Abstract
This study was designed to evaluate the effect of aging on the activity of metabosensitive afferent fibers (thin muscle afferents from group III and IV) and to determine if physical activity performed at old age may influence the afferent discharge. Afferents from tibialis anterior and soleus muscles were recorded on non-exercised rats aged of 3, 6, 12, and 20 months and on animals aged of 12 and 20 months performing a daily incremental treadmill exercise protocol during the last 8 weeks preceding the recordings. Metabosensitive afferent fibers were activated with potassium chloride (KCl) and lactic acid (LA) injections into the blood stream or by muscle electrically-induced fatigue (EIF). Results indicated that aging is associated to a decrease in the magnitude of the responses to chemical injections and EIF. Unfortunately, physical activity did not allow restoring the metabosensitive afferents responses. These results indicate an alteration of the thin afferent fibers with aging and should be taken into account regarding the management of muscle fatigue and potential alterations of exercise pressor reflex (EPR) occurring with aging.
Highlights
Muscle contractions enhance neuronal adjustments regulated by activation of afferents originating from activated muscles
In accordance with previous ones performed in the tibialis anterior and soleus muscles of SpragueDawley rats, we observed that the activation of muscle afferents by lactic acid (LA) culminated for the 1 mM concentration and declined whereas there was a relationship between the doses of KCl and the change in afferent discharge rate (Decherchi et al, 1998; Martin et al, 2009; Caron et al, 2014, 2015)
The pattern of responses of metabosensitive muscle afferents activated by increased interstitial concentrations of LA or KCl consisted of a burst of activity beginning within 5–10 s after the bolus injection
Summary
Muscle contractions enhance neuronal adjustments regulated by activation of afferents originating from activated muscles. Among muscle afferents, metabosensitive fibers from groups III and IV are activated by metabolic, mechanical and thermal modification of their receptive fields occurring during and after repetitive contractions (Laurin et al, 2015) Metabolic agents such as lactic acid (LA) and potassium chloride (KCl), and electrically induced exercise (EIF) are known to be specific activators of these thin metabosensitive afferents fibers (Rotto and Kaufman, 1988; Victor et al, 1988; Decherchi et al, 1998, 2001). When stimulated, these afferents change the motoneurons excitability in the spinal cord (Dousset et al, 2004; Laurin et al, 2010). These afferents are responsible for the sensation of muscle pain (Mense, 2009) and project to brainstem level to induce an exercise pressor reflex (EPR), a neural drive originating from skeletal muscles that result in an increase in the sympathetic activity associated with an up-regulation of both heart and ventilation rate, and arterial blood pressure (McCloskey and Mitchell, 1972).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
