Cortical 5-HT2A receptor signaling modulates anxiety-like behaviors in mice

GPER-Deficient Rats Exhibit Lower Serum Corticosterone Level and Increased Anxiety-Like Behavior

Ample evidence suggests that estrogens have strong influences on the occurrence of stress-related mood disorders, but the underlying mechanisms remain poorly understood. Through multiple approaches, we demonstrate that the G protein-coupled estrogen receptor (GPER) is widely distributed along the HPA axis and in brain structures critically involved in mood control. Genetic ablation of GPER in the rat resulted in significantly lower basal serum corticosterone level but enhanced ACTH release in response to acute restraint stress, especially in the female. GPER^−/− rats of either sex displayed increased anxiety-like behaviors and deficits in learning and memory. Additionally, GPER deficiency led to aggravation of anxiety-like behaviors following single-prolonged stress (SPS). SPS caused significant decreases in serum corticosterone in WT but not in GPER-deficient rats. The results highlight an important role of GPER at multiple sites in regulation of the HPA axis and mood.

Human-Derived Bifidobacterium dentium Modulates the Mammalian Serotonergic System and Gut-Brain Axis

BACKGROUND & AIMS

The human gut microbiota can regulate production of serotonin (5-hydroxytryptamine [5-HT]) from enterochromaffin cells. However, the mechanisms underlying microbial-induced serotonin signaling are not well understood.

METHODS

Adult germ-free mice were treated with sterile media, live Bifidobacterium dentium, heat-killed B dentium, or live Bacteroides ovatus. Mouse and human enteroids were used to assess the effects of B dentium metabolites on 5-HT release from enterochromaffin cells. In vitro and in vivo short-chain fatty acids and 5-HT levels were assessed by mass spectrometry. Expression of tryptophan hydroxylase, short-chain fatty acid receptor free fatty acid receptor 2, 5-HT receptors, and the 5-HT re-uptake transporter (serotonin transporter) were assessed by quantitative polymerase chain reaction and immunostaining. RNA in situ hybridization assessed 5-HT-receptor expression in the brain, and 5-HT-receptor-dependent behavior was evaluated using the marble burying test.

RESULTS

B dentium mono-associated mice showed increased fecal acetate. This finding corresponded with increased intestinal 5-HT concentrations and increased expression of 5-HT receptors 2a, 4, and serotonin transporter. These effects were absent in B ovatus-treated mice. Application of acetate and B dentium-secreted products stimulated 5-HT release in mouse and human enteroids. In situ hybridization of brain tissue also showed significantly increased hippocampal expression of 5-HT-receptor 2a in B dentium-treated mice relative to germ-free controls. Functionally, B dentium colonization normalized species-typical repetitive and anxiety-like behaviors previously shown to be linked to 5-HT-receptor 2a.

CONCLUSIONS

These data suggest that B dentium, and the bacterial metabolite acetate, are capable of regulating key components of the serotonergic system in multiple host tissues, and are associated with a functional change in adult behavior.

Coronaridine congeners potentiate GABAA receptors and induce sedative activity in mice in a benzodiazepine-insensitive manner

To determine whether (+)-catharanthine induces sedative- or anxiolytic/anxiogenic-like activity in male mice, proper animal paradigms were used. The results showed that (+)-catharanthine induces sedative-like activity in the 63-72 mg/Kg dose range in a flumazenil-insensitive manner, but neither this effect nor anxiolytic/anxiogenic-like activity was observed at lower doses. To determine the underlying molecular mechanism of the sedative-like activity, electrophysiological and radioligand binding experiments were performed with (+)-catharanthine and (±)-18-methoxycoronaridine [(±)-18-MC] on GABA_A (GABA_ARs) and glycine receptors (GlyRs). Coronaridine congeners both activated and potentiated a variety of human (h) GABA_ARs, except hρ1. (+)-Catharanthine-induced potentiation followed this receptor selectivity (EC₅₀'s in μM): hα1β2 (4.6 ± 0.8) > hα2β2γ2 (12.6 ± 3.8) ~ hα1β2γ2 (14.4 ± 4.6) indicating that both α1 and α2 are equally important, whereas γ2 is not necessary. (+)-Catharanthine was >2-fold more potent and efficient than (±)-18-MC at hα1β2γ2. (+)-Catharanthine also potentiated, whereas (±)-18-MC inhibited, hα1 GlyRs with very low potency. Additional [³H]-flunitrazepam competition binding experiments using rat cerebellum membranes clearly demonstrated that these ligands do not bind to the benzodiazepine site. This is supported by the observed activity at hα1β2 (lacking the BDZ site) and similar effects between α1- and α2-containing GABA_ARs. Our study shows, for the first time, that (+)-catharanthine induced sedative-like effects in mice, and coronaridine congeners potentiated human α1β2γ2, α1β2, and hα2β2γ2, but not ρ1, GABA_ARs, both in a benzodiazepine-insensitive fashion, whereas only (+)-catharanthine slightly potentiated GlyRs.

Physiological and behavioral responses to observing a sibling experience a direct stressor in prairie voles

Uncontrollable stress precipitates negative mental and physical health outcomes. Furthermore, the vicarious experience of stress (e.g. observing another individual experience a direct stressor) can mimic the effects of directly experiencing the stressor. The current experiment examined the behavioral and physiological effects of the vicarious experience of stress using the socially monogamous prairie vole. Male prairie voles were exposed to either an empty open field chamber, or a chamber in which the animal observed a sibling undergoing a concurrent direct physical stressor (tail suspension test) for five minutes. Exploratory and anxiety-like behaviors were recorded in all observers during the test session. Cardiac indices of heart rate and heart rate variability were recorded in a subset of observers prior to, during, and following the test session. Corticosterone levels were measured in all observers and siblings following the test session. When compared to animals exposed to an empty open field chamber, animals that observed a sibling undergo a direct physical stressor exhibited increased heart rate and circulating corticosterone, and decreased heart rate variability. These physiological stress indicators were supported by behavioral changes, including increased freezing followed immediately by orienting of the head toward the center of the apparatus, and decreased locomotion, grooming, and rearing. These preliminary results suggest that prairie voles experience stress vicariously, and provide a foundation for additional studies focused on the underlying mechanisms of vicarious stress. The use of this model may inform our understanding of the social transmission of stress among social species, including humans.LAY SUMMARYThe experience of stress, including observing stress in a loved one, has negative consequences on mental and physical health. This study used a social rodent (prairie voles) to demonstrate that stress transfers among social individuals, consequently producing an increased physiological and behavioral stress response in prairie voles observing their siblings experience stress. This research informs our understanding of the interactions of social experiences and stress in humans.

Expression of serotonin 1A and 2A receptors in molecular- and projection-defined neurons of the mouse insular cortex

The serotonin (5-HT) system is the target of multiple anxiolytics, including Buspirone, which is a partial agonist of the serotonin 1A receptor (5-HT1A). Similarly, ligands of the serotonin 2A receptor (5-HT2A) were shown to alter anxiety level. The 5-HT1A and 2A receptors are widely expressed across the brain, but the target region(s) underlying the influence of those receptors on anxiety remain unknown. Interestingly, recent studies in human and non-human primates have shown that the 5-HT1A and 5-HT2A binding potentials within the insular cortex (insula) are correlated to anxiety. As an initial step to define the function of 5-HT transmission in the insula, we quantified the proportion of specific neuronal populations of the insula expressing 5-HT1A or 5-HT2A. We analyzed seven neural populations, including three defined by a molecular marker (putative glutamate, GABA or parvalbumin), and four defined by their projections to different downstream targets. First, we found that more than 70% of putative glutamatergic neurons, and only 30% of GABAergic neurons express the 5-HT1A. Second, within insular projection neurons, 5-HT1A is highly expressed (75-80%) in the populations targeting one sub-nuclei of the amygdala (central or basolateral), or targeting the rostral or caudal sections of the lateral hypothalamus (LH). Similarly, 70% of putative glutamatergic neurons and only 30% of insular GABAergic neurons contain 5-HT2A. Finally, the 5-HT2A is present in a majority of insula-amygdala and insula-LH projection neurons (73-82%). These observations suggest that most glutamatergic neurons can respond to 5-HT through 5-HT1A or 5-HT2A in the insula, and that 5-HT directly affects a limited number of GABAergic neurons. This study defines a molecular and neuroanatomical map of the 5-HT system within the insular cortex, providing ground knowledge to identify the potential role of serotonergic modulation of selective insular populations in anxiety.

Ferulic acid through mitigation of NMDA receptor pathway exerts anxiolytic-like effect in mouse model of maternal separation stress

Background Experiencing early-life stress plays an important role in the pathophysiology of anxiety disorders. Ferulic acid is a phenolic compound found in some plants which has several pharmacological properties. N-methyl-D-aspartate (NMDA) receptors are involved in the pathophysiology of mood disorders. In this study we aimed to assess the anxiolytic-like effect of ferulic acid in a mouse model of maternal separation (MS) stress by focusing on the possible involvement of NMDA receptors. Methods Mice were treated with ferulic acid (5 and 40 mg/kg) alone and in combination with NMDA receptor agonist/antagonist. Valid behavioral tests were performed, including open field test (OFT) and elevated plus maze test (EPM), while quantitative real time polymerase chain reaction (qRT-PCR) was used to evaluate gene expression of NMDA subunits (GluN2A and GluN2B) in the hippocampus. Results Findings showed that treatment of MS mice with ferulic acid increased the time spent in the central zone of the OFT and increased both open arm time and the percent of open arm entries in the EPM. Ferulic acid reduced the expression of NMDA receptor subunit genes. We showed that administration of NMDA receptor agonist (NMDA) and antagonist (ketamine) exerted anxiogenic and anxiolytic-like effects, correspondingly. Results showed that co-administration of a sub-effective dose of ferulic acid plus ketamine potentiated the anxiolytic-like effect of ferulic acid. Furthermore, co-administration of an effective dose of ferulic acid plus NMDA receptor agonist (NMDA) attenuated the anxiolytic-like effect of ferulic acid. Conclusions In deduction, our findings showed that NMDA, partially at least, is involved in the anxiolytic-like effect of ferulic acid in the OFT and EPM tests.

Mechanical Regulation Underlies Effects of Exercise on Serotonin-Induced Signaling in the Prefrontal Cortex Neurons

Mechanical forces are known to be involved in various biological processes. However, it remains unclear whether brain functions are mechanically regulated under physiological conditions. Here, we demonstrate that treadmill running and passive head motion (PHM), both of which produce mechanical impact on the head, have similar effects on the hallucinogenic 5-hydroxytryptamine (5-HT) receptor subtype 2A (5-HT_2A) signaling in the prefrontal cortex (PFC) of rodents. PHM generates interstitial fluid movement that is estimated to exert shear stress of a few pascals on cells in the PFC. Fluid shear stress of a relevant magnitude on cultured neuronal cells induces ligand-independent internalization of 5-HT_2A receptor, which is observed in mouse PFC neurons after treadmill running or PHM. Furthermore, inhibition of interstitial fluid movement by introducing polyethylene glycol hydrogel eliminates the effect of PHM on 5-HT_2A receptor signaling in the PFC. Our findings indicate that neuronal cell function can be physiologically regulated by mechanical forces in the brain.

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Mechanical forces regulate brain functions under physiological conditions

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Intracerebral interstitial fluid has mechanical roles in regulating brain functions

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Mechanical impact on the head mediates effects of exercise on the brain

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Fluid shear stress physiologically modulates signaling in nervous cells

Mapping the physiological and molecular markers of stress and SSRI antidepressant treatment in S100a10 corticostriatal neurons

In mood disorders, psychomotor and sensory abnormalities are prevalent, disabling, and intertwined with emotional and cognitive symptoms. Corticostriatal neurons in motor and somatosensory cortex are implicated in these symptoms, yet mechanisms of their vulnerability are unknown. Here, we demonstrate that S100a10 corticostriatal neurons exhibit distinct serotonin responses and have increased excitability, compared with S100a10-negative neurons. We reveal that prolonged social isolation disrupts the specific serotonin response which gets restored by chronic antidepressant treatment. We identify cell-type-specific transcriptional signatures in S100a10 neurons that contribute to serotonin responses and strongly associate with psychomotor and somatosensory function. Our studies provide a strong framework to understand the pathogenesis and create new avenues for the treatment of mood disorders.

Preclinical characterization of ACH-000029, a novel anxiolytic compound acting on serotonergic and alpha-adrenergic receptors

Anxiety disorders are serious and common mental diseases, yet there is still a need for the development of more effective anxiolytics with better safety profiles than benzodiazepines and serotonin reuptake inhibitors. The serotonergic and noradrenergic systems have reciprocal interactions and are intricately related to the pathogenesis of anxiety. In this study, the anxiolytic-like effect of the novel compound ACH-000029, 3-(2-(4-(2-methoxyphenyl) piperazine-1-yl) ethyl) quinazoline-4(3H)-one, is reported. This compound acts at selected serotonergic (5-HT1A and 5-HT1D partial agonism and 5-HT2A antagonism) and α-adrenergic (α-1A, 1B and 1D antagonism) receptors, with good selectivity over other G-protein-coupled receptors. ACH-000029 exhibited high blood-brain barrier permeation and acute anxiolytic effects in the marble burying (MB) and light-dark box (LDB) models of anxiety over the dose ranges of 8-32 mg/kg i.p. and 16-30 mg/kg p.o. The anxiolytic activity was comparable to that observed for serotonin reuptake inhibitors (paroxetine and fluoxetine) and benzodiazepines (alprazolam, diazepam and clobazam). The analysis of the whole-brain c-fos expression following oral dosing showed that ACH-000029 regulated regions highly associated with the processing of environmental stimuli and anxiety behavior, such as the amygdala, paraventricular nucleus of the thalamus, retrosplenial dorsal, pallidum, bed nuclei of the stria terminalis, and locus ceruleus. No safety concerns were identified for ACH-000029 in the functional observational battery up to 50 mg/kg i.p. and in the nonprecipitated withdrawal test up to 30 mg/kg p.o. twice daily for 20 days. This work supports the further development of ACH-000029 as a drug candidate for the treatment of anxiety disorders. The analysis of the in vitro pharmacology and brain regions regulated by this compound may also lead to the exploration of other indications within the psychiatry field.

Alternative splicing in serotonergic system: Implications in neuropsychiatric disorders

BACKGROUND

The serotonergic system is a key component of physiological brain function and is essential for proper neurological activity. Numerous neuropsychiatric disorders are associated with deregulation of the serotonergic system. Accordingly, many pharmacological treatments are focused on modulation of this system. While providing a promising line of therapeutic moderation, these approaches may be complicated due to the presence of alternative splicing events for key genes in this pathway. Alternative splicing is a co-transcriptional process by which different mRNA transcripts can be produced from the same gene. These different isoforms may have diverse activities and functions, and their relative balance is often critical for the maintenance of homeostasis. Alternative splicing greatly increases the production of proteins, augmenting cell plasticity, and provides an important control point for regulation of gene expression.

AIM

The objective of this narrative review is to discuss the potential impact of alternative splicing of different components of the serotonergic system and speculate on their involvement in several neuropsychiatric disorders.

CONCLUSIONS

The specific role of each isoform in disease and their relative activities in the signalling pathways involved are yet to be determined. We need to gain a better understanding of the basis of alternative isoforms of the serotonergic system in order to fully understand their impact and be able to develop new effective pharmacological isoform-specific targets.

Exercise exerts an anxiolytic effect against repeated restraint stress through 5-HT2A-mediated suppression of the adenosine A2A receptor in the basolateral amygdala

Repeated or chronic stressful stimuli induce emotion- and mood-related abnormalities, such as anxiety and depression. Conversely, regular exercise exerts protective effects. Here, we found that exercise recovered anxiety-like behaviors, as measured using the open field and elevated plus maze tests in an anxiety mouse model. In addition to behavioral improvement, exercise enhanced the synaptic density of the 5-hydroxytryptamine 2A receptor (5-HT_2AR), but not the 5-HT_1AR in the basolateral amygdala (BLA) region in this mouse model. Furthermore, global treatment with a selective 5-HT_2AR antagonist (MDL11930) generated an anxiety phenotype. Thus, synaptic recruitment of 5-HT_2AR in BLA neurons may mediate the anxiolytic effects of exercise. The exercise regimen also reduced adenosine A_2A receptor (A_2AR)-mediated protein kinase A (PKA) activation, and the anxiolytic effect of the exercise was blunted by local activation of A_2AR within the BLA using CGS21680, a selective A_2AR agonist. Particularly, A_2AR-mediated PKA activity was shown to be dependent on 5-HT_2AR signaling in the BLA. These results imply that repeated stress upregulates A_2AR-mediated adenosine signaling to facilitate PKA activation, whereas regular exercise inhibits A_2AR function by increasing 5-HT_2AR in the BLA. Accordingly, this integrated modulation of 5-HT and adenosine signaling, via 5-HT_2AR and A_2AR respectively, may be a mechanism underlying the anxiolytic effect of regular exercise.

Creation of the 5-hydroxytryptamine receptor 7 knockout rat as a tool for cardiovascular research

Using CRISPR-Cas9 technology, we created a 5-HT7 receptor global knockout (KO) rat, on a Sprague-Dawley background, for use in cardiovascular physiology studies focused on blood pressure regulation. A stable line carrying indels in exons 1 and 2 of the rat Htr7 locus was established and validated. Surprisingly, 5-HT7 receptor mRNA was still present in the KO rat. However, extensive cDNA and genomic sequencing of KO tissues confirmed an 11 bp deletion in exon 1 and 4 bp deletion in exon 2. The exon 1 deletion resulted in a frameshifted mRNA sequence coding for a nonfunctional protein. While the Htr1B locus was a potential off-target for the guide RNAs designed for exon 2 of Htr7, there were no off-target sequence changes at this locus in the originating founder. When the F2 generation of KO was compared with wild-type (WT) counterparts, neither the male nor female KO rats were different in body size, fat weights, or mass of organs (kidney, heart, and brain) important to blood pressure. Females were smaller in mass than their counterpart males. Clinical measures of plasma from nonfasted rats revealed largely similar values, comparing WT and KO, of glucose, blood urea nitrogen, creatinine, phosphate, calcium, and albumin to name a few. Loss of a functional 5-HT7 receptor was validated by the complete loss of relaxation to the 5-HT1/7 receptor agonist 5-carboxamidotryptamine in the isolated abdominal vena cava. This newly created 5-HT7 receptor KO rat will be of use to investigate the importance of the 5-HT7 receptor in blood pressure regulation.

A Discrete Dorsal Raphe to Basal Amygdala 5-HT Circuit Calibrates Aversive Memory

Despite a wealth of clinical and preclinical data implicating the serotonin (5-HT) system in fear-related affective disorders, a precise definition of this neuromodulator's role in fear remains elusive. Using convergent anatomical and functional approaches, we interrogate the contribution to fear of basal amygdala (BA) 5-HT inputs from the dorsal raphe nucleus (DRN). We show the DRN→BA 5-HT pathway is engaged during fear memory formation and retrieval, and activity of these projections facilitates fear and impairs extinction. The DRN→BA 5-HT pathway amplifies fear-associated BA neuronal firing and theta power and phase-locking. Although fear recruits 5-HT and VGluT3 co-expressing DRN neurons, the fear-potentiating influence of the DRN→BA 5-HT pathway requires signaling at BA 5-HT1A/2A receptors. Input-output mapping illustrates how the DRN→BA 5-HT pathway is anatomically distinct and connected with other brain regions that mediate fear. These findings reveal how a discrete 5-HT circuit orchestrates a broader neural network to calibrate aversive memory.

In vivo electrophysiological recordings of the effects of antidepressant drugs

Antidepressant drugs are a standard biological treatment for various neuropsychiatric disorders, yet relatively little is known about their electrophysiologic and synaptic effects on mood systems that set moment-to-moment emotional tone. In vivo electrical recording of local field potentials (LFPs) and single neuron spiking has been crucial for elucidating important details of neural processing and control in many other systems, and yet electrical approaches have not been broadly applied to the actions of antidepressants on mood-related circuits. Here we review the literature encompassing electrophysiologic effects of antidepressants in animals, including studies that examine older drugs, and extending to more recently synthesized novel compounds, as well as rapidly acting antidepressants. The existing studies on neuromodulator-based drugs have focused on recording in the brainstem nuclei, with much less known about their effects on prefrontal or sensory cortex. Studies on neuromodulatory drugs have moreover focused on single unit firing patterns with less emphasis on LFPs, whereas the rapidly acting antidepressant literature shows the opposite trend. In a synthesis of this information, we hypothesize that all classes of antidepressants could have common final effects on limbic circuitry. Whereas NMDA receptor blockade may induce a high powered gamma oscillatory state via direct and fast alteration of glutamatergic systems in mood-related circuits, neuromodulatory antidepressants may induce similar effects over slower timescales, corresponding with the timecourse of response in patients, while resetting synaptic excitatory versus inhibitory signaling to a normal level. Thus, gamma signaling may provide a biomarker (or “neural readout”) of the therapeutic effects of all classes of antidepressants.

FCPR16, a novel phosphodiesterase 4 inhibitor, produces an antidepressant-like effect in mice exposed to chronic unpredictable mild stress

The canonical phosphodiesterase 4 (PDE4) inhibitors produce antidepressant-like effects in a variety of animal models. However, severe side effects, particularly vomiting and nausea, limit their clinical application. FCPR16 is a novel PDE4 inhibitor with less vomiting potential. However, whether it will exert an antidepressant-like effect remains unclear. Here, we aimed to evaluate the effect of FCPR16 in mice subjected to chronic unpredictable mild stress (CUMS). Our results showed that FCPR16 produced antidepressant-like effects in multiple behavioral tests, including a forced swimming test, tail suspension test, sucrose preference test and novelty suppression feeding test. Simultaneously, data indicated that FCPR16 enhanced the levels of several proteins, including cAMP, brain derived neurotrophic factor, exchange protein directly activated by cAMP 2 (EPAC-2), synapsin1, postsynaptic density protein 95, phosphorylated cAMP response element binding protein and extracellular regulated protein kinases 1/2, which were downregulated by CUMS in both the cerebral cortex and hippocampus. The number of DCX⁺ cells in the hippocampus of CUMS mice was increased after FCPR16 treatment. Moreover, treatment with FCPR16 resulted in decreased expression of pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) and increased expression of anti-inflammatory cytokines (IL-10) in mice challenged with CUMS. Consistently, the mRNA levels of microglial M1 markers (iNOS and TNF-α) were downregulated, while M2 markers (Arginase 1 and CD206) were upregulated in CUMS-exposed mice after FCPR16 treatment. Immunofluorescence analysis showed that FCPR16 inhibited the activation of microglial cells and increased the number of CD206⁺ in CUMS-exposed mice. Collectively, these results suggested that FCPR16 is a potential compound with effects against depressive-like behaviors, and the antidepressant-like effect of FCPR16 is possibly mediated through activation of the cAMP-mediated signaling pathways and inhibition of neuroinflammation in both the cerebral cortex and hippocampus.

Tobacco smoke and ethanol during adolescence: Both combined- and single-drug exposures lead to short- and long-term disruption of the serotonergic system in the mouse brain

The impairment of the serotonergic system contributes to nicotine and ethanol effects on mood, suggesting that this system is targeted by each of these drugs and that co-exposure possibly worsens the disruption. Here, we tested this hypothesis in an adolescent mice model of tobacco smoke and/or ethanol exposure. From postnatal day (PN) 30-45, Swiss mice were exposed to one of the following: 1) tobacco smoke (SMK; research cigarettes 2R1F, whole-body exposure, 8 h/daily); 2) ethanol (ETOH; 2 g/kg i.p., every other day); 3) SMK + ETOH; 4) Control (VEH). At PN45 (end-of-exposure), hippocampal serotonin transporter (5 H TT) binding was increased in SMK and decreased in ETOH male mice. At PN50 (short-term deprivation), cortical 5 H TT was reduced in all drug-exposed mice. In the hippocampus, similar deficits were identified in females. In both brain regions, the effects of SMK + ETOH deprivation on 5 H TT were equivalent to the damage caused by either drug. At PN50, hippocampal 5 H T1A receptor binding was reduced in ETOH and SMK + ETOH mice. Similar results were observed in the male cortex. In females, deficits were identified in SMK mice. In both brain regions, SMK + ETOH 5 H T1A deficits reflected the summation of SMK and ETOH outcomes. At PN75 (long-term deprivation), there was a late-emergent increase in cortical 5 H T1A binding in SMK mice, while cortical 5 H T2 receptor binding was similarly increased in SMK and SMK + ETOH groups. Adolescent SMK and/or ETOH serotonergic impairment is sex-dependent and most evident during short-term deprivation. SMK + ETOH deprivation evokes serotonergic disruption that is at least equivalent to that caused by either drug alone.

5-HT2A receptor loss does not alter acute fluoxetine-induced anxiety and exhibit sex-dependent regulation of cortical immediate early gene expression

Background: Acute treatment with the selective serotonin reuptake inhibitor (SSRI), fluoxetine (Flx), induces anxiety-like behavioral effects. The serotonin_2A receptor (5-HT_2A) is implicated in the modulation of anxiety-like behavior, however its contribution to the anxiogenic effects of acute Flx remains unclear. Here, we examined the role of the 5-HT_2A receptor in the effects of acute Flx on anxiety-like behavior, serum corticosterone levels, neural activation and immediate early gene (IEG) expression in stress-responsive brain regions, using 5-HT_2A receptor knockout (5-HT_2A^−/−) mice of both sexes. Methods: 5-HT_2A^−/− and wild-type (WT) male and female mice received a single administration of Flx or vehicle, and were examined for anxiety-like behavior, serum corticosterone levels, FBJ murine osteosarcoma viral oncogene homolog peptide (c-Fos) positive cell numbers in stress-responsive brain regions of the hypothalamus and prefrontal cortex (PFC), and PFC IEG expression. Results: The increased anxiety-like behavior and enhanced corticosterone levels evoked by acute Flx were unaltered in 5-HT_2A^−/− mice of both sexes. 5-HT_2A^−/− female mice exhibited a diminished neural activation in the hypothalamus in response to acute Flx. Further, 5-HT_2A^−/− male, but not female, mice displayed altered baseline expression of several IEGs (brain-derived neurotrophic factor (Bdnf), Egr2, Egr4, FBJ osteosarcoma gene (Fos), FBJ murine osteosarcoma viral oncogene homolog B (Fosb), Fos-like antigen 2 (Fosl2), Homer scaffolding protein (Homer) 1-3 (Homer1-3), Jun proto-oncogene (Jun)) in the PFC. Conclusion: Our results indicate that the increased anxiety and serum corticosterone levels evoked by acute Flx are not influenced by 5-HT_2A receptor deficiency. However, the loss of function of the 5-HT_2A receptor alters the degree of neural activation of the paraventricular nucleus (PVN) of the hypothalamus in response to acute Flx, and baseline expression of several IEGs in the PFC in a sexually dimorphic manner.

GRP Receptor Regulates Depression Behavior via Interaction With 5-HT2a Receptor

OBJECTIVE

Accumulating evidences indicate that gastrin-releasing peptide receptor (GRPR) may contribute to the pathophysiology of depression. However, the mechanism of the involvement of GRPR in the progression of depression remains unclear. Here, we showed the extent to which stress and antidepressant treatment impact GRPR expression, and explored the interactions between 5-HT2a receptor (5-HT2aR) and GRPR at the cellular level.

METHODS

The rat depression models were created with chronic unpredictable mild stress (CUMS). Then, these rats were treated with fluoxetine for 4 weeks after CUMS. We measured body weight and performed behavioral tests to determine the effects of stress and fluoxetine on depressive-like behaviors. Real-time PCR and western blotting were used to measure the mRNA and protein expression levels of GRPR in the hypothalamus. Then, Flag-tagged protein (pcmv-Flag-5HT2aR) and Myc-tagged protein (pcmv-Myc-GRPR) expression vectors were constructed, identified, and transfected into human embryo kidney 293 (HEK293) cells. The interaction between 5-HT2aR and GRPR was detected by coimmunoprecipitation and double-label immunofluorescence.

RESULTS

The rats subjected to 4 weeks of CUMS showed depressive-like behaviors, including decreased body weight, sucrose preference, and distance traveled, rearing frequency and velocity in the open field test and increased immobility time in the forced swimming test. Fluoxetine treatment reversed CUMS-induced depressive-like behavior. The mRNA and protein expression of GRPR in the hypothalamus was significantly increased after 4 weeks CUMS exposure, and treatment with fluoxetine reversed these changes. Coimmunoprecipitation showed that 5-HT2aR and GRPR combine with each other in vitro. Immunofluorescence revealed that the 5-HT2aR and GRPR were colocalization in both the cell membrane and cytoplasm.

CONCLUSION

Our study enhances the understanding of the involvement of GRPR in depression. This study also provides in vitro experimental evidence of the interaction between 5-HT2aR and GRPR, which may play an important role in the pathogenesis of depression.

Association of rs4680 COMT, rs6280 DRD3, and rs7322347 5HT2A With Clinical Features of Youth-Onset Schizophrenia

We investigated the associations of rs4680 COMT, rs6280 DRD3, and rs7322347 5HT2A with youth-onset schizophrenia in the Russian population in a case-control study, and the role of the genotype in the severity of clinical features. The association between rs7322347 and schizophrenia (p = 0.0001) is described for the first time. Furthermore, we found a link with rs6280 and rs4680 in females (p = 0.001 and p = 0.02 respectively) and with rs7322347 in males (p = 0.002). Clinical symptoms were assessed on three scales: the Clinician-Rated Dimensions of Psychosis Symptom Severity scale, Positive and Negative Syndrome Scale, and Frontal Assessment Battery. Gender differences in clinical features are of particular interest. In our study we found gender differences in the severity of clinical features-higher scores for delusions (Positive and Negative Syndrome Scale and Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition) in males and higher scores for depression, delusions, somatic concern, motor retardation, poor attention were found in females.

A Novel Bio-Psychosocial-Behavioral Treatment Model of Panic Disorder

To conceptualize a novel bio-psychosocial-behavioral treatment model of panic disorder (PD), it is necessary to completely integrate behavioral, psychophysiological, neurobiological, and genetic data. Molecular genetic research on PD is specifically focused on neurotransmitters, including serotonin, neuropeptides, glucocorticoids, and neurotrophins. Although pharmacological interventions for PD are currently available, the need for more effective, faster-acting, and more tolerable pharmacological interventions is unmet. Thus, glutamatergic receptor modulators, orexin receptor antagonists, corticotrophin-releasing factor 1 receptor antagonists, and other novel mechanism-based anti-panic therapeutics have been proposed. Research on the neural correlates of PD is focused on the dysfunctional "cross-talk" between emotional drive (limbic structure) and cognitive inhibition (prefrontal cortex) and the fear circuit, which includes the amygdala-hippocampus-prefrontal axis. The neural perspective regarding PD supports the idea that cognitive-behavioral therapy normalizes alterations in top-down cognitive processing, including increased threat expectancy and attention to threat. Consistent with the concept of "personalized medicine," it is speculated that Research Domain Criteria can enlighten further treatments targeting dysfunctions underlying PD more precisely and provide us with better definitions of moderators used to identify subgroups according to different responses to treatment. Structuring of the "negative valence systems" domain, which includes fear/anxiety, is required to define PD. Therefore, targeting glutamate- and orexin-related molecular mechanisms associated with the fear circuit, which includes the amygdala-hippocampus-prefrontal cortex axis, is required to define a novel bio-psychosocial-behavioral treatment model of PD.

Chronic clozapine treatment restrains via HDAC2 the performance of mGlu2 receptor agonism in a rodent model of antipsychotic activity

Preclinical findings in rodent models pointed toward activation of metabotropic glutamate 2/3 (mGlu2/3) receptors as a new pharmacological approach to treat psychosis. However, more recent studies failed to show clinical efficacy of mGlu2/3 receptor agonism in schizophrenia patients. We previously proposed that long-term antipsychotic medication restricted the therapeutic effects of these glutamatergic agents. However, little is known about the molecular mechanism underlying the potential repercussion of previous antipsychotic exposure on the therapeutic performance of mGlu2/3 receptor agonists. Here we show that this maladaptive effect of antipsychotic treatment is mediated mostly via histone deacetylase 2 (HDAC2). Chronic treatment with the antipsychotic clozapine led to a decrease in mouse frontal cortex mGlu2 mRNA, an effect that required expression of both HDAC2 and the serotonin 5-HT_2A receptor. This transcriptional alteration occurred in association with HDAC2-dependent repressive histone modifications at the mGlu2 promoter. We found that chronic clozapine treatment decreased via HDAC2 the capabilities of the mGlu2/3 receptor agonist LY379268 to activate G-proteins in the frontal cortex of mice. Chronic clozapine treatment blunted the antipsychotic-related behavioral effects of LY379268, an effect that was not observed in HDAC2 knockout mice. More importantly, co-administration of the class I and II HDAC inhibitor SAHA (vorinostat) preserved the antipsychotic profile of LY379268 and frontal cortex mGlu2/3 receptor density in wild-type mice. These findings raise concerns on the design of previous clinical studies with mGlu2/3 agonists, providing the rationale for the development of HDAC2 inhibitors as a new epigenetic-based approach to improve the currently limited response to treatment with glutamatergic antipsychotics.

Pimavanserin and Lorcaserin Attenuate Measures of Binge Eating in Male Sprague-Dawley Rats

Binge eating disorder (BED) is characterized by dysregulated feeding and reward-related processes, and treatment is often challenged by limited therapeutic options. The serotonin (5-HT) 5-HT_2A receptor (5-HT_2AR) and 5-HT_2CR are implicated in both feeding-related and reward-related behaviors and are thus poised to regulate BED-related behaviors. The purpose of this study was to assess the efficacy of the FDA-approved medications pimavanserin, a 5-HT_2AR antagonist/inverse agonist, and lorcaserin, a 5-HT_2CR agonist, in a rodent model of binge eating. The effects of pimavanserin (0.3–3.0 mg/kg), lorcaserin (0.25–1.0 mg/kg), and the lowest effective dose of pimavanserin (0.3 mg/kg) plus lorcaserin (1.0 mg/kg) were tested in a high-fat food (HFF) intermittent access binge eating model in adult male Sprague-Dawley rats (n = 64). We assessed three measures related to binge eating – binge episode occurrence, binge intake, and weight gain associated with HFF access. Pimavanserin decreased binge intake and weight gain associated with HFF access, but did not prevent binge episode occurrence. Lorcaserin decreased binge intake, but did not prevent binge episode occurrence or weight gain associated with HFF access. Combined pimavanserin plus lorcaserin prevented binge episode occurrence in addition to decreasing binge intake and weight gain associated with HFF access. These preclinical findings in male rats suggest that pimavanserin and lorcaserin may be effective in treating patients with BED. Our studies further indicate that administration of one or both drugs may be more effective in certain sub-populations of patients with BED because of the unique profile each treatment elicits. These data support future assessment in clinical populations with BED.

Role of mGlu2 in the 5-HT2A receptor-dependent antipsychotic activity of clozapine in mice

BACKGROUND

Serotonin 5-HT_2A and metabotropic glutamate 2 (mGlu2) are neurotransmitter G protein-coupled receptors (GPCRs) involved in the signaling mechanisms underlying psychosis and schizophrenia treatment. Previous findings in mGlu2 knockout (KO) mice suggested that mGlu2 is necessary for head-twitch behavior, a rodent phenotype characteristic of hallucinogenic 5-HT_2A receptor agonists. However, the role of mGlu2 in the behavioral effects induced by antipsychotic drugs remains poorly understood. Here, we tested antipsychotic-like behavioral phenotypes induced by the atypical antipsychotic clozapine in mGlu2-KO mice and wild-type control littermates.

METHODS

Locomotor activity was tested in mGlu2-KO mice and control littermates injected (i.p.) with clozapine (1.5 mg/kg) or vehicle followed by MK801 (0.5 mg/kg), PCP (7.5 mg/kg), amphetamine (6 mg/kg), scopolamine (2 mg/kg), or vehicle. Using a virally (HSV) mediated transgene expression approach, the role of frontal cortex mGlu2 in the modulation of MK801-induced locomotor activity by clozapine treatment was also evaluated.

RESULTS

The effect of clozapine on hyperlocomotor activity induced by the dissociative drugs MK801 and phencyclidine (PCP) was decreased in mGlu2-KO mice as compared to controls. Clozapine treatment, however, reduced hyperlocomotor activity induced by the stimulant drug amphetamine and the deliriant drug scopolamine in both wild-type and mGlu2-KO mice. Virally mediated over-expression of mGlu2 in the frontal cortex of mGlu2-KO mice rescued the ability of clozapine to reduce MK801-induced hyperlocomotion.

CONCLUSION

These findings further support the existence of a functionally relevant crosstalk between 5-HT_2A and mGlu2 receptors in different preclinical models of antipsychotic activity.

Interactions of Hallucinogens with the Glutamatergic System: Permissive Network Effects Mediated Through Cortical Layer V Pyramidal Neurons

Recordings made from layer V (L5) pyramidal cells of the prefrontal cortex (PFC) and neocortex in rodent slice preparations have shown that serotonin (5-hydroxytryptamine, 5-HT) and serotonergic hallucinogens induce an increase in the frequency of spontaneous excitatory postsynaptic currents (EPSCs) in the apical dendritic field by activating 5-HT_2A receptors. Serotonergic hallucinogens induce late EPSCs and increase recurrent network activity when subcortical or mid-cortical regions are stimulated at low frequencies (e.g., 0.1 Hz). A range of agonists or positive allosteric modulators (PAMs) for mostly G_i/o-coupled receptors, including metabotropic glutamate₂ (mGlu₂), adenosine A₁, or μ-opioid receptors, suppress these effects of 5-HT_2A receptor stimulation. Furthermore, a range of mostly G_q/11-coupled receptors (including orexin₂ [OX₂]; α₁-adrenergic, and mGlu₅ receptors) similarly induce glutamate (Glu) release onto L5 pyramidal cells. Evidence implicates a number of brain regions in mediating these effects of serotonergic hallucinogens and G_q/11-coupled receptors including the midline and intralaminar thalamic nuclei, claustrum, and neurons in deep PFC. These effects on 5-HT_2A receptors and related GPCRs appear to play a major role in the behavioral effects of serotonergic hallucinogens, such as head twitches in rodents and higher order behaviors such as rodent lever pressing on the differential-reinforcement-of-low rate 72-s (DRL 72-s) schedule. This implies that the effects of 5-HT_2A receptor activation on the activity of L5 pyramidal cells may be responsible for mediating a range of behaviors linked to limbic circuitry with connectivity between the PFC, striatum, thalamus, claustrum, striatum, amygdala, and the hippocampal formation.

Effects of anxiety on suicidal ideation: exploratory analysis of a paroxetine versus bupropion randomized trial

It is unclear whether anxiety increases or decreases suicidal risk. This may contribute to the lack of guidance on which antidepressant medications are best for suicidal depressed patients who present with high anxiety. This study explored whether anxiety predicts suicidal ideation in depressed individuals treated with paroxetine or bupropion. An 8-week double-blind trial comparing controlled-release paroxetine (N=36) versus extended-release bupropion (N=38) for effect on suicidal ideation and behavior in depressed patients with suicidal ideation, past attempt, or both found an advantage for paroxetine, but anxiety effects were not investigated. This secondary analysis explored the relationship, measured at baseline and weekly, of anxiety with suicidal ideation. Anxiety severity measured weekly correlated with suicidal ideation severity irrespective of treatment (P=0.012). Patients with high baseline anxiety showed a trend toward faster reduction of suicidal ideation with paroxetine compared with bupropion treatment (standard P=0.047; bootstrap P=0.077). The latter finding, if confirmed in larger samples, could enhance choice of antidepressant medication for suicidal, depressed patients presenting with high levels of anxiety.

Serotonin receptors in depression and anxiety: Insights from animal studies

Serotonin regulates many physiological processes including sleep, appetite, and mood. Thus, serotonergic system is an important target in the treatment of psychiatric disorders, such as major depression and anxiety. This natural neurotransmitter interacts with 7 families of its receptors (5-HT1-7), which cause a variety of pharmacological effects. Using genetically modified animals and selective or preferential agonists and antagonist, numerous studies demonstrated the involvement of almost all serotonin receptor subtypes in antidepressant- or anxiolytic-like effects. In this review, based on animal studies, we discuss the possible involvement of serotonin receptor subtypes in depression and anxiety.

Neurotransmitter, Peptide, and Steroid Hormone Abnormalities in PTSD: Biological Endophenotypes Relevant to Treatment

PURPOSE OF REVIEW

This review summarizes neurotransmitter, peptide, and other neurohormone abnormalities associated with posttraumatic stress disorder (PTSD) and relevant to development of precision medicine therapeutics for PTSD.

RECENT FINDINGS

As the number of molecular abnormalities associated with PTSD across a variety of subpopulations continues to grow, it becomes clear that no single abnormality characterizes all individuals with PTSD. Instead, individually variable points of molecular dysfunction occur within several different stress-responsive systems that interact to produce the clinical PTSD phenotype. Future work should focus on critical interactions among the systems that influence PTSD risk, severity, chronicity, comorbidity, and response to treatment. Effort also should be directed toward development of clinical procedures by which points of molecular dysfunction within these systems can be identified in individual patients. Some molecular abnormalities are more common than others and may serve as subpopulation biological endophenotypes for targeting of currently available and novel treatments.

HDAC2-dependent Antipsychotic-like Effects of Chronic Treatment with the HDAC Inhibitor SAHA in Mice

Antipsychotic drugs, including both typical such as haloperidol and atypical such as clozapine, remain the current standard for schizophrenia treatment. These agents are relatively effective in treating hallucinations and delusions. However, cognitive deficits are at present essentially either persistent or exacerbated following chronic antipsychotic drug exposure. This underlines the need of new therapeutic approaches to improve cognition in treated schizophrenia patients. Our previous findings suggested that upregulation of histone deacetylase 2 (HDAC2) expression upon chronic antipsychotic treatment may lead to negative effects on cognition and cortical synaptic structure. Here we tested different phenotypes of psychosis, synaptic plasticity, cognition and antipsychotic drug action in HDAC2 conditional knockout (HDAC2-cKO) mice and controls. Conditional depletion of HDAC2 function in glutamatergic pyramidal neurons led to a protective phenotype against behavior models induced by psychedelic and dissociative drugs, such as DOI and MK801, respectively. Immunoreactivity toward synaptophysin, which labels presynaptic terminals of functional synapses, was decreased in the frontal cortex of control mice chronically treated with clozapine - an opposite effect occurred in HDAC2-cKO mice. Chronic treatment with the class I and class II HDAC inhibitor SAHA prevented via HDAC2 the disruptive effects of MK801 on recognition memory. Additionally, chronic SAHA treatment affected transcription of numerous plasticity-related genes in the frontal cortex of control mice, an effect that was not observed in HDAC2-cKO animals. Together, these findings suggest that HDAC2 may represent a novel target to improve synaptic plasticity and cognition in treated schizophrenia patients.

5-HT2a receptor in mPFC influences context-guided reconsolidation of object memory in perirhinal cortex

Context-dependent memories may guide adaptive behavior relaying in previous experience while updating stored information through reconsolidation. Retrieval can be triggered by partial and shared cues. When the cue is presented, the most relevant memory should be updated. In a contextual version of the object recognition task, we examined the effect of medial PFC (mPFC) serotonin 2a receptor (5-HT2aR) blockade during retrieval in reconsolidation of competing objects memories. We found that mPFC 5-HT2aR controls retrieval and reconsolidation of object memories in the perirhinal cortex (PRH), but not in the dorsal hippocampus in rats. Also, reconsolidation of objects memories in PRH required a functional interaction between the ventral hippocampus and the mPFC. Our results indicate that in the presence of conflicting information at retrieval, mPFC 5-HT2aR may facilitate top-down context-guided control over PRH to control the behavioral response and object memory reconsolidation.

Possible involvement of monoamine neurons in the emotional abnormality in Kir6.2-deficient mice

ATP-sensitive potassium (K_ATP) channels consist of two structurally different subunits: a pore-forming subunit of the Kir6.0-family (Kir6.1 or Kir6.2) and a regulatory sulfonylurea receptor subunit (SUR1, SUR2A or SUR2B). Although Kir6.2 is widely distributed in the brain, the mechanisms that underlie the impact of Kir6.2 on emotional behavior are not yet fully understood. To clarify the role of Kir6.2 in emotional behavior, in the present study, we investigated the behavioral characteristics of Kir6.2-knockout (Kir6.2^-/-) mice. Kir6.2^-/- mice showed impaired general behavior in a locomotor activity test and open field test. In addition, anxiety-like behavior was observed in the open field test, elevated plus-maze test and light-dark test. In particular, excessive anxiety-like behavior was observed in female Kir6.2^-/- mice. Moreover, we investigated whether Kir6.2 is expressed on monoamine neurons in the brain. Immunohistochemical studies showed that Kir6.2 was co-localized with tryptophan hydroxylase (TPH), a marker of serotonergic neurons, in dorsal raphe nuclei. Kir6.2 was also co-localized with tyrosine hydroxylase (TH), a marker of dopaminergic/noradrenergic neurons, in the ventral tegmental area and locus coeruleus. Next, we checked the protein levels of TH and TPH in the midbrain. Interestingly, TPH expression was significantly elevated in female Kir6.2^-/- mice. These results suggest that Kir6.2 in monoamine neurons, especially serotonergic neurons, could play a key role in emotional behavior.

Yokukansan, a traditional Japanese herbal medicine, enhances the anxiolytic effect of fluvoxamine and reduces cortical 5-HT2A receptor expression in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Yokukansan is a traditional Japanese herbal medicine that has been approved in Japan as a remedy for neurosis, insomnia, and irritability in children. It has also been reported to improve behavioral and psychological symptoms in patients with various forms of dementia.

AIM OF THE STUDY

To evaluate the usefulness of co-treatment with an antidepressant and an herbal medicine in the psychiatric field, the current study examined the effect of yokukansan on the anxiolytic-like effect of fluvoxamine in mice.

MATERIALS AND METHODS

The anxiolytic-like effect in mice was estimated by the contextual fear conditioning paradigm. Contextual fear conditioning consisted of two sessions, i.e., day 1 for the conditioning session and day 2 for the test session. The expression levels of 5-HT_1A and 5-HT_2A receptor in the mouse brain regions were quantified by western blot analysis.

RESULTS

A single administration of fluvoxamine (5-20 mg/kg, i.p.) before the test session dose-dependently and significantly suppressed freezing behavior in mice. In the combination study, a sub-effective dose of fluvoxamine (5 mg/kg, i.p.) significantly suppressed freezing behavior in mice that had been repeatedly pretreated with yokukansan (0.3 and 1 g/kg, p.o.) once a day for 6 days after the conditioning session. Western blot analysis revealed that the expression level of 5-HT_2A receptor was specifically decreased in the prefrontal cortex of mice that had been administered yokukansan and fluvoxamine. Furthermore, microinjection of the 5-HT_2A receptor antagonist ketanserin (5 nmol/mouse) into the prefrontal cortex significantly suppressed freezing behavior.

CONCLUSION

The present findings indicate that repeated treatment with yokukansan synergistically enhances the anxiolytic-like effect of fluvoxamine in the contextual fear conditioning paradigm in mice in conjunction with a decrease in 5-HT_2A receptor-mediated signaling in the prefrontal cortex. Therefore, combination therapy with fluvoxamine and yokukansan may be beneficial for the treatment of anxiety disorders.

Novel Bivalent 5-HT2A Receptor Antagonists Exhibit High Affinity and Potency in Vitro and Efficacy in Vivo

The 5-HT_2A receptor (5-HT_2AR) plays an important role in various neuropsychiatric disorders, including substance use disorder and schizophrenia. Homodimerization of this receptor has been suggested, but tools that allow direct assessment of the relevance of the 5-HT_2AR:5-HT_2AR homodimer in these disorders are necessary. We chemically modified the selective 5-HT_2AR antagonist M100907 to synthesize a series of homobivalent ligands connected by ethylene glycol linkers of varying lengths that may be useful tools for probing 5-HT_2AR:5-HT_2AR homodimer function. We tested these molecules for 5-HT_2AR antagonist activity in a cell line stably expressing the functional 5-HT_2AR and quantified a downstream signaling target, activation (phosphorylation) of extracellular regulated kinases 1/2 (ERK_1/2), in comparison to in vivo efficacy of altering spontaneous or cocaine-evoked locomotor activity in rats. All of the synthetic compounds inhibited 5-HT-mediated phosphorylation of ERK_1/2 in the cellular signaling assay; the potency of the bivalent ligands varied as a function of linker length, with the intermediate linker lengths being the most potent. The K_i values for the binding of bivalent ligands to 5-HT_2AR were only slightly lower than the values for the parent (+)-M100907 compound, but significant selectivity for 5-HT_2AR over 5-HT_2BR or 5-HT_2CR binding was retained. In addition, the 11-atom-linked bivalent 5-HT_2AR antagonist (2 mg/kg, intraperitoneally) demonstrated efficacy on par with that of (+)-M100907 in inhibiting cocaine-evoked hyperactivity. As we develop further strategies for ligand-evoked receptor assembly and analyses of diverse signaling and functional roles, these novel homobivalent 5-HT_2AR antagonist ligands will serve as useful in vitro and in vivo probes of 5-HT_2AR structure and function.

GDNF/GFRα1 Complex Abrogates Self-Renewing Activity of Cortical Neural Precursors Inducing Their Differentiation

The balance between factors leading to proliferation and differentiation of cortical neural precursors (CNPs) determines the correct cortical development. In this work, we show that GDNF and its receptor GFRα1 are expressed in the neocortex during the period of cortical neurogenesis. We show that the GDNF/GFRα1 complex inhibits the self-renewal capacity of mouse CNP cells induced by fibroblast growth factor 2 (FGF2), promoting neuronal differentiation. While GDNF leads to decreased proliferation of cultured cortical precursor cells, ablation of GFRα1 in glutamatergic cortical precursors enhances its proliferation. We show that GDNF treatment of CNPs promoted morphological differentiation even in the presence of the self-renewal-promoting factor, FGF2. Analysis of GFRα1-deficient mice shows an increase in the number of cycling cells during cortical development and a reduction in dendrite development of cortical GFRα1-expressing neurons. Together, these results indicate that GDNF/GFRα1 signaling plays an essential role in regulating the proliferative condition and the differentiation of cortical progenitors.

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GFRα1 receptor is expressed in the neocortex during the period of neurogenesis

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GDNF/GFRα1 complex inhibits self-renewing of cortical neuronal precursors

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GDNF and GFRα1 promote neurogenic differentiation of cortical neural progenitors

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Requirement of GFRα1 for proper dendrite development of cortical neurons

Multiple role of 3-mercaptopyruvate sulfurtransferase: antioxidative function, H2 S and polysulfide production and possible SOx production

Rat 3-mercaptopyruvate sulfurtransferase (MPST) is a 32 808 Da simple protein. Cys247 is a catalytic site, and Cys154 and Cys263 are on the enzyme surface. MPST is found in all tissues, particularly in the kidneys, although the localization of its activity differs in each tissue. In this review, four functions of MPST are reviewed: (i) antioxidative function: Cys247 is redox-sensitive and serves as a redox-sensing switch. It is oxidized to cysteine sulfenate, which has a low redox potential, upon which the enzyme is inactivated. Then, reduced thioredoxin (Trx) with a reducing system (Trx reductase and NADPH) reduces the sulfenate to restore activity; meanwhile, Cys154 and Cys263 form an intermolecular disulfide bond, which serves as another redox-sensing switch. Consequently, Trx specifically cleaves the intermolecular disulfide bond by converting it from the inactive form (dimer) to the active form (monomer). (ii) Hydrogen sulfide and polysulfide production: hydrogen sulfide is produced via reduction of the persulfurated sulfur-acceptor substrate by reduced Trx or Trx with a reducing system; as an alternative process, stable polysulfurated or persulfurated Cys247 as a reaction intermediate is reduced by Trx with a reducing system to release hydrogen sulfide and polysulfides. (iii) Possible sulfur oxide production: sulfur oxides (SO, SO2 and SO3 ) can be produced in the redox cycle of sulfane sulfur formed at the catalytic site Cys247 (Cys-SO- , Cys-SO2- and Cys-SO3- ) as reaction intermediates and released by reduced Trx or Trx with a reducing system. (iv) Possible anxiolytic-like effects: MPST-knockout mice exhibited anxiolytic-like effects.

Neuromodulatory Systems and Their Interactions: A Review of Models, Theories, and Experiments

Neuromodulatory systems, including the noradrenergic, serotonergic, dopaminergic, and cholinergic systems, track environmental signals, such as risks, rewards, novelty, effort, and social cooperation. These systems provide a foundation for cognitive function in higher organisms; attention, emotion, goal-directed behavior, and decision-making derive from the interaction between the neuromodulatory systems and brain areas, such as the amygdala, frontal cortex, hippocampus, and sensory cortices. Given their strong influence on behavior and cognition, these systems also play a key role in disease states and are the primary target of many current treatment strategies. The fact that these systems interact with each other either directly or indirectly, however, makes it difficult to understand how a failure in one or more systems can lead to a particular symptom or pathology. In this review, we explore experimental evidence, as well as focus on computational and theoretical models of neuromodulation. Better understanding of neuromodulatory systems may lead to the development of novel treatment strategies for a number of brain disorders.

Perinatal nutrition interacts with genetic background to alter behavior in a parent-of-origin-dependent manner in adult Collaborative Cross mice

Previous studies in animal models and humans have shown that exposure to nutritional deficiencies in the perinatal period increases the risk of psychiatric disease. Less well understood is how such effects are modulated by the combination of genetic background and parent-of-origin (PO). To explore this, we exposed female mice from 20 Collaborative Cross (CC) strains to protein deficient, vitamin D deficient, methyl donor enriched or standard diet during the perinatal period. These CC females were then crossed to a male from a different CC strain to produce reciprocal F1 hybrid females comprising 10 distinct genetic backgrounds. The adult F1 females were then tested in the open field, light/dark, stress-induced hyperthermia, forced swim and restraint stress assays. Our experimental design allowed us to estimate effects of genetic background, perinatal diet, PO and their interactions on behavior. Genetic background significantly affected all assessed phenotypes. Perinatal diet exposure interacted with genetic background to affect body weight, basal body temperature, anxiety-like behavior and stress response. In 8 of 9 genetic backgrounds, PO effects were observed on multiple phenotypes. Additionally, we identified a small number of diet-by-PO effects on body weight, stress response, anxiety- and depressive-like behavior. Our data show that rodent behaviors that model psychiatric disorders are affected by genetic background, PO and perinatal diet, as well as interactions among these factors.

A focus on reward in anorexia nervosa through the lens of the activity-based anorexia rodent model

Patients suffering anorexia nervosa (AN) become anhedonic, unable or unwilling to derive normal pleasures and tend to avoid rewarding outcomes, most profoundly in food intake. The activity-based anorexia model recapitulates many of the pathophysiological and behavioural hallmarks of the human condition, including a reduction in food intake, excessive exercise, dramatic weight loss, loss of reproductive cycles, hypothermia and anhedonia, and therefore it allows investigation into the underlying neurobiology of anorexia nervosa. The use of this model has directed attention to disruptions in central reward neurocircuitry, which may contribute to disease susceptibility. The purpose of this review is to demonstrate the utility of this unique model to provide insight into the mechanisms of reward relevant to feeding and weight loss, which may ultimately help to unravel the neurobiology of anorexia nervosa and, in a broader sense, the foundation of reward-based feeding.

Serotonin and brain function: a tale of two receptors

Previous attempts to identify a unified theory of brain serotonin function have largely failed to achieve consensus. In this present synthesis, we integrate previous perspectives with new and older data to create a novel bipartite model centred on the view that serotonin neurotransmission enhances two distinct adaptive responses to adversity, mediated in large part by its two most prevalent and researched brain receptors: the 5-HT1A and 5-HT2A receptors. We propose that passive coping (i.e. tolerating a source of stress) is mediated by postsynaptic 5-HT1AR signalling and characterised by stress moderation. Conversely, we argue that active coping (i.e. actively addressing a source of stress) is mediated by 5-HT2AR signalling and characterised by enhanced plasticity (defined as capacity for change). We propose that 5-HT1AR-mediated stress moderation may be the brain's default response to adversity but that an improved ability to change one's situation and/or relationship to it via 5-HT2AR-mediated plasticity may also be important - and increasingly so as the level of adversity reaches a critical point. We propose that the 5-HT1AR pathway is enhanced by conventional 5-HT reuptake blocking antidepressants such as the selective serotonin reuptake inhibitors (SSRIs), whereas the 5-HT2AR pathway is enhanced by 5-HT2AR-agonist psychedelics. This bipartite model purports to explain how different drugs (SSRIs and psychedelics) that modulate the serotonergic system in different ways, can achieve complementary adaptive and potentially therapeutic outcomes.

3,4-Methylenedioxymethamphetamine Increases Affiliative Behaviors in Squirrel Monkeys in a Serotonin 2A Receptor-Dependent Manner

3,4-Methylenedioxymethamphetamine (MDMA) increases sociality in humans and animals. Release of serotonin (5-HT) is thought to have an important role in the increase in social behaviors, but the mechanisms underlying these effects are poorly understood. Despite the advantages of nonhuman primate models, no studies have examined the mechanisms of the social effects of MDMA in nonhuman primates. The behavior and vocalizations of four group-housed squirrel monkeys were examined following administration of MDMA, its enantiomers, and methamphetamine. 5-HT receptor antagonists and agonists were given as drug pretreatments. Data were analyzed using linear mixed-effects models. MDMA and its enantiomers increased affiliative social behaviors and vocalizations, whereas methamphetamine had only modest effects on affiliative behaviors. Pretreatment with a 5-HT_2A receptor antagonist and a 5-HT_2C receptor agonist attenuated the MDMA-induced increase in social behaviors, while a 5-HT_1A receptor antagonist did not alter affiliative vocalizations and increased MDMA-induced social contact. Nonhuman primates show MDMA-specific increases in affiliative social behaviors following MDMA administration, in concordance with human and rodent studies. MDMA-induced increases in social behaviors are 5-HT_2A, but not 5-HT_1A, receptor dependent. Understanding the neurochemical mechanisms mediating the prosocial effects of MDMA could help in the development of novel therapeutics with the unique social effects of MDMA but fewer of its limitations.

Hierarchy in the home cage affects behaviour and gene expression in group-housed C57BL/6 male mice

Group-housed male mice exhibit aggressive behaviour towards their cage mates and form a social hierarchy. Here, we describe how social hierarchy in standard group-housed conditions affects behaviour and gene expression in male mice. Four male C57BL/6 mice were kept in each cage used in the study, and the social hierarchy was determined from observation of video recordings of aggressive behaviour. After formation of a social hierarchy, the behaviour and hippocampal gene expression were analysed in the mice. Higher anxiety- and depression-like behaviours and elevated gene expression of hypothalamic corticotropin-releasing hormone and hippocampal serotonin receptor subtypes were observed in subordinate mice compared with those of dominant mice. These differences were alleviated by orally administering fluoxetine, which is an antidepressant of the selective serotonin reuptake inhibitor class. We concluded that hierarchy in the home cage affects behaviour and gene expression in male mice, resulting in anxiety- and depression-like behaviours being regulated differently in dominant and subordinate mice.