Allison Kim

Limited inclusion of ethnically diverse and socioeconomically disadvantaged populations in pain research undermines external validity, generalizability, and equity. This comprehensive review synthesized evidence on effective strategies to recruit and retain these populations in pain studies. We searched Medline, Web of Science, Embase, Scopus, and CENTRAL (12 April 2025) and included studies in which ethnically diverse and socioeconomically disadvantaged participants comprised ≥75% of the sample. Quantitative data were pooled using random-effects meta-analyses of proportions, with prespecified subgroup analyses, and qualitative findings were integrated through thematic synthesis. Certainty of evidence was evaluated using GRADE. Eighteen studies (n = 4611; 11 experimental, 5 observational, 2 qualitative), primarily from the United States and involving chronic pain, met inclusion criteria. Overall enrollment among ethnically diverse and socioeconomically disadvantaged groups was 37% (95% CI 18–58%), with significantly higher enrollment in observational studies (84%, 95% CI 78–90%) than in experimental trials (22%, 95% CI 10–36%; p < 0.001). Overall retention was 77% (95% CI 64–88%) and did not differ significantly by study design. Statewide disease-clinic networks, purposive community-leader engagement, and snowball sampling produced the highest enrollment, whereas medical-record screening yielded the lowest enrollment but the highest retention. Compensation and reminder strategies were similarly effective for retention. Thematic synthesis highlighted trust, culturally and linguistically tailored communication, hybrid and flexible visit schedules, transportation assistance, and clinician engagement as key facilitators. GRADE certainty was low for enrollment and moderate for retention. Community-engaged recruitment strategies, clinician referrals, culturally tailored materials, hybrid procedures, and modest incentives can substantially improve participation of ethnically diverse and socioeconomically disadvantaged populations in pain research. Standardized CONSORT-style reporting of recruitment/retention flowcharts according to strategy and ethnicity/socioeconomic status is essential to refine evidence-based strategies in the future.

Parkinson’s disease (PD) is a progressive neurodegenerative disorder primarily characterized by motor impairments resulting from dopaminergic neuron degeneration in the substantia nigra. However, PD is increasingly recognized as a multisystem disorder, where non-motor symptoms such as cognitive impairment, mood disturbances, sleep disorders, and autonomic dysfunction significantly impact patients’ quality of life. These non-motor symptoms often exhibit poor responsiveness to traditional dopaminergic therapies, underscoring a critical gap in current treatment strategies. Our systematic review investigates established methods of PD induction in rodent models and evaluates the methodologies used to assess non-motor symptoms. The review was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) and the Cochrane handbook. Thirty-two studies from 832 articles were included. The studies were characterized by MPTP, 6-OHDA, and rotenone. Our results indicate that there was considerable heterogeneity in behavioral and motor tests, which poses challenges for data comparability and highlights the lack of consensus regarding the most appropriate modeling strategies for specific PD-related behavioral outcomes. All three models demonstrated behavioral changes consistent with dopaminergic impairment when compared to control groups. MPTP-induced models showed significant non-motor deficits across various tests, except in social recognition and novelty-suppressed feeding. The 6-OHDA model consistently produced non-motor impairments, supporting its utility in replicating PD-like neurotoxicity. Rotenone-treated animals exhibited reduced social interaction, decreased sucrose preference, and increased immobility in behavioral assays, further supporting its validity. Overall, our findings indicate that these neurotoxin-based models are effective in reproducing non-motor symptoms of PD, though methodological heterogeneity highlights the need for greater standardization in future preclinical research.