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)

Annual variations in the secretion of LH are responsible for seasonal changes in ovulatory activity in ewes. This hormonal pattern reflects an increase in the intensity of the negative feedback exerted by oestradiol under long days. Neuropharmacological studies have shown that this inhibition of LH secretion involves activation of catecholaminergic systems from preoptic and mediobasal hypothalamus (MBH) by oestradiol during anoestrus, and that 5-hydroxytryptamine inputs may also play a role. Within the MBH, the most important structures appear to be the retrochiasmatic region of the hypothalamus, which contains the A15 dopaminergic nucleus, and the median eminence, which contains the axon terminals of the GnRH cells controlling the pulsatile release of LH. In ovariectomized ewes in which oestradiol tonically inhibits LH secretion during the anoestrous season, LH pulse frequency is increased when the cells of the A15 nucleus are destroyed. The median eminence and other mediobasal structures contain more catecholamines and their metabolites under long days than under short days. Microdialysis of the A15 nucleus in vivo during long days revealed increased catecholaminergic activity under oestradiol treatment due to stimulation of tyrosine hydroxylase, the rate-limiting enzyme in the pathway of catecholaminergic synthesis. Tyrosine hydroxylase activity within the median eminence is increased under the various photoperiodic regimens that inhibit LH secretion. Neurochemical changes in the A15 nucleus and median eminence, in response to photoperiodic or oestradiol treatments, suggest a functional relationship which acts at the level of the GnRH axon terminals.
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PMID:Dopaminergic control of LH secretion by the A15 nucleus in anoestrous ewes. 762 20

In the ewe, the inhibition of LH secretion during long days results from increased negative feedback by estradiol. This effect depends on aminergic systems, mainly in the lateral retrochiasmatic area, a region that includes the dopaminergic A15 nucleus. Recently we demonstrated that the inhibition of LH secretion by estradiol under long days is accompanied by an increase in extracellular levels of amine metabolites (3,4-dihydroxyphenylacetic acid [DOPAC], homovanillic acid [HVA], and 5-hydroxyindolacetic acid [5-HIAA]) in the lateral retrochiasmatic area of the hypothalamus. The increase in catecholamine metabolite levels could be due to stimulation of tyrosine hydroxylase (TH) activity in the catecholaminergic systems of this region. In the present study, we tested this hypothesis by incorporating in vivo measurement of TH activity in the brain into our microdialysis model. We used this approach to first examine the effect of estradiol on TH activity in both the lateral retrochiasmatic area and the caudate nucleus during long days (experiment 1). Two dialysis sessions were carried out on each of six ewes: one after a 10-day estradiol treatment (s.c. implant) and the other after 10 days without estradiol treatment. Estradiol treatment reduced pulsatile LH secretion without affecting the secretion of prolactin. The steroid also significantly increased TH activity in the lateral retrochiasmatic area as assessed by the formation of L-3-4 dihydroxyphenylalanine (L-DOPA). There was no variation in the TH activity of the catecholaminergic systems of the caudate nucleus, suggesting that the effect of estradiol is specifically hypothalamic. In experiment 2, we estimated the relative contribution to the accumulation of L-DOPA in the lateral retrochiasmatic area by dopamine (DA) synthesis in the dopaminergic neurons and noradrenaline (NA) synthesis in the noradrenergic afferents of the A15 nucleus. This study also allowed us to test whether DOPAC and HVA molecules released in this medium originate from DA metabolism in dopaminergic cells of the A15 nucleus or in its noradrenergic afferents. We monitored TH activity as well as amine metabolite concentrations in the lateral retrochiasmatic area after a partial destruction of noradrenergic nerves in the brain using intracerebroventricular (i.c.v.) injections of nomifensine followed by 6-hydroxydopamine (6-OHDA) injections. We compared the responses in four experimental ewes with those in four control ewes receiving a single i.c.v. injection of nomifensine only. Decreases in extracellular concentrations of 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG) in the left lateral retrochiasmatic area and the tissue content of NA in the contralateral structure confirmed the effectiveness of the lesion of the noradrenergic endings.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Estradiol increases tyrosine hydroxylase activity of the A15 nucleus dopaminergic neurons during long days in the ewe. 791 58

Double immunocytochemical labelling with antibodies raised against tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase was used on semi-thin sections of sheep hypothalamus to investigate possible morphological relationships between dopamine neurons of group A15 and noradrenaline afferents to this area. Dopamine-beta-hydroxylase-immunoreactive (IR) fibres were found in the close proximity of dendrites of TH-IR neurons. At electron microscopic level, single immunocytochemical staining with TH antibodies revealed the presence of synaptic contacts between labelled or unlabelled axon terminals and anti-TH labelled dendrites. These observations suggest that in the sheep, TH-IR neurons of group A15 are controlled by non-catecholaminergic and catecholaminergic afferents. Catecholamine inputs could contain either dopamine or noradrenaline. The hypothesis of noradrenaline inputs to A15 is strongly supported by the results obtained after double labelling on semi-thin sections. Tyrosine hydroxylase-immunoreactive perikarya and dendrites often seemed to be partly surrounded by glial processes. This latter observation suggests that the synaptic investment of these neurons might be controlled by glial cells.
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PMID:Morphological relationships between tyrosine hydroxylase-immunoreactive neurons and dopamine-beta-hydroxylase-immunoreactive fibres in dopamine cell group A15 of the sheep. 809 98

The lateral habenular nucleus of the rat contains a dense plexus of dopaminergic fibers, which are more marked in the medial part of the lateral habenular nucleus than in its lateral counterpart. Employing a combination of fluorescent retrograde axonal tracing with fluorogold and tyrosine hydroxylase immunofluorescence histochemistry, we investigated the distribution of cells of origin of the dopaminergic afferent fibers to the lateral habenular nucleus in the rat. The cells double-labeled with both fluorogold injected into the lateral habenular nucleus and tyrosine hydroxylase antisera were seen in a variety of fore- and midbrain regions, including the bed nucleus of the stria terminalis, medial preoptic area, periventricular, ventromedial, and dorsomedial hypothalamic nuclei, ventral tegmental area, interfascicular nucleus, substantia nigra pars compacta, ventrolateral division of the midbrain periaqueductal gray, and dorsal raphe nucleus. The double-labeled cells were located bilaterally with an ipsilateral predominance, and constituted approximately 10% of the total fluorogold-positive cell population. We have further observed by anterograde axonal tracing with Phaseolus vulgaris-leucoagglutinin that projection fibers arising from the sites of origin of the dopaminergic afferent fibers to the lateral habenular nucleus terminate mainly in the medial part of the lateral habenular nucleus, and to a lesser extent in its lateral counterpart. Thus, we have found in the present study that the dopaminergic neurons sending their axons to the lateral habenular nucleus are widely distributed in the A9, A10, A14, and A15 dopaminergic cell groups. Such dopaminergic neurons may exert regulatory influences upon many limbic-associated brain regions via the lateral habenular nucleus.
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PMID:The sites of origin of dopaminergic afferent fibers to the lateral habenular nucleus in the rat. 810 49

Immunocytochemical staining for the presence of catecholamine synthesizing enzymes, tyrosine hydroxylase and dopamine beta-hydroxylase, was used to characterize the regional distribution of catecholaminergic neurons in the hypothalamus and adjacent areas of domestic cattle, Bos taurus. In steers, heifers and cows, tyrosine hydroxylase-immunoreactive perikarya was located throughout periventricular regions of the third cerebral ventricle, in both anterior and retrochiasmatic divisions of the supraoptic nucleus, suprachiasmatic nucleus, and ventral and dorsolateral regions of the paraventricular nucleus, dorsal hypothalamus, ventrolateral aspects of the arcuate nucleus, along the ventral hypothalamic surface between the median eminence and optic tract, and in the posterior hypothalamus. Immunostained perikarya ranged from small (10-20 microns, parvicellular) to large (30-50 microns, magnocellular) and were of multiple shapes: round, triangular, fusiform or multipolar, often with 2-5 processes of branched arborization. There were no dopamine-beta-hydroxylase immunoreactive perikarya observed within the hypothalamus and adjacent structures. However, both tyrosine hydroxylase and dopamine-beta-hydroxylase immunoreactive fibers and punctate varicosities were observed throughout regions of tyrosine hydroxylase immunoreactivity perikarya. Generally, the location and pattern of hypothalamic tyrosine hydroxylase immunoreactivity and dopamine-beta-hydroxylase immunoreactive were similar to those reported for most other large brain mammalian species, however, there were several differences with commonly used small laboratory animals. These included intense tyrosine hydroxylase immunoreactivity of perikarya within the retrochiasmatic division of the supraoptic nucleus (ventral A15 region), the absence of tyrosine hydroxylase immunoreactive perikarya below the anterior commissure or within the bed nucleus of stria terminalis (absence of the dorsal A15 region), an abundance of tyrosine hydroxylase immunoreactive perikarya within the ependymal layer of the median eminence, heavy innervation of the arcuate nucleus with dopamine-beta-hydroxylase immunoreactive fibers and varicosities, and the paucity of dopamine-beta-hydroxylase immunoreactive throughout the median eminence.
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PMID:Immunocytochemical localization of the catecholamine-synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase, in the hypothalamus of cattle. 858 33

This study describes the distribution of catecholaminergic neurons in the hypothalamus and the pituitary gland of the domestic pig, Sus scrofa, an animal that is widely used as an experimental model of human physiology in addition to its worldwide agricultural importance. Hypothalamic catecholamine neurons were identified by immunocytochemical staining for the presence of the catecholamine synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase. Tyrosine hydroxylase-immunoreactive perikarya were observed in the periventricular region throughout the extent of the third ventricle, the anterior and retrochiasmatic divisions of the supraoptic nucleus, the suprachiasmatic nucleus, the ventral and dorsolateral regions of the paraventricular nucleus and adjacent dorsal hypothalamus, the ventrolateral arcuate nucleus, and the posterior hypothalamus. Perikarya ranged from parvicellular (10-15 microns) to magnocellular (25-50 microns) and were of multiple shapes (rounded, fusiform, triangular, or multipolar) and generally had two to five processes with branched arborization. No dopamine-beta-hydroxylase immunoreactive perikarya were observed within the hypothalamus or in the adjacent basal forebrain structures. Both tyrosine hydroxylase- and dopamine-beta-hydroxylase-immunoreactive fibers and punctate varicosities were observed throughout areas containing tyrosine hydroxylase perikarya, but dopamine-beta-hydroxylase immunoreactivity was very sparse within the median eminence. Within the pituitary gland, only tyrosine hydroxylase fibers, and not dopamine-beta-hydroxylase immunoreactive fibers, were located throughout the neurohypophyseal tract and within the posterior pituitary in both pars intermedia and pars nervosa regions. Generally, the location and patterns of both catecholamine-synthesizing enzymes were similar to those reported for other mammalian species except for the absence of the A15 dorsal group and the very sparse dopamine-beta-hydroxylase immunoreactive fibers and varicosities in the median eminence in the pig. These findings provide an initial framework for elucidating behavioral and neuroendocrine species differences with regard to catecholamine neurotransmitters.
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PMID:Immunocytochemical distribution of catecholamine-synthesizing neurons in the hypothalamus and pituitary gland of pigs: tyrosine hydroxylase and dopamine-beta-hydroxylase. 878 82

A major factor responsible for seasonal anestrus in sheep is a striking increase in the ability of estradiol (E) to inhibit pulsatile GnRH and LH secretion. Previous studies suggest that dopaminergic neurons in the A14 and A15 groups of the ovine hypothalamus play a key role in conveying the inhibitory effects of E in anestrous ewes. The present study tested the hypothesis that A14/A15 neurons in anestrous ewes are activated in response to E, and that this activation is specifically related to seasonal changes in E negative feedback. Expression of the immediate early gene products, Fos and the Fos-related antigens (FRAs), was used as a marker of neuronal activation. Ovariectomized anestrous ewes received either blank implants (no E) or 0.5-cm long E implants sc and were killed 6 h later (E+6h) or 7 days later (E+7d and no E groups). During the breeding season, two additional groups of ovariectomized ewes were perfused 7 days after insertion of either blank or E implants. During anestrus, E completely suppressed LH pulses in the E+7d group, but had no effect in the E+6h group. In the E+7d anestrous group, there was also a significant increase in the mean percentage of tyrosine hydroxylase (TH)-positive cells that expressed nuclear Fos/FRAs in A14 and A15 areas compared to that in either the no E or E+6h group. By contrast, during the breeding season, E had no effect on LH pulse frequency, and there were relatively few TH-positive cells in A14 and A15 that coexpressed Fos/FRAs in either the no E or E+7d group. No significant steroidal or seasonal differences in Fos/FRA expression were seen in other hypothalamic dopaminergic cell groups (A12 and A13) or in the preoptic area-anterior hypothalamus or suprachiasmatic nucleus. Furthermore, E did not alter the total number of TH-positive neurons in A14/A15 or other cell groups. There were seasonal differences in the number of TH-positive neurons, with a significantly greater number of cells in the A13 and A15 of breeding season animals compared to anestrous ewes. Thus, E increased Fos/FRA expression in A14/A15 neurons only during anestrus at a time when it also inhibited LH pulse frequency. These findings are consistent with the view that activation of dopaminergic cells in A14 and A15 is a critical link in the chain of events leading to seasonal shifts in sensitivity to E negative feedback in the ewe.
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PMID:Dopaminergic A14/A15 neurons are activated during estradiol negative feedback in anestrous, but not breeding season, ewes. 882 6

The neural components underlying the influence of photoperiod upon reproductive functioning are poorly understood. In this study, we have used immunocytochemistry to examine whether changes in photoperiod may influence specific neuronal cell populations implicated in mediating gonadal steroid feedback actions on GnRH neurons. Short day (SD) exposed ewes in the midluteal stage of the estrous cycle and long day (LD) anestrous ewes were perfused in pairs and hypothalamic brain sections immunostained for tyrosine hydroxylase (TH), neuropeptide Y (NPY), beta-endorphin (betaE), and the estrogen receptor (ER). The number of ER-immunoreactive cells detected within the preoptic area, but not the hypothalamus, was approximately 20% higher (P < 0.05) in LD ewes compared with SD animals. The numbers of TH-immunoreactive neurons comprising the A12, A14, and A15 cell groups were not different between LD and SD ewes, and the percentage of A12 (approximately 15%) and A14 (approximately 25%) neurons expressing ERs was similarly unaffected by photoperiod. The number of betaE neurons detected in the arcuate nucleus was 50% lower (P < 0.05) in SD vs. LD ewes, whereas NPY-immunoreactive cell numbers in the median eminence were 300% higher (P < 0.05). Approximately 3% of NPY neurons in the median eminence, and 10% in the arcuate nucleus, expressed ER immunoreactivity in a photoperiod-independent manner. These studies indicate that changes in photoperiod may regulate ER expression within the preoptic area and suggest that hypothalamic NPY and betaE neurons are involved in the seasonal regulation of reproductive activity in the ewe.
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PMID:Effects of photoperiod on estrogen receptor, tyrosine hydroxylase, neuropeptide Y, and beta-endorphin immunoreactivity in the ewe hypothalamus. 916 52

By using a double immunocytochemical method we examined the distribution of dopaminergic neurons expressing neuromedin K receptor (NKR; NK3) in the rat brain. The distribution of NKR-like immunoreactive (-LI) neurons completely overlapped that of tyrosine hydroxylase (TH)-LI neurons in the retrorubral field (A8), substantia nigra (A9), ventral tegmental area and nucleus raphe linealis (A10). Completely or partially overlapping distributions of NKR- and TH-LI neurons were found in certain regions of the hypothalamus (A11-A15) and olfactory bulb (A16). Neurons showing both NKR- and TH-like immunoreactivities, however, were only found in A8-A10: All of the NKR-LI neurons displayed TH-like immunoreactivity, and about 71-86% of the TH-LI neurons expressed NKR-like immunoreactivity. The present results provided morphological evidence for physiological modulation of dopaminergic neurons by tachykinins through NKR in A8-A10.
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PMID:Mesencephalic dopaminergic neurons expressing neuromedin K receptor (NK3): a double immunocytochemical study in the rat 947 42

By using a double immunocytochemical method we examined the distribution of dopaminergic neurons expressing neuromedin K receptor (NKR; NK3) in the rat brain. The distribution of NKR-like immunoreactive (-LI) neurons completely overlapped that of tyrosine hydroxylase (TH)-LI neurons in the retrorubral field (A8), substantia nigra (A9), ventral tegmental area and nucleus raphe linealis (A10). Completely or partially overlapping distributions of NKR- and TH-LI neurons were found in certain regions of the hypothalamus (A11-A15) and olfactory bulb (A16). Neurons showing both NKR- and TH-like immunoreactivities, however, were only found in A8-A10: All of the NKR-LI neurons displayed TH-like immunoreactivity, and about 71-86% of the TH-LI neurons expressed NKR-like immunoreactivity. The present results provided morphological evidence for physiological modulation of dopaminergic neurons by tachykinins through NKR in A8-A10.
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PMID:Mesencephalic dopaminergic neurons expressing neuromedin K receptor (NK3): a double immunocytochemical study in the rat. 949 91


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