Effects of melatonin injection on running-wheel activity and body temperature differ by the time of day.
Melatonin, which is released from the pineal gland, influences many physiological events concerned with circadian rhythm. Body temperature levels and rhythmicity are tightly coupled with locomotor activity. To understand the functions of melatonin, we determined the effects of melatonin injection on locomotor activity measured by running-wheel activity and body temperature in rats. The rats were kept under a 12-h light and 12-h dark lighting condition, with the light on at zeitgeber time 0 (ZT 0, correspond to 7:00 JST). Melatonin injection, between ZT 3 and ZT 5 (light period) and between ZT 15 and ZT 17 (dark period), attenuated the wheel-running activity in a dose-dependent manner (10 microg to 1 mg/100 g body weight [bw]). A significant attenuation of activity by melatonin was recognized when injected at ZT 8, ZT 14 and ZT 20. After the injection of melatonin, the animal's body temperature was elevated at ZT 2 and ZT 8 (during light), while it fell at ZT 14 and ZT 20 (during darkness). We propose a plausible explanation underlying the observed changes in body temperature during the light and dark periods accompanying the suppression of activity induced by melatonin.
Isobe
Yoshiaki
Y
Department of Physiology, Nagoya City University, Mizuho-ku, Nagoya, 467-8601, Japan. yisobe@med.nagoya-cu.ac.jp
Torri
Takako
T
Konishi
Eiichi
E
Fujioi
Junko
J
D000818:Animals; D001831:Body Temperature / Q000187:drug effects* / Q000502:physiology; D002940:Circadian Rhythm / Q000187:drug effects* / Q000502:physiology; D005080:Exercise Test / Q000187:drug effects*; D007274:Injections, Intraperitoneal; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
D008550:Melatonin