Distribution of monoamines within the median eminence in rats.
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The concentration of dopamine, norepinephrine, epinephrine and serotonin was determined in 6 rostrocaudal segments of the median eminence, 2 segments in the pituitary stalk, in the retrochiasmatic area and the pituitary lobes by radioenzymatic microassay in adult rats. The level of dopamine and norepinephrine was measured separately in the medial and lateral portions of the median eminence. All four amines measured were found unevenly distributed inside the median eminence: 1. the highest dopamine level was detected in the middle-caudal portions of the median eminence and in the rostral parts of the pituitary stalk; 2. high norepinephrine concentration was found in the retrochiasmatic area and this gradually diminished caudalwards; 3. relatively high epinephrine level was present in the rostral median eminence and retrochiasmatic area, but that in the caudal median eminence and pituitary stalk was low; 4. the level of serotonin increased caudalwards and showed a highest value in the caudal portion of the pituitary stalk. Relatively high dopamine and serotonin levels were also detectable in all three pituitary lobes where the concentration of norepinephrine was low and that of epinephrine was undetectable.Keywords:
Median eminence
Pituitary stalk
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In lactating rats that were separated from their pups for 8 hours, suckling induced a rapid rise in plasma prolactin levels. Correlatively, it induced a depletion in dopamine (DA) and serotonin (5-HT) concentrations within the hypothalamus as early as 5 min after the onset of suckling. This depletion lasted as long as the stimulus was maintained. A parallel increase in the level of the metabolite of 5-HT, 5-hydroxyindolacetic acid (5-HIAA), was observed. Under these conditions, the ratio of 5-HIAA/5-HT is augmented. This ratio is a good index of turnover of the transmitter. Suckling affected neither the content of noradrenaline (NA) in the hypothalamus nor the levels of any amine tested in the cerebral cortex. When pups were separated from their mother for 24 hours, suckling no longer resulted in changes in either plasma prolactin levels or hypothalamic DA, 5-HT, or 5-HIAA concentrations. We have concluded that the activation of a discrete system of 5-HT containing neurons is associated with the triggering effect of suckling on prolactin release. (Endocrinology99: 445, 1976)
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The effect of immobilization stress was studied in rats in which the CRF and arginine vasopressin-containing innervation of the median eminence was destroyed by an anterolateral cut (ALC) around the medial basal hypothalamus. One week after surgery, the rats with ALC were subjected to immobilization and they showed a normal rise in plasma corticosterone, a smaller than normal rise of plasma ACTH, and an increased response of plasma epinephrine and norepinephrine. When in rats with an ALC the response of plasma catecholamines was prevented by guanethidine pretreatment and adrenal enucleation the small rise in plasma ACTH was unchanged during immobilization. In addition, the plasma corticosterone and ACTH rises during immobilization in the rats with ALC were not influenced by prior treatment with phentolamine (2.5 mg/kg ip) or propranolol (2.5 mg/kg ip). These findings suggest that the large rises in plasma epinephrine and norepinephrine levels during immobilization do not contribute to changes in plasma ACTH or corticosterone levels when hypothalamic regulation via CRF and/or arginine vasopressin is interrupted by ALC.
Median eminence
Corticosterone
Phentolamine
Basal (medicine)
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Neurochemical
Human brain
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The concentration of dopamine, norepinephrine, epinephrine and serotonin was determined in 6 rostrocaudal segments of the median eminence, 2 segments in the pituitary stalk, in the retrochiasmatic area and the pituitary lobes by radioenzymatic microassay in adult rats. The level of dopamine and norepinephrine was measured separately in the medial and lateral portions of the median eminence. All four amines measured were found unevenly distributed inside the median eminence: 1. the highest dopamine level was detected in the middle-caudal portions of the median eminence and in the rostral parts of the pituitary stalk; 2. high norepinephrine concentration was found in the retrochiasmatic area and this gradually diminished caudalwards; 3. relatively high epinephrine level was present in the rostral median eminence and retrochiasmatic area, but that in the caudal median eminence and pituitary stalk was low; 4. the level of serotonin increased caudalwards and showed a highest value in the caudal portion of the pituitary stalk. Relatively high dopamine and serotonin levels were also detectable in all three pituitary lobes where the concentration of norepinephrine was low and that of epinephrine was undetectable.
Median eminence
Pituitary stalk
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The effects of ketamine (50 mg/kg i.p.) on brain monoamines, including epinephrine, norepinephrine, dopamine, serotonin and its metabolite 5-hydroxy indoleacetic acid, were studied in three groups of male Sprague-Dawley rats. A rapid, simple, accurate, and sensitive spectrophotoflurometric method was developed to determine monoamines extracted from rat brain. Ketamine significantly increased brain epinephrine (25%), serotonin (28%) and 5-hydroxy indoleacetic acid (32%) in rats. In contrast, norepinephrine (43%) and dopamine (58%) levels were significantly reduced at 30 minutes. The increase in epinephrine (13%) and decrease in norepinephrine (31%) and dopamine (38%) levels remained significant 12 hours after ketamine injection. Serotonin and 5-hydroxy indoleacetic acid levels returned to almost normal in ketamine pretreated animals after 12 hours. Thus, the ability of ketamine to interfere with monoamine metabolism was revealed.
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Chronically ovariectomized rats with intact pituitary glands were implanted with anterior pituitary homografts under the kidney capsule. Rats which received a transplanted anterior pituitary exhibited significantly higher basal plasma prolactin levels than rats receiving no transplants. Rats received systemic infusions of norepinephrine, dopamine, and serotonin. Only dopamine was capable of significantly suppressing prolactin secretion from the pituitary homograft. Norepinephrine and serotonin had no effect on plasma prolactin levels. These results demonstrate the direct effect of dopamine on prolactin release by the anterior pituitary and are consistent with the view that dopamine may be PIF.
Prolactin cell
Renal capsule
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