N. Murakami et al., DAILY INJECTIONS OF MELATONIN ENTRAIN THE CIRCADIAN ACTIVITY RHYTHMS OF NOCTURNAL RATS BUT NOT DIURNAL CHIPMUNKS, Brain research, 775(1-2), 1997, pp. 240-243
It is well known that daily injections of melatonin entrain the free-r
unning rhythms of nocturnal rodents (rats and hamster) and diurnal sau
ropside (birds and lizard). Here, we asked whether daily injections of
melatonin entrain the free-running rhythm of the chipmunk, a diurnal
rodent, and, if they do, is the phase relationship between the time of
injection and onset of the activity interval similar to that in sauro
pside rather than that of nocturnal rodents? Contrary to our expectati
ons, daily injections of melatonin did not entrain the free-running rh
ythm in 9 of 10 chipmunks, even when a high dose of melatonin (1 mg/kg
, b.wt.) was used. These results indicate that the entraining effect o
f daily injections of melatonin on free-running rhythm varies among ma
mmalian species. (C) 1997 Elsevier Science B.V.