Serotonin Transporter Knockout Mice Research Articles

Serotonin Transporter Deficiency Induces Metabolic Alterations in the Ileal Mucosa.

Serotonin transporter (SERT) deficiency has been implicated in metabolic syndrome, intestinal inflammation, and microbial dysbiosis. Interestingly, changes in microbiome metabolic capacity and several alterations in host gene expression, including lipid metabolism, were previously observed in SERT-/- mice ileal mucosa. However, the precise host or microbial metabolites altered by SERT deficiency that may contribute to the pleiotropic phenotype of SERT KO mice are not yet understood. This study investigated the hypothesis that SERT deficiency impacts lipid and microbial metabolite abundances in the ileal mucosa, where SERT is highly expressed. Ileal mucosal metabolomics was performed by Metabolon on wild-type (WT) and homozygous SERT knockout (KO) mice. Fluorescent-activated cell sorting (FACS) was utilized to measure immune cell populations in ileal lamina propria to assess immunomodulatory effects caused by SERT deficiency. SERT KO mice exhibited a unique ileal mucosal metabolomic signature, with the most differentially altered metabolites being lipids. Such changes included increased diacylglycerols and decreased monoacylglycerols in the ileal mucosa of SERT KO mice compared to WT mice. Further, the ileal mucosa of SERT KO mice exhibited several changes in microbial-related metabolites known to play roles in intestinal inflammation and insulin resistance. SERT KO mice also had a significant reduction in the abundance of ileal group 3 innate lymphoid cells (ILC3). In conclusion, SERT deficiency induces complex alterations in the ileal mucosal environment, indicating potential links between serotonergic signaling, gut microbiota, mucosal immunity, intestinal inflammation, and metabolic syndrome.

Serotonin reuptake transporter deficiency promotes liver steatosis and impairs intestinal barrier function in obese mice fed a Western-style diet.

Intestinal barrier dysfunctions have been associated with liver steatosis and metabolic diseases. Besides nutritional factors, like a Western-style diet (WSD), serotonin has been linked with leaky gut. Therefore, we aimed to evaluate the role of serotonin in the pathogenesis of intestinal barrier dysfunctions and liver steatosis in mice fed high-fat and high-sugar diets. 6-8 weeks old male serotonin reuptake transporter knockout mice (SERT-/- ) and wild-type controls (SERT+/+ ) were fed either a WSD or a control diet (CD) ad libitum with or without fructose 30% (F) added to the drinking water for 12 weeks. Markers of liver steatosis and intestinal barrier function were assessed. SERT-/- mice showed increased weight gain compared with SERT+/+ mice when fed a WSD ± F for 12 weeks (p < 0.05), whereby SERT-/- mice exhibited reduced energy (-21%) intake. Furthermore, SERT knockout resulted in a more pronounced liver steatosis (p < 0.05), enhanced levels of endotoxin in portal vein plasma (p < 0.05), and increased liver expression of Tnf and Myd88 (p < 0.05), when mice were fed a WSD ± F. Finally, SERT-/- mice, when compared with SERT+/+ mice, had a decreased mRNA expression of Muc2 (p < 0.01), Ocln (p < 0.05), Cldn5 (p = 0.054) and 7 (p < 0.01), Defa5 (p < 0.05) and other antimicrobial peptides in the ileum. On the protein level, ZO-1 (p < 0.01) and DEFA5 protein (p < 0.0001) were decreased. Our data demonstrate that SERT knockout causes weight gain, liver steatosis, and leaky gut, especially in mice fed a WSD. Therefore, SERT induction could be a novel therapeutic approach to improve metabolic diseases associated with intestinal barrier dysfunction.

Acute cannabidiol treatment enhances social interaction in adult male mice.

Cannabidiol (CBD) is a non-intoxicating phytochemical from Cannabis sativa that is increasingly used to manage pain. The potential for CBD to ameliorate dimensional behavior symptoms occurring in multiple psychiatric disorders was suggested, including social interaction impairments. To test this hypothesis, adult male BTBRT+Itpr3tf/J (BTBR) mice, a model of idiopathic autism exhibiting social preference deficits and restrictive repetitive behaviors, were acutely treated with vehicle or 0.1, 1, or 10 mg/kg CBD. Social interaction preference was assessed 50 min after treatment, followed by social novelty preference at 60 min, marble burying at 75 min and social dominance at 120 min. CBD (10 mg/kg) enhanced BTBR social interaction but not social novelty preference, marble burying or dominance, with serum levels = 29 ± 11 ng/mg at 3 h post-injection. Next, acute 10 mg/kg CBD was compared to vehicle treatment in male serotonin transporter (SERT) knock-out mice, since SERT deficiency is an autism risk factor, and in their wildtype background strain controls C57BL/6J mice. CBD treatment generally enhanced social interaction preference and attenuated social novelty preference, yet neither marble burying nor dominance was affected. These findings show acute treatment with as little as 10 mg/kg purified CBD can enhance social interaction preference in male mice that are otherwise socially deficient.

Behavioral phenotype, intestinal microbiome, and brain neuronal activity of male serotonin transporter knockout mice

The serotonin transporter (5-HTT) plays a critical role in the regulation of serotonin neurotransmission. Mice genetically deficient in 5-HTT expression have been used to study the physiological functions of 5-HTT in the brain and have been proposed as a potential animal model for neuropsychiatric and neurodevelopmental disorders. Recent studies have provided evidence for a link between the gut-brain axis and mood disorders. However, the effects of 5-HTT deficiency on gut microbiota, brain function, and behavior remain to be fully characterized. Here we investigated the effects of 5-HTT deficiency on different types of behavior, the gut microbiome, and brain c-Fos expression as a marker of neuronal activation in response to the forced swim test for assessing depression-related behavior in male 5-HTT knockout mice. Behavioral analysis using a battery of 16 different tests showed that 5-HTT−/− mice exhibited markedly reduced locomotor activity, decreased pain sensitivity, reduced motor function, increased anxiety-like and depression-related behavior, altered social behavior in novel and familiar environments, normal working memory, enhanced spatial reference memory, and impaired fear memory compared to 5-HTT+/+ mice. 5-HTT+/− mice showed slightly reduced locomotor activity and impaired social behavior compared to 5-HTT+/+ mice. Analysis of 16S rRNA gene amplicons showed that 5-HTT−/− mice had altered gut microbiota abundances, such as a decrease in Allobaculum, Bifidobacterium, Clostridium sensu stricto, and Turicibacter, compared to 5-HTT+/+ mice. This study also showed that after exposure to the forced swim test, the number of c-Fos-positive cells was higher in the paraventricular thalamus and lateral hypothalamus and was lower in the prefrontal cortical regions, nucleus accumbens shell, dorsolateral septal nucleus, hippocampal regions, and ventromedial hypothalamus in 5-HTT−/− mice than in 5-HTT+/+ mice. These phenotypes of 5-HTT−/− mice partially recapitulate clinical observations in humans with major depressive disorder. The present findings indicate that 5-HTT-deficient mice serve as a good and valid animal model to study anxiety and depression with altered gut microbial composition and abnormal neuronal activity in the brain, highlighting the importance of 5-HTT in brain function and the mechanisms underlying the regulation of anxiety and depression.

Novel Antidepressant-Like Properties of the Iron Chelator Deferiprone in a Mouse Model of Depression

Depressed individuals who carry the short allele for the serotonin-transporter-linked promotor region of the gene are more vulnerable to stress and have reduced response to first-line antidepressants such as selective serotonin reuptake inhibitors. Since depression severity has been reported to correlate with brain iron levels, the present study aimed to characterise the potential antidepressant properties of the iron chelator deferiprone. Using the serotonin transporter knock-out (5-HTT KO) mouse model, we assessed the behavioural effects of acute deferiprone on the Porsolt swim test (PST) and novelty-suppressed feeding test (NSFT). Brain and blood iron levels were also measured following acute deferiprone. To determine the relevant brain regions activated by deferiprone, we then measured c-Fos expression and applied network-based analyses. We found that deferiprone reduced immobility time in the PST in 5-HTT KO mice and reduced latency to feed in the NSFT in both genotypes, suggesting potential antidepressant-like effects. There was no effect on brain or blood iron levels following deferiprone treatment, potentially indicating an acute iron-independent mechanism. Deferiprone reversed the increase in c-Fos expression induced by swim stress in 5-HTT KO mice in the lateral amygdala. Functional network analyses suggest that hub regions of activity in mice treated with deferiprone include the caudate putamen and prefrontal cortex. The PST-induced increase in network modularity in wild-type mice was not observed in 5-HTT KO mice. Altogether, our data show that the antidepressant-like effects of deferiprone could be acting via an iron-independent mechanism and that these therapeutic effects are underpinned by changes in neuronal activity in the lateral amygdala.

The Serotonin Transporter Modulates the Kinetics and Quantal Size of Vesicular Fusion Events in Sympathoadrenal Chromaffin Cells

The antidepressant‐sensitive serotonin transporter (SERT) is a key regulator of serotonin (5‐HT) signaling and availability in the CNS. The robust expression of SERT in adrenal chromaffin cells (ACCs), which comprise the neuroendocrine arm of the sympathetic nervous system, is less well understood. ACCs synthesize and secrete catecholamines (epinephrine, norepinephrine) which mediate the physiological response to stress. They do not synthesize 5‐HT, but do accumulate small amounts through SERT‐mediated uptake (5‐HT content is &lt;0.15% of the epinephrine content). We hypothesized that the chromaffin cells utilize this 5‐HT for autocrine / paracrine control of the sympathoadrenal stress response. Consistent with this hypothesis, we previously reported that 5‐HT1A receptors inhibit catecholamine secretion by reducing the number of secretory vesicles that fuse with the plasma. The objective of the current study was to investigate an additional, receptor‐independent mechanism by which SERT controls adrenal catecholamine secretion.We used carbon fiber amperometry to analyze catecholamine secretion from ACCs that were isolated from either wild type mice, global SERT‐knockout mice (SERT‐/‐), or sympathoadrenal system‐specific SERT knockout mice (SERTΔTH). Transmitter release from individual vesicle fusion events can be resolved as amperometric spikes. There was no difference in the number or time‐course of amperometric spikes evoked by 30mM KCl. The charge of the spikes is directly proportional to the amount of transmitter released by a single vesicle (i.e. quantal size). Spike charge was significantly smaller (~35%) and spike duration (half‐width) was significantly shorter in SERT‐knockout cells compared to matched controls. This was surprising given that HPLC analysis revealed no change in the catecholamine content of adrenal glands isolated from knockout mice compared to wild‐type controls; the 5‐HT content was significantly reduced but this accounted for &lt;0.15% of the total monoamine content. Changes in calcium entry can modulate the quantal size of catecholamine release in ACCs, but patch‐clamp recording revealed there was no significant difference in voltage‐gated calcium channel currents in SERT knockout cells and ratiometric calcium imaging found no difference in KCl‐evoked calcium entry. The decrease in quantal size was mimicked in wild‐type cells by treating for &gt;24 hours with escitalopram (an SSRI antidepressant which blocks SERT), or by depleting extracellular 5‐HT from the culture medium for &gt;24 hours (use of dialyzed serum in the culture media). In contrast, acute (minutes) or short‐term (&lt;6‐8 hrs) treatment with escitalopram or 5‐HT depletion had no effect. Adrenal chromaffin cells lack the rate limiting enzyme for 5‐HT synthesis (tryptophan hydroxylase), but if the product of this enzyme (5‐hydroxytryptophan; 5‐HTP) is provided it can be converted into 5‐HT. Treating ACCs with 5‐HTP for 1‐3 hrs had no effect but 24 hr treatment rescued the reduced spike charge seen in SERT knockout cells. Together, our data suggest that, following SERT‐mediated uptake, intracellular 5‐HT modulates the kinetics and thus fraction of secretory vesicle content that is released during a fusion event.

Acute Low Dose Cannabidiol Treatment Boosts Social Interaction Preference in Male Mice

Cannabidiol (CBD) is a non‐addictive psychoactive phytochemical from Cannabis sativa that is increasingly used to manage pain. The potential for CBD to ameliorate some psychiatric disorder symptoms has been suggested, including the social behavior deficits of autism. To test this hypothesis, adult male BTBRT+Itpr3tf/J (BTBR) mice, a model of idiopathic autism, were acutely treated with vehicle or 0.1, 1, or 10 mg/kg CBD. Social interaction preference was assessed 50 min after treatment, followed by social novelty preference at 60 min, marble burying at 75 min and social dominance at 120 min. CBD (10 mg/kg) enhanced BTBR social interaction but not social novelty preference, marble burying or dominance, with serum levels = 29 ± 11 ng/mg at 3 h post‐injection. Next, acute 10 mg/kg CBD was compared to vehicle treatment in serotonin transporter (SERT) knockout mice, as SERT deficiency is an autism risk factor, and in C57BL6/J mice. CBD treatment generally enhanced social interaction preference and attenuated social novelty preference, yet neither marble burying nor dominance was affected. These findings show acute treatment with purified CBD can enhance social interaction preference at a relatively low dose. However, the pharmacological target(s) by which this low dose of CBD enhanced sociability remain to be demonstrated. Any use of unregulated CBD products to treat autism symptoms in children is not advisable until product purity and dose are strictly controlled, and acute versus long term treatment effects are better known.

What is the mechanism of loudness hyperacusis in autism?

Loudness hyperacusis is common in autistic children and adults. The symptoms of loudness hyperacusis are thought to be generated by a pathological increase in central auditory gain. However, there remains unknown why increased sound-evoked activity in the auditory cortex occur in autism. It is well-known that transient early expression of serotonin transporter in glutamatergic thalamocortical projection neurons regulate sensory map elaboration in the barrel cortex in mice. In addition, in thalamic neuron-specific serotonin transporter knockout mice, hyperserotonin conditions cause the reduction of somatostatin-expressing GABAergic neurons.Serotonin transporter is also expressed in the medial geniculate body from E12 to P10 in the rat brain, and this period coincides with geniculocortical projections. In addition, hyperserotonin conditions in the developing brain are frequently seen in autism. Taken together, we propose the following hypothesis; (1) Hyperserotonin conditions in the developing brain frequently occur in autism patients. (2) These hyperserotonin conditions induce the reduction of GABA neurons in auditory cortex. (3) This reduction of inhibitory neurons in auditory cortex causes hyperacusis in autism patients.

Role of the cAMP–PKA–CREB–BDNF pathway in abnormal behaviours of serotonin transporter knockout mice

Serotonin transporter gene-linked polymorphic region polymorphisms are associated with anxiety, neuroticism, affective disorders and vulnerability to stressful life events; however, the relevant physiological mechanisms are not well understood. Serotonin transporter knockout mice have been widely used as a model of allelic variation of serotonin transporter function in humans; herein, wild-type mice and heterozygous and homozygous knockout mice models were established to explore the behavioural changes related to different genotypes and the possible physiological mechanisms. Behavioural changes were assessed using behavioural tests, namely, elevated plus maze, open field, Morris water maze and rotarod tests. Serum indicators were detected using the enzyme-linked immunosorbent assay. Compared with wild-type mice, homozygous mice showed significant anxiety-like behaviours in the plus maze and open field tests; conversely, anxiety-like behaviours in heterozygous mice were less pronounced. Homozygous mice also showed cognitive impairment and motor inhibition in the Morris water maze and rotarod tests. Serotonin levels decreased in both heterozygous and homozygous mice, and 5-hydroxytryptophan, protein kinase A, adenylyl cyclase, cyclic adenosine monophosphate response element-binding protein and brain-derived neurotrophic factor levels were lower in homozygous mice than in wild-type and heterozygous mice, whereas no statistical differences were found between wild-type and heterozygous mice. Additionally, there was a correlation between serological and behavioural indicators. This study provided experimental evidence that the cyclic adenosine monophosphate–protein kinase A–cyclic adenosine monophosphate response element-binding protein–brain-derived neurotrophic factor pathway may be involved in the regulation of polymorphism to stress and enriched the behavioural and physiological characteristics of serotonin transporter knockout mice.

Placental Changes in the serotonin transporter (Slc6a4) knockout mouse suggest a role for serotonin in controlling nutrient acquisition.

The mouse placenta accumulates and possibly produces serotonin (5-hydroxytryptamine; 5-HT) in parietal trophoblast giant cells (pTGC) located at the interface between the placenta and maternal deciduum. However, the roles of 5-HT in placental function are unclear. This lack of information is unfortunate, given that selective serotonin-reuptake inhibitors are commonly used to combat depression in pregnant women. The high affinity 5-HT transporter SLC6A4 (also known as SERT) is the target of such drugs and likely controls much of 5-HT uptake into pTGC and other placental cells. We hypothesized that ablation of the Slc6a4 gene would result in morphological changes correlated with placental gene expression changes, especially for those involved in nutrient acquisition and metabolism, and thereby, provide insights into 5-HT placental function. Placentas were collected at embryonic age (E) 12.5 from Slc6a4 knockout (KO) and wild-type (WT) conceptuses. Histological analyses, RNAseq, qPCR, and integrative correlation analyses were performed. Slc6a4 KO placentas had a considerable increased pTGC to spongiotrophoblast area ratio relative to WT placentas and significantly elevated expression of genes associated with intestinal functions, including nutrient sensing, uptake, and catabolism, and blood clotting. Integrative correlation analyses revealed upregulation of many of these genes was correlated with pTGC layer expansion. One other key gene was dopa decarboxylase (Ddc), which catalyzes conversion of L-5-hydroxytryptophan to 5-HT. Our studies possibly suggest a new paradigm relating to how 5-HT operates in the placenta, namely as a factor regulating metabolic functions and blood coagulation. We further suggest that pTGC might be functional analogs of enterochromaffin 5-HT-positive cells of the intestinal mucosa, which regulate similar activities within the gut. Further work, including proteomics and metabolomic studies, are needed to buttress our hypothesis.

Serotonin Transporter Defect Disturbs Structure and Function of the Auditory Cortex in Mice.

Serotonin transporter (SERT) modulates the level of 5-HT and significantly affects the activity of serotonergic neurons in the central nervous system. The manipulation of SERT has lasting neurobiological and behavioral consequences, including developmental dysfunction, depression, and anxiety. Auditory disorders have been widely reported as the adverse events of these mental diseases. It is unclear how SERT impacts neuronal connections/interactions and what mechanism(s) may elicit the disruption of normal neural network functions in auditory cortex. In the present study, we report on the neuronal morphology and function of auditory cortex in SERT knockout (KO) mice. We show that the dendritic length of the fourth layer (L-IV) pyramidal neurons and the second-to-third layer (L-II/III) interneurons were reduced in the auditory cortex of the SERT KO mice. The number and density of dendritic spines of these neurons were significantly less than those of wild-type neurons. Also, the frequency-tonotopic organization of primary auditory cortex was disrupted in SERT KO mice. The auditory neurons of SERT KO mice exhibited border frequency tuning with high-intensity thresholds. These findings indicate that SERT plays a key role in development and functional maintenance of auditory cortical neurons. Auditory function should be examined when SERT is selected as a target in the treatment for psychiatric disorders.

Gene Expression and Histopathological Changes in the Placenta of the Serotonin Transporter (Slc6a4) Knockout Mouse Suggest a Role for Serotonin in Controlling Nutrient Acquisition

Gene Expression and Histopathological Changes in the Placenta of the Serotonin Transporter (Slc6a4) Knockout Mouse Suggest a Role for Serotonin in Controlling Nutrient Acquisition

Exercise ameliorates aberrant synaptic plasticity without enhancing adult-born cell survival in the hippocampus of serotonin transporter knockout mice.

Deficits in hippocampal cellular and synaptic plasticity are frequently associated with cognitive and mood disorders, and indeed common mechanisms of antidepressants are thought to involve neuroplastic processes. Here, we investigate hippocampal adult-born cell survival and synaptic plasticity (long-term potentiation, LTP, and long-term depression, LTD) in serotonin transporter (5-HTT) knockout (KO) mice. From 8weeks of age, mice either continued in standard-housing conditions or were given access to voluntary running wheels for 1month. Electrophysiology was performed on hippocampal slices to measure LTP and LTD, and immunohistochemistry was used to assess cell proliferation and subsequent survival in the dentate gyrus. The results revealed a reduced LTP in 5-HTT KO mice that was restored to wild-type (WT) levels after chronic exercise. While LTD appeared normal in 5-HTT KO, exercise decreased the magnitude of LTD in both WT and 5-HTT KO mice. Furthermore, although 5-HTT KO mice had normal hippocampal adult-born cell survival, they did not benefit from the pro-proliferative effects of exercise observed in WT animals. Taken together, these findings suggest that reduced 5-HTT expression is associated with significant alterations to functional neuroplasticity. Interestingly, 5-HTT appeared necessary for exercise-induced augmentation of adult-born hippocampal cell survival, yet exercise corrected the LTP impairment displayed by 5-HTT KO mice. Together, our findings further highlight the salience of serotonergic signalling in mediating the neurophysiological benefits of exercise.

Dual actions of 5-MeO-DIPT at the serotonin transporter and serotonin 5-HT1A receptor in the mouse striatum and prefrontal cortex.

Aims5‐Methoxy‐N,N‐diisopropyltryptamine (5‐MeO‐DIPT) is a synthetic orally active hallucinogenic tryptamine analogue. The present study examined whether the effects of 5‐MeO‐DIPT involve the serotonin transporter (SERT) and serotonin 5‐hydroxytryptamine‐1A (5‐HT1A) receptor in the striatum and prefrontal cortex (PFC).MethodsWe investigated the effects of 5‐MeO‐DIPT on extracellular 5‐HT (5‐HTex) and dopamine (DAex) levels in the striatum and PFC in wildtype and SERT knockout (KO) mice using in vivo microdialysis, and for comparison the effects of the 5‐HT1A receptor antagonist WAY100635 and the 5‐HT1A receptor agonist 8‐OH‐DPAT on 5‐HTex.Results5‐MeO‐DIPT decreased 5‐HTex levels in the striatum, but not PFC. In SERT‐KO mice, 5‐MeO‐DIPT did not affect 5‐HTex levels in the striatum or PFC. In the presence of WAY100635, 5‐MeO‐DIPT substantially increased 5‐HTex levels, suggesting that 5‐MeO‐DIPT acts on SERT and these effects are masked by its 5‐HT1A actions in the absence of WAY100635. 8‐OH‐DPAT decreased 5‐HTex levels in the striatum and PFC in wildtype mice. WAY100635 antagonized the 8‐OH‐DPAT‐induced decrease in 5‐HTex levels. In SERT‐KO mice, 8‐OH‐DPAT did not decrease 5‐HTex levels in the striatum and PFC. 5‐MeO‐DIPT dose‐dependently increased DAex levels in the PFC, but not striatum, in wildtype and SERT‐KO mice. The increase in DAex levels that was induced by 5‐MeO‐DIPT was not antagonized by WAY100635.Conclusion5‐MeO‐DIPT influences both 5‐HTex and DAex levels in the striatum and PFC. 5‐MeO‐DIPT dually acts on SERT and 5‐HT1A receptors so that elevations in 5‐HTex levels produced by reuptake inhibition are limited by actions of the drug on 5‐HT1A receptors.

Food Anticipatory Activity on Circadian Time Scales Is Not Dependent on Central Serotonin: Evidence From Tryptophan Hydroxylase-2 and Serotonin Transporter Knockout Mice.

A number of studies implicate biogenic amines in regulating circadian rhythms. In particular, dopamine and serotonin influence the entrainment of circadian rhythms to daily food availability. To study circadian entrainment to feeding, food availability is typically restricted to a short period within the light cycle daily. This results in a notable increase in pre-meal activity, termed “food anticipatory activity” (FAA), which typically develops within about 1 week of scheduled feeding. Several studies have implicated serotonin as a negative regulator of FAA: (1) aged rats treated with serotonin 5-HT2 and 3 receptor antagonists showed enhanced FAA, (2) mice lacking for the 2C serotonin receptor demonstrate enhanced FAA, and (3) pharmacologically increased serotonin levels suppressed FAA while decreased serotonin levels enhanced FAA in mice. We sought to confirm and extend these findings using genetic models with impairments in central serotonin production or re-uptake, but were surprised to find that both serotonin transporter (Slc6a4) and tryptophan hydroxylase-2 knockout mice demonstrated a normal behavioral response to timed, calorie restricted feeding. Our data suggest that FAA is largely independent of central serotonin and/or serotonin reuptake and that serotonin may not be a robust negative regulator of FAA.

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.

P.044 Effects of exercise and environmental enrichment in serotonin transporter knock-out mice

P.044 Effects of exercise and environmental enrichment in serotonin transporter knock-out mice

REM sleep and cataplexy regulation in hcrt and serotonin transporter knockout mice

REM sleep and cataplexy regulation in hcrt and serotonin transporter knockout mice

Serotonin transporter deficiency alters socioemotional ultrasonic communication in rats

It has been widely established that serotonin plays important role in the regulation of emotional and social behaviour. Rodents with a genetic deletion of the serotonin reuptake transporter (SERT) are used as a model to study lifelong consequences of increased extracellular 5‐HT levels due to its impaired reuptake. SERT knock-out (SERT-KO) mice and rats consistently showed anxiety-like symptoms and social deficits. Nevertheless, the impact of SERT deletion on socioemotional ultrasonic communication has not been addressed. Here we investigated the impact of lifelong serotonin abundance on ultrasonic vocalisation accompanying social interactions and open field exploration in rats. SERT-KO rats displayed reduced overall duration of social contacts, but increased time spent on following the conspecific. The altered pattern of social behaviour in SERT-KO rats was accompanied by the structural changes in ultrasonic vocalisations, as they differed from their controls in distribution of call categories. Moreover, SERT deletion resulted in anxiety-like behaviours assessed in the open field test. Their anxious phenotype resulted in a lower tendency to emit appetitive 50-kHz calls during novelty exploration. The present study demonstrates that genetic deletion of SERT not only leads to the deficits in social interaction and increased anxiety but also affects ultrasonic communication.

Attenuation of auditory mismatch negativity in serotonin transporter knockout mice with anxiety-related behaviors

As the first-line antidepressant drugs, selective serotonin reuptake inhibitors (SSRIs) have efficacy in controlling the symptoms of depression. However, adverse events such as anxiety and hearing disorders were usually observed in patients and even healthy volunteers during the initial phase of SSRI administration. Hearing disorders, including auditory hallucination and tinnitus, are not only highly comorbid with mental disorders but also acknowledged factors that induce psychiatric disorders. The pharmacological and neural mechanisms underlying SSRI-induced anxiety and hearing disorders are not clear. In particularly, the methods evaluating hearing disorders are not well established in animal models, limiting the pre-clinical research on its mechanism. In the present study, we examined the mismatch negativity (MMN), a cognitive component of auditory event-related potential (ERP), to evaluate the hearing process of auditory cortex in mice. Under the acute administration of citalopram, a widely used SSRI, the anxiety-related behaviors and reduced MMN were observed in mice. Serotonin transporter (SERT) is a potential target of SSRIs. The anxiety-related behaviors and reduced MMN were also observed in SERT knockout mice, implying the role of SERT in anxiety and hearing disorders induced by SSRIs. Meanwhile, the auditory brainstem response and initial components of auditory ERP were kept intact in SERT knockout mice, suggesting that hearing neural pathway is less affected by serotonergic system. Our study suggests that the SERT deficient mice might represent a useful animal model in the investigation of the anxiety and hearing disorders during the SSRI treatment.