Injection of bicuculline elicits firing of luteinizing hormone releasing hormone pulse generator in muscimol-treated ovariectomized rats.
We have already demonstrated that, although exogenous gamma-aminobutyric acidA (GABAA) receptor agonist is capable of inhibiting the activity of luteinizing hormone releasing hormone (LHRH) pulse generator, the reduction in the endogenous GABAA receptor activity does not have a significant effect in ovariectomized rats, suggesting a minor role of inhibitory GABA neurons in the control of pulsatile release of LHRH. In this study, we further analyzed the role of the GABAA receptor system in the regulation of LHRH pulse generator activity observed by recording the multiunit activity (MUA) in the hypothalamus of ovariectomized rats. An abrupt increase (volley) in the MUA in the arcuate nucleus (ARC)-median eminence region (ME) was accompanied by the initiation of a luteinizing hormone (LH) pulse, determined by measuring LH concentrations in blood sampled simultaneously. The injection of 1-3 mg/kg muscimol (MUS), a GABAA receptor agonist, decreased the basal MUA and delayed the occurrence of the next MUA volley, but it did not change the LH pulse amplitude. I.v. injection of 5 mg/kg bicuculline (BIC), a GABAA receptor antagonist, during continuous infusion of MUS (5 mg/kg/h) which decreased the basal MUA and prevented the MUA volley from occurring, evoked MUA volleys and LH pulses whose amplitudes were similar to those found before the MUS infusion. Injection of the same dose of BIC during the infusion of saline increased the MUA transiently, but this increase was not accompanied by an LH pulse and afterwards there occurred MUA volleys at ordinary intervals accompanied by LH pulses with unchanged pulse amplitudes.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Physiology, Yokohama City University School of Medicine, Japan.
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Hiruma
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Sano
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Kimura
D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000502:physiology; D001640:Bicuculline / Q000494:pharmacology*; D004558:Electric Stimulation; D004594:Electrophysiology / Q000379:methods; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D008473:Median Eminence / Q000502:physiology; D009118:Muscimol / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010052:Ovariectomy; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D009118:Muscimol; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D001640:Bicuculline