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Query: UNIPROT:P01178 (oxytocin)
 15,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The posterior pituitary hormone, oxytocin (OT), has been shown to have either a stimulatory or an inhibitory effect on PRL secretion depending on the route of administration. Whether its central inhibitory effect involves the tuberoinfundibular dopaminergic (TIDA) neuron was the focus of this study. Adult female Sprague-Dawley rats ovariectomized for 1 week, implanted with sc estrogen-containing capsules and intracerebroventricular cannulas for 6 more days were used. TIDA neuron activity was determined by measuring the concentration of 3,4-dihydroxyphenylacetic acid or 3,4-dihydroxyphenylalanine in the median eminence by HPLC with electrochemical detection. Intracerebroventricular injection of OT induced both dose (0.01-1 microgram/rat)- and time (30-90 min)-dependent increases in 3,4-dihydroxyphenylalanine or 3,4-dihydroxyphenylacetic acid levels in the median eminence. Serum PRL levels were also decreased 30 min after the injection. The use of a specific OT antagonist, [d(CH2)5, Tyr(Me)2, Orn8]vasotocin, not only blocked the effect of OT on TIDA neuron activity, it further lowered it to below control levels, indicating the existence of an endogenous OT activity. When 1 microgram OT was administered at 1200 h, it also reversed the diurnal decrease in TIDA neuron activity at 1500 h. The effects of OT on the electrical activities of dorsomedial arcuate neurons were also tested using single unit recording in brain slices. In 33 neurons tested with OT, 66.7% were stimulated by OT in 0.5- to 50-nmol doses, and no inhibitory effect was observed. The rest were not responsive. In conclusion, both neurochemical and electrophysiological studies demonstrated that central OT may play a stimulatory role in regulating the TIDA neurons and, in turn, inhibition of PRL secretion.
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PMID:Stimulatory effect of central oxytocin on tuberoinfundibular dopaminergic neuron activity and inhibition on prolactin secretion: neurochemical and electrophysiological studies. 882 66

Hatano high-avoidance (HAA) and low-avoidance (LAA) animals were originally selected from Sprague-Dawley rats for good and poor active avoidance learning in a shuttle box. We studied the endocrinological profile in lactating rats to determine the effect of suckling during mid-lactation in HAA and LAA rats. The pups were separated from their mother rats 6 h before the onset of suckling and blood samples were drawn from unanaesthetized mother rats via a jugular cannula at 0, 5 and 15 min after the suckling stimulus and then 15, 45 and 105 min after pups were removed. Plasma concentrations of oxytocin in HAA rats were significantly higher than in LAA rats during the suckling period. Plasma concentrations of prolactin and ACTH in HAA rats were significantly higher than in LAA rats during the suckling period, and at 15 min and 45 min after the pups were removed. However, there were no strain differences in circulating corticosterone between the two lines, indicating that the response of the hypothalamo-pituitary axis to the suckling stimulus was greater in HAA rats than in LAA rats, whereas the ACTH-induced adrenal response of corticosterone release was higher in LAA rats than in HAA rats. Since dopamine from the median eminence inhibits prolactin secretion from the lactotrophs of the anterior pituitary, and tuberoinfundibular dopaminergic neurones are partially regulated by the level of circulating prolactin, we evaluated the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine biosynthesis. TH, measured by the accumulation of 3,4-dihydroxyphenylalanine, was significantly higher in HAA rats than in LAA rats before the suckling stimulus. After the suckling stimulus, TH activity in HAA rats was significantly lower than before suckling, whereas TH activity in LAA rats was not changed. These findings clearly demonstrated that apparent differences between the two Hatano lines exist in endocrinological profiles during suckling. These strain differences probably originate from neurotransmitter changes, such as dopamine.
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PMID:Endocrinological responses during suckling in Hatano high- and low-avoidance rats. 1528 87