Startle response circadian rhythm in rats: Lack of correlation with motor activity

Abstract

Acoustic startle response magnitude in rats exhibits an age related circadian rhythm beginning at sexual maturity rising to a peak between 70 and 100 days followed by a fall. At 90 days the night startle response magnitude is over 90 per cent greater than during the day. Night startle response latency is also significantly shorter at this age. Startle response magnitude did not correlate with motor activity when immature and mature animals were compared during day and night conditions. A dose of amylobarbitone sodium causing 50 per cent reduction in motor activity at night did not affect startle response magnitude, and this was also observed following a dose of dexamphetamine causing a 36 per cent increase in motor activity during the day.