Aging alters properties of the circadian pacemaker controlling the locomotor activity rhythm in males of Drosophila nasuta

Effects of aging on the circadian rhythm of locomotor activity in males of Drosophila nasuta were investigated. The adult life of males was divided in 1-3 stages according to spontaneous changes in free-running period tau in constant-darkness (DD): stage 1, days 1-19; stage 2, days 20-36; stage 3, d ays 37-43. Stage 1 was characterized by a bimodal activity-pattern with a s hort light-induced morning peak and a prolonged evening peak when: the flie s were entrained to light-dark cycles of 12 hours of light, 12 hours of dar kness (LD 12:12). The morning peak had a phase angle difference Psi(m) (Psi , the time:from lights on in LD 12:12 cycles to the onset of morning peak) of about 0.1h, while Psi(e) (Psi of evening peak) was about 9h at stage 1. The transient morning peak was curtailed at the end of stage 1. At stage 2, the Psi(e) was about 10h, and the activity end was delayed by an addition of about 3h of activity in:the scotophase. The changes in tau during DD fre e runs Were determined in two groups of flies: flies reared in LD 12:12 and flies I eared in DD. In:both groups, tau increased from about 23h at stage 1 to about 25h at stage 2:Stage 3 was characterized by arrhythmicity assoc iated with highest mean activity level (total number of passes/fly/day) in the entrained and both free-running groups. The mean activity level increas ed significantly:from stage 1 to stage 3 in all three groups of flies.