title: Ramelteon (TAK-375) accelerates reentrainment of circadian rhythm after a phase advance of the light-dark cycle in rats.
abstract: In vivo pharmacological effects of ramelteon (TAK-375), a novel, highly MT1/MT2-selective receptor agonist, were studied in rats to determine ramelteon's ability to reentrain the circadian rhythm after an abrupt phase advance. Experiments were also conducted to assess the potential cognitive side effects of ramelteon and its potential to become a drug of abuse. After an abrupt 8-h phase shift, ramelteon (0.1 and 1 mg/kg, p.o.) and melatonin (10 mg/kg, p.o.) accelerated reentrainment of running wheel activity rhythm to the new lightdark cycle. Ramelteon (3-30 mg/kg, p.o.) and melatonin (10-100 mg/kg, p.o.) did not affect learning or memory in rats tested by the water maze task and the delayed match to position task, although diazepam and triazolam impaired both of the tasks. Neither ramelteon (3-30 mg/kg, p.o.) nor melatonin (10-100 mg/kg, p.o.) demonstrated a rewarding property in the conditioned place-preference test, implying that MT1/MT2 receptor agonists have no abuse potential. In contrast, benzodiazepines and morphine showed rewarding properties in this test. The authors' results suggest that ramelteon may be useful for treatment of circadian rhythm sleep disorders without adverse effects typically associated with benzodiazepine use, such as learning and memory impairment, and drug dependence.
authors.affiliation: Pharmacology Research Laboratories I, Pharmaceutical Research Division, Takeda Pharmaceutical Company Ltd., Osaka, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Hirai
authors.forename: Muneto
authors.initials: M
authors.lastname: Kita
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
authors.forename: Hisao
authors.initials: H
authors.lastname: Nishikawa
authors.forename: Yuu
authors.initials: Y
authors.lastname: Fujiwara
authors.forename: Shigenori
authors.initials: S
authors.lastname: Ohkawa
authors.forename: Masaomi
authors.initials: M
authors.lastname: Miyamoto
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects*; D003624:Darkness; D007192:Indenes / Q000494:pharmacology*; D008027:Light; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D017208:Rats, Wistar
chemical_list: D007192:Indenes; C495910:ramelteon