[Effect of socioeconomic status on life expectancy From the population to patients]. / Effet du statut socioéconomique sur l'espérance de vie. De la population aux patients.

Life expectancy exists along a social gradient, where those with a high socioeconomic status (SES) live longer. The effect of SES can be explained via behavioral, material, and psychosocial pathways, which can be modified through social and public health policies. The behavioral pathway states that harmful health behaviors, like smoking, are more common among those of lower SES. The material pathway states that SES give access to different health-beneficial resources, like safe housing or healthy food. Finally, the psychosocial pathway states that a low SES causes a lack of autonomy leading to chronic stress. Understanding how SES affects life expectancy has clinical implications and is important to reduce socioeconomic health inequalities at the population level.

L'espérance de vie suit un gradient social, les personnes avec statut socioéconomique (SSE) élevé vivant plus longtemps. L'effet du SSE sur l'espérance de vie peut être expliqué par des mécanismes comportementaux, matériels et psychosociaux, modifiables par des politiques sociales et de santé publique. Ainsi, les comportements délétères pour la santé, comme le tabagisme, sont plus fréquents chez les personnes ayant un SSE relativement bas. D'un point de vue matériel, le SSE détermine l'accès à des ressources comme un logement de bonne qualité ou une alimentation saine. Enfin, d'un point de vue psychosocial, il est associé notamment au stress chronique. Comprendre comment le SSE affecte l'espérance de vie a des implications cliniques et offre des pistes pour réduire les inégalités en matière de santé à l'échelle de la population.

Educational inequalities in multimorbidity at older ages: a multi-generational population-based study.

BACKGROUND: Social inequalities in multimorbidity may occur due to familial and/or individual factors and may differ between men and women. Using population-based multi-generational data, this study aimed to (1) assess the roles of parental and individual education in the risk of multimorbidity and (2) examine the potential effect modification by sex. METHODS: Data were analysed from 62 060 adults aged 50+ who participated in the Survey of Health, Ageing and Retirement in Europe, comprising 14 European countries. Intergenerational educational trajectories (exposure) were High-High (reference), Low-High, High-Low and Low-Low, corresponding to parental-individual educational attainments. Multimorbidity (outcome) was ascertained between 2013 and 2020 as self-reported occurrence of ≥2 diagnosed chronic conditions. Inequalities were quantified as multimorbidity-free years lost (MFYL) between the ages of 50 and 90 and estimated via differences in the area under the standardized cumulative risk curves. Effect modification by sex was assessed via stratification. RESULTS: Low individual education was associated with higher multimorbidity risk regardless of parental education. Compared to the High-High trajectory, Low-High was associated with -0.2 MFYL (95% confidence intervals: -0.5 to 0.1), High-Low with 3.0 (2.4-3.5), and Low-Low with 2.6 (2.3-2.9) MFYL. This pattern was observed for both sexes, with a greater magnitude for women. This effect modification was not observed when only diseases diagnosed independently of healthcare-seeking behaviours were examined. CONCLUSIONS: Individual education was the main contributor to intergenerational inequalities in multimorbidity risk among older European adults. These findings support the importance of achieving a high education to mitigate multimorbidity risk.

Long-Term Impacts on Clinical Practice Along the HIV Care Continuum: Addressing Workforce Gaps Through a Clinician Scholars Program.

The Clinician Scholars Program (CSP) was designed to expand the HIV care workforce by improving the clinical capacity of clinicians in underserved areas. This evaluation assessed program participants' long-term practice changes and system changes. The year-long program combined mentoring, training, and on-site clinical observation. Qualitative interviews (N = 46) were conducted with Scholars at least 2 years following CSP, supplemented by a 2023 survey. Multiple coders analyzed transcripts using open coding. Thematic analysis explored practice changes and efforts to move patients along the HIV care continuum. Findings indicate positive long-term impacts of CSP regarding the HIV care continuum and care system engagement. Over 90% of Scholars remained working in HIV care, with 75% maintaining or increasing patient loads and 72% making changes to their clinical practice. This training model appears to enhance care along the HIV care continuum and may be adaptable to other contexts that address complex chronic conditions.

Life course epidemiology and public health.

Life course epidemiology aims to study the effect of exposures on health outcomes across the life course from a social, behavioural, and biological perspective. In this Review, we describe how life course epidemiology changes the way the causes of chronic diseases are understood, with the example of hypertension, breast cancer, and dementia, and how it guides prevention strategies. Life course epidemiology uses complex methods for the analysis of longitudinal, ideally population-based, observational data and takes advantage of new approaches for causal inference. It informs primordial prevention, the prevention of exposure to risk factors, from an eco-social and life course perspective in which health and disease are conceived as the results of complex interactions between biological endowment, health behaviours, social networks, family influences, and socioeconomic conditions across the life course. More broadly, life course epidemiology guides population-based and high-risk prevention strategies for chronic diseases from the prenatal period to old age, contributing to evidence-based and data-informed public health actions. In this Review, we assess the contribution of life course epidemiology to public health and reflect on current and future challenges for this field and its integration into policy making.

Interplay of Digital Proximity App Use and SARS-CoV-2 Vaccine Uptake in Switzerland: Analysis of Two Population-Based Cohort Studies.

Objectives: Our study aims to evaluate developments in vaccine uptake and digital proximity tracing app use in a localized context of the SARS-CoV-2 pandemic. Methods: We report findings from two population-based longitudinal cohorts in Switzerland from January to December 2021. Failure time analyses and Cox proportional hazards regression models were conducted to assess vaccine uptake and digital proximity tracing app (SwissCovid) uninstalling outcomes. Results: We observed a dichotomy of individuals who did not use the SwissCovid app and did not get vaccinated, and who used the SwissCovid app and got vaccinated during the study period. Increased vaccine uptake was observed with SwissCovid app use (aHR, 1.51; 95% CI: 1.40-1.62 [CI-DFU]; aHR, 1.79; 95% CI: 1.62-1.99 [CSM]) compared to SwissCovid app non-use. Decreased SwissCovid uninstallation risk was observed for participants who got vaccinated (aHR, 0.55; 95% CI: 0.38-0.81 [CI-DFU]; aHR, 0.45; 95% CI: 0.27-0.78 [CSM]) compared to participants who did not get vaccinated. Conclusion: In evolving epidemic contexts, these findings underscore the need for communication strategies as well as flexible digital proximity tracing app adjustments that accommodate different preventive measures and their anticipated interactions.

Development of a PNGase Rc Column for Online Deglycosylation of Complex Glycoproteins during HDX-MS.

Protein glycosylation is one of the most common PTMs and many cell surface receptors, extracellular proteins, and biopharmaceuticals are glycosylated. However, HDX-MS analysis of such important glycoproteins has so far been limited by difficulties in determining the HDX of the protein segments that contain glycans. We have developed a column containing immobilized PNGase Rc (from Rudaea cellulosilytica) that can readily be implemented into a conventional HDX-MS setup to allow improved analysis of glycoproteins. We show that HDX-MS with the PNGase Rc column enables efficient online removal of N-linked glycans and the determination of the HDX of glycosylated regions in several complex glycoproteins. Additionally, we use the PNGase Rc column to perform a comprehensive HDX-MS mapping of the binding epitope of a mAb to c-Met, a complex glycoprotein drug target. Importantly, the column retains high activity in the presence of common quench-buffer additives like TCEP and urea and performed consistent across 114 days of extensive use. Overall, our work shows that HDX-MS with the integrated PNGase Rc column can enable fast and efficient online deglycosylation at harsh quench conditions to provide comprehensive analysis of complex glycoproteins.

Changes in socioeconomic resources and mental health after the second COVID-19 wave (2020-2021): a longitudinal study in Switzerland.

BACKGROUND: During the 2020/2021 winter, the labour market was under the impact of the COVID-19 pandemic. Changes in socioeconomic resources during this period could have influenced individual mental health. This association may have been mitigated or exacerbated by subjective risk perceptions, such as perceived risk of getting infected with SARS-CoV-2 or perception of the national economic situation. Therefore, we aimed to determine if changes in financial resources and employment situation during and after the second COVID-19 wave were prospectively associated with depression, anxiety and stress, and whether perceptions of the national economic situation and of the risk of getting infected modified this association. METHODS: One thousand seven hundred fifty nine participants from a nation-wide population-based eCohort in Switzerland were followed between November 2020 and September 2021. Financial resources and employment status were assessed twice (Nov2020-Mar2021, May-Jul 2021). Mental health was assessed after the second measurement of financial resources and employment status, using the Depression, Anxiety and Stress Scale (DASS-21). We modelled DASS-21 scores with linear regression, adjusting for demographics, health status, social relationships and changes in workload, and tested interactions with subjective risk perceptions. RESULTS: We observed scores above thresholds for normal levels for 16% (95%CI = 15-18) of participants for depression, 8% (95%CI = 7-10) for anxiety, and 10% (95%CI = 9-12) for stress. Compared to continuously comfortable or sufficient financial resources, continuously precarious or insufficient resources were associated with worse scores for all outcomes. Increased financial resources were associated with higher anxiety. In the working-age group, shifting from full to part-time employment was associated with higher stress and anxiety. Perceiving the Swiss economic situation as worrisome was associated with higher anxiety in participants who lost financial resources or had continuously precarious or insufficient resources. CONCLUSION: This study confirms the association of economic stressors and mental health during the COVID-19 pandemic and highlights the exacerbating role of subjective risk perception on this association.

Intergenerational educational trajectories and inequalities in longevity: A population-based study of adults born before 1965 in 14 European countries.

Background: While educational gradients in longevity have been observed consistently in adult Europeans, these inequalities have been understudied within the context of family- and country-level influences. We utilized population-based multi-generational multi-country data to assess the role (1) of parental and individual education in shaping intergenerational inequalities in longevity, and (2) of country-level social net expenditure in mitigating these inequalities. Methods: We analyzed data from 52,271 adults born before 1965 who participated in the Survey of Health, Ageing and Retirement in Europe, comprising 14 countries. Mortality from all causes (outcome) was ascertained between 2013 and 2020. Educational trajectories (exposure) were High-High (reference), Low-High, High-Low, and Low-Low, corresponding to the sequence of parental-individual educational attainment. We quantified inequalities as years of life lost (YLL) between the ages of 50 and 90 estimated via differences in the area under standardized survival curves. We assessed the association between country-level social net expenditure and YLL via meta-regression. Results: Inequalities in longevity due to educational trajectories were associated with low individual education regardless of parental education. Compared to High-High, having High-Low and Low-Low led to 2.2 (95% confidence intervals: 1.0 to 3.5) and 2.9 (2.2 to 3.6) YLL, while YLL for Low-High were 0.4 (-0.2 to 0.9). A 1% increase in social net expenditure led to an increase of 0.01 (-0.3 to 0.3) YLL for Low-High, 0.007 (-0.1 to 0.2) YLL for High-Low, and a decrease of 0.02 (-0.1 to 0.2) YLL for Low-Low. Conclusion: In European countries, individual education could be the main driver of inequalities in longevity for adults older than 50 years of age and born before 1965. Further, higher social expenditure is not associated with smaller educational inequalities in longevity.

Seroprevalence trends of anti-SARS-CoV-2 antibodies and associated risk factors: a population-based study.

PURPOSE: We aimed to assess the seroprevalence trends of SARS-CoV-2 antibodies in several Swiss cantons between May 2020 and September 2021 and investigate risk factors for seropositivity and their changes over time. METHODS: We conducted repeated population-based serological studies in different Swiss regions using a common methodology. We defined three study periods: May-October 2020 (period 1, prior to vaccination), November 2020-mid-May 2021 (period 2, first months of the vaccination campaign), and mid-May-September 2021 (period 3, a large share of the population vaccinated). We measured anti-spike IgG. Participants provided information on sociodemographic and socioeconomic characteristics, health status, and adherence to preventive measures. We estimated seroprevalence with a Bayesian logistic regression model and the association between risk factors and seropositivity with Poisson models. RESULTS: We included 13,291 participants aged 20 and older from 11 Swiss cantons. Seroprevalence was 3.7% (95% CI 2.1-4.9) in period 1, 16.2% (95% CI 14.4-17.5) in period 2, and 72.0% (95% CI 70.3-73.8) in period 3, with regional variations. In period 1, younger age (20-64) was the only factor associated with higher seropositivity. In period 3, being aged ≥ 65 years, with a high income, retired, overweight or obese or with other comorbidities, was associated with higher seropositivity. These associations disappeared after adjusting for vaccination status. Seropositivity was lower in participants with lower adherence to preventive measures, due to a lower vaccination uptake. CONCLUSIONS: Seroprevalence sharply increased over time, also thanks to vaccination, with some regional variations. After the vaccination campaign, no differences between subgroups were observed.

Life course socioeconomic conditions and multimorbidity in old age - A scoping review.

Multimorbidity disproportionally affects individuals exposed to socioeconomic disadvantage. It is, however, unclear how adverse socioeconomic conditions (SEC) at different periods of the life course predict the occurrence of multimorbidity in later life. In this scoping review, we investigate the association between life course SEC and later-life multimorbidity, and assess to which extent it supports different life course causal models (critical period, sensitive period, accumulation, pathway, or social mobility). We identified four studies (25,209 participants) with the first measure of SEC in childhood (before age 18). In these four studies, childhood SEC was associated with multimorbidity in old age, and the associations were partially or fully attenuated upon adjustment for later-life SEC. These results are consistent with the sensitive period and the pathway models. We identified five studies (91,236 participants) with the first measure of SEC in young adulthood (after age 18), and the associations with multimorbidity in old age as well as the effects of adjustment for later-life SEC differed from one study to the other. Among the nine included studies, none tested the social mobility or the accumulation models. In conclusion, SEC in early life could have an effect on multimorbidity, attenuated at least partly by SEC in adulthood.

Hydrogen/deuterium exchange mass spectrometry with improved electrochemical reduction enables comprehensive epitope mapping of a therapeutic antibody to the cysteine-knot containing vascular endothelial growth factor.

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) has become a popular method for analysis of the conformational dynamics and interactions of proteins. Disulfide-bonded proteins, however, present a challenge to HDX-MS as they require efficient disulfide bond reduction prior to enzymatic proteolysis. Electrochemical reduction (ER) provides an attractive solution to tackle disulfide-bonded proteins that are resistant to conventional chemical reduction during HDX-MS. However, ER-enabled HDX-MS has been limited by technical challenges including partial unwanted protein oxidation side-reactions, incompatibility with certain buffer components and most importantly, a lack of overall method robustness. In this study, we have sought to address these challenges. We perform a systematic screening of the compatibility of ER to buffers commonly used in HDX-MS samples by using a reliable and simple system suitability test (SST). Furthermore, we demonstrate the benefits of a new design of the electrochemical cell (EC) for ER-enabled HDX-MS, which include a) high repeatability and robustness over large sample batches without the need for electrode polishing and b) high reduction efficiency of disulfide-bonded proteins without unwanted oxidation side-reactions. We show the real-world applicability of the optimized ER-enabled HDX-MS workflow by performing an epitope mapping of a Fab fragment of a therapeutic monoclonal antibody (mAb) to the cysteine knot-containing vascular endothelial growth factor (VEGF). The results allow us to comprehensively map sites in VEGF involved in mAb binding. Overall, our findings show how ER and HDX-MS can be combined to enable analysis of the conformation and interactions of challenging disulfide-rich proteins.

Recommendations for performing, interpreting and reporting hydrogen deuterium exchange mass spectrometry (HDX-MS) experiments.

Hydrogen deuterium exchange mass spectrometry (HDX-MS) is a powerful biophysical technique being increasingly applied to a wide variety of problems. As the HDX-MS community continues to grow, adoption of best practices in data collection, analysis, presentation and interpretation will greatly enhance the accessibility of this technique to nonspecialists. Here we provide recommendations arising from community discussions emerging out of the first International Conference on Hydrogen-Exchange Mass Spectrometry (IC-HDX; 2017). It is meant to represent both a consensus viewpoint and an opportunity to stimulate further additions and refinements as the field advances.

Professional Identity Formation in HIV Care: Development of Clinician Scholars in a Longitudinal, Mentored Training Program.

INTRODUCTION: The Clinician Scholars Program is designed to improve the capacity and quality of HIV care by training clinicians in underserved areas. A mentoring approach is used to deliver individualized educational opportunities over the course of a year focused on preparing clinicians to provide high-quality patient-centered HIV care. Evaluation of the program has illustrated increases in knowledge, skills, and practice behavior, yet critical domains remain unexplored, particularly the potential for the program to affect professional identity formation and networking between individual clinicians. METHODS: Qualitative exit interviews (N = 50) were conducted over 4 years of the Clinician Scholars Program. Interviews were transcribed and analyzed using an open-coding process with multiple coders. Interrater reliability was assessed. Themes related to professional development and networking emerged. RESULTS: Thematic analysis revealed changes in several professional development domains, including self-efficacy, HIV care clinician identity, and career development. In addition, clinicians began to develop key connections with mentors, other clinicians, and health systems-gaining a foundation in the HIV care community, enabled and strengthened by growth in professional confidence and competence within the clinician's care context. DISCUSSION: Evaluations of clinical training programs often focus on knowledge and skill gains without addressing professional identity development and place within the care community. This study illustrates that a longitudinal clinician training program has the potential to influence professional identify development, particularly affect how clinicians view themselves as a resource in the HIV care community and begins to facilitate necessary connections to other clinicians and the wider care system.

Impacts of Longitudinal Mentorship to Strengthen the HIV Workforce: Qualitative Evidence of Changes in Clinicians' Knowledge, Attitudes, and Practice.

The Clinician Scholars Program at the Midwest AIDS Training and Education Center strengthens the workforce by increasing knowledge and skills related to HIV prevention and care. The 1-year individualized training program for minority-serving clinicians includes intensive mentoring and networking. Qualitative exit interviews (N = 50) conducted over 4 years demonstrate the effectiveness of the training, including changes at the individual and systems levels. Findings show that almost all graduates reported improvements in knowledge, two-thirds reported changes in empathic capacity and cultural competence, and nearly three-quarters reported changes in clinical practice. Scholars indicated improvements in knowledge and practice of HIV prevention, including pre-exposure prophylaxis and managing medications and comorbidities. A third of the Scholars reported improvements in their clinical practices related to linking and retaining patients in HIV care, which demonstrated positive movement along the HIV care continuum, a key focus area of the National HIV AIDS Strategy.

Developing the HIV Workforce: The MATEC Clinician Scholars Program.

Engaging new clinical providers in the HIV workforce is a critical need due to rapidly evolving treatment paradigms, aging out of existing providers, and special population needs. The 1-year competency-based Clinician Scholar Program for minority-serving providers with limited HIV care experience was individually tailored for each provider (n = 74), mostly nurse practitioners, physicians, and clinical pharmacists. Baseline and endpoint self-assessments of clinical knowledge and skills showed significant improvements in all 11 targeted competencies, particularly in managing antiretroviral medications, screening and testing methods, incorporating prevention into HIV care, understanding risk reduction methods, and describing current care standards. Faculty mentor assessments also showed significant improvement in most competencies. Additional benefits included ongoing access to mentorship and training, plus sustained engagement in local and statewide HIV care networks. Our intensive mentoring program model is replicable in other AIDS Education and Training Centers and in other structured training programs.

Hapten-directed spontaneous disulfide shuffling: a universal technology for site-directed covalent coupling of payloads to antibodies.

Humanized hapten-binding IgGs were designed with an accessible cysteine close to their binding pockets, for specific covalent payload attachment. Individual analyses of known structures of digoxigenin (Dig)- and fluorescein (Fluo) binding antibodies and a new structure of a biotin (Biot)-binder, revealed a "universal" coupling position (52(+2)) in proximity to binding pockets but without contributing to hapten interactions. Payloads that carry a free thiol are positioned on the antibody and covalently linked to it via disulfides. Covalent coupling is achieved and driven toward complete (95-100%) payload occupancy by spontaneous redox shuffling between antibody and payload. Attachment at the universal position works with different haptens, antibodies, and payloads. Examples are the haptens Fluo, Dig, and Biot combined with various fluorescent or peptidic payloads. Disulfide-bonded covalent antibody-payload complexes do not dissociate in vitro and in vivo. Coupling requires the designed cysteine and matching payload thiol because payload or antibody without the Cys/thiol are not linked (<5% nonspecific coupling). Hapten-mediated positioning is necessary as hapten-thiol-payload is only coupled to antibodies that bind matching haptens. Covalent complexes are more stable in vivo than noncovalent counterparts because digoxigeninylated or biotinylated fluorescent payloads without disulfide-linkage are cleared more rapidly in mice (approximately 50% reduced 48 hour serum levels) compared with their covalently linked counterparts. The coupling technology is applicable to many haptens and hapten binding antibodies (confirmed by automated analyses of the structures of 140 additional hapten binding antibodies) and can be applied to modulate the pharmacokinetics of small compounds or peptides. It is also suitable to link payloads in a reduction-releasable manner to tumor- or tissue-targeting delivery vehicles.

Age-dependent changes of the antioxidant system in rat livers are accompanied by altered MAPK activation and a decline in motor signaling.

Aging is characterized by a progressive decrease of cellular functions, because cells gradually lose their capacity to respond to injury. Increased oxidative stress is considered to be one of the major contributors to age-related changes in all organs including the liver. Our study has focused on elucidating whether important antioxidative enzymes, the mTOR pathway, and MAPKs exhibit age-dependent changes in the liver of rats during aging. We found an age-dependent increase of GSH in the cytosol and mitochondria. The aged liver showed an increased SOD enzyme activity, while the CAT enzyme activity decreased. HO-1 and NOS-2 gene expression was lower in adult rats, but up-regulated in aged rats. Western blot analysis revealed that SOD1, SOD2, GPx, GR, γ-GCL, and GSS were age-dependent up-regulated, while CAT remained constant. We also demonstrated that the phosphorylation of Akt, JNK, p38, and TSC2(Ser1254) decreased while ERK1/2 and TSC2(Thr1462) increased age-dependently. Furthermore, our data show that the mTOR pathway seems to be activated in livers of aged rats, and hence stimulating cell proliferation/regeneration, as confirmed by an age-dependent increase of PCNA and p-eIF4E(Ser209) protein expression. Our data may help to explain the fact that liver cells only proliferate in cases of necessity, like injury and damage. In summary, we have demonstrated that, age-dependent changes of the antioxidant system and stress-related signaling pathways occur in the livers of rats, which may help to better understand organ aging.

Metabolome analysis: the potential of in vivo labeling with stable isotopes for metabolite profiling.

Metabolome analysis technologies are still in early development because, unlike genome, transcriptome and proteome analyses, metabolome analysis has to deal with a highly diverse range of biomolecules. Combinations of different analytical platforms are therefore required for comprehensive metabolomic studies. Each of these platforms covers only part of the metabolome. To establish multiparallel technologies, thorough standardization of each measured metabolite is required. Standardization is best achieved by addition of a specific stable isotope-labeled compound, a mass isotopomer, for each metabolite. This suggestion, at first glance, seems unrealistic because of cost and time constraints. A possible solution to this problem is discussed in this article. Saturation in vivo labeling with stable isotopes enables the biosynthesis of differentially mass-labeled metabolite mixtures, which can be exploited for highly standardized metabolite profiling by mass isotopomer ratios.

Herpes simplex virus type-1 induces IFN-alpha production via Toll-like receptor 9-dependent and -independent pathways.

Type I IFN production in response to the DNA virus herpes simplex virus type-1 (HSV-1) is essential in controlling viral replication. We investigated whether plasmacytoid dendritic cells (pDC) were the major tissue source of IFN-alpha, and whether the production of IFN-alpha in response to HSV-1 depended on Toll-like receptor 9 (TLR9). Total spleen cells or bone marrow (BM) cells, or fractions thereof, including highly purified pDC, from WT, TLR9, and MyD88 knockout mice were stimulated with known ligands for TLR9 or active HSV-1. pDC freshly isolated from both spleen and BM were the major source of IFN-alpha in response to oligodeoxynucleotides containing CpG motifs, but in response to HSV-1 the majority of IFN-alpha was produced by other cell types. Moreover, IFN-alpha production by non-pDC was independent of TLR9. The tissue source determined whether pDC responded to HSV-1 in a strictly TLR9-dependent fashion. Freshly isolated BM pDC or pDC derived from culture of BM precursors with FMS-like tyrosine kinase-3 ligand, produced IFN-alpha in the absence of functional TLR9, whereas spleen pDC did not. Heat treatment of HSV-1 abolished maturation and IFN-alpha production from all TLR9-deficient DC but not WT DC. Thus pDC and non-pDC produce IFN-alpha in response to HSV-1 via both TLR9-independent and -dependent pathways.

Intraduodenal serotonin elicits non-propagating spike potentials in the small intestine of the rat.

Serotonin (5-hydroxytryptamine, 5-HT) is an endogenous signalling molecule capable of altering small intestinal motility. Serotonin is normally present in the intestinal lumen and released by enterochromaffin cells of the mucosal epithelium. We found that intraduodenal infusion of exogenous serotonin causes a dose-dependent myoelectric response in the smooth muscle of the small intestine in the conscious rat. The response consists of repetitive bursts of action potentials (RBAP) that are characterized as short bursts of non-propagative myoelectric spiking. RBAP occur intermittently and only during the first 15 min after intralumenal serotonin infusion. After the initial 15 min period, the frequency of RBAP declines, and the myoelectric pattern shifts to prolonged and continuous spiking, eliminating the interdigestive migrating myoelectric pattern. The effects of intralumenal serotonin are not replicated by parenteral or intraperitoneal infusion nor by intralumenal infusion of 5-hydroxytryptophan or 5-hydroxyindoleacetic acid. The response to intralumenal serotonin was eliminated by several specific 5-HT receptor antagonists. On repeated intralumenal administration of serotonin, the RBAP response decreased demonstrating a decreased sensitivity of the muscle contraction on re-exposure to serotonin. We conclude that intralumenal infusion of serotonin can temporarily initiate specific small intestinal muscle events that are not generated by serotonin from other non-lumenal administration sites. We speculate that an afferent neuro-pathway is necessary for the induction of RBAP, since RBAP are not observed from in vitro muscle preparations.