title: Effects of aging on evoked retrusive tongue actions.
abstract: OBJECTIVE
  Tongue strength, timing, and coordination deficits may underlie age-related swallowing function. Retrusive tongue actions are likely important in retrograde bolus transport. However, age-related changes in retrusive tongue muscle contractile properties have not been identified in animal studies. Because previous studies employed whole hypoglossal nerve stimulation that activated both protrusive and retrusive tongue muscles, co-contraction may have masked retrusive muscle force decrements. The hypotheses of this study were: (1) retrusive tongue muscle contraction forces would be diminished and temporal characteristics prolonged in old rats when lateral nerves were selectively activated, and (2) greater muscle contractile forces with selective lateral branch stimulation would be found relative to whole hypoglossal nerve stimulation.
  
  
  METHODS
  Nineteen Fischer 344/Brown Norway rats (9 old, 10 young adult) underwent tongue muscle contractile property recording elicited by: (1) bilateral whole hypoglossal nerve stimulation, and (2) selective lateral branch stimulation. Twitch contraction time (CT), half-decay time, maximal twitch and tetanic forces, and a fatigue index were measured.
  
  
  RESULTS
  For whole nerve stimulation, CT was significantly longer in the old group. No significant age group differences were found with selective lateral nerve stimulation. Significantly reduced twitch forces (old group only), increased tetanic forces and significantly less fatigue were found with selective lateral nerve stimulation than with whole hypoglossal stimulation.
  
  
  CONCLUSIONS
  Retrusive tongue forces are not impaired in old rats. Deficits observed in swallowing with aging may be due to other factors such as inadequate bolus propulsive forces, mediated by protrusive tongue muscles, or timing/coordination of muscle actions.
authors.affiliation: Department of Surgery, Division of Otolaryngology-Head and Neck Surgery, University of Wisconsin, Madison, WI, United States.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Becker
authors.affiliation: Department of Surgery, Division of Otolaryngology-Head and Neck Surgery, University of Wisconsin, Madison, WI, United States.
authors.forename: John A
authors.initials: JA
authors.lastname: Russell
authors.affiliation: Department of Surgery, Division of Otolaryngology-Head and Neck Surgery, University of Wisconsin, Madison, WI, United States; Department of Communication Sciences and Disorders, University of Wisconsin, Madison, WI, United States. Electronic address: connor@surgery.wisc.edu.
authors.forename: Nadine P
authors.initials: NP
authors.lastname: Connor
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D004558:Electric Stimulation; D007002:Hypoglossal Nerve / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D051381:Rats; D011916:Rats, Inbred F344; D014059:Tongue / Q000502:physiology*
keywords: Aging; Deglutition; Deglutition disorders; Hypoglossal nerve; Tongue
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