Abstract
Obesity is associated with balance and motor control deficits. We have recently shown that Group Ia muscle spindle afferents, the sensory arm of the muscle stretch reflex, are less responsive in mice fed a high‐fat diet. Here we test the hypothesis that reflex excitability to sensory information from Group Ia muscle spindle afferents is altered in a mouse model of diet‐induced obesity. We measured the anesthetized Hoffmann’s or H‐reflex, the electrical analog of the muscle stretch reflex. Adult mice of both sexes were fed a control diet (CD; 10% kcal from fat) or a high‐fat diet (HFD; 60% kcal from fat) for 5, 10, or 15 weeks. We used three quantitative measures of H‐reflex excitability: (1) H‐reflex latency; (2) the percentage of motor neurons recruited from electrical stimulation of Group Ia muscle spindle afferents (Hmax/Mmax); and (3) rate‐dependent depression (RDD), the decrease in H‐reflex amplitude to high frequency stimulation (20 stimuli at 5 Hz). A HFD did not significantly alter H latency (P = 0.16) or Hmax/Mmax ratios (P = 0.06), but RDD was significantly lower in HFD compared to CD groups (P < 0.001). Interestingly, HFD males exhibited decreased RDD compared to controls only after 5 and 10 weeks of feeding, but females showed progressive decreases in RDD that were only significant at 10 and 15 weeks on the HFD. These results suggest that high‐fat feeding increases H‐reflex excitability. Future studies are needed to determine whether these changes alter muscle stretch reflex strength and/or balance and to determine the underlying mechanism(s).
Highlights
Obesity is a metabolic disorder characterized by excess adiposity and chronic low-grade systemic inflammation that often occurs with cardiovascular disease, arthritis, and type 2 diabetes (Kopelman 2007)
Half of the cages were randomly switched to a high-fat diet (HFD; 60% kcal from fat; D12492; Research Diets) while the other half remained on the control diet (CD) for 5, 10, or 15 weeks
Leptin levels were significantly greater in HFD groups than CD groups at all time points except for in 5 week females and 15 weeks males (Welch’s t-test, M 5 weeks P < 0.001, F 5 weeks P = 0.56, M 10 weeks P = 0.01, F 10 weeks P = 0.006, M 15 weeks P = 0.07, F 15 weeks P = 0.001; Fig. 2A)
Summary
Obesity is a metabolic disorder characterized by excess adiposity and chronic low-grade systemic inflammation that often occurs with cardiovascular disease, arthritis, and type 2 diabetes (Kopelman 2007). Individuals with obesity exhibit balance deficits due to increased sway during standing (Greve et al 2007) and altered gait (Lai et al 2008; Ko et al 2010), both of which are risk factors for falling (Ganz et al 2007). The increased sway during standing seen in people with obesity is at least partially due to increased body weight (McGraw et al 2000; Hue et al 2007; Teasdale et al 2007) and a shifted center of mass (Corbeil et al (2001)). Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society
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