Naloxone increases the frequency of the electrical activity of luteinizing hormone-releasing hormone pulse generator in long-term ovariectomized rats.
Characteristic increases in neuronal activity accompanied by the initiation of each luteinizing hormone (LH) pulse have been successfully recorded in freely moving ovariectomized rats by means of multiunit activity (MUA) recording techniques. In the present study, the effect of the opioid receptor antagonist naloxone on this neuronal activity was examined in rats ovariectomized for 6-10 weeks. Electrodes were chronically implanted into the medial basal hypothalamus (n = 78) or the medial preoptic area (n = 29). During the MUA recording, blood samples were taken through an indwelling atrial cannula at 3- or 6-min intervals to determine the serum LH concentration. Naloxone was administered intravenously for 1 h by either intermittent injection every 6 min (0.05 mg/kg, 10 times) or continuous infusion (0.1, 0.2 and 0.5 mg/kg/h). Explosive rises in the MUA (volleys) associated with the initiation of LH pulse were recorded in 7 animals in which the tips of electrodes were located in the arcuate nucleus-median eminence region. In 5 animals studied, the mean (+/- SE) duration and interval of the MUA volleys were 2.1 +/- 0.1 and 22.1 +/- 0.9 min, respectively. Naloxone given every 6 min significantly increased the duration to 2.6 +/- 0.1 min, and decreased the interval to 9.5 +/- 0.9 min. This naloxone treatment disturbed the clear pulsatility of LH secretion observed in the pretreatment control period. Analysis of the effects of naloxone infused at 3 different doses revealed that the facilitatory effects of naloxone on the duration and frequency of the MUA volleys were dose-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)
Kimura
F
F
Department of Physiology, Yokohama City University School of Medicine, Japan.
Nishihara
M
M
Hiruma
H
H
Funabashi
T
T
D000818:Animals; D004594:Electrophysiology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology*; D007986:Luteinizing Hormone / Q000378:metabolism; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D010052:Ovariectomy; D010507:Periodicity; D051381:Rats; D011919:Rats, Inbred Strains
D007987:Gonadotropin-Releasing Hormone; D009270:Naloxone; D007986:Luteinizing Hormone