systems-Level G Protein-Coupled Receptor Therapy Across a Neurodegenerative Continuum by the GLP-1 Receptor System

With our increasing appreciation of the true complexity of diseases and pathophysiologies, it is clear that this knowledge needs to inform the future development of pharmacotherapeutics. For many disorders, the disease mechanism itself is a complex process spanning multiple signaling networks, tissues, and organ systems. Identifying the precise nature and locations of the pathophysiology is crucial for the creation of systemically effective drugs. Diseases once considered constrained to a limited range of organ systems, e.g., central neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington' disease (HD), the role of multiple central and peripheral organ systems in the etiology of such diseases is now widely accepted. With this knowledge, it is increasingly clear that these seemingly distinct neurodegenerative disorders (AD, PD, and HD) possess multiple pathophysiological similarities thereby demonstrating an inter-related continuum of disease-related molecular alterations. With this systems-level appreciation of neurodegenerative diseases, it is now imperative to consider that pharmacotherapeutics should be developed specifically to address the systemic imbalances that create the disorders. Identification of potential systems-level signaling axes may facilitate the generation of therapeutic agents with synergistic remedial activity across multiple tissues, organ systems, and even diseases. Here, we discuss the potentially therapeutic systems-level interaction of the glucagon-like peptide 1 (GLP-1) ligand-receptor axis with multiple aspects of the AD, PD, and HD neurodegenerative continuum.