Circadian rhythms in firing rate of individual suprachiasmatic nucleus neurons from adult and middle-aged mice

The suprachiasmatic nucleus contains a biological clock that drives circadi an rhythms in vivo and in vitro. It has been suggested that the suprachiasm atic nucleus is a primary target of the aging process, because age-related changes in behavioral rhythms are mirrored in alterations in circadian pace maker function. Using long-term, single-cell recording, we assessed the eff ect of age on firing-rate patterns of individual suprachiasmatic nucleus ne urons of young adult (2-4 months) and middle-aged (9-11 months) C3H mice. I ndividual suprachiasmatic nucleus neurons from adult mice maintained in cul ture for at least one week exhibited robust circadian rhythms in spontaneou s activity that were similar in the free-running period (23.7 +/- 0.3 h mea n +/- S.E.M.) to recordings from neurons dispersed from neonatal tissue, an d showed evidence of entrainment to prior light cycles by exhibiting peak a ctivity, in vitro, approximately 4.0 +/- 0.3 h (mean S.E.M.) after the time of expected light onset. Aging led to a decreased amplitude of impulse act ivity in dispersed suprachiasmatic nucleus neurons and increased variabilit y in the circadian waveform. From these results we suggest that age-related deterioration in circadian c lock function occurs at the level of individual cells, which may account fo r some of the a.-e-related deficits observed in the expression of behaviora l rhythmicity. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.