Common principles for odour coding across vertebrates and invertebrates.

The olfactory system is an ideal and tractable system for exploring how the brain transforms sensory inputs into behaviour. The basic tasks of any olfactory system include odour detection, discrimination and categorization. The challenge for the olfactory system is to transform the high-dimensional space of olfactory stimuli into the much smaller space of perceived objects and valence that endows odours with meaning. Our current understanding of how neural circuits address this challenge has come primarily from observations of the mechanisms of the brain for processing other sensory modalities, such as vision and hearing, in which optimized deep hierarchical circuits are used to extract sensory features that vary along continuous physical dimensions. The olfactory system, by contrast, contends with an ill-defined, high-dimensional stimulus space and discrete stimuli using a circuit architecture that is shallow and parallelized. Here, we present recent observations in vertebrate and invertebrate systems that relate the statistical structure and state-dependent modulation of olfactory codes to mechanisms of perception and odour-guided behaviour.

Structural insights into BCDX2 complex function in homologous recombination.

Homologous recombination (HR) fulfils a pivotal role in the repair of DNA double-strand breaks and collapsed replication forks1. HR depends on the products of several paralogues of RAD51, including the tetrameric complex of RAD51B, RAD51C, RAD51D and XRCC2 (BCDX2)2. BCDX2 functions as a mediator of nucleoprotein filament assembly by RAD51 and single-stranded DNA (ssDNA) during HR, but its mechanism remains undefined. Here we report cryogenic electron microscopy reconstructions of human BCDX2 in apo and ssDNA-bound states. The structures reveal how the amino-terminal domains of RAD51B, RAD51C and RAD51D participate in inter-subunit interactions that underpin complex formation and ssDNA-binding specificity. Single-molecule DNA curtain analysis yields insights into how BCDX2 enhances RAD51-ssDNA nucleoprotein filament assembly. Moreover, our cryogenic electron microscopy and functional analyses explain how RAD51C alterations found in patients with cancer3-6 inactivate DNA binding and the HR mediator activity of BCDX2. Our findings shed light on the role of BCDX2 in HR and provide a foundation for understanding how pathogenic alterations in BCDX2 impact genome repair.

RAD51 Gene Family Structure and Function.

Accurate DNA repair and replication are critical for genomic stability and cancer prevention. RAD51 and its gene family are key regulators of DNA fidelity through diverse roles in double-strand break repair, replication stress, and meiosis. RAD51 is an ATPase that forms a nucleoprotein filament on single-stranded DNA. RAD51 has the function of finding and invading homologous DNA sequences to enable accurate and timely DNA repair. Its paralogs, which arose from ancient gene duplications of RAD51, have evolved to regulate and promote RAD51 function. Underscoring its importance, misregulation of RAD51, and its paralogs, is associated with diseases such as cancer and Fanconi anemia. In this review, we focus on the mammalian RAD51 structure and function and highlight the use of model systems to enable mechanistic understanding of RAD51 cellular roles. We also discuss how misregulation of the RAD51 gene family members contributes to disease and consider new approaches to pharmacologically inhibit RAD51.

RAD51AP1 Is an Essential Mediator of Alternative Lengthening of Telomeres.

Alternative lengthening of telomeres (ALT) is a homology-directed repair (HDR) mechanism of telomere elongation that controls proliferation in aggressive cancers. We show that the disruption of RAD51-associated protein 1 (RAD51AP1) in ALT+ cancer cells leads to generational telomere shortening. This is due to RAD51AP1's involvement in RAD51-dependent homologous recombination (HR) and RAD52-POLD3-dependent break induced DNA synthesis. RAD51AP1 KO ALT+ cells exhibit telomere dysfunction and cytosolic telomeric DNA fragments that are sensed by cGAS. Intriguingly, they activate ULK1-ATG7-dependent autophagy as a survival mechanism to mitigate DNA damage and apoptosis. Importantly, RAD51AP1 protein levels are elevated in ALT+ cells due to MMS21 associated SUMOylation. Mutation of a single SUMO-targeted lysine residue perturbs telomere dynamics. These findings indicate that RAD51AP1 is an essential mediator of the ALT mechanism and is co-opted by post-translational mechanisms to maintain telomere length and ensure proliferation of ALT+ cancer cells.

Unlicensed origin DNA melting by MCV and SV40 polyomavirus LT proteins is independent of ATP-dependent helicase activity.

Cellular eukaryotic replication initiation helicases are first loaded as head-to-head double hexamers on double-stranded (ds) DNA origins and then initiate S-phase DNA melting during licensed (once per cell cycle) replication. Merkel cell polyomavirus (MCV) large T (LT) helicase oncoprotein similarly binds and melts its own 98-bp origin but replicates multiple times in a single cell cycle. To examine the actions of this unlicensed viral helicase, we quantitated multimerization of MCV LT molecules as they assembled on MCV DNA origins using real-time single-molecule microscopy. MCV LT formed highly stable double hexamers having 17-fold longer mean lifetime (τ, >1,500 s) on DNA than single hexamers. Unexpectedly, partial MCV LT assembly without double-hexamer formation was sufficient to melt origin dsDNA as measured by RAD51, RPA70, or S1 nuclease cobinding. DNA melting also occurred with truncated MCV LT proteins lacking the helicase domain, but was lost from a protein without the multimerization domain that could bind only as a monomer to DNA. SV40 polyomavirus LT also multimerized to the MCV origin without forming a functional hexamer but still melted origin DNA. MCV origin melting did not require ATP hydrolysis and occurred for both MCV and SV40 LT proteins using the nonhydrolyzable ATP analog, adenylyl-imidodiphosphate (AMP-PNP). LT double hexamers formed in AMP-PNP, and melted DNA, consistent with direct LT hexamer assembly around single-stranded (ss) DNA without the energy-dependent dsDNA-to-ssDNA melting and remodeling steps used by cellular helicases. These results indicate that LT multimerization rather than helicase activity is required for origin DNA melting during unlicensed virus replication.

Deep brain stimulation for refractory major depressive disorder: a comprehensive review.

Deep brain stimulation (DBS) has emerged as a promising treatment for select patients with refractory major depressive disorder (MDD). The clinical effectiveness of DBS for MDD has been demonstrated in meta-analyses, open-label studies, and a few controlled studies. However, randomized controlled trials have yielded mixed outcomes, highlighting challenges that must be addressed prior to widespread adoption of DBS for MDD. These challenges include tracking MDD symptoms objectively to evaluate the clinical effectiveness of DBS with sensitivity and specificity, identifying the patient population that is most likely to benefit from DBS, selecting the optimal patient-specific surgical target and stimulation parameters, and understanding the mechanisms underpinning the therapeutic benefits of DBS in the context of MDD pathophysiology. In this review, we provide an overview of the latest clinical evidence of MDD DBS effectiveness and the recent technological advancements that could transform our understanding of MDD pathophysiology, improve the clinical outcomes for MDD DBS, and establish a path forward to develop more effective neuromodulation therapies to alleviate depressive symptoms.

Hrq1/RECQL4 regulation is critical for preventing aberrant recombination during DNA intrastrand crosslink repair and is upregulated in breast cancer.

Human RECQL4 is a member of the RecQ family of DNA helicases and functions during DNA replication and repair. RECQL4 mutations are associated with developmental defects and cancer. Although RECQL4 mutations lead to disease, RECQL4 overexpression is also observed in cancer, including breast and prostate. Thus, tight regulation of RECQL4 protein levels is crucial for genome stability. Because mammalian RECQL4 is essential, how cells regulate RECQL4 protein levels is largely unknown. Utilizing budding yeast, we investigated the RECQL4 homolog, HRQ1, during DNA crosslink repair. We find that Hrq1 functions in the error-free template switching pathway to mediate DNA intrastrand crosslink repair. Although Hrq1 mediates repair of cisplatin-induced lesions, it is paradoxically degraded by the proteasome following cisplatin treatment. By identifying the targeted lysine residues, we show that preventing Hrq1 degradation results in increased recombination and mutagenesis. Like yeast, human RECQL4 is similarly degraded upon exposure to crosslinking agents. Furthermore, over-expression of RECQL4 results in increased RAD51 foci, which is dependent on its helicase activity. Using bioinformatic analysis, we observe that RECQL4 overexpression correlates with increased recombination and mutations. Overall, our study uncovers a role for Hrq1/RECQL4 in DNA intrastrand crosslink repair and provides further insight how misregulation of RECQL4 can promote genomic instability, a cancer hallmark.

Homologous recombination-deficient mutation cluster in tumor suppressor RAD51C identified by comprehensive analysis of cancer variants.

Mutations in homologous recombination (HR) genes, including BRCA1, BRCA2, and the RAD51 paralog RAD51C, predispose to tumorigenesis and sensitize cancers to DNA-damaging agents and poly(ADP ribose) polymerase inhibitors. However, ∼800 missense variants of unknown significance have been identified for RAD51C alone, impairing cancer risk assessment and therapeutic strategies. Here, we interrogated >50 RAD51C missense variants, finding that mutations in residues conserved with RAD51 strongly predicted HR deficiency and disrupted interactions with other RAD51 paralogs. A cluster of mutations was identified in and around the Walker A box that led to impairments in HR, interactions with three other RAD51 paralogs, binding to single-stranded DNA, and ATP hydrolysis. We generated structural models of the two RAD51 paralog complexes containing RAD51C, RAD51B-RAD51C-RAD51D-XRCC2 and RAD51C-XRCC3. Together with our functional and biochemical analyses, the structural models predict ATP binding at the interface of RAD51C interactions with other RAD51 paralogs, similar to interactions between monomers in RAD51 filaments, and explain the failure of RAD51C variants in binding multiple paralogs. Ovarian cancer patients with variants in this cluster showed exceptionally long survival, which may be relevant to the reversion potential of the variants. This comprehensive analysis provides a framework for RAD51C variant classification. Importantly, it also provides insight into the functioning of the RAD51 paralog complexes.

Histone locus regulation by the Drosophila dosage compensation adaptor protein CLAMP.

The conserved histone locus body (HLB) assembles prior to zygotic gene activation early during development and concentrates factors into a nuclear domain of coordinated histone gene regulation. Although HLBs form specifically at replication-dependent histone loci, the cis and trans factors that target HLB components to histone genes remained unknown. Here we report that conserved GA repeat cis elements within the bidirectional histone3-histone4 promoter direct HLB formation in Drosophila In addition, the CLAMP (chromatin-linked adaptor for male-specific lethal [MSL] proteins) zinc finger protein binds these GA repeat motifs, increases chromatin accessibility, enhances histone gene transcription, and promotes HLB formation. We demonstrated previously that CLAMP also promotes the formation of another domain of coordinated gene regulation: the dosage-compensated male X chromosome. Therefore, CLAMP binding to GA repeat motifs promotes the formation of two distinct domains of coordinated gene activation located at different places in the genome.

Advances in Deep Brain Stimulation: From Mechanisms to Applications.

Deep brain stimulation (DBS) is an effective therapy for various neurologic and neuropsychiatric disorders, involving chronic implantation of electrodes into target brain regions for electrical stimulation delivery. Despite its safety and efficacy, DBS remains an underutilized therapy. Advances in the field of DBS, including in technology, mechanistic understanding, and applications have the potential to expand access and use of DBS, while also improving clinical outcomes. Developments in DBS technology, such as MRI compatibility and bidirectional DBS systems capable of sensing neural activity while providing therapeutic stimulation, have enabled advances in our understanding of DBS mechanisms and its application. In this review, we summarize recent work exploring DBS modulation of target networks. We also cover current work focusing on improved programming and the development of novel stimulation paradigms that go beyond current standards of DBS, many of which are enabled by sensing-enabled DBS systems and have the potential to expand access to DBS.

Associations of tubal ligation and hysterectomy with serum androgen and estrogen metabolites among postmenopausal women in the Women's Health Initiative Observational Study.

PURPOSE: Hysterectomy is associated with subsequent changes in circulating hormone levels, but the evidence of an association for tubal ligation is unclear. We evaluated whether circulating concentrations of androgens and estrogens differ by tubal ligation or hysterectomy status in postmenopausal women from the Women's Health Initiative (WHI)-Observational Study (OS). METHODS: Serum androgens and estrogens were measured in 920 postmenopausal women who did not use menopausal hormone therapy at the time of blood draw, of whom 139 self-reported a history of tubal ligation and 102 reported hysterectomy (with intact ovaries). Geometric mean hormone concentrations (GMs) and 95% confidence intervals (CIs) associated with a history of tubal ligation or hysterectomy (ever/never), as well as time since procedures, were estimated using adjusted linear regression with inverse probability of sampling weights to account for selection. RESULTS: Circulating levels of 12 androgen/androgen metabolites and 20 estrogen/estrogen metabolites did not differ by tubal ligation status. Among women reporting prior hysterectomy compared to women without hysterectomy, we observed lower levels of several androgens (e.g., testosterone (nmol/L): GMyes 0.46 [95% CI:0.37-0.57] vs. GMno 0.62 [95% CI:0.53-0.72]) and higher levels of estrogen metabolites, for example, 2-hydroxyestrone-3-methyl ether (GMyes 11.1 [95% CI:8.95-13.9] pmol/L vs. GMno 8.70 [95% CI:7.38-10.3]) and 4-methoxyestrone (GMyes 6.50 [95% CI:5.05-8.37] vs. GMno 4.92 [95% CI:4.00-6.05]). CONCLUSION: While we did not observe associations between prior tubal ligation and postmenopausal circulating hormone levels, our findings support that prior hysterectomy was associated with lower circulating testosterone levels and higher levels of some estrogen metabolites, which may have implications for future hormone-related disease risks.

Responsive Versus Continuous Deep Brain Stimulation for Speech in Essential Tremor: A Pilot Study.

BACKGROUND: Responsive deep brain stimulation (rDBS) uses physiological signals to deliver stimulation when needed. rDBS is hypothesized to reduce stimulation-induced speech effects associated with continuous DBS (cDBS) in patients with essential tremor (ET). OBJECTIVE: To determine if rDBS reduces cDBS speech-related side effects while maintaining tremor suppression. METHODS: Eight ET participants with thalamic DBS underwent unilateral rDBS. Both speech evaluations and tremor severity were assessed across three conditions (DBS OFF, cDBS ON, and rDBS ON). Speech was analyzed using intelligibility ratings. Tremor severity was scored using the Fahn-Tolosa-Marin Tremor Rating Scale (TRS). RESULTS: During unilateral cDBS, participants experienced reduced speech intelligibility (P = 0.025) compared to DBS OFF. rDBS was not associated with a deterioration of intelligibility. Both rDBS (P = 0.026) and cDBS (P = 0.038) improved the contralateral TRS score compared to DBS OFF. CONCLUSIONS: rDBS maintained speech intelligibility without loss of tremor suppression. A larger prospective chronic study of rDBS in ET is justified. © 2024 International Parkinson and Movement Disorder Society.

Population-level changes in perinatal death for pregnancies prior to and during the COVID-19 pandemic: A pregnancy cohort analysis.

BACKGROUND: Results of population-level studies examining the effect of the COVID-19 pandemic on the risks of perinatal death have varied considerably. OBJECTIVES: To explore trends in the risk of perinatal death among pregnancies beginning prior to and during the pandemic using a pregnancy cohort approach. METHODS: This secondary analysis included data from singleton pregnancies ≥20 weeks' gestation in Alberta, Canada, beginning between 5 March 2017 and 4 March 2021. Perinatal death (i.e. stillbirth or neonatal death) was the primary outcome considered. The risk of this outcome was calculated for pregnancies with varying gestational overlap with the pandemic (i.e. none, 0-20 weeks, entire pregnancy). Interrupted time series analysis was used to further determine temporal trends in the outcome by time period of interest. RESULTS: There were 190,853 pregnancies during the analysis period. Overall, the risk of perinatal death decreased with increasing levels of pandemic exposure; this outcome was experienced in 1.0% (95% confidence interval [CI] 0.9, 1.0), 0.9% (95% CI 0.8, 1.1) and 0.8% (95% CI 0.7, 0.9) of pregnancies with no overlap, partial overlap and complete pandemic overlap respectively. Pregnancies beginning during the pandemic that had high antepartum risk scores less frequently led to perinatal death compared to those beginning prior; 3.3% (95% CI 2.7, 3.9) versus 5.7% (95% CI 5.0, 6.5) respectively. Interrupted time-series analysis revealed a decreasing temporal trend in perinatal death for pregnancies beginning ≤40 weeks prior to the start of the COVID-19 pandemic (i.e. with pandemic exposure), with no trend for pregnancies beginning >40 weeks pre-pandemic (i.e. no pandemic exposure). CONCLUSION: We observed a decrease in perinatal death for pregnancies overlapping with the COVID-19 pandemic in Alberta, particularly among those at high risk of these outcomes. Specific pandemic control measures and government response programmes in our setting may have contributed to this finding.

Exploring the impact of coping self-efficacy on psychological distress among violence-affected people living with HIV.

ABSTRACTThis study examines the relationship between coping self-efficacy, concurrent stress, and psychological distress (borderline/clinical anxiety, depression, and PTSD symptoms) among people living with HIV (PLWH). Using data from a cohort of PLWH living in a southern peri-urban area, logistic regression analyses were conducted to determine the effects of self-reported coping self-efficacy on psychological distress in a sample of 85 violence-affected PLWH. We also tested the moderating effect of coping self-efficacy on the concurrent stress-psychological distress relationships. In adjusted models, coping self-efficacy was significantly associated with symptoms of anxiety and PTSD, but not depressive symptoms. Findings indicate that high coping self-efficacy may reduce one's likelihood of anxiety and PTSD symptoms among PLWH.

Candidemia in Adult Patients in the ICU: A Reappraisal of Susceptibility Testing and Antifungal Therapy.

OBJECTIVE: To provide updates on the epidemiology and recommendations for management of candidemia in patients with critical illness. DATA SOURCES: A literature search using the PubMed database (inception to March 2023) was conducted using the search terms "invasive candidiasis," "candidemia," "critically ill," "azoles," "echinocandin," "antifungal agents," "rapid diagnostics," "antifungal susceptibility testing," "therapeutic drug monitoring," "antifungal dosing," "persistent candidemia," and "Candida biofilm." STUDY SELECTION/DATA EXTRACTION: Clinical data were limited to those published in the English language. Ongoing trials were identified through ClinicalTrials.gov. DATA SYNTHESIS: A total of 109 articles were reviewed including 25 pharmacokinetic/pharmacodynamic studies and 30 studies including patient data, 13 of which were randomized controlled clinical trials. The remaining 54 articles included fungal surveillance data, in vitro studies, review articles, and survey data. The current 2016 Infectious Diseases Society of America (IDSA) Clinical Practice Guideline for the Management of Candidiasis provides recommendations for selecting empiric and definitive antifungal therapies for candidemia, but data are limited regarding optimized dosing strategies in critically ill patients with dynamic pharmacokinetic changes or persistent candidemia complicated. RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE: Outcomes due to candidemia remain poor despite improved diagnostic platforms, antifungal susceptibility testing, and antifungal therapy selection for candidemia in critically ill patients. Earlier detection and identification of the species causing candidemia combined with recognition of patient-specific factors leading to dosing discrepancies are crucial to improving outcomes in critically ill patients with candidemia. CONCLUSIONS: Treatment of candidemia in critically ill patients must account for the incidence of non-albicans Candida species and trends in antifungal resistance as well as overcome the complex pathophysiologic changes to avoid suboptimal antifungal exposure.

At loose ends: resecting a double-strand break.

Double-strand break (DSB) repair is critical for maintaining genomic integrity and requires the processing of the 5' DSB ends. Recent studies have shed light on the mechanism and regulation of DNA end processing during DSB repair by homologous recombination.

The Integration of Sleep Research Into Eating Disorders Research: Recommendations and Best Practices.

OBJECTIVE: Sleep disturbance is common among individuals with eating disorders (EDs), with approximately 50% of patients with EDs reporting sleep disturbance. Sleep problems may promote, exacerbate, or maintain ED symptoms through a variety of hypothesized mechanisms, such as impaired executive function, increased negative affect, and disruptions to appetitive rhythms. Although research investigating the role of sleep in EDs is growing, the current literature suffers from methodological limitations and inconsistencies, which reduce our ability to translate findings to improve clinical practice. The purpose of this forum is to propose a coordinated approach to more seamlessly integrate sleep research into ED research with particular emphasis on best practices in the definition and assessment of sleep characteristics. METHODS: In this article, we will describe the current status of sleep-related research and relevant gaps within ED research practices, define key sleep characteristics, and review common assessment strategies for these sleep characteristics. Throughout the forum, we also discuss study design considerations and recommendations for future research aiming to integrate sleep research into ED research. RESULTS/DISCUSSION: Given the potential role of sleep in ED maintenance and treatment, it is important to build upon preliminary findings using a rigorous and systematic approach. Moving forward as a field necessitates a common lens through which future research on sleep and EDs may be conducted, communicated, and evaluated.

Negative Affect as a Mediator Between Exposure to Fitspiration and Thinspiration and Disordered Eating Behaviors: An Ecological Momentary Assessment Study.

OBJECTIVE: Although social media use, such as Instagram, has been associated with ED pathology, mechanisms connecting social media use to disordered eating behaviors (DEBs) remain largely unevaluated. Based on Dual Process, Tripartite, and Affect Regulation models of ED pathology, we proposed a moderated mediation model evaluating impacts of exposure to fitspiration/thinspiration on Instagram. METHOD: We evaluated a hypothesized pathway from exposure to fitspiration/thinspiration (i.e., ED-salient content) on Instagram to disordered eating mediated by negative affect and tested individual differences in weight bias internalization, trait self-esteem, and trait self-comparison as moderators. We recruited 173 undergraduate women who reported engaging in DEBs on average at least once per week over the past 3 months. Participants completed a seven-day ecological momentary assessment protocol, during which they reported their ED-salient content exposure on Instagram, affect, and engagement in DEBs. RESULTS: Multilevel modeling was used to assess moderated mediation. Negative affect partially mediated associations between viewing ED-salient content and subsequent engagement in objective binge eating and restricting but did not mediate the pathway to purging or excessive exercise. Higher weight bias internalization intensified the association between viewing ED-salient content and negative affect. DISCUSSION: The association between viewing ED-salient content and engaging in objective binge eating and restricting may be a partial consequence of elevated negative affect; however, effects were small. Individuals with higher weight bias internalization may be more vulnerable to negative consequences from viewing ED-salient content. Findings suggested that reducing negative affect responses (e.g., via emotion regulation) could reduce negative consequences of viewing ED-salient content.

Examining associations between disordered eating and harmful substance use in a nationally representative sample of US veterans.

OBJECTIVE: The association between eating disorders (EDs) and harmful substance use (substance use that causes psychosocial impairment) is well recognized in the literature, and military veterans may be at heightened risk for both issues due to deployment-related stressors. However, little is known about which ED-related symptoms are associated with harmful substance use in veterans, and whether gender plays a differential role in this relationship. Our aims were to: (1) examine gender differences in ED-related symptoms; and (2) examine whether ED-related symptoms differentially predict harmful substance use in US veteran men and women who had recently separated from service. METHOD: This study was based on a nationally representative four-wave longitudinal sample of post-9/11 veterans (N = 835; 61.2% female). Longitudinal mixed modeling was used to test whether specific ED-related behaviors at baseline predicted harmful substance use at follow-ups. RESULTS: We replicated gendered patterns of ED-related symptoms observed in civilian populations, wherein men had higher weight-and-body-related concerns (including excessive exercise and muscle building) and negative attitude toward obesity, and women had higher bulimic and restricting symptoms. For women, alcohol, drug, and marijuana problems were predicted by higher bulimic symptoms, whereas for men, these problems were predicted by higher restricting symptoms. CONCLUSION: Gender played a differential role in the relationship between EDs and harmful substance use. Bulimic symptoms were the most robust predictor for harmful substance use among veteran women, whereas restricting was the most robust predictor for harmful substance use among veteran men. PUBLIC SIGNIFICANCE: The current study found that veteran women had higher bulimic symptoms (characterized by binge eating and purging) and restricting than veteran men. In women, bulimic symptoms predicted future harmful use of alcohol, marijuana, and other drugs. In contrast, veteran men had higher weight-and-body-related concerns (characterized by excessive exercise and muscle building) than veteran women. In men, restricting symptoms predicted future harmful use of alcohol, marijuana, and other drugs.

Effect of video angle on detection of induced front limb lameness in horses.

BACKGROUND: Lameness examinations are commonly performed in equine medicine. Advancements in digital technology have increased the use of video recordings for lameness assessment, however, standardization of ideal video angle is not available yielding videos of poor diagnostic quality. The objective of this study was to evaluate the effect of video angle on the subjective assessment of front limb lameness. A randomized, blinded, crossover study was performed. Six horses with and without mechanically induced forelimb solar pain were recorded using 9 video angles including horses trotting directly away and towards the video camera, horses trotting away and towards a video camera placed to the left and right side of midline, and horses trotting in a circle with the video camera placed on the inside and outside of the circle. Videos were randomized and assessed by three expert equine veterinarians using a 0-5 point scoring system. Objective lameness parameters were collected using a body-mounted inertial sensor system (Lameness Locator®, Equinosis LLC). Interobserver agreement for subjective lameness scores and ease of grading scores were determined. RESULTS: Induction of lameness was successful in all horses. There was excellent agreement between objective lameness parameters and subjective lameness scores (AUC of the ROC = 0.87). For horses in the "lame" trials, interobserver agreement was moderate for video angle 2 when degree of lameness was considered and perfect for video angle 2 and 9 when lameness was considered as a binary outcome. All other angles had no to fair agreement. For horses in the "sound" trials, interobserver agreement was perfect for video angle 5. All other video angles had slight to moderate agreement. CONCLUSIONS: When video assessment of forelimb lameness is required, a video of the horse trotting directly towards the video camera at a minimum is recommended. Other video angles may provide supportive information regarding lameness characteristics.