Interleukin-1b (IL-1b) is posited to play an important physiological role in brain functions in addition to
its better defined role in pathology. The experiments described herein were performed to determine if IL-
1b mRNA and b-actin display diurnal rhythms in various areas of brain. Rats were sacrificed at 4-h
intervals across a 12:12 h light/dark cycle. Hypothalamic, hippocampal, and cortical IL-1b mRNA
peaked just after lights were turned on, declined slightly during the remaining light period and stayed
low in the dark. There were no significant changes in IL-1b mRNA in brain stem or cerebellum samples.
b-actin mRNA levels were relatively constant across the day in the hypothalamus, brain stem and
cerebellum. However, b-actin mRNA levels were lower during the day than during the night in the
hippocampus and cortex.