Serotonin and the regulation of hypothalamic-pituitary-adrenal axis function

5'-Untranslated region of the tryptophan hydroxylase-2 gene harbors an asymmetric bidirectional promoter but not internal ribosome entry site in vitro

Tryptophan hydroxylase-2 (TPH2) catalyzes the synthesis of neuronal serotonin, a major neurotransmitter involved in many brain functions and psychiatric disorders. We have previously revealed a critical role of the human TPH2 (hTPH2) 5'-UTR in gene expression regulation. This study aimed to further characterize mechanism(s) by which the hTPH2 5'-UTR regulates gene expression. An internal ribosome entry site (IRES) activity in hTPH2 5'-UTR was suggested by the conventional bicistronic reporter assay; however, further stringent experiments, including in vitro translation, quantitative real-time PCR, Northern blot, ribonuclease protection assay, and monocistronic reporter assay, demonstrated that the hTPH2 5'-UTR harbors a bidirectional promoter, but not IRES, within its downstream segment (61-141). The antisense promoter is much stronger than the sense promoter, but the strength of both promoters are cell-line dependent, with the highest and lowest activities being observed in HEK-293T and SK-N-MC cells, respectively. In accordance with our previous findings, the upstream segment (1-60) of hTPH2 5'-UTR suppresses the neighboring promoter of both direction, independent of the cell line and its location in the 5'- or 3'-flanking regions of the gene. In summary, this study demonstrates that no IRES but an asymmetric bidirectional promoter is present in the downstream segment of hTPH2 5'-UTR, and this promoter is susceptible to a gene silencing effect caused by the upstream segment (1-60) of hTPH2 5'-UTR. Our findings point to the potential involvement of antisense transcription and non-coding RNA in the regulation of TPH2 gene expression.

Chronically restricted sleep leads to depression-like changes in neurotransmitter receptor sensitivity and neuroendocrine stress reactivity in rats

STUDY OBJECTIVES

Frequently disrupted and restricted sleep is a common problem for many people in our Western society. In the long run, insufficient sleep may have repercussions for health and may sensitize individuals to psychiatric diseases. In this context, we applied an animal model of chronic sleep restriction to study effects of sleep loss on neurobiological and neuroendocrine systems that have been implied in the pathophysiology of depression, particularly the serotonergic system and the hypothalamic-pituitary-adrenal (HPA) axis.

DESIGN

Adult rats were exposed to a schedule of chronic partial sleep deprivation allowing them only 4 h of sleep per day. Sleep restriction was achieved by placing the animals in slowly rotating drums. To examine the regulation and reactivity of the HPA axis, blood samples were collected to measure adrenocorticotropin (ACTH) and corticosterone (CORT) responses.

MEASUREMENTS AND RESULTS

While one day of restricted sleep had no significant effect on HPA axis stress reactivity, sleep restriction for a week caused a blunted pituitary ACTH response in a conditioned fear paradigm. Despite this lower ACTH response, adrenal CORT release was normal. The blunted pituitary response may be related to reduced sensitivity of serotonin-1A receptors and/or receptors for corticotropin-releasing hormone (CRH), since sleep restricted rats showed similar reductions in ACTH release to direct pharmacological stimulation with a serotonin-1A agonist or CRH.

CONCLUSIONS

Chronic sleep restriction may lead to changes in neurotransmitter receptor systems and neuroendocrine reactivity in a manner similar to that seen in depression. This experimental study thus supports the hypothesis that disrupted and restricted sleep may contribute to the symptomatology of psychiatric disorders.

Behavioral despair is differentially affected by the length and timing of photic stimulation in the dark phase of an L/D cycle

The effect of varying the length and timing of photic stimulation in the dark phase of an L/D lighting cycle on behavioral despair was investigated in female Wistar rats. Animals were kept in a vivarium on an L/D 12 h:12 h light cycle (lights on at 0700 h) except for a single day of light exposure in an insulated chamber in the dark phase of the L/D schedule. Light pulses provided by an incandescent lamp (15- and 25-W, for Exps. 1 and 2, respectively) either 2-h (Exp. 1) or 30-min in length (Exp. 2) were administered to independent groups of rats (n=8 each) either in the early, middle or late hours of the dark phase of the L/D cycle in the insulated chamber. Light pulses were delivered beginning 2 1/2, 5 1/2 or 7 1/2 h (Exp. 1) or 3 1/4, 6 1/4 and 8 1/4 h (Exp. 2) after dark onset. Control animals were treated similarly except for photic stimulation. In each experiment, an additional group received a light pulse of the appropriate length both in the early and late portion of the dark phase (double double-pulse groups): beginning 2 1/2 and 7 1/2 h (Exp. 1) or 3 1/4 and 8 1/4 h (Exp. 2) after dark onset. All animals then underwent two forced swim tests separated by 24 h with the first test occurring in the light (starting at 1500 h) following the dark phase when photic stimulation was administered. Total duration of immobility in the second swim test was measured to gauge behavioral despair. In Exp. 1, the 2-h double double-pulse group showed significantly shorter immobility compared to controls (p<0.05). In Exp. 2, 30-min light pulse delivered late in the dark phase reduced immobility significantly compared to controls and all the other light-treated groups (p<0.01). Results indicate that photic stimulation may have antidepressant effect on behavioral despair depending on the timing and the duration of photic stimulation.

Physiological endpoints for potential SSRI interactions in fish

Selective serotonin reuptake inhibitors (SSRIs) are among the pharmaceutical compounds frequently detected in sewage treatment plant effluents and surface waters, albeit at very low concentrations, and have therefore become a focus of interest as environmental pollutants. These neuroactive drugs are primarily used in the treatment of depression but have also found broader use as medication for other neurological dysfunctions, consequently resulting in a steady increase of prescriptions worldwide. SSRIs, via inhibition of the serotonin (5-hydroxytryptamine, 5-HT) reuptake mechanism, induce an increase in extracellular 5-HT concentration within the central nervous system of mammals. The phylogenetically ancient and highly conserved neurotransmitter and neurohormone 5-HT has been found in invertebrates and vertebrates, although its specific physiological role and mode of action is unknown for many species. Consequently, it is difficult to assess the impact of chronic SSRI exposure in the environment, especially in the aquatic ecosystem. In view of this, the current knowledge of the functions of 5-HT in fish physiology is reviewed and, via comparison to the physiological role and function of 5-HT in mammals, a characterization of the potential impact of chronic SSRI exposure on fish is provided. Moreover, the insight on the physiological function of 5-HT strongly suggests that the experimental approaches currently used are inadequate if not entirely improper for routine environmental risk assessment of pharmaceuticals (e.g., SSRIs), as relevant endpoints are not assessed or impossible to determine.

The metabolism of serotonin in neuronal cells in culture and platelets

The aim of this study is to find a relationship between serotonin (5-HT) and its metabolite 5-hydroxy indol acetic acid (5-HIAA) in hippocampus, frontal neocortex and platelets. Serotonin and 5-HIAA were measured in cultured neurons and compared with those produced by human platelets. The cortical neuronal 5-HIAA/serotonin ratio was 4.7 and for hippocampal neurons it was 3.2. In human platelets, this ratio was 1.35 suggesting that the highest serotonin metabolism occurs in the frontal neocortex followed by the hippocampus and platelets. In the presence of 0.3 microM of p-chlorophenylalanine both cultured neurons and platelets exhibited an approximately 50% decrease in serotonin and 5-HIAA concentration suggesting similarities in the metabolic profile in both preparations. In addition, we found that serotonin by itself does not play any role in platelet aggregation but potentiates this phenomenon in the presence of calcium ionophore A23187. This synergistic interaction between serotonin (2-5 microM) and A23187 (0.5-2 microM) was inhibited by serotonin receptor blockers [methysergide (IC50 = 18 microM) and cyproheptadine (IC50, 20 microM)] and calcium channel blockers (verapamil and diltiazem, IC50 = 20 and 40 microM, respectively) that indicate both mechanisms are receptor mediated. Similarly, U73122, an inhibitor of phospholipase C (PLC), blocked the synergistic effect of serotonin and ionophore at an IC50 value of 9.2 microM. Wortmannin, a phosphoinositide 3-kinase (PI 3-K) inhibitor, also blocked the response (IC50 = 2.6 microM) by inhibiting respiratory burst. However, neither genistein, a tyrosine-specific protein kinase inhibitor, nor chelerythrine, a protein kinase C (PKC) inhibitor, affected aggregation. Our results are strongly suggestive of a synergistic interaction between serotonin type-2 and Ca-ionophore via a PLC/Ca signalling pathway.

Genetic evaluation of the serotonergic system in chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a debilitating disorder of unknown etiology with no known lesions, diagnostic markers or therapeutic intervention. The pathophysiology of CFS remains elusive, although abnormalities in the central nervous system (CNS) have been implicated, particularly hyperactivity of the serotonergic (5-hydroxytryptamine; 5-HT) system and hypoactivity of the hypothalamic-pituitary-adrenal (HPA) axis. Since alterations in 5-HT signaling can lead to physiologic and behavioral changes, a genetic evaluation of the 5-HT system was undertaken to identify serotonergic markers associated with CFS and potential mechanisms for CNS abnormality. A total of 77 polymorphisms in genes related to serotonin synthesis (TPH2), signaling (HTR1A, HTR1E, HTR2A, HTR2B, HTR2C, HTR3A, HTR3B, HTR4, HTR5A, HTR6, and HTR7), transport (SLC6A4), and catabolism (MAOA) were examined in 137 clinically evaluated subjects (40 CFS, 55 with insufficient fatigue, and 42 non-fatigued, NF, controls) derived from a population-based CFS surveillance study in Wichita, Kansas. Of the polymorphisms examined, three markers (-1438G/A, C102T, and rs1923884) all located in the 5-HT receptor subtype HTR2A were associated with CFS when compared to NF controls. Additionally, consistent associations were observed between HTR2A variants and quantitative measures of disability and fatigue in all subjects. The most compelling of these associations was with the A allele of -1438G/A (rs6311) which is suggested to have increased promoter activity in functional studies. Further, in silico analysis revealed that the -1438 A allele creates a consensus binding site for Th1/E47, a transcription factor implicated in the development of the nervous system. Electrophoretic mobility shift assay supports allele-specific binding of E47 to the A allele but not the G allele at this locus. These data indicate that sequence variation in HTR2A, potentially resulting in its enhanced activity, may be involved in the pathophysiology of CFS.

Effects of acute tryptophan depletion on affective processing in first-degree relatives of depressive patients and controls after exposure to uncontrollable stress

RATIONALE

Individuals with a family history of depression may be more likely to develop depression due to an innate vulnerability of their serotonergic system. However, even though serotonergic vulnerability may constitute a risk factor in the development of depression, it does not seem to be sufficient to cause a depressive episode. Based on previous data, it is suggested that stress may be a mediating factor.

OBJECTIVES

This study examined the role of serotonin (5-HT) in stress coping in individuals with or without a family history of depression.

MATERIALS AND METHODS

Nineteen healthy first-degree relatives of depressive patients (FH+) and 19 healthy controls without a family history of depression (FH-) were tested in a double-blind placebo-controlled design for affective processing under acute stress exposure, following acute tryptophan depletion (ATD) or placebo.

RESULTS

Significant negative effects were found of stress on affective processing in FH- and FH+. In addition, FH- responded slower to positive words after stress only following ATD, whereas FH+ responded marginally slower under stress already after placebo and before stress following ATD.

CONCLUSION

Acute stress exposure reduces positive affective bias; supporting the role of stress as an important predecessor in the development of depression. Furthermore, FH+ may be more susceptible than FH- to the negative effects of stress as well as to the negative effects of ATD. The results support the assumption that the 5-HT system is involved in stress resilience and may be more vulnerable in first-degree relatives of depression.

Dexamethasone reduces food intake, weight gain and the hypothalamic 5-HT concentration and increases plasma leptin in rats

This study was conducted to define the regulatory mechanisms underlying stress-induced decreases in food intake and weight gain. Rats received a single or 4 daily injections of dexamethasone (0.1 or 1 mg/kg). Food intake and weight gain were recorded, and plasma leptin, brain contents of serotonin (5-hydroxytryptamine; 5-HT), 5-hydroxy-indole-acetic acid (5-HIAA) and the raphe expression of tryptophan hydroxylase (TPH), monoamine oxidase A (MAO-A) and 5-HT reuptake transporter (5-HTT) genes were examined. A single injection of dexamethasone did not acutely affect food intake, but cumulative food intake and weight gain were suppressed dose-dependently by daily injections of dexamethasone. Both a single and repeated injections of dexamethasone elevated plasma leptin in a dose dependent manner. 5-HT contents in the hypothalamus was decreased, but 5-HIAA increased, both by a single and repeated dexamethasone. A single injection of dexamethasone did not affect mRNA expressions of TPH, MAO-A and 5-HTT genes, but repeated dexamethasone increased them in the dorsal raphe nucleus. These results suggest that plasma leptin may play a role in dexamethasone-induced anorexia. Additionally, increased expression of MAO-A and 5-HTT genes by repeated dexamethasone appears to be implicated in decreases of the brain 5-HT contents.

Polymorphism of the 5-HT(2A) receptor gene: association with stress-related indices in healthy middle-aged adults

Past research has concentrated on the stress system and personality in order to explain the variance found in cognitive performance in old age. A growing body of research is starting to focus on genetic polymorphism as an individual difference factor to explain the observed heterogeneity in cognitive function. While the functional mechanism is still under investigation, polymorphism of the 5-HT(2A) receptor gene (-1438A/G) has been linked to certain behavioral and physiological outcomes, including cortisol secretion, the expression of certain personality traits, and memory performance. It was the goal of the present study to investigate the association between the -1438A/G polymorphism and stress hormone secretion, stress-related psychological measures, and cognitive performance in a group of adults between the ages of 50 and 65. To examine these associations, 101 middle-aged adults were recruited, completed a battery of psychological questionnaires and were administered a battery of cognitive tasks that assess frontal lobe and hippocampal function. Basal and stress-reactive salivary cortisol levels were collected, at home and in the laboratory. Analyses on psychological measures showed that participants with the GG genotype reported significantly higher levels of neuroticism compared to the AG group and higher levels of depression and more emotion-based coping strategies compared to both the AG and AA group. In terms of cortisol secretion, the AA genotype was related to a significantly higher awakening cortisol response (ACR) compared to the AG and GG group and the GG genotype group displayed a greater increase in cortisol secretion following a psychosocial stressor compared to the two other groups. On measures of cognitive performance, the AA genotype group performed significantly better on a test of declarative memory and selective attention compared to the other two groups. Together, these results suggest that carriers of the GG genotype are more susceptible to low mood and display a greater potential for an overactive stress system, which may influence cognitive function in later years.

Functional characterization of the human TPH2 5' regulatory region: untranslated region and polymorphisms modulate gene expression in vitro

Tryptophan hydroxylase-2 (TPH2) is a recently identified TPH isoform responsible for neuronal serotonin (5-HT) synthesis, and TPH2 polymorphisms are associated with a range of behavioral traits and psychiatric disorders. This study characterized cis-acting elements and three common polymorphisms (-703G/T, -473T/A, and 90A/G) in the 5' regulatory region of human TPH2 by using luciferase reporter assay, quantitative real-time PCR, and electrophoretic mobility shift assay (EMSA). The core promoter of human TPH2 was localized to the region between -107 and +7, and the segment of +8 to +53 within the 5'-UTR was found to exert a potent inhibitory effect on gene expression at both transcriptional and post-transcriptional levels. In both RN46A and HEK-293 cell lines, the TTA (-703T/-473T/90A) haplotype of the three polymorphisms showed the lowest gene expression compared with other haplotypes, and the -703G/T and -473T/A polymorphisms tended to exert a synergic effect on gene expression dependent upon the sequence of the 5'-UTR. In RN46A, the 90A/G polymorphism significantly increased luciferase activity and mRNA level irrespective of the other two polymorphisms, while in HEK-293 cells the effect of 90A/G was dependent on the alleles at loci -703 and -473. EMSA showed that all the three polymorphisms potentially alter DNA-protein interactions, while the 90A/G polymorphism predictably alters the 5'-UTR secondary structure of mRNA and influences RNA-protein interactions. In conclusion, our present study demonstrates that both the 5'-UTR and common polymorphisms (especially the 90A/G) in the 5' regulatory region of human TPH2 have a significant impact on gene expression.

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.

Review: Serotonin by stress interaction: a susceptibility factor for the development of depression?

A genetic predisposition to depression may be a potential risk factor in the development of depression. Although the neurobiological equivalent of the predisposition remains unclear, it seems as though the brain serotonin (5-HT) system plays an important mediating role. Therefore, individuals with a family history of depression (FH+) may be more likely to develop depression due to an innate vulnerability related to altered serotonergic neurotransmission in the brain. A major problem, however, is that the role of brain 5-HT in depression is complex and this serotonin-related innate vulnerability, by itself, is not sufficient enough to cause a depressive episode. In the search for additional factors, stress has received particular attention. Stressful life events influence and precede the onset of depression. Furthermore, depression is associated with stress hormone dysregulation and bidirectional interactions are thought to occur between stress-related changes in the neuroendocrine stress system and the 5-HT system. In the current review, we argue that healthy individuals with a positive family history of depression are more prone to develop depression due to a genetic 5-HT susceptibility, which deteriorates stress coping mechanisms and increases stress vulnerability.

The effects of pharmacological blockade of the 5-HT(6) receptor on formalin-evoked nociceptive behaviour, locomotor activity and hypothalamo-pituitary-adrenal axis activity in rats

5-hydroxytryptamine (5-HT) mediates behavioural and neuroendocrine responses to noxious or stressful stimuli. 5-HT(6) receptors are expressed in brain regions involved in nociceptive processing, however, their role in nociception is unknown. Here we demonstrate that acute, systemic administration of the 5-HT(6) receptor antagonist, 5-chloro-N-(4-methoxy-3-benzothio-phenesulfonamide (SB-271046), reduces formalin-evoked nociceptive behaviour and increases plasma corticosterone. SB-271046 dose-dependently reduced pre-formalin distance moved, rearing, grooming and defecation. These data provide the first evidence for 5-HT(6) receptor-mediated regulation of nociception and hypothalamo-pituitary-adrenal axis activity in a model of persistent pain although effects on locomotor activity demand that the putative antinociceptive effect of SB-271046 be interpreted with some caution.

The behavioral effects of enriched housing are not altered by serotonin depletion but enrichment alters hippocampal neurochemistry

To assess a possible role for serotonin in the mediation of the behavioral changes induced by enriched housing conditions (EC), adult female Long-Evans rats sustaining a serotonin depletion (150 microg of 5,7-dihydroxytryptamine, icv) and sham-operated rats were housed postoperatively for 30 days in enriched (12 rats/large cage containing various objects) or standard housing conditions (2 rats/standard laboratory cage). Thereafter, anxiety responses (elevated plus-maze), locomotor activity (in the home-cage), sensori-motor capabilities (beam-walking task), and spatial memory (eight-arm radial maze) were assessed. Monoamine levels were subsequently measured in the frontoparietal cortex and the hippocampus. Overall, EC reduced anxiety-related responses, enhanced sensori-motor performance and improved the memory span in the initial stage of the spatial memory task. Despite a substantial reduction of serotonergic markers in the hippocampus (82%) and the cortex (74%), these positive effects of EC were not altered by the lesion. EC reduced the serotonin levels in the ventral hippocampus (particularly in unlesioned rats: -23%), increased serotonin turnover in the entire hippocampus (particularly in lesioned rats: +36%) and augmented the norepinephrine levels in the dorsal hippocampus (+68% in unlesioned and +49% in lesioned rats); no such alterations were found in the frontoparietal cortex. Our data suggest that an intact serotonergic system is not a prerequisite for the induction of positive behavioral effects by EC. The neurochemical changes found in the hippocampus of EC rats, however, show that the monoaminergic innervation of the hippocampus is a target of EC.

Influence of Stress and Nutrition on Cattle Immunity

Today, the scientific community readily embraces the fact that stress and nutrition impact every physiologic process in the body. At last, the specific mechanisms by which stress and nutrition affect the immune function are being elucidated. The debate among animal scientists concerning the definition and quantification of stress as it relates to animal productivity and well-being is ongoing. However, an increased appreciation and understanding of the effects of stress on livestock production has emerged throughout the scientific community and with livestock producers. The intent of this article is to provide an overview of the general concepts of stress and immunology, and to review the effects of stress and nutrition on the immune system of cattle.

Pharmacokinetic/Pharmacodynamic Feedback Modelling of the Functional Corticosterone Response in Rats after Acute Treatment with Escitalopram

The objective of this study was to characterize the pharmacokinetic/pharmacodynamic (PK/PD) relationship of the drug-induced corticosterone response after administration of escitalopram in rats. To achieve this, a mechanistic feedback turnover model mimicking the acute mechanism of action of selective serotonin reuptake inhibitors was assessed. Conscious and freely moving rats received constant rate infusions of 2.5, 5 or 10 mg/kg escitalopram or vehicle over 60 min. Automated serial blood sampling was conducted to determine escitalopram and corticosterone concentrations. The PK/PD model consisted of a turnover model of escitalopram-evoked changes in response, which included an inhibitory feedback moderator function. Accordingly, response acted linearly on the production (k(tol)) of the moderator, which acted inversely on the production (k(in)) of response. The escitalopram plasma kinetics served as input to an inhibitory function acting on the loss (k(out)) of response. The corticosterone responses were successfully described using the model by fitting responses from all doses simultaneously resulting in estimation of drug parameters (I(max), IC(50) and n) in addition to system parameters (k(in), k(out) and k(tol)) for the whole exposure range. Thus, the applicability of the model for analysis of the acute selective serotonin reuptake inhibitor-induced corticosterone response including acute auto-inhibitory feedback was demonstrated.

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.

Central fatigue: the serotonin hypothesis and beyond

The original central fatigue hypothesis suggested that an exercise-induced increase in extracellular serotonin concentrations in several brain regions contributed to the development of fatigue during prolonged exercise. Serotonin has been linked to fatigue because of its well known effects on sleep, lethargy and drowsiness and loss of motivation. Several nutritional and pharmacological studies have attempted to manipulate central serotonergic activity during exercise, but this work has yet to provide robust evidence for a significant role of serotonin in the fatigue process. However, it is important to note that brain function is not determined by a single neurotransmitter system and the interaction between brain serotonin and dopamine during prolonged exercise has also been explored as having a regulative role in the development of fatigue. This revised central fatigue hypothesis suggests that an increase in central ratio of serotonin to dopamine is associated with feelings of tiredness and lethargy, accelerating the onset of fatigue, whereas a low ratio favours improved performance through the maintenance of motivation and arousal. Convincing evidence for a role of dopamine in the development of fatigue comes from work investigating the physiological responses to amphetamine use, but other strategies to manipulate central catecholamines have yet to influence exercise capacity during exercise in temperate conditions. Recent findings have, however, provided support for a significant role of dopamine and noradrenaline (norepinephrine) in performance during exercise in the heat. As serotonergic and catecholaminergic projections innervate areas of the hypothalamus, the thermoregulatory centre, a change in the activity of these neurons may be expected to contribute to the control of body temperature whilst at rest and during exercise. Fatigue during prolonged exercise clearly is influenced by a complex interaction between peripheral and central factors.

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.

Puberty, hormones, and sex differences in alcohol abuse and dependence

Sex differences in patterns of drinking and rates of alcohol abuse and dependence begin to emerge during the transition from late puberty to young adulthood. Increases in pubertal hormones, including gonadal and stress hormones, are a prominent developmental feature of adolescence and could contribute to the progression of sex differences in alcohol drinking patterns during puberty. This paper reviews experimental and correlational studies of gonadal and stress-related hormone changes and their effects on alcohol drinking and other associated actions of alcohol. Mechanisms are suggested by which reproductive hormones and stress-related hormones may modulate neural circuits within the brain reward system to produce sex differences in alcohol drinking patterns and vulnerability to alcohol abuse and dependence which become apparent during the late pubertal period.

Neuroendocrine and Behavioral Mechanisms Mediating the Relationship between Anger Expression and Cardiovascular Risk: Assessment Considerations and Improvements

The hypothesis that intense anger experience may increase risk for or exacerbate cardiovascular diseases has been under active theoretical and empirical interest for decades. Biopsychological models of disease suggest that persons displaying exaggerated physiological responses to acute emotional or stressful states are at a greater risk to develop cardiovascular disorders. The last two decades have witnessed active work to refine means by which anger expression can be assessed, and laboratory research has produced evidence suggesting that certain expression styles may predict enhanced physiological responses to acute stress. In this paper, we review methodological and definition issues related to the assessment of anger, and we summarize recent improvements on the assessment of anger expression. We also review recent studies addressing the association between anger and cardiovascular diseases, and we present potential neuroendocrine and behavioral mechanisms through which anger expression may increase risk for cardiovascular disease.

Tryptophan hydroxylase-2 gene polymorphisms in rhesus monkeys: association with hypothalamic-pituitary-adrenal axis function and in vitro gene expression

Tryptophan hydroxylase-2 (TPH2) is a newly identified second form of TPH responsible for serotonin synthesis in the brain and has been increasingly implicated as a contributor to the etiology of various psychiatric disorders. In this study, we have identified the constellation of polymorphisms in rhesus monkey TPH2 and investigated genotype/phenotype association as well as gene expression effects of specific polymorphisms. Genomic DNA was obtained from 247 rhesus monkeys, among which 24 had been previously examined for plasma cortisol level, dexamethasone suppression, and combined dexmethasone/ACTH challenge. Polymorphisms in all exons, splicing junctions and approximately 2 kb of the 5'-flanking region (5'-FR) of TPH2 were identified by sequencing. We identified 17 single nucleotide polymorphisms (SNPs) including two that are predictive of amino-acid change (25Pro>His and 75Gly>Ser, respectively), two mononucleotide repeats, one dinucleotide repeat, and one 159-bp insertion polymorphism. The 3'-UTR polymorphisms were significantly associated with hypothalamic-pituitary-adrenal (HPA) axis activity, especially 2051A>C, which was strikingly correlated with plasma cortisol level in the morning only (F=10.203, P=0.001). Luciferase reporter gene assays showed that the 3'-UTR polymorphisms and haplotypes had a profound effect on in vitro gene expression. Accordingly, these investigations revealed that polymorphisms in 3'-UTR of rhesus monkey TPH2 modulate HPA axis function, presumably by affecting levels of TPH2 expression.

Cell-type-specific limitation on in vivo serotonin storage following ectopic expression of the Drosophila serotonin transporter, dSERT

The synaptic machinery for neurotransmitter storage is cell-type specific. Although most elements of biosynthesis and transport have been identified, it remains unclear whether additional factors may be required to maintain this specificity. The Drosophila serotonin transporter (dSERT) is normally expressed exclusively in serotonin (5-HT) neurons in the CNS. Here we examine the effects of ectopic transcriptional expression of dSERT in the Drosophila larval CNS. We find a surprising limitation on 5-HT storage following ectopic expression of dSERT and green fluorescence protein-tagged dSERT (GFP-dSERT). When dSERT transcription is driven ectopically in the CNS, 5-HT is detectable only in 5-HT, dopamine (DA), and a very limited number of additional neurons. Addition of exogenous 5-HT does not dramatically broaden neuronal storage sites, so this limitation is only partly due to restricted intercellular diffusion of 5-HT. Furthermore, this limitation is not due to gross mislocalization of dSERT, because cells lacking or containing 5-HT show similar levels and subcellular distribution of GFP-dSERT protein, nor is it due to lack of the vesicular transporter, dVMAT. These data suggest that a small number of neurons selectively express factor(s) required for 5-HT storage, and potentially for function of dSERT.

Hypothalamic-pituitary-gut axis dysregulation in irritable bowel syndrome: plasma cytokines as a potential biomarker?

BACKGROUND & AIMS

Irritable bowel syndrome (IBS) is a functional disorder with an etiology that has been linked to both psychological stress and infection. The primary aim of this study was to examine the hypothalamic-pituitary-adrenal axis in patients with IBS and to relate such response to plasma cytokine profiles.

METHODS

A total of 151 subjects, 76 patients and 75 controls, were recruited. The patients with IBS were diagnosed according to Rome II criteria. Forty-nine patients and 48 matched controls had cytokine levels measured, and a subset of 21 patients and 21 controls also underwent a corticotropin-releasing hormone (CRH) stimulation test with plasma levels of adrenocorticotropic hormone (ACTH) and cortisol measured. The remaining 27 patients and 27 controls underwent a dexamethasone (1 mg) challenge.

RESULTS

Cortisol and the proinflammatory cytokines interleukin (IL)-6 (together with its soluble receptor) and IL-8 were elevated in all IBS subgroups (diarrhea predominant, constipated, and alternators), although the elevation was most marked in the constipated subgroup. There was no alteration in the anti-inflammatory cytokine IL-10. Following CRH infusion, an exaggerated release of both ACTH and cortisol was observed in patients with IBS. There was a significant correlation between the ACTH response (deltaACTH) and the IL-6 levels. A similar relationship existed between the deltaACTH/deltacortisol ratio and the IL-6 levels. Dexamethasone suppression of cortisol was similar in patients and controls.

CONCLUSIONS

IBS is characterized by an overactivation of the hypothalamic-pituitary-adrenal axis and a proinflammatory cytokine increase.

Mathematical modeling of the hypothalamic-pituitary-adrenal system activity

Mathematical modeling has proven to be valuable in understanding of the complex biological systems dynamics. In the present report we have developed an initial model of the hypothalamic-pituitary-adrenal system self-regulatory activity. A four-dimensional non-linear differential equation model of the hormone secretion was formulated and used to analyze plasma cortisol levels in humans. The aim of this work was to explore in greater detail the role of this system in normal, homeostatic, conditions, since it is the first and unavoidable step in further understanding of the role of this complex neuroendocrine system in pathophysiological conditions. Neither the underlying mechanisms nor the physiological significance of this system are fully understood yet.

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.

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.

Platelet monoamine oxidase B (MAO-B) activity and its relationship to DL-fenfluramine-induced prolactin response in healthy men

Several techniques are used to assess central serotonergic neurotransmission in man, e.g. challenge tests (hormonal and physiological responses to serotonin active drugs), platelet MAO-B activity as well as brain imaging techniques. Little is known about how these tests relate to each other. The aim of the present study was therefore to investigate if platelet MAO-B activity could be related to hormonal and temperature responses to the serotonin active drug DL-fenfluramine in healthy men. Twelve male subjects without any history of psychiatric disorders or drug abuse/dependencies were recruited. Prior to the challenge with 60 mg DL-fenfluramine, which was given orally, blood for determination of platelet MAO-B activity was drawn. Blood samples for determination of serum prolactin and serum cortisol were drawn at baseline and thereafter every hour for the following six hours. In addition, body temperature was measured at the same time-points. Delta-values were calculated as the difference between the baseline values and the highest (prolactin and cortisol) or lowest value (temperature) thereafter. There was a strong positive correlation (r = 0.75, p < 0.02) between platelet MAO-B activity and Delta-prolactin. No correlations were found to Delta-cortisol, Delta-temperature or any of the baseline values. The results support the notion that the peripheral marker platelet MAO-B activity is related to the function of the central serotonergic neurotransmitter system as assessed by the prolactin response to 60 mg DL-fenfluramin.

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.

Tamoxifen fails to affect central serotonergic tone but increases indices of anxiety in female rhesus macaques

The selective estrogen receptor modulator (SERM), tamoxifen, effectively slows the progression of estrogen-positive breast cancer and aids in the prevention of cancer in at-risk women. Tamoxifen is well characterized with regards to its effects on breast cancer, but its effects on other estrogen-related systems, particularly neural circuits regulating brain function and mood, are poorly understood. Using ovariectomized rhesus monkeys, we examined the effects of tamoxifen, with and without estrogen replacement therapy (ERT), on social behavior and central serotonin (5HT) systems thought to influence these behaviors. Relative to placebo treatments, estrogen treatment increased serotonergic tone, based on response in prolactin and cortisol to fenfluramine, a 5HT releasing agent. Tamoxifen neither blocked nor enhanced this effect, indicating it to be neither an antagonist nor an agonist on serotonergic activity. In contrast, CSF measures of the 5HT metabolite, 5HIAA, were not significantly affected by treatment. Tamoxifen-treated animals showed increases in measures of anxiety, compared with ERT-treated animals, suggesting that this SERM may be anxiogenic. Co-treatment with estrogen attenuated the anxiogenic properties of tamoxifen. These data show that tamoxifen administration increased anxiety levels, but the affect was not associated with differences in central levels of the serotonin tone.

Socially-mediated differences in brain monoamines in rainbow trout: effects of trace metal contaminants

Monoaminergic systems play a crucial role in linking behaviour and physiology. Here the physiological and behavioural effects of metal exposure in relation to monoaminergic systems were considered by exposing rainbow trout dyads, demonstrating stable dominance relationships, to cadmium or lead. Fish exposed to 4 microg l(-1) cadmium accumulated more cadmium at the gill than fish held in control water. Fish exposed to 7 microg l(-1) cadmium had higher gill, liver and kidney cadmium concentrations. No significant lead accumulation was seen after exposure to 46 microg l(-1) for 48 h but exposure to 325 microg l(-1) lead caused an increase in gill, liver and kidney lead concentrations. Brain accumulation of both cadmium and lead was only seen after exposure to the highest concentrations. Exposure to 4 or 7 microg l(-1) cadmium, or 46 or 325 microg l(-1) lead for 48 h did not disrupt established dominance hierarchies. As expected with this stable behavioural situation, in control pairs, animals of different social status displayed different physiological profiles. Subordinate fish had higher concentrations of circulating plasma cortisol and telencephalic 5-hydroxyindoleacetic acid/5-hydroxytryptamine (serotonin) (5-HIAA/5-HT) ratios. However, these physiological profiles were affected by metal exposure, with a trend towards higher serotonergic activity in dominant fish. Dominants exposed to 325 microg l(-1) lead had significantly higher hypothalamic 5-HIAA/5-HT ratios when compared with subordinates. The results demonstrate that if stable social hierarchies are established in control water they may not be affected by exposure to cadmium and lead although physiological changes may be evident.

Role of stress in the pathogenesis of the metabolic syndrome

Excess body fat, obesity, is one of the most common disorders in clinical practice. In addition, there is a clustering of several risk factors with obesity, including hypertension, glucose intolerance, diabetes mellitus, and hyperlipidemia, which is observed more frequently than by chance alone. This has led to the suggestion that these represent a single syndrome and is referred to as the Metabolic Syndrome. A growing body of evidence suggests that glucocorticoid secretion is associated with this complex phenotype. Continuously changing and sometimes threatening external environment may, when the challenge exceeds a threshold, activate central pathways that stimulate the adrenals to release glucocorticoids. In this review, we will discuss how such processes mediate a pathogenetic role in the Metabolic Syndrome.

Increased cerebrospinal fluid corticotropin-releasing factor concentrations during tryptophan depletion in healthy adults

BACKGROUND

Brain serotonin neurotransmission and hypothalamic-pituitary-adrenal axis function are implicated in the pathophysiology of depression, and these systems interact in a reciprocal modulatory fashion. This study examined the effect of tryptophan depletion, which acutely reduces brain serotonin concentrations, on serial cerebrospinal fluid concentrations of corticotropin-releasing factor in healthy humans.

METHODS

Five subjects completed a standard tryptophan depletion protocol, and four subjects participated in a comparison condition. Subjects underwent continuous sampling of cerebrospinal fluid via lumbar peristaltic pump. Concentrations of cerebrospinal fluid corticotropin-releasing factor were measured by radioimmunoassay.

RESULTS

No mood changes were observed in either group. Tryptophan-depleted subjects exhibited significantly greater increases in corticotropin-releasing factor concentrations over time than subjects in the comparison condition.

CONCLUSIONS

These findings highlight the potential importance of corticotropin-releasing factor and serotonin interactions and suggest that activation of corticotropin-releasing-factor-containing neurons could play a role in the emergence of mood symptoms following tryptophan depletion in vulnerable individuals.

Platelet serotonin and plasma prolactin and cortisol in healthy, depressed and schizophrenic women

Serotonin (5-hydroxytryptamine, 5-HT) is involved in the regulation of hypothalamic-pituitary-adrenal axis (HPA) activity and prolactin (PRL) secretion. The present study examined the relationship between platelet 5-HT and plasma cortisol and PRL concentrations in 20 schizophrenic, 25 depressed, and 25 healthy women. At the time of blood sampling, the schizophrenic and depressed patients had been drug-free for at least 7 days. Platelet 5-HT, plasma cortisol and PRL concentrations were determined by spectrofluorimetric, radioimmunoassay and immunoradiometric methods, respectively. Platelet 5-HT concentration was significantly higher in schizophrenic patients than in depressed patients or in healthy controls, while it was significantly lower in depressed patients than in healthy controls or in schizophrenic patients. Plasma cortisol levels were significantly increased both in schizophrenic and in depressed patients compared with values in healthy controls. Values of plasma PRL were similar across groups. A significant correlation was found between platelet 5-HT and plasma cortisol, and platelet 5-HT and plasma PRL concentrations in healthy controls, but not in schizophrenic or depressed patients. There was no significant relationship between plasma PRL and cortisol levels in any of the groups. Our data, although obtained on peripheral biochemical markers, indicate that depression and schizophrenia are characterized by disturbed 5-HT transmission and dysregulated HPA axis activity.

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.

Cerebral perturbations provoked by prolonged exercise

This review addresses cerebral metabolic and neurohumoral alterations during prolonged exercise in humans with special focus on associations with fatigue. Global energy turnover in the brain is unaltered by the transition from rest to moderately intense exercise, apparently because exercise-induced activation of some brain regions including cortical motor areas is compensated for by reduced activity in other regions of the brain. However, strenuous exercise is associated with cerebral metabolic and neurohumoral alterations that may relate to central fatigue. Fatigue should be acknowledged as a complex phenomenon influenced by both peripheral and central factors. However, failure to drive the motorneurons adequately as a consequence of neurophysiological alterations seems to play a dominant role under some circumstances. During exercise with hyperthermia excessive accumulation of heat in the brain due to impeded heat removal by the cerebral circulation may elevate the brain temperature to >40 degrees C and impair the ability to sustain maximal motor activation. Also, when prolonged exercise results in hypoglycaemia, perceived exertion increases at the same time as the cerebral glucose uptake becomes low, and centrally mediated fatigue appears to arise as the cerebral energy turnover becomes restricted by the availability of substrates for the brain. Changes in serotonergic activity, inhibitory feed-back from the exercising muscles, elevated ammonia levels, and alterations in regional dopaminergic activity may also contribute to the impaired voluntary activation of the motorneurons after prolonged and strenuous exercise. Furthermore, central fatigue may involve depletion of cerebral glycogen stores, as signified by the observation that following exhaustive exercise the cerebral glucose uptake increases out of proportion to that of oxygen. In summary, prolonged exercise may induce homeostatic disturbances within the central nervous system (CNS) that subsequently attenuates motor activation. Therefore, strenuous exercise is a challenge not only to the cardiorespiratory and locomotive systems but also to the brain.

Programming of the hypothalamo-pituitary-adrenal axis: serotonergic involvement

The ability of the early environment to programme the developing hypothalamo-pituitary-adrenal (HPA) axis has been reported in several animal species. There is considerable evidence that a similar process can occur in the human, and that long-term alterations in HPA function are associated with altered susceptibility to disease in later life. The phenotype of HPA function following early manipulation depends on the timing and intensity of the manipulation as well as the gender of the fetus/neonate. There is considerable interplay between the developing HPA and the reproductive axes and emerging evidence indicates that this interaction is modified by early environmental manipulation. Studies are rapidly unravelling the mechanisms that underlie developmental programming of the HPA axis. In this context, the serotonergic system has been identified as a primary system involved in this process. Understanding the mechanisms involved in neuroendocrine programming will facilitate the development of interventions aimed at reversing or ameliorating the impact of an adverse intrauterine environment.

Hormonal and temperature responses to flesinoxan in normal volunteers: an antagonist study

RATIONALE

Flesinoxan is a highly potent and selective 5-HT1A agonist. In a recent study, in normal volunteers, flesinoxan induced a significant and dose-dependent increase in adrenocorticotropic hormone (ACTH), cortisol, prolactin (PRL), growth hormone (GH) and a decrease in body temperature.

OBJECTIVES

In order to better define the role of 5-HT receptor subtypes in response to flesinoxan, we assessed the influence of 5-HT1A and 5-HT2 antagonists on hormonal and temperature responses to flesinoxan.

METHODS

Hormonal and temperature responses were studied in 6 volunteers with or without pretreatment with pindolol (30 mg p.o.), a 5-HT1A antagonist, or ritanserin (10 mg p.o.), a selective 5-HT2 antagonist, using a double-blind crossover design.

RESULTS

Pindolol significantly antagonized ACTH, PRL, GH and temperature responses to flesinoxan and ritanserin exhibited similar activity on PRL and ACTH responses.

CONCLUSIONS

These results show the role of 5-HT1A mechanisms in the PRL, ACTH, GH, and temperature responses to flesinoxan, and the role of 5-HT2 mechanisms in PRL and ACTH responses. Therefore, they confirm the interest of flesinoxan as a 5-HT neuroendocrine probe.

Serotonin modulation of cerebral glucose metabolism in normal aging

Age-related alterations in serotonin function may increase the vulnerability to psychiatric and neurodegenerative disorders in late life. The neuroendocrine and cerebral metabolic response to the acute administration of the selective serotonin reuptake inhibitor, citalopram (40mg, IV), was measured in 17 normal control subjects using positron emission tomography (PET) to evaluate changes in serotonin function with normal aging. The citalopram-induced change in cerebral metabolism was positively correlated with age in the right precuneus, right paracentral lobule, and left middle temporal gyrus and negatively correlated with age in the left anterior cingulate gyrus, right inferior and middle frontal gyri, right insula, and right inferior parietal lobule. The positive correlations in mainly posterior brain regions indicate that normal aging is associated with an increase in metabolism after citalopram administration, whereas the negative correlations in mainly anterior brain regions indicate that normal aging is associated with a greater decrease in metabolism. These results suggest different compensatory processes in anterior compared to posterior brain regions secondary to the age-related loss of serotonin innervation.

Hyperforin-containing extracts of St John's wort fail to alter gene transcription in brain areas involved in HPA axis control in a long-term treatment regimen in rats

We previously showed that a methanolic extract of St John's wort (SJW) (Hypericum) and hypericin, one of its active constituents, both have delayed regulation of genes that are involved in the control of the hypothalamic-pituitary-adrenal (HPA) axis. Hyperforin, another constituent of SJW, is active in vitro and has been proposed to be the active constituent for therapeutic efficacy in depression. We therefore examined if hyperforin has delayed effects on HPA axis control centers similar to those of Hypericum and hypericin. We used in situ hybridization histochemistry to examine in rats the effects of short-term (2 weeks) and long-term (8 weeks) oral administration of two hyperforin preparations, fluoxetine (positive control), and haloperidol (negative control) on the expression of genes involved in the regulation of the HPA axis. Fluoxetine (10 mg/kg) given daily for 8 weeks, but not 2 weeks, significantly decreased levels of corticotropin-releasing hormone (CRH) mRNA by 22% in the paraventricular nucleus (PVN) of the hypothalamus and tyrosine hydroxylase (TH) mRNA by 23% in the locus coeruleus. Fluoxetine increased levels of mineralocorticoid (MR) (17%), glucocorticoid (GR) (18%), and 5-HT(1A) receptor (21%) mRNAs in the hippocampus at 8, but not 2, weeks. Comparable to haloperidol (1 mg/kg), neither the hyperforin-rich CO(2) extract (27 mg/kg) nor hyperforin-trimethoxybenzoate (8 mg/kg) altered mRNA levels in brain structures relevant for HPA axis control at either time point. These data suggest that hyperforin and hyperforin derivatives are not involved in the regulation of genes that control HPA axis function.

Hippocampal and Hypothalamic Function after Chronic Stress

Hyperactivity of the hypothalamo-pituitary-adrenal (HPA) axis is often observed in association with and even prior to the onset of major depression. It is presently unclear (1) which molecular and cellular processes contribute to hyperactivity of parvocellular hypothalamic neurons (key regulators of the HPA system) and (2) how HPA axis hyperactivity can lead to attenuation of central serotonergic transmission, a crucial factor in the onset of clinical symptoms. In an attempt to address these issues in an experimental model we used rats exposed to chronic unpredictable stressors, a paradigm causing prolonged HPA-axis hyperactivity. In the first study spontaneous and evoked GABA-mediated input to parvocellular neurons in the paraventricular hypothalamic nucleus was recorded with the whole cell patch-clamp technique. The frequency, but not other properties, of spontaneous GABA-mediated inhibitory postsynaptic currents was reduced after chronic stress, resulting in a reduced amplitude of the evoked GABA current. This potentially would disinhibit parvocellular neurons, provided that other inputs are unchanged. In the second study, responses of CA1 hippocampal neurons to serotonin were recorded with microelectrodes. It appeared that the membrane hyperpolarization caused by activation of serotonin-1A receptors is attenuated in tissue from chronically stressed rats. However, no apparent changes in expression of the serotonin-1A or corticosteroid receptors were observed. This supports the notion that chronic stress eventually results in attenuation of serotonergic responsiveness by a mechanism not involving transcriptional regulation of the receptor. Follow-up studies will need to examine whether treatment with corticosteroid receptor antagonists can normalize the attenuated transmission after chronic stress.

Effects of venlafaxine on extracellular 5-HT, dopamine and noradrenaline in the hippocampus and on peripheral hormone concentrations in the rat in vivo

The purpose of the present study was to study the effect of an acute dose of the serotonin (5-HT) - noradrenaline (NA) reuptake inhibitor venlafaxine on extracellular concentrations of 5-HT, NA and dopamine (DA) in the hippocampus and on the peripheral hormone concentrations in freely moving rats. Blood obtained from a catheter placed in the vena femoralis was analyzed for adrenocorticotropin (ACTH), beta-endorphins, prolactin (PRL), growth hormone (GH) and cortisol. Collections are referred to pre and post injection of 20 mg/kg of venlafaxine. Extracellular hippocampal NA and 5-HT as determined with in vivo microdialysis increased significantly after drug injection. PRL and ACTH were significantly affected by the drug. At the selected dose venlafaxine is able to increase the release of 5-HT but also of NA in rat hippocampus. Due to the dual reuptake properties of the drug and the functional interconnection of the NA and the 5-HT systems, the observed effects on peripheral hormones are possibly mediated by a combined action of these 2 systems.

Serotonin and the neuroendocrine regulation of the hypothalamic--pituitary-adrenal axis in health and disease

Serotonin (5-hydroxytryptamine, 5-HT)-containing neurons in the midbrain directly innervate corticotropin-releasing hormone (CRH)-containing cells located in paraventricular nucleus of the hypothalamus. Serotonergic inputs into the paraventricular nucleus mediate the release of CRH, leading to the release of adrenocorticotropin, which triggers glucocorticoid secretion from the adrenal cortex. 5-HT1A and 5-HT2A receptors are the main receptors mediating the serotonergic stimulation of the hypothalamic-pituitary-adrenal axis. In turn, both CRH and glucocorticoids have multiple and complex effects on the serotonergic neurons. Therefore, these two systems are interwoven and communicate closely. The intimate relationship between serotonin and the hypothalamic-pituitary-adrenal axis is of great importance in normal physiology such as circadian rhythm and stress, as well as pathophysiological disorders such as depression, anxiety, eating disorders, and chronic fatigue.

Characterization of monoaminergic systems in brain regions of prematurely ageing mice

We have previously shown that differences in life span among members of Swiss mouse populations appear to be related to their exploration of a T-maze, with a slow exploration ("slow mice") being linked to increased levels of emotionality/anxiety, an impaired immune function and a shorter life span. Thus, we proposed the slow mice as prematurely ageing mice (PAM). We have now compared the monoaminergic systems of the PAM and of the non-prematurely ageing mice (NPAM), in discrete brain regions. PAM had decreased noradrenaline (NA) levels in all the brain regions analysed, whereas the 3-methoxy-4-hydroxyphenyl glycol (MHPG)/NA ratios were not significantly modified. PAM also showed decreased serotonine (5-HT) levels in hypothalamus, striatum and midbrain, as well as increased 5-hydroxyindol-3-acetic acid (5-HIAA)/5-HT ratios in hypothalamus and hippocampus. The dopamine (DA) content was lower in PAM in most regions, whereas the 3,4-dihydroxyphenylacetic acid (DOPAC)/DA and homovanillic acid (HVA)/DA ratios were either increased or unchanged depending on the region analysed. In most cases, the differences between PAM and NPAM involved both sexes. One exception was the hypothalamus where the differences only affected the male mice. The neurochemical alterations found in PAM resemble some changes reported for aged animals and are related with their behavioural features.