title: Caloric restriction does not offset age-associated changes in the biophysical properties of motoneurons.
abstract: Age-associated changes in neuromuscular function may be due to a loss of motor neurons as well as changes in their biophysical properties. Neuronal damage imposed by reactive oxygen species may contribute to age-related deficits in CNS function. Thus we hypothesized that aging would alter the functional properties of motoneurons and that caloric-restriction would offset these changes. Intracellular recordings were made from lumbar motoneurons of old Fisher Brown Norway (FBN) fed ad libitum (oldAL, 30.8+/-1.3 mo) or on a fortified calorie-restricted diet from 14 wk of age (oldCR, 31.0+/-1.8 mo). Basic and rhythmic firing properties recorded from these aged motoneurons (MNs) were compared with properties recorded from young FBN controls (young, 8.4+/-4.6 mo). Compared with young MNs, old MNs had a 104% greater (P<0.001) afterhyperpolarization potential (AHP), a 21.1% longer AHP half-decay time (P<0.05), 28.7% lower rheobase (P<0.001), 49.7% greater (P<0.001) input resistance, 21.1% (P<0.0001) less spike frequency adaptation, lower minimal (30.2%, P<0.0001) and maximal (16.7%, P<0.0001) steady-state firing frequencies, a lower (35.5%, P<0.0001) frequency-current slope, and an increased incidence of persistent inward current. Because basic properties became more diverse in old MNs and the slope of the frequency-current relationship, which is normally similar for high- and low-threshold MNs, was lower in the old group, we conclude that aging alters the biophysical properties of MNs in a fashion that cannot be simply attributed to a loss of high-threshold MNs. Surprisingly, caloric restriction, which is known to attenuate aging-associated changes in hindlimb muscles, had no effect on the progress of aging in the innervating MNs.
authors.affiliation: Spinal Cord Research Center, Department of Physiology, University of Manitoba, 730 William Ave., 436 BMSB, Winnipeg, Manitoba R3E 3J7, Canada.
authors.forename: Jayne M
authors.initials: JM
authors.lastname: Kalmar
authors.forename: Duane C
authors.initials: DC
authors.lastname: Button
authors.forename: Kalan
authors.initials: K
authors.lastname: Gardiner
authors.forename: Farrell
authors.initials: F
authors.lastname: Cahill
authors.forename: Phillip F
authors.initials: PF
authors.lastname: Gardiner
mesh_terms: D000375:Aging / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D055592:Biophysical Phenomena / Q000502:physiology*; D031204:Caloric Restriction / Q000379:methods*; D016009:Chi-Square Distribution; D004553:Electric Conductivity; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D008564:Membrane Potentials / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000166:cytology