EFFECTS OF DARK-LIGHT STEP TRANSITIONS ON CIRCADIAN LOCOMOTOR-ACTIVITY RHYTHMS OF THE HAGFISH, EPTATRETUS-BURGERI

Captive hagfish, Eptatretus burgeri, were subjected to step transition s from continuous dark (DD) ts continuous light (LL) and their locomot or activity patterns recorded. Free-running activity rhythms occurred in both the DD and LL regimes. The timing of the transition influenced the circadian period (tau), the relationship between the period respo nse (Delta tau or tau(LL)-tau(DD) change in the circadian period) and the former being represented by a cosine curve, Delta tau became most positive and most negative when hagfish underwent a DD-LL transition s hortly before the beginning of the duration of activity (alpha) and sh ortly after the enc of such, respectively. The phase response (Delta-p hase, change in the relative timing of the activity phase) was charact erized by a delay in the activity phase after the DD-LL transition, al though its magnitude bore no relation to the timing of the transition.