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This Article Full Text Full Text (PDF) All Versions of this Article: 101/2/548    most recent 90617.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kalmar, J. M. Articles by Gardiner, P. F. Search for Related Content PubMed PubMed Citation Articles by Kalmar, J. M. Articles by Gardiner, P. F.

Caloric Restriction Does Not Offset Age-Associated Changes in the Biophysical Properties of Motoneurons

Spinal Cord Research Center, Department of Physiology, University of Manitoba, Winnipeg, Manitoba, Canada

Submitted 28 May 2008; accepted in final form 4 September 2008

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.