Citations

Clonus is a disabling symptom of upper motor neuron dysfunction in patients with multiple sclerosis (MS). We report immediate termination of mechanically evoked clonus by epidural lumbosacral spinal cord stimulation (ES) in a 58-year-old man with secondary progressive MS. This observation was captured during training using video and skin surface electromyography of soleus muscle activity. ES immediately reduced mechanically evoked clonus duration and cycle count compared to trials without stimulation, as determined by a Kruskal–Wallis test ( p < 0.05, n = 2–3 trials), and reverted to baseline status when stimulation was off.

Objective: To explore potential differences in physical activity and sedentary behavior volumes and patterns among postmenopausal women with and without premenopausal bilateral oophorectomy (PBO). Methods: Women with a history of PBO (n = 50) and age-matched postmenopausal referent women (n = 50) were recruited. Participants wore accelerometers on both ankles for 7 days. Volume metrics of sedentary behavior and physical activity, such as step counts, active time, and sedentary time, as well as the sedentary behavior and habitual physical activity distribution, and accumulation patterns, were quantified from the accelerometer data and compared between groups. Results: Metrics indicating volume of sedentary behavior and physical activity were not statistically different between groups. PBO was significantly associated with higher variability in stepping bout time ( P = 0.022), indicating a potentially more complex walking pattern. In addition, PBO was significantly associated with lower variability in sedentary break time ( P = 0.012), and lower activity time Gini index ( Z = −2.428, P = 0.015). This suggests that women with PBO may have broken up their sedentary time with shorter and less variable activity bouts, and because they had relatively shorter average daily active time, they might be at a higher risk of subsequent adverse health outcomes such as low bone mineral density. Conclusions: Although there were no differences in overall activity volume, some differences in activity patterns emerged between women with PBO and referent women. The study highlights the need for longitudinal research to understand how physical activity and sedentary behavior patterns evolve in postmenopausal women with a history of PBO.

Background Falls in people with multiple sclerosis (pwMS) lead to morbidity and expense. Objective Identify clinical metrics associated with falls. Methods Eighty-six pwMS completed fall surveys, timed 25-foot walk (T25FW), and motion analysis with Clario Opal devices. Logistic regression models were created. Results Median age was 54.5 years (range 21–73), 62% (53) were female. The cohort included 58% with relapsing (50) and 42% with progressive MS (36). Those who reported falling in the last year were older (median age 58 vs 52.5, p = .03) and had a higher Patient Determined Disease Step (PDDS) score (median 3 vs 1, p < .0001). Falls were associated with worse balance metrics including sway area (median 2.3 degrees 2 vs 1.2, p = .01), jerk (median 3.3 m 2 /s 5 vs 1.6, p = .005), and slower T25FW (median 11.5 s vs 8; p < .0001). A multivariable regression model based on gait aid use and T25FW time >10.8 s (c = 0.80) was derived. Having both features portended a probability of falling of 0.97, while having neither, a probability of 0.26. Conclusions Falls in pwMS are more frequent in patients who are older, have higher PDDS, slower walking, and worse balance. Gait aid use and T25FW >10.8 s were strongly associated with falls in the past year.

Autophagy impairments have been implicated in various aging conditions. Previous studies in cervical motor neurons show an age-dependent increase in the key autophagy proteins LC3 and p62, reflecting autophagy impairment and autophagosome accumulation. Chloroquine is commonly used to inhibit autophagy by preventing autophagosome–lysosome fusion and may thus emulate the effects of aging on the neuromuscular system. Indeed, acute chloroquine administration in old mice decreases maximal transdiaphragmatic pressure generation, consistent with aging effects. We hypothesized that chloroquine alters diaphragm muscle neuromuscular junction (NMJ) morphology and increases denervation. Adult male and female C57BL/6 × 129J mice between 5 and 8 months of age were used to examine diaphragm muscle NMJ morphology and denervation following daily intraperitoneal injections of chloroquine (10 mg/kg/d) or vehicle for 7 days. The motor end-plates and pre-synaptic terminals were fluorescently labeled with α-bungarotoxin and anti-synaptophysin, respectively. Confocal microscopy was used to assess pre- and post-synaptic morphology and denervation. At diaphragm NMJs, chloroquine treatment decreased pre-synaptic volume by 12% compared to the vehicle (p < 0.05), with no change in post-synaptic volume. Chloroquine treatment increased the proportion of partially denervated NMJs by 2.7-fold compared to vehicle treatment (p < 0.05). The morphological changes observed were similar to those previously reported in the diaphragm muscles of 18-month-old mice. These findings highlight the importance of autophagy in the maintenance of the structural properties at adult NMJs in vivo.

Aging disrupts multiple homeostatic processes, including autophagy, a cellular process for the recycling and degradation of defective cytoplasmic structures. Acute treatment with the autophagy inhibitor chloroquine blunts the maximal forces generated by the diaphragm muscle, but the mechanisms underlying neuromuscular dysfunction in old age remain poorly understood. We hypothesized that chloroquine treatment increases the presynaptic retention of the styryl dye FM 4-64 following high-frequency nerve stimulation, consistent with the accumulation of unprocessed bulk endosomes. Diaphragm-phrenic nerve preparations from 24-month-old male and female C57BL/6 × 129 J mice were incubated with FM 4-64 (5 µM) and either chloroquine (50 µM) or vehicle during 80 Hz phrenic nerve stimulation. Acute chloroquine treatment significantly decreased FM 4-64 intensity at diaphragm neuromuscular junctions following 80 Hz phrenic nerve stimulation, consistent with disrupted synaptic vesicle recycling. A similar reduction was evident in regions with the greatest FM 4-64 fluorescence intensity, which most likely surround synaptic vesicle release sites. In the absence of nerve stimulation, chloroquine treatment significantly increased FM 4-64 intensity at diaphragm neuromuscular junctions. These findings highlight the importance of autophagy in regulating presynaptic vesicle retrieval (including vesicle recycling and endosomal processing) and support the role of autophagy impairments in age-related neuromuscular dysfunction.

Abstract Ageing‐related neuromuscular dysfunction is associated with reduced tropomyosin‐related kinase receptor subtype B (TrkB) signalling and accumulation of damaged cytoplasmic aggregates in motor neurons. Autophagy functions to remove these damaged aggregates, and we previously reported increased cervical motor neuron expression of LC3 and p62 in old age. We hypothesized that inhibition of TrkB kinase activity results in an increase in the relative expression of both LC3 and p62 in cervical motor neurons, consistent with impaired progression of autophagy. TrkB F616A mice, which possess a mutation that renders TrkB kinase activity susceptible to rapid inhibition by 1NMPP1, were treated at 6, 18 or 24 months of age with vehicle or 1NMPP1 for 7 days. Immunofluorescence intensity was measured to determine LC3 and p62 expression in choline acetyltransferase‐positive motor neurons in the cervical spinal cord. The effect of inhibiting TrkB kinase activity on progression of autophagy was age dependent. In 6‐month‐old mice, inhibiting TrkB kinase activity increased cervical motor neuron expression of LC3 by 11% ( P < 0.001) and p62 by 8% ( P = 0.019) compared with vehicle treatment. In 18‐ and 24‐month‐old mice, there was no effect of inhibiting TrkB kinase activity on motor neuron LC3 or p62 expression. We provide evidence that inhibition of TrkB signalling impairs progression of autophagy in motor neurons of young mice, similar to the response to ageing. Accordingly, a reduction of TrkB signalling in old age might contribute to neuromuscular dysfunction by impairing progression of autophagy in motor neurons.

Spinal cord stimulation for motor recovery after spinal cord injury is a popular research intervention, though off-target effects are a concern. Using continual blood pressure and heart rate recordings during passive spinal cord stimulation parameter testing, we identified frequent episodes of autonomic dysreflexia that were rarely associated with symptoms. This presents a previously unrecognized risk of spinal cord stimulation and appropriate vigilance in targeted monitoring is urged to maintain participant safety.

Chloroquine is an antimalarial agent commonly used as an autophagy inhibitor by preventing autolysosomal fusion. Autophagy is an important cellular process through which defective cytoplasmic structures are recycled and degraded that has been implicated in aging neuromuscular effects. We recently showed that acute chloroquine treatment blunts the maximal forces generated by the diaphragm muscle, likely by impairing neuromuscular transmission generally consistent with aging effects in the diaphragm muscle. In addition, old mice show increased accumulation of autophagy proteins in phrenic motor neurons, consistent with impaired autophagy flux. In the present study, we hypothesized that chloroquine treatment results in accumulation of bulk endosomes pre-synaptically. Each hemidiaphragm with attached phrenic nerve was excised from 24-month-old male and female C57BL/6 mice to evaluate frequency dependent (0 vs 80 Hz stimulation) uptake of the styryl dye FM4-64, given that 80-Hz stimulation frequency induces bulk endocytosis after synaptic vesicle retrieval. Diaphragm-phrenic nerve preparations were incubated in 5 μM FM4-64 for 1 h prior to 6-min nerve stimulation (0.5 ms supramaximal pulses in 80 Hz, 200 ms trains delivered at 40% duty cycle) followed by a 5-min post-stimulation incubation. FM4-64 uptake at diaphragm neuromuscular junctions (NMJs) was measured using confocal microscopy. Preparations were randomly assigned to co-incubation with chloroquine (50 μM) or vehicle (Rees-Simpson solution). There was minimal FM4-64 uptake in the absence of phrenic nerve stimulation, consistent with the activity-dependent uptake of the styryl dye. With 80 Hz stimulation, high levels of FM4-64 uptake were evident in both the chloroquine and vehicle-treated groups without significant differences across groups. FM4-64 fluorescence was evident throughout the presynpatic terminal with few areas of dense accumulation, consistent with retention of endosomes. There was no evidence of greater endosome accumulation with chloroquine treatment. Of note, a slight increase in FM4-64 uptake was evident in the chloroquine treated groups compared to vehicle in the non-stimulated NMJs. These results are consistent with FM4-64 uptake reflecting bulk endocytosis that mainly occurs during high frequency stimulation. The impairment in autophagy flux following chloroquine treatment is expected to result in endosome accumulation but it is possible that the stimulation protocol was insuffcient to elucidate this possibility. Collectively, the findings of this study are consistent with impaired autophagy at diaphragm presynaptic terminals which may underlie neuromuscular deficits observed in old age. Supported by NIH grant R01 AG057052 and the Mayo Clinic. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Chloroquine (CQ), an antimalarial agent, inhibits autophagy by preventing the autophagosome from fusing with the lysosome, emulating the effects of aging. Autophagy is a cellular digestion process that contributes to homeostasis through degradation of cytoplasmic structures in the cell. Aging effects include autophagy impairment, leading to the accumulation of altered proteins and organelles, thus contributing to subsequent cell damage and death. Previous studies in phrenic motor neurons show an age-dependent increase in key autophagy proteins LC3 and p62, reflecting autophagy impairment and autophagosome accumulation. In addition, acute chloroquine administration in old mice decreases maximal transdiaphragmatic pressure generation, suggesting a neuromuscular effect in aging. We hypothesized that treatment with the autophagy inhibitor chloroquine alters pre-synaptic morphology and increases the proportion of denervated diaphragm muscle fibers. Adult male and female 6-month C57BL6 mice were used to examine diaphragm muscle neuromuscular junction (NMJ) morphology and denervation. The autophagy inhibitor chloroquine (10 mg/kg/d) or vehicle was administered via daily intraperitoneal injections for 7 days. Confocal microscopy was used to compare pre- and post-synaptic morphology and denervation. There was evidence of a decrease in pre-synaptic volume without evidence of post-synaptic volume changes in chloroquine treated mice compared to vehicle. As expected, vehicle treated mice did not show evidence of substantial denervation. In contrast, chloroquine treated mice showed an increased proportion of denervated NMJs. The morphological changes observed were similar to those previously reported in the diaphragm muscles of 24-month-old mice. These findings reveal the effects at the neuromuscular junction of inhibiting autophagy and implicate impaired autophagy as a mechanism of aging effects. Supported by NIH R01 AG057052 and Mayo Clinic. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.