Dr. Widman et W. Timberlake, 2 POSSIBLE DETERMINANTS OF THE TIMING OF DAILY EPISODES OF BEHAVIOR IN RATS, Physiology & behavior, 58(6), 1995, pp. 1227-1236
The present experiment examined endogenous ultradian rhythms and regul
atory metabolic processes as two potential determinants of daily out-o
f-nest episodes (ONEs) and feeding episodes (FEs) in rats living in a
24-h environment. Two types of photoperiod were used: a Standard 12:12
h L/D schedule and a Skeleton 12:12 h schedule. During each type of p
hotoperiod rats were exposed to 4 feeding conditions of 7 to 12 days e
ach: (a) a baseline of ad lib food and water; (b) food restricted to t
he diurnal (inactive) portion of the cycle; (c) both food and water re
stricted to the inactive period; and (d) return to baseline. Time seri
es analyses of nocturnal ONEs in baseline revealed a strong circadian
rhythm and weaker ultradian rhythms with periods between 2 and 6 h. An
alyses of FEs, though, revealed a general absence of circadian rhythms
but strong ultradian rhythms with periods similar to those observed i
n ONEs. When food and water were restricted to the inactive part of th
e cycle, ONEs showed no change in frequency, but a decrease in average
duration and changes in ultradian periodicities. The results indicate
d control of daily episodes of behavior in rats by ultradian oscillato
rs that are weaker and more variable in effect than those found in vol
es, but similar in period.