Sex- and SERT-mediated differences in stimulated serotonin revealed by fast microdialysis

Complex 33-beam simulated galactic cosmic radiation exposure impacts cognitive function and prefrontal cortex neurotransmitter networks in male mice

Astronauts will encounter extended exposure to galactic cosmic radiation (GCR) during deep space exploration, which could impair brain function. Here, we report that in male mice, acute or chronic GCR exposure did not modify reward sensitivity but did adversely affect attentional processes and increased reaction times. Potassium (K+)-stimulation in the prefrontal cortex (PFC) elevated dopamine (DA) but abolished temporal DA responsiveness after acute and chronic GCR exposure. Unlike acute GCR, chronic GCR increased levels of all other neurotransmitters, with differences evident between groups after higher K+-stimulation. Correlational and machine learning analysis showed that acute and chronic GCR exposure differentially reorganized the connection strength and causation of DA and other PFC neurotransmitter networks compared to controls which may explain space radiation-induced neurocognitive deficits.

Flexible and Implantable Polyimide Aptamer-Field-Effect Transistor Biosensors

Monitoring neurochemical signaling across time scales is critical to understanding how brains encode and store information. Flexible (vs stiff) devices have been shown to improve in vivo monitoring, particularly over longer times, by reducing tissue damage and immunological responses. Here, we report our initial steps toward developing flexible and implantable neuroprobes with aptamer-field-effect transistor (FET) biosensors for neurotransmitter monitoring. A high-throughput process was developed to fabricate thin, flexible polyimide probes using microelectromechanical-system (MEMS) technologies, where 150 flexible probes were fabricated on each 4 in. Si wafer. Probes were 150 μm wide and 7 μm thick with two FETs per tip. The bending stiffness was 1.2 × 10^-11 N·m². Semiconductor thin films (3 nm In₂O₃) were functionalized with DNA aptamers for target recognition, which produces aptamer conformational rearrangements detected via changes in FET conductance. Flexible aptamer-FET neuroprobes detected serotonin at femtomolar concentrations in high-ionic strength artificial cerebrospinal fluid. A straightforward implantation process was developed, where microfabricated Si carrier devices assisted with implantation such that flexible neuroprobes detected physiological relevant serotonin in a tissue-hydrogel brain mimic.

Optogenetic Stimulation of Midbrain Dopamine Neurons Produces Striatal Serotonin Release

Targeting neurons with light-driven opsins is widely used to investigate cell-specific responses. We transfected midbrain dopamine neurons with the excitatory opsin Chrimson. Extracellular basal and stimulated neurotransmitter levels in the dorsal striatum were measured by microdialysis in awake mice. Optical activation of dopamine cell bodies evoked terminal dopamine release in the striatum. Multiplexed analysis of dialysate samples revealed that the evoked dopamine was accompanied by temporally coupled increases in striatal 3-methoxytyramine, an extracellular dopamine metabolite, and in serotonin. We investigated a mechanism for dopamine-serotonin interactions involving striatal dopamine receptors. However, the evoked serotonin associated with optical stimulation of dopamine neurons was not abolished by striatal D1- or D2-like receptor inhibition. Although the mechanisms underlying the coupling of striatal dopamine and serotonin remain unclear, these findings illustrate advantages of multiplexed measurements for uncovering functional interactions between neurotransmitter systems. Furthermore, they suggest that the output of optogenetic manipulations may extend beyond opsin-expressing neuronal populations.

Sex-Specific and Long-Term Impacts of Early-Life Venlafaxine Exposure in Zebrafish

Venlafaxine, a selective serotonin and norepinephrine reuptake inhibitor, is a widely prescribed antidepressant that is detected in municipal wastewater effluents at µg/L concentrations. It has been shown to impact the early life stages of fish, including neurodevelopment and behaviour in larvae, but whether such early exposures have longer-term consequences are far from clear. Here, we sought to determine whether zygotic deposition of venlafaxine, mimicking a maternal transfer scenario, disturbs the metabolic rate and behavioural performance using zebrafish (Danio rerio). This was tested using freshly fertilized embryos (1-4 cell stage) microinjected with either 0, 1 or 10 ng of venlafaxine and raised to either juvenile (60 days post-fertilization) or adult (10-12 months post-fertilization). Zygotic venlafaxine exposure led to a reduction in the active metabolic rate and aerobic scope, but this was only observed in female fish. On the other hand, the total distance travelled in an open field assessment was greater at the highest concentration of venlafaxine only in the adult males. At the juvenile stage, behavioural assessments demonstrated that venlafaxine exposure may increase boldness-including hyperactivity, lower thigmotaxis, and a reduction in the distance to a novel object. Taken together, these results demonstrate that zygotic venlafaxine exposure may impact developmental programming in a sex-specific manner in fish.

Implantable aptamer-field-effect transistor neuroprobes for in vivo neurotransmitter monitoring

While tools for monitoring in vivo electrophysiology have been extensively developed, neurochemical recording technologies remain limited. Nevertheless, chemical communication via neurotransmitters plays central roles in brain information processing. We developed implantable aptamer–field-effect transistor (FET) neuroprobes for monitoring neurotransmitters. Neuroprobes were fabricated using high-throughput microelectromechanical system (MEMS) technologies, where 150 probes with shanks of either 150- or 50-μm widths and thicknesses were fabricated on 4-inch Si wafers. Nanoscale FETs with ultrathin (~3 to 4 nm) In₂O₃ semiconductor films were prepared using sol-gel processing. The In₂O₃ surfaces were coupled with synthetic oligonucleotide receptors (aptamers) to recognize and to detect the neurotransmitter serotonin. Aptamer-FET neuroprobes enabled femtomolar serotonin detection limits in brain tissue with minimal biofouling. Stimulated serotonin release was detected in vivo. This study opens opportunities for integrated neural activity recordings at high spatiotemporal resolution by combining these aptamer-FET sensors with other types of Si-based implantable probes to advance our understanding of brain function.

Simultaneous serotonin and dopamine monitoring across timescales by rapid pulse voltammetry with partial least squares regression

Many voltammetry methods have been developed to monitor brain extracellular dopamine levels. Fewer approaches have been successful in detecting serotonin in vivo. No voltammetric techniques are currently available to monitor both neurotransmitters simultaneously across timescales, even though they play integrated roles in modulating behavior. We provide proof-of-concept for rapid pulse voltammetry coupled with partial least squares regression (RPV-PLSR), an approach adapted from multi-electrode systems (i.e., electronic tongues) used to identify multiple components in complex environments. We exploited small differences in analyte redox profiles to select pulse steps for RPV waveforms. Using an intentionally designed pulse strategy combined with custom instrumentation and analysis software, we monitored basal and stimulated levels of dopamine and serotonin. In addition to faradaic currents, capacitive currents were important factors in analyte identification arguing against background subtraction. Compared to fast-scan cyclic voltammetry-principal components regression (FSCV-PCR), RPV-PLSR better differentiated and quantified basal and stimulated dopamine and serotonin associated with striatal recording electrode position, optical stimulation frequency, and serotonin reuptake inhibition. The RPV-PLSR approach can be generalized to other electrochemically active neurotransmitters and provides a feedback pipeline for future optimization of multi-analyte, fit-for-purpose waveforms and machine learning approaches to data analysis.

Imaging in vivo acetylcholine release in the peripheral nervous system with a fluorescent nanosensor

The ability to monitor the release of neurotransmitters during synaptic transmission would significantly impact the diagnosis and treatment of neurological diseases. Here, we present a DNA-based enzymatic nanosensor for quantitative detection of acetylcholine (ACh) in the peripheral nervous system of living mice. ACh nanosensors consist of DNA as a scaffold, acetylcholinesterase as a recognition component, pH-sensitive fluorophores as signal generators, and α-bungarotoxin as a targeting moiety. We demonstrate the utility of the nanosensors in the submandibular ganglia of living mice to sensitively detect ACh ranging from 0.228 to 358 μM. In addition, the sensor response upon electrical stimulation of the efferent nerve is dose dependent, reversible, and we observe a reduction of ∼76% in sensor signal upon pharmacological inhibition of ACh release. Equipped with an advanced imaging processing tool, we further spatially resolve ACh signal propagation on the tissue level. Our platform enables sensitive measurement and mapping of ACh transmission in the peripheral nervous system.

Divalent Cation Dependence Enhances Dopamine Aptamer Biosensing

Oligonucleotide receptors (aptamers), which change conformation upon target recognition, enable electronic biosensing under high ionic-strength conditions when coupled to field-effect transistors (FETs). Because highly negatively charged aptamer backbones are influenced by ion content and concentration, biosensor performance and target sensitivities were evaluated under application conditions. For a recently identified dopamine aptamer, physiological concentrations of Mg²⁺ and Ca²⁺ in artificial cerebrospinal fluid produced marked potentiation of dopamine FET-sensor responses. By comparison, divalent cation-associated signal amplification was not observed for FET sensors functionalized with a recently identified serotonin aptamer or a previously reported dopamine aptamer. Circular dichroism spectroscopy revealed Mg²⁺- and Ca²⁺-induced changes in target-associated secondary structure for the new dopamine aptamer, but not the serotonin aptamer nor the old dopamine aptamer. Thioflavin T displacement corroborated the Mg²⁺ dependence of the new dopamine aptamer for target detection. These findings imply allosteric binding interactions between divalent cations and dopamine for the new dopamine aptamer. Developing and testing sensors in ionic environments that reflect intended applications are best practices for identifying aptamer candidates with favorable attributes and elucidating sensing mechanisms.

Imaging Neurotransmitter and Neuromodulator Dynamics In Vivo with Genetically Encoded Indicators

The actions of neuromodulation are thought to mediate the ability of the mammalian brain to dynamically adjust its functional state in response to changes in the environment. Altered neurotransmitter (NT) and neuromodulator (NM) signaling is central to the pathogenesis or treatment of many human neurological and psychiatric disorders, including Parkinson's disease, schizophrenia, depression, and addiction. To reveal the precise mechanisms by which these neurochemicals regulate healthy and diseased neural circuitry, one needs to measure their spatiotemporal dynamics in the living brain with great precision. Here, we discuss recent development, optimization, and applications of optical approaches to measure the spatial and temporal profiles of NT and NM release in the brain using genetically encoded sensors for in vivo studies.

Flexible Multiplexed In2O3 Nanoribbon Aptamer-Field-Effect Transistors for Biosensing

Flexible sensors are essential for advancing implantable and wearable bioelectronics toward monitoring chemical signals within and on the body. Developing biosensors for monitoring multiple neurotransmitters in real time represents a key in vivo application that will increase understanding of information encoded in brain neurochemical fluxes. Here, arrays of devices having multiple In₂O₃ nanoribbon field-effect transistors (FETs) were fabricated on 1.4-μm-thick polyethylene terephthalate (PET) substrates using shadow mask patterning techniques. Thin PET-FET devices withstood crumpling and bending such that stable transistor performance with high mobility was maintained over >100 bending cycles. Real-time detection of the small-molecule neurotransmitters serotonin and dopamine was achieved by immobilizing recently identified high-affinity nucleic-acid aptamers on individual In₂O₃ nanoribbon devices. Limits of detection were 10 fM for serotonin and dopamine with detection ranges spanning eight orders of magnitude. Simultaneous sensing of temperature, pH, serotonin, and dopamine enabled integration of physiological and neurochemical data from individual bioelectronic devices.

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We fabricated flexible In₂O₃ nanoribbon transistors using cleanroom-free processes

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Flexible In₂O₃ transistors withstood crumpling and bending with stable performance

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Flexible aptamer biosensors detect neurotransmitters in real time

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Multiplexed sensors monitor temperature, pH, serotonin, and dopamine simultaneously

High-throughput evolution of near-infrared serotonin nanosensors

Imaging neuromodulation with synthetic probes is an emerging technology for studying neurotransmission. However, most synthetic probes are developed through conjugation of fluorescent signal transducers to preexisting recognition moieties such as antibodies or receptors. We introduce a generic platform to evolve synthetic molecular recognition on the surface of near-infrared fluorescent single-wall carbon nanotube (SWCNT) signal transducers. We demonstrate evolution of molecular recognition toward neuromodulator serotonin generated from large libraries of ~6.9 × 1010 unique ssDNA sequences conjugated to SWCNTs. This probe is reversible and produces a ~200% fluorescence enhancement upon exposure to serotonin with a K d = 6.3 μM, and shows selective responsivity over serotonin analogs, metabolites, and receptor-targeting drugs. Furthermore, this probe remains responsive and reversible upon repeat exposure to exogenous serotonin in the extracellular space of acute brain slices. Our results suggest that evolution of nanosensors could be generically implemented to develop other neuromodulator probes with synthetic molecular recognition.

A rotating operant chamber for use with microdialysis

BACKGROUND

Recently, the time resolution of microdialysis followed by a chemical separation for quantitative analysis has improved. The advent of faster microdialysis measurements promises to aid in behavioral research on awake animals. However, microdialysis with awake animals generally employs a fluidic commutator (swivel). The swivel's volume is inimical to the time resolution of the measurements.

NEW METHOD

Animals can be housed in rotating cages so that the swivel is not required, but rotating operant chambers are not available. Here we describe the design and construction of a rotating operant chamber with microdialysis capability. We modified a rotating cage by adding operant behavior testing components to the side of the bowl-shaped cage. A modular on-board controller facilitates operant component/computer communication. A battery provides power to the controller and the operant components. The battery and controller rotate with the cage, and the controller communicates with the computer wirelessly.

RESULTS

The rotating operant chamber can be used to train a rat to retrieve a sucrose pellet following a cue. Microdialysis and online liquid chromatography can be used to measure dopamine at one minute intervals while the rat moves freely and interacts with operant behavior testing components.

COMPARISON WITH EXISTING METHOD(S)

We are not aware of one-minute dopamine measurements in awake animals in an operant chamber.

CONCLUSIONS

Rotating cage modifications are straightforward. One-minute observations of striatal dopamine can be accomplished while an animal is awake, moving, and interacting with its surroundings.

Sexually dimorphic responses of rats to fluoxetine in the forced swimming test are unrelated to the function of the serotonin transporter in the brain

Due to the prevalence of depression in women, female rats may be a better models for antidepressant research than males. In male rats, fluoxetine inhibited the serotonin (5-hydroxytryptamine, 5-HT) transporter (SERT) which is reducing the immobility time in the repeated forced swimming test (rFST). The performance of female rats in this test is unknown. In this study, responses of male and female rats in the rFST under chronic treatment with fluoxetine and the function of SERT in their brains were examined. Wistar rats received oral fluoxetine (females: 0, 1, 2.5, or 5 mg kg^-1  day^-1 ; males: 0 or 2.5 mg kg^-1  day^-1 ; in sucrose 10%, 1.5 ml/rat) 1 hr before the test daily for 12 days over the course of the rFST. rFST consisted of a 15 min pretest followed by 5 min sessions of swimming at 1 (test), 7 (retest 1), and 14 (retest 2) days later. SERT functioning was assessed by ex vivo assays of the frontal cortex and hippocampus of rats. Fluoxetine reduced immobility time of males in the rFST while it failed to do so in females. In vitro treatment with fluoxetine inhibited the uptake of 5-HT of both sexes similarly, while in vivo chronic administration of fluoxetine failed to do so. In summary, rats responded to the chronic treatment with fluoxetine in a sexually dimorphic fashion during the rFST despite the functioning of SERT in their brains remaining equally unchanged. Hence, our data suggest that sexually dimorphic responses to fluoxetine in rFST may be unrelated to the function of SERT in rat brains.

In Utero Exposure to Citalopram Mitigates Maternal Stress Effects on Fetal Brain Development

Human epidemiological and animal-model studies suggest that separate exposure to stress or serotonin-selective reuptake inhibitor (SSRI) antidepressants during pregnancy increases risks for neurodevelopmental disorders in offspring. Yet, little is known about the combined effects of maternal stress and SSRIs with regard to brain development in utero. We found that the placenta is highly permeable to the commonly prescribed SSRI (±)-citalopram (CIT) in humans and mice, allowing rapid exposure of the fetal brain to this drug. We investigated the effects of maternal chronic unpredictable stress in mice with or without maternal oral administration of CIT from embryonic day (E)8 to E17. We assessed fetal brain development using magnetic resonance imaging and quantified changes in serotonergic, thalamocortical, and cortical development. In utero exposure to maternal stress did not affect overall fetal brain growth. However, serotonin tissue content in the fetal forebrain was increased in association with maternal stress; this increase was reversed by maternal CIT. In utero exposure to stress increased the numbers of deep-layer neurons in specific cortical regions, whereas CIT increased overall cell numbers without changing the proportions of layer-specific neurons to offset the effects of stress on deep-layer cortical development. These findings suggest that stress and SSRI exposure in utero differentially impact serotonin-dependent fetal neurodevelopment such that CIT reverses key effects of maternal gestational stress on offspring brain development.

Review Article: Tools and trends for probing brain neurochemistry

The brain is composed of complex neuronal networks that interact on spatial and temporal scales that span several orders of magnitude. Uncovering how this circuitry gives rise to multifaceted phenomena such as perception, memory, and behavior remains one of the grand challenges in science today. A wide range of investigative methods have been developed to delve deeper into the inner workings of the brain, spanning the realms of molecular biology, genetics, chemistry, optics, and engineering, thereby forming a nexus of discovery that has accelerated our understanding of the brain. Whereas neuronal electrical excitability is a hallmark property of neurons, chemical signaling between neurons-mediated by hundreds of neurotransmitters, neuromodulators, hormones, and other signaling molecules-is equally important, but far more elusive in its regulation of brain function for motor control, learning, and behavior. To date, the brain's neurochemical state has been interrogated using classical tools borrowed from analytical chemistry, such as liquid chromatography and amperometry, and more recently, newly developed fluorescent sensors. Here, the authors review advances in the development of functional fluorescent probes that are beginning to expand their understanding of the neurochemical basis of brain function alongside device-based analytical tools that have already made extensive contributions to the field. The emphasis herein is on the paradigms of probe and device development, which follow certain design principles unique to the interrogation of brain chemistry.

In vivo Hippocampal Serotonin Dynamics in Male and Female Mice: Determining Effects of Acute Escitalopram Using Fast Scan Cyclic Voltammetry

Depression is a highly prevalent psychiatric disorder, impacting females at a rate roughly twice that of males. This disparity has become the focus of many studies which are working to determine if there are environmental or biological underpinnings to depression pathology. The biology of depression is not well understood, but experts agree that a key neurotransmitter of interest is serotonin. Most research on basic serotonin neurochemistry, by us and others, has predominantly focused on male models. Thus, it is now critical to include female models to decipher possible fundamental differences between the sexes that may underlie this disorder. In this paper, we seek to determine any such differences using fast-scan cyclic voltammetry (FSCV) and fast-scan controlled adsorption voltammetry. These techniques allow us to probe the serotonergic system via measurement of evoked and ambient serotonin at carbon fiber microelectrodes (CFMs). Our data reveal no statistical differences, in the hippocampus, in female serotonin chemistry during the different stages of the estrous cycle compared to the mean female response. Furthermore, no difference was observed in evoked serotonin release and reuptake, nor ambient extracellular serotonin levels between male and female mice. We applied a previously developed mathematical model that fits our serotonin signals as a function of several synaptic processes that control the extracellular levels of this transmitter. We used the model to study potential system differences between males and females. One hypothesis brought fourth, that female mice exhibit tighter autoreceptor control of serotonin, is validated via literature and methiothepin challenge. We postulate that this tight regulation may act as a control mechanism against changes in the serotonin signal mediated by estrogen spikes. Importantly, this safety mechanism has no consequence for acutely administered escitalopram’s (ESCIT’s) ability to increase extracellular serotonin between the sexes. This work demonstrates little fundamental differences in in vivo hippocampal serotonin between the sexes, bar control mechanisms in female mice that can be observed under extraneous circumstances. We thus highlight the importance of considering sex as a biological factor in determining pharmacodynamics for personalized medical treatments that involve targeting serotonin receptors.

Kappa Opioid Receptors Drive a Tonic Aversive Component of Chronic Pain

Pain is a multidimensional experience and negative affect, or how much the pain is "bothersome", significantly impacts the sufferers' quality of life. It is well established that the κ opioid system contributes to depressive and dysphoric states, but whether this system contributes to the negative affect precipitated by the occurrence of chronic pain remains tenuous. Using a model of persistent pain, we show by quantitative real-time-PCR, florescence in situ hybridization, Western blotting and GTPgS autoradiography an upregulation of expression and the function of κ opioid receptors (KORs) and its endogenous ligand dynorphin in the mesolimbic circuitry in animals with chronic pain compared with surgical controls. Using in vivo microdialysis and microinjection of drugs into the mesolimbic dopamine system, we demonstrate that inhibiting KORs reinstates evoked dopamine release and reward-related behaviors in chronic pain animals. Chronic pain enhanced KOR agonist-induced place aversion in a sex-dependent manner. Using various place preference paradigms, we show that activation of KORs drives pain aversive states in male but not female mice. However, KOR antagonist treatment was effective in alleviating anxiogenic and depressive affective-like behaviors in both sexes. Finally, ablation of KORs from dopamine neurons using AAV-TH-cre in KOR^loxP mice prevented pain-induced aversive states as measured by place aversion assays. Our results strongly support the use of KOR antagonists as therapeutic adjuvants to alleviate the emotional, tonic-aversive component of chronic pain, which is argued to be the most significant component of the pain experience that impacts patients' quality of life.SIGNIFICANCE STATEMENT We show that KORs are sufficient to drive the tonic-aversive component of chronic pain; the emotional component of pain that is argued to significantly impact a patient's quality of life. The impact of our study is broadly relevant to affective disorders associated with disruption of reward circuitry and thus likely contributes to many of the devastating sequelae of chronic pain, including the poor response to treatment of many patients, debilitating affective disorders (other disorders including anxiety and depression that demonstrate high comorbidity with chronic pain) and substance abuse. Indeed, coexisting psychopathology increases pain intensity, pain-related disability and effectiveness of treatments (Jamison and Edwards, 2013).

Toward Serotonin Fluorescent False Neurotransmitters: Development of Fluorescent Dual Serotonin and Vesicular Monoamine Transporter Substrates for Visualizing Serotonin Neurons

Ongoing efforts in our laboratories focus on design of optical reporters known as fluorescent false neurotransmitters (FFNs) that enable the visualization of uptake into, packaging within, and release from individual monoaminergic neurons and presynaptic sites in the brain. Here, we introduce the molecular probe FFN246 as an expansion of the FFN platform to the serotonergic system. Combining the acridone fluorophore with the ethylamine recognition element of serotonin, we identified FFN54 and FFN246 as substrates for both the serotonin transporter and the vesicular monoamine transporter 2 (VMAT2). A systematic structure-activity study revealed the basic structural chemotype of aminoalkyl acridones required for serotonin transporter (SERT) activity and enabled lowering the background labeling of these probes while maintaining SERT activity, which proved essential for obtaining sufficient signal in the brain tissue (FFN246). We demonstrate the utility of FFN246 for direct examination of SERT activity and SERT inhibitors in 96-well cell culture assays, as well as specific labeling of serotonergic neurons of the dorsal raphe nucleus in the living tissue of acute mouse brain slices. While we found only minor FFN246 accumulation in serotonergic axons in murine brain tissue, FFN246 effectively traces serotonin uptake and packaging in the soma of serotonergic neurons with improved photophysical properties and loading parameters compared to known serotonin-based fluorescent tracers.

Ginkgo biloba Extract (GbE) Stimulates the Hypothalamic Serotonergic System and Attenuates Obesity in Ovariectomized Rats

Menopause is associated with increased risk to develop obesity but the mechanisms involved are not fully understood. We have shown that Ginkgo biloba extract (GbE) improved diet-induced obesity. Since GbE might be effective in the treatment of obesity related to menopause, avoiding the side effects of hormone replacement therapy, we investigated the effect of GbE on hypothalamic systems controlling energy homeostasis. Wistar rats were either ovariectomized (OVX) or Sham-operated. After 2 months, either 500 mg.kg^-1 of GbE or vehicle were administered daily by gavage for 14 days. A subset of animals received an intracerebroventricular (i.c.v.) injection of serotonin (300 μg) or vehicle and food intake was measured after 12 and 24 h. Another subset was submitted to in vivo microdialysis and 5-HT levels of the medial hypothalamus were measured by high performance liquid chromatography, before and up to 2 h after the administration of 500 mg.kg^-1 of GbE. Additional animals were used for quantification of 5-HT_1A, 5-HT_1B, 5-HT_2C, 5-HTT, and pro-opiomelanocortin hypothalamic protein levels by Western blotting. OVX increased food intake and body weight and adiposity while GbE attenuated these alterations. i.c.v. serotonin significantly reduced food intake in Sham, Sham + GbE, and OVX + GbE groups while it failed to do so in the OVX group. In the OVX rats, GbE stimulated 5-HT microdialysate levels while it reduced hypothalamic 5-HTT protein levels. The results indicate that GbE improved the ovariectomy-induced resistance to serotonin hypophagia, at least in part through stimulation of the hypothalamic serotonergic activity. Since body weight gain is one of the most important consequences of menopause, the stimulation of the serotonergic transmission by GbE may represent a potential alternative therapy for menopause-related obesity.

Is there sexual dimorphism of hyperserotonemia in autism spectrum disorder?

Approximately 30% of individuals with autism spectrum disorder (ASD) have elevated whole blood serotonin (5-HT) levels. Genetic linkage and association studies of ASD and of whole blood 5-HT levels as a quantitative trait have revealed sexual dimorphism. Few studies have examined the presence of a sex difference on hyperserotonemia within ASD. To assess whether the rate of hyperserotonemia is different in males than in females with ASD, we measured whole blood 5-HT levels in 292 children and adolescents with ASD, the largest sample in which this biomarker has been assessed. Based upon previous work suggesting that hyperserotonemia is more common prior to puberty, we focused our analysis on the 182 pre-pubertal children with ASD. 42% of pre-pubertal participants were within the hyperserotonemia range. In this population, we found that males were significantly more likely to manifest hyperserotonemia than females (P = 0.03). As expected, no significant difference was found in the post-pubertal population. Additional work will be needed to replicate this intriguing finding and to understand whether it could potentially explain differences in patterns of ASD risk between males and females. Autism Res 2017, 10: 1417-1423. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

Monitoring Dopamine Responses to Potassium Ion and Nomifensine by in Vivo Microdialysis with Online Liquid Chromatography at One-Minute Resolution

Recently, our laboratory has demonstrated the technical feasibility of monitoring dopamine at 1 min temporal resolution with microdialysis and online liquid chromatography. Here, we monitor dopamine in the rat striatum during local delivery of high potassium/low sodium or nomifensine in awake-behaving rats. Microdialysis probes were implanted and perfused continuously with or without dexamethasone in the perfusion fluid for 4 days. Dexamethasone is an anti-inflammatory agent that exhibits several positive effects on the apparent health of the brain tissue surrounding microdialysis probes. Dopamine was monitored 1 or 4 days after implantation under basal conditions, during 10 min applications of 60 mM or 100 mM K⁺, and during 15 min applications of 10 μM nomifensine. High K⁺ and nomifensine were delivered locally by adding them to the microdialysis perfusion fluid using a computer-controlled, low-dead-volume six-port valve. Each day/K⁺/dexamethasone combination elicited specific dopamine responses. Dexamethasone treatment increased dopamine levels in basal dialysates (i.e., in the absence of K⁺ or nomifensine). Applications of 60 mM K⁺ evoked distinct responses on days one and four after probe implantation, depending upon the presence or absence of dexamethasone, consistent with dexamethasone's ability to mitigate the traumatic effect of probe implantation. Applications of 100 mM K⁺ evoked dramatic oscillations in dopamine levels that correlated with changes in the field potential at a metal electrode implanted adjacent to the microdialysis probe. This combination of results indicates the role of spreading depolarization in response to 100 mM K⁺. With 1 min temporal resolution, we find that it is possible to characterize the pharmacokinetics of the response to the local delivery of nomifensine. Overall, the findings reported here confirm the benefits arising from the ability to monitor dopamine via microdialysis at high sensitivity and at high temporal resolution.

Ovarian Sex Hormones Modulate Compulsive, Affective and Cognitive Functions in A Non-Induced Mouse Model of Obsessive-Compulsive Disorder

There is currently a lack of understanding of how surgical menopause can influence obsessions, compulsions and associated affective and cognitive functions in female obsessive-compulsive disorder (OCD) patients. Early menopause in women due to surgical removal of ovaries not only causes dramatic hormonal changes, but also may induce affective and cognitive disorders. Here, we tested if surgical removal of ovaries (ovariectomy, OVX), which mimics surgical menopause in humans, would result in exacerbation of compulsive, affective and cognitive behaviors in mice strains that exhibit a spontaneous compulsive-like phenotype. Female mice from compulsive-like BIG, non-compulsive SMALL and randomly-bred Control strains were subjected to OVX or sham-surgery. After 7 days animals were tested for nest building and marble burying to measure compulsive-like behavior. The elevated plus maze and open field tests measured anxiety-like behaviors, while memory was assessed by the novel object recognition. Acute OVX resulted in exacerbation of compulsive-like and anxiety-like behaviors in compulsive-like BIG mice. No significant effects of OVX were observed for the non-compulsive SMALL and Control strains. Object recognition memory was impaired in compulsive-like BIG female mice compared to the Control mice, without an effect of OVX on the BIG mice. We also tested whether 17 β-estradiol (E2) or progesterone (P4) could reverse the effects of OVX. E2, but not P4, attenuated the compulsive-like behaviors in compulsive-like BIG OVX female mice. The actions of the sex steroids on anxiety-like behaviors in OVX females were strain and behavioral test dependent. Altogether, our results indicate that already existing compulsions can be worsened during acute ovarian deprivation concomitant with exacerbation of affective behaviors and responses to hormonal intervention in OVX female mice can be influenced by genetic background.

Sex differences in abuse-related neurochemical and behavioral effects of 3,4-methylenedioxymethamphetamine (MDMA) in rats

3,4-Methylenedioxymethamphetamine (MDMA) is a substrate for dopamine (DA), norepinephrine and serotonin (5HT) transporters that produces greater pharmacological effects on certain endpoints in females than males in both clinical and rodent preclinical studies. To evaluate potential for sex differences in abuse-related MDMA effects, the present study compared MDMA effects on intracranial self-stimulation (ICSS) and on in vivo microdialysis measurements of DA or 5HT in the nucleus accumbens (NAc) in female and male Sprague-Dawley rats. For ICSS studies, electrodes were implanted in the medial forebrain bundle and rats trained to press for electrical stimulation over a range of frequencies (56-158Hz, 0.05 log increments) under a fixed-ratio 1 schedule, and the potency (0.32-3.2mg/kg, 10min pretreatment) and time course (3.2. mg/kg, 10-180min pretreatment) of MDMA effects were determined. For in vivo microdialysis, rats were implanted with bilateral guide cannulae targeting the NAc, and the time course of MDMA effects (1.0-3.2mg/kg, 0-180min) on DA and 5HT was determined. MDMA produced qualitatively similar effects in both sexes on ICSS (both increases in low ICSS rates maintained by low brain-stimulation frequencies and decreases in high ICSS rates maintained by high brain-stimulation frequencies) and microdialysis (increases in both DA and 5HT). The duration and peak levels of both abuse-related ICSS facilitation and increases in NAc DA were longer in females. MDMA was also more potent to increase 5HT in females. These results provide evidence for heightened sensitivity of females to abuse-related behavioral and neurochemical effects of MDMA in rats.

Developmental changes in serotonin signaling: Implications for early brain function, behavior and adaptation

The neurotransmitter serotonin (5-HT) plays a central role in brain development, regulation of mood, stress reactivity and risk of psychiatric disorders, and thus alterations in 5-HT signaling early in life have critical implications for behavior and mental health across the life span. Drawing on preclinical and emerging human evidence this narrative review paper will examine three key aspects when considering the consequences of early life changes in 5-HT: (1) developmental origins of variations of 5-HT signaling; (2) influence of genetic and epigenetic factors; and (3) preclinical and clinical consequences of 5-HT-related changes associated with antidepressant exposure (SSRIs). The developmental consequences of altered prenatal 5-HT signaling varies greatly and outcomes depend on an ongoing interplay between biological (genetic/epigenetic variations) and environmental factors, both pre and postnatally. Emerging evidence suggests that variations in 5-HT signaling may increase sensitivity to risky home environments, but may also amplify a positive response to a nurturing environment. In this sense, factors that change central 5-HT levels may act as 'plasticity' rather than 'risk' factors associated with developmental vulnerability. Understanding the impact of early changes in 5-HT levels offers critical insights that might explain the variations in early typical brain development that underlies behavioral risk.

Differential Uptake Mechanisms of Fluorescent Substrates into Stem-Cell-Derived Serotonergic Neurons

The actions of the neurotransmitters serotonin, dopamine, and norepinephrine are partly terminated by diffusion and in part by their uptake into neurons via the selective, high-affinity transporters for serotonin (SERT), dopamine (DAT), and norepinephrine (NET), respectively. There is also growing evidence that all three monoamines are taken up into neurons by low-affinity, high-capacity organic cation transporters (OCT) and the plasma membrane monoamine transporter (PMAT). Pharmacological characterization of these low-affinity recombinant transporter proteins in heterologous expression systems has revealed that they are not antagonized by classical inhibitors of SERT, DAT, or NET but that decynium-22 (D22) antagonizes OCT3 and PMAT, whereas corticosterone and progesterone selectively inhibit OCT3. Here, we show that SERT, PMAT, and OCT3, but not OCT1 and OCT2, are coexpressed in murine stem cell-derived serotonergic neurons. Using selective antagonists, we provide evidence that uptake of the fluorescent substrates FFN511, ASP+, and 5-HT into stem cell-derived serotonergic neurons is mediated differentially by these transporters and also involves an as yet unknown transport mechanism.