Impaired hypothalamic-pituitary-adrenal axis and its feedback regulation in serotonin transporter knockout mice

Antidepressants as Endocrine Disrupting Compounds in Fish

As antidepressant usage by the global population continues to increase, their persistent detection in aquatic habitats from municipal wastewater effluent release has led to concerns of possible impacts on non-target organisms, including fish. These pharmaceuticals have been marketed as mood-altering drugs, specifically targeting the monoaminergic signaling in the brain of humans. However, the monoaminergic systems are highly conserved and involved in the modulation of a multitude of endocrine functions in vertebrates. While most studies exploring possible impact of antidepressants on fish have focused on behavioural perturbations, a smaller spotlight has been placed on the endocrine functions, especially related to reproduction, growth, and the stress response. The purpose of this review is to highlight the possible role of antidepressants as endocrine disruptors in fish. While studies linking the effects of environmentally relevant levels of antidepressant on the endocrine system in fish are sparse, the emerging evidence suggests that early-life exposure to these compounds have the potential to alter the developmental programming of the endocrine system, which could persist as long-term and multigenerational effects in teleosts.

Chronic Social Defeat During Adolescence Induces Short- and Long-Term Behavioral and Neuroendocrine Effects in Male Swiss-Webster Mice

Chronic stress exposure during adolescence is a significant risk factor for the development of depression. Chronic social defeat (CSD) in rodents is an animal model of depression with excellent ethological, predictive, discriminative, and face validity. Because the CSD model has not been thoroughly examined as a model of stress-induced depression within the adolescence stage, the present study analyzed the short- and long-term behavioral and neuroendocrine effects of CSD during early adolescence. Therefore, adolescent male Swiss-Webster (SW) mice were exposed to the CSD model from postnatal day (PND) 28 to PND37. Twenty-four hours (mid-adolescence) or 4 weeks (early adulthood) later, mice were tested in two models of depression; the social interaction test (SIT) and forced swimming test (FST); cognitive deficits were evaluated in the Barnes maze (BM). Finally, corticosterone and testosterone content was measured before, during, and after CSD exposure, and serotonin transporter (SERT) autoradiography was studied after CSD in adolescent and adult mice. CSD during early adolescence induced enduring depression-like behaviors as inferred from increased social avoidance and immobility behavior in the SIT and FST, respectively, which correlated in an age-dependent manner with SERT binding in the hippocampus; CSD during early adolescence also induced long-lasting learning and memory impairments in the Barnes maze (BM). Finally, CSD during early adolescence increased serum corticosterone levels in mid-adolescence and early adulthood and delayed the expected increase in serum testosterone levels observed at this age. In conclusion: (1) CSD during early adolescence induced long-lasting depression-like behaviors, (2) sensitivity of SERT density during normal brain development was revealed, (3) CSD during early adolescence induced enduring cognitive deficits, and (4) results highlight the vulnerability of the adolescent brain to social stressors on the adrenal and gonadal axes, which emphasizes the importance of an adequate interaction between both axes during adolescence for normal development of brain and behavior.

Zygotic exposure to venlafaxine disrupts cortisol stress axis activity in multiple generations of zebrafish

Ubiquitous use of antidepressants has resulted in increased concentrations of these pharmaceuticals in waterways receiving municipal wastewater effluent. Amongst these, venlafaxine, a selective serotonin and norepinephrine reuptake inhibitor, is commonly found at concentrations surpassing 1 ppb in surface waters. We recently showed that the deposition of venlafaxine in zebrafish (Danio rerio) embryos impacts neural development in the hypothalamus, suggesting the possibility of neuroendocrine disruptions due to this antidepressant. Here, we tested the hypothesis that early developmental exposure to venlafaxine disrupts the long-term functioning of the hypothalamus-pituitary-interrenal (HPI) axis in zebrafish. Embryos (1-4 cell stage) were injected with either 0, 1, or 10 ng venlafaxine, and the ontogeny of cortisol content, as well as changes in cortisol levels following a stressor in larvae and adults were assessed across 3 generations. Zygotic venlafaxine exposure did not affect the ontogeny of cortisol production, but there was a disruption in the cortisol response to stressor exposure, which was also evident in multiple generations. In the F₀ generation, venlafaxine exposure did not affect cortisol levels in response to stressor exposure in larvae, but adult females, and not males, showed an attenuated cortisol response compared to control fish. This reduction in cortisol levels in the females was rescued by stimulation with adrenocorticotropic hormone, suggesting that the disruption was at the level of the hypothalamus-pituitary axis. Venlafaxine-mediated disruption in HPI axis functioning was also evident in the F₁ and F₂ generations, including impaired cortisol responses to a stressor in adult female and larval fish, respectively. Taken together, our results suggest that venlafaxine is an endocrine disruptor, and early developmental exposure to this antidepressant may have long-term and generational consequences on cortisol stress axis activity in zebrafish.

Neurokinin-1 receptor antagonist reverses functional CNS alteration caused by combined γ-rays and carbon nuclei irradiation

BACKGROUND

Ionizing radiation (IR) is one of the major limiting factors for human deep-space missions. Preventing IR-induced cognitive alterations in astronauts is a critical success factor. It has been shown that cognitive alterations in rodents can be inferred by alterations of a psycho-emotional balance, primarily an anxiogenic effect of IR. In our recent work we hypothesized that the neurokinin-1 (NK1) receptor may be instrumental for such alterations.

OBJECTIVE

The NK1 receptor antagonist rolapitant and the classic anxiolytic diazepam (as a comparison drug) were selected to test this hypothesis on Wistar rats.

METHOD

Pharmacological substances were administered through intragastric probes. We used a battery of tests for a comprehensive ethological analysis. A high-performance liquid chromatography was applied to quantify monoamines content. An analysis of mRNA expression was performed by real-time PCR. Protein content was studied by Western blotting technique.

RESULTS

Our salient finding includes no substantial changes in anxiety, locomotor activity and cognitive abilities of treated rats under irradiation. No differences were found in the content of monoamines. We discovered a synchronous effect on mRNA expression and protein content of 5-HT2a and 5-HT4 receptors in the prefrontal cortex, as well as decreased content of serotonin transporter and increased content of tryptophan hydroxylase in the hypothalamus of irradiated rats. Rolapitant affected the protein amount of a number of serotonin receptors in the amygdala of irradiated rats.

CONCLUSION

Rolapitant may be the first atypical radioprotector, providing symptomatic treatment of CNS functional disorders in astronauts caused by IR.

Brain stimulation rewarding experience attenuates neonatal clomipramine-induced adulthood anxiety by reversal of pathological changes in the amygdala

Major depressive disorder (MDD) is associated with enhanced anxiety and reduced reward processing leading to impaired cognitive flexibility. These pathological changes during depression are accompanied by dysfunctional hypothalamic-pituitary-adrenal (HPA) axis and its impaired regulation by the amygdala. Notably, the electrical stimulation of brain reward areas produces an antidepressant effect in both MDD patients and animal models of depression. However, the effects of chronic electrical self-stimulation of lateral hypothalamus - medial forebrain bundle (LH-MFB) on depression-associated anxiety and accompanying changes in plasma corticosterone levels, structural, and neurochemical alterations in the amygdala are unknown. Here, we used the neonatal clomipramine (CLI) model of depression. During adulthood, neonatal CLI and vehicle administered rats were subjected to bilateral electrode implantation at LH-MFB and trained to receive intracranial self-stimulation (ICSS) for 14 days. Rats were then tested for anhedonic and anxiety-like behaviors, followed by estimation of plasma corticosterone levels, assessment of amygdalar volumes and neuronal/glial numbers, levels of monoamines and their metabolites in the amygdala. We found that chronic ICSS of LH-MFB reverses CLI-induced anhedonia and anxiety. Interestingly, amelioration of CLI-induced enhanced anhedonia and anxiety in ICSS rats was associated with partial reversal of enhanced plasma corticosterone levels, hypertrophy of basolateral amygdala (BLA), and altered noradrenaline (NA) metabolism in the amygdalar complex. We suggest that beneficial effects of ICSS on CLI-induced anxiety at least in part mediated by the restoration of amygdalar and HPA axis functioning. Our results support the hypothesis that brain stimulation rewarding experience might be evolved as a therapeutic strategy for reversal of amygdalar dysfunction in depression.

Evolution of brain-wide activity in the awake behaving mouse after acute fear by longitudinal manganese-enhanced MRI

Life threatening fear after a single exposure evolves in a subset of vulnerable individuals to anxiety, which may persist for their lifetime. Yet neither the whole brain's response to innate acute fear nor how brain activity evolves over time is known. Sustained neuronal activity may be a factor in the development of a persistent fear response. We couple two experimental protocols to provoke acute fear leading to prolonged fear: Predator stress (PS), a naturalistic approach to induce fear in rodents; and Serotonin transporter knockout mouse (SERT-KO) that responds to PS with sustained defensive behavior. Behavior was monitored before, during and at short and long times after PS in wild type (WT) and SERT-KO mice. Both genotypes responded to PS with defensive behavior. SERT-KO retained defensive behavior for 23 days, while WT mice returned to baseline exploratory behavior by 9 days. Thus, differences in neural activity between WT and SERT-KO 9 days after PS identifies neural correlates of persistent defensive behavior, in mice. We used longitudinal manganese-enhanced magnetic resonance imaging (MEMRI) to identify brain-wide neural activity associated with different behaviors. Mn2+ accumulation in active neurons occurs in awake, behaving mice and is retrospectively imaged. Following the same two cohorts of mice, WT and SERT-KO, longitudinally allowed unbiased quantitative comparisons of brain-wide activity by statistical parametric mapping (SPM). During natural behavior in WT, only low levels of activity-induced Mn2+-accumulation were detected, while much more accumulation appeared immediately after PS in both WT and SERT-KO, and evolved at 9 days to a new activity pattern (p < 0.0001, uncorr., T = 5.4). Patterns of accumulation differed between genotypes, with more regions of the brain and larger volumes within regions involved in SERT-KO than WT. A new computational segmentation analysis, using our InVivo Atlas based on a manganese-enhanced MR image of a living mouse, revealed dynamic changes in the volume of significantly enhanced voxels within each segment that differed between genotypes across 45 of 87 segmented regions. At Day 9 after PS, the striatum and ventral pallidum were active in both genotypes but more so in the SERT-KO. SERT-KO also displayed sustained or increased volume of Mn2+ accumulations between Post-Fear and Day 9 in eight segments where activity was decreased or silenced in WT. C-fos staining, an alternative neural activity marker, of brains from the same mice fixed at conclusion of imaging sessions confirmed that MEMRI detected active neurons. Intensity measurements in 12 regions of interest (ROIs) supported the SPM results. Between group comparisons by SPM and of ROI measurements identified specific regions differing between time points and genotypes. We report brain-wide activity in response to a single exposure of acute fear, and, for the first time, its evolution to new activity patterns over time in individuals vulnerable to persistent fear. Our results show multiple regions with dynamic changes in neural activity and that the balance of activity between segments is disordered in the SERT-KO. Thus, longitudinal MEMRI represents a powerful approach to discover how brain-wide activity evolves from the natural state either after an experience or during a disease process.

Metabolic, Molecular, and Behavioral Effects of Western Diet in Serotonin Transporter-Deficient Mice: Rescue by Heterozygosity?

Reduced function of the serotonin transporter (SERT) is associated with increased susceptibility to anxiety and depression and with type-2 diabetes, which is especially true in older women. Preference for a "Western diet" (WD), enriched with saturated fat, cholesterol, and sugars, may aggravate these conditions. In previous studies, decreased glucose tolerance, central and peripheral inflammation, dyslipidemia, emotional, cognitive, and social abnormalities were reported in WD-fed young female mice. We investigated the metabolic, molecular, and behavioral changes associated with a 3-week-long dietary regime of either the WD or control diet in 12-month-old female mice with three different Sert genotypes: homozygous (Slc6a4) gene knockout (Sert ^-/-: KO), heterozygous (Sert ^+/-: HET), or wild-type mice (Sert ^+/+: WT). In the WT-WD and KO-WD groups, but not in HET-WD-fed mice, most of changes induced by the WD paralleled those found in the younger mice, including brain overexpression of inflammatory marker Toll-like receptor 4 (Tlr4) and impaired hippocampus-dependent performance in the marble test. However, the 12-month-old female mice became obese. Control diet KO mice exhibited impaired hippocampal-dependent behaviors, increased brain expression of the serotonin receptors Htr2c and Htr1b, as well as increased Tlr4 and mitochondrial regulator, peroxisome proliferator-activated receptor gamma-coactivator-1a (Ppargc1a). Paradoxically, these, and other changes, were reversed in KO-WD mutants, suggesting a complex interplay between Sert deficiency and metabolic factors as well as potential compensatory molecular mechanisms that might be disrupted by the WD exposure. Most, but not all, of the changes in gene expression in the brain and liver of KO mice were not exhibited by the HET mice fed with either diet. Some of the WD-induced changes were similar in the KO-WD and HET-WD-fed mice, but the latter displayed a "rescued" phenotype in terms of diet-induced abnormalities in glucose tolerance, neuroinflammation, and hippocampus-dependent performance. Thus, complete versus partial Sert inactivation in aged mice results in distinct metabolic, molecular, and behavioral consequences in response to the WD. Our findings show that Sert ^+/- mice are resilient to certain environmental challenges and support the concept of heterosis as evolutionary adaptive mechanism.

Presence of Mother Reduces Early-Life Social Stress: Linking the Alteration in Hypothalamic-Pituitary-Adrenal Axis and Serotonergic System

In this study, we examined whether the presence of mother suppresses early-life stressful social experience (SSE)-induced anxiety-like behavior and impairment of short-term memory later in life. On postnatal day (PND)-5, mothers with pups were grouped as follows: (i) control; (ii) maternal separation (MS); (iii) pups with mother experience the presence of a stranger (M+P-ST); and (iv) maternal separated pups experience the presence of a stranger (MSP-ST). Individuals were subjected to light-dark box and spontaneous alternation from PND-29 to 32. We observed that the MSP-ST group exhibits anxiety-like behavior and impairment in short-term memory. Further, SSE significantly elevated the adrenocorticotropic hormone, corticosterone and expression of glucocorticoid receptor (GR) in MSP-ST pups. Similarly, serotonin (5-hydroxytryptamine; 5-HT), dopamine, noradrenaline and expression of serotonin transporter levels were significantly elevated in MSP-ST pups. These observations suggest that during early postnatal days, the pups may recognize strangers by the sense of smell, and the presence of mother reduces the SSE-induced stress.

Brainstem-Evoked Transcription of Defensive Genes After Spinal Cord Injury

The spinal cord after injury shows altered transcription in numerous genes. We tested in a pilot study whether the nucleus raphé magnus, a descending serotonergic brainstem region whose stimulation improves recovery after incomplete spinal cord injury (SCI), can influence these transcriptional changes. Rats received 2 h of low-frequency electrical stimulation in the raphé magnus 3 days after an impact contusion at segment T8. Comparison groups lacked injuries or activated stimulators or both. Immediately following stimulation, spinal cords were extracted, their RNA transcriptome sequenced, and differential gene expression quantified. Confirming many previous studies, injury primarily increased inflammatory and immune transcripts and decreased those related to lipid and cholesterol synthesis and neuronal signaling. Stimulation plus injury, contrasted with injury alone, caused significant changes in 43 transcripts (39 increases, 4 decreases), all protein-coding. Injury itself decreased only four of these 43 transcripts, all reversed by stimulation, and increased none of them. The non-specific 5-HT7 receptor antagonist pimozide reversed 25 of the 43 changes. Stimulation in intact rats principally caused decreases in transcripts related to oxidative phosphorylation, none of which were altered by stimulation in injury. Gene ontology (biological process) annotations comparing stimulation with either no stimulation or pimozide treatment in injured rats highlighted defense responses to lipopolysaccharides and microorganisms, and also erythrocyte development and oxygen transport (possibly yielding cellular oxidant detoxification). Connectivity maps of human orthologous genes generated in the CLUE database of perturbagen-response transcriptional signatures showed that drug classes whose effects in injured rats most closely resembled stimulation without pimozide include peroxisome proliferator-activated receptor agonists and angiotensin receptor blockers, which are reportedly beneficial in SCI. Thus the initial transcriptional response of the injured spinal cord to raphé magnus stimulation is upregulation of genes that in various ways are mostly protective, some probably located in recently arrived myeloid cells.

Constitutive Serotonin Transporter Reduction Resembles Maternal Separation with Regard to Stress-Related Gene Expression

Interactive effects between allelic variants of the serotonin transporter (5-HTT) promoter-linked polymorphic region (5-HTTLPR) and stressors on depression symptoms have been documented, as well as questioned, by meta-analyses. Translational models of constitutive 5-htt reduction and experimentally controlled stressors often led to inconsistent behavioral and molecular findings and often did not include females. The present study sought to investigate the effect of 5-htt genotype, maternal separation, and sex on the expression of stress-related candidate genes in the rat hippocampus and frontal cortex. The mRNA expression levels of Avp, Pomc, Crh, Crhbp, Crhr1, Bdnf, Ntrk2, Maoa, Maob, and Comt were assessed in the hippocampus and frontal cortex of 5-htt ^± and 5-htt ^+/+ male and female adult rats exposed, or not, to daily maternal separation for 180 min during the first 2 postnatal weeks. Gene- and brain region-dependent, but sex-independent, interactions between 5-htt genotype and maternal separation were found. Gene expression levels were higher in 5-htt ^+/+ rats not exposed to maternal separation compared with the other experimental groups. Maternal separation and 5-htt ^+/- genotype did not yield additive effects on gene expression. Correlative relationships, mainly positive, were observed within, but not across, brain regions in all groups except in non-maternally separated 5-htt ^+/+ rats. Gene expression patterns in the hippocampus and frontal cortex of rats exposed to maternal separation resembled the ones observed in rats with reduced 5-htt expression regardless of sex. These results suggest that floor effects of 5-htt reduction and maternal separation might explain inconsistent findings in humans and rodents.

Cellular Changes in Injured Rat Spinal Cord Following Electrical Brainstem Stimulation

Spinal cord injury (SCI) is a major cause of disability and pain, but little progress has been made in its clinical management. Low-frequency electrical stimulation (LFS) of various anti-nociceptive targets improves outcomes after SCI, including motor recovery and mechanical allodynia. However, the mechanisms of these beneficial effects are incompletely delineated and probably multiple. Our aim was to explore near-term effects of LFS in the hindbrain's nucleus raphe magnus (NRM) on cellular proliferation in a rat SCI model. Starting 24 h after incomplete contusional SCI at C5, intermittent LFS at 8 Hz was delivered wirelessly to NRM. Controls were given inactive stimulators. At 48 h, 5-bromodeoxyuridine (BrdU) was administered and, at 72 h, spinal cords were extracted and immunostained for various immune and neuroglial progenitor markers and BrdU at the level of the lesion and proximally and distally. LFS altered cell marker counts predominantly at the dorsal injury site. BrdU cell counts were decreased. Individually and in combination with BrdU, there were reductions in CD68 (monocytes) and Sox2 (immature neural precursors) and increases in Blbp (radial glia) expression. CD68-positive cells showed increased co-staining with iNOS. No differences in the expression of GFAP (glia) and NG2 (oligodendrocytes) or in GFAP cell morphology were found. In conclusion, our work shows that LFS of NRM in subacute SCI influences the proliferation of cell types implicated in inflammation and repair, thus providing mechanistic insight into deep brain stimulation as a neuromodulatory treatment for this devastating pathology.

Changes in PPARδ expression in a rat model of stress-induced depression

Depression is a common mental disorder that has been linked to a decrease in the expression of serotonin and/or the serotonin transporter in the brain. Antidepressants that target the monoaminergic system are widely used in the clinical setting. Peroxisome proliferator-activated receptor δ (PPAR δ) overexpression or activation is thought to improve depression-like behaviours in rodents. The present study was designed to characterize the changes in PPARδ expression in the hippocampus in rats with stress-induced depression. We used an unpredictable chronic mild stress (CMS) model in rats to study the role of PPARδ in the hippocampus. Behaviour was evaluated via a forced swim test (FST), a tail suspension test (TST), and a sucrose preference test (SPT). Then, the changes in PPARδ expression and other signals were determined using Western blots. We found that PPARδ expression in the hippocampus was markedly reduced in rats with depression. Moreover, the expression of the serotonin transporter was also significantly decreased. Treatment with a PPARδ agonist enhanced the expression of PPARδ and the serotonin transporter in the hippocampus of rats with stress-induced depression. Additionally, treatment with a PPARδ agonist increased the expression of the serotonin transporter in cultured hippocampal (H19-7) cells, and this action was ablated in the absence of PPARδ, which was attenuated with shRNA. Taken together, we found that PPARδ plays an important role in the regulation of serotonin transporter expression and that chronic stress may lower PPARδ expression in the brain via apoptosis and may attenuate serotonin transporter expression, thus inducing depression in rats.

The Serotonin Transporter and Early Life Stress: Translational Perspectives

The interaction between the serotonin transporter (SERT) linked polymorphic region (5-HTTLPR) and adverse early life stressing (ELS) events is associated with enhanced stress susceptibility and risk to develop mental disorders like major depression, anxiety, and aggressiveness. In particular, human short allele carriers are at increased risk. This 5-HTTLPR polymorphism is absent in the rodent SERT gene, but heterozygous SERT knockout rodents (SERT^+/−) show several similarities to the human S-allele carrier, therefore creating an animal model of the human situation. Many rodent studies investigated ELS interactions in SERT knockout rodents combined with ELS. However, underlying neuromolecular mechanisms of the (mal)adaptive responses to adversity displayed by SERT rodents remain to be elucidated. Here, we provide a comprehensive review including studies describing mechanisms underlying SERT variation × ELS interactions in rodents. Alterations at the level of translation and transcription but also epigenetic alterations considerably contribute to underlying mechanisms of SERT variation × ELS interactions. In particular, SERT^+/− rodents exposed to adverse early rearing environment may be of high translational and predictive value to the more stress sensitive human short-allele carrier, considering the similarity in neurochemical alterations. Therefore, SERT^+/− rodents are highly relevant in research that aims to unravel the complex psychopathology of mental disorders. So far, most studies fail to show solid evidence for increased vulnerability to develop affective-like behavior after ELS in SERT^+/− rodents. Several reasons may underlie these failures, e.g., (1) stressors used might not be optimal or severe enough to induce maladaptations, (2) effects in females are not sufficiently studied, and (3) few studies include both behavioral manifestations and molecular correlates of ELS-induced effects in SERT^+/− rodents. Of course, one should not exclude the (although unlikely) possibility of SERT^+/− rodents not being sensitive to ELS. In conclusion, future studies addressing ELS-induced effects in the SERT^+/− rodents should extensively study both long-term behavioral and (epi)genetic aspects in both sexes. Finally, further research is warranted using more severe stressors in animal models. From there on, we should be able to draw solid conclusions whether the SERT^+/− exposed to ELS is a suitable translational animal model for studying 5-HTTLPR polymorphism and stress interactions.

Clinical and Neurobiological Relevance of Current Animal Models of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social and communication impairments, as well as repetitive and restrictive behaviors. The phenotypic heterogeneity of ASD has made it overwhelmingly difficult to determine the exact etiology and pathophysiology underlying the core symptoms, which are often accompanied by comorbidities such as hyperactivity, seizures, and sensorimotor abnormalities. To our benefit, the advent of animal models has allowed us to assess and test diverse risk factors of ASD, both genetic and environmental, and measure their contribution to the manifestation of autistic symptoms. At a broader scale, rodent models have helped consolidate molecular pathways and unify the neurophysiological mechanisms underlying each one of the various etiologies. This approach will potentially enable the stratification of ASD into clinical, molecular, and neurophenotypic subgroups, further proving their translational utility. It is henceforth paramount to establish a common ground of mechanistic theories from complementing results in preclinical research. In this review, we cluster the ASD animal models into lesion and genetic models and further classify them based on the corresponding environmental, epigenetic and genetic factors. Finally, we summarize the symptoms and neuropathological highlights for each model and make critical comparisons that elucidate their clinical and neurobiological relevance.

Dexamethasone Treatment Leads to Enhanced Fear Extinction and Dynamic Fkbp5 Regulation in Amygdala

Posttraumatic stress disorder (PTSD) is both a prevalent and debilitating trauma-related disorder associated with dysregulated fear learning at the core of many of its signs and symptoms. Improvements in the currently available psychological and pharmacological treatments are needed in order to improve PTSD treatment outcomes and to prevent symptom relapse. In the present study, we used a putative animal model of PTSD that included presentation of immobilization stress (IMO) followed by fear conditioning (FC) a week later. We then investigated the acute effects of GR receptor activation on the extinction (EXT) of conditioned freezing, using dexamethasone administered systemically which is known to result in suppression of the HPA axis. In our previous work, IMO followed by tone-shock-mediated FC was associated with impaired fear EXT. In this study, we administered dexamethasone 4 h before EXT training and then examined EXT retention (RET) 24 h later to determine whether dexamethasone suppression rescued EXT deficits. Dexamethasone treatment produced dose-dependent enhancement of both EXT and RET. Dexamethasone was also associated with reduced amygdala Fkbp5 mRNA expression following EXT and after RET. Moreover, DNA methylation of the Fkbp5 gene occurred in a dose-dependent and time course-dependent manner within the amygdala. Additionally, we found dynamic changes in epigenetic regulation, including Dnmt and Tet gene pathways, as a function of both fear EXT and dexamethasone suppression of the HPA axis. Together, these data suggest that dexamethasone may serve to enhance EXT by altering Fkbp5-mediated glucocorticoid sensitivity via epigenetic regulation of Fkbp5 expression.

Acute selective serotonin reuptake inhibitors regulate the dorsal raphe nucleus causing amplification of terminal serotonin release

Selective serotonin reuptake inhibitors (SSRIs) were designed to treat depression by increasing serotonin levels throughout the brain via inhibition of clearance from the extracellular space. Although increases in serotonin levels are observed after acute SSRI exposure, 3–6 weeks of continuous use is required for relief from the symptoms of depression. Thus, it is now believed that plasticity in multiple brain systems that are downstream of serotonergic inputs contributes to the therapeutic efficacy of SSRIs. The onset of antidepressant effects also coincides with desensitization of somatodendritic serotonin autoreceptors in the dorsal raphe nucleus (DRN), suggesting that disrupting inhibitory feedback within the serotonin system may contribute to the therapeutic effects of SSRIs. Previously, we showed that chronic SSRI treatment caused a frequency‐dependent facilitation of serotonin signaling that persisted in the absence of uptake inhibition. In this work, we use in vivo fast‐scan cyclic voltammetry in mice to investigate a similar facilitation after a single treatment of the SSRI citalopram hydrobromide. Acute citalopram hydrobromide treatment resulted in frequency‐dependent increases of evoked serotonin release in the substantia nigra pars reticulata. These increases were independent of changes in uptake velocity, but required SERT expression. Using microinjections, we show that the frequency‐dependent enhancement in release is because of SERT inhibition in the DRN, demonstrating that SSRIs can enhance serotonin release by inhibiting uptake in a location distal to the terminal release site. The novel finding that SERT inhibition can disrupt modulatory mechanisms at the level of the DRN to facilitate serotonin release will help future studies investigate serotonin's role in depression and motivated behavior.

In this work, stimulations of the dorsal raphe nucleus (DRN) evoke serotonin release that is recorded in the substantia nigra pars reticulata (SNpr) using in vivo fast‐scan cyclic voltammetry. Systemic administration of a selective serotonin reuptake inhibitor (SSRI) causes both an increase in t_1/2 and an increase in [5‐HT]_max in the SNpr. Local application of SSRI to the DRN recapitulates the increase in [5‐HT]_max observed in the SNpr without affecting uptake. Thus, SSRIs increase serotonin signaling via two distinct SERT‐mediated mechanisms.

Upregulating serotonin transporter expression and downregulating monoamine oxidase-A and indoleamine 2, 3-dioxygenase expression involved in the antidepressant effect of sodium valproate in a rat model

Sodium valproate (VPA) is widely used as an antiepileptic agent and mood stabilizer. In recent years, VPA has been increasingly used as a psychotherapeutic drug to treat depression. In this article, a possible antidepressant mechanism of VPA was investigated by studying the expression and therefore the involvement of tryptophan hydroxylase, serotonin transporter (5-HTT), monoamine oxidase-A (MAO-A), and indoleamine 2, 3-dioxygenase (IDO) in rats exposed to chronic unpredicted stress. Male Sprague-Dawley rats were divided into four groups: the vehicle-treated control group (CG), the VPA-treated control group (VPAC), the vehicle-treated model group (MG), and the VPA-treated model group (VPAM). VPA (300 mg/kg once daily) was administered to VPAC and VPAM rats by means of intragastric gavage while an equivalent volume of vehicle was given to vehicle-treated CG and MG rats. Rat behavior and expression of tryptophan hydroxylase, 5-HTT, MAO-A, and IDO in the hippocampus were determined. A significant reduction in depression-like behaviors was observed with an upregulation of 5-HTT expression and a downregulation of MAO-A and IDO expression in VPAM rats, compared with MG rats. The results may suggest that the antidepressant mechanism of VPA is partly related to elevated serotonin level and its reuse in the vesicles of presynaptic nerve endings.

The Association of 5-HTTLPR XLL Genotype with Higher Cortisol Levels in African Americans

Genetic variants of the human serotonin transporter (SERT) may contribute to HPA axis dysregulation. SERT has two promoter region polymorphisms (5-HTTLPR: VNTR and SNP: rs25531), which may alter levels of SERT protein and its function. Combining these polymorphisms creates a functional polymorphism (FN) which may modulate mRNA expression. This study examines the relationship between these genetic variants and morning and evening salivary samples of both cortisol and dehydroepiandrosterone sulfate (DHEAS) concentrations in 269 African American (AA) adults. Resultant allele frequencies for the VNTR, SNP, and FN genotypes were 70% L (2% XLL), 84% A, and 54% LA (2% XLLA), respectively. The XLL genotype was associated with significantly higher concentrations of cortisol (~3X) and DHEAS (~2X) for both VNTR and FN polymorphisms. No significant differences were found for SNP genotypes. Conclusions were that persons with VNTR and FN XLL polymorphisms had significantly higher cortisol and DHEAS concentrations than other genotypes. AAs also appear to have a higher frequency of the rare XL allele than Caucasians. Whether the XLL genotype predisposes AAs to greater health challenges will require further research to determine the implications of these findings.

Monoamine-sensitive developmental periods impacting adult emotional and cognitive behaviors

Development passes through sensitive periods, during which plasticity allows for genetic and environmental factors to exert indelible influence on the maturation of the organism. In the context of central nervous system development, such sensitive periods shape the formation of neurocircuits that mediate, regulate, and control behavior. This general mechanism allows for development to be guided by both the genetic blueprint as well as the environmental context. While allowing for adaptation, such sensitive periods are also vulnerability windows during which external and internal factors can confer risk to disorders by derailing otherwise resilient developmental programs. Here we review developmental periods that are sensitive to monoamine signaling and impact adult behaviors of relevance to psychiatry. Specifically, we review (1) a serotonin-sensitive period that impacts sensory system development, (2) a serotonin-sensitive period that impacts cognition, anxiety- and depression-related behaviors, and (3) a dopamine- and serotonin-sensitive period affecting aggression, impulsivity and behavioral response to psychostimulants. We discuss preclinical data to provide mechanistic insight, as well as epidemiological and clinical data to point out translational relevance. The field of translational developmental neuroscience has progressed exponentially providing solid conceptual advances and unprecedented mechanistic insight. With such knowledge at hand and important methodological innovation ongoing, the field is poised for breakthroughs elucidating the developmental origins of neuropsychiatric disorders, and thus understanding pathophysiology. Such knowledge of sensitive periods that determine the developmental trajectory of complex behaviors is a necessary step towards improving prevention and treatment approaches for neuropsychiatric disorders.

Early life adversity and serotonin transporter gene variation interact at the level of the adrenal gland to affect the adult hypothalamo-pituitary-adrenal axis

The short allelic variant of the serotonin transporter (5-HTT) promoter-linked polymorphic region (5-HTTLPR) has been associated with the etiology of major depression by interaction with early life stress (ELS). Furthermore, 5-HTTLPR has been associated with abnormal functioning of the stress-responsive hypothalamo-pituitary-adrenal (HPA) axis. Here, we examined if, and at what level, the HPA-axis is affected in an animal model for ELS × 5-HTTLPR interactions. Heterozygous and homozygous 5-HTT knockout rats and their wild-type littermates were exposed daily at postnatal days 2-14 to 3 h of maternal separation. When grown to adulthood, plasma levels of adrenocorticotropic hormone (ACTH), and the major rat glucocorticoid, corticosterone (CORT), were measured. Furthermore, the gene expression of key HPA-axis players at the level of the hypothalamus, pituitary and adrenal glands was assessed. No 5-HTT genotype × ELS interaction effects on gene expression were observed at the level of the hypothalamus or pituitary. However, we found significant 5-HTT genotype × ELS interaction effects for plasma CORT levels and adrenal mRNA levels of the ACTH receptor, such that 5-HTT deficiency was associated under control conditions with increased, but after ELS with decreased basal HPA-axis activity. With the use of an in vitro adrenal assay, naïve 5-HTT knockout rats were furthermore shown to display increased adrenal ACTH sensitivity. Therefore, we conclude that basal HPA-axis activity is affected by the interaction of 5-HTT genotype and ELS, and is programmed, within the axis itself, predominantly at the level of the adrenal gland. This study therefore emphasizes the importance of the adrenal gland for HPA-related psychiatric disorders.

Diurnal cortisol rhythms in youth from risky families: effects of cumulative risk exposure and variation in the serotonin transporter gene-linked polymorphic region (5-HTTLPR) [corrected]

Building on research on cumulative risk and psychopathology, this study examines how cumulative risk exposure is associated with altered diurnal cortisol rhythms in an ethnically diverse, low-income sample of youth. In addition, consistent with a diathesis-stress perspective, this study explores whether the effect of environmental risk is moderated by allelic variation in the promoter region of the serotonin transporter gene-linked polymorphic region (5-HTTLPR). Results show that youth with greater cumulative risk exposure had flatter diurnal cortisol slopes, regardless of 5-HTTLPR genotype. However, the association of cumulative risk with average cortisol output (area under the curve [AUC]) was moderated by the 5-HTTLPR genotype. Among youth homozygous for the long allele, greater cumulative risk exposure was associated with lower cortisol AUC, driven by significant reductions in cortisol levels at waking. In contrast, there was a trend-level association between greater cumulative risk and higher cortisol AUC among youth carrying the short allele, driven by a trend-level increase in bedtime cortisol levels. Findings are discussed with regard to the relevance of dysregulated diurnal cortisol rhythms for the development of psychopathology and the implications of genetically mediated differences in psychophysiological adaptations to stress.

5-HTT deficiency affects neuroplasticity and increases stress sensitivity resulting in altered spatial learning performance in the Morris water maze but not in the Barnes maze

The purpose of this study was to evaluate whether spatial hippocampus-dependent learning is affected by the serotonergic system and stress. Therefore, 5-HTT knockout (-/-), heterozygous (+/-) and wildtype (+/+) mice were subjected to the Barnes maze (BM) and the Morris water maze (WM), the latter being discussed as more aversive. Additionally, immediate early gene (IEG) expression, hippocampal adult neurogenesis (aN), and blood plasma corticosterone were analyzed.

While the performance of 5-HTT-/- mice in the BM was undistinguishable from both other genotypes, they performed worse in the WM. However, in the course of the repeated WM trials 5-HTT-/- mice advanced to wildtype level. The experience of a single trial of either the WM or the BM resulted in increased plasma corticosterone levels in all genotypes. After several trials 5-HTT-/- mice exhibited higher corticosterone concentrations compared with both other genotypes in both tests. Corticosterone levels were highest in 5-HTT-/- mice tested in the WM indicating greater aversiveness of the WM and a greater stress sensitivity of 5-HTT deficient mice.

Quantitative immunohistochemistry in the hippocampus revealed increased cell counts positive for the IEG products cFos and Arc as well as for proliferation marker Ki67 and immature neuron marker NeuroD in 5-HTT-/- mice compared to 5-HTT+/+ mice, irrespective of the test. Most differences were found in the suprapyramidal blade of the dentate gyrus of the septal hippocampus. Ki67-immunohistochemistry revealed a genotype x environment interaction with 5-HTT genotype differences in naïve controls and WM experience exclusively yielding more Ki67-positive cells in 5-HTT+/+ mice. Moreover, in 5-HTT-/- mice we demonstrate that learning performance correlates with the extent of aN.

Overall, higher baseline IEG expression and increased an in the hippocampus of 5-HTT-/- mice together with increased stress sensitivity may constitute the neurobiological correlate of raised alertness, possibly impeding optimal learning performance in the more stressful WM.

Effects of fluoxetine on CRF and CRF1 expression in rats exposed to the learned helplessness paradigm

RATIONALE

Stress is a common antecedent reported by people suffering major depression. In these patients, extrahypothalamic brain areas, like the hippocampus and basolateral amygdala (BLA), have been found to be affected. The BLA synthesizes CRF, a mediator of the stress response, and projects to hippocampus. The main hippocampal target for this peptide is the CRF subtype 1 receptor (CRF1). Evidence points to a relationship between dysregulation of CRF/CRF1 extrahypothalamic signaling and depression.

OBJECTIVE

Because selective serotonin reuptake inhibitors (SSRIs) are the first-line pharmacological treatment for depression, we investigated the effect of chronic treatment with the SSRI fluoxetine on long-term changes in CRF/CRF1 signaling in animals showing a depressive-like behavior.

METHODS

Male Wistar rats were exposed to the learned helplessness paradigm (LH). After evaluation of behavioral impairment, the animals were treated with fluoxetine (10 mg/kg i.p.) or saline for 21 days. We measured BLA CRF expression with RT-PCR and CRF1 expression in CA3 and the dentate gyrus of the hippocampus with in situ hybridization. We also studied the activation of one of CRF1's major intracellular signaling targets, the extracellular signal-related kinases 1 and 2 (ERK1/2) in CA3.

RESULTS

In saline-treated LH animals, CRF expression in the BLA increased, while hippocampal CRF1 expression and ERK1/2 activation decreased. Treatment with fluoxetine reversed the changes in CRF and CRF1 expressions, but not in ERK1/2 activation.

CONCLUSION

In animals exposed to the learned helplessness paradigm, there are long-term changes in CRF and CRF1 expression that are restored with a behaviorally effective antidepressant treatment.

Glucocorticoid receptor and molecular chaperones in the pathogenesis of adrenal incidentalomas: potential role of reduced sensitivity to glucocorticoids

Glucocorticoid (GC) sensitivity depends on glucocorticoid receptor (GR) and heat shock proteins (Hsps). We investigated whether common GR genes (ER22/23EK, N363S, Bcl I, and 9β) and adrenocorticotropin receptor promoter polymorphisms influence susceptibility for unilateral adrenal incidentaloma (AI), plus GR and Hsp expression in tumorous (n = 19), peritumorous (n = 13) and normal adrenocortical (n = 11) tissues. Patients (n = 112), population-matched controls (n = 100) and tumor tissues (n = 32) were genotyped for these polymorphisms. Postdexamethasone serum cortisol was higher in patients (p < 0.001). GR gene variants, larger allele of Bcl I (odds ratio [OR] 2.9; 95% confidence interval [CI] 1.7-5.1; p < 0.001] and minor allele of 9β (OR 3.0; 95% CI 1.6-5.7; p < 0.001) were independent predictors of AI. In patients, the first allele is linked with larger tumors (p = 0.002) and the latter with higher postdexamethasone cortisol levels (p = 0.025). Both allele carriers had lesser waist circumference (p = 0.02), similar adrenocorticotropin and higher basal (p = 0.024) and postdexamethasone cortisol concentrations (p < 0.001). Tumorous and constitutional genotypes were similar. GR-D is the major receptor isoform in normal adrenal cortex by Western blotting. Loss of other receptor isoforms, decrease in immunostaining for GR (p < 0.0001), underexpression of chaperones (p ≤ 0.01) and the presence of inducible Hsp70 were found in adenomas. In conclusion, GR gene variants, C allele of Bcl I and minor allele of 9β, are associated with AIs. Their concurrent presence in patients reduces GC sensitivity. Normal adrenal cortex preferentially expresses GR-D. In adenomas, the lack of other GR isoforms and underexpression of heat shock proteins perhaps permanently impair GC signaling, which could promote dysregulated cortisol production and tumor growth. The innate GC sensitivity probably modifies these effects.

Environmental enrichment rescues female-specific hyperactivity of the hypothalamic-pituitary-adrenal axis in a model of Huntington's disease

Huntington's disease (HD) has long been regarded as a disease of the central nervous system, partly due to typical disease symptoms that include loss of motor control, cognitive deficits and neuropsychiatric disturbances. However, the huntingtin gene is ubiquitously expressed throughout the body. We had previously reported a female-specific depression-related behavioural phenotype in the R6/1 transgenic mouse model of HD. One hypothesis suggests that pathology of the hypothalamic-pituitary-adrenal (HPA) axis, the key physiological stress-response system that links central and peripheral organs, is a cause of depression. There is evidence of HPA axis pathology in HD, but whether it contributes to the female R6/1 behavioural phenotype is unclear. We have examined HPA axis response of R6/1 mice following acute stress and found evidence of a female-specific dysregulation of the HPA axis in R6/1 mice, which we further isolated to a hyper-response of adrenal cortical cells to stimulation by adrenocorticotrophin hormone. Interestingly, the adrenal pathophysiology was not detected in mice that had been housed in environmentally enriching conditions, an effect of enrichment that was also reproduced in vitro. This constitutes the first evidence that environmental enrichment can in fact exert a lasting influence on peripheral organ function. Cognitive stimulation may therefore not only have benefits for mental function, but also for overall physiological wellbeing.

Ingestion of theanine, an amino acid in tea, suppresses psychosocial stress in mice

The antistress effect of theanine (γ-glutamylethylamide), an amino acid in tea, was investigated using mice that were psychosocially stressed from a conflict among male mice in conditions of confrontational housing. Two male mice were housed in the same cage separated by a partition to establish a territorial imperative. When the partition was removed, the mice were co-housed confrontationally. As a marker for the stress response, changes in the adrenal gland were studied in comparison to group-housed control mice (six mice in a cage). Significant adrenal hypertrophy was observed in mice during confrontational housing, which was developed within 24 h and persisted for at least 1 week. The size of cells in the zona fasciculata of the adrenal gland, from which glucocorticoid is mainly secreted, increased (∼1.11-fold) in mice during confrontational housing, which was accompanied by a flattened diurnal rhythm of corticosterone and ACTH in blood. The ingestion of theanine (>5 μg ml(-1)) prior to confrontational housing significantly suppressed adrenal hypertrophy. An antidepressant, paroxetin, suppressed adrenal hypertrophy in a similar manner in mice during confrontational housing. In mice that ingested theanine, behavioural depression was also suppressed, and a diurnal rhythm of corticosterone and ACTH was observed, even in mice that were undergoing confrontational housing. Furthermore, the daily dose of theanine (40 μg ml(-1)) blocked the counteracting effects of caffeine (30 μg ml(-1)) and catechin (200 μg ml(-1)). The present study demonstrated that theanine prevents and relieves psychosocial stress through the modulation of hypothalamic-pituitary-adrenal axis activity.

Long term impact of prenatal exposure to SSRIs on growth and body weight in childhood: evidence from animal and human studies

Prenatal exposure to SSRIs has the potential to alter fetal 5-HT signalling during critical periods of development: the long-term consequences of which have not been well studied. Of particular interest are the potential long-term effects of prenatal SSRI exposure on growth and body weight in later life, given the role of the serotonergic system in regulating food intake and body weight. Animal studies demonstrate that changes in 5-HT homeostasis during critical periods of fetal development can lead to sex-specific molecular and functional alterations in the serotonergic and HPA systems, leading to an increased risk of overweight in male, but not female, offspring in later life. This review highlights the evidence and the need for studies in humans to determine whether prenatal SSRI exposure is associated with alterations in child growth and body weight and the importance of delineating these effects from those of the underlying maternal illness.

Dysfunction of the hypothalamic-pituitary-adrenal axis in STX1A knockout mice

HPC-1/syntaxin1A (STX1A) is considered to regulate exocytosis in neurones and endocrine cells. Previously, we reported that STX1A null mutant (STX1A KO) mice unexpectedly showed normal glutamatergic and GABAergic fast synaptic transmission but exhibited disturbances in monoaminergic transmission, such as serotonin, 5-hydroxytryptamine (5-HT), which may induce attenuation of latent inhibition. These results suggest that STX1A may contribute to dense-core vesicle exocytosis in vivo. Thus, we hypothesised that the lack of STX1A might affect the secretion of several hormones, as also mediated by dense-core vesicles exocytosis. In the present study, we focused on the hypothalamic-pituitary-adrenal (HPA) axis, which is a neuroendocrine system that regulates responses to stress stimuli and is considered to be associated with neuropsychiatric disorders. Specifically, we examined whether the HPA axis is impaired in STX1A KO mice. Interestingly, plasma concentrations of both corticosterone (CORT) and adrenocorticotrophin hormone (ACTH) during the resting condition decreased in STX1A KO mice compared to WT mice. Additionally, elevated plasma CORT, ACTH and corticotrophin-releasing hormone (CRH) which were usually observed after acute restraint stress, were also reduced in STX1A KO mice. We also observed the suppression of 5-HT-induced CRH release in STX1A KO mice in vitro. Furthermore, an in vivo microdialysis study revealed that the elevation of extracellular 5-HT in the hypothalamus, which was induced by the selective serotonin reuptake inhibitor, fluoxetine, was significantly reduced in STX1A KO mice compared to WT mice. 5-HT elevation in the hypothalamus, which was induced by acute restraint stress, was also reduced in STX1A KO mice. Finally, STX1A KO mice showed abnormal behavioural responses after mild restraint stress. These results indicate that the lack of STX1A could induce dysfunction of the HPA axis, and the deficit may result in abnormal behavioural properties, such as unusual responses to stress stimuli.

Stressful life events at onset of obsessive-compulsive disorder are associated with a distinct clinical pattern

BACKGROUND

Environmental stressors are considered to play an important role in the triggering of mental disorders such as obsessive-compulsive disorder (OCD). Although there is extensive literature on traumatic life events, little is known about the role of nontraumatic but nonetheless stressful life events (SLEs) in OCD. The aim of this study was to establish whether OCD preceded by an SLE presents a different clinical pattern compared to non-SLE-preceded OCD.

METHODS

We interviewed 412 OCD patients to assess both SLEs at onset of OCD and other clinical variables, including OCD symptom dimensions. Logistic regression was then applied to explore the relationship between clinical variables and OCD preceded by an SLE.

RESULTS

The SLE-preceded OCD group showed a later onset of the disorder (OR = 1.04, P = .015), a history of complicated birth (OR = 5.54, P<.001), less family history of OCD (OR = 0.42, P = .014), and the presence of contamination/cleaning symptoms (OR = 1.99, P = .01).

CONCLUSIONS

Patients with OCD onset close to an SLE and those without an SLE close to OCD onset show a distinct clinical pattern.

Annual Research Review: Transgenic mouse models of childhood-onset psychiatric disorders

Childhood-onset psychiatric disorders, such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), mood disorders, obsessive compulsive spectrum disorders (OCSD), and schizophrenia (SZ), affect many school-age children, leading to a lower quality of life, including difficulties in school and personal relationships that persist into adulthood. Currently, the causes of these psychiatric disorders are poorly understood, resulting in difficulty diagnosing affected children, and insufficient treatment options. Family and twin studies implicate a genetic contribution for ADHD, ASD, mood disorders, OCSD, and SZ. Identification of candidate genes and chromosomal regions associated with a particular disorder provide targets for directed research, and understanding how these genes influence the disease state will provide valuable insights for improving the diagnosis and treatment of children with psychiatric disorders. Transgenic mouse models are one important approach in the study of human diseases, allowing for the use of a variety of experimental approaches to dissect the contribution of a specific chromosomal or genetic abnormality in human disorders. While it is impossible to model an entire psychiatric disorder in a single mouse model, these models can be extremely valuable in dissecting out the specific role of a gene, pathway, neuron subtype, or brain region in a particular abnormal behavior. In this review we discuss existing transgenic mouse models for childhood-onset psychiatric disorders. We compare the strength and weakness of various transgenic mouse models proposed for each of the common childhood-onset psychiatric disorders, and discuss future directions for the study of these disorders using cutting-edge genetic tools.

Serotonin transporter knockout and repeated social defeat stress: impact on neuronal morphology and plasticity in limbic brain areas

Low expression of the human serotonin transporter (5-HTT) gene presumably interacts with stressful life events enhancing susceptibility for affective disorders. 5-Htt knockout (KO) mice display an anxious phenotype, and behavioural differences compared to wild-type (WT) mice are exacerbated after repeated loser experience in a resident-intruder stress paradigm. To assess whether genotype-dependent and stress-induced behavioural differences are reflected in alterations of neuronal morphology in limbic areas, we studied dendritic length and complexity of pyramidal neurons in the anterior cingulate and infralimbic cortices (CG, IL), hippocampus CA1 region, and of pyramidal neurons and interneurons in the lateral (La) and basolateral (BL) amygdaloid nuclei in Golgi-Cox-stained brains of male WT and 5-Htt KO control and loser mice. Spine density was analysed for IL apical and amygdaloid apical and basal pyramidal neuron dendrites. While group differences were absent for parameters analysed in CG, CA1 and amygdaloid interneurons, pyramidal neurons in the IL displayed tendencies to shorter and less spinous distal apical dendrites in 5-Htt KO controls, and to extended proximal dendrites in WT losers compared to WT controls. In contrast, spine density of several dendritic compartments of amygdaloid pyramids was significantly higher in 5-Htt KO mice compared to WT controls. While a tendency to increased spine density was observed in the same dendritic compartments in WT after stress, changes were lacking in stressed compared to control 5-Htt KO mice. Our findings indicate that disturbed 5-HT homeostasis results in alterations of limbic neuronal morphology, especially in higher spinogenesis in amygdaloid pyramidal neurons. Social stress leads to similar but less pronounced changes in the WT, and neuroplasticity upon stress is reduced in 5-Htt KO mice.

The serotonin transporter promoter polymorphism is associated with cortisol response to psychosocial stress

BACKGROUND

Across multiple mental health-related measures, a polymorphism (5-HTTLPR) within the promoter of the serotonin transporter gene has been associated with differential psychological sensitivity to stressful experiences. Yet, the specific mechanisms by which this polymorphism contributes to risk for psychological dysfunction is unclear. Therefore, we investigated cortisol reactivity to psychosocial stress as a potential intermediate phenotype that might predispose to such risk.

METHODS

A psychologically healthy sample of 182 young adults were genotyped for the 5-HTTLPR. Each participant delivered a speech and performed mental arithmetic in one of three audience conditions: a critical evaluative audience, a supportive evaluative audience, or no audience. Salivary cortisol was sampled at baseline and at 20, 40, and 75 min after stressor onset.

RESULTS

The two evaluative audience conditions elicited similar, significant increases in cortisol that were significantly greater than in the no audience control. Together, the evaluative audience conditions revealed a significant relationship between cortisol reactivity and the 5-HTTLPR, with the short/short genotype showing the greatest reactivity. Internal analyses revealed that the 5-HTTLPR was significantly associated with cortisol reactivity in the negative audience condition only, suggesting that short/short individuals might be especially vulnerable to social threat.

CONCLUSIONS

The short/short genotype of the 5-HTTLPR is associated with greater cortisol reactivity to social threat. When short/short individuals experience stressful life events, they might be at greater risk for the adverse psychological and physical health consequences associated with heightened cortisol exposure.

Serotonin transporter deficiency increases abdominal fat in female, but not male rats

Depression and abdominal obesity often co-occur, predominantly in women, and are associated with an increased risk for the development of glucose intolerance and subsequently type 2 diabetes. The underlying mechanisms are poorly understood. We found that female, but not male, depression-prone serotonin transporter knockout (SERT(-/-)) rats had a strong increase (54%) in abdominal fat, whereas no increases in plasma concentrations of glucose and insulin were observed. Surprisingly, application of a high-fat, high-sucrose (HFHS)-choice diet, which results in increased abdominal fat deposition and increased plasma glucose levels in wild-type rats, did not result in elevated plasma glucose levels in female SERT(-/-) rats. Our results show that serotonin transporter deficiency affects abdominal fat deposition in a sex-dependent way, but protects against rises in glucose levels, and thereby potentially glucose intolerance. The increased abdominal fat formation could result from serotonin-mediated developmental changes and provides heuristic value for understanding the effects of the depression-associated serotonin transporter promoter polymorphism in humans.

Altered expression and modulation of activity-regulated cytoskeletal associated protein (Arc) in serotonin transporter knockout rats

A gene variant in the human serotonin transporter (SERT) can increase the vulnerability to mood disorders. SERT knockout animals show similarities to the human condition and represent an important tool to investigate the mechanisms underlying the pathologic condition in humans. Along this line of thinking, we used SERT KO rats (SERT(+/-) and SERT(-/-)) to investigate abnormalities in the expression and function of the activity-regulated gene Arc (Activity-regulated cytoskeletal associated protein) and the early inducible gene Zif-268, (zinc finger binding protein clone 268), which are important players in neuronal plasticity. We found lower basal Arc mRNA levels in hippocampus and prefrontal cortex of mutant rats in comparison with wild-type animals. Moreover SERT mutant rats show altered stress responsiveness. Indeed an acute swim stress significantly up-regulated the levels of Arc mRNA in hippocampus and prefrontal cortex, as well as of Zif-268 in frontal cortex, only in SERT(+/-) and SERT(-/-) rats. These alterations may be associated to behavioral traits linked to SERT and may contribute to the neuroplastic and morphological changes observed in depression.

Interaction between 5-HTTLPR and BDNF Val66Met polymorphisms on HPA axis reactivity in preschoolers

This study examined whether the interaction between the serotonin transporter promoter region (5-HTTLPR) and brain-derived neurotrophic factor (BDNF) Val66Met polymorphisms was associated with hypothalamic-pituitary-adrenal (HPA) axis reactivity to stress. A community sample of 144 preschool-aged children was genotyped and exposed to stress-inducing laboratory tasks. Salivary cortisol was obtained at four time points during a standardized laboratory assessment before and after stressors involving separation from a parent and frustrating tasks. Children homozygous for the short-5-HTTLPR allele and carrying the Met-BDNF allele evidenced a significantly lower initial level of cortisol, followed by a positive increase in cortisol in response to the laboratory stressors. In contrast, children who were homozygous for the short-5-HTTLPR and the Val-BDNF alleles evidenced a greater decline in cortisol in response to the laboratory stressors. Findings indicated that the BDNF gene moderated the association between 5-HTTLPR and children's biological stress responses, suggesting that epistatic effects play a role in individual differences in stress regulation, and possibly genetic vulnerability to stress-related disorders.