Intra- and inter-individual relationships between central and peripheral serotonergic activity in humans: a serial cerebrospinal fluid sampling study

Peripheral serotonin levels as a predictor of antidepressant treatment response: A systematic review

There are currently no reliable biomarkers to predict clinical response to pharmacological treatments of depressive disorders. Peripheral blood 5-hydroxytryptamine (5-HT; serotonin) has been suggested as a biomarker of antidepressant treatment response, but there has not been an attempt to systematically summarize and evaluate the scientific evidence of this hypothesis. In this systematic review we searched MEDLINE, Embase, PsycINFO, and the Cochrane Central Register of Controlled Trials. Twenty-six relevant studies investigating peripheral 5-HT as an antidepressant biomarker were identified. In all, we did not find robust support for an association between baseline 5-HT and treatment response. Several larger studies with lower risk of bias, however, showed that higher baseline 5-HT was associated with a greater antidepressant response to SSRIs, prompting future studies to investigate this hypothesis. Our results also confirm previous reports that SSRI treatment is associated with a decrease in peripheral 5-HT levels; however, we were not able to confirm that larger decreases of 5-HT are associated with better treatment outcome as results were inconclusive.

Sex-Specific Effects of Blood Serotonin on Reproductive Effort in a Small Passerine

AbstractLaboratory animal models have shown that blood serotonin levels reflect consistent individual differences in behavioral decision-making and maternal behavior. Serotonin could also help to understand intraspecific variation in reproductive strategies, although the mechanisms are poorly understood. In this study, the relationships of plasma serotonin with breeding parameters and parental behavior were examined in wild great tits (Parus major). Females who laid eggs earlier had higher levels of serotonin in the second half of the nestling period, while no significant relationship of serotonin with clutch size, brood size, and body size was detected. In males, serotonin levels were negatively related to clutch size and brood size and positively related to body size. The association of serotonin with provisioning behavior was sex specific, and acute fear stress induced by a predator presentation did not change this relationship. Food provisioning was positively related to size-corrected serotonin levels in females and negatively related to size-corrected serotonin levels in males. These results suggest that peripheral serotonin is a sensitive marker of parental behavior and reproductive effort in wild birds, while the mechanisms linking this neurotransmitter to reproduction are probably mediated by interplay between the serotonergic system, sex hormones, and other neurotransmitters.

Treatment Response Biomarkers in Anxiety Disorders: From Neuroimaging to Neuronally-Derived Extracellular Vesicles and Beyond

Multiple and diverse psychotherapeutic or psychopharmacologic treatments effectively reduce symptoms for many patients with anxiety disorders, but the trajectory and magnitude of response vary considerably. This heterogeneity of treatment response has invigorated the search for biomarkers of treatment response in anxiety disorders, across the lifespan. In this review, we summarize evidence for biomarkers of treatment response in children, adolescents and adults with generalized, separation and social anxiety disorders as well as panic disorder. We then discuss the relationship between these biomarkers of treatment response and the pathophysiology of anxiety disorders. Finally, we provide context for treatment response biomarkers of the future, including neuronally-derived extracellular vesicles in anxiety disorders and discuss challenges that must be overcome prior to the debut of treatment response biomarkers in the clinic. A number of promising treatment response biomarkers have been identified, although there is an urgent need to replicate findings and to identify which biomarkers might guide clinicians in selecting from available treatments rather than just simply identifying patients who may be less likely to respond to a given intervention.

No major influence of regular tobacco smoking on cerebrospinal fluid monoamine metabolite concentrations in patients with psychotic disorder and healthy individuals

Metabolism of the monoamines dopamine, serotonin and noradrenaline, is altered in the central nervous system of people with schizophrenia, and their major metabolites homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG), respectively, have been intensively studied as indirect measures of these neurotransmitters in cerebrospinal fluid (CSF). Regular tobacco smoking has been shown to alter neurotransmitter metabolism in the brain and studies have found CSF monoamine metabolite concentrations to be substantially lower in smokers. However, few studies investigating these monoamines in CSF have controlled for regular tobacco smoking. We investigated if regular tobacco smoking influences CSF HVA, 5-HIAA and MHPG concentrations in patients treated for psychotic disorders (n = 69) and healthy non-psychotic human volunteers (n = 200). After lumbar puncture CSF samples were analyzed with mass fragmentography. CSF HVA, 5-HIAA and MHPG concentrations did not significantly differ between smokers and non-smokers neither in patients, nor in healthy subjects, whereas back-length predicted HVA and 5-HIAA and antipsychotic medication MHPG concentrations. The results indicate that regular tobacco smoking has no significant effect on monoamine metabolite concentrations in CSF. This suggests that lack of controlling for regular tobacco smoking should not substantially violate the results in studies of the major monoamine metabolites in CSF.

Depletion of serotonin in the basolateral amygdala elevates glutamate receptors and facilitates fear-potentiated startle

Our previous experiments demonstrated that systemic depletion of serotonin (5-hydroxytryptamine, 5-HT), similar to levels reported in patients with emotional disorders, enhanced glutamateric activity in the lateral nucleus of the amygdala (LA) and potentiated fear behaviors. However, the effects of isolated depletion of 5-HT in the LA, and the molecular mechanisms underlying enhanced glutamatergic activity are unknown. In the present study, we tested the hypothesis that depletion of 5-HT in the LA induces increased fear behavior, and concomitantly enhances glutamate receptor (GluR) expression. Bilateral infusions of 5,7-dihydroxytryptamine (4 μg per side) into the LA produced a regional reduction of serotonergic fibers, resulting in decreased 5-HT concentrations. The induction of low 5-HT in the LA elevated fear-potentiated startle, with a parallel increase in GluR1 mRNA and GluR1 protein expression. These findings suggest that low 5-HT concentrations in the LA may facilitate fear behavior through enhanced GluR-mediated mechanisms. Moreover, our data support a relationship between 5-HT and glutamate in psychopathologies.

Effect of traumatic imagery on cerebrospinal fluid dopamine and serotonin metabolites in posttraumatic stress disorder

Dopaminergic mechanisms may be involved in the pathophysiology of posttraumatic stress disorder (PTSD), although the evidence for this is limited; serotonergic mechanisms are implicated largely by virtue of the modest efficacy of serotonergic drugs in the treatment of the disorder. Basal cerebrospinal fluid (CSF) dopamine and serotonin metabolite concentrations are normal in PTSD patients. However, in the present experiment, we postulated that perturbations in CSF dopamine and serotonin metabolites could be induced by acute psychological stress. Ten volunteers with war-related chronic PTSD underwent 6-h continuous lumbar CSF withdrawal on two occasions per patient (6-9 weeks apart), using a randomized, within subject-controlled, crossover design. During one session a 1-h video with trauma-related footage (traumatic video) was shown and in the other session subjects viewed a 1-h neutral video. We quantified the dopamine metabolite homovanillic acid (HVA) and the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in CSF at 10-min intervals, before, during, and after video provocation. Blood pressure, heart rate, and subjective anxiety and mood were monitored. Significant drop in mood and increases in anxiety and blood pressure occurred during the traumatic relative to the neutral movie. CSF HVA concentrations diminished significantly after the traumatic video (p < 0.05), in comparison with the neutral, while 5-HIAA tended to diminish (p < 0.10). We conclude that an acute decline in CNS HVA concentrations is associated with laboratory-induced symptoms in chronic PTSD patients. While further research is required to determine if the stress-induced dopaminergic changes are normative or pathological, the present data suggest that increasing dopaminergic neurotransmission be explored as a potential therapy, or adjunctive therapy, for PTSD.

Physiologic changes associated with violence and abuse exposure: an examination of related medical conditions

Although the extant evidence is replete with data supporting linkages between exposure to violence or abuse and the subsequent development of medical illnesses, the underlying mechanisms of these relationships are poorly defined and understood. Physiologic changes occurring in violence- or abuse-exposed individuals point to potentially common biological pathways connecting traumatic exposures with medical outcomes. Herein, the evidence describing the long-term physiologic changes in abuse- and violence-exposed populations and associated medical illnesses are reviewed. Current data support that (a) specific neurobiochemical changes are associated with exposure to violence and abuse; (b) several biological pathways have the potential to lead to the development of future illness; and (c) common physiologic mechanisms may moderate the severity, phenomenology, or clinical course of medical illnesses in individuals with histories of exposure to violence or abuse. Importantly, additional work is needed to advance our emerging understanding of the biological mechanisms connecting exposure to violence and abuse and negative health outcomes.

The co-occurrence of cigarette smoking and bipolar disorder: phenomenology and treatment considerations

OBJECTIVES

  Despite recent advances in understanding the causes and treatment of nicotine dependence among individuals with psychiatric disorders, smoking among individuals with bipolar disorder (BD) has received little attention. The goal of this review is to synthesize the literature on the epidemiology, consequences, and treatment of smoking and nicotine dependence among individuals with BD and to delineate a future research agenda.

METHODS

  We conducted a PubMed search of English-language articles using the search terms bipolar disorder, mania, tobacco, nicotine, and smoking, followed by a manual search of the literature cited in the identified articles. Articles were chosen by the authors on the basis of their relevance to the topic areas covered in this selective review.

RESULTS

  Adults with BD are two to three times more likely to have started smoking and, on the basis of epidemiological data, may be less likely to initiate and/or maintain smoking abstinence than individuals without psychiatric disorders. Smoking cessation is achievable for individuals with BD, but challenges such as chronic mood dysregulation, high prevalence of alcohol and drug use, more severe nicotine dependence, and limited social support can make quitting more difficult. Effective treatments for tobacco cessation are available, but no controlled trials in smokers with BD have been conducted.

CONCLUSIONS

  Cigarette smoking is a prevalent and devastating addiction among individuals with BD and should be addressed by mental health providers. Additional research on the mechanisms of, and optimal treatment for, smoking and nicotine dependence in this population is desperately needed.

Blood 5-hydroxytryptamine, 5-hydroxyindoleacetic acid and melatonin levels in patients with either Huntington's disease or chronic brain injury

Following a study of oxidative tryptophan metabolism to kynurenines, we have now analysed the blood of patients with either Huntington's disease or traumatic brain injury for levels of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and melatonin. There were no differences in the baseline levels of these compounds between patients and healthy controls. Tryptophan depletion did not reduce 5-HT levels in either the controls or in the patients with Huntington's disease, but it increased 5-HT levels in patients with brain injury and lowered 5-HIAA in the control and Huntington's disease groups. An oral tryptophan load did not modify 5-HT levels in the patients but increased 5-HT in control subjects. The tryptophan load restored 5-HIAA to baseline levels in controls and patients with brain injury, but not in those with Huntington's disease, in whom 5-HIAA remained significantly depressed. Melatonin levels increased on tryptophan loading in all subjects, with levels in patients with brain injury increasing significantly more than in controls. Baseline levels of neopterin and lipid peroxidation products were higher in patients than in controls. It is concluded that both groups of patients exhibit abnormalities in tryptophan metabolism, which may be related to increased inflammatory status and oxidative stress. Interactions between the kynurenine, 5-HT and melatonin pathways should be considered when interpreting changes of tryptophan metabolism.

Serotonin function is associated with behavioral response to a novel conspecific in marmosets

The function of the central nervous system neurotransmitter serotonin (5-HT) contributes to individual differences in impulsive behavior in humans and nonhuman primates. We investigated the relationship between 5-HT function and behavioral responses to a novel social scenario in marmosets. In the first study, marmosets (n=10) were treated orally with fluoxetine HCl (FLX) or vehicle for two trial periods and exposed to a novel conspecific for a 20-min trial following each treatment. Levels of behavioral inhibition in response to a novel conspecific were quantified. The animals exhibited less inhibition toward the novel conspecific following the 14-day FLX treatment than they did following the vehicle treatment. In the second study we first characterized the parameters of the marmoset peripheral 5-HT system and further assessed the relationship between natural variation in peripheral 5-HT and 5-HIAA levels with behavioral inhibition in response to a novel conspecific (n=14). Individual peripheral 5-HT and 5-HIAA levels were higher in animals that exhibited more inhibition in response toward the stranger. We conclude that serotonergic influences play a role in behavioral response to a novel conspecific in marmosets.