Citations

Effective neuromotor function may be considered the combination of activating motor units of a type, matching the desired force and fatigue requirements of a behaviour; and the timing of these activations in concert with motor units of other motor pools and/or with contextual/sensory cues. Although the former is well-established as being impaired with age (i.e., sarcopenia), the latter timing issues remain poorly defined in terms of aging. Indeed, sarcopenia may be considered the apotheosis of a degenerative process that first affects the timing and effective activation of motor units prior to overt weakness. We hypothesized that mild motor impairment (i.e., timing deficiencies and motor neuron synaptic pathology) would precede overt striated muscle weakness and motor neuron death. To test this hypothesis, we evaluated the neuromotor system for swallow, where striated muscle activities do not create torque across a joint (a confounder in aging studies) but pressure in the oropharynx and coordination with ventilation. We used female and male Fischer 344 rats (F344) at 6- (young), 18- (late middle-age) and 24-months-old (old) rats. Behavioral evaluations consisted of pharyngeal and thoracic pressures during naturalistic (0.5 ml oral water bolus) swallow. Synapse evaluations consisted of golgi-cox evaluation of nucleus ambiguus and hypoglossal motor neurons, and serial blockface electron microscopy evaluation of hypoglossal motor neurons. We assessed longitudinal (intrinsic) and genioglossus (extrinsic) muscle function and histopathology using platinum plate electrodes and immunohistochemistry for myosin heavy chain (MyHC) expression, respectively. Overall, we show that swallow timing abnormalities occur at late middle-age, contemporaneous with dendritic synaptic and mitochondrial deficits. Notably, motor neuron survival and muscle function and cross-sectional areas were unchanged in late middle- age, with sarcopenia and nucleus ambiguus and hypoglossal motor neuron death only apparent from old age. These results are consistent with the concept of “mild motor impairment” being a harbinger of striated muscle sarcopenia and frailty. There is every reason to suggest that these early motor timing deficits occur in spinal motor neurons. These results illustrate the importance motor neuron health has on maintenance of motor function into old age. Funding: This study was supported by R56 HL166204 & R01 AG086136 (MJF) 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.

Brain derived neurotrophic factor (BDNF) signals through its high-affinity full-length tropomyosin receptor kinase-B (TrkB.FL) and plays role in maintaining the survival and function of phrenic motor neurons (PhMNs), neuromuscular transmission and synaptic activity. Disruption of this pathway is a hallmark of several neurodegenerative diseases associated with dysfunction and death of PhMNs with impaired mitochondrial function. BDNF/TrkB.FL signaling phosphorylates CREB at serine 133 (pCREBS133) and promotes its nuclear localization in cervical ventral horn of rats, however its downstream molecular pathway has not yet been established. Recently, we demonstrated that in human airway smooth muscle cells, pCREBS133, as a transcription factor, binds to the CRE sequence in the PGC1a promoter and activates its expression. PGC1a co-transcriptionally activates mitochondrial transcription factor A (TFAM) expression promoting mitochondrial DNA (mtDNA) replication and mitochondrial biogenesis. In the present study, we hypothesized that BDNF/TrkB.FL signaling promotes pCREBS133 phosphorylation and transcriptional activation of PGC1a and downstream expression of TFAM, leading to mitochondrial biogenesis. In this study, we employed a loss of function approach using a novel chemogenetic rat model (TrkBF616A) with a knock-in allele sensitive to the selective kinase inhibitor 1NMPP1 to inhibit TrkB.FL kinase activity. One group of female and male rats were treated intrathecally at C4 with either artificial cerebrospinal fluid (aCSF) or BDNF (450 ng/ 300 g b.w.; diluted in aCSF) for 40 mins, followed by collection of C3-C6 cervical ventral horn. In a second group, female and male rats were treated with 1NMPP1 (25 uM; i.p.) or the vehicle DMSO for 2 h. After 2 h, both groups were treated intrathecally with BDNF for 40 min and the C3-C6 cervical ventral horn collected. Intrathecal BDNF increased the pTrkB.FLY817 autophosphorylation and downstream phosphorylation of pCREBS133. Bioinformatic analysis identified a putative binding site of pCREBS133 on PGC1a promoter, which was confirmed by Chromatin immunoprecipitation (ChIP) assay. Consistent with this, BDNF treatment increased the expression of PGC1a and downstream TFAM, with an increase in mtDNA copy number. 1NMPP1 inhibition of TrkB.FL kinase (blunted BDNF-induced pTrkB.FLY817 phosphorylation) inhibited downstream activation of the pCREBS133/PGC1a/TFAM signaling cascade. Additionally, 1NMPP1 treatment blunted the BDNF-induced increase in mtDNA copy number. We conclude that BDNF/TrKB.FL signaling mediates mitochondrial biogenesis in the cervical ventral horn suggesting that interventions targeting this pathway could be a therapeutic strategy for neurodegenerative diseases. This research was funded by NIH Grants HL146114 & AG44615. 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.

In the aerodigestive system (ventilation, swallow, speech and airway defense manoeuvres), age-related neuromotor declines contribute to the increased risk of aspiration pneumonia, a leading cause of mortality in the elderly. In the Fischer 344 (F344) rat model, we and others have identified that brainstem hypoglossal motor neuron (MN) degenerations and death contribute to motor dyscoordination and tongue muscle weakness, respectively. In F344 rats, both MNs and striated muscle exhibit morphological and functional deficits of mitochondria in aging, consistent with elderly human post mortem results. However, to date the dendritic and axonal compartments have been relatively ignored. In young (6-months old; n=6 rats) and old (24-months-old; n=6 rats) female and male F344 hypoglossal motor axons were assessed using serial block face scanning electron microscopy (SDFEM). Within myelinated hypoglossal motor axons and hypoglossal MN dendrites, mitochondrial volume density and morphology (mitochondrial CSA, form factor and aspect ratios) were assessed. In old age, mitochondrial volume density was reduced in dendrites and, surprisingly, increased in axons. Mitochondrial fragmentation (reduced CSA, form factors and aspect ratios was apparent in dendrites. In axons, old age mitochondria were larger, but more simplistic. We interpret these dendritic findings to be consistent with altered neural network function in old age. In the axons, excessive mitochondria may physically impair the anterograde and retrograde transit along the axons. Our results suggest that a more nuanced compartment-specific evaluation of mitochondrial structure and function is required to fully elucidate the pathophysiology underlying age-related neuromotor dysfunction. Funding for this research was provided by National Institutes of Health (NIH) grant AG086136 (MJF). 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.

Tongue-muscle associated behaviours (swallow, speech) are impaired in the elderly. In the Fischer 344 (F344) rat model of aging, hypoglossal MNs and intrinsic tongue muscle weakness and atrophy are evident. Here we evaluated young (6-months; n=6 rats) and old (24-months-old; n=6 rats) F344 rat longitudinal muscles for neuromuscular junction (NMJ) innervation. In 140 µm free floating sections, presynaptic components were labelled with synaptophysin and neurofilament. Postsynaptic acetylcholine receptors were labelled with α-Bungarotoxin. NMJs were imaged using confocal microscopy with presynaptic invasion of the postsynaptic endplate quantified (n=200 young NMJs, n=180 old NMJs). We found marked denervation of tongue NMJs in old age,. Our findings underpin the significant role that tongue dysfunction has in the increased risk of aspiration pneumonia and obstructive sleep apnea in the elderly. 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.

The motor unit consists of an individual motor neuron (MN) and the muscle fibers it innervates. In humans and rodents, muscle weakness in aging (sarcopenia) has focused on altered motor unit discharge properties and intrinsic skeletal muscle pathophysiology, with MNs relatively ignored. In the brainstem, the intrinsic and extrinsic tongue muscles are innervated by hypoglossal MNs. In the spinal cord, the hindlimb muscles are innervated by the lumbar motor enlargement. Both aerodigestive and locomotor behaviours are affected in old age. In Fischer 344 rats, age-related MN death is evident by 24 months, disproportionately affecting larger (likely fast fatiguable motor unit) MNs. Here, we evaluated hypoglossal and lumbar MN survival in female and male Sprague Dawley rats at young (6-months-old; n=12) and old (24-months-old; n=6) ages. Stereological assessment of hypoglossal MN numbers and surface areas were performed on 16 µm Nissl-stained brainstem and spinal cord cryosections. We observed a robust loss of ~20% of hypoglossal MNs and a modest ~15% reduction in their surface areas with age. In the larger size tertile of hypoglossal MNs, age-associated loss of MNs approached ~30%. Similarly, we observed an ~20% lumbar MN loss, with a striking ~25% reduction in somal surface area. In the larger size tertile of lumbar MNs, age-associated loss of MNs approached ~40%. These findings underscore a marked neurogenic component to age-related neuromotor dysfunction, with reliability of findings across rat strains. This MN death likely contribute to physiologically relevant aerodigestive and locomotor impairments in old age. 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: Vascular endothelial dysfunction is a key antecedent to cardiovascular diseases (CVD) in older adults. Reduced nitric oxide (NO) bioavailability secondary to excess mitochondria-related reactive oxygen species (mitoROS) bioactivity are key mechanisms of endothelial dysfunction with aging. Cellular senescence is a state of largely irreversible cell cycle arrest that drives endothelial dysfunction. This occurs in part through secretion of bioactive factors into serum, collectively referred to as the circulating senescence-associated secretory phenotype (SASP), that promote excess mitoROS and reduce NO. We have shown fisetin improves endothelium-dependent dilation in old mice by reducing cellular senescence and mitoROS. Here, we sought to translate our preclinical findings to older adults. Hypotheses: We tested the primary hypothesis that intermittent fisetin treatment would improve endothelial function in older adults and that this would be mediated by reductions in mitoROS and associated with lower cell senescence. We also determined if fisetin altered the serum to improve endothelial cell (EC) NO and reduce whole-cell ROS and mitoROS ex vivo. Exploratory analyses assessed if fisetin changed circulating SASP factors. Methods: In a randomized, placebo-controlled, parallel-group design pilot trial, 41 older men and postmenopausal women were randomized to fisetin (2 mg/kg/day) (age: 71±1 yrs [mean±SEM], n=22 [13 W]) or placebo (age: 71±1 yrs, n=19 [12 W]) administered in an intermittent manner (2, 3-day dosing periods separated by 14 days). Outcomes were measured at baseline and 1-3 weeks after the final dose. Endothelial function was assessed as brachial artery flow-mediated dilation (FMDBA). The change in FMDBA with an acute supratherapeutic dose (160mg) of the mitochondrial antioxidant MitoQ was used to assess mitoROS-related inhibition of endothelial function. Gene expression of cellular senescence markers Cdkn1a (encodes p21) and Lmnb1 (encodes Lamin B1) were assessed in peripheral blood mononuclear cells (PBMCs) by Q-PCR. Human aortic ECs (HAECs) in culture were exposed to 10% participant serum for 2 hrs; acetylcholine (ACh)-stimulated NO production (DAR-4M-AM) and basal whole-cell ROS (CellROX) and mitoROS (MitoBright Deep Red) bioactivity were assessed via immunofluorescence. Luminex analyses (Biotechne) measured circulating levels of SASP factors in serum. Results: FMDBA was improved by 41% with fisetin (pre: 3.9±0.4%, post: 5.5±0.5%, P< 0.0001), but unchanged with placebo (pre: 4.4±0.5%, post: 4.5±0.4%) (group x time interaction effect: P< 0.01). Similar efficacy was observed in men and women. Acute MitoQ enhanced FMDBA at baseline and after placebo (all P< 0.05) but led to no further improvements in FMDBA after fisetin treatment. Consistent with lower cell senescence, expression of Cdkn1a was reduced (P< 0.05) by 12% and expression of Lmnb1 increased (P=0.06) by 16% in PBMCs collected after fisetin but not placebo. Compared with pre-intervention, serum collected after fisetin, but not placebo, increased HAEC ACh-stimulated NO by 6% (P< 0.01) and lowered whole-cell and mitoROS bioactivity by ~10% (both P< 0.05). Protein levels of CXCL12 in serum were 5% lower (P< 0.05) after fisetin compared with pre-intervention and after placebo. Traditional cardiometabolic risk factors were unchanged. Conclusions: Intermittent fisetin treatment improves vascular endothelial function in older adults in part by suppressing mitoROS. These effects are linked to reduced cell senescence and select changes to the circulating SASP. Funding: AHA 23CDA1056582; NIH F31AG087709; NIH/NCATS CTSA UL1TR002535; Life Extension® provided fisetin (BioFisetin) and placebo. 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.

Accurate assessment of arterial wall mechanics is essential for detecting vascular pathologies. The technique described herein incorporates a commercially available ultrasound system and applanation tonometry to noninvasively evaluate the local mechanical properties of the common carotid artery (CCA). Pressure waveforms were acquired using a tonometer combined with ultrasound-based diameter of the CCA. The signals were temporally aligned, converted to physical units using brachial systolic and diastolic pressure, and interpolated over uniform strain increments. Hoop stress was estimated using thick-wall assumptions, and hoop strain was derived from mid-wall circumferential stretch. Incremental elastic modulus was computed from local linear fits to the stress–strain data, and the area of the resulting hysteresis loop was used as a surrogate for viscoelastic energy loss, quantified by the energy dissipation ratio (EDR). The method was applied to healthy subjects (HS) and those with cardiovascular risk or confirmed atherosclerosis. In HS, pressure–strain elastic modulus (Ep) ranged from 50–55 kPa and EDR from 2%–6%, while non-healthy subjects showed higher EDR values (10%–20%), reflecting increased arterial viscoelasticity. Results revealed nonlinear pressure–diameter relationships with clear hysteresis, reflecting viscoelastic effects. The technique offers potential as a diagnostic tool for evaluating early, localized vascular alterations.

Color Doppler twinkling improves visibility and ultrasound-guided localization of biopsy markers made of polymethyl methacrylate (PMMA). This study examines the time- and frequency-domain features of twinkling. We performed beamforming on the raw radiofrequency (RF) data collected using a L7-4 transducer, followed by in-phase/quadrature (IQ) demodulation and wall filtering. Frequency content variations were evaluated both within individual Doppler ensembles (pulse-to-pulse) and across multiple frames. Normalized FFT magnitude spectra were computed for both twinkling and non-twinkling (metal) cases using beamformed RF and IQ data. The median of the normalized FFT magnitude (3–10 MHz) was consistently higher for the twinkling case compared to the metal case across RF (–13.75 dB vs –17.29 dB) and the IQ real component (–12.72 dB vs –16.15 dB), indicating broader and more energetic spectral content in twinkling. The frequency spread above the –20 dB threshold was approximately 2.5 times wider (5.38 MHz vs 1.95 MHz) in the twinkling case compared to the metal case. In time domain, the RMS of the standard deviation for the twinkling signal was approximately 28 times higher than that of the metal case across both RF and IQ data. These findings indicate that the ultrasound data from twinkling exhibits a more distributed frequency profile, consistent with observed aperiodic nature.

Color Doppler twinkling is associated with rough-surfaced objects like kidney stones, some clinical breast biopsy markers, and polymethyl methacrylate (PMMA) bone cement. Microbubbles are theorized as the predominant source of twinkling, supported by decreased twinkling under increased pressure. PMMA, metallic breast markers, a low-twinkling PMMA sample, and a non-twinkling metal rod were scanned in a pressure chamber up to 1000 psi using a General Electric Logiq E9 system and C1-6 probe (1.7–3.6 MHz Doppler transmit frequency). Clinical markers maintained distinct twinkling up to 250 psi. PMMA often twinkled at higher pressures, sometimes up to 1000 psi. The controls showed no twinkling. To understand physical structure associations with twinkling, the samples were scanned in a micro-CT system with a pixel resolution of 2 μm. Analysis of PMMA and Cork internal voids showed no correlation with twinkling. However, a correlation between Sa (average difference between the mean surface profile and actual surface profile) values and twinkling was found. This indicates that internal structure is not important for twinkling, and certain surface roughness is critical, possibly providing sites for surface microbubbles to oscillate from incident ultrasound waves.