Obligatory roles of dopamine D1 receptors in the dentate gyrus in antidepressant actions of a selective serotonin reuptake inhibitor, fluoxetine

Synergistic Antidepressant-like Effects of Biotics and n-3 Polyunsaturated Fatty Acids on Dopaminergic Pathway through the Brain-Gut Axis in Rats Exposed to Chronic Mild Stress

Probiotics, postbiotics, and n-3 polyunsaturated fatty acids (PUFA) have antidepressant-like effects. However, the underlying mechanisms of the dopaminergic pathway are unclear. The present study investigated the hypothesis that probiotics and postbiotics combined with n-3 PUFA synergistically improve depression by modulating the dopaminergic pathway through the brain-gut axis. Rats were randomly divided into seven groups: non-chronic mild stress (CMS) with n-6 PUFA, and CMS with n-6 PUFA, n-3 PUFA, probiotics, postbiotics, probiotics combined with n-3 PUFA, and postbiotics combined with n-3 PUFA. Probiotics, postbiotics, and n-3 PUFA improved depressive behaviors, decreased blood concentrations of interferon-γ, and interleukin-1β, and increased the brain and gut concentrations of short chain fatty acids and dopamine. Moreover, probiotics, postbiotics, and n-3 PUFA increased the brain and gut expression of glucocorticoid receptor and tyrosine hydroxylase; brain expression of l-type amino acid transporter 1 and dopamine receptor (DR) D1; and gut expression of DRD2. The expression of phosphorylated protein kinase A/protein kinase A and phosphorylated cAMP response element-binding protein/cAMP response element-binding protein increased in the brain, however, decreased in the gut by the supplementation of probiotics, postbiotics, and n-3 PUFA. There was synergistic effect of probiotics and postbiotics combined with n-3 PUFA on the depressive behaviors and dopaminergic pathway in blood, brain, and gut. Moreover, no significant difference in the dopaminergic pathways between the probiotics and postbiotics was observed. In conclusion, probiotics and postbiotics, combined with n-3 PUFA have synergistic antidepressant-like effects on the dopaminergic pathway through the brain-gut axis in rats exposed to CMS.

CCNP Innovations in Neuropsychopharmacology Award: The psychopharmacology of psychedelics: where the brain meets spirituality

For 3000 years, psychedelics have been used in religious contexts to enhance spiritual thinking, well-being, and a sense of community. In the last few years, a renaissance in the use of psychedelic drugs for mental disorders has occurred in Western society; consequently, a pressing scientific need to elucidate the intricate mechanisms underlying their actions has arisen. Psychedelics mainly bind to serotonin (5-HT) receptors, particularly 5-HT2A receptors, but may also bind to other receptors. Unlike conventional psychotropic drugs used in psychiatry, psychedelics introduce a distinctive complexity. They not only engage in receptor activation, but also exert influence over specific neural circuits, thereby facilitating transformative cognitive experiences and fostering what many have identified as a spiritual contemplation or mystical experience. This comprehensive review describes clinical studies that have examined the propensity of psychedelics to enhance spiritual, mystical, and transcendent cognitive states. This multifaceted nature, encompassing diverse components and paradigms, necessitates careful consideration during the investigation of psychedelic mechanisms of action to avoid oversimplification. The present review endeavours to elucidate the mechanisms underlying the actions of 2 principal psychedelic substances, psilocybin and lysergic acid diethylamide (LSD), with a focus on monoamine and glutamate receptor mechanisms; molecular aspects, such as neuroplasticity and epigenetics; as well as the impact of psychedelics on brain circuits, including the default mode network and the cortico-striato-thalamo-cortical network. Given their distinctive and intricate mechanisms of action, psychedelics necessitate a novel conceptual framework in psychiatry, offering insight into the treatment of mental health disorders and facilitating the integration of the realms of brain, mind, and spirituality.

Direct serotonin release in humans shapes aversive learning and inhibition

The role of serotonin in human behaviour is informed by approaches which allow in vivo modification of synaptic serotonin. However, characterising the effects of increased serotonin signalling in human models of behaviour is challenging given the limitations of available experimental probes, notably selective serotonin reuptake inhibitors. Here we use a now-accessible approach to directly increase synaptic serotonin in humans (a selective serotonin releasing agent) and examine its influence on domains of behaviour historically considered core functions of serotonin. Computational techniques, including reinforcement learning and drift diffusion modelling, explain participant behaviour at baseline and after week-long intervention. Reinforcement learning models reveal that increasing synaptic serotonin reduces sensitivity for outcomes in aversive contexts. Furthermore, increasing synaptic serotonin enhances behavioural inhibition, and shifts bias towards impulse control during exposure to aversive emotional probes. These effects are seen in the context of overall improvements in memory for neutral verbal information. Our findings highlight the direct effects of increasing synaptic serotonin on human behaviour, underlining its role in guiding decision-making within aversive and more neutral contexts, and offering implications for longstanding theories of central serotonin function.

Characterization of rice endosperm-derived antidepressant-like peptide (REAP): An orally active novel tridecapeptide derived from rice protein

It is ideal to ingest bioactive substances from daily foods to stay healthy. Rice is the staple food for almost half of the human population. We found that an orally administered enzymatic digest of rice endosperm protein exhibits antidepressant-like effects in the tail suspension test (TST) using mice. A comprehensive peptide analysis of the digest using liquid chromatography-tandem mass spectrometry was performed, and a tridecapeptide QQFLPEGQSQSQK, detected in the digest, was chemosynthesized. Oral administration of the tridecapeptide exhibited antidepressant-like effects at a low dose comparable to classical antidepressant in the TST. This also exhibited anti-depressant-like effect in the forced swim test. We named it rice endosperm-derived antidepressant-like peptide (REAP). Intriguingly, intraperitoneal administration had no effect. Orally administered REAP(8-13) but not REAP(1-7) exhibited antidepressant-like activity, suggesting that the C-terminal structure is important for the antidepressant-like effect. We confirmed the presence of REAP, corresponding to rice glutelin type B4(130-142) and B5(130-142), in the digest. The effects of REAP were blocked by both dopamine D1 and D2 antagonists. These results suggest that it exerts its antidepressant-like activity through activation of the dopamine system. Taken together, oral administration of a novel tridecapeptide exhibited antidepressant-like effects via the dopamine system. This is the first report of a rice-derived peptide that exhibits antidepressant-like effects.

Dopaminergic Modulation and Computational ADMET Insights for the Antidepressant-like Effect of N-(3-(Phenylselanyl)prop-2-yn-1-yl)benzamide

The compound N-(3-(phenylselanyl)prop-2-yn-1-yl)benzamide (SePB), which combines a selenium atom and a benzamide nucleus in an organic structure, has demonstrated a fast antidepressant-like effect in mice. This action is influenced by the serotonergic system and represents a promising development in the search for novel antidepressant drugs to treat major depressive disorder (MDD), which often resists conventional treatments. This study aimed to further explore the mechanism underlying the antidepressant-like effect of SePB by investigating the involvement of the dopaminergic and noradrenergic systems in the tail suspension test (TST) in mice and evaluating its pharmacokinetic profile in silico. Preadministration of the dopaminergic antagonists haloperidol (0.05 mg/kg, intraperitoneally (i.p.)), a nonselective antagonist of dopamine (DA) receptors, SCH23390 (0.01 mg/kg, subcutaneously (s.c.)), a D1 receptor antagonist, and sulpiride (50 mg/kg, i.p.), a D2/3 receptor antagonist, before SePB (10 mg/kg, intragastrically (i.g.)) prevented the anti-immobility effect of SePB in the TST, demonstrating that these receptors are involved in the antidepressant-like effect of SePB. Administration of the noradrenergic antagonists prazosin (1 mg/kg, i.p.), an α1-adrenergic antagonist, yohimbine (1 mg/kg, i.p.), an α2-adrenergic antagonist, and propranolol (2 mg/kg, i.p.), a β-adrenergic antagonist, did not block the antidepressant-like effect of SePB on TST, indicating that noradrenergic receptors are not involved in this effect. Additionally, the coadministration of SePB and bupropion (a noradrenaline/dopamine reuptake inhibitor) at subeffective doses (0.1 and 3 mg/kg, respectively) produced antidepressant-like effects. SePB also demonstrated good oral bioavailability and low toxicity in computational absorption, distribution, metabolism, excretion, and toxicity (ADMET) analyses. These findings suggest that SePB has potential as a new antidepressant drug candidate with a particular focus on the dopaminergic system.

Nicotine suppresses crystalline silica-induced astrocyte activation and neuronal death by inhibiting NF-κB in the mouse hippocampus

AIMS

Exposure to crystalline silica (CS) in occupational settings induces chronic inflammation in the respiratory system and, potentially, the brain. Some workers are frequently concurrently exposed to both CS and nicotine. Here, we explored the impact of nicotine on CS-induced neuroinflammation in the mouse hippocampus.

METHODS

In this study, we established double-exposed models of CS and nicotine in C57BL/6 mice. To assess depression-like behavior, experiments were conducted at 3, 6, and 9 weeks. Serum inflammatory factors were analyzed by ELISA. Hippocampus was collected for RNA sequencing analysis and examining the gene expression patterns linked to inflammation and cell death. Microglia and astrocyte activation and hippocampal neuronal death were assessed using immunohistochemistry and immunofluorescence staining. Western blotting was used to analyze the NF-κB expression level.

RESULTS

Mice exposed to CS for 3 weeks showed signs of depression. This was accompanied by elevated IL-6 in blood, destruction of the blood-brain barrier, and activation of astrocytes caused by an increased NF-κB expression in the CA1 area of the hippocampus. The elevated levels of astrocyte-derived Lcn2 and upregulated genes related to inflammation led to higher neuronal mortality. Moreover, nicotine mitigated the NF-κB expression, astrocyte activation, and neuronal death, thereby ameliorating the associated symptoms.

CONCLUSION

Silica exposure induces neuroinflammation and neuronal death in the mouse hippocampal CA1 region and depressive behavior. However, nicotine inhibits CS-induced neuroinflammation and neuronal apoptosis, alleviating depressive-like behaviors in mice.

Phosphoproteomics implicates glutamatergic and dopaminergic signalling in the antidepressant-like properties of the iron chelator deferiprone

BACKGROUND

Current antidepressants have limitations due to insufficient efficacy and delay before improvement in symptoms. Polymorphisms of the serotonin transporter (5-HTT) gene have been linked to depression (when combined with stressful life events) and altered response to selective serotonergic reuptake inhibitors. We have previously revealed the antidepressant-like properties of the iron chelator deferiprone in the 5-HTT knock-out (KO) mouse model of depression. Furthermore, deferiprone was found to alter neural activity in the prefrontal cortex of both wild-type (WT) and 5-HTT KO mice.

METHODS

In the current study, we examined the molecular effects of acute deferiprone treatment in the prefrontal cortex of both genotypes via phosphoproteomics analysis.

RESULTS

In WT mice treated with deferiprone, there were 22 differentially expressed phosphosites, with gene ontology analysis implicating cytoskeletal proteins. In 5-HTT KO mice treated with deferiprone, we found 33 differentially expressed phosphosites. Gene ontology analyses revealed phosphoproteins that were predominantly involved in synaptic and glutamatergic signalling. In a drug-naïve cohort (without deferiprone administration), the analysis revealed 21 differentially expressed phosphosites in 5-HTT KO compared to WT mice. We confirmed the deferiprone-induced increase in tyrosine hydroxylase serine 40 residue phosphorylation (pTH-Ser40) (initially revealed in our phosphoproteomics study) by Western blot analysis, with deferiprone increasing pTH-Ser40 expression in WT and 5-HTT KO mice.

CONCLUSION

As glutamatergic and synaptic signalling are dysfunctional in 5-HTT KO mice (and are the target of fast-acting antidepressant drugs such as ketamine), these molecular effects may underpin deferiprone's antidepressant-like properties. Furthermore, dopaminergic signalling may also be involved in deferiprone's antidepressant-like properties.

Overweight during development dysregulates cellular metabolism and critical genes that control food intake in the prefrontal cortex

BACKGROUNDS AND AIMS

Childhood obesity is increasing substantially across the world. The World Obesity Federation (WOF) and World Health Organization (WHO) predicted that in 2030 > 1 billion people will be obese, and by 2035 over 4 billion will reach obesity worldwide. According to WHO, the world soon cannot afford the economic cost of obesity, and we need to act to stop obesity acceleration now. Data in the literature supports that the first 1000 days of life are essential in preventing obesity and related adversities. Therefore, using basic research, the present a study that focuses on the immediate effect of overnutrition and serotonin modulation during the lactation period.

METHODS

Using a neonatal overfeeding model, male Wistar rats were divided into four groups based on nutrition or serotonin modulation by pharmacological treatment up to 22 days of life. Cellular and mitochondrial function markers, oxidative stress biomarkers and mRNA levels of hedonic and homeostatic genes were evaluated.

RESULTS

Our data showed that overfeeding during lactation decrease NAD/NADH ratio, citrate synthase activity, and increase ROS production. Lipid and protein oxidation were increased in overfed animals, with a decrease in antioxidant defenses, we also observe a differential expression of mRNA levels of homeostatic and hedonic genes. On the contrary, serotonin modulation with selective serotonin reuptake inhibitors treatment reduces harmful effects caused by overnutrition.

CONCLUSION

Early effects of overnutrition significantly affect the prefrontal cortex at molecular and cellular level, which could mediate obesity-related neurodegenerative dysfunction.

Social environment enrichment alleviates anxiety-like behavior in mice: Involvement of the dopamine system

Rearing environment plays a vital role in maintaining physical and mental health of both animals and humans. Plenty of studies have proved that physical environment enrichment in adolescence has protective effects on emotion, social behavior, learning and memory deficits. However, the following effects of social environment enrichment in adolescence remain largely elusive. Using the paradigm of companion rotation (CR), the present study found that social environment enrichment reduced anxiety-like behaviors of early adult male C57BL/6J mice. CR group also showed significantly higher expression of tyrosine hydroxylase in the ventral tegmental area and dopamine 1 receptor mRNA in the nucleus accumbens shell than control group. Taken together, these findings demonstrate that CR from adolescence to early adulthood can suppress the level of anxiety and upregulate dopaminergic neuron activity in early adult male C57BL/6J mice.

D1R-5-HT2AR Uncoupling Reduces Depressive Behaviours via HDAC Signalling

Dopamine and serotonin signalling are associated with major depressive disorder, which is a prevalent life-threatening illness worldwide. Numerous FDA-approved dopamine/serotonin signalling-modifying drugs are available but are associated with concurrent side effects and limited efficacy. Thus, identifying and targeting their signalling pathway is crucial for improving depression treatment. Here, we determined that serotonin receptor 2A (5-HT2AR) abundantly forms a protein complex with dopamine receptor 1 (D1R) in high abundance via its carboxy-terminus in the brains of mice subjected to various chronic stress paradigms. Furthermore, the D1R/5-HT2AR interaction elicited CREB/ERK/AKT modulation during synaptic regulation. An interfering peptide (TAT-5-HT2AR-SV) agitated the D1R/5-HT2AR interaction and attenuated depressive symptoms accompanied by CREB/ERK molecule costimulation. Interestingly, HDAC antagonism but not TrkB antagonism reversed the antidepressant effect of competitive peptides. These findings revealed a novel D1R/5-HT2AR heteroreceptor complex mechanism in the pathophysiology of depression, and their uncoupling ameliorates depressive-like behaviours through HDAC-, and not BDNF-, dependent mechanisms.

Natural psychedelics in the treatment of depression; a review focusing on neurotransmitters

Natural psychedelic compounds are emerging as potential novel therapeutics in psychiatry. This review will discuss how natural psychedelics exert their neurobiological therapeutic effects, and how different neurotransmission systems mediate the effects of these compounds. Further, current therapeutic strategies for depression, and novel mechanism of action of natural psychedelics in the treatment of depression will be discussed. In this review, our focus will be on N, N-dimethyltryptamine (DMT), reversible type A monoamine oxidase inhibitors, mescaline-containing cacti, psilocybin/psilocin-containing mushrooms, ibogaine, muscimol extracted from Amanita spp. mushrooms and ibotenic acid.

Boophone disticha attenuates five day repeated forced swim-induced stress and adult hippocampal neurogenesis impairment in male Balb/c mice

Depression is one of the most common neuropsychiatric disorders and is associated with dysfunction of the neuroendocrine system and alterations in specific brain proteins. Boophone disticha (BD) is an indigenous psychoactive bulb that belongs to the Amaryllidacae family, which is widely used in Southern Africa to treat depression, with scientific evidence of potent antidepressant-like effects. The present study examined the antidepressant effects of BD and its mechanisms of action by measuring some behavioural parameters in the elevated plus maze, brain content of corticosterone, brain derived neurotropic factor (BDNF), and neuroblast differentiation in the hippocampus of Balb/c mice exposed to the five day repeated forced swim stress (5d-RFSS). Male Balb/c mice were subjected to the 5d-RFSS protocol to induce depressive-like behaviour (decreased swimming, increased floating, decreased open arm entry, decreased time spent in the open arms and decreased head dips in the elevated plus maze test) and treated with distilled water, fluoxetine and BD. BD treatment (10 mg/kg/p.o for 3 weeks) significantly attenuated the 5d-RFSS-induced behavioural abnormalities and the elevated serum corticosterone levels observed in stressed mice. Additionally, 5d-RFSS exposure significantly decreased the number of neuroblasts in the hippocampus and BDNF levels in the brain of Balb/c mice, while fluoxetine and BD treatment attenuated these changes. The antidepressant effects of BD were comparable to those of fluoxetine, but unlike fluoxetine, BD did not show any anxiogenic effects, suggesting better pharmacological functions. In conclusion, our study shows that BD exerted antidepressant-like effects in 5d-RFSS mice, mediated in part by normalizing brain corticosterone and BDNF levels.

Protective effect of Nr4a2 (Nurr1) against LPS-induced depressive-like behaviors via regulating activity of microglia and CamkII neurons in anterior cingulate cortex

Neuroinflammation is tightly associated with onset of depression. The nuclear receptor related 1 protein (Nurr1, also called Nr4a2), its roles in dopaminergic neurons is well understood, which can alleviate inflammation. Nevertheless, potential effects of Nr4a2 on neuroinflammation associated with depression still remains unclear. Chronic lipopolysaccharides (LPS) stress induced depressive-behaviors were confirmed via behavioral tests. Differentially expressed genes were detected by using RNA-sequencing. The anterior cingulate cortex (ACC) tissues were collected for biochemical experiments. The Golgi-Cox staining and virus labeling were used to evaluate the dendritic spines. We applied fluoxetine (FLX) and amodiaquine dihydrochloride (AQ, a highly selective agonist of Nr4a2) in mice. Overexpression experiments were performed by injecting with AAV-Nr4a2-EGFP into ACC. Chemogenetic activation of CamkII neurons via injecting the hM3Dq virus. Mice treated with LPS displayed depressive- and anxiety-like behaviors. The reduction of Nr4a2 and FosB induced by LPS were rescued by pretreatment with FLX or AQ. More importantly, LPS-induced behavior deficits in mice were also alleviated via fluoxetine treatment and pharmacological activation the expression of Nr4a2. Meanwhile, enhancing the level of Nr4a2 could improve dendritic spines loss of neuron and morphological changes in microglia. Overexpression of Nr4a2 in ACC reversed the depressive- and anxiety-like behaviors caused by LPS administration. Activation of CamkII neurons in ACC could robustly increase the expression of Nr4a2 and improve LPS-induced behavior deficits. Our findings demonstrate that the Nr4a2 may regulate depressive-like behaviors via alleviating the impairment of morphology and function on microglia and CamkII neurons induced by chronic neuroinflammation.

D1 receptor-expressing neurons in ventral tegmental area alleviate mouse anxiety-like behaviors via glutamatergic projection to lateral septum

Dopamine (DA) acts as a key regulator in controlling emotion, and dysfunction of DA signal has been implicated in the pathophysiology of some psychiatric disorders, including anxiety. Ventral tegmental area (VTA) is one of main regions with DA-producing neurons. VTA DAergic projections in mesolimbic brain regions play a crucial role in regulating anxiety-like behaviors, however, the function of DA signal within VTA in regulating emotion remains unclear. Here, we observe that pharmacological activation/inhibition of VTA D1 receptors will alleviate/aggravate mouse anxiety-like behaviors, and knockdown of VTA D1 receptor expression also exerts anxiogenic effect. With fluorescence in situ hybridization and electrophysiological recording, we find that D1 receptors are functionally expressed in VTA neurons. Silencing/activating VTA D1 neurons bidirectionally modulate mouse anxiety-like behaviors. Furthermore, knocking down D1 receptors in VTA DA and glutamate neurons elevates anxiety-like state, but in GABA neurons has the opposite effect. In addition, we identify the glutamatergic projection from VTA D1 neurons to lateral septum is mainly responsible for the anxiolytic effect induced by activating VTA D1 neurons. Thus, our study not only characterizes the functional expression of D1 receptors in VTA neurons, but also uncovers the pivotal role of DA signal within VTA in mediating anxiety-like behaviors.

The immediate effect of overnutrition and fluoxetine treatment during the critical period of development on the hippocampus

It is well known that overnutrition, overweight, and obesity in children can modulate brain mechanisms of plasticity, monoaminergic systems, and mitochondrial function. The immediate effect of overnutrition during the developmental period has not been thoroughly examined in rats until the present. This study sought to evaluate the impact on adult rats of early life overfeeding and fluoxetine treatment from post-natal day 1 (PND1) to post-natal day 21 (PND21) relative to mitochondrial function, oxidative balance, and expression of specific monoaminergic genes in the hippocampus. The following were evaluated: mitochondrial function markers, oxidative stress biomarkers, dopamine-and serotonin-related genes, and BDNF mRNA levels. Overfeeding during the lactation period deregulates cellular metabolism and the monoaminergic systems in the hippocampus. Strikingly, serotonin modulation by fluoxetine treatment protected against some of the effects of early overnutrition. We conclude that overfeeding during brain development induce detrimental effects in mitochondria and in the genes that regulate homeostatic status that can be the molecular mechanisms related to neurological diseases.

Forebrain-specific conditional calcineurin deficiency induces dentate gyrus immaturity and hyper-dopaminergic signaling in mice

Calcineurin (Cn), a phosphatase important for synaptic plasticity and neuronal development, has been implicated in the etiology and pathophysiology of neuropsychiatric disorders, including schizophrenia, intellectual disability, autism spectrum disorders, epilepsy, and Alzheimer's disease. Forebrain-specific conditional Cn knockout mice have been known to exhibit multiple behavioral phenotypes related to these disorders. In this study, we investigated whether Cn mutant mice show pseudo-immaturity of the dentate gyrus (iDG) in the hippocampus, which we have proposed as an endophenotype shared by these disorders. Expression of calbindin and GluA1, typical markers for mature DG granule cells (GCs), was decreased and that of doublecortin, calretinin, phospho-CREB, and dopamine D1 receptor (Drd1), markers for immature GC, was increased in Cn mutants. Phosphorylation of cAMP-dependent protein kinase (PKA) substrates (GluA1, ERK2, DARPP-32, PDE4) was increased and showed higher sensitivity to SKF81297, a Drd1-like agonist, in Cn mutants than in controls. While cAMP/PKA signaling is increased in the iDG of Cn mutants, chronic treatment with rolipram, a selective PDE4 inhibitor that increases intracellular cAMP, ameliorated the iDG phenotype significantly and nesting behavior deficits with nominal significance. Chronic rolipram administration also decreased the phosphorylation of CREB, but not the other four PKA substrates examined, in Cn mutants. These results suggest that Cn deficiency induces pseudo-immaturity of GCs and that cAMP signaling increases to compensate for this maturation abnormality. This study further supports the idea that iDG is an endophenotype shared by certain neuropsychiatric disorders.

Regulation of adult-born and mature neurons in stress response and antidepressant action in the dentate gyrus of the hippocampus

The dentate gyrus (DG) of the hippocampus has been implicated in the regulation of stress responses, and in the pathophysiology and treatment of depression. This review discusses the cellular changes caused by chronic stress and the cellular role of the DG in stress-induced behavioral changes and its antidepressant-like effects. Regarding adult-born neurogenic processes in the DG, chronic stress, such as repeated social defeat, suppresses cell proliferation during and immediately after stress; however, this effect is transient. The subsequent differentiation and survival processes are differentially regulated depending on the timing and sensitivity of stress. The activation of young adult-born neurons during stress contributes to stress resilience, while the transient increase in the survival of adult-born neurons after the cessation of stress seems to promote stress susceptibility. In mature granule neurons, the predominant cells in the DG, synaptic plasticity is suppressed by chronic stress. However, a group of mature granule neurons is activated by chronic stress. Chronic antidepressant treatment can transform mature granule neurons to a phenotype resembling that of immature neurons, characterized as "dematuration". Adult-born neurons suppress the activation of mature granule neurons during stress, indicating that local neural interactions within the DG are important for the stress response. Elucidating the stress-associated context- and timing-dependent cellular changes and functions in the DG will provide insights into stress-related psychiatric diseases.

Noradrenaline activation of hippocampal dopamine D1 receptors promotes antidepressant effects

Dopamine D₁ receptors (D₁Rs) in the hippocampal dentate gyrus (DG) are essential for antidepressant effects. However, the midbrain dopaminergic neurons, the major source of dopamine in the brain, only sparsely project to DG, suggesting possible activation of DG D₁Rs by endogenous substances other than dopamine. We have examined this possibility using electrophysiological and biochemical techniques and found robust activation of D₁Rs in mouse DG neurons by noradrenaline. Noradrenaline at the micromolar range potentiated synaptic transmission at the DG output and increased the phosphorylation of protein kinase A substrates in DG via activation of D₁Rs and β adrenergic receptors. Neuronal excitation preferentially enhanced noradrenaline-induced synaptic potentiation mediated by D₁Rs with minor effects on β-receptor-dependent potentiation. Increased voluntary exercise by wheel running also enhanced noradrenaline-induced, D₁R-mediated synaptic potentiation, suggesting a distinct functional role of the noradrenaline-D₁R signaling. We then examined the role of this signaling in antidepressant effects using mice exposed to chronic restraint stress. In the stressed mice, an antidepressant acting on the noradrenergic system induced a mature-to-immature change in the DG neuron phenotype, a previously proposed cellular substrate for antidepressant action. This effect was evident only in mice subjected to wheel running and blocked by a D₁R antagonist. These results suggest a critical role of noradrenaline-induced activation of D₁Rs in antidepressant effects in DG. Experience-dependent regulation of noradrenaline-D₁R signaling may determine responsiveness to antidepressant drugs in depressive disorders.

Molecular and Cellular Adaptations in Hippocampal Parvalbumin Neurons Mediate Behavioral Responses to Chronic Social Stress

Parvalbumin-expressing interneurons (PV neurons) maintain inhibitory control of local circuits implicated in behavioral responses to environmental stressors. However, the roles of molecular and cellular adaptations in PV neurons in stress susceptibility or resilience have not been clearly established. Here, we show behavioral outcomes of chronic social defeat stress (CSDS) are mediated by differential neuronal activity and gene expression in hippocampal PV neurons in mice. Using in vivo electrophysiology and chemogenetics, we find increased PV neuronal activity in the ventral dentate gyrus is required and sufficient for behavioral susceptibility to CSDS. PV neuron-selective translational profiling indicates mitochondrial oxidative phosphorylation is the most significantly altered pathway in stress-susceptible versus resilient mice. Among differentially expressed genes associated with stress-susceptibility and resilience, we find Ahnak, an endogenous regulator of L-type calcium channels which are implicated in the regulation of mitochondrial function and gene expression. Notably, Ahnak deletion in PV neurons impedes behavioral susceptibility to CSDS. Altogether, these findings indicate behavioral effects of chronic stress can be controlled by selective modulation of PV neuronal activity or a regulator of L-type calcium signaling in PV neurons.

Novel Pharmacological Approaches to the Treatment of Depression

Major depressive disorder is one of the most prevalent mental health disorders. Monoamine-based antidepressants were the first drugs developed to treat major depressive disorder. More recently, ketamine and other analogues were introduced as fast-acting antidepressants. Unfortunately, currently available therapeutics are inadequate; lack of efficacy, adverse effects, and risks leave patients with limited treatment options. Efforts are now focused on understanding the etiology of depression and identifying novel targets for pharmacological treatment. In this review, we discuss promising novel pharmacological targets for the treatment of major depressive disorder. Targeting receptors including N-methyl-D-aspartate receptors, peroxisome proliferator-activated receptors, G-protein-coupled receptor 39, metabotropic glutamate receptors, galanin and opioid receptors has potential antidepressant effects. Compounds targeting biological processes: inflammation, the hypothalamic-pituitary-adrenal axis, the cholesterol biosynthesis pathway, and gut microbiota have also shown therapeutic potential. Additionally, natural products including plants, herbs, and fatty acids improved depressive symptoms and behaviors. In this review, a brief history of clinically available antidepressants will be provided, with a primary focus on novel pharmaceutical approaches with promising antidepressant effects in preclinical and clinical studies.

An Investigation into the Association Between Dopamine Receptor D1 Multilocus Genetic Variation, Multiparametric Magnetic Resonance Imaging, and Antidepressant Treatment

BACKGROUND

Combining genetic variants with neuroimaging phenotypes may facilitate understanding of the biological mechanisms for the etiology and pharmacology of antidepressant treatment of major depressive disorder (MDD).

PURPOSE

To explore the latent pathway of dopamine gene-hierarchical brain network-antidepressant treatment.

STUDY TYPE

Retrospective.

POPULATION

One hundred and sixty-eight MDD inpatients divided into responders (N = 98) or nonresponders (N = 70) based on the treatment outcome of antidepressant.

FIELD STRENGTH/SEQUENCE

Diffusion tensors imaging and resting-state functional magnetic resonance imaging at 3.0T using echo-planar sequence.

ASSESSMENT

Four genetic variations of the dopamine receptor D1 (DRD1) were genotyped. Strengths of rich-club, feeder, and local connections were calculated based on the rich-club organizations of structural and functional brain networks at baseline and following 4 weeks of selective serotonin reuptake inhibitor (SSRI) therapy.

STATISTICAL TESTS

Logistic and linear regressions were used to analyze the impact of DRD1 multilocus genetic profile score on the treatment response of SSRI, and their associations with strengths of rich-club, feeder, and local connections. Mediation models were developed to explore the mediation role of rich-club organizations on the relationship between DRD1 and SSRI therapy response. A P value <0.05 was considered to be statistically significant.

RESULTS

Multiple genetic variations of DRD1 were significantly related to the strengths of feeder connections both in structural and functional networks, and to the treatment response of SSRI. Furthermore, the strength of the structural feeder connection significantly modulated the effect of DRD1 variants on SSRI treatment outcome.

DATA CONCLUSION

DRD1 displayed close connections both with SSRI treatment outcome and rich-club organizations of structural and functional data. Moreover, structural feeder connection played a mediating role in the relationship between DRD1 and antidepressant therapy.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 4.

Distinct Role of Dopamine in the PFC and NAc During Exposure to Cocaine-Associated Cues

BACKGROUND

Dopamine neurotransmission plays a critical role in reward in drug abuse and drug addiction. However, the role of dopamine in the recognition of drug-associated environmental stimuli, retrieval of drug-associated memory, and drug-seeking behaviors is not fully understood.

METHODS

Roles of dopamine neurotransmission in the prefrontal cortex (PFC) and nucleus accumbens (NAc) in the cocaine-conditioned place preference (CPP) paradigm were evaluated using in vivo microdialysis.

RESULTS

In mice that had acquired cocaine CPP, dopamine levels in the PFC, but not in the NAc, increased in response to cocaine-associated cues when mice were placed in the cocaine chamber of an apparatus with 2 separated chambers. The induction of the dopamine response and the development of cocaine CPP were mediated through activation of glutamate NMDA (N-methyl-D-aspartate)/AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor signaling in the PFC during conditioning. Activation of dopamine D1 or D2 receptor signaling in the PFC was required for cocaine-induced locomotion, but not for the induction of the dopamine response or the development of cocaine CPP. Interestingly, dopamine levels in the NAc increased in response to cocaine-associated cues when mice were placed at the center of an apparatus with 2 connected chambers, which requires motivated exploration associated with cocaine reward.

CONCLUSIONS

Dopamine neurotransmission in the PFC is activated by the exposure to the cocaine-associated cues, whereas dopamine neurotransmission in the NAc is activated in a process of motivated exploration of cues associated with cocaine reward. Furthermore, the glutamate signaling cascade in the PFC is suggested to be a potential therapeutic target to prevent the progression of drug addiction.

Activation of the p11/SMARCA3/Neurensin-2 pathway in parvalbumin interneurons mediates the response to chronic antidepressants

The delayed behavioral response to chronic antidepressants depends on dynamic changes in the hippocampus. It was suggested that the antidepressant protein p11 and the chromatin remodeling factor SMARCA3 mediate this delayed response by inducing transcriptional changes in hippocampal neurons. However, what target genes are regulated by the p11/SMARCA3 complex to mediate the behavioral response to antidepressants, and what cell type mediates these molecular changes remain unknown. Here we report that the p11/SMARCA3 complex represses Neurensin-2 transcription in hippocampal parvalbumin-expressing interneurons after chronic treatment with Selective Serotonin Reuptake Inhibitors (SSRI). The behavioral response to antidepressants requires upregulation of p11, accumulation of SMARCA3 in the cell nucleus, and a consequent repression of Neurensin-2 transcription in these interneurons. We elucidate a functional role for p11/SMARCA3/Neurensin-2 pathway in regulating AMPA-receptor signaling in parvalbumin-expressing interneurons, a function that is enhanced by chronic treatment with SSRIs. These results link SSRIs to dynamic glutamatergic changes and implicate p11/SMARCA3/Neurensin-2 pathway in the development of more specific and efficient therapeutic strategies for neuropsychiatric disorders.

Chinese Medicine Formula Kai-Xin-San Ameliorates Neuronal Inflammation of CUMS-Induced Depression-like Mice and Reduces the Expressions of Inflammatory Factors via Inhibiting TLR4/IKK/NF-κB Pathways on BV2 Cells

Kai-Xin-San (KXS) is a traditional Chinese medicinal formula composed of Ginseng Radix et Rhizoma, Polygalae Radix, Acori Tatarinowii Rhizoma, and Poria for relieving major depressive disorder and Alzheimer's disease in traditional Chinese medicine (TCM) clinics. Previous studies on the antidepressant mechanism of KXS mainly focused on neurotransmitter and neurotrophic factor regulation, but few reports exist on neuronal inflammation regulation. In the current study, we found that KXS exerted antidepressant effects in chronic unpredictable mild stress-induced depression-like mice according to the results of behavioral tests. Meanwhile, KXS also inhibited the activation of microglia and significantly reduced the expression of pro-inflammatory cytokines such as IL-1β, IL-2, and TNF-α in the hippocampus of mice. In mice BV2 microglia cell lines, KXS extract reduced the expression of inflammatory factors in BV2 cells induced by lipopolysaccharide via inhibiting TLR4/IKK/NF-κB pathways, which was also validated by the treatment of signaling pathway inhibitors such as TAK-242 and JSH-23. T0hese data implied that the regulation of pro-inflammatory cytokines in microglia might account for the antidepressant effect of KXS, thereby providing more scientific information for the development of KXS as an alternative therapy for major depressive disorder.

Discovering the Lost Reward: Critical Locations for Endocannabinoid Modulation of the Cortico-Striatal Loop That Are Implicated in Major Depression

Depression, the most prevalent psychiatric disorder in the Western world, is characterized by increased negative affect (i.e., depressed mood, cost value increase) and reduced positive affect (i.e., anhedonia, reward value decrease), fatigue, loss of appetite, and reduced psychomotor activity except for cases of agitative depression. Some forms, such as post-partum depression, have a high risk for suicidal attempts. Recent studies in humans and in animal models relate major depression occurrence and reoccurrence to alterations in dopaminergic activity, in addition to other neurotransmitter systems. Imaging studies detected decreased activity in the brain reward circuits in major depression. Therefore, the location of dopamine receptors in these circuits is relevant for understanding major depression. Interestingly, in cortico-striatal-dopaminergic pathways within the reward and cost circuits, the expression of dopamine and its contribution to reward are modulated by endocannabinoid receptors. These receptors are enriched in the striosomal compartment of striatum that selectively projects to dopaminergic neurons of substantia nigra compacta and is vulnerable to stress. This review aims to show the crosstalk between endocannabinoid and dopamine receptors and their vulnerability to stress in the reward circuits, especially in corticostriatal regions. The implications for novel treatments of major depression are discussed.

Entacapone promotes hippocampal neurogenesis in mice

Entacapone, a catechol-O-methyltransferase inhibitor, can strengthen the therapeutic effects of levodopa on the treatment of Parkinson’s disease. However, few studies are reported on whether entacapone can affect hippocampal neurogenesis in mice. To investigate the effects of entacapone, a modulator of dopamine, on proliferating cells and immature neurons in the mouse hippocampal dentate gyrus, 60 mice (7 weeks old) were randomly divided into a vehicle-treated group and the groups treated with 10, 50, or 200 mg/kg entacapone. The results showed that 50 and 200 mg/kg entacapone increased the exploration time for novel object recognition. Immunohistochemical staining results revealed that after entacapone treatment, the numbers of Ki67-positive proliferating cells, doublecortin-positive immature neurons, and phosphorylated cAMP response element-binding protein (pCREB)-positive cells were significantly increased. Western blot analysis results revealed that treatment with tyrosine kinase receptor B (TrkB) receptor antagonist significantly decreased the exploration time for novel object recognition and inhibited the expression of phosphorylated TrkB and brain-derived neurotrophic factor (BDNF). Entacapone treatment antagonized the effects of TrkB receptor antagonist. These results suggest that entacapone treatment promoted hippocampal neurogenesis and improved memory function through activating the BDNF-TrkB-pCREB pathway. This study was approved by the Institutional Animal Care and Use Committee of Seoul National University (approval No. SNU-130730-1) on February 24, 2014.

Hop Bitter Acids Increase Hippocampal Dopaminergic Activity in a Mouse Model of Social Defeat Stress

As daily lifestyle is closely associated with mental illnesses, diet-based preventive approaches are receiving attention. Supplementation with hop bitter acids such as iso-α-acids (IAA) and mature hop bitter acids (MHBA) improves mood states in healthy older adults. However, the underlying mechanism remains unknown. Since acute oral consumption with IAA increases dopamine levels in hippocampus and improves memory impairment via vagal nerve activation, here we investigated the effects of chronic administration of hop bitter acids on the dopaminergic activity associated with emotional disturbance in a mouse model of repeated social defeat stress (R-SDS). Chronic administration of IAA and MHBA significantly increased dopaminergic activity based on the dopamine metabolite to dopamine ratio in the hippocampus and medial prefrontal cortex following R-SDS. Hippocampal dopaminergic activity was inversely correlated with the level of R-SDS-induced social avoidance with or without IAA administration. Therefore, chronic treatment with hop bitter acids enhances stress resilience-related hippocampal dopaminergic activity.

Selective activation of D1 dopamine receptors exerts antidepressant-like activity in rats

BACKGROUND

Major depressive disorder is a common illness that severely decreases psychosocial functioning. Due to the major limitations of current treatments including response failure, it is crucial to develop better therapy strategies. Evidence suggests that dopamine dysregulation might play a major role in major depressive disorder physiopathology.

AIMS

This study investigates whether the dopamine D1 receptor agonist A77636 modulates antidepressant-like activity in rats.

METHODS

Rats were injected with an acute single dose of A77636 (0.75, 1.5 or 3 mg/kg), a potent and selective dopamine D1-like receptor agonist. Their locomotor activity, social interactions and behavioural response to the forced swim test were analysed 30 min after the injection.

RESULTS

During the forced swim test, the D1 agonist dose dependently reduced the immobility while the time of bursting was increased. Social interactions were significantly increased in the animals exposed to 3 mg/kg of A77636 whereas no significant changes were measured in general motor activity.

CONCLUSIONS

The present results provide evidence that pharmacological modulation of D1 receptor by the selective agonist A77636 induces antidepressant-like effects in rats, which encourages further studies regarding D1-specific modulation in major depressive disorder treatment.

Sex Differences in Dendritic Spine Formation in the Hippocampus and Animal Behaviors in a Mouse Model of Hyperthyroidism

Thyroid hormones are critical for the regulation of development and differentiation of neurons and glial cells in the central nervous system (CNS). We have previously reported the sex-dependent changes of glial morphology in the brain under the state of hyperthyroidism. Here, we examined sex-dependent changes in spine structure of granule neurons in the dentate gyrus of hippocampus in male and female mice with hyperthyroidism. Using FIB/SEM (focused ion beam/scanning electron microscopy), three-dimensional reconstructed structures of dendritic spines in dentate granule cells were analyzed. Dendritic spine density in granule cells increased significantly in both male and female mice with hyperthyroidism. The decrease in spine volume was observed only in female mice. These findings suggest that hyperthyroidism induces the formation of spines with normal size in male mice but the formation of spines with small size in female mice. To evaluate an outcome of neuronal and previously observed glial changes, behavioral tests were performed. Male mice with hyperthyroidism showed increased locomotor activity in the open field test, while female mice showed elevated immobility time in the tail suspension test, reflecting depression-like behavior. Although direct link between changes in spine and behavioral modifications requires further analysis, our results may help to understand gender-dependent neurological and psychological symptoms observed in patients with hyperthyroidism.

How do stupendous cannabinoids modulate memory processing via affecting neurotransmitter systems?

In the present study, we wanted to review the role of cannabinoids in learning and memory in animal models, with respect to their interaction effects with six principal neurotransmitters involved in learning and memory including dopamine, glutamate, GABA (γ-aminobutyric acid), serotonin, acetylcholine, and noradrenaline. Cannabinoids induce a wide-range of unpredictable effects on cognitive functions, while their mechanisms are not fully understood. Cannabinoids in different brain regions and in interaction with different neurotransmitters, show diverse responses. Previous findings have shown that cannabinoids agonists and antagonists induce various unpredictable effects such as similar effect, paradoxical effect, or dualistic effect. It should not be forgotten that brain neurotransmitter systems can also play unpredictable roles in mediating cognitive functions. Thus, we aimed to review and discuss the effect of cannabinoids in interaction with neurotransmitters on learning and memory. In addition, we mentioned to the type of interactions between cannabinoids and neurotransmitter systems. We suggested that investigating the type of interactions is a critical neuropharmacological issue that should be considered in future studies.

Deciphering cell-type specific signal transduction in the brain: Challenges and promises

Signal transduction designates the set of molecular events that take place within a cell upon extracellular stimulation to mediate a functional outcome. Decades after the discovery that dopamine triggers opposing signaling pathways in D1- and D2-expressing medium spiny neurons, it is now clear that there are as many different flavors of signaling pathways in the brain as there are neuron types. One of the biggest challenges in molecular neuroscience is to elucidate cell-type specific signaling, in order to understand neurological diseases with regional vulnerability, but also to identify targets for precision drugs devoid of off-target effects. Here, we make a case for the importance of the study of neuron-type specific molecular characteristics. We then review the technologies that exist to study neurons in their full diversity and highlight their disease-relevant idiosyncrasies.

The State of Our Understanding of the Pathophysiology and Optimal Treatment of Depression: Glass Half Full or Half Empty?

Major depressive disorder is a remarkably common and often severe psychiatric disorder associated with high levels of morbidity and mortality. Patients with major depression are prone to several comorbid psychiatric conditions, including posttraumatic stress disorder, anxiety disorders, obsessive-compulsive disorder, and substance use disorders, and medical conditions, including cardiovascular disease, diabetes, stroke, cancer, which, coupled with the risk of suicide, result in a shortened life expectancy. The goal of this review is to provide an overview of our current understanding of major depression, from pathophysiology to treatment. In spite of decades of research, relatively little is known about its pathogenesis, other than that risk is largely defined by a combination of ill-defined genetic and environmental factors. Although we know that female sex, a history of childhood maltreatment, and family history as well as more recent stressors are risk factors, precisely how these environmental influences interact with genetic vulnerability remains obscure. In recent years, considerable advances have been made in beginning to understand the genetic substrates that underlie disease vulnerability, and the interaction of genes, early-life adversity, and the epigenome in influencing gene expression is now being intensively studied. The role of inflammation and other immune system dysfunction in the pathogenesis of major depression is also being intensively investigated. Brain imaging studies have provided a firmer understanding of the circuitry involved in major depression, providing potential new therapeutic targets. Despite a broad armamentarium for major depression, including antidepressants, evidence-based psychotherapies, nonpharmacological somatic treatments, and a host of augmentation strategies, a sizable percentage of patients remain nonresponsive or poorly responsive to available treatments. Investigational agents with novel mechanisms of action are under active study. Personalized medicine in psychiatry provides the hope of escape from the current standard trial-and-error approach to treatment, moving to a more refined method that augurs a new era for patients and clinicians alike.

Contribution of D1R-expressing neurons of the dorsal dentate gyrus and Cav1.2 channels in extinction of cocaine conditioned place preference

Cocaine-associated contextual cues can trigger relapse behavior by recruiting the hippocampus. Extinction of cocaine-associated contextual memories can reduce cocaine-seeking behavior, however the molecular mechanisms within the hippocampus that underlie contextual extinction behavior and subsequent reinstatement remain poorly understood. Here, we extend our previous findings for a role of Ca_v1.2 L-type Ca²⁺ channels in dopamine 1 receptor (D1R)-expressing cells in extinction of cocaine conditioned place preference (CPP) in adult male mice. We report that attenuated cocaine CPP extinction in mice lacking Ca_v1.2 channels in D1R-expressing cells (D1^cre, Ca_v1.2^fl/fl) can be rescued through chemogenetic activation of D1R-expressing cells within the dorsal dentate gyrus (dDG), but not the dorsal CA1 (dCA1). This is supported by the finding that Ca_v1.2 channels are required in excitatory cells of the dDG, but not in the dCA1, for cocaine CPP extinction. Examination of the role of S1928 phosphorylation of Ca_v1.2, a protein kinase A (PKA) site using S1928A Ca_v1.2 phosphomutant mice revealed no extinction deficit, likely due to homeostatic scaling up of extinction-dependent S845 GluA1 phosphorylation in the dDG. However, phosphomutant mice failed to show cocaine-primed reinstatement which can be reversed by chemogenetic manipulation of excitatory cells in the dDG during extinction training. These findings outline an essential role for the interaction between D1R, Ca_v1.2, and GluA1 signaling in the dDG for extinction of cocaine-associated contextual memories.

Hippocampal mossy cell involvement in behavioral and neurogenic responses to chronic antidepressant treatment

Most antidepressants, including selective serotonin reuptake inhibitors (SSRIs), initiate their drug actions by rapid elevation of serotonin, but they take several weeks to achieve therapeutic onset. This therapeutic delay suggests slow adaptive changes in multiple neuronal subtypes and their neural circuits over prolonged periods of drug treatment. Mossy cells are excitatory neurons in the dentate hilus that regulate dentate gyrus activity and function. Here we show that neuronal activity of hippocampal mossy cells is enhanced by chronic, but not acute, SSRI administration. Behavioral and neurogenic effects of chronic treatment with the SSRI, fluoxetine, are abolished by mossy cell-specific knockout of p11 or Smarca3 or by an inhibition of the p11/AnxA2/SMARCA3 heterohexamer, an SSRI-inducible protein complex. Furthermore, simple chemogenetic activation of mossy cells using Gq-DREADD is sufficient to elevate the proliferation and survival of the neural stem cells. Conversely, acute chemogenetic inhibition of mossy cells using Gi-DREADD impairs behavioral and neurogenic responses to chronic administration of SSRI. The present data establish that mossy cells play a crucial role in mediating the effects of chronic antidepressant medication. Our results indicate that compounds that target mossy cell activity would be attractive candidates for the development of new antidepressant medications.

Expression of progenitor cell/immature neuron markers does not present definitive evidence for adult neurogenesis

It is agreed upon that adult hippocampal neurogenesis (AHN) occurs in the dentate gyrus (DG) in rodents. However, the existence of AHN in humans, particularly in elderly individuals, remains to be determined. Recently, several studies reported that neural progenitor cells, neuroblasts, and immature neurons were detected in the hippocampus of elderly humans, based on the expressions of putative markers for these cells, claiming that this provides evidence of the persistence of AHN in humans. Herein, we briefly overview the phenomenon that we call "dematuration," in which mature neurons dedifferentiate to a pseudo-immature status and re-express the molecular markers of neural progenitor cells and immature neurons. Various conditions can easily induce dematuration, such as inflammation and hyper-excitation of neurons, and therefore, the markers for neural progenitor cells and immature neurons may not necessarily serve as markers for AHN. Thus, the aforementioned studies have not presented definitive evidence for the persistence of hippocampal neurogenesis throughout adult life in humans, and we would like to emphasize that those markers should be used cautiously when presented as evidence for AHN. Increasing AHN has been considered as a therapeutic target for Alzheimer's disease (AD); however, given that immature neuronal markers can be re-expressed in mature adult neurons, independent of AHN, in various disease conditions including AD, strategies to increase the expression of these markers in the DG may be ineffective or may worsen the symptoms of such diseases.

Prior Activation of 5-HT7 Receptors Modulates the Conditioned Place Preference With Methylphenidate

The serotonin receptor subtype 7 (5-HT7R) is clearly involved in behavioral functions such as learning/memory, mood regulation and circadian rhythm. Recent discoveries proposed modulatory physiological roles for serotonergic systems in reward-guided behavior. However, the interplay between serotonin (5-HT) and dopamine (DA) in reward-related behavioral adaptations needs to be further assessed. TP-22 is a recently developed arylpiperazine-based 5-HT7R agonist, which is also showing high affinity and selectivity towards D1 receptors. Here, we report that TP-22 displays D1 receptor antagonist activity. Moreover, we describe the first in vivo tests with TP-22: first, a pilot experiment (assessing dosage and timing of action) identified the 0.25 mg/kg i.v. dosage for locomotor stimulation of rats. Then, a conditioned place preference (CPP) test with the DA-releasing psychostimulant drug, methylphenidate (MPH), involved three rat groups: prior i.v. administration of TP-22 (0.25 mg/kg), or vehicle (VEH), 90 min before MPH (5 mg/kg), was intended for modulation of conditioning to the white chamber (saline associated to the black chamber); control group (SAL) was conditioned with saline in both chambers. Prior TP-22 further increased the stimulant effect of MPH on locomotor activity. During the place-conditioning test, drug-free activity of TP-22+MPH subjects remained steadily elevated, while VEH+MPH subjects showed a decline. Finally, after a priming injection of TP-22 in MPH-free conditions, rats showed a high preference for the MPH-associated white chamber, which conversely had vanished in VEH-primed MPH-conditioned subjects. Overall, the interaction between MPH and pre-treatment with TP-22 seems to improve both locomotor stimulation and the conditioning of motivational drives to environmental cues. Together with recent studies, a main modulatory role of 5-HT7R for the processing of rewards can be suggested. In the present study, TP-22 proved to be a useful psychoactive tool to better elucidate the role of 5-HT7R and its interplay with DA in reward-related behavior.

Search for factors contributing to resistance to the electroconvulsive seizure treatment model using adrenocorticotrophic hormone-treated mice

Approximately one third of patients with depression remain treatment resistant with existing antidepressants, suggesting that the currently-available antidepressants cannot induce appropriate responses in the brains of all patients. Long-term exposure to adrenocorticotrophic hormone (ACTH) has been proposed as a model that mimics at least some aspects of clinical treatment-resistant depression in rodents. The purpose of this study was to explore potential causes of antidepressant treatment resistance using the chronic ACTH-treated mouse model. We subjected ACTH-treated mice to a rodent model of electroconvulsive therapy, i.e., electroconvulsive seizure (ECS), which induces various molecular and cellular changes, including in gene expression and adult neurogenesis in the hippocampus. First, behavioral effect of repeated ECS in the forced swim test (FST) was examined. In our experimental setting, ACTH-treated mice showed resistance to the antidepressant-like effect of ECS in the FST. We then examined which cellular and molecular changes induced by ECS were attenuated by ACTH administration. Chronic ACTH treatment suppressed the increase of gene expression such as of Bdnf, Npy, and Drd1 induced by ECS in the hippocampus. In contrast, there was no difference in ECS-induced promotion of the early neurogenetic process in the hippocampus between ACTH-treated and control mice. Our results suggest the possibility that impaired neuromodulation and monoamine signaling in the hippocampus are among the factors contributing to antidepressant treatment resistance.

Fluoxetine-induced dematuration of hippocampal neurons and adult cortical neurogenesis in the common marmoset

The selective serotonin reuptake inhibitor fluoxetine (FLX) is widely used to treat depression and anxiety disorders. Chronic FLX treatment reportedly induces cellular responses in the brain, including increased adult hippocampal and cortical neurogenesis and reversal of neuron maturation in the hippocampus, amygdala, and cortex. However, because most previous studies have used rodent models, it remains unclear whether these FLX-induced changes occur in the primate brain. To evaluate the effects of FLX in the primate brain, we used immunohistological methods to assess neurogenesis and the expression of neuronal maturity markers following chronic FLX treatment (3 mg/kg/day for 4 weeks) in adult marmosets (n = 3 per group). We found increased expression of doublecortin and calretinin, markers of immature neurons, in the hippocampal dentate gyrus of FLX-treated marmosets. Further, FLX treatment reduced parvalbumin expression and the number of neurons with perineuronal nets, which indicate mature fast-spiking interneurons, in the hippocampus, but not in the amygdala or cerebral cortex. We also found that FLX treatment increased the generation of cortical interneurons; however, significant up-regulation of adult hippocampal neurogenesis was not observed in FLX-treated marmosets. These results suggest that dematuration of hippocampal neurons and increased cortical neurogenesis may play roles in FLX-induced effects and/or side effects. Our results are consistent with those of previous studies showing hippocampal dematuration and increased cortical neurogenesis in FLX-treated rodents. In contrast, FLX did not affect hippocampal neurogenesis or dematuration of interneurons in the amygdala and cerebral cortex.

Transcriptomic evidence for immaturity induced by antidepressant fluoxetine in the hippocampus and prefrontal cortex

Aims

The molecular and cellular mechanisms underlying the antidepressant effects of fluoxetine in the brain are not fully understood. Emerging evidence has led to the hypothesis that chronic fluoxetine treatment induces dematuration of certain types of mature neurons in rodents. These studies have focused on the properties of typical molecular and/or electrophysiological markers for neuronal maturation. Nevertheless, it remains unknown whether dematuration‐related phenomena are present at the genome‐wide gene expression level.

Methods

Based on the aforementioned hypothesis, we directly compared transcriptome data between fluoxetine‐treated adult mice and those of naive infants in the hippocampus and medial prefrontal cortex (mPFC) to assess similarities and/or differences. We further investigated whether fluoxetine treatment caused dematuration in these brain regions in a hypothesis‐free manner using a weighted gene co‐expression network analysis (WGCNA).

Results

Gene expression patterns in fluoxetine‐treated mice resembled those in infants in the mPFC and, to a large extent, in the hippocampus. The gene expression patterns of fluoxetine‐treated adult mice were more similar to those of approximately 2‐week‐old infants than those of older mice. WGCNA confirmed that fluoxetine treatment was associated with maturation abnormalities, particularly in the hippocampus, and highlighted respective co‐expression modules for maturity and immaturity marker genes in the hippocampus in response to fluoxetine treatment.

Conclusions

Our results strongly support the hypothesis that chronic fluoxetine treatment induces dematuration in the adult mouse brain from a transcriptomic standpoint. Detection of discrete transcriptomic regulatory networks related to fluoxetine treatment may help to further elucidate the mechanisms of antidepressant action.

This study compares the transcriptomic profile of adult mice treated with clinically relevant dose of FLX and that of naïve infants in the hippocampus and medial prefrontal cortex (mPFC). We observed that gene expression profiles in FLX‐treated adult mice resembled those of infants in the mPFC and hippocampus. Our results provide support for the hypothesis that FLX can cause dematuration of the adult mouse brain to a more immature phenotype.