Citations

Skeletal muscle is a heterogenous tissue composed of fibers (i.e., cells) with distinct metabolic and contractile properties. Muscle fibers are classified into 2 separate groups: Type 1 fibers which are primarily oxidative, and Type 2 fibers (further subdivided to Types 2a and 2x) which are predominantly glycolytic. Acute exercise induces transcriptional changes in skeletal muscle. However, these changes have been studied at the whole muscle level. The effects of exercise on differential gene expression in distinct muscle fiber types in response to acute exercise remains unclear. In this study, we evaluated gene expression in Type 1, 2a, and 2x muscle fibers in response to acute aerobic exercise. Muscle biopsies were collected from 5 (31±3 yrs) apparently healthy individuals before and 3hrs following an acute 45 min session of cycling exercise performed at 65% of maximal heart rate. Individual muscle fibers (n=138) were isolated from the muscle biopsy sample manually under a microscope. Half of the fiber was used to characterize it as Type 1, 2a, or 2x based on its myosin heavy chain isoform expression content using single fiber SDS-PAGE. The other half of the fiber underwent RNA sequencing. The effects of exercise on fiber types were analyzed using subject specific pseudo-bulk differential expression before and after exercise (Type 1 n=28, 2a n=28, and 2x n=12). Gene counts were normalized as counts per million (CPM) and log2 transformed with a pseudocount of +1. The top 200 differentially expressed genes (DEG’s) were then used to calculate fold changes between fiber types at baseline and in response to exercise. After exercise, 73.5% of DEG’s were upregulated in Type 1 fibers, 52% were upregulated in Type 2a fibers, and 60.5% were downregulated in 2x fibers, relative to baseline. Type 1 fibers showed the greatest increases in gene expression (notably, TPM1 log2FC = 2.46, ATP2A1 log2FC = 3.23, and UQCRB log2FC=0.39) and displayed transcriptional changes consistent with oxidative phosphorylation, calcium signaling, and cytoskeletal remodeling pathways. Type 2a fibers displayed modest increases (ATP2A1 log2FC = 0.34, TNNC2 log2FC = 0.21 and ENO3 log2FC=0.35) and an overall upregulation of glycogenic/gluconeogenesis pathways. Conversely, Type 2x fibers exhibited broad transcriptional suppression and downregulation of calcium signaling pathways. In conclusion, acute aerobic exercise induces gene expression in muscle that is fiber type-specific. Type 1 fibers upregulate genes related to oxidative phosphorylation and calcium signaling, whereas Type 2a fibers upregulate genes related to glycolysis. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Study objective: To characterize physiologic autonomic dysfunction in humans after chronic spinal cord injury (SCI) relative to uninjured controls and to identify autonomic correlates to neuroimmune deficits. Hypothesis: Individuals with greater autonomic dysfunction after SCI will have more pronounced immune dysfunction, which will be further influenced by sympathetically mediated increases in catecholamine levels. Methodology: Both uninjured controls and individuals with SCI completed a battery of autonomic physiology tests aimed at characterizing preservation of supralesional/sublesional sympathetic activation and global sympathetic inhibition. The autonomic testing battery included 3-minute hand and foot cold pressor tests, 3 Valsalva maneuvers with goal expiratory pressure of 30 mmHg, a novel bladder pressor test (5 minutes of sustained bladder pressure at 35 cmH20 with room temperature sterile water infusion), paced breathing at 0.25 Hz for heart rate/blood pressure variability, and successive doses of bolus intravenous phenylephrine (Oxford technique). A subset of individuals in both cohorts had baseline and cold pressor stressed levels of catecholamines/cortisol drawn and immunologic assessments. Peripheral blood mononuclear cells were extracted from this baseline sample and assessed with flow cytometry for cellular exhaustion markers (CD69, PD-1, TIGIT, TIM-3). Antigen recall response, with/without primed exposure of catecholamines was also completed to identify how sympathetic activation variably impacted functional immune performance with exposure to viral peptides. Data: n=35 uninjured controls; n=29 individuals with SCI Summary of Results: When compared to uninjured controls, individuals with SCI demonstrated significant autonomic dysfunction in all three domains, with decreased supralesional sympathetic activation (Valsalva pressure recovery time, p< 0.0001), abnormal sublesional sympathetic activation (increased bradycardia, p< 0.0001), and impaired sympathetic inhibition (larger dose/body-weight adjusted increase in mean arterial pressure, p=0.0006). As expected, autonomic dysfunction in those with SCI existed on a continuum, with some having largely normal autonomic regulation and others exhibiting profound deficits. Principal component analysis confirmed these three domains as the primary drivers of variability. Cellular exhaustion markers were increased in those with SCI, with positive correlation (R2=0.42) between degree of global autonomic dysfunction (Z-score over 2.0) and CD3+ CD8+ T-cell TIM-3 immunologic exhaustion markers. Antigen recall response was impaired in those with SCI and autonomic dysfunction on physiologic testing, with pronounced decrement in response when catecholamines were added (mean 57% of response lost in CD69 T-cells to Epstein-Barr virus antigen exposure, 53% lost to Flu antigen). Conclusions: In humans with SCI, early evidence supports that individuals have greater autonomic dysfunction and that this is correlated to increased immunologic deficits. Funding Sources: NIH K23HD102663, R01NS115126 This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Obesity is associated with altered skeletal muscle protein metabolism. While plasma amino acids (AA) stimulate protein synthesis in muscle, it remains unclear how aerobic exercise modifies this response in obesity. In this study, we evaluated basal and amino acid-stimulated skeletal muscle protein fractional synthesis rate (FSR) in humans with obesity, induced by a primed, constant AA infusion (15% Clinisol; 4 mg·kg FFM-1·min-1), immediately after a single bout of acute aerobic exercise. We studied two groups of subjects with obesity: Group 1: AA infusion alone for 240 mins (AA; N = 8; BMI: 34.9 ± 1 kg/m 2 ; body fat percent: 35.2 ± 2) and group 2: acute aerobic exercise followed by AA infusion for 240 mins (AA+EX; N=8; BMI: 36.1 ± 2 kg/m 2 ; body fat percent: 42.4 ± 2). Subjects in the AA+EX group performed 45 minutes of cycling on a stationary bike at 65% VO2 max, and their amino acid infusion started immediately after the exercise ended. A d10-leucine tracer was infused for the entire duration of the study to measure mixed-muscle protein FSR (MMP-FSR). Muscle biopsies from the vastus lateralis were taken at baseline, 45 mins after the start of the amino acid infusion and at the end of the infusion study to determine MMP-FSR. Baseline MMP-FSR values did not differ between groups (p > 0.05). Participants receiving the AA infusion alone exhibited a significant increase in MMP-FSR from baseline to post-infusion (0.060 ± 0.005 to 0.119 ± 0.011 %/hr; p < 0.0001), whereas the AA+EX group showed no significant change from baseline (0.067 ± 0.004 to 0.084 ± 0.009 %/hr; p > 0.05). Plasma insulin concentrations increased significantly in response to the amino acid infusion (p < 0.0001) but did not differ between groups (p > 0.05). Baseline amino acid concentrations were not different between groups (p > 0.05). Among the plasma amino acids (μmol/L) changed, baseline plasma leucine (AA:137 ± 8, AA+EX: 144 ± 10; p > 0.05) increased significantly in both groups during AA infusion but was higher in the AA (424 ± 15) than the AA+EX (226 ± 13) group (p< 0.0001). Similarly, baseline plasma valine (AA: 226 ± 7, AA+EX: 234 ± 19; p > 0.05) increased significantly in both groups during AA infusion but was higher in the AA (553 ± 28) than the AA+EX (456 ± 23) group (p< 0.002). In contrast baseline arginine (AA: 59 ± 5, AA+EX: 71±11; p > 0.05), although it increased significantly in both groups during AA infusion, was lower in the AA (197 ± 3) than the AA+EX (266 ± 11) group (p< 0.0001). Despite marked increases in plasma amino acid and insulin concentrations, the AA+EX group exhibited a blunted muscle protein synthesis response to amino acid stimulation compared with the AA group. In conclusion, aerobic exercise blunts the amino acid-stimulated increase in muscle anabolism in the immediate period after exercise in humans with obesity. This research was supported by the National Institutes of Health/ National Institute of Diabetes and Digestive and Kidney Diseases. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Sarcopenia is the age-associated muscle weakness and atrophy. As this muscle weakens, so does the capacity for an animal to perform its associated behaviors. The tibialis anterior (TA) muscle is a lower leg muscle that is important for dorsiflexion during actions such as jumping and running. In humans and Fischer 344 rats, behavioral and pathophysiological assessments show spinal cord motor unit dysfunctions with age are primarily of fast fatigueable motor units, comprising larger MN and the type IIx/b fibers they innervate. In addition, mitochondrial dysfunctions are implicated in aging neuromotor dysfunction and muscle weakness, however, little fiber type specific knowledge exists regarding the function of aged mitochondria in type-identified muscle fibers. Based on the specific atrophy and reduced oxidative capacity (succinate dehydrogenase [SDH] enzymatic function) of type IIx/b fibers in respiratory muscle, we expected to observe type-specific atrophy and reduced SDH activity in type IIx/b TA fibers. In young (6-months-old, n=12) and old (24-months-old, n=12) female and male F344 rats, cut serial TA sections (8 µm) on a cryostat to evaluate type specific morphology and SDH. To determine CSA TA fibers were labelled with MyHCSlow (Novus NBP2 50299), MyHC2A (Novus N1551) and anti-Laminin antibodies, with alexa488, alexa555 and alexa408 secondaries, respectively. SDH was determined using 10 min incubation n 80 mM succinate with 1.5mM nitro blue tetrazolium, with precipitate imaged using a Nikon AR1 inverted microscope with a 579nm high pass filter. We observed a fiber type-specific atrophy of IIx/b fibers in old TA fibers. We also observed a marked reduction in TA SDH activity in old age, confined to type IIx/b fibers. These findings illustrate consistent fast fatigue resistant motor unit degeneration in old age. Strategies specifically targeted to these motor units are imperative in interventions of sarcopenia. Funding: This study was supported by R56 HL166204 (MJF), R01 AG086136 (MJF) and AG44615 (GCS) from the NIH. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Background: Diabetic gastroparesis (DG) is associated with a loss in anti-inflammatory muscularis macrophages (MMs), contributing to delayed gastric emptying (DGE). Lyve1 macrophages, known for their anti-inflammatory phenotype, are involved in lipid metabolism across organs. While diabetes is typically associated with increased lipid levels, the dependence of lipid handling on altered function of Lyve1+ MMs in the stomach remains unknown. Aim: To investigate lipid accumulation in MMs and test the effect of palmitate and CD36 on Lyve1+ macrophages. Methods: FACS sorted CD45+ cells were isolated from the gastric muscularis of non-diabetic mice and analyzed using 10X Genomics Cellranger and Seurat package. Gene Set Enrichment Analysis was performed to identify enriched pathways. Separately, the cells underwent flow cytometry to identify Lyve1+/- MMs then determining lipid accumulation by LipidTox intensity. RAW 264.7 macrophage cells were cultured with macrophage colony stimulating factor (M-CSF), IL-4, and dexamethasone for 7 days to induce Lyve1 expression. RNA was collected from cells treated with palmitate and a CD36 inhibitor, Sulfosuccinimidyl oleate (SSO), for RT-qPCR. Lyve1+ and Lyve1- macrophages treated with 300µM palmitate overnight were collected for lipidomic analysis. Untargeted lipidomic analysis was done with Thermo Orbitrap Exploris 120, and data were analyzed using principal component analysis for group clustering and unpaired t-tests for differential analysis. Results: Unbiased clustering analysis revealed 6 transcriptionally distinct gastric MM populations, one of which was notably enriched in Lyve1 expression. Pathway analysis identified that Lyve1 enriched cluster was associated with lysosomal pathways and receptors involved in lipid uptake, such as CD36, as well as anti-inflammatory markers such as HO1 and CD206. Flow cytometry quantification showed that Lyve1+ MMs had higher accumulation of lipids compared to Lyve1- MMs (10.1±0.7 vs 2.9±0.2 mean fluorescence intensity/cell count, p=0.0002). RT-qPCR validated that Lyve1+ RAW 264.7 macrophages exhibited significantly higher expression of Lyve1 (6.95 times fold change, p=0.023) and CD36 (3.27 times fold change, p=0.011) compared to Lyve1- macrophages. Post palmitate treatment, Lyve1+ macrophages had increased expression of the pro-apoptotic gene caspase-3 (12.15-times fold change, p=0.033), as well as the fatty acid oxidation marker ACADM (4.98 times fold change, p=0.045). Notably, these differences were not found in the presence of SSO. Lipidomic analysis identified 171 differentially expressed lipids, particularly increased levels of ceramides and diacylglycerols in Lyve1+ macrophages compared to Lyve1- macrophages when both are treated with palmitate. Conclusions: Lyve1+ macrophages preferentially uptake lipids compared to Lyve1- macrophages consistent with increased expression of CD36. Lipid treatment of Lyve1+ macrophages increases expression of apoptosis and oxidation markers in a CD36-dependent manner that may lead to cell loss. These mechanisms may contribute to Lyve1+ MMs loss in DG. Funding: DK127992; DK129297; DK115255; ANMS Young Investigator grant; AGA grant#36; P30DK084567; Robert and Arlene Kogod Center on Aging Fundamental Mechanisms of Aging Award. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Aging is associated with increased aortic stiffness and exaggerated stress-induced blood pressure (BP) responsiveness, both of which contribute to the risk of cardiovascular disease. Supplementation with inorganic nitrate increases nitric oxide (NO) bioavailability and is a promising potential treatment to improve vascular function. While the acute effects of dietary inorganic nitrate supplementation on various measures of vascular function and BP have been demonstrated in several studies, the effects of increasing NO bioavailability through prolonged use (i.e. weeks) is unclear. Therefore, we tested the hypothesis that 4-weeks of inorganic nitrate supplementation will effectively increase NO bioavailability (as measured by plasma nitrate and nitrite) and reduce central BP, aortic stiffness, and BP responsiveness to a cold pressor test (CPT) in older adults. Thirteen older adults (67±3 years; 7 males and 6 females) completed a randomized, double-blind, placebo-controlled, crossover trial consisting of two 4-week supplementation periods (nitrate vs. placebo) separated by a 4-week washout. Central BP and carotid-femoral pulse wave velocity (cfPWV) were measured via applanation tonometry. Peripheral BP responses were assessed using beat-by-beat BP at baseline and during CPT. Plasma [nitrate] (40±24 to 76±46 µM, P< 0.01) and [nitrite] (289±94 to 413± 28 nM, P< 0.01) increased following inorganic nitrate supplementation, but remained unchanged after placebo ([nitrate] 39±20 to 39±16 µM, P=0.97; [nitrite] 303±108 to 302±87 nM, P=0.95). Four weeks of inorganic nitrate supplementation reduced resting measures of central systolic BP (cSBP; 116±12 to 113±10 mmHg, P< 0.05) and diastolic BP (cDBP; 79±8 to 74±6 mmHg, P< 0.05), as well as cfPWV (10.2±1.3 to 9.4±1.0 m/sec, P< 0.01), whereas no changes were observed following placebo (cSBP 112±10 to 115±10 mmHg; cDBP 75±7 to 78±7 mmHg; cfPWV 10.0±1.1 to 9.8±1.0 m/sec, P >0.05 for all). Additionally, the peak change (Δ from baseline) in peripheral SBP (28±10 to 23±6 mmHg, P< 0.05) and mean arterial pressure (MAP; 17±6 to 14±3 mmHg, P< 0.05) during the CPT were reduced following nitrate with no changes observed after placebo (SBP 25±8 to 26±12 mmHg, P=0.51; MAP 14±4 to 16±8 mmHg, P=0.19). Our findings demonstrate 4-weeks of inorganic dietary nitrate supplementation has favorable effects on central BP, aortic stiffness and BP responsiveness in older adults. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Introduction: Inflammatory bowel disease is characterized by remitting and relapsing bouts of intestinal inflammation accompanied by sensory and motor dysfunction that persists beyond the active periods of inflammation. Evidence suggests that neural pathways of the Gut-Brain Axis, particularly the sensory and sympathetic nervous system, are involved in pathophysiology, but until recently technical restrictions have limited our understanding of the underlying neural circuit mechanisms. In this study, we examined how sensory-sympathetic circuits are modified by colitis and how these alterations contribute to dysfunction during both active inflammation and post-inflammatory recovery. Methods: E2a-GCaMP mice were treated with vehicle or 3% dextran sodium sulfate (DSS) for 5 days to induce experimental colitis and switched to normal drinking water. Mice were assessed at two time points: Day 7 (two days after ending DSS treatment), representing active inflammation, and Day 21 to represent recovery. Inflammation and mucosal damage were evaluated using disease activity index scores and hematoxylin and eosin (H&E) staining. Colon motility was assessed in vivo via colonic bead expulsion and ex vivo using whole-colon preparations. We performed Ca 2+ imaging of sympathetic motor neurons in prevertebral ganglia (PVG) and sensory neurons in dorsal root ganglia (DRG) neurons in ex vivo preparations that preserve extrinsic neural circuitry with the colon (intestinofugal-sympathetic and spinal cord-sympathetic pathways). Results: Histological analysis confirmed hallmark features of colitis, including colon shortening, immune infiltration, and mucosal damage at 7 days post-DSS (p< 0.05, n=3–4), which resolved after recovery. During active inflammation, in vivo colon transit time was significantly faster, and this persisted after recovery (p< 0.05, n=7-9). Ex vivo motility assays in isolated colons also revealed DSS-induced dysmotility during active inflammation, but the irregular colon motor complexes became normal after recovery (p< 0.05, n=7-9), suggesting that extrinsic neural pathways contribute to prolonged dysmotility. In preparations without the spinal cord, PVG neurons exhibited increased activity and increased responses to distension during active inflammation but returned to baseline after recovery (p< 0.05, n=3-4), suggesting alternative sensory-PVG pathways contribute to persistent dysmotility. In preparations with spinal circuits intact, thoracolumbar (TL), but not lumbosacral (LS), DRG sensory neurons were hypersensitive to colonic distension during inflammation (p< 0.05, n=8-9). Furthermore, TL spinal stimulation evoked more responses in PVG neurons during active inflammation, but this was associated with decreased inhibition of ENS motor circuits (p< 0.05, n=6-7) and increased Ca 2+ signaling in the epithelium (p< 0.05, n=5), suggesting shifts in TL spinal-sympathetic motor output. Preliminary studies show an increase in spontaneous activity of TL DRG neurons in recovery that does not occur at LS levels (p< 0.05, n=3-6), which suggests that thoracolumbar spinal pathways remain hyperexcitable after recovery.Conclusions: Our findings indicate that TL spinal pathways associated with sympathetic motor outflow contribute to pain and dysmotility during active inflammation and may contribute to the post-inflammatory recovery processes that seem to go awry in IBD patients with relapsing inflammation. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

~80% of kidney stones (KS) are composed of calcium oxalate and small increases in urinary oxalate significantly enhance the stone risk. We previously discovered Oxalobacter formigenes (Of)-derived secreted factors which stimulate oxalate transport by human intestinal Caco2-BBE (C2) cells and reduce urinary oxalate excretion in hyperoxaluric mice by enhancing colonic oxalate secretion (JASN, 2017). The small Sel1-like protein-derived peptides (P8 and P9) were identified as the major Of-derived factors (AJP Cell Physiol, 2023), acting via the oxalate transporters SLC26A6 (A6) and SLC26A2 (A2). P8/9-induced stimulation of oxalate transport in C2 cells is likely PKA-dependent based on studies using the PKA inhibitor H89. Enhancing gut oxalate secretion with subsequent fecal excretion represents a novel therapeutic pathway for getting rid of body oxalate. Building on these findings, the study objective is to test the hypothesis that the observed regulation is indeed PKA-mediated, through mechanisms potentially involving other signaling pathways and/or altering A6 total and/or surface protein expression. To provide further evidence that it is PKA-dependent, we successfully identified the binding mode of P8/9 bound to PKA using molecular docking (ZDOCK). The regulatory subunit of PKA binds two cyclic AMPs and P8/P9 are predicted to interact at the cyclic AMP binding site according to our PKA-peptide modeling studies. To directly confirm the role of PKA, we used siRNA to knockdown its α catalytic subunit (PKA-α) in C2 cells. PKA-α mRNA expression is reduced by >90% as assessed by qPCR. Importantly, siRNA knockdown of PKA-α completely abolished P8/P9-induced stimulation of 14C-oxalate uptake by C2 cells in pilot studies, confirming the role of PKA in P8/9-mediated stimulatory regulation of intestinal oxalate transport. To identify the signaling pathways potentially upstream and/or downstream of PKA we used relatively selective pharmacological inhibitors. Interestingly, the stimulatory effects of P9 on 14C-oxalate uptake by C2 cells are significantly blocked by the ERK1/2 inhibitor U0126 (~90%), the PI3K inhibitor LY294002 (~84%), and the p38 inhibitor SB 202190 (~73%), while the general tyrosine kinase inhibitor genistein has no effect. Inhibitors alone did not affect baseline transport. These results support the involvement of the MAPK ERK1/2, PI3K, and p38 in the signaling pathways regulating intestinal oxalate transport by P8/9. We used immunoblotting and surface biotinylation studies to evaluate whether P8/9 stimulates oxalate transport in C2 cells by increasing its total and/or surface protein expression. P8/9 peptides did not affect A6 total and surface protein expression levels in preliminary studies. We could not assess A2 total and surface protein expression due to lack of good working antibodies. In view of our previous findings that the observed regulation is due to P9-induced increase in Vmax and reduction in Km, and since P8/9 did not affect A6 surface protein expression, it is likely possible that the observed stimulation is due to mechanisms including P8/9-induced enhanced A6 transport activity resulting from an increase in the intrinsic activity of the preexisting A6 membrane transporters. We conclude that P8/9 stimulates intestinal oxalate transport in C2 cells via signaling pathways including PKA, ERK1/2, PI3K, and p38 and through mechanisms including P8/9-induced enhanced A6 transport activity. Having the P8/9-PKA bound conformation determined, we plan to optimize P8/P9 into small molecule like drugs with better stability and clinical translational potential in terms of stimulating intestinal oxalate secretion, leading to reduced plasma and urinary oxalate levels. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Background: Exogenous and endogenous polyamines are critical for gastrointestinal (GI) barrier integrity, of which putrescine, spermidine and spermine are most well studied. Our recent work shows n-acetylputrescine, a putrescine derivative, correlates with increased intestinal permeability and loss of microbial diversity. Despite this, bacterial mechanisms of n-acetylputrescine production or direct effects on barrier integrity are unknown. Aim: Determine the role of microbiota in shaping n-acetylputrescine abundance and the effect on barrier integrity. Methods: N-acetylputrescine effects on barrier were assessed both in vitro using Caco-2 and ex vivo in Ussing using colonic strips from conventional mice. Germ-free (GF) mice were monocolonized with wild-type E. coli (SK929) or E.coli SK930 (2-weeks, n=4mice/group), strains given by Dr. Shin Kurihara. E. coli SK930 is deficient in SpeC, SpeF and SpeB, genes generating putrescine, required for n-acetylputrescine production. Untargeted metabolomics (Metabolon) was performed on fecal pellets. Targeted isotope tracing with [13C6, 15N4]-arginine delivered via enema was done to track bacterial production of n-acetylputrescine by Fusobacterium varium, a known producer, in vivo with isotopolog labeling measured by LC/HRMS. Results: In vitro n-acetylputrescine (100mM) addition to Caco-2 monolayers caused significant barrier disruption compared to controls (%Baseline TER, 13.7±6.7 vs 102.8±9.4, 3h postexposure, n=3 p=0.0002), not seen at lower (10mM) concentration. N-acetylputrescine caused increased flux of 300Da fluorescein (12.6±2.0 vs 6.0±0.2 mg/mL, n=3 p=0.004) and 4kDa FITC-Dextran flux on Ussing compared to untreated controls (999±94 vs 562±121 ng/hr/cm2, n=3 p= 0.01). Mutant E. coli SK930 monocolonized mice had similar fecal n-acetylputrescine to GF animals. In contrast, wild type E. coli SK929 monocolonization led to significantly greater n-acetylputrescine (5-fold, FDR< 0.001) compared to SK930, indicating a bulk of n-acetylputrescine production is driven by bacterial mechanisms. Pathway enrichment analysis predicted decreased spermidine and spermine biosynthesis in SK930 monocolonization, indicative of impaired polyamine metabolism, compared to SK929 (FDR< 0.01). Targeted metabolomics on fecal pellets showed a shift in the production of isotopolog [13C1, 15N0]-N-acetylputrescine to increased isotopolog [13C4, 15N2]-N-acetylputrescine concentration after monocolonization with F. varium compared to GF mice (5.9±5.0 vs. 2.1±3.6 pg/mg stool, n=3mice/group p=0.05) suggesting microbiota driven shifts in n-acetylputrescine metabolism. Conclusion: Luminal n-acetylputrescine production and profile is driven by bacteria in the GI tract. Concentration dependent effects of n-acetylputrescine suggest insufficient regulation by intestinal microbiota can lead to accumulation of n-acetylputrescine and the intestinal barrier disruption seen in human studies. Ongoing studies aim to identify bacterial taxa critical for n-acetylputrescine suppression, the mechanisms involved, and impact on GI health. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Background: As part of the bidirectional gut-brain communication system that influences gastrointestinal function, vagal pathways coordinate with the activity of interstitial cells of Cajal (ICC) to regulate gastric motility. Impairments in ICC slow wave activity and altered vagal tone have been implicated in diabetic gastroparesis and obesity, but technical limitations have restricted our ability to measure integrated and bidirectional activity in vagal-ICC pathways. Furthermore, the influence of physiological and meal-induced stimuli like gastric distension on these pathways is not well understood. We aimed to develop a calcium imaging approach in ex vivo nodose ganglion-vagus nerve-stomach preparations to investigate vagal-ICC pathways and test the effects of gastric distension on vagal activation, ICC network activity, and their functional interactions. Methods: Calcium imaging was performed in ex vivo preparations, in which the stomach and vagus nerves (with or without the ganglion) remain intact. EIIa-GCaMP6 (n=3) and cKit-GCaMP6 (n=3) mice were used to image Ca 2 + signals from both vagal neurons and ICC or ICC alone, respectively. Two-minute recordings were captured in the following stomach conditions: (1) Undistended; (2) Undistended + vagal nerve stimulation (VNS, 20 Hz, 1 s); (3) Distended (0.25 ml volume distension); (4) Distended + VNS. Ca 2 + signals in ICC and neurons, along with tissue displacement, were analyzed using Image J. Data from both GCaMP models were pooled for ICC. Results: Acute gastric distension significantly activated vagal sensory neurons in nodose ganglion compared to baseline (p=0.0193), and VNS evoked Ca 2 + responses in ICC and neurons, confirming intact nerve pathways. Both VNS and gastric distension altered the direction of ICC propagation, significantly increasing retrograde waves (p=0.0025 and p=0.0032, respectively), and VNS had no effect on retrograde waves in distended stomachs. VNS and distension also reduced length of propagation of anterograde ICC waves (p=0.019 and p=0.0004, respectively), and again, VNS effects were not observed during distension. VNS increased the velocity of ICC wave propagation, but only in undistended stomach (p=0.0283). Finally, VNS increased ICC pacemaker frequency regardless of the distension state (p=0.0123). Conclusion: Both acute gastric distension and VNS altered ICC network activity, with similar effects on network parameters. However, most of the VNS effects on ICC were blocked during distension. VNS increased the frequency of ICC network waves in both undistended and distended stomachs, suggesting that VNS can influence ICC pacemakers regardless of distension state. These findings have important implications for designing therapeutic strategies for gastroparesis. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.