Electrophysiological actions of oxytocin in the dorsal vagal complex of the female rat in vitro: changing responsiveness during the oestrous cycle and after steroid treatment.
The effect of the oxytocin-specific agonist Thr4,Gly7-oxytocin (TGOT) was tested on neurones in tissue slices of the dorsal vagal complex, obtained from virgin female rats at different stages of the oestrous cycle. The proportion of neurones excited by TGOT (0.1 microM) was independent of the day of the cycle, but both the basal activity and magnitude of response induced by TGOT were significantly reduced on the day of oestrus by comparison with dioestrus. This was due to a small but significant shift in the dose-response relationship. The magnitude of the excitation of neurones obtained from animals at proestrus did not differ significantly from either oestrus or dioestrus, but lay between the two. Ovariectomy 6 days prior to recording reduced the proportion of responsive neurones (35% vs. 69% at dioestrus), but had only a small effect on the amplitude of the averaged responses. Daily injection of 10 micrograms oestradiol benzoate had no additional effect on the proportion of responsive neurones (40%), but caused a marked suppression of the amplitude of the response at all doses (change in firing rate caused by 0.1 microM: 1.68 +/- 0.27 Hz vs. 2.69 +/- 0.39 Hz). In contrast, injections of 5 mg progesterone caused a small increase in the amplitude of the response. The data show that ovarian steroids have a marked effect on oxytocin-sensitive neurones of the dorsal vagal complex, causing dynamic changes in responsiveness over the oestrous cycle. This is discussed with respect to the effects of ovarian steroids on central oxytocin receptors and the possible involvement in regulating autonomic functions.
Department of Anatomy, School of Medical Sciences, University of Bristol, UK.
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Tolchard
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Ingram
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D004971:Estrus / Q000502:physiology*; D005260:Female; D010052:Ovariectomy; D010121:Oxytocin / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013256:Steroids / Q000494:pharmacology*; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology*
D013256:Steroids; D010121:Oxytocin