Intracerebroventricular injection of naloxone blocks melatonin-dependent brain [3H]flunitrazepam binding.
The pineal hormone melatonin modulates the brain benzodiazepine binding sites and its circadian rhythm. In the present study the effects of intracerebroventricular (i.c.v.) administration of naloxone (10-20 ng), alone or in association with melatonin and/or beta-endorphin, on [3H]flunitrazepam ([3H]FNZ) binding to the rat cerebral cortex of hypophysectomized rats was investigated. Melatonin (10-20 ng), beta-endorphin (10-20 ng), and melatonin + beta-endorphin (10-20 ng of each compound) all increased [3H]FNZ binding to a similar extent and in a dose-related manner. The effects of melatonin (10 ng) on [3H]FNZ binding were prevented by simultaneous injection with the specific opioid antagonist naloxone. Naloxone also blocks, although to a lesser extent, the effects of beta-endorphin and of melatonin + beta-endorphin injections. Moreover, naloxone blocks the hypophysectomy-dependent increase in [3H]FNZ binding. These results implicate the modulation of melatonin-dependent changes on brain benzodiazepine receptors by opioid peptides.
Gomar
M D
MD
Departamento de Fisiología, Facultad de Medicina, Universidad de Granada, Spain.
Castillo
J L
JL
del Aguila
C M
CM
Fernández
B
B
Acuña-Castroviejo
D
D
D000305:Adrenal Cortex Hormones / Q000502:physiology; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005445:Flunitrazepam / Q000493:pharmacokinetics*; D007016:Hypophysectomy; D066298:In Vitro Techniques; D007276:Injections, Intraventricular; D008297:Male; D008550:Melatonin / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*; D001615:beta-Endorphin / Q000494:pharmacology
D000305:Adrenal Cortex Hormones; D011963:Receptors, GABA-A; D009270:Naloxone; D001615:beta-Endorphin; D005445:Flunitrazepam; D008550:Melatonin