AGE-DEPENDENT MODULATION OF CIRCADIAN PARAMETERS IN THE FIELD-MOUSE MUS BOODUGA

The locomotor activity of the field mouse Mus booduga was monitored un der continuous darkness (DD) for extended periods of 275 to 388 days. Free-running period (tau) activity time (alpha) and rest time (rho) we re computed from the activity records for all the animals (n = 10). De creases in the circadian period (tau) with age were observed in some o f the animals at an early age (<ca. 100 days) and then tau remained re latively constant for rest of their life span. The activity time (alph a), rest time (rho), and their ratio (alpha/rho), however, did not sho w any consistent trend of increase/decrease. The initial decrease in t au is consistent with previous models suggesting a time-dependent incr ease in the number of cells generating oscillations in the suprachiasm atic nucleus (SCN) and/or increase in the strength of coupling between these cells. In such models, after an optimal number of cells launch themselves into a state of self-sustained oscillation, tau stabilizes, achieving relative constancy, a pattern similar to the one observed i n our study. (C) 1998 Wiley-Liss, Inc.