AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 6 857-R864, Copyright © 1983 by American Physiological Society
Circadian pacemakers in lizards: phase-response curves and effects of pinealectomy
H. Underwood
Phase-response curves (PRCs) for 6-h fluorescent light pulses are described
for both intact (sham-pinealectomized) and pinealectomized iguanid lizards
(Sceloporus occidentalis). Although strongly diurnal in habit the PRC for
intact lizards is more typical of those seen in nocturnal rodents. Other
"nocturnal" characteristics of this lizard include the fact that the
average free-running period (tau) is less than 24 h and the average tau in
continuous light is longer than that observed in continuous darkness. The
PRC for pinealectomized lizards is greatly distorted relative to that
obtained from intact lizards. This "distortion" is discussed in terms of
the role of the pineal as a coupling device or as a pacemaker within a
multioscillator circadian system. In some individuals pinealectomy was also
associated with 1) increased instability in free-running activity rhythms
or arrhythmicity and 2) nocturnal entrainment to LD 12:12.
