Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.14.16.2 (tyrosine hydroxylase)
 14,760 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of hypothalamic dopamine on the functional differentiation of prolactin cells was investigated in the developing rat brain. The treatment of pregnant rats with alpha-methyl-p-tyrosine (tyrosine hydroxylase inhibitor) resulted in a noticeable decrease of dopamine concentration in the hypothalamus at birth and at 5 days of age of offspring. Moreover, treatment with this regimen caused a marked decrease in the population of prolactin cells and in the production of prolactin at birth and at 5 days of age of offspring. It seems, then, that hypothalamic dopaminergic neurons precede the functional differentiation of prolactin cells in the developing brains and that hypothalamic dopamine may play an important role in producing prolactin in the anterior pituitary during development.
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PMID:Hypothalamic dopamine may play a role in inducing prolactin in pituitary cells. 345 76

The role of tuberoinfundibular dopamine (DA) in the histamine-induced rise of plasma prolactin was studied in male rats. Right lateral ventricle (icv) histamine injection (30 micrograms/rat) caused a significant rise of plasma prolactin at 15 and 30 min; at 60 min values returned to basal levels. Histamine does not modified steady-state DA concentrations. For turnover evaluation, histamine was icv injected immediately or 30 min after the tyrosine hydroxylase inhibitor alpha-methyltyrosine (250 mg/kg i.p.) and DA concentration in the median eminence was measured at 0, 1 and 2 hours after the inhibitor injection. Rate constants of DA decline and DA synthesis rates were found similar in both controls (cerebrospinal fluid) and histamine-injected rats. These results indicate that the stimulatory action of histamine on prolactin release might not be associated to DA. It would be due mainly to its action on prolactin-releasing factors and to a minor extent, to changes in the dopaminergic system.
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PMID:Histamine-induced prolactin release and activity of tuberoinfundibular dopaminergic neurons in male rats. 370 20

The effects of thyroidectomy (4 weeks) on dopamine (DA) and noradrenaline (NA) turnover rates were determined by means of regression analysis. The disappearance of catecholamine (CA) fluorescence (using quantitative histofluorimetry) after tyrosine hydroxylase inhibition (alpha-methyl-DL-p-tyrosine methyl ester) has been investigated in discrete hypothalamic and forebrain DA and NA nerve terminal systems of the male rat. A time-dependent monophasic CA fluorescence disappearance was observed in all CA nerve terminal systems of the sham-operated and thyroidectomized rats. In the thyroidectomized rat, DA turnover in the anterior nucleus accumbens and in the medial and lateral palisade zones of the median eminence (ME) was reduced while DA turnover in the posterior nucleus accumbens was increased as compared to control rats. Furthermore, NA turnover was increased in the paraventricular hypothalamic nucleus (PA) and reduced in the dorsomedial hypothalamic nucleus (DM) and in the 'border zone' (lateral hypothalamus). Radioimmunoassay of hormones in serum demonstrated marked increases in TSH levels and reduced concentrations of GH, prolactin, corticosterone, triiodothyronine and thyroxine. The reduced DA turnover in the external layer of the ME and the increased NA turnover in the PA may indicate an inhibitory dopaminergic mechanism in the ME and a facilitatory noradrenergic mechanism in the PA in the regulation of TSH secretion. These mechanisms seem to interact with thyroid hormones. The reduced NA turnover demonstrated in the DM and in the border zone may be related to the lowering of growth hormone levels and pulsatility caused by thyroidectomy. Finally, the DA nerve terminal systems in the anterior and posterior parts of the nucleus accumbens are differently regulated by changes in the brain-pituitary-thyroid axis.
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PMID:Regression analysis of catecholamine utilization in discrete hypothalamic and forebrain regions of the male rat: effects of thyroidectomy. 388 91

Using catecholamine (CA) fluorescence histochemistry in combination with quantitative microfluorimetry, it has been shown that chronic treatment with triiodothyronine (T3) and thyroxine (T4; 2 X 10 and 2 X 36 micrograms/kg i.p., respectively, twice daily for 10 days), but not acute treatment (1 and 3.6 mg/kg i.p., respectively, 2 h before killing), increases CA utilization in the medial and lateral palisade zones of the median eminence and reduces noradrenaline (NA) utilization in the parvocellular part and magnocellular part of the paraventricular hypothalamic nucleus of the hypophysectomized male rat. Following chronic T4 treatment it could also be shown that the CA levels in the medial and lateral palisade zones of the median eminence were increased, while the NA levels were reduced in the parvocellular part of the paraventricular hypothalamic nucleus. Chronic T3 treatment induced similar changes - increased CA levels in the medial palisade zone and reduced NA levels in the magnocellular part of the paraventricular hypothalamic nucleus. Within the telencephalon, chronic but not acute treatment with T3 or T4 selectively increased dopamine (DA) utilization within the diffuse type of DA nerve terminal systems of the nucleus accumbens. This action of chronic treatment of T3 or T4 was highly selective and no changes in DA levels could be demonstrated in any DA nerve terminals analyzed in the nucleus caudatus putamen; nucleus accumbens and tuberculum olfactorium. In all the experiments the TSH levels remained undetectable and the low basal serum prolactin levels were not modulated in any experimental group in spite of the treatment with a tyrosine hydroxylase inhibitor in the CA utilization experiments. Following 2-3 weeks after hypophysectomy, serum T3 and T4 were decreased by 30-50%. In the acute experiments with T3 or T4, serum T3 levels and T3 as well as T4 levels were markedly elevated after the respective treatments. In the chronic experiments, the T4 treatment resulted in significant increases in the serum levels of both T3 and T4. The present results indicate that discrete DA and NA nerve terminal systems within the median eminence (DA), nucleus accumbens (DA) and paraventricular hypothalamic nucleus (NA) can slowly respond to chronic treatment with T3 or T4. This effect is the result of a direct action of the thyroid hormones on the brain since TSH is absent in the hypophysectomized rat.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The effects of acute and chronic treatment with triiodothyronine and thyroxine on the hypothalamic and telencephalic catecholamine nerve terminal systems of the hypophysectomized male rat. Chronic treatment modulates catecholamine utilization in discrete catecholamine nerve terminal systems. 401 Aug 88

The effects of acute stress on serum prolactin concentrations and tuberoinfundibular dopaminergic (TIDA) neuronal activity were studied in female rats. TIDA neuronal activity was estimated by measuring the rate of dihydroxyphenylalanine (DOPA) accumulation after the administration of a decarboxylase inhibitor (NSD 1015) and the rate of decline of dopamine (DA) after the administration of a tyrosine hydroxylase inhibitor (alpha-methyltyrosine) in the median eminence. Serum prolactin concentrations were increased following 30 min of supine immobilization (restraint stress), but returned to control levels by 2, 8, and 16 h after the onset of this stress. The rate of DOPA accumulation was decreased during the 30 min of restraint; it was still further reduced 2 h later but had returned to control levels 8 and 16 h later. No change in the rate of DOPA accumulation was observed in the striatum or neurointermediate lobe of the pituitary at any time after the start of restraint. Restraint stress also decreased the rate of DA turnover in the median eminence, but was without effect on the rates of DA turnover in the striatum or neurointermediate lobe. These results suggest that restraint stress activates an inhibitory neuronal pathway which decreases the activity of TIDA neurons and may be responsible, at least in part, for the increase in serum prolactin concentrations. The responsiveness of TIDA neurons to the stress-induced decrease in activity was not influenced by the time of day or the stage of the estrous cycle. Not all stressful manipulations decreased TIDA neuronal activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Acute restraint stress decreases dopamine synthesis and turnover in the median eminence: a model for the study of the inhibitory neuronal influences on tuberoinfundibular dopaminergic neurons. 405 76

The basal activity o f tuberoinfundibular dopaminergic (TIDA) neurons is higher and the response of these neurons to the stimulatory actions of prolactin is greater in the female than in the male rat. In the female rat, the restraint-stress-induced increase in serum prolactin concentrations is accompanied by a concurrent decrease in the activity of TIDA neurons. The purpose of the present study was to compare these effects of restraint in male and female rats. TIDA neuronal activity was estimated by measuring the rate of dopamine (DA) synthesis (DOPA accumulation after the administration of a decarboxylase inhibitor, NSD 1015) and the rate of DA turnover (decline of DA after administration of a tyrosine hydroxylase inhibitor; alpha-methyltyrosine) in the median eminence. Thirty minutes of restraint increased serum prolactin concentrations in both male and female rats, but a greater response was observed in the females. Restraint also decreased the rates of synthesis and turnover of DA in the median eminence of the female but not the male rat. The difference in the response of TIDA neurons in male and female rats to restraint is not the consequence of neuronal differentiation resulting from neonatal androgen exposure, because restraint aso decreased the activity of TIDA neurons in androgen-sterilized female rats. The inability of restraint stress to reduce TIDA neuronal activity in the male rat appears to be the consequence of testosterone, since TIDA neurons were responsive to restraint following castration of the males.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Acute restraint stress decreases tuberoinfundibular dopaminergic neuronal activity: evidence for a differential response in male versus female rats. 408 91

The purpose of this study was to examine the thesis that increasing concentrations of prolactin within the cerebrospinal fluid (CSF) increase the activity of dopaminergic terminals within the median eminence and that this increased dopaminergic activity is temporally associated with a suppression of endogenous prolactin secretion. To avoid difficulties encountered in performing catecholamine turnovers in the undisturbed rat, the measurement of tyrosine hydroxylase was validated as an index of dopaminergic activity within the median eminence. In the median eminence, but not the medial preoptic area, parallel increases in the activity of tyrosine hydroxylase and the turnover of dopamine (but not norepinephrine) occurred following hyperprolactinemia. Twenty-six hours but not 2.5 h after the subcutaneous administration of ovine prolactin, the activity of tyrosine hydroxylase was increased in the median eminence, and endogenous prolactin secretion was inhibited. During a 26 h continuous intracerebroventricular (icv) infusion (88 ng/h) of rat prolactin, there was a complete suppression of endogenous prolactin secretion. Twenty-six but not 2.5 h after the initiation of the icv infusion of prolactin, there was an increase in tyrosine hydroxylase activity in the median eminence. The results of these studies suggest that: (1) measurement of tyrosine hydroxylase activity within the median eminence is a useful index of the activity of dopaminergic terminals; (2) increasing concentrations of prolactin within the CSF suppressed prolactin secretion by the anterior pituitary; (3) this suppression of prolactin is accompanied by an increased activity of dopaminergic terminals within the median eminence; (4) those neural structures concerned with the regulation of prolactin secretion respond directly to prolactin itself; (5) the autoregulation by prolactin of its own secretion manifests a certain latency more characteristic of a tonic rather than a phasic inhibitory control; and finally, (6) dopaminergic terminals in the median eminence but not the preoptic area appear uniquely sensitive to prolactin.
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PMID:Prolactin in cerebrospinal fluid: a probable site of prolactin autoregulation. 610 86

These studies report that chronic hypothyroidism in the rat is accompanied by decreased serum prolactin. An investigation of those mechanisms by which hypothyroidism decreases prolactin secretion revealed the following findings: (1) activation of tyrosine hydroxylase in the median eminence (ME) and increase in the turnover-rate of dopamine (DA) in the ME; (2) a decreased content and in vitro release of prolactin by pituitaries from hypothyroid rats; (3) decreased [3H]spiroperidol binding to pituitary homogenates obtained from hypothyroid rats, and (4) normal increase of serum prolactin following administration of haloperidol. Comparison of the effects of hypothyroidism on dopaminergic terminals of the striatum with those of the ME was made and the following tentative conclusions proposed. Hypothyroidism presumably increases the release of DA into the pituitary portal system. A deficiency of thyroid hormone desensitizes the pituitary lactrotrope to inhibition by DA, decreases the total pituitary prolactin content and presumable also reduces the peripheral catabolism of prolactin. The overall net effect of hypothyroidism is, therefore, a decrease in serum prolactin levels which can increase normally following haloperidol. The mechanism by which a deficiency of thyroid hormone alters the function of the tuberoinfundibular and striatal dopaminergic systems is unknown.
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PMID:Studies of the neural mechanisms by which hypothyroidism decreases prolactin secretion in the rat. 610 34

The activities of tyrosine hydroxylase and dopamine-beta-hydroxylase were measured in the medial basal hypothalamus and remaining hyothalamic tissue of female rats at various times during diestrus 2, proestrus and estrus. Tyrosine hydroxylase activity in the medial basal hypothalamus was significantly lower at 12.00 h compared with other times on proestrus. This decrease preceded the elevation of serum prolactin and LH during the afternoon of proestrus. Tyrosine hydroxylase activity did not change significantly during diestrus 2 or estrus nor was it altered at any time in the remainder of the hypothalamus. Dopamine-beta-hydroxylase activity in the basal medial hypothalamus was significantly elevated at 12.00 h on proestrus and at 14.00 h on diestrus. The results provide further evidence for a decrease in dopaminergic neuron activity in the medial basal hypothalamus which may precipitate the series of events leading to the LH surge during proestrus. The increase in dopamine-beta-hydroxylase activity suggests that an increase in noradrenergic neuron activity may also be involved in triggering the release of LH.
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PMID:Catecholamine synthesizing enzymes in the hypothalamus during the estrous cycle. 610 10

The effect of fusaric acid, an inhibitor of dopamine-beta-hydroxylase (DBH), on luteinizing hormone (LH) and prolactin levels during the estrous cycle was determined. Fusaric acid was found to cause a selective dose- and time-dependent inhibition of DBH activity in the medial basal hypothalamus without altering tyrosine hydroxylase activity. When DBH was inhibited during the afternoon of diestrus, the proestrous surges of both LH and, to a lesser extent, prolactin were inhibited. These results suggest that noradrenergic neuronal activity in the mediobasal hypothalamus is required during the afternoon preceding proestrus in order for the LH and prolactin surges to occur. It is possible that the rise in serum estrogen during late diestrus 2 is blocked by fusaric acid treatment. This estrogen increase is necessary for LH and prolactin surges to occur during proestrus. When DBH was inhibited during the afternoon of proestrus, the LH and prolactin surges were completely eliminated. This indicates that noradrenergic neuronal activity in the mediobasal hypothalamus during the afternoon of proestrus is important for both the LH and prolactin surges to occur.
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PMID:Inhibition of LH and prolactin release in the cycling rat following inhibition of dopamine-beta-hydroxylase. 611 41


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