AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 3 326-R332, Copyright © 1982 by American Physiological Society
Entrainment of the circadian rhythm from the eye of Aplysia: role of serotonin
G. Corrent, A. Eskin and I. Kay
The finding that serotonin (5-HT) treatments as short as 1.5 h in duration
produce phase shifts in a circadian rhythm from the isolated eye of Aplysia
suggested that release of 5-HT was part of an ocular entrainment pathway.
Since light cycles entrain this rhythm, we compared phase shifting by 5-HT
and by light. The similarity in the shapes of the phase-response curves for
5-HT and light pulses indicates that 5-HT treatments are capable of
entraining the rhythm. Also, "skeleton" 5-HT treatments phase shift as well
as continuous 5-HT treatments. However, 5-HT does not appear to mediate the
phase shifts produced by light, since 1) treatments that should block
transmitter release do not change the phase shifts produced by light
pulses; 2) the response curves of 5-HT and light pulses are displaced by 12
h relative to one another on the phase axis of the response curve; and 3)
light-induced phase shifts are apparent almost immediately, whereas
5-HT-induced phase shifts become evident only about 24 h after 5-HT
treatment. The eye appears to contain two independent entrainment pathways,
one for light and one utilizing 5-HT.
