Estimation of separable direct and indirect effects in a continuous-time illness-death model.

In this article we study the effect of a baseline exposure on a terminal time-to-event outcome either directly or mediated by the illness state of a continuous-time illness-death process with baseline covariates. We propose a definition of the corresponding direct and indirect effects using the concept of separable (interventionist) effects (Robins and Richardson in Causality and psychopathology: finding the determinants of disorders and their cures, Oxford University Press, 2011; Robins et al. in arXiv:2008.06019 , 2021; Stensrud et al. in J Am Stat Assoc 117:175-183, 2022). Our proposal generalizes Martinussen and Stensrud (Biometrics 79:127-139, 2023) who consider similar causal estimands for disentangling the causal treatment effects on the event of interest and competing events in the standard continuous-time competing risk model. Unlike natural direct and indirect effects (Robins and Greenland in Epidemiology 3:143-155, 1992; Pearl in Proceedings of the seventeenth conference on uncertainty in artificial intelligence, Morgan Kaufmann, 2001) which are usually defined through manipulations of the mediator independently of the exposure (so-called cross-world interventions), separable direct and indirect effects are defined through interventions on different components of the exposure that exert their effects through distinct causal mechanisms. This approach allows us to define meaningful mediation targets even though the mediating event is truncated by the terminal event. We present the conditions for identifiability, which include some arguably restrictive structural assumptions on the treatment mechanism, and discuss when such assumptions are valid. The identifying functionals are used to construct plug-in estimators for the separable direct and indirect effects. We also present multiply robust and asymptotically efficient estimators based on the efficient influence functions. We verify the theoretical properties of the estimators in a simulation study, and we demonstrate the use of the estimators using data from a Danish registry study.

Sub-anesthetic doses of ketamine increase single cell entrainment in the rat auditory cortex during auditory steady-state response.

BACKGROUND: Understanding the effects of the N-methyl-D-aspartate receptor (NMDA-R) antagonist ketamine on brain function is of considerable interest due to the discovery of its fast-acting antidepressant properties. It is well known that gamma oscillations are increased when ketamine is administered to rodents and humans, and increases in the auditory steady-state response (ASSR) have also been observed. AIMS: To elucidate the cellular substrate of the increase in network activity and synchrony observed by sub-anesthetic doses of ketamine, the aim was to investigate spike timing and regularity and determine how this is affected by the animal's motor state. METHODS: Single unit activity and local field potentials from the auditory cortex of awake, freely moving rats were recorded with microelectrode arrays during an ASSR paradigm. RESULTS: Ketamine administration yielded a significant increase in ASSR power and phase locking, both significantly modulated by motor activity. Before drug administration, putative fast-spiking interneurons (FSIs) were significantly more entrained to the stimulus than putative pyramidal neurons (PYRs). The degree of entrainment significantly increased at lower doses of ketamine (3 and 10 mg/kg for FSIs, 10 mg/kg for PYRs). At the highest dose (30 mg/kg), a strong increase in tonic firing of PYRs was observed. CONCLUSIONS: These findings suggest an involvement of FSIs in the increased network synchrony and provide a possible cellular explanation for the well-documented effects of ketamine-induced increase in power and synchronicity during ASSR. The results support the importance to evaluate different motor states separately for more translational preclinical research.

Heavy prenatal alcohol exposure and overall morbidities: a Danish nationwide cohort study from 1996 to 2018.

BACKGROUND: Heavy prenatal alcohol exposure is harmful and can lead to fetal alcohol spectrum disorders. A systematic review and meta-analysis identified 428 comorbidities in individuals with fetal alcohol spectrum disorders, and reported pooled prevalence estimates. We aimed to investigate overall risk of morbidities in heavy prenatal alcohol-exposed children by estimating risk of the identified comorbidities, and previously unidentified diseases and health-related problems. METHODS: Our Danish nationwide register-based cohort study included all singleton births. Individuals were followed up to age 18 years, between 1996 and 2018. Stillbirths and children of immigrants were not included in the study, and births of women who migrated within 1 year before or during pregnancy were also excluded due to loss to follow-up. Data on health and education were extracted from the Danish Medical Birth Register, the Danish National Patient Registry, the Danish National Prescription Registry, the Danish Civil Registration System, and the Population Education Register. We estimated crude and standardised risk differences of hospital diagnoses. Heavy prenatal alcohol exposure was defined by hospital contacts with alcohol-attributable diagnoses given to the mother or her child, or by maternal redeemed prescriptions for drugs to treat alcohol dependence 1 year before or during pregnancy. FINDINGS: Of 1 407 689 identified singleton births, 219 186 were excluded for reasons including they were born to immigrants, lost to follow-up, or were stillbirths. Of the remaining 1 188 503 children, 4799 (0·4%) had heavy prenatal alcohol exposure and 1 183 704 (99·6%) were classified as non-alcohol-exposed births. 578 179 (48·6%) babies were female and 610 324 (51·4%) were male. We found 234 of 428 previously identified comorbidities in individuals with fetal alcohol spectrum disorder, of which 29 conditions had a standardised risk difference of at least 0·5%, predominantly related to brain function, behavioural disorders, infections, and neonatal conditions. The four highest standardised risk differences were found for low birthweight (4·70% [95% CI 3·70-5·71]), small for gestational age (4·63% [3·72-5·55]), delayed milestone (3·81% [2·99-4·64]), and other preterm infants (2·69% [1·71-3·68]). Of previously unidentified diseases and health-related problems, 32 of 719 had a standardised risk difference of at least 1·0%, mainly related to brain function, some injuries, substance-related conditions, and childhood adversities. INTERPRETATION: Heavy prenatal alcohol exposure is associated with an overall increased risk of child morbidities and previously unrecognised alcohol-related health problems. Prenatal alcohol exposure is a key public health issue with a potential negative impact on child and adolescent health. This study urges for renewed efforts and substantiates the profound degree to which pre-conceptional care is mandatory. FUNDING: The Obel Family Foundation, The Health Foundation, TrygFonden, Aase and Ejnar Danielsens Foundation, The North Denmark Region Health Science and Research Foundation, Holms Memorial Foundation, Dagmar Marshalls Foundation, the A.P. Møller Foundation, King Christian X Foundation, Torben and Alice Frimodts Foundation, the Axel and Eva Kastrup-Nielsens Foundation, and the A.V. Lykfeldts Foundation.

Catheter ablation and mortality, stroke and heart failure readmission with atrial fibrillation.

BACKGROUND: Recent randomised clinical trials have suggested prognostic benefits of catheter ablation in highly selected patients with atrial fibrillation (AF) and heart failure (HF). OBJECTIVES: This study sought to identify the treatment effect associated with catheter ablation in a broad population of patients with AF and HF. METHODS: Through nationwide administrative registers in Denmark, we estimated the 2-year average treatment effect (ATE) of catheter ablation for AF on a composite endpoint of HF readmission, stroke and all-cause mortality at 1-year and 5-year landmark analyses. The primary cohort was patients with AF before HF, and the second cohort of patients with HF before AF. RESULTS: A total of 13 756 patients were included with 9904 patients in the primary cohort, and 3852 in the secondary. An ATE (95% CI) reduction of the composite endpoint of 7.0% (4.5% to 9.5%) was observed in the primary cohort and 11.8% (6.0% to 17.6%) in the secondary in the 1-year landmark analysis with a reduction in all-cause mortality of 5.8% (3.7%-7.8%) and 6.3% (0.9%-11.7%), respectively. At the 5-year landmark, catheter ablation was associated with reductions in the composite endpoint and all-cause mortality in the primary (4.7% (2.3% to 7.2%), and 3.6% (1.0% to 6.3%), respectively), but not in the secondary cohort. CONCLUSIONS: Ablation was associated with decreased risk of HF readmission, stroke and all-cause mortality in patients with AF and HF. The effect is most substantial in patients with AF before HF and with catheter ablation after 1 year from the diagnosis of both conditions.

Does type 2 diabetes confer higher relative rates of cardiovascular events in women compared with men?

AIMS: To investigate whether diabetes confers higher relative rates of cardiovascular events in women compared with men using contemporary data, and whether these sex-differences depend on age. METHODS AND RESULTS: All Danish residents aged 40-89 years without a history major adverse cardiovascular events, including heart failure, as of 1 January 2012 until 31 December 2016 were categorized by diabetes-status and characterized by individual-level linkage of Danish nationwide administrative registers. We used Poisson regression to calculate overall and age-dependent incidence rates, incidence rate ratios, and women-to-men ratios for myocardial infarction, heart failure, ischaemic stroke, or cardiovascular death (MACE-HF). Among 218 549 (46% women) individuals with diabetes, the absolute rate of MACE-HF was higher in men than in women (24.9 vs. 19.9 per 1000 person-years). Corresponding absolute rates in men and women without diabetes were 10.1 vs. 7.0 per 1000 person-years. Comparing individuals with and without diabetes, women had higher relative rates of MACE-HF than men [2.8 (confidence interval, CI 2.9-2.9) in women vs. 2.5 (CI 2.4-2.5) in men] with a women-to-men ratio of 1.15 (CI 1.11-1.19, P < 0.001). The relative rates of MACE-HF were highest in the youngest and decreased with advancing age for both men and women, but the relative rates were higher in women across all ages, with the highest women-to-men ratio between age 50 and 60 years. CONCLUSION: Although men have higher absolute rates of cardiovascular complications, the relative rates of cardiovascular complications associated with diabetes are higher in women than in men across all ages in the modern era.

Parental age in relation to the severity of cleft lip and/or palate.

OBJECTIVE: To investigate parental age in relation to the severity of cleft diagnosis in a population-based consecutive sample of individuals with clefts. SETTING/SAMPLE: Retrospective, consecutive. MATERIAL/METHODS: The sample comprised 545 consecutive cases with nonsyndromic clefts (437 individuals with cleft lip with/without cleft palate [CL ± P] and 106 individuals with isolated cleft palate [CP]) and parental ages recorded. The groups were subdivided according to the extent/severity of cleft. Unilateral clefts were divided according to left/right sidedness. Logistic regression was used to analyse the association between parental age and risk of severe cleft separately for CL ± P and CP, as well as between parental age and risk of right-sided cleft. RESULTS: In CL ± P, the risk of a complete cleft in the offspring increases with maternal age when the paternal age exceeds approximately 29 years. Moreover, the risk is higher when both parents are old than when both parents are young. In CP, no statistically significant results were identified. However, there were clear trends that indicated a similar pattern as that for CL ± P. No association was identified between increased parental age and the sidedness of clefts. CONCLUSIONS: Parental age seems to contribute to cleft severity, as older parents showed a higher risk of having offspring with a complete cleft than younger parents.

Pharmacological rescue of mutated Kv3.1 ion-channel linked to progressive myoclonus epilepsies.

Progressive myoclonus epilepsies (PMEs) constitute a cluster of inherent, genetically diverse, rare seizure disorders characterized by ataxia, tonic-clonic seizures, and action myoclonus. Recently, a mutation in the KCNC1 gene (Arg320His) was described in a group of PME patients. The KCNC1 gene encodes the Kv3.1 potassium ion channel responsible for the rapid repolarization of the membrane potential following action potential firing in fast spiking GABAergic interneurons (FSI), thereby enabling high firing frequency. In the present study, we demonstrate that the Arg320His mutation cause a reduction in the Kv3.1 current amplitude and acts in a dominantly negative fashion. The mutation profoundly affects channel activation and deactivation kinetics, and we further find that it impairs recruitment of the Kv3.1 channel to the plasma membrane. The Kv3 activating compound, RE01, partly rescues the electrophysiological deficit, suggesting that pharmacological activation of Kv3.1 activity might be a feasible approach for treatment of this cohort of PME patients.

Extension of Helix 12 in Munc18-1 Induces Vesicle Priming.

UNLABELLED: Munc18-1 is essential for vesicle fusion and participates in the docking of large dense-core vesicles to the plasma membrane. Recent structural data suggest that conformational changes in the 12th helix of the Munc18-1 domain 3a within the Munc18-1:syntaxin complex result in an additional interaction with synaptobrevin-2/VAMP2 (vesicle-associated membrane protein 2), leading to SNARE complex formation. To test this hypothesis in living cells, we examined secretion from Munc18-1-null mouse adrenal chromaffin cells expressing Munc18-1 mutants designed to either perturb the extension of helix 12 (Δ324-339), block its interaction with synaptobrevin-2 (L348R), or extend the helix to promote coil-coil interactions with other proteins (P335A). The mutants rescued vesicle docking and syntaxin-1 targeting to the plasma membrane, with the exception of P335A that only supported partial syntaxin-1 targeting. Disruptive mutations (L348R or Δ324-339) lowered the secretory amplitude by decreasing vesicle priming, whereas P335A markedly increased priming and secretory amplitude. The mutants displayed unchanged kinetics and Ca(2+) dependence of fusion, indicating that the mutations specifically affect the vesicle priming step. Mutation of a nearby tyrosine (Y337A), which interacts with closed syntaxin-1, mildly increased secretory amplitude. This correlated with results from an in vitro fusion assay probing the functions of Munc18-1, indicating an easier transition to the extended state in the mutant. Our findings support the notion that a conformational transition within the Munc18-1 domain 3a helix 12 leads to opening of a closed Munc18-1:syntaxin complex, followed by productive SNARE complex assembly and vesicle priming. SIGNIFICANCE STATEMENT: The essential postdocking role of Munc18-1 in vesicular exocytosis has remained elusive, but recent data led to the hypothesis that the extension of helix 12 in Munc18 within domain 3a leads to synaptobrevin-2/VAMP2 interaction and SNARE complex formation. Using both lack-of-function and gain-of-function mutants, we here report that the conformation of helix 12 predicts vesicle priming and secretory amplitude in living chromaffin cells. The effects of mutants on secretion could not be explained by differences in syntaxin-1 chaperoning/localization or vesicle docking, and the fusion kinetics and calcium dependence were unchanged, indicating that the effect of helix 12 extension is specific for the vesicle-priming step. We conclude that a conformational change within helix 12 is responsible for the essential postdocking role of Munc18-1 in neurosecretion.

A Post-Docking Role of Synaptotagmin 1-C2B Domain Bottom Residues R398/399 in Mouse Chromaffin Cells.

Synaptotagmin-1 (Syt1) is the principal Ca(2+) sensor for vesicle fusion and is also essential for vesicle docking in chromaffin cells. Docking depends on interactions of the Syt1-C2B domain with the t-SNARE SNAP25/Syntaxin1 complex and/or plasma membrane phospholipids. Here, we investigated the role of the positively charged "bottom" region of the C2B domain, proposed to help crosslink membranes, in vesicle docking and secretion in mouse chromaffin cells and in cell-free assays. We expressed a double mutation shown previously to interfere with lipid mixing between proteoliposomes and with synaptic transmission, Syt1-R398/399Q (RQ), in syt1 null mutant cells. Ultrastructural morphometry revealed that Syt1-RQ fully restored the docking defect observed previously in syt1 null mutant cells, similar to wild type Syt1 (Syt1-wt). Small unilamellar lipid vesicles (SUVs) that contained the v-SNARE Synaptobrevin2 and Syt1-R398/399Q also docked to t-SNARE-containing giant vesicles (GUVs), similar to Syt1-wt. However, unlike Syt1-wt, Syt1-RQ-induced docking was strictly PI(4,5)P2-dependent. Unlike docking, neither synchronized secretion in chromaffin cells nor Ca(2+)-triggered SUV-GUV fusion was restored by the Syt1 mutants. Finally, overexpressing the RQ-mutant in wild type cells produced no effect on either docking or secretion. We conclude that the positively charged bottom region in the C2B domain--and, by inference, Syt1-mediated membrane crosslinking--is required for triggering fusion, but not for docking. Secretory vesicles dock by multiple, PI(4,5)P2-dependent and PI(4,5)P2-independent mechanisms. The R398/399 mutations selectively disrupt the latter and hereby help to discriminate protein regions involved in different aspects of Syt1 function in docking and fusion. SIGNIFICANCE STATEMENT: This study provides new insights in how the two opposite sides of the C2B domain of Synaptotagmin-1 participate in secretory vesicle fusion, and in more upstream steps, especially vesicle docking. We show that the "bottom" surface of the C2B domain is required for triggering fusion, but not for docking. Synaptotagmin-1 promotes docking by multiple, PI(4,5)P2-dependent and PI(4,5)P2-independent mechanisms. Mutations in the C2B bottom surface (R398/399) selectively disrupt the latter. These mutations help to discriminate protein regions involved in different aspects of Synaptotagmin-1 function in docking and fusion.

Visual patch clamp recording of neurons in thick portions of the adult spinal cord.

The study of visually identified neurons in slice preparations from the central nervous system offers considerable advantages over in vivo preparations including high mechanical stability in the absence of anaesthesia and full control of the extracellular medium. However, because of their relative thinness, slices are not appropriate for investigating how individual neurons integrate synaptic inputs generated by large numbers of neurons. Here we took advantage of the exceptional resistance of the turtle to anoxia to make slices of increasing thicknesses (from 300 to 3000 microm) from the lumbar enlargement of the spinal cord. With a conventional upright microscope in which the light condenser was carefully adjusted, we could visualize neurons present at the surface of the slice and record them with the whole-cell patch clamp technique. We show that neurons present in the middle of the preparation remain alive and capable of generating action potentials. By stimulating the lateral funiculus we can evoke intense synaptic activity associated with large increases in conductance of the recorded neurons. The conductance increases substantially more in neurons recorded in thick slices suggesting that the size of the network recruited with the stimulation increases with the thickness of the slices. We also find that that the number of spontaneous excitatory postsynaptic currents (EPSCs) is higher in thick slices compared with thin slices while the number of spontaneous inhibitory postsynaptic currents (IPSCs) remains constant. These preliminary data suggest that inhibitory and excitatory synaptic connections are balanced locally while excitation dominates long-range connections in the spinal cord.

Erythropoietin receptor in human skeletal muscle and the effects of acute and long-term injections with recombinant human erythropoietin on the skeletal muscle.

The presence and potential physiological role of the erythropoietin receptor (Epo-R) were examined in human skeletal muscle. In this study we demonstrate that Epo-R is present in the endothelium, smooth muscle cells, and in fractions of the sarcolemma of skeletal muscle fibers. To study the potential effects of Epo in human skeletal muscle, two separate studies were conducted: one to study the acute effects of a single Epo injection on skeletal muscle gene expression and plasma hormones and another to study the effects of long-term (14 wk) Epo treatment on skeletal muscle structure. Subjects (n = 11) received a single Epo injection of 15,000 IU (double blinded, cross over, placebo). A single Epo injection reduced myoglobin and increased transferrin receptor and MRF-4 mRNA content within 10 h after injection. Plasma hormones remained unaltered. Capillarization and fiber hypertrophy was studied in subjects (n = 8) who received long-term Epo administration, and muscle biopsies were obtained before and after. Epo treatment did not alter mean fiber area (0.84 +/- 0.2 vs. 0.72 +/- 0.3 mm(2)), capillaries per fiber (4.3 +/- 0.5 vs. 4.4 +/- 1.3), or number of proliferating endothelial cells. In conclusion, the Epo-R is present in the vasculature and myocytes in human skeletal muscle, suggesting a role in both cell types. In accordance, a single injection of Epo regulates myoglobin, MRF-4, and transferrin receptor mRNA levels. However, in contrast to our hypothesis, prolonged Epo administration had no apparent effect on capillarization or muscle fiber hypertrophy.