Acute effects of reserpine on tryptophan hydroxylase activity and mRNA in rat brain

The present study examined changes in tryptophan hydroxylase (TPH) activity in the rat brainstem 1–4 days after i.p. reserpine administration. TPH enzyme activity was significantly decreased day 1 posttreatment and followed by a small but significant increase on days 2–4. Maximal TPH activity on day 4 was elevated only 42% above control level. This small increase in TPH activity was not preceded by any change of in situ hybridization signal of TPH message on day 1. In contrast, adrenal tyrosine hydroxylase (TH) activity in these same reserpinized animals was 2.5-fold higher than control on 4 day posttreatment. In addition, TH message was correspondingly increased day 1 posttreatment. Taken together, these results indicate a trend of small increase in TPH activity and no alteration in message after reserpine treatment unlike catecholaminergic systems.     

Effects of long-term hypoxia and hypoxic exercise on brain monoamine levels in rat

This study clarified the effects of long-term hypoxia and hypoxic exercise on monoamines in the whole brain, and in four specific regions of the rat brain. The male Wistar rat progenitors (P1 group) were randomly assigned to three groups: hypoxia (16.0% oxygen) and exercise (MHE-P1), hypoxia and sedentary (MHS-P1), normoxia and sedentary (MNS-P1). The male children of P1 (the first generation of hypoxic rats; F1) were randomly divided into two groups: hypoxia and exercise (MHE-F1) and hypoxic sedentary (MHS-F1). The monoamines of whole brain were measured in P1 males, and monoamines of cerebellum, frontal lobe, striatum and hippocampus were measured in F1 males. The monoamine levels of MHE-P1 were significantly lower than those of MHS-P1 and MNS-P1. No significant difference was found in monoamine levels between MHS-P1 and MNS-P1. Epinephrine, norepinephrine, and dopamine levels of the MHE-F1 group significantly decreased in the frontal lobe, cerebellum and striatum, compare with the other groups (hypoxic and sedentary; normoxic and sedentary, respectively). These monoamines in the hippocampus were not influenced by the hypoxia or hypoxic exercise conditions. This study suggests that long-term hypoxic exercise decreased monoamine levels in whole brain, and that sensitivity to hypoxia and hypoxic exercise differed according to brain region.     

Effects of biogenic aldehydes and aldehyde dehydrogenase inhibitors on rat brain tryptophan hydroxylase activity in vitro

The effect of indole-3-acetaldehyde, 5-hydroxyindole-3-acetaldehyde, disulfiram, diethyldithiocarbamate, coprine, and 1-amino-cyclopropanol on tryptophan hydroxylase activity was studied in vitro using high performance liquid chromatography with electro-chemical detection. With the analytical method developed, 5-hydroxytryptophan, serotonin, and 5-hydroxyindole-3-acetic acid could be measured simultaneously. Indole-3-acetaldehyde (12-1200 microM) was found to cause a 6-33% inhibition of the enzyme. Dependent upon the nature of the sulfhydryl- or reducing-agent (dithiotreitol, glutathione, or ascorbate) present in the incubates, the degree of inhibition by disulfiram varied, probably due to the formation of various mixed disulfides. Also the presence of diethyldithiocarbamate (160-1600 microM) was found to inhibit tryptophan hydroxylase (28-91%), while 5-hydroxyindole-3-acetaldehyde, coprine, or 1-aminocyclopropanol appeared to have no effect on the enzyme activity.     

Daily variations in in vivo tryptophan hydroxylation and in the contents of serotonin and 5-hydroxyindoleacetic acid in discrete brain areas of the rat

Summary The in vivo rate of brain tryptophan hydroxylation was determined through 5-hydroxytryptophan accumulation (5-HTPacc) following the administration of NSD 1015, a L-aromatic amino-acid decarboxylase inhibitor. This measurement was performed every 4 h throughout a 24 h hour period in 10 discrete brain areas of rats maintained on a regular 12 h/12 h light-dark cycle. The concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were also determined in untreated rats. Daily variations in 5-HTPacc were found in all the areas studied, the 5-HTPacc being higher during the dark period in most structures. These results strongly suggest that tryptophan hydroxylation is involved in the control of the 5-HT biosynthesis circadian rhythm. However, various patterns of 5-HT and 5-HIAA daily variations were observed, suggesting that the circadian factors affecting serotonin metabolism can be different among brain areas.     

Functional gene variants of the serotonin-synthesizing enzyme tryptophan hydroxylase 2 in migraine

Serotonin (5-HT) plays an important role in the pathophysiology of migraine. Tryptophan hydroxylase 2 (TPH2) is the rate-limiting enzyme in the biosynthesis of 5-HT in the brain and is therefore a major factor in the availability of 5-HT and its rate of production. We hypothesized that functional TPH2 gene variants are associated with migraine. In a case–control study approach, two proven functional and two putatively functional variants of the TPH2 gene were investigated in 266 migraine patients and 153 controls. Genotype, allele, and haplotype frequencies did not differ between healthy subjects and migraineurs. A subgroup analysis for the occurrence of aura or clinical characteristics, including the number of attacks, did not reveal a positive association for the investigated polymorphisms. Our data argue against a major influence of the TPH2 gene promoter region in migraine.     

Tyrosine hydroxylase,tryptophan hydroxylase,biopterin, and neopterin in the brain of anorexia nervosa

Summary The activities of tyrosine hydroxylase and tryptophan hydroxylase and contents of biopterin and neopterin were measured for the first time in various regions of human brain from a patient with anorexia nervosa (AN). In AN as compared with controls, tyrosine hydroxylase activity was markedly reduced in all brain regions analyzed, while tryptophan hydroxylase activity and biopterin content had a tendency to increase. Neopterin content did not change dramatically. The opposite changes of tyrosine hydroxylase and tryptophan hydroxylase suggest an imbalance between the activity of catecholaminergic neurons and that of serotonergic neurons, and may be related to pathogenesis of AN.     

Lipopolysaccharide administration produces time-dependent and region-specific alterations in tryptophan and tyrosine hydroxylase activities in rat brain

Summary. The present study examined the effect of systemic administration of lipopolysaccharide (LPS; 100 and 250 μg/kg, i.p.) on tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH) activities in frontal cortex, striatum and midbrain of the rat. Enzyme activities were determined by measuring accumulation of the transient intermediates 5-hydroxytrptophan (5-HTP) and L-dihydroxyphenylalanine (L-DOPA) following in vivo administration of the decarboxylase inhibitor, NSD 1015. TPH activity was increased 2 hours after administration of LPS (100 and 250 μg/kg) in both frontal cortex and midbrain, and a secondary increase was seen in the midbrain 12 hours after challenge. LPS provoked an increase in TH activity in the midbrain only, and this was evident for up to 24 hours after LPS administration. Thus in addition to previous studies demonstrating that LPS increases in vivo NA, DA and 5-HT release, this study shows that LPS increases the activity of the rate-limiting enzymes responsible for their synthesis. Received May 4, 2000; accepted June 16, 2000     

Acetylcholine content in different regions of the rat brain

Acetylcholine content of different rat brain regions was measured. A correlation between acetylcholine content and cholineacetyltransferase (ChAc) activity in discrete brain regions was found. However there are regions such as cerebellar nuclei, cerebellar hemisphere, caudal medial forebrain bundle, zone incerta, nucleus vestibularis lateralis where the acetylcholine content is relatively much higher than the ChAc activity, and regions such as n.cochleares, n.motor n.V., N.motor N.VII., n.motor, n.XII where ChAc activity was high and the content of acetylcholine is relatively low.     

精神分裂症患者攻击行为与单胺氧化酶A、色氨酸羟化酶基因多态性的关联研究

目的探讨精神分裂症患者攻击行为与单胺氧化酶A(MAOA)、色氨酸羟化酶(TPH)基因多态性的相关性。方法参照ICD-10诊断标准,选取212例精神分裂症患者,应用修订版外显攻击行为量表(MOAS)进行评定,98例MOAS加权总分≥4分者纳入有攻击行为组(研究组),114例MOAS加权总分0分者为无攻击行为组(对照组)。采用聚合酶链式反应扩增及限制性片段长度多态性技术检测单胺氧化酶A基因、色氨酸羟化酶基因多态性,与精神分裂症患者攻击行为进行关联分析。结果 MAOA、TPH基因型频率和等位基因频率在有攻击行为患者组与无攻击行为患者组比较无显著差异(P0.05)。结论单胺氧化酶A、色氨酸羟化酶基因多态性与精神分裂症患者攻击行为无关联。     

Somatostatin co-localizes with tyrosine hydroxylase in the nerve cells of discrete hypothalamic regions in rats

The co-expression of somatostatin (SOM)- and tyrosine hydroxylase (TH)-like immunoreactivities in nerve cells of the rat hypothalamus was investigated by the simultaneous application to the same sections of immuno-beta-galactosidase staining and the peroxidase-antiperoxidase (PAP) method. SOM-like immunoreactive cells stained blue with immuno-beta-galactosidase staining and TH-like immunoreactive cells stained brown with the PAP method. Double-labeled cells with overlapping blue and brown immunoreaction products were frequently identified in the preoptic periventricular nucleus (pope). These double-labeled cells were seen in clusters within the ventral half of the rostral pope. The periventricular hypothalamic nucleus at the level of the anterior hypothalamic nucleus contained only scattered nerve cells with both SOM- and TH-like immunoreactivities, despite the presence of many nerve cells immunoreactive for either SOM or TH in this nucleus. Double-labeled cells were also observed in some regions of the medial-basal hypothalamus, including the boundary between the ventromedial hypothalamic nucleus and the arcuate hypothalamic nucleus, and areas dorsal and lateral to the ventromedial hypothalamic nucleus. These findings may provide insight into the mechanisms underlying previously described catecholamine-mediated modulation of SOM release from the hypothalamus.     

Lithium and chlorimipramine differentially alter the stability properties of tryptophan hydroxylase as seen in allosteric and scattering kinetics

Compared to control, both lithium and chlorimipramine (CMI) slow the frequency of variation in tryptophan hydroxylase (TPOH) velocity functions measured across increasing (nearly physiological) cofactor concentrations or across continuous (long residence) time. The common effect appears to be generated by different statistical mechanisms in view of the diverse patterns observed when, for multiple 60-point experiments for each condition, mean frequencies were plotted against mean amplitudes of variation: lithium constricted the frequencies over a range of amplitudes; CMI fixed amplitude across the range of frequencies. Initial rate, short residence time experiments suggest that at the micromolecular level, before the emergence of time-dependent macro-kinetic organization as seen in the long residence time assays, lithium may uncouple the elementary constituents of the system, allowing subsequent phase gathering and emergent stability around a statistically dominant frequency, whereas CMI may augment coupling, leading to unstable complexity in the population dynamics. The relationship between these effects and allosteric kinetic functions is discussed.     

Regulation of tryptophan hydroxylase expression by a retinal circadian oscillator in vitro

Many aspects of retinal physiology are controlled by a circadian clock including at least two steps in the melatonin synthetic pathway: the activity of the enzyme,N-acetyltransferase (NAT), and mRNA levels of the rate-limiting enzyme tryptophan hydroxylase (TPH). Light and dopamine (through D2-like dopamine receptors) can phase shift the clock, and can also acutely inhibit NAT activity, resulting in supressed melatonin synthesis. In this paper, we show that eyecups cultured in constant darkness maintain a clock-controlled rhythm in TPH mRNA, with low levels in early day, rising to a peak in early night. Both eyecups and isolated retinas, cultured in light during the day, also exhibit a similar increase in TPH mRNA levels, indicating that this expression is not acutely inhibited by light. Treatment with light or quinpirole (D2 dopamine receptor agonist) in early night, at a time and dose that acutely inhibits NAT activity, does not change levels of TPH mRNA. Addition of eticlopride (D2 dopamine receptor antagonist) during the day, also has no effect on the normal daytime increase in TPH message levels. Therefore, TPH mRNA level is controlled by a circadian clock located within the eye, but acute effects of light or dopamine are not detected.     

Single nucleotide polymorphism and haplotype analysis of a novel tryptophan hydroxylase isoform (TPH2) gene in suicide victims.

BACKGROUND: Tryptophan hydroxylase, the rate-limiting enzyme in the biosynthesis of serotonin, represents a major candidate in numerous genetic association analyses of suicidal behavior; however, the results are so far inconclusive. Recently, a second tryptophan hydroxylase isoform (TPH2) was identified in mice, which was exclusively present in the brain. In a previous postmortem study of our own group, we could demonstrate that TPH2 is also expressed in the human brain but not in peripheral tissues. METHODS: We performed single nucleotide polymorphisms, haplotypes, and linkage disequilibrium studies on 263 suicide victims and 266 healthy control subjects with 10 single nucleotide polymorphisms in the TPH2 gene. RESULTS: Significant association was detected between one single nucleotide polymorphism (p = .004, global p = .01) and suicide. Additionally, haplotype analysis also produced support for association (p < .0001, global p = .0001). CONCLUSIONS: This is the first report about an association between TPH2 gene polymorphisms and completed suicide. Our findings provide evidence for an involvement of genetic variants in the TPH2 gene in suicidal behavior. These results might open up new research strategies for the analysis of the observed disturbances in the serotonergic system in several other psychiatric disorders.     

Regional specificity of the long-term regulation of tyrosine hydroxylase in some catecholaminergic rat brainstem areas. I. Influence of long-term hypoxia

The present study was carried out to investigate the influence of long-term hypoxia on tyrosine hydroxylase (TH) protein quantity in some catecholaminergic rat brainstem areas such as the dorsomedial medulla (DMM), the ventrolateral medulla (VLM) and the locus coeruleus (LC). TH protein quantity was also measured in a dopaminergic structure, the substantia nigra (SN). Male Sprague-Dawley rats were exposed to normobaric hypoxia (10% O₂/90% N₂) for 3, 7, 14 or 22 days. Controls were kept in normoxia for the same period. This study demonstrates that: (1) 3 days of hypoxia produced a 50% and a 26% increase in the quantity of TH protein in the rostral and caudal LC, respectively; (2) 14 days of hypoxia produced a 44% increase of TH protein content exclusively in the caudal part of DMM and a 31% increase in the VLM area; and (3) the stimulus failed to alter the TH protein quantity in the SN. After 14 and 22 days of hypoxia respectively, the TH protein content in the LC and DMM returned to the level of controls. To determine whether the increase in TH protein quantity could be related to a change in norepinephrine (NE) content, the rate constant of disappearance (k) of NE was measured in the catecholaminergic areas of intact or chemodenervated rats submitted to long-term hypoxia. Our results show that hypoxia causes an increase of TH protein quantity within the subpopulations of catecholaminergic areas additionally with an elevation in the NE content. These data suggest a selective response of the TH regulation to long-term hypoxia within the caudal DMM catecholaminergic area which receives chemosensory inputs.     

Advances in the molecular characterization of tryptophan hydroxylase

The neurotransmitter serotonin has been implicated in numerous physiological functions and pathophysiological disorders. The hydroxylation of the aromatic amino acid tryptophan is rate-limiting in the synthesis of serotonin. Tryptophan hydroxylase (TPH), as the rate-limiting enzyme, determines the concentrations of serotonin in vivo. Relative serotonin concentrations are clearly important in neural transmission, but serotonin has also been reported to function as a local antioxidant. Identification of the mechanisms regulating TPH activity has been hindered by its low levels in tissues and the instability of the enzyme. Several TPH expression systems have been developed to circumvent these problems. In addition, eukaryotic expressions systems are currently being developed and represent a new avenue of research for identifying TPH regulatory mechanisms. Recombinant DNA technology has enabled the synthesis of TPH deletions, chimeras, and point mutations that have served as tools for identifying structural and functional domains within TPH. Notably, the experiments have proven long-held hypotheses that TPH is organized intoN-terminal regulatory and C-terminal catalytic domains, that serine-58 is a site for PKA-mediated phosphorylation, and that a C-terminal leucine zipper is involved in formation of the tetrameric holoenzyme. Several new findings have also emerged regarding regulation of TPH activity by posttranslational phosphorylation, kinetic inhibition, and covalent modification. Inhibition of TPH byl-DOPA may have implications for depression in Parkinson’s disease (PD) patients. In addition, TPH inactivation by nitric oxide may be involved in amphetamine-induced toxicity. These regulatory concepts, in conjunction with new systems for studying TPH activity, are the focus of this article.     

The effect of bolus methylprednisolone in prevention of brain edema in hypoxic ischemic brain injury: an experimental study in 7-day-old rat pups

One of the major mechanisms responsible for tissue injury in hypoxic ischemic brain damage is the formation of free radicals. We studied the efficacy of methylprednisolone, which is claimed to cause rapid congealing of membranes, and to protect the cells against the free radicals present in the environment, in preventing the brain edema that occurs in hypoxic ischemic brain injury. Hypoxic ischemic brain injury to the right hemisphere in 7-day-old rat pups is produced by cauterization of the right common carotid artery followed by hypoxia in 8% oxygen and 92% nitrogen for 3 h. The animals were divided into the groups. One group received methylprednisolone at 30 mg/kg body weight and the other an equal volume of saline 40 min before hypoxia. At 42 h of recovery, some of the rats were killed for measurement of water content in the right and left hemispheres whereas others were killed at 40 days for neuropathological examination. The water content in the right hemisphere was significantly lower in the 19 methylprednisolone-treated pups than it was in 20 saline-treated pups, mean +/- S.E.M. was 83.913 +/- 0.313% and 86.681 +/- 0.377%, respectively. The differences between the means were significant (P less than 0.001) according to the Mann-Whitney U-test. The difference of the mean water contents between the two hemispheres was significantly higher in the saline-treated group (2.695 +/- 0.372%) than it was in the methylprednisolone-treated group (0.432 +/- 0.088%), P less than 0.0001 by independent samples t-test. Neuropathological study was performed on 4 rat pups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Postnatal developmental changes of tryptophan hydroxylase activity in serotonergic cell bodies and terminals of rat brain

Tryptophan hydroxylase (TPH) is the rate limiting enzyme in serotonin biosynthesis, so its development is very important to the functional maturation of the serotonergic neurons. In the present study, we examined changes of TPH activity in serotonergic cell bodies and terminals of rat brain during postnatal development. TPH activity reached its peak in the cell body regions at 24 days after birth, while the enzyme activity in a terminal region rose to its plateau at day 30. TPH activity in adult rat is the highest in nucleus raphe dorsalis, then nucleus raphe centralis and hypothalamus in a decreasing order.     

Identification of dopamine-containing cell bodies in the dorsal and median raphe nuclei of the rat brain using tyrosine hydroxylase immunochemistry

Using immunohistochemical methods with antibodies specific to tyrosine hydroxylase, we examined the distribution of dopaminergic cells in the dorsal and median raphe nucleus of the rat brain. Although dopamine-containing cell bodies were previously thought to be almost exclusively confined to the substantia nigra pars compacta, ventral tegmental area, and tuberoinfundibular system, we found numerous cell bodies which stained for tyrosine hydroxylase in the dorsal and median raphe nuclei.