Liver tryptophan pyrrolase activity and metabolism of brain 5-HT in rat

Neurochemical Anatomy of Cushing's Syndrome

The neurochemical anatomy underlying Cushing's syndrome is examined for regional brain metabolism as well as neurotransmitter levels and receptor binding of biogenic amines and amino acids. Preliminary studies generally indicate that glucose uptake, blood flow, and activation on fMRI scans decreased in neocortical areas and increased in subcortical areas of patients with Cushing's syndrome or disease. Glucocorticoid-mediated increases in hippocampal metabolism occurred despite in vitro evidence of glucocorticoid-induced decreases in glucose uptake or consumption, indicating that in vivo increases are the result of indirect, compensatory, or preliminary responses. In animal studies, glucocorticoid administration decreased 5HT levels and 5HT1A receptor binding in several brain regions while adrenalectomy increased such binding. Region-specific effects were also obtained in regard to the dopaminergic system, with predominant actions of glucocorticoid-induced potentiation of reuptake blockers and releasing agents. More in-depth neuroanatomical analyses are warranted of these and amino acid-related neurotransmission.

Antidepressant effect of taurine in chronic unpredictable mild stress-induced depressive rats

Depression, a psychiatric and dysthymic disorder, severely affects the learning, work and life quality. The main pathogenesis of depression is associated with central nervous system (CNS) dysfunction. Taurine has been demonstrated to exert protective effects on the brain development and can improve learning ability and memory. Our study investigated the antidepressant-like effects of taurine pre-treatment by examining the changes in depression-like behavior, hormones, neurotransmitters, inflammatory factors and neurotrophic factors in the hippocampus of a chronic unpredictable mild stress (CUMS)-induced depressive rat model. Taurine was found to inhibit the decrease of sucrose consumption and prevent the deficiency of spatial memory and anxiety in rats exposed to CUMS, suggesting a preventive effect of taurine on depression-like behavior. Furthermore, the decreased levels of 5-hydroxytryptamine, dopamine, noradrenaline; the increased levels of glutamate, corticosterone; and the decreased expressions of fibroblast growth factor-2, vascular endothelial growth factor and brain derived neurotrophic factor in depressive rats were hindered by taurine pre-administration. However, tumor necrosis factor-α and interleukin-1β levels were not significantly changed by taurine. The results demonstrated that the anti-depressive effect of taurine may be involved in the regulation of hypothalamic-pituitary-adrenal (HPA) axis and the promotion of neurogenesis, neuronal survival and growth in the hippocampus.

Transcriptomic analysis of Rongchang pig brains and livers

Recent developments in high-throughput RNA sequencing (RNA-seq) technology have led to a dramatic impact on our understanding of the structure and expression profiles of the mammalian transcriptome. To gain insights into the usefulness of swine production and biomedical model, the transcriptome profiling of Rongchang pig brains and livers was characterized using RNA-seq technology to uncover functional candidate molecules. In the study, total RNAs from brains and livers of Rongchang pig were sequenced and 8.6Gb sequencing data was obtained. This analysis revealed tissue specificity through the identification of 5575 and 4600 differentially expressed genes (DEGs) in brains and livers, respectively and the functional analysis of DEGs. Furthermore, 83 neuropeptide gene transcripts, 69 neuropeptide receptor gene transcripts, 10 pro-neuropeptide convertase gene transcripts and many other neuropeptide related protein gene transcripts were identified. Totally, the major characteristics of the transcriptional profiles of Rongchang pig brains and livers were present.

EPR and Mössbauer spectroscopy show inequivalent hemes in tryptophan dioxygenase

Tryptophan 2,3-dioxygenase (TDO) is an essential enzyme in the pathway of NAD biosynthesis and important for all living organisms. TDO catalyzes oxidative cleavage of the indole ring of L-tryptophan (L-Trp), converting it to N-formylkynurenine (NFK). The crystal structure of TDO shows a dimer of dimer quaternary structure of the homotetrameric protein. The four catalytic sites of the protein, one per subunit, contain a heme that catalyzes the activation and insertion of dioxygen into L-Trp. Because of the alpha(4) structure and because only one type of heme center has been identified in previous spectroscopic studies, the four hemes sites have been presumed to be equivalent. The present work demonstrates that the heme sites of TDO are not equivalent. Quantitative interpretation of EPR and Mössbauer spectroscopic data indicates the presence of two dominant inequivalent heme species in reduced and oxidized states of the enzyme, which is consistent with a dimer of dimer protein quaternary structure that now extends to the electronic properties of the hemes. The electronic properties of the hemes in the reduced state of TDO change significantly upon L-Trp addition, which is attributed to a change in the protonation state of the proximal histidine to the hemes. The binding of O(2) surrogates NO or CO shows two inequivalent heme sites. The heme-NO complexes are 5- and 6-coordinate without L-Trp, and both 6-coordinate with L-Trp. NO can be selectively photodissociated from only one of the heme-NO sites and only in the presence of L-Trp. Cryoreduction of TDO produces a novel diamagnetic heme species, tentatively assigned as a reduced heme-OH complex. This work presents a new description of the heme interactions with the protein, and with the proximal His, which must be considered during the general interpretation of physical data as it relates to kinetics, mechanism, and function of TDO.

Glucocorticoid interaction with aggression in non-mammalian vertebrates: reciprocal action

Socially aggressive interaction is stressful, and as such, glucocorticoids are typically secreted during aggressive interaction in a variety of vertebrates, which may both potentiate and inhibit aggression. The behavioral relationship between corticosterone and/or cortisol in non-mammalian (as well as mammalian) vertebrates is dependent on timing, magnitude, context, and coordination of physiological and behavioral responses. Chronically elevated plasma glucocorticoids reliably inhibit aggressive behavior, consistent with an evolutionarily adaptive behavioral strategy among subordinate and submissive individuals. Acute elevation of plasma glucocorticoids may either promote an actively aggressive response via action in specialized local regions of the brain such as the anterior hypothalamus, or is permissive to escalated aggression and/or activity. Although the permissive effect of glucocorticoids on aggression does not suggest an active role for the hormone, the corticosteroids may be necessary for full expression of aggressive behavior, as in the lizard Anolis carolinensis. These effects suggest that short-term stress may generally be best counteracted by an actively aggressive response, at least for socially dominant proactive individuals. An acute and active response may be evolutionarily maladaptive under chronic, uncontrollable and unpredictable circumstances. It appears that subordinate reactive individuals often produce compulsorily chronic responses that inhibit aggression and promote submissive behavior.

Rapid glucocorticoid stimulation and GABAergic inhibition of hippocampal serotonergic response: in vivo dialysis in the lizard anolis carolinensis

Central serotonin (5-HT) is activated during stressful situations and aggressive interactions in a number of species. Glucocorticoids secreted peripherally during stressful events feed back on central systems and may affect 5-HT mediation of stress-induced behavioral events. To test the neuromodulatory effect of stress hormone secretion, serotonin overflow was measured from the hippocampus of the lizard Anolis carolinensis. Microdialysis was used to collect repeated samples from anesthetized lizards, with perfusate measured by HPLC with electrochemical analysis. Following initially high levels of 5-HT, concentrations stabilized to basal levels after approximately 2 h. Intracortical infusion of 200 ng/ml corticosterone evoked transient increases in 5-HT release of approximately 400%. The effect of corticosterone on 5-HT overflow appears to be dose dependent as 20 ng/ml stimulated an increase of 200%, whereas 2 ng/ml stimulated a 50% increase. Administration of 0.1 and 1 ng/ml GABA via the dialysis probe significantly inhibited 5-HT overflow by 20 and 40%, respectively. The duration of GABA inhibition is greater than the stimulatory response for glucocorticoids. Short-lived glucocorticoid stimulation of 5-HT release suggests a possible mechanism for endocrine mediation of continuously changing social behavioral events.

Tryptophan availability and the susceptibility to stress in multiple sclerosis: a hypothesis

In his seminal description of the clinical manifestations of multiple sclerosis (MS) in 1868 Charcot suggested that psychological stress is an important factor in the pathogenesis of the disease. MS patients often relate that mental stress exacerbates their symptoms and even provokes attacks of their disease. Moreover, a subgroup of MS patients experiences exacerbation of symptoms following a period of mental stress rather than occurring at times when stress is maximal, i.e., attacks are reported to occur on the rebound from stress. Psychological stress may also contribute to the onset and long term clinical deterioration of the disease. Mental stress is associated with activation of the hypothalamic-pituitary adrenal (HPA) axis resulting in increased release of ACTH and cortisol secretion. Stress-induced activation of the HPA axis is associated with an increased metabolism of cerebral serotonin (5-HT) the synthesis of which is dependent upon the availability of its precursor tryptophan. Thus, increased tryptophan availability may partly underlie the general response to stress. Plasma and CSF tryptophan levels are diminished in chronic MS patients and it is suggested that plasma tryptophan levels are even lower in patients who are stressed. Attenuated increase in the availability of systemic tryptophan in response to stress is thought to underlie the susceptibility of MS patients to stress. This hypothesis is supported by the findings in chronic MS patients of a significantly diminished adrenal cortisol reactivity to insulin-induced hypoglycemia which is considered a stress response mediated through the 5-HT system. Consequently, since patients with MS exhibit an abnormal response to stress it follows that increased tryptophan availability through dietary supplementation would diminish their vulnerability to psychological stress. Additionally, if sustained or repeated stress contributes to progression and clinical deterioration of the disease then chronic tryptophan supplementation also may halt its progression.

Mode of inhibition of rat liver tryptophan 2,3-dioxygenase by melatonin

Liver tryptophan 2,3-dioxygenase is a cytosolic enzyme that plays a crucial role in the regulation of circulating levels of tryptophan. Stimulation of the activity of this enzyme by heme enhances the catabolism of tryptophan, making less tryptophan available for uptake into the brain. Melatonin, the major hormone of the pineal gland, is shown to cause competitive inhibition of this enzyme (Ki = 2.70 microM). This structural analog of the substrate L-tryptophan is a negative homotropic cooperative modulator of the enzyme. The enzyme has a Km = 100 microM, and the substrate concentration required for optimum activity was found to be 2.5 mM with substrate inhibition becoming a feature at higher levels of tryptophan.

Mechanism of decline in rat brain 5-hydroxytryptamine after induction of liver tryptophan pyrrolase by hydrocortisone: roles of tryptophan catabolism and kynurenine synthesis

1 Two mechanisms have been proposed to explain the decline in brain tryptophan and 5-hydroxytryptamine (5-HT) after administration of hydrocortisone and the subsequent induction of liver pyrrolase. These are depletion of tryptophan by high rates of tryptophan catabolism and inhibition of tryptophan uptake by elevated levels of the tryptophan catabolite, kynurenine.2 The increase in plasma kynurenine after hydrocortisone injection (25 mg/kg) was small, and kynurenine, at a concentration ten fold greater, did not inhibit tryptophan uptake by brain as measured by the Oldendorf technique. Thus, inhibition of tryptophan uptake by kynurenine is not an important mechanism in the control of brain tryptophan and 5-HT.3 The decline in brain tryptophan after hydrocortisone was comparable to that seen in other tissues, which comprise more than half of the body weight of a rat.4 The total decline in free tryptophan stores in whole animals treated with hydrocortisone was estimated to be about 450 mug. This amount of tryptophan would be catabolized by tryptophan pyrrolase in about 20 min, when the enzyme is induced, according to an earlier estimate of the rate of tryptophan catabolism in vivo.5 Tryptophan pyrrolase activity remains high for much longer than 20 min, suggesting that there is net protein catabolism, which releases tryptophan and prevents non-protein tryptophan levels falling very far.6 These results demonstrate that the decline in brain tryptophan and 5-HT after hydrocortisone is caused by depletion of tryptophan stores due to the high activity of tryptophan pyrrolase. However, our data suggest that this effect is diminished by release of tryptophan from proteins. Thus, peripheral protein metabolism may be an important factor in the control of brain tryptophan levels and 5-HT synthesis.

Biochemical and ultrastructural aspects of the inhibited phagocytosis by neutrophil granulocytes in acute brain-damaged patients

In a study of 60 head-injured patients inhibition of phagocytosis by neutrophil granulocytes was observed over a period of up to 5 weeks. This inhibition of phagocytosis could be correlated with the severity of head injury as well as with the state of unconsciousness at the time of the investigation. No correlation was found between neutrophil granulocyte counts and the inhibition of phagocytosis. A good correlation could be demonstrated between the level of lumbar CSF 5-HIAA and the inhibition of phagocytosis. After in vitro incubation with albumin the cells showed a recovery of phagocytosis. Electron micrographs of the cells showed ultrastructural appearances suggesting a changed permeability of the plasma membrane and, in addition, alterations in the cytoplasmic region beneath the plasma membrane. It is suggested that head injury may influence the pituitary-adrenal system and the autonomic nervous system, giving changes of neutrophil function and of neurotransmitter metabolism; these changes may represent an adaptation mechanism.