5HT Levels Research Articles

Alterations and interactions of subcortical modulatory systems in Alzheimer's disease.

The pathogenesis of Alzheimer's disease (AD) is not fully understood. Here we summarize current knowledge on the involvement of the serotonergic, noradrenergic, dopaminergic, cholinergic, and opioid systems in AD, emphasizing the importance of interactions between the serotonergic and the other subcortical modulatory systems during the progression of AD. In physiological conditions, all neurotransmitter systems function in concert and are interdependent at both the neuroanatomical and molecular levels. Through their early involvement in AD, cognitive and behavioral abilities that rely on their interactions also become disrupted. Considering that serotonin (5HT) regulates the release of noradrenaline (NA), dopamine (DA) and acetylcholine (ACh), any alteration in 5HT levels leads to disturbance of NA, DA, and ACh homeostasis in the brain. One of the earliest pathological changes during the prodromal phase of AD is a decrease of serotonergic transmission throughout the brain, with serotonergic receptors being also affected. Additionally, serotonergic and noradrenergic as well as serotonergic and dopaminergic nuclei are reciprocally interconnected. As the serotonergic dorsal raphe nucleus (DRN) is affected by pathological changes early in AD, and the noradrenergic locus coeruleus (LC) and dopaminergic ventral tegmental area (VTA) exhibit AD-related pathological changes, their connectivity also becomes altered in AD. Such disrupted interactions among neurotransmitter systems in AD can be used in the development of multi-target drugs. Some of the potential AD therapeutics (such as ASS234, RS67333, tropisetron) target multiple neurotransmitter systems to achieve the best possible improvement of cognitive and behavioral deficits observed in AD. Here, we review how serotonergic system interacts with other subcortical modulatory systems (noradrenergic, dopaminergic, cholinergic, and opioid systems) during AD.

Addition of Saturated and Trans-fatty Acids to the Diet Induces Depressive and Anxiety-like Behaviors in Drosophila melanogaster

This study aimed to evaluate the effects of the addition of saturated fat and hydrogenated vegetable fat (HVF) to the diet on depressive and anxiety-like behaviors in Drosophila melanogaster. Flies were exposed to experimental diets: regular diet (RD), or HVF in the concentrations of the substitute (SHVF), HVF 10% and HVF 20%, or Lard (L) in the concentrations of the substitute (SL), L 10% and L 20%, during seven days. Our results showed that flies fed with the HVF diet presented similar behaviors to depression, anxiety, and a higher number of aggressive events. Flies exposed to L showed only depressive-like behavior. Regarding serotonin levels (5HT), there was a significant reduction in the flies exposed to SHVF, HVF 10%, HVF 20%, and L 20%. Regarding the levels of octopamine (OA), there was a significant reduction in the flies exposed to both HVF and L rich diets when compared with the RD group. Also, there was a significant negative correlation between 5HT or OA levels and behaviors of aggressiveness, negative geotaxis, immobility time, light/dark, and grooming in the flies. This study shows that D. melanogaster can serve as a valuable model for understanding psychiatric disorders and that the type of fatty acid (FA) offered in the diet can influence these disorders. This demonstrates the importance of the composition of the FAs in the neural pathways, being able to influence the signaling of neurotransmitters, such as 5HT and OA, and thus, cause behavioral changes.

It Is Time to Rethink Biomarkers for Surveillance of Small Bowel Neuroendocrine Tumors.

Tumor biomarkers(TBMs)reflect disease burden andcorrelate withsurvival for small bowel neuroendocrine tumors (SBNETs).This study sought to determine the performance ofchromogranin A (CgA),pancreastatin(PST), neurokinin A (NKA), and serotonin (5HT) duringfollow-up assessmentof resected SBNETs. An institutional database identified patients undergoing surgery for SBNETs. Tumor biomarker levels were assessed as categorical (normal vs elevated) and continuous variables for association withprogression-free survival (PFS) and overall survival (OS)viathe Kaplan-Meier method withCoxmultivariable models adjusted for confounders. Sensitivity, specificity, and predictive values ofTBMlevels in identifying imaging-confirmed progression werecalculated. In 218 patients (44% female, 92% node + , 73% metastatic, 97% G1 or G2), higher levels of CgA, PST, NKA, and 5HT correlated with higher-grade and metastatic disease at presentation (p < 0.05). Elevated pre- and postoperative CgA, PST, and NKA correlated with lower PFS and OS (p < 0.05; median follow-up period, 49.6months). Normal CgA, PST, and NKA were present in respectively 20.3%, 16.9%, and 72.6% of the patients with progression, whereas elevated levels were present in respectively 69.5%, 24.8%, and 1.3% of the patients without progression. Using TBMs to determine progression showed superiority of PST (78.9% accuracy) over CgA (63.3% accuracy) or CgA and PST together (60.3% accuracy). Although specific for progression, NKA was rarely elevated, limiting its usefulness. Pre- and postoperative PST and CgA correlated with disease burden and survival, with PST providing better discrimination of outcomes. During the follow-up period, use of PST most accurately detected progression. These results suggest that PSTshouldreplaceCgAforSBNET surveillance.

Plant Perception of Light: The role of indoleamines in Scutellaria species

Light mediates plant growth through diverse mechanisms and signaling networks including plant growth regulators (PGRs). We hypothesized that a novel class of PGRs, the indoleamines, are plant signaling molecules that perceive changes in light composition and initiate a cascade of metabolic responses. We used three Scutellaria model species (skullcap): S. lateriflora, S. galericulata and S. racemosa that produce high levels of melatonin and serotonin to investigate this hypothesis. Axenic Scutellaria cultures were exposed to red, blue, green or full spectrum white light spectra provided by light emitting diode (LED) lighting systems, or daylight fluorescent bulbs. Melatonin (MEL), serotonin (5HT), abscisic acid (ABA), auxin (IAA), and jasmonic acid (JA), were quantified by liquid chromatography with tandem mass spectrometry. Melatonin was detected consistently in plants grown under blue light in all species of Scutellaria. In S. galericulata, significant quantities of ABA were detected in plants grown under white light but not detected in plants grown under other light spectra. In timeline studies of S. racemosa plants exposed to limited red or blue light spectra had significantly reduced levels of tryptamine (TRM), 5HT and MEL in the shoots initially but melatonin was detected after 12 hours and quantifiable amounts of 5HT were detected after 7 days. Supplementation of the culture medium with MEL or 5HT did not change the pattern of MEL in blue light grown cultures but did change patterns of 5HT accumulation. 5HT was highest in plants grown under red light immediately after culture and decreased over 7 days. These data indicate that the relative amounts of MEL and 5HT are responsive to light spectra and redirect metabolic resources to enable plant adaptations to changing environments.

Sub‐diaphragmatic vagal nerve stimulation alleviates rodent hypertension associated with gut dysbiosis and reduced serotonergic vagal afferent signaling

IntroductionThe gut‐brain vagal axis, of which serotonin (5HT) is an important mediator, can be altered by the gut microbiota. Low vagal tone and autonomic imbalance is present in conditions marked by gut dysbiosis including in hypertension (HTN); however, the effect of gut dysbiosis on vagal sensory/afferent function in HTN is unknown. We hypothesized that HTN‐associated gut dysbiosis will decrease serotonergic vagal afferent signaling from the gut and cause autonomic imbalance leading to increased blood pressure (BP). Moreover, we propose that restoring the vagal gut‐brain axis by chronic vagal stimulation will alleviate HTN.MethodsFecal matter transplant (FMT) was performed from either the spontaneously hypertensive (SHR) or Wistar‐Kyoto rats (WKY) to control WKY. BP and autonomic variables were recorded using radiotelemetry. Colonic 5HT, expression of 5HT3a receptors (5HT3aR) along the vagal gut‐brain axis, and cardiovascular responses to systemic 5HT3aR agonist injection were determined in the FMT rats, WKY and SHR. In vivo Ca2+ imaging was performed in gCAMP‐labeled nodose ganglia (NG) neurons in response to 5HT3aR agonist in WKY and SHR. Lastly, SHR were implanted with cuff electrodes on the sub‐diaphragmatic ventral vagal trunk for chronic vagal stimulation (sVNS) while measuring BP and autonomic variables using radiotelemetry. Endpoint bacterial 16s sequencing determined the effects of sVNS on SHR gut dysbiosis.ResultsFMT from SHR but not WKY significantly increased BP (P&lt;0.05 vs baseline) and resulted in autonomic imbalance (P&lt;0.05 vs baseline) in control WKY. This was associated with reduced colonic 5HT levels (P&lt;0.01 vs FMT from WKY), as well as reduced 5HT3aR gene expression in vagal sensory (NG) neurons (p&lt;0.05 vs FMT from WKY) and the brainstem region receiving vagal sensory projections (P&lt;0.01 vs FMT from WKY). Furthermore, NG neuronal firing in response to 5HT3aR agonist corresponded with a time‐locked reduction in the HR in WKY, but both 5HT3aR agonist‐induced NG firing rates and HR responses were significantly blunted in the SHR (P&lt;0.05). In addition, 5HT3aR agonist‐dependent HR responses were also reduced in the WKY following FMT from SHR (P&lt;0.05 vs FMT from WKY). Crucially, chronic sVNS alleviated SHR HTN over eight weeks (P&lt;0.05 vs SHAM SHR), without reversing gut dysbiosis, suggesting that the observed BP effect may primarily be due to restoration of the vagal afferent gut‐brain signaling.ConclusionsHTN‐associated gut dysbiosis reduces serotonergic gut‐brain vagal signaling and increases BP. Restoring vagal afferent tone is effective in alleviating HTN in the SHR.

Pyrrolopyrazoles: Synthesis, Evaluation and Pharmacological Screening as Antidepressant Agents.

Pyrroles and fused pyrroles are of great interest as biologically active compounds, among these activities; antidepressant activity is of special concern. Synthesis of a series of pyrrolopyrazoles and their pyrimidine derivatives and their characterization using spectral data to be monitored for antidepressant activity using behavioral techniques. A control group was administered the vehicle i.p., positive control group received fluoxetine as standard and all other groups were administered the tested compounds. The groups were subjected to tail suspension test (TST) to determine the antidepressant activity compared with fluoxetine as a standard drug. The compounds exhibiting antidepressant activity were then used to analyze changes in serotonin (5HT) level in the brain of albino mice. TST results showed that both pyrazoles and pyrazolopyrimidines derivatives exhibit promising anti-depressant activity. Compounds [pyrazoles & pyrazlopyrimidines] showed promising antidepressant activity possibly mediated by the increased levels of 5HT.

Modulation of the Tryptophan Hydroxylase 1/Monoamine Oxidase-A/5-Hydroxytryptamine/5-Hydroxytryptamine Receptor 2A/2B/2C Axis Regulates Biliary Proliferation and Liver Fibrosis During Cholestasis.

Serotonin (5HT) is a neuroendocrine hormone synthetized in the central nervous system (CNS) as well as enterochromaffin cells of the gastrointestinal tract. Tryptophan hydroxylase (TPH1) and monoamine oxidase (MAO-A) are the key enzymes for the synthesis and catabolism of 5HT, respectively. Previous studies demonstrated that 5-hydroxytryptamine receptor (5HTR)1A/1B receptor agonists inhibit biliary hyperplasia in bile-duct ligated (BDL) rats, whereas 5HTR2B receptor antagonists attenuate liver fibrosis (LF) in mice. Our aim was to evaluate the role of 5HTR2A/2B/2C agonists/antagonists in cholestatic models. While in vivo studies were performed in BDL rats and the multidrug resistance gene 2 knockout (Mdr2-/- ) mouse model of PSC, in vitro studies were performed in cell lines of cholangiocytes and hepatic stellate cells (HSCs). 5HTR2A/2B/2C and MAO-A/TPH1 are expressed in cholangiocytes and HSCs from BDL rats and Mdr2-/- - mice. Ductular reaction, LF, as well as the mRNA expression of proinflammatory genes increased in normal, BDL rats, and Mdr2-/- - mice following treatment 5HTR2A/2B/2C agonists, but decreased when BDL rats and Mdr2-/- mice were treated with 5HTR2A/2B/2C antagonists compared to BDL rats and Mdr2-/- mice, respectively. 5HT levels increase in Mdr2-/- mice and in PSC human patients compared to their controls and decrease in serum of Mdr2-/- mice treated with 5HTR2A/2B/2C antagonists compared to untreated Mdr2-/- mice. In vitro, cell lines of murine cholangiocytes and human HSCs express 5HTR2A/2B/2C and MAO-A/TPH1; treatment of these cell lines with 5HTR2A/2B/2C antagonists or TPH1 inhibitor decreased 5HT levels as well as expression of fibrosis and inflammation genes compared to controls. Modulation of the TPH1/MAO-A/5HT/5HTR2A/2B/2C axis may represent a therapeutic approach for management of cholangiopathies, including PSC.

Repeated caffeine administration aggravates post-traumatic stress disorder-like symptoms in rats

BackgroundCaffeine is the widely consumed central nervous system stimulant in form of coffee and other beverages. However, the repeated administration of caffeine induces anxiety, disturbance in hypothalamic-pituitary-adrenal (HPA) axis and psychiatric symptoms in humans. As much evidence links PTSD to HPA axis dysfunction, and anxiety is a hallmark symptom, repeated and/or large doses of caffeine may exacerbate symptoms of PTSD. ObjectiveIn our present study, we evaluated the effect of repeated administration of caffeine on stress re-stress (SRS) model of PTSD. MethodsAs per the protocol, male rats were restrained for 2 h followed by 20 min forced swim and halothane anaesthesia on day 2 (D-2). Then the rats were re-stressed (forced swim) at 6-days interval between D-8 to D-32. After exposure to SRS, depressive, anxiety-like behaviour, and cognitive functions were evaluated by forced swim test (FST), elevated plus maze (EPM) and Y-maze tests respectively. Caffeine (10, 20 and 30 mg/kg, i.p.) dosing was started from D-8 and continued up to D-32. The corticosterone level was measured in plasma followed by serotonin and glucocorticoid receptor (GR) and mineralocorticoid receptors (MR) estimation in hippocampus (HIP), prefrontal cortex (PFC) and amygdala (AMY). ResultsSRS-induced depressive and anxiety-like behaviour was aggravated by caffeine at dose of 20 and 30 mg/kg. Caffeine (30 mg/kg) treated control animals showed depressive, anxiety-like behaviour and cognitive impairments. SRS-induced decrease in plasma corticosterone level and increase in serotonin (5HT) levels in the PFC, HIP and AMY were not altered by caffeine. Caffeine did not modulate the SRS-induced decrease in glucocorticoid receptor (GR) and mineralocorticoid receptor (MR). In contrast, caffeine per se decreased GR and MR expression and their ratio in unstressed animals. ConclusionRepeated intake of caffeine aggravates PTSD-like symptoms in stress-exposed rats and induces PTSD-like symptoms in unstressed rats by altering the expression of glucocorticoid receptors.

An investigation into serotonergic and environmental interventions against depression in a simulated delayed reward paradigm

The disruption of the serotonergic (5HT) system has been implicated in causing major depression and the standard view is that a lack of serotonin is to blame for the resulting symptoms. Consequently, pharmacological interventions aim to increase serotonin concentration in its target areas or stimulating excitatory 5HT receptors. A standard approach is to use serotonin reuptake inhibitors (SSRIs) which cause a higher accumulation of serotonin. Another approach is to stimulate excitatory serotonin receptors with psychedelic drugs. This article compares these two approaches by first setting up a system-level limbic system model of the relevant brain areas and then modelling a delayed reward paradigm which is known to be disrupted by a lack of 5HT. Central to our model is how serotonin changes the response characteristics of decision-making neurons where low levels of 5HT allow small signals to pass through, whereas high levels of 5HT create a barrier for smaller signals but amplifying the larger ones. We show with both standard behavioural simulations and model checking that SSRIs perform significantly better against interventions with psychedelics. However, psychedelics might work better in other paradigms where a high level of exploration is beneficial to obtain rewards.

Effect of Flavobacterium psychrophilum on the neuroendocrine response of rainbow trout (Oncorhynchus mykiss) in a time course experiment

The aim of this study was to examine the effects of Flavobacterium psychrophilum, a pathogen that is economically important in the aquaculture sector, on the neuroendocrine response of Oncorhynchus mykiss during a time course experiment with sampling at 0.5, 1, 2, 6, 10, and 30 days post injection (dpi). In the brain, serotonin (5HT) content increased in the infected group at all the measured time points, a similar pattern was observed for 5-hydroxyindole-3-acetic acid (5HIAA). Infected fish presented an increase in brain dopamine levels on day 0.5 and 1 dpi. A non-significant variation in noradrenaline levels was observed on all treatment days. Foregut 5-HT and 5-HIAA content in the infected group presented the highest 5-HT concentrations with 248.6 and 983.5 ng/g tissue at 0.5 dpi respectively. Midgut 5-HT and 5-HIAA levels presented the highest 5-HT concentrations, 486.9 ng/g tissue and 1006.4 ng/g tissue respectively, at the beginning of the experiment (0.5 dpi). 5-HT levels in the hindgut presented the highest concentrations with 233.9 ng/g tissue at 0.5 dpi, while 5-HIAA presented the highest concentrations, 690.5 ng/g tissue, at the same time point. After injection with F. psychrophilum the neuroendocrine response in rainbow trout was tissue dependent. Brain levels of 5HT and 5HIIA indicate that the neuroendocrine response increased together with dopamine following intramuscular infection. These increases are in line with reports from other authors, indicating an early response of catecholamines as neurotransmitters to stressful stimulus. In addition the intestinal response was also increased, implying that there could be a possible relationship between the serotonergic system at the intestinal level and the immune system.

The effect of alterations in salinity and temperature on neuroendocrine responses of the Antarctic fish Harpagifer antarcticus

Increased levels of tissue monoaminergic neurotransmitters, as well as circulating catecholamines, appear to play a role in the regulation of the physiological responses of teleost fish. Harpagifer antarcticus is a stenothermic, Antarctic notothenioid fish. The aim of this study was to determine the effect of increased seawater temperature and decreased salinity on the levels of 5-HT, 5-HIAA, DA, and Noradrenaline in the brain, stomach, and gut of H. antarcticus. Wild-gathered fish were acclimatized to habitat conditions (2 °C, 33 PSU) prior to placement in aquaria with 4 temperatures (2, 5, 8 and 11 °C) and 3 salinities (23, 28 and 33 PSU) for 10 days. Fish exposed to 11 °C had higher levels of the brain neurotransmitters than those at 2 °C. Concomitant exposure to low salinity exacerbated the effect of exposure to 11 °C. At lower temperatures, concomitant alterations in salinity induced differential effects on brain neurotransmitters. When fish were exposed to 28 PSU, 5-HIAA, DA, and Noradrenaline levels at 5 and 8 °C presented no significant differences with those at 2 °C. In contrast, only 5HT and 5-HIAA levels in fish at 33 PSU were elevated at 5 and 8 °C respectively. Fish at 28 and 33 PSU had lower Gut 5HT levels at the 3 elevated temperatures, meanwhile fish at 23 PSU showed a biphasic effect when exposed to elevated temperatures. 5-HIAA levels decreased at 5 and 8 °C at 33 PSU. Stomach 5HT levels also showed a differential response at the 3 salinity levels when exposed to increased temperatures. At 11 °C, 5HT levels were markedly higher than those at 2 °C for fish at 33 PSU, moderately elevated for fish at 28 PSU, and lower for fish at 23 PSU, meanwhile 5-HIAA levels only increased with temperature at 33 PSU. These findings indicate that rapid exposure to alterations in temperate with or without concomitant changes in salinity is associated with differential responses in tissue monoaminergic neurotransmitter levels. The relatively high changes in neurotransmitter levels in fish exposed to moderate salinity and high temperature changes may indicate the physiological plasticity of H. antarcticus to possible changes in ocean temperature and salinity.

Platelet Serotonin Levels Are Associated with Plasma Soluble Leptin Receptor Concentrations in Normoglycemic Women.

Most peripheral serotonin (5-hydroxytryptamine (5HT)) is synthetized in the gut with platelets being its main circulating reservoir. 5HT is acting as a hormone in key organs to regulate glucose and lipid metabolism. However, the relation between platelet 5HT levels and traits related to glucose homeostasis and lipid metabolism in humans remains poorly explored. The objectives of this study were (a) to assess the association between platelet 5HT levels and plasma concentration of nonesterified fatty acids (NEFAs) and some adipokines including leptin and its soluble leptin receptor (sOb-R), (b) to assess the association between platelet 5HT levels and anthropometric traits and indexes of insulin secretion/sensitivity derived from oral glucose tolerance test (OGTT), and (c) to evaluate changes in platelet 5HT levels in response to OGTT. In a cross-sectional study, 59 normoglycemic women underwent a standard 2-hour OGTT. Plasma leptin, sOb-R, total and high molecular weight adiponectin, TNFα, and MCP1 were determined by immunoassays. Platelet 5HT levels and NEFAs were measured before and after OGTT. The free leptin index was calculated from leptin and sOb-R measurements. Insulin sensitivity indexes derived from OGTT (HOMA-S and Matsuda ISICOMP) and plasma NEFAs (Adipose-IR, Revised QUICKI) were also calculated. Our data show that among metabolic traits, platelet 5HT levels were associated with plasma sOb-R (r = 0.39, p = 0.003, corrected p = 0.018). Platelet 5HT levels were reduced in response to OGTT (779 ± 237 vs.731 ± 217 ng/109 platelets, p = 0.005). In conclusion, platelet 5HT levels are positively associated with plasma sOb-R concentrations and reduced in response to glucose intake possibly indicating a role of peripheral 5HT in leptin-mediated appetite regulation.

Role of Cortical Catecholamines in the Paradoxical Action of Psychostimulants

Attention deficit hyperactivity disorder (ADHD) affects young children and manifests symptoms such as hyperactivity, impulsivity and cognitive disabilities. The primary line of treatment for ADHD are the psychostimulant class of drugs including amphetamine (Adderall) and methylphenidate (Ritalin). Several theories have been postulated on the paradoxical calming effect of psychostimulants on ADHD patients, but even after decades of research, their exact mechanism of action is unknown. Clinical studies have shown reduced levels of dopamine (DA) receptor and DA transporters (DAT) in ADHD patients, presumably due to elevated caudate DA levels. Studies using the dopamine (DA) transporter (DAT) knockout mice, which have elevated striatal DA levels and are considered an animal model of ADHD, have suggested that the paradoxical calming effect of psychostimulants might be through the parallel actions of other monoamine neurotransmitters. On the other hand, newer non‐stimulant classes of drugs such as atomoxetine and Intuniv suggest that targeting the norepinephrine (NE) system might explain the paradoxical calming effect. Again, the molecular and cellular mechanisms of action for these drugs or neurotransmitters in ADHD therapy is unknown.Previous work has shown that DA levels in the PFC have a reciprocal effect on striatal DA levels and locomotion. Our preliminary data suggest that PFC D2+ pyramidal neurons project to the striatum and midbrain dopamine neurons and that infusion of D2 agonists in the PFC inhibits locomotion. We hypothesize that PFC DA through the action of PFC D2+ pyramidal neurons regulates striatal DA release and locomotion. To test our hypothesis we use ex vivo neurotransmitter release from mouse PFC slices, microdialysis and locomotor measurements, in NET and DAT knockout mice. Our preliminary data suggest that NET and SERT blockers not only increase extracellular levels of NE and 5HT, but also DA. These data suggest a possible role for cortical catecholamines in regulating the paradoxical effects of psychostimulants. Our future studies will not only shed light on the mechanism of psychostimulant action in ADHD therapy, but will facilitate development of newer therapies based on mechanistic evidence.Support or Funding InformationBrain Behavior Research Foundation 27765 to N. UrsThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Biological profiling of piperazinediones for the management of anxiety

The anxiolytic effect of earlier reported piperazinediones was assessed by elevated plus maze (EPM), hole-board and open-field (OFT) tests. The rats were administered pretreatment of three different doses i.e. 2, 1 and 0.5 mg/kg of compounds 52, 53 and 55 for seven consecutive days. Compound 52 and diazepam showed increase in open arm entries, increase in time spent therein and total arm entries at 1 mg/kg dose. The compound also produced increase in the number of head dip, sniffing behavior and total number of squares crossed compared to diazepam. In OFT paradigm grooming behavior, number of central squares crossed and the time spent in central area did not reveal statistical differences for diazepam and compound 52 at 1 mg/kg dose. Flumazenil mediated antagonism experiments of these showed that they were acting through benzodiazepine site on GABAA receptor. The levels of 5HT and 5HIAA were estimated in amygdalar region. Level of 5HT was found to be equivalent in case of compound 52 and diazepam treatment at dose of 1 mg/kg. Interestingly, compound 52 did not display sedative effect at higher dose in both animal models. Thus, present study indicated that compound 52 produced anti-anxiety property through modulation of GABAergic transmission.

Photoaffinity‐Mediated Identification of a Third Citalopram Analog Binding Site on the Serotonin Transporter

In the CNS, serotonin (5HT) controls anxiety and mood, and disorders caused by imbalanced 5HT include Major Depressive Disorder and Autism Spectrum Disorder. The serotonin transporter (SERT) is a major regulator of synaptic 5HT levels and is the target for antidepressants such as escitalopram (S‐CIT) and fluoxetine, which bind to and inhibit the transporter to elevate free transmitter. The efficacy of these drugs is moderate and many patients experience inadequate relief, indicating the need for better understanding of mechanisms or development of novel therapeutics. Antidepressant effects on SERT are complex, as many induce high‐affinity actions at the S1 orthosteric site, as well as allosteric modulation of S1 function through low‐affinity binding to a distinct S2 domain. To examine S‐CIT mechanisms we developed two novel photoaffinity ligands, [125I]VK 03‐83 and [125I]VK 03‐51, that possess identical S‐CIT pharmacophores but have cross‐linking moieties appended to different positions on the citalopram core. Our findings show that both ligands bind to SERT, inhibit 5HT transport, and allosterically regulate S1 function, but display distinct pharmacological characteristics that indicate differential binding mechanisms. [125I]VK 03‐83 labeling of SERT is fully inhibited by 5HT and typical SERT inhibitors, with an S‐CIT Ki of ~1 nM, consistent with binding to S1. In contrast, although [125I]VK 03‐51 labeling is fully displaced by the homologous ligand, it is inhibited only ~30% by S‐CIT or other standard SERT inhibitors, and shows no displacement by 10 μM 5HT, indicative of binding to multiple sites. The S‐CIT‐displaceable portion of [125I]VK 03‐51 labeling occurs with a Ki of ~1 nM, consistent with binding at S1, whereas the fraction of labeling that is not sensitive to ≥10 μM concentrations of S‐CIT, other inhibitors, or 5HT likely does not occur at either S1 or S2, which should both be fully occupied by these conditions. These findings suggest that [125I]VK 03‐51 interacts with SERT at a third site that has not been previously detected by reversible binding or co‐crystallization approaches, but is revealed by covalent cross‐linking. This site may function in transport inhibition or allosteric regulation, and suggests a domain for exploration of transporter mechanisms or medication development.Support or Funding InformationNIH DA027845 and UNDSMHS Seed Grant (LKH and RAV), NIDA Intramural Research Program (AHN)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Chrysin reverses the depressive-like behavior induced by hypothyroidism in female mice by regulating hippocampal serotonin and dopamine

Hypothyroidism is often associated with psychiatric disorders such as depression. In this study, we evaluated the effect of chrysin on depressive-like behavior and monoamine levels in hypothyroid female mice. Hypothyroidism was induced by continuous exposure to 0.1% methimazole (MTZ) in drinking water for 31 days. Exposure to MTZ was associated with low plasma levels of thyroid hormones T3 and T4 compared with the control group. Subsequently, euthyroid and MTZ-induced hypothyroid mice were intragastrically administered vehicle or chrysin (20mg/kg) once a day for 28 consecutive days. After treatments, the following behavioral assessments were performed: Open-Field Test (OFT), Tail suspension test (TST), and Forced Swimming Test (FST). Additionally, T3 and T4 levels were measured again, and serotonin (5HT), dopamine, and noradrenaline levels were analyzed in the prefrontal cortex and the hippocampus. Chrysin treatment could not reverse T3 and T4 levels. Hypothyroid mice showed an increased immobility time in TST and FST; chrysin treatment reversed these effects. Reduced levels of 5HT and dopamine in the prefrontal cortex and the hippocampus were observed in the hypothyroid mice than in the euthyroid mice. Chrysin treatment recovered 5HT content in both structures and dopamine content only in the hippocampus. Noradrenaline content was not altered by treatments. Together, our results have demonstrated that chrysin treatment reverses depressive-like behaviors in hypothyroid female mice and suggests the involvement of 5HT and dopamine in these effects.

Central monoaminergic systems sensitivity to acute hypoxia with hypercapnia changes after the maintenance under the long-term social isolation

The experiments were performed in male albino outbred mice kept in a group and under the conditions of long-term social isolation. The changes in the monoaminergic systems of the left and right hemispheres of the brain after acute hypoxia with hypercapnia have been studied. The levels of dopamine (DA), serotonin (5-HT) and their metabolites - dioxyphenylacetic (DOPAC), homovanillic (HVA), and 5-hydroxyindoleacetic (5-HIAA) acids - were determined by HPLC in the cerebral cortex, hippocampus and striatum of the right and left sides of the brain. In the control mice kept both in the group and under the conditions of social isolation, a higher content of DA in the cortex of the left hemisphere has been found. In the other brain structures the monoamine content was symmetric. In the cerebral cortex of the mice in the group, acute hypoxia with hypercapnia led to a right-sided increase in the DA and 5HT levels. At the same time, the DOPAC content decreased in the left cortex. In mice in the group, under the hypoxia with hypercapnia conditions, the DA level in the left hippocampus increased. In the striatum, the content of monoamines and their metabolites did not change significantly. In animals kept for a long time under the conditions of social isolation, hypoxia with hypercapnia no statistically significant changes in the monoamines and their metabolites levels were found. It has been concluded that the preliminary maintenance under the conditions of prolonged social isolation changes the reaction of central monoaminergic systems to acute hypoxia with hypercapnia.

Cathepsin C Aggravates Neuroinflammation Involved in Disturbances of Behaviour and Neurochemistry in Acute and Chronic Stress-Induced Murine Model of Depression.

Major depression has been interpreted as an inflammatory disease characterized by cell-mediated immune activation, which is generally triggered by various stresses. Microglia has been thought to be the cellular link between inflammation and depression-like behavioural alterations. The expression of cathepsin C (Cat C), a lysosomal proteinase, is predominantly induced in microglia in neuroinflammation. However, little is known about the role of Cat C in pathophysiology of depression. In the present study, Cat C transgenic mice and wild type mice were subjected to an intraperitoneal injection of LPS (0.5mg/kg) and 6-week unpredictable chronic mild stress (UCMS) exposure to establish acute and chronic stress-induced depression model. We examined and compared the behavioural and proinflammatory cytokine alterations in serum and depression-targeted brain areas of Cat C differentially expressed mice in stress, as well as indoleamine 2,3-dioxygenase (IDO) and 5-hydroxytryptamine (5HT) levels in brain. The results showed that Cat C overexpression (Cat C OE) promoted peripheral and central inflammatory response with significantly increased TNFα, IL-1β and IL-6 in serum, hippocampus and prefrontal cortex, and resultant upregulation of IDO and downregulation of 5HT expression in brain, and thereby aggravated depression-like behaviours accessed by open field test, forced swim test and tail suspension test. In contrast, Cat C knockdown (Cat C KD) partially prevented inflammation, which may help alleviate the symptoms of depression in mice. To the best of our knowledge, we are the first to demonstrate that Cat C aggravates neuroinflammation involved in disturbances of behaviour and neurochemistry in acute and chronic stress-induced murine model of depression.

29: Exposure to a high fat diet is associated with persistent alterations in behavior and the gut microbiome in juvenile offspring primates

Prior work from our consortium shows that maternal high-fat diet (HFD) consumption is associated with modifications in behavior and the central serotonergic system in juveniles at 1 year of age. Additionally, we have described dysbiosis of the gut microbiome occurring at this age with exposure to maternal HFD. Intriguingly, ∼90% of serotonin (5HT) is made in the gut, and microbes and their metabolites function as important regulators of 5HT production. Here, we aimed to determine the importance of exposure to a HFD as a persistent behavioral mediator in juvenile offspring by examining the associations between diet, behavior, and the gut microbiome. Using our Japanese macaque model of maternal HFD exposure, we performed 16S or whole genome shotgun (WGS) sequencing on stool samples (n=15) collected at 1 & 3 years of age. WGS was performed on the Illumina HiSeq platform and resultant sequences were trimmed/quality filtered using KneadData. Taxonomic classification and functional annotation of species-specific (MetaPhlAn2) and community level metabolic pathways (HUMAnN2) was performed. Stool 5HT levels were assayed by ELISA. Behavioral testing (i.e. novel objects, repetitive behavior) occurred to associate with 5HT and microbiome data. Exposure to HFD in gestation is associated with persistent behavioral modifications (increased anxiety) in offspring at 3 years of age (Fig A). Additionally, we found alterations in metabolic pathways by metagenomic analysis (0.9 billion reads, average 62 million reads/sample) that have been previously shown to modulate 5HT; this includes L-tryptophan biosynthesis, of which Phascolarctobacterium succinatutens was identified as a primary contributor (Fig B). Furthermore, we detected significant inverse correlations with specific taxa, including Phascolarctobacterium and 5HT at 3 years of age (Fig C). Altogether, our data suggest HFD exposure leads to persistent gut microbial dysbiosis associated with reductions in serotonergic signaling mediators and 5HT synthesis that are detectable at 3 years. The interplay between the gut microbiome and serotonergic signaling potentially contribute to behavioral modifications observed with HFD exposure during fetal life, even with consumption of a postnatal control diet.

Impact of Gestational Chronic Intermittent Hypoxia and Hypertension on the Serotonergic System and Autoresuscitation in the Developmental Rat

Sudden infant death syndrome (SIDS) is characterized by the sudden death of a seemingly healthy infant during a sleep period under the age of 12 months. Abnormalities in the medullary serotonin (5HT) system, e.g. decreased tissue levels of 5HT and 5HTT, and increased immature 5HT neurons, have been identified in approximately 70% of infants that died of SIDS. Failed autoresuscitation (inability to recover breathing and heart rate following hypoxic apnea) is considered a possible mechanism of SIDS deaths, and animal studies have shown that 5HT neurons are critical for neonatal mice and rats to survive repeated episodes of severe hypoxia/asphyxia. Gestational chronic intermittent hypoxia (CIH) and preeclampsia both are risk factors for SIDS. In this study we asked whether the stressors, e.g. gestational/prenatal chronic intermittent hypoxia (CIH) and/or hypertension, would increase stress hormone levels, impair the maturity and integrity of medullary 5HT neurons and the ability to autoresuscitate from repetitive asphyxia in developing rat pups. The pregnant dams of normotensive Sprague Dawley (SD) rats and spontaneously hypertensive rats (SHR) were exposed to CIH or room air (RA) from gestation E4‐21, and then the serum corticosterone level (ELISA), the number and integrity of the medullary serotonin neurons (immunostainings), and in vivo autoresuscitation were assessed in the offspring pups at Postnatal (P) days 5–15.We found 1) SHR‐CIH pups have significantly higher serum corticosterone levels than SHR‐RA and SD‐RA pups at P7 (11,485 vs. 8078 &amp; 8970 pg/mL respectively, P&lt;0.05) and P10 (11,708 vs. 9040 &amp; 6,529 pg/mL respectively, P&lt;0.05). At P15 SD‐CIH, SHR‐CIH and SHR‐RA pups all have significantly higher corticosterone levels than SD‐RA pups; 2) Relative to the SD‐RA pups, SD‐CIH pups have a significantly higher total number of 5HT neurons and primarily due to increased number of Ki67/5HT‐ir positive neurons in the medulla. When compared to SD rats, we noticed that SHR pups appear to have more Ki67/5HT‐ir neurons which contribute to an increase in total number of 5HT neurons in the medulla than SD‐CIH &amp; SD‐RA (P&lt;0.01); and 3) the offspring pups of SHRs have the highest mortality rate during repetitive exposure of anoxia at all ages tested. Our data suggest that both gestational CIH and uncontrolled hypertension may lead to an impaired 5HT system in the offspring pups. The uncontrolled high blood pressure during pregnancy may cause placental insufficiency and contribute to failed autoresuscitation in response to repetitive anoxia in early postnatal life.Support or Funding InformationDartmouth UGAR, NIH HD036379, NIH HL28066