Physiopharmacological interactions between stress hormones and central serotonergic systems

CSF 5-HIAA and DST non-suppression -independent biomarkers in suicide attempters?

BACKGROUND

Two major biomarkers of suicidal behaviour; low 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid (CSF) and non-suppression in the dexamethasone suppression test (DST) have evidence for predictive power for suicide in mood disorders. Previous suicide attempt is the most robust clinical risk factor.

PURPOSE OF STUDY

To study the interrelationship of suicide risk factors: low CSF 5-HIAA and the DST non-suppression in mood disorder patients with and without an index suicide attempt.

METHODS

Fifty-eight hospitalised mood disorder patients (twenty-five with an index suicide attempt), who were not receiving any treatment with antidepressants, underwent lumbar puncture and DST. Plasma cortisol levels were determined from blood samples drawn the following day at 8:00 a.m., 4:00 p.m. and 11:00 p.m. and analysed in relation to CSF 5-HIAA.

RESULTS

In the sample as a whole, the serum cortisol level at 4:00 p.m. showed a significant positive correlation to CSF 5-HIAA (r=0.3, p<0.02). In the patients with an index suicide attempt, the serum cortisol at 4.00 p.m. correlated positively with CSF 5-HIAA (r=0.65, p<0.0006), but not in the non-attempters (NS).

CONCLUSION

The positive correlation means that low CSF 5-HIAA and DST non-suppression are relatively independent biomarkers of suicide risk in suicide attempters. The interrelation of the two systems seems to be different in suicide attempters compared to depressed inpatients without suicide attempt.

Rehabilitation of decreased motor performance in patients with chronic fatigue syndrome: should we treat low effort capacity or reduced effort tolerance?

Aim: The aetiology, pathophysiology, diagnostic delineation and treatment of chronic fatigue syndrome (CFS) remain a matter of debate. Here some aspects of the debate are elucidated, with a particular focus on the patients' decreased motor performance.

Hypothesis: The pathophysiological basis of decreased motor performance in CFS may, theoretically, involve three components: (1) a peripheral energetic deficit (impaired oxidative metabolism and/or physical deconditioning); (2) a central perceptual disturbance (higher effort sense or increased `interoception'); and (3) a fundamental failure of the neurobiological stress system, leading to an abnormal `sickness response'. It is proposed that the first two components may lead to low effort capacity, while the third component may lead to reduced effort tolerance. Although there is evidence for low effort capacity influencing symptoms and functional limitations in CFS, it is assumed that reduced effort tolerance might be the primary disturbance in CFS.

Diagnostic implications: Distinguishing low effort capacity and reduced effort tolerance may contribute to a refinement of current diagnostic criteria of CFS and the identification of subgroups.

Therapeutic implications: The above-mentioned distinction may make it possible to formulate a rationale for an effective implementation and adequate outcome evaluation of rehabilitation strategies in CFS.

Research implications: This new heuristic framework may inform future research aimed at disentangling the complex determination of impaired motor performance in CFS, as well as studies aimed at customizing treatment to different subtypes of patients.

Actions of 3,4-methylenedioxymethamphetamine (MDMA) on cerebral dopaminergic, serotonergic and cholinergic neurons

3,4-Methylenedioxymethamphetamine (MDMA) is an amphetamine derivative and a popular drug of abuse that exhibits mild hallucinogenic and rewarding properties and engenders feelings of connectedness and openness. The unique psychopharmacological profile of this drug of abuse most likely is derived from the property of MDMA to promote the release of dopamine and serotonin (5-HT) in multiple brain regions. The present review highlights primarily data from studies employing in vivo microdialysis that detail the actions of MDMA on the release of these neurotransmitters. Data from in vivo microdialysis experiments indicate that MDMA, like most amphetamine derivatives, increases the release of dopamine in the striatum, n. accumbens and prefrontal cortex. However, the release of dopamine evoked by MDMA in each of these brain regions appears to be modulated by concomitantly released 5-HT and the subsequent activation of 5-HT2A/C or 5-HT2B/C receptors. In addition to its stimulatory effect on the release of monoamines, MDMA also enhances the release of acetylcholine in the striatum, hippocampus and prefrontal cortex, and this cholinergic response appears to be secondary to the activation of histaminergic, dopaminergic and/or serotonergic receptors. Beyond the acute stimulatory effect of MDMA on neurotransmitter release, MDMA also increases the extracellular concentration of energy substrates, e.g., glucose and lactate in the brain. In contrast to the acute stimulatory actions of MDMA on the release of monoamines and acetylcholine, the repeated administration of high doses of MDMA is thought to result in a selective neurotoxicity to 5-HT axon terminals in the rat. Additional studies are reviewed that focus on the alterations in neurotransmitter responses to pharmacological and physiological stimuli that accompany MDMA-induced 5-HT neurotoxicity.

Hippocampal neurogenesis, depressive disorders, and antidepressant therapy

There is a growing body of evidence that neural stem cells reside in the adult central nervous system where neurogenesis occurs throughout lifespan. Neurogenesis concerns mainly two areas in the brain: the subgranular zone of the dentate gyrus in the hippocampus and the subventricular zone, where it is controlled by several trophic factors and neuroactive molecules. Neurogenesis is involved in processes such as learning and memory and accumulating evidence implicates hippocampal neurogenesis in the physiopathology of depression. We herein review experimental and clinical data demonstrating that stress and antidepressant treatments affect neurogenesis in opposite direction in rodents. In particular, the stimulation of hippocampal neurogenesis by all types of antidepressant drugs supports the view that neuroplastic phenomena are involved in the physiopathology of depression and underlie—at least partly—antidepressant therapy.

Genetically Determined Variation in Stress Responsiveness in Rainbow Trout: Behavior and Neurobiology

It is becoming increasingly recognized that the diversity in stressors, their intensity, predictability and the context in which they are experienced, will result in behavioral and physiological responses just as diverse. In addition, stress responses are characterized by individual variations where the physiological and behavioral reactions are associated in such a manner that distinct stress coping styles encompassing suites of correlated traits can be identified. These are often referred to as proactive and reactive stress coping styles. Proactive coping is characterized by more aggression, higher general activity and higher sympathetic activation, whereas reactive coping is characterized by immobility, lack of initiative and a higher parasympathetic/hypothalamic activation. Stable coping styles appear to coexist within populations, and these strategies appear to be largely innate. Moreover, the physiological and behavioral traits of coping styles appear to be heritable. These stress coping styles have proven to play a major role in competitive ability and subsequent social position in different species of vertebrates. However, there are also studies showing that social position can affect parameters encompassing the stress coping style of individuals. In this regard it is important, but not always easy, to distinguish between causes and effects of behavioral and physiological responses to stressors. The question raised is to what extent and rigidness stress coping styles are guided by genetic factors.

Mechanisms of cancer-related fatigue

Cancer-related fatigue (CRF) is one of the most prevalent symptoms patients with cancer experience, both during and after treatment. CRF is pervasive and affects patients' quality of life considerably. It is important, therefore, to understand the underlying pathophysiology of CRF in order to develop useful strategies for prevention and treatment. At present, the etiology of CRF is poorly understood and the relative contributions of the neoplastic disease, various forms of cancer therapy, and comorbid conditions (e.g., anemia, cachexia, sleep disorders, depression) remain unclear. In any individual, the etiology of CRF probably involves the dysregulation of several physiological and biochemical systems. Mechanisms proposed as underlying CRF include 5-HT neurotransmitter dysregulation, vagal afferent activation, alterations in muscle and ATP metabolism, hypothalamic-pituitary-adrenal axis dysfunction, circadian rhythm disruption, and cytokine dysregulation. Currently, these hypotheses are largely based on evidence from other conditions in which fatigue is a characteristic, in particular chronic fatigue syndrome and exercise-induced fatigue. The mechanisms that lead to fatigue in these conditions provide a theoretical basis for future research into the complex etiology of this distressing and debilitating symptom. An understanding of relevant mechanisms may offer potential routes for its prevention and treatment in patients with cancer.Disclosure of potential conflicts of interest is found at the end of this article.

Co-localization of corticotropin-releasing factor and vesicular glutamate transporters within axon terminals of the rat dorsal raphe nucleus

Electrophysiological, microdialysis and behavioral studies support a modulatory role for corticotropin-releasing factor (CRF) in regulating the dorsal raphe nucleus (DRN)-serotonin (5-HT) system. CRF and 5-HT are implicated in the pathophysiology of depression, thus neuroanatomical substrates of CRF-DRN-5-HT interactions are of interest. Identification of co-transmitters within DRN CRF axon terminals is important for elucidating the complex effects underlying CRF afferent regulation of DRN neurons. This study investigated whether CRF-labeled axon terminals within the DRN contain immunoreactivity for vesicular glutamate transporters (isoforms vGlut1 and vGlut2) indicative of the excitatory neurotransmitter glutamate. Dual immunohistochemistry for CRF and either vGlut1 or vGlut2 was conducted within the same tissue section and immunofluorescence results indicated patterns of immunoreactivity consistent with previous reports. Abundant vGlut1- and vGlut2-immunoreactivity was found in puncta exhibiting a largely uniform distribution, whereas CRF-immunoreactivity was localized to topographically distributed varicose processes within the DRN. Profiles containing both CRF- and either vGlut1- or vGlut2-immunoreactivity were apparent in the DRN. Electron microscopy confirmed that immunoreactivity for CRF and vGlut1 was localized primarily to separate axon terminals in the DRN, with a subset co-localizing CRF and vGlut1. Examination of CRF and vGlut2 immunoreactivities in the DRN indicated that CRF and vGlut2 were found within the same axon terminal more frequently than CRF and vGlut1. Overall, these anatomical findings suggest that CRF may function, in part, with the excitatory neurotransmitter glutamate in the modulation of neuronal activity in the DRN.

Attenuation of stress-induced anorexia in brown trout (Salmo trutta) by pre-treatment with dietary l-tryptophan

The general consensus is that brain serotonin (5-HT) inhibits feed intake in teleost fishes and other vertebrates. Dietary manipulations with the 5-HT precursor tryptophan (TRP) have, however, yielded contradictory effects on feed intake, while studies of the endocrine response to stress indicate that the effects of TRP-enriched feed are context dependent. A characteristic behavioural response to stress is a reduction in feed intake, and in the present study we investigated whether pre-treatment with TRP-enriched feed affected stress-induced changes in feeding behaviour in brown trout (Salmo trutta). After acclimatisation in observation aquaria, isolated fish were fed control or TRP-supplemented feed for 7 d, whereupon they were transferred to a novel environment, in which all fish were fed control feed. Transfer to a new environment resulted in decreased feeding in both the TRP pre-treated and the control-treated group. However, this decrease was more pronounced in the control-treated group. Previous experiments have concluded that stimulation of brain 5-HT systems by TRP enhancement does not affect feed intake in salmonid fishes, but in these studies food intake was observed in unstressed animals only. The present study suggests that pre-treatment with dietary TRP attenuates stress-induced anorexia. Hence, it appears that the effect of dietary manipulations of TRP on feeding behaviour is dependent on the stress levels experienced by experimental animals. These behavioural data are discussed in the context of the involvement of 5-HT in appetite regulation.

Milnacipran, a serotonin and norepinephrine reuptake inhibitor, induces appetite-suppressing effects without inducing hypothalamic stress responses in mice

Milnacipran, a selective serotonin (5-HT) and norepinephrine (NE) reuptake inhibitor, increases extracellular 5-HT and NA levels equally in the central nervous system. Here, we report that systemic administration of milnacipran (20–60 mg/kg) significantly suppressed food intake after fasting in C57BL6J mice. The appetite-suppressing effects of milnacipran were sustained for 5 h. Neither SB242084, a selective 5-HT2C receptor antagonist, nor SB224289, a selective 5-HT1B receptor antagonist, reversed the appetite-suppressing effects of milnacipran. Milnacipran suppressed food intake and body weight in wild-type mice and in Ay mice, which have ectopic expression of the agouti protein. Moreover, milnacipran significantly increased hypothalamic proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) mRNA levels, while having no effect on hypothalamic neuropeptide Y, ghrelin, corticotropin-releasing hormone (CRH), and suppressor of cytokine signaling-3 mRNA levels. Interestingly, milnacipran did not increase plasma corticosterone and blood glucose levels, whereas fenfluramine, which inhibits 5-HT reuptake and stimulates 5-HT release, significantly increased plasma corticosterone and blood glucose levels in association with increased hypothalamic CRH mRNA levels. The appetite-suppressing effects of milnacipran had no effects on food intake in food-restricted, wild-type mice and Ay mice. On the other hand, fenfluramine suppressed food intake in food-restricted wild-type mice, but it had no effects in food-restricted Ay mice. These results suggest that inhibition of 5-HT and NA reuptake induces appetite-suppressing effects independent of 5-HT2C and 5-HT1B receptors, and increases hypothalamic POMC and CART gene expression without increasing plasma corticosterone and blood glucose levels in mice.

Effect of chronic citalopram on serotonin-related and stress-regulated genes in the dorsal raphe nucleus of the rat

Using a model of depression in which chronic social stress induces depressive-like symptoms, we investigated effects of the selective serotonin-reuptake inhibitor (SSRI) citalopram on gene expression in the dorsal raphe nucleus of male rats. Expression of tryptophan hydroxylase (TPH) protein was found to be upregulated by the stress and normalized by citalopram, while mRNAs for genes TPH 1 and 2 were differentially affected. Citalopram had no effect on serotonin transporter mRNA but reduced serotonin-1A autoreceptor mRNA in stressed animals. The SSRI prevented the stress-induced upregulation of mRNA for CREB binding protein, synaptic vesicle glycoprotein 2b and the glial N-myc downstream-regulated gene 2, but increased mRNA for neuron-specific enolase (NSE) in both stressed and unstressed animals having no effect on stress-induced upregulation of NSE protein. These findings demonstrate that in the dorsal raphe nucleus of chronically stressed rats, citalopram normalizes TPH expression and blocks stress effects on distinct genes related to neurotransmitter release and neuroplasticity.

Hypothalamic?Pituitary?Adrenal Responses to 5-HT1Aand 5-HT2A/CAgonists Are Differentially Altered in Female and Male Rats Prenatally Exposed to Ethanol

BACKGROUND

Prenatal ethanol exposure alters the development of the hypothalamic-pituitary-adrenal (HPA) axis, resulting in HPA hyper-responsiveness to stressors in adulthood. Prenatal ethanol exposure also alters the development and activity of the serotoninergic (5-HT) system. We have previously shown that 5-HT(1A) and 5-HT(2A/C) receptor-mediated behavioral and physiological function are altered in fetal ethanol-exposed offspring. As there are extensive interactions between the HPA axis and the 5-HT system, the present study tested the hypothesis that prenatal ethanol exposure would alter 5-HT(1A) and 5-HT(2A/C) receptor-mediated HPA function.

METHODS

The 5-HT(1A) agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.2 mg/kg), and the 5-HT(2A/C) agonist, (+)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI; 0.3 mg/kg), or vehicle (1 mL/kg) were administered to adult female and male offspring from prenatal ethanol-exposed (E), pair-fed control (PF), and ad libitum-fed control (C) dams. The plasma concentration of adrenocorticotropin (ACTH) and corticosterone (CORT) were determined at 0, 15, 30, 60, and 120 minutes postinjection. In addition, corticotropin releasing hormone (CRH) mRNA expression in the paraventricular nucleus of the hypothalamus, and 5-HT(1A) and 5-HT(2A/C) receptor mRNA expression in the hippocampus and prefrontal cortex, respectively, were determined by in situ hybridization.

RESULTS

Ethanol-exposed females showed a blunted ACTH response to 8-OH-DPAT at 15 and 30 minutes, and conversely, an increased ACTH response to DOI at all time points postinjection, compared with PF and C females. Differences among E, PF, and C males failed to reach significance. Centrally, however, DOI resulted in a trend toward lower CRH mRNA levels in E and PF compared with C females, but higher CRH mRNA levels in E compared with control males. There were no differences among prenatal groups in 5-HT(2A) receptor expression in the prefrontal cortex following either 8-OH-DPAT or DOI treatment. However, following 8-OH-DPAT, hippocampal 5-HT(1A) receptor expression was higher in E than in PF females in CA1, with a trend toward higher expression in E than in C females in CA2, whereas following DOI, a prenatal group by subfield interaction suggests lower 5-HT(1A) mRNA levels in E and PF compared with C females in CA1 and the dentate gyrus.

CONCLUSIONS

These data are the first to demonstrate that prenatal ethanol exposure has differential long-term effects on 5-HT(1A)-mediated and 5-HT(2A)-mediated neuroendocrine function in females and males, and suggest a sex-specific ethanol-induced alteration in the interaction between the HPA axis and the serotonin system.

The physiology and evolution of urea transport in fishes

This review summarizes what is currently known about urea transporters in fishes in the context of their physiology and evolution within the vertebrates. The existence of urea transporters has been investigated in red blood cells and hepatocytes of fish as well as in renal and branchial cells. Little is known about urea transport in red blood cells and hepatocytes, in fact, urea transporters are not believed to be present in the erythrocytes of elasmobranchs nor in teleost fish. What little physiological evidence there is for urea transport across fish hepatocytes is not supported by molecular evidence and could be explained by other transporters. In contrast, early findings on elasmobranch renal urea transporters were the impetus for research in other organisms. Urea transport in both the elasmobranch kidney and gill functions to retain urea within the animal against a massive concentration gradient with the environment. Information on branchial and renal urea transporters in teleost fish is recent in comparison but in teleosts urea transporters appear to function for excretion and not retention as in elasmobranchs. The presence of urea transporters in fish that produce a copious amount of urea, such as elasmobranchs and ureotelic teleosts, is reasonable. However, the existence of urea transporters in ammoniotelic fish is curious and could likely be due to their ability to manufacture urea early in life as a means to avoid ammonia toxicity. It is believed that the facilitated diffusion urea transporter (UT) gene family has undergone major evolutionary changes, likely in association with the role of urea transport in the evolution of terrestriality in the vertebrates.

Behavioral and neurophysiological responses of European sea bass groups reared under food constraint

The individual food-demand behavior of juvenile European sea bass (Dicentrarchus labrax, L.) reared in groups under self-feeding conditions was investigated. The triggering activity on self-feeder, i.e. index of the food-demand activity, agonistic interactions and territorial behavior were monitored for periods of 42 to 68 days in six groups of 50 fish. The specific growth rate was calculated and the brain serotonergic activity was used as a stable index of social stress. Inter-individual differences appeared in triggering activity and three groups were distinguished: 3-5 high-triggering fish, 17-30 low-triggering fish and the remaining individuals were null-triggering fish. There were no significant differences in specific growth rates calculated at the end of the experiment (day 42 or day 68) between individuals with high, low, and null food-demand (ANOVA, p>0.05). No territorial or agonistic behaviors were observed, however, there were significant differences in brain serotonergic activity between the three triggering groups (ANOVA, p=0.050 in telencephalon and p=0.004 in cerebellum). Specifically, high-triggering fish had lower serotonergic turnover than low or null-triggering fish. We put forth the hypothesis that fish with low or null-triggering activity could be stressed by the high activity of high-triggering individuals.

Tryptophan hydroxylase-1 gene variants associated with schizophrenia

BACKGROUND

Serotonin (5-HT) has been implicated in the pathophysiology of schizophrenia. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin (5-HT), and as such it might be related to the pathogenesis of schizophrenia. Two isoforms are known, TPH-1 and TPH-2. TPH-1 association with schizophrenia is debated.

METHODS

A case-control design was employed for gene-disease association in 155 schizophrenic psychosis patients and 253 healthy controls, all North European Caucasians. Six single nucleotide polymorphisms (SNPs) with a haplotype block structure spanning over 23 kb of the total TPH-1 29 kb were analyzed. Linkage disequilibrium and haplotype analyses were performed. Bonferroni correction was used for multiple testing.

RESULTS

Single marker association analyses showed two SNPs significantly associated with schizophrenia. Several haplotypes were associated with the disease. A "sliding window" analysis attributed the strongest disease association to a haplotype configuration localized between the promoter region and intron 3.

CONCLUSIONS

Our data indicate that TPH-1 associates with schizophrenia. It appears that specific combinations of promoter variants vis-à-vis gene transcript variants contribute to genetic predisposition to the disease.

Tryptophan hydroxylase-1 gene variants associate with a group of suicidal borderline women

Alterations in the serotonin (5-HT) system have been related to impulsive aggression and suicidal behavior, common features of the borderline personality disorder (BPD). Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in 5-HT biosynthesis. Two isoforms are known, TPH-1 and TPH-2. TPH-1 has been correlated to various psychiatric and behavioral disorders by gene polymorphism association studies. We aimed to determine whether specific TPH-1 haplotypes associate with BPD. A case-control design was employed. The control group included 98 women without psychiatric history. In all, 95 patients were included, all Caucasian women with a BPD diagnosis who had attempted suicide at least twice during their lifetime. Exclusion criteria were: (i) substance dependence; (ii) dementia or other irreversible organic brain syndromes; (iii) psychotic disorders or major depressive illness with melancholic features; (iv) life-threatening eating disorders. Six single-nucleotide polymorphisms (SNPs) were found at significant linkage disequilibrium across 23 kb of the TPH-1 gene in both patients and controls, suggesting a haplotype block structure. While no individual SNP showed association, several haplotypes associated with the BPD group. In particular, one six-SNP haplotype was absent from the control group while representing about one-quarter of all haplotypes in the BPD group (corrected P<<10(-5)). A 'sliding window' analysis attributed the strongest disease association to haplotype configurations located between the gene promoter and intron 3. We conclude that TPH-1 associates with BPD in suicidal women. Our data support the expectation that haplotype analysis is superior to single locus analysis in gene-disease, case-control association studies.

Neuroendocrine mechanisms of innate states of attenuated responsiveness of the hypothalamo-pituitary adrenal axis to stress

Neuroendocrine responses to stress vary between sexes and reproductive states and are influenced by the type of stressor. Stress responses are attenuated in some physiological states, such as lactation and conditions of low visceral adipose tissue. Moreover, some individuals within a species characteristically display reduced stress responses. The neuroendocrine mechanisms for stress hyporesponsiveness are likely to include reduced synthesis and secretion of corticotropin releasing hormone (CRH) and arginine vasopressin (AVP) from the hypothalamus as a result of enhanced glucocorticoid negative feedback and/or reduced noradrenergic stimulatory input from the brain stem. A major limitation of research to date is the lack of direct measures of CRH and AVP secretion. Attenuated stress responsiveness is also commonly associated with reduced pituitary responsiveness to CRH and AVP. The possible roles of inhibitory central inputs to CRH and AVP neurons and of oxytocin and prolactin in attenuating the HPA axis responses to stress are unknown.

Effects of cytokines and infections on brain neurochemistry

Administration of cytokines to animals can elicit many effects on the brain, particularly neuroendocrine and behavioral effects. Cytokine administration also alters neurotransmission, which may underlie these effects. The most well studied effect is the activation of the hypothalamo-pituitary-adrenocortical (HPA) axis, especially that by interleukin-1 (IL-1). Peripheral and central administration of IL-1 also induces norepinephrine (NE) release in the brain, most markedly in the hypothalamus. Small changes in brain dopamine (DA) are occasionally observed, but these effects are not regionally selective. IL-1 also increases brain concentrations of tryptophan, and the metabolism of serotonin (5-HT) throughout the brain in a regionally nonselective manner. Increases of tryptophan and 5-HT, but not NE, are also elicited by IL-6, which also activates the HPA axis, although it is much less potent in these respects than IL-1. IL-2 has modest effects on DA, NE and 5-HT. Like IL-6, tumor necrosis factor-α (TNFα) activates the HPA axis, but affects NE and tryptophan only at high doses. The interferons (IFN's) induce fever and HPA axis activation in man, but such effects are weak or absent in rodents. The reported effects of IFN's on brain catecholamines and serotonin have been very varied. However, interferon-γ, and to a lesser extent, interferon-α, have profound effects on the catabolism of tryptophan, effectively reducing its concentration in plasma, and may thus limit brain 5-HT synthesis.Administration of endotoxin (LPS) elicits responses similar to those of IL-1. Bacterial and viral infections induce HPA activation, and also increase brain NE and 5-HT metabolism and brain tryptophan. Typically, there is also behavioral depression. These effects are strikingly similar to those of IL-1, suggesting that IL-1 secretion, which accompanies many infections, may mediate these responses. Studies with IL-1 antagonists, support this possibility, although in most cases the antagonism is incomplete, suggesting the existence of multiple mechanisms. Because LPS is known to stimulate the secretion of IL-1, IL-6 and TNFα, it seems likely that these cytokines mediate at least some of the responses, but studies with antagonists indicate that there are multiple mechanisms. The neurochemical responses to cytokines are likely to underlie the endocrine and behavioral responses. The NE response to IL-1 appears to be instrumental in the HPA activation, but other mechanisms exist. Neither the noradrenergic nor the serotonergic systems appear to be involved in the major behavioral responses. The significance of the serotonin response is unknown.

Diet rich in alpha-lactalbumin improves memory in unmedicated recovered depressed patients and matched controls

Depression is associated with reduced brain serotonin (5-hydroxytryptamine; 5-HT) function and with cognitive dysfunctions. A diet rich in alpha-lactalbumin protein has been found to increase the ratio tryptophan /large neutral amino acids (Trp/SigmaLNAA), and to improve cognitive functioning in individuals with high neuroticism scores. Since cognitive dysfunctions sometimes persist after remission of depression, the present study investigated the effects of alpha-lactalbumin-enriched diet on cognition in recovered depressed patients. Twenty-three recovered depressed patients and 20 healthy matched controls without a history of depression consumed meals rich in alpha-lactalbumin or casein protein in a double-blind crossover design. Mood, cognitive function and plasma amino acids were assessed at both sessions before and after dietary intake. Alpha-lactalbumin protein had no effect on mood, but improved abstract visual memory and impaired simple motor performance. These effects were independent of history of depression. Supplements of lactalbumin may be useful for nutrition research in relation to age- or disease-related memory decline. The present findings should be further examined in different (e.g. medicated) samples. The long-term effects of alpha-lactalbumin should also be investigated.

Altered hypothalamo-pituitary-adrenal and sympatho-adrenomedullary activities in rats bred for high anxiety: central and peripheral correlates

Wistar rats have been selectively bred for high (HABs) or low (LABs) anxiety-related behavior based on results obtained in the elevated-plus maze. They also display robust behavioral differences in a variety of additional anxiety tests. The present study was undertaken to further characterize physiological substrates that contribute to the expression of this anxious trait. We report changes in brain and peripheral structures involved in the regulation of both the hypothalamo-pituitary-adrenal (HPA) and sympatho-adrenal systems. Following exposure to a mild stressor, HABs displayed a hyper-reactivity of the HPA axis associated with a hypo-reactivity of the sympatho-adrenal system and a lower serotonin turnover in the lateral septum and amygdala. At rest, HABs showed a higher adrenal weight and lower tyrosine hydroxylase and phenylethanolamine-N-methyltransferase mRNAs expression in their adrenals than LABs. In the anterior pituitary, HABs also exhibited increased proopiomelanocortin and decreased vasopressin V1b receptor mRNAs expression, whereas glucocorticoid receptor mRNA levels remained unchanged. These results indicate that the behavioral phenotype of HABs is associated with peripheral and central alterations of endocrine mechanisms involved in stress response regulation. Data are discussed in relation to coping strategies adopted to manage stressful situations. In conclusion, HABs can be considered as an useful model to study the etiology and pathophysiology of stress-related disorders and their neuroendocrine substrates.

Effects of anpirtoline on regional serotonin synthesis in the rat brain: an autoradiographic study

Anpirtoline has been described as an agonist at 5-HT1B receptors with a relatively high potency. It also acts as an agonist at 5-HT1A receptors, but has a lower potency than at the 5-HT1B sites. There is very little known about the mechanism by which anpirtoline influences regional 5-HT synthesis. The aim of the present study was to investigate the effects of acutely and chronically administered anpirtoline on 5-HT synthesis in the rat brain using the autoradiographic alpha-[14C]methyl-L-tryptophan method. In the acute study, anpirtoline (2.0 mg/kg) was administered intraperitoneally 30 min before the tracer injection. The control rats were injected with the same volume of saline. In the chronic study, anpirtoline (2 mg/kg per day) was injected subcutaneously in saline once a day for 10 days. There were no significant differences between the plasma-free and total tryptophan concentrations between the anpirtoline treatment and the respective control groups. In the acute experiment, 5-HT synthesis rates in all of the brain areas investigated were significantly decreased by anpirtoline when compared to the saline-treated group. In the chronic anpirtoline experiment, 5-HT synthesis rates of almost all of the projection areas, as well as the raphe nuclei, were normalized or had a tendency to be normalized. These results suggest that it is likely that the terminal 5-HT1B receptors are involved in the regulation of 5-HT synthesis in the projection areas and that 5-HT synthesis, in the raphe, is likely influenced by anpirtoline's 5-HT1A and/or 5-HT1B agonistic properties.

What is the functional significance of chronic stress-induced CA3 dendritic retraction within the hippocampus?

Chronic stress produces consistent and reversible changes within the dendritic arbors of CA3 hippocampal neurons, characterized by decreased dendritic length and reduced branch number. This chronic stress-induced dendritic retraction has traditionally corresponded to hippocampus-dependent spatial memory deficits. However, anomalous findings have raised doubts as to whether a CA3 dendritic retraction is sufficient to compromise hippocampal function. The purpose of this review is to outline the mechanism underlying chronic stress-induced CA3 dendritic retraction and to explain why CA3 dendritic retraction has been thought to mediate spatial memory. The anomalous findings provide support for a modified hypothesis, in which chronic stress is proposed to induce CA3 dendritic retraction, which then disrupts hypothalamic-pituitary-adrenal axis activity, leading to dysregulated glucocorticoid release. The combination of hippocampal CA3 dendritic retraction and elevated glucocorticoid release contributes to impaired spatial memory. These findings are presented in the context of clinical conditions associated with elevated glucocorticoids.

Haplotype analysis reveals tryptophan hydroxylase (TPH) 1 gene variants associated with major depression

BACKGROUND

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin (5-HT) and might be related to the pathogenesis of major depression (MD). Two isoforms are known, TPH-1 and TPH-2. Tryptophan hydroxylase-1 association with MD is still debated.

METHODS

A single nucleotide polymorphism (SNP) screening strategy was used to define TPH-1 haplotypes spanning over 23 kilobase (kb) of the 29 kb gene length. Genotyping was performed in 228 MD patients and 253 healthy control subjects.

RESULTS

Six SNPs were found at linkage disequilibrium in both patients and control subjects, suggesting a haplotype block structure. Single marker association analyses showed only one SNP significantly associated with MD. Several haplotypes were associated with MD. When all six locus haplotypes were divided into two groups, above or below a 5% threshold, the compound haplotype group below a 5% frequency resulted as associated with the disease (31.6% vs. 18.0% in control subjects, p < 10(-5)). A "sliding window" analysis attributed the strongest disease association to a haplotype configuration localized between introns 7 and 8 (p < 10(-5)).

CONCLUSIONS

Haplotype analysis indicates that TPH-1 associates with MD. The most common TPH-1 variants appear to carry no risk, while some of the less frequent variants might contribute to genetic predisposition to MD.

The tryptophan hydroxylase activation inhibitor, AGN-2979, decreases regional 5-HT synthesis in the rat brain measured with alpha-[14C]methyl-L-tryptophan: an autoradiographic study

Many experimental conditions are stressful for animals. It is well known that stress induces tryptophan hydroxylase (TPH) activation, resulting in increased serotonin (5-HT) synthesis. In our experimental procedure to measure 5-HT synthesis using alpha-[(14)C]methyl-L-tryptophan (alpha-MTrp) autoradiographic method, the hind limbs of animals are restrained using a loose-fitted plaster cast such that the forelimbs of the animal remain free. The objective of the present investigation was to evaluate the changes, if any, in 5-HT synthesis, after injecting these restrained rats with the TPH activation inhibitor AGN-2979. The effect on regional 5-HT synthesis was studied using the alpha-MTrp autoradiographic method. The hypothesis was that the TPH activation inhibitor would reduce 5-HT synthesis, if TPH activation was induced by this restraint. The rats received injection of AGN-2979 (10 mg/kg, i.p.) or distilled water vehicle (1 mL/kg, i.p.) 1 h prior to tracer administration. The free- and total tryptophan concentrations were not significantly different between the treatment and control groups. The results demonstrate that 5-HT synthesis in AGN-2979 treated rats is significantly decreased (-12 to -35%) in both the raphe nuclei and their terminal areas when compared to the control rats. These findings suggest that restrained conditions, such as those used in our experimental protocol, induce TPH activation resulting in an increased 5-HT synthesis throughout the brain. The reduction in 5-HT synthesis in the AGN-2979 group is not related to a change in the plasma tryptophan. Because there was no activation in the pineal body, the structure having a different isoform of TPH, we can propose that it is only the brain TPH that becomes activated with this specific restraint.

Role of sex and sex steroids in mediating pituitary-adrenal responses to acute buspirone treatment in sheep

Systematic characterisation of sex differences in the serotonergic modulation of the hypothalamic-pituitary-adrenal (HPA) axis may assist with our understanding of why stress-related disorders are disproportionately represented in women. In this study, we examined the acute effects of buspirone, a serotonergic 1A receptor subtype agonist, on the endocrine endpoints of adrenocorticotrophin (ACTH) and cortisol secretion in gonadectomised male and female sheep. Each sheep was treated with an acute i.v. injection containing vehicle or buspirone (0.03, 0.1 and 0.3 mg/kg) in the presence and absence of sex steroid replacement (SSR). In males, SSR treatment consisted of testosterone (2 x 200 mg s.c. pellets) and, in females, the mid-luteal phase of the oestrus cycle was simulated by treatment with oestradiol (1 cm s.c. implant) and an intravaginal controlled internal drug release device containing 0.3 g progesterone. ACTH, cortisol, testosterone and progesterone were measured in jugular blood. Basal ACTH levels were higher in males, whereas basal cortisol levels were higher in females, regardless of sex steroid status. The magnitude of the increase in ACTH and cortisol secretion following buspirone treatment was dose-dependent. There were no differences in the ACTH responses of males and females to buspirone treatment, either in the presence or absence of sex steroid replacement. However, although the cortisol response to buspirone was greater in females, there was no discernable effect of sex steroid status in addition to this sex difference on either basal or buspirone-stimulated cortisol release. We conclude that the larger basal and buspirone-stimulated cortisol response measured in females may reflect a sex difference, either in the sensitivity of the adrenal gland to ACTH or in the catecholaminergic innervation of the adrenal gland. The lack of effect of sex and sex steroids in the ACTH secretory response to buspirone may indicate that the sex differences in serotonergic modulation of the HPA axis, as reported previously by our group, were mediated via serotonergic receptor subtypes other than the 1A receptor.

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.

Modulation of aggressive behaviour by fighting experience: mechanisms and contest outcomes

Experience in aggressive contests often affects behaviour during, and the outcome of, later contests. This review discusses evidence for, variations in, and consequences of such effects. Generally, prior winning experiences increase, and prior losing experiences decrease, the probability of winning in later contests, reflecting modifications of expected fighting ability. We examine differences in the methodologies used to study experience effects, and the relative importance and persistence of winning and losing experiences within and across taxa. We review the voluminous, but somewhat disconnected, literature on the neuroendocrine mechanisms that mediate experience effects. Most studies focus on only one of a number of possible mechanisms without providing a comprehensive view of how these mechanisms are integrated into overt behaviour. More carefully controlled work on the mechanisms underlying experience effects is needed before firm conclusions can be drawn. Behavioural changes during contests that relate to prior experience fall into two general categories. Losing experiences decrease willingness to engage in a contest while winning experiences increase willingness to escalate a contest. As expected from the sequential assessment model of contest behaviour, experiences become less important to outcomes of contests that escalate to physical fighting.A limited number of studies indicate that integration of multiple experiences can influence current contest behaviour. Details of multiple experience integration for any species are virtually unknown. We propose a simple additive model for this integration of multiple experiences into an individual's expected fighting ability. The model accounts for different magnitudes of experience effects and the possible decline in experience effects over time. Predicting contest outcomes based on prior experiences requires an algorithm that translates experience differences into contest outcomes. We propose two general types of model, one based solely on individual differences in integrated multiple experiences and the other based on the probability contests reach the escalated phase. The difference models include four algorithms reflecting possible decision rules that convert the perceived fighting abilities of two rivals into their probabilities of winning. The second type of algorithm focuses on how experience influences the probability that a subsequent contest will escalate and the fact that escalated contests may not be influenced by prior experience. Neither type of algorithm has been systematically investigated.Finally, we review models for the formation of dominance hierarchies that assume that prior experience influences contest outcome. Numerous models have reached varied conclusions depending on which factors examined in this review are included. We know relatively little about the importance of and variation in experience effects in nature and how they influence the dynamics of aggressive interactions in social groups and random assemblages of individuals. Researchers should be very active in this area in the next decade. The role of experience must be integrated with other influences on contest outcome, such as prior residency, to arrive at a more complete picture of variations in contest outcomes. We expect that this integrated view will be important in understanding other types of interactions between individuals, such as mating and predator-prey interactions, that also are affected significantly by prior experiences.

Does Individual Variation in Stress Responses and Agonistic Behavior Reflect Divergent Stress Coping Strategies in Juvenile Rainbow Trout?

Individual rainbow trout were transferred to visual isolation in experimental aquaria. As a measure of the speed of acclimation, individual food intake was quantified during the first 6 d following transfer. Following acclimation, aggression was quantified by subjecting the fish to three resident-intruder tests, with 30 d of recovery between the tests. Moreover, between the resident-intruder tests (i.e., two times) the fish were exposed to an unfamiliar environment and their cortisol response was measured. The results of this study show that individuals of juvenile rainbow trout differ distinctly in their response to changes in their environment, and that this diversity in behavior is reflected by consistent behavioral traits displayed by individual fish. These traits have proven to be consistent not only over time but also across situations, revealing two distinct behavioral profiles, in the same manner as shown in studies on proactive and reactive mammals. Our results also show that the reactivity of the hypothalamic-pituitary-interrenal (HPI) axis, when exposed to a stressor, is a consistent physiological trait in juvenile rainbow trout. We found that difference in HPI axis reactivity is linked to the different behavioral profiles. However, HPI axis reactivity could not be linked directly to the singular behavioral traits measured. In other words, we did not find that the consistent behavioral traits shown by the fish were associated with a difference in HPI axis reactivity in the same manner as the reactivity of the hypothalamic-pituitary-adrenocortical axis does in mammals. Taken together, our results show that stress coping strategies akin to what has been described as reactive and proactive stress coping in mammals appear to exist in juvenile rainbow trout.

Acute noise stress analgesia in relation to 5-HT2 and μ-opioid receptor changes in the frontal cortex of young mice

A number of studies have reported that exposure to stress provoked behavioural changes, including analgesia, in rodents. Differences have been observed in these responses to different types of stress and a link between hormones and neurotransmitters proposed. We studied the effect of acute noise stress on nociception and the possible changes in the serotonergic and opioidergic systems in young mice of both sexes. Naloxone pre-treatment was also investigated. Noise stress was produced by a sound source, nociception was measured by the hot-plate test and binding characteristics were evaluated by a radioligand binding technique using membrane preparation from the total frontal cortex. Acute noise stress provoked an antinociceptive effect, associated with an increase in plasma corticosterone levels, a decrease in the number of 5-HT2 receptors in stressed male and female mice and a decrease in the number of mu receptors in both sexes. The behavioural and biochemical effects were antagonized by 1 mg/kg of naloxone. Acute noise stress behaves like other types of stress on nociception. The opioidergic system seems to be involved in this behaviour but also the serotonergic system may play a role. Sex differences were detected in the number of 5-HT2 and mu receptors between male and female mice not subjected to stress, while the percentage decrease in 5-HT2 and mu receptors did not differ significantly between the two sexes.

Cortisol and cytokines in chronic and treatment-resistant patients with schizophrenia: association with psychopathology and response to antipsychotics

The bilateral communication between the immune and neuroendocrine systems plays an essential role in modulating the adequate response of the hypothalamic-pituitary-adrenal (HPA) axis to the stimulatory influence of cytokines and stress-related mediators. Growing evidence suggests that neuro-immune-endocrine crosstalk may be impaired in schizophrenia. We determined the relationship between cortisol, cytokines interleukin-2 (IL-2) and interleukin-6 (IL-6), and symptoms in schizophrenia during treatment with typical and atypical antipsychotic drugs. Subjects included 30 healthy controls (HC) and 78 schizophrenic (SCH) in-patients. SCH were randomly assigned to 12-week treatment with 6 mg/day of risperidone or 20 mg/day of haloperidol using a double-blind design. Clinical efficacy was determined using the Positive and Negative Syndrome Scale (PANSS). Serum cortisol and IL-2 levels were assayed by radioimmunometric assay, and serum IL-6 levels by quantitative enzyme-linked immunosorbent assay. Following a 2-week washout period, serum levels of cortisol, IL-2, and IL-6 were increased in patients with schizophrenia compared to HC. Elevations in cortisol were associated with increase in both IL-2 and IL-6 in SCH. Moreover, elevations in cortisol were associated with negative symptoms and IL-2 with positive symptoms. In all, 12 weeks of risperidone treatment significantly decreased elevated cortisol and improved negative symptoms, but produced similar effects on IL-2 and IL-6 as well as on positive symptoms compared to haloperidol. The improvement of negative symptoms was related to the change in cortisol. Our results suggest that the imbalance in the HPA axis and cytokine system in patients with SCH is implicated in clinical symptoms, and is improved with atypical antipsychotic treatment.

Serotonin, but not melatonin, plays a role in shaping dominant-subordinate relationships and aggression in rainbow trout

The aim of this study was to clarify to what extent the effects of elevated dietary L-tryptophan (Trp) on aggressive behavior and stress responsiveness in rainbow trout are mediated by circulating melatonin and central serotonin (5-HT), respectively. Isolated rainbow trout were paired for 1h a day for 7 days in order to create fish with experience of being dominant and subordinate. Following this week, the fish were tested for aggressive behavior using a resident-intruder test after which they were subjected to one of four treatments: (1) tryptophan, (2) the selective serotonin reuptake inhibitor (SSRI) citalopram, (3) melatonin, and (4) no treatment (controls). After 7 days of treatment, the fish were subjected to a second resident-intruder test. Trp-supplemented feed resulted in a suppression of aggressive behavior in fish with experience of being dominant. Moreover, fish fed Trp-supplemented feed, regardless of social experience, also displayed lower plasma cortisol levels than controls. These effects of elevated dietary Trp were closely mimicked by citalopram treatment, whereas exogenous melatonin had no effect on either aggressive behavior or plasma cortisol. Thus, the effect of elevated dietary Trp on aggressive behavior and stress responses does not appear to be mediated by melatonin even though elevated dietary intake of Trp resulted in an increase in plasma melatonin concentrations.

The effects of cortisol administration on social status and brain monoaminergic activity in rainbow troutOncorhynchus mykiss

The hypothesis that circulating cortisol levels influence the outcome of social interactions in rainbow trout was tested. Juvenile rainbow trout Oncorhynchus mykiss were given a single intraperitoneal (i.p.)implant containing either cortisol (110 mg kg–1 fish), or cortisol plus the glucocorticoid receptor antagonist RU486 (mifepristone; 1100 mg kg–1 fish), and sampled after 5 days of social interactions with either a similar sized (&lt;1.5% difference in fork length)or smaller conspecific (&gt;5% difference). Within size-matched pairs of fish,cortisol treatment significantly increased the probability that the treated fish within each pair became subordinate, an effect that was abolished by simultaneous administration of RU486. Cortisol treatment also reduced the usual success of the larger fish within a pair to preferentially become dominant from 86% to 40% of pairs. To investigate one potential mechanism underlying the apparent effect of cortisol in predisposing trout to low social status, fish were treated with cortisol or cortisol+RU486 for 5 days, after which brain monoamines [5-hydroxytryptamine (5-HT); dopamine (DA)] and their major metabolites [5-hydroxyindolacetic acid (5-HIAA);3,4-dihydroxy-phenylacetic acid (DOPAC)] were measured. Significant increases of serotonergic activity ([5-HIAA]/[5-HT] ratio) were detected in the telencephalon with cortisol treatment, an effect that was eliminated by simultaneous administration of RU486. Also, cortisol treatment significantly decreased dopaminergic activity in the telencephalon. Somewhat surprisingly,the effects of cortisol treatment on monoaminergic activity in the hypothalamus were opposite to those in the telencephalon. Moreover, in no case did administration of RU486 abolish these effects. These results suggest that the effects of cortisol on social status in rainbow trout may be mediated via the modulation of central signaling systems and subsequent changes in behaviour and/or competitive ability, although the exact site of action in the brain remains uncertain.

Increased urinary excretion rates of serotonin and metabolites during bedrest

Astronauts are often on a voluntarily reduced energy intake during space missions, possibly caused by a metabolic or emotional stress response with involvement of the central serotonergic system (SES). We investigated 24 h urinary excretion (24 h-E) of serotonin (5-HT) and 5-hydroxyindol acidic acid as indicators of the SES in healthy males under two different normocaloric conditions: normal physical activity (NPA) and -6 degree head-down-tilt (HDT). HDT or NPA were randomly arranged with a recovery period of 6 months in between. 24 h-E of hormones varied widely among individuals. Values were higher in HDT compared to NPA. Assuming that the 24 h-E values are, beside being indicators for alterations in the number and metabolism of platelets. Also indicators of central SES, HDT condition seems to activate central SES in a higher degree compared to NPA. Therefore, changes in central SES might be involved in the mechanisms associated with space flight or microgravity, including possible maladaptations such as voluntary undernutrition.

A serotonin receptor antagonist, but not melatonin, modulates hormonal responses to capture stress in two populations of garter snakes (Thamnophis sirtalis parietalis and Thamnophis sirtalis concinnus)

Hormonal and behavioral responses to a stressor depend on many factors, including the influence of other hormones. We examined the role of melatonin in modulating hormonal responses to capture stress in two populations of male garter snakes, Thamnophis sirtalis. Studies of red-sided (T. sirtalis parietalis) and red-spotted (T. sirtalis concinnus) garter snakes were conducted in the field with free-living snakes. Populations of red-sided garter snakes in south-central Manitoba, Canada undergo a period of winter dormancy for approximately 8 months each year followed by an attenuated mating season (4-5 weeks) in early spring. In contrast, the mid-latitude red-spotted garter snake in western Oregon, USA has an extended breeding season and can be active during 10-12 months of the year given appropriate environmental conditions. We chose to study these two populations of garter snakes to investigate possible variation in melatonin function among snakes with different suites of environmental adaptations. To better address these questions, we also examined the effects of 5-hydroxytryptophan (a precursor of melatonin synthesis) and ketanserin (a serotonergic type 2A receptor antagonist) on hormonal responses to capture stress. We observed a trend of increased corticosterone and decreased androgen concentrations in northern-latitude red-sided garter snakes (T. sirtalis parietalis) subjected to 4 h of capture stress during the spring. However, these differences were not statistically significant. During the fall, red-sided garter snakes showed no change in corticosterone or androgen concentrations in response to the capture stress treatments. We speculate that northern-latitude red-sided garter snakes suppress hormonal responses to capture stress during preparation for winter dormancy. Treatment with melatonin, 5-hydroxytryptophan, or ketanserin did not significantly influence corticosterone or androgen concentrations of northern-latitude red-sided garter snakes during the spring or fall. Mid-latitude red-spotted garter snakes (T. sirtalis concinnus) from Oregon showed a statistically significant increase in corticosterone concentrations in response to 4 h of capture stress; treatment with melatonin, 5-hydroxytryptophan, or ketanserin prior to capture stress had no significant influence on plasma corticosterone concentrations. Androgen concentrations of mid-latitude red-spotted garter snakes in response to capture stress were significantly lower than those of non-stressed control snakes. Neither melatonin nor 5-hydroxytryptophan influenced the change in androgen concentrations during capture stress. However, androgen concentrations of snakes treated with ketanserin prior to 4 h of capture stress did not differ significantly from those of non-stressed control snakes. These studies suggest that melatonin does not modulate hormonal responses to capture stress in this ectothermic model. Our results also suggest that a serotonin-regulated system may play a role in modulating the activity of the hypothalamic-pituitary-gonadal axis during physiological stress responses.

Differential regulation of serotonin (5HT)2A receptor mRNA and protein levels after single and repeated stress in rat brain: role in learned helplessness behavior

Stress-induced learned helplessness in animals serves as a model of behavioral depression and other stress-related disorders. Our recent report that repeated stress prolongs the duration of learned helplessness behavior in rats may be important since acute and recurrent disorders may have different responsive mechanisms. To examine the role of serotonergic (5HT) mechanisms in such behavior, we studied the expression of 5HT2A receptors in different brain areas of rats, and further investigated whether the alterations in expression of 5HT2A receptors are similar after single versus repeated stress. Rats exposed to inescapable shock once on day 1, or twice, on day 1 and day 7, were tested for escape latency on days 2 and 4, or day 14, respectively. Higher escape latencies were observed on day 2 after single, and on day 14 after repeated shock. Whereas the single-stress paradigm produced a significant decrease of 5HT2A receptor mRNA and protein expression in hippocampus of non-learned helpless and learned helpless rats as compared with tested controls, repeated stress resulted in increase in frontal cortex but decrease in hippocampus and hypothalamus of learned helpless rats only, as compared with tested control rats. These results demonstrate differential regulation of 5HT2A receptors in LH rats after single and repeated stress, which may be critical in the pathophysiology of depression/other stress-related disorders.

Influence of forced swimming stress on 5-HT1A receptors and serotonin levels in mouse brain

Several stressful factors are able to modify 5-HT1A receptors; for example, different schemes of forced swimming-induced stress (FS) produce a variety of changes in synthesis as well as in 5-HT1A binding in the brain. In addition, it is known that the concentration of 5-HT in the brain is modified as a consequence of acute stressing. The main purpose of this study was to characterize the influence of 15 min of FS on 5-HT levels and on 5-HT1A receptor density in specific brain areas. Mice stressed 24 h before were sacrificed and their brains processed by means of a quantitative autoradiography technique. The following areas were studied: dorsal raphe nucleus (DRN); median raphe nucleus (MRN); thalamus; hypothalamus; amygdala, and hippocampus. 5-HT and 5-hydroxyindolacetic acid (5-HIAA) concentrations in the brainstem, thalamus-hypothalamus, and hippocampus of stressed (ST) mice were analyzed 24 h after stressing by high performance liquid chromatography (HPLC) with fluorometric detection. All data were compared with corresponding unstressed (UST) controls. A significant decrease in 5-HT1A receptor density in DRN, MRN, and hippocampus, accompanied by an increase in labeling of 5-HT1A receptor in thalamus, hypothalamus, and amygdala was observed in ST animals. FS induced a decrease in the 5-HT concentration in the thalamus-hypothalamus, accompanied by an increase in hippocampus areas without affecting 5-HT concentration in the brainstem. Additionally, 5-HIAA/5-HT ratio in the thalamus-hypothalamus area was increased. This study showed that stress alters both 5-HT concentration and 5-HT1A receptors in a region-specific manner.

Brain 5-HT1A receptor binding in chronic fatigue syndrome measured using positron emission tomography and [11C]WAY-100635

BACKGROUND

Research from neuroendocrine challenge and other indirect studies has suggested increased central 5-HT function in chronic fatigue syndrome (CFS) and increased 5-HT1A receptor sensitivity. We assessed brain 5-HT1A receptor binding potential directly using the specific radioligand [11C]WAY-100635 and positron emission tomography (PET).

METHODS

We selected 10 patients from a tertiary referral clinic who fulfilled the CDC consensus criteria for CFS. To assemble a homogenous group and avoid confounding effects, we enrolled only subjects who were completely medication-free and did not have current comorbid psychiatric illness. We also scanned 10 healthy control subjects.

RESULTS

There was a widespread reduction in 5-HT1A receptor binding potential in CFS relative to control subjects. This was particularly marked in the hippocampus bilaterally, where a 23% reduction was observed.

CONCLUSIONS

There is evidence of decreased 5-HT1A receptor number or affinity in CFS. This may be a primary feature of CFS, related to the underlying pathophysiology, or a finding secondary to other processes, such as previous depression, other biological changes or the behavioral consequences of CFS.

Acute fluoxetine administration differentially affects brain C-Fos expression in fasted and refed rats

In the present study we investigated the effect of acute fluoxetine administration on the expression of c-Fos in the rat brain under two different metabolic conditions: fed and fasting states. Wistar male rats, weighing 220+/-30g, received i.p. injections of saline solution or fluoxetine (10mg/kg), and were killed 2 h later. The brains were removed after transcardiac perfusion with phosphate-buffered saline followed by paraformaldehyde, and were then processed for immunohistochemistry. Fos-like immunoreactivity was quantified by a computerized system. Fasted animals faced an 18-h suppression of food intake, while fed groups were submitted to an initial 14-h period of fast followed by a 4-h period in which food was freely available. Both in fasting and fed states, fluoxetine-treated animals presented a significant increase in c-Fos expression in hypothalamic areas, limbic structures, circumventricular areas, and in mesencephalic and rhomboencephalic regions, as compared with saline-treated controls. The quantitative comparison of data obtained from fasted and fed animals showed that fasted rats treated with fluoxetine presented a higher c-Fos expression in the ventromedial hypothalamus and the paraventricular nuclei compared with the fed group, while in fluoxetine-treated fed rats c-Fos expression was higher in the arcuate nuclei, medial amygdala, locus coeruleus and dorsal raphe nuclei, as compared with fasted, fluoxetine-treated animals. These data indicate that the metabolic condition of the animals significantly modifies fluoxetine-induced brain c-Fos expression, suggesting that visceral and behavioral fluoxetine effects may be influenced by the metabolic state of the individual.

Decreased hippocampal 5-HT(2A) receptor binding in older depressed patients using [18F]altanserin positron emission tomography

Serotonin receptor changes have been associated with the pathophysiology and treatment of major depression. Only one other study has investigated serotonin receptor changes in older depressed patients. We used positron emission tomography (PET) and [18F]altanserin, a ligand with high affinity for the 5-HT(2A) receptor, to examine the relationship between 5-HT(2A) receptor density and depression. Depressed subjects (n = 16), age > 50 years, were recruited as part of a larger study. Older depressed subjects consisted of early-onset recurrent depression (EORD, n = 11) and late-onset depression (LOD, n = 5). An age-matched control group (n = 9) was also recruited. All subjects were right-handed, nonsmokers and antidepressant-free. Regions of interest were determined on a summed MPRAGE scan transformed into Talairach space and coregistered with the PET images. Depressed subjects had less hippocampal 5-HT(2A) receptor binding than controls (p = 0.05). No significant differences in receptor binding were found between EORD and LOD subjects. Depressed subjects not previously treated for depression (n = 6) had less hippocampal 5-HT(2A) receptor binding (p = 0.04) than previously treated subjects (n = 10). It may be that prior medication treatment provides a compensatory upregulation of the 5-HT(2A) receptor.

Effects of melatonin on the behavioral and hormonal responses of red-sided garter snakes (Thamnophis sirtalis parietalis) to exogenous corticosterone

We investigated possible interactions between melatonin and corticosterone in modulating the reproductive behavior of male red-sided garter snakes (Thamnophis sirtalis parietalis) following spring emergence. We also examined whether melatonin's modulatory actions could be explained by its potential properties as a serotonin receptor antagonist. Exogenous corticosterone significantly reduced courtship behavior of male snakes in a dose-dependent manner. Melatonin also significantly reduced courtship behavior of male garter snakes. Pretreatment with melatonin before administering corticosterone treatments further suppressed courtship behavior of red-sided garter snakes. These results indicate additive inhibitory effects of melatonin and corticosterone in modulating reproductive behavior. Snakes receiving ketanserin, a serotonergic type 2A receptor antagonist, followed by corticosterone also showed reduced courtship behavior; this serotonin receptor antagonist followed by treatment with vehicle did not significantly influence courtship behavior of male snakes. Neither melatonin nor corticosterone treatments significantly influenced testosterone + 5-alpha-dihydrotestosterone concentrations of male garter snakes, supporting a direct effect of melatonin and corticosterone on courtship behavior that is independent of any effect on androgen concentrations. We propose that a serotonin system is involved in the modulation of male courtship behavior by melatonin and corticosterone. In addition, our data support the hypothesis that melatonin may function as a serotonin receptor antagonist. Further research is necessary to discern whether the actions of melatonin and corticosterone are converging on the same pathway or if their effects on different pathways are having additive inhibitory effects on courtship behavior.

Cognition in mania and depression: psychological models and clinical implications

Affective disorders, including bipolar disorder and major depressive disorder, are highly prevalent throughout the world and are extremely disabling. Diagnostic and Statistical Manual criteria and psychological models strongly implicate cognitive dysfunctions as being integral to our understanding of these disorders. We review the findings from studies that have used neurocognitive tests and functional imaging techniques to explore abnormal cognition in affective disorders. In particular, we highlight the evidence for cognitive dysfunctions that persist into full clinical remission, and the recent trend toward the use of "hot" processing tasks, involving emotionally charged stimuli, as a means of differentiating between the cognitive underpinnings of mania and depression. The clinical relevance of these developments is discussed.

Glucocorticoid receptors are involved in the regulation of pulsatile urea excretion in toadfish

The objectives of this study were to characterize the pattern of pulsatile urea excretion in the gulf toadfish in the wake of exogenous cortisol loading and to determine the receptors involved in the regulation of this mechanism. Toadfish were fitted with indwelling arterial catheters and were infused with isosmotic NaCl for 48 h after which fish were treated with cortisol alone, cortisol + peanut oil, cortisol + RU486 (a glucocorticoid receptor antagonist) or cortisol + spironolactone (a mineralocorticoid receptor antagonist). Upon cortisol loading, fish treated with cortisol alone, cortisol + oil or cortisol + spironolactone experienced a two- to threefold reduction in pulsatile urea excretion. This reduction was due to a decrease in urea pulse size with no effect on pulse frequency compared to values measured during the control NaCl infusion period. In addition, these fish showed an increase in plasma urea concentrations upon treatment. These apparent effects of cortisol treatment were abolished in fish treated with cortisol + RU486. In contrast, these fish showed an increase in pulsatile urea excretion mediated by a twofold increase in pulse size with no change in frequency. Likewise, fish treated with cortisol + RU486 showed a significant decrease in plasma urea concentrations over the course of the experiment. The findings of this study indicate that high levels of cortisol reduce pulsatile urea excretion by decreasing pulse size. In addition, it appears that glucocorticoid receptors and not mineralocorticoid receptors are involved in the regulation of the toadfish pulsatile urea excretion mechanism.

Opposite morphological responses of partially denervated cortical serotonergic and noradrenergic axons to repeated stress in adult rats

We examined plastic changes in serotonin (5-HT) axons following repeated stress in the adult rat brain, and compared stress-induced changes between 5-HT and noradrenaline (NA) axons. We locally injected the specific neurotoxin to 5-HT axons or to NA axons into the frontal cortex to cause partial denervation. The animals were mildly restrained from 1 day after the neurotoxin injection and this stress was repeated daily for 20 min during the first 2 days and for 40 min during the next 11 days. On the fourteenth day after injection, the brains were removed to visualize 5-HT and NA axons by immunohistochemistry. Repeated stress did not significantly alter the denervation area of 5-HT or NA axons, but the density of 5-HT axons was increased whereas that of NA axons was decreased in cortical regions outside the denervation site. In addition, the expression of brain-derived neurotrophic factor (BDNF) was increased in cortical regions where the 5-HT axon density was increased in response to stress. These results suggest that repeated stress causes opposite changes in the morphology of partially denervated 5-HT and NA axons in the cerebral cortex. The stress-induced increase in BDNF expression may contribute to 5-HT axon sprouting following repeated stress.

Role of maternal adrenal glands on the developing serotoninergic and aminoacidergic systems of the postnatal rat brain

Serotonin, gamma-aminobutyric acid and glutamate, which are regulated by glucocorticoids in the central nervous system, are involved in neuroendocrine functions and the development of the brain. The present study investigates the effect of maternal adrenalectomy on the developing serotoninergic, GABAergic and glutamatergic systems. Neurotransmitter levels were measured in four brain areas of both male and female offspring on postnatal days 1, 8, 12 and 22. At postnatal day 1 and 8, the pups of adrenalectomized dams showed higher concentrations of serotonin than controls in all the brain areas studied. Serotonin levels decreased significantly in males at postnatal day 22 in the hippocampus and cortex. During the first 2 weeks of postnatal life, the lack of maternal corticosterone produced an increase in glutamate and a reduction in gamma-aminobutyric acid concentrations, mainly in males. Further, on postnatal day 1, increased serotonin and glutamate levels and lower levels of gamma-aminobutyric were observed in the hypothalamus of male pups born to adrenalectomized dams. The absence of maternal corticosterone affects the pattern of development of the serotoninergic system, especially in the hippocampus and cortex, and particularly in males. A delay in the maturation of the aminoacidergic systems, mainly of the GABAergic system and in males, was also seen. A sexually dimorphic response to the removal of maternal glucocorticoids was seen in terms of neurotransmitter levels, mainly in the hippocampus and hypothalamus.

Dogmas and controversies in the handling of nitrogenous wastes:5-HT2-like receptors are involved in triggering pulsatile urea excretion in the gulf toadfish,Opsanus beta

When injected arterially, serotonin (5-hydroxytryptamine; 5-HT) has been shown to elicit naturally sized urea pulse events in the gulf toadfish, Opsanus beta. The goal of the present study was to determine which 5-HT receptor(s) was involved in mediating this serotonergic stimulation of the pulsatile excretion mechanism. Toadfish were surgically implanted with caudal arterial catheters and intraperitoneal catheters and injected with either 8-OH-DPAT (1 μmol kg–1), a selective 5-HT1A receptor agonist, α-methyl-5-HT (1 μmol kg–1), a 5-HT2 receptor agonist, or ketanserin, a 5-HT2 receptor antagonist (0.01, 0.1, 1 and 10 μmol kg–1) plus α-methyl-5-HT. 8-OH-DPAT injection did not mediate an increase in urea excretion, ruling out the involvement of 5-HT1A receptors in pulsatile excretion. However, within 5 min,α-methyl-5-HT injection caused an increase in the excretion of urea in&gt;95% (N=27) of the fish injected, with an average pulse size of 652±102 μmol N kg–1 (N=26). Withα-methyl-5-HT injection there was no corresponding increase in ammonia or [3H]PEG 4000 permeability. Urea pulses elicited byα-methyl-5-HT were inhibited in a dose-dependent fashion by the 5-HT2 receptor antagonist ketanserin, which at low doses caused a significant inhibition of pulse size and at higher doses significantly inhibited the occurrence of pulsatile excretion altogether. However, neither 8-OH-DPAT nor α-methyl 5-HT injection had an effect on plasma cortisol or plasma urea concentrations. These findings suggest the involvement of a 5-HT2-like receptor in the regulation of pulsatile urea excretion.

Serotonergic response to social stress and artificial social sign stimuli during paired interactions between male Anolis carolinensis

Serotonergic activity is influenced by social status and manipulation of social signals. In the lizard Anolis carolinensis, eyespot formation, i.e. darkening of postorbital skin from green to black, appears during stressful and agonistic situations, forming first in males that become dominant. To assess the effect of eyespots on central serotonergic activity during social interaction, males were paired by weight and painted postorbitally with green or black paint. Manipulation of eyespot color influenced social interactions and status. All males that viewed an opponent with black painted eyespots became subordinate. In these subordinate animals, serotonergic activity was elevated in hippocampus, striatum, nucleus accumbens and locus ceruleus. In contrast, males that viewed opponents with hidden eyespots (painted green) and became dominant had increased serotonergic activity in hypothalamus, medial amygdala and raphé. Pre-painted eyespots produced results that distinguish dominant and subordinate relationships based on serotonergic activity not previously seen in unmanipulated pairs. Results from experiments using pairs are similar to those using mirrors for medial amygdala and locus ceruleus, but not hippocampus, nucleus accumbens or raphé. Decreased hypothalamic serotonin was associated with increased aggressive behavior. These results, when compared with previous studies, suggest some flexibility in central serotonergic systems, which may shape dominant and subordinate rank acquisition, and appear to be influenced by the completion of social role formation. Furthermore, social status and central serotonergic activity was influenced by a visual cue, the presence or absence of postorbital eyespots on an opponent.

Psychological stress and fibromyalgia: a review of the evidence suggesting a neuroendocrine link

The present review attempts to reconcile the dichotomy that exists in the literature in relation to fibromyalgia, in that it is considered either a somatic response to psychological stress or a distinct organically based syndrome. Specifically, the hypothesis explored is that the link between chronic stress and the subsequent development of fibromyalgia can be explained by one or more abnormalities in neuroendocrine function. There are several such abnormalities recognised that both occur as a result of chronic stress and are observed in fibromyalgia. Whether such abnormalities have an aetiologic role remains uncertain but should be testable by well-designed prospective studies.

Implicações do sistema serotoninérgico no exercício físico

Este trabalho revisa as alterações cerebrais de serotonina quando da oferta de nutrientes (carboidratos, proteínas e aminoácidos) durante atividade física. Utilizando a estratégia nutricional, o foco é o aminoácido precursor da serotonina cerebral: o triptofano; sendo um aminoácido essencial, é possível sua modulação via dieta. Uma abordagem emergente e polêmica está relacionada à fadiga durante atividade de curta e longa duração e sua relação com a função serotoninérgica cerebral. Os mecanismos propostos para o desenvolvimento de fadiga precoce durante o exercício se apresentam amplamente inexplorados. Assim serão discutidos os prováveis mecanismos envolvidos na "hipótese da fadiga central" e a oferta de carboidratos e aminoácidos como estratégia para retardar este fato durante atividade física e alcançar melhora no rendimento esportivo.

Hyperglycemia induced by acute central fluoxetine administration: role of the central CRH system and 5-HT3 receptors

Brain serotonin and CRH systems participate in the control of blood glucose levels. We have previously demonstrated that the pharmacological stimulation of central 5-HT3 receptors, the target for several therapeutic agents used as antiemetics in the course of chemotherapy, induces hyperglycemia. The aim of the present study was to investigate the participation of the brain CRH component and 5-HT3 receptors in basal blood glucose levels as well as in the hyperglycemia induced by third ventricle injections of fluoxetine, a serotonin reuptake inhibitor with a broad range of clinical use. In this study, we used fasted adult Wistar male rats (220 +/- 20 g) whose third ventricles were cannulated 7 days prior to the experiments. Acute third ventricle injections of fluoxetine caused a significant increase in plasma glucose levels throughout the experiment. Pretreatment with alpha-helical CRH, a selective CRH antagonist, significantly blunted fluoxetine-induced hyperglycemia. Also, pretreatment with two distinct selective 5-HT3 receptor antagonists (LY-278,584 and ondansetron) significantly impaired the rise in plasma glucose levels observed in fluoxetine-treated animals pretreated with isotonic saline solution. None of these antagonists was able to modify blood glucose levels when injected alone into the third ventricle. Animals receiving third ventricle injections of fluoxetine, in spite of being hyperglycemic, presented plasma insulin levels similar to those displayed by normoglycemic, saline-treated controls. It is suggested that the acute increase in brain serotonergic activity caused by third ventricle injections of fluoxetine induces a hyperglycemic response that requires the functional integrity of the brain CRH system and 5-HT3 receptors. Also, it is proposed that the absence of a compensatory increase in plasma insulin levels may contribute to the generation of a hyperglycemic response after central fluoxetine administration.

Stress and alcohol drinking

The concept of stress-relief by alcohol has led to many investigations in order to elucidate the mechanisms of interactions of stress and alcohol, and the stress-reducing effect of alcohol as a motivation for alcohol consumption. The hypothalamo-pituitary-adrenocortical (HPA) system is one of the biological systems affected by both stress and alcohol. However, there is a high individual variation in the response of the HPA axis to either stress or alcohol. Factors like quality, severity and duration of stress, dose of alcohol and frequency of stress or alcohol exposure add to the individual response to stress or alcohol. The individual response is determined by interactions of genetic, environmental and experiential factors. Facing that complexity, with even more factors to be named, the often reported inconsistencies in both human and animal studies are not only attributable to methodological differences. Nevertheless, there are studies showing an influence of stress on alcohol consumption which most likely depends on the sample of probands examined. To our view, the concept of stress-relief by alcohol as a basic motivation for developing alcohol drinking habits is only applicable to subgroups of drinkers. Individuals with a dysfunctional HPA axis, inherited and/or acquired, might represent such a subgroup of stress-motivated drinkers.