Interplay between serotonin 5-HT1A and 5-HT7 receptors in depressive disorders

Ingestion of Bifidobacterium longum subspecies infantis strain CCFM687 regulated emotional behavior and the central BDNF pathway in chronic stress-induced depressive mice through reshaping the gut microbiota

Probiotics which enhance the biosynthesis of 5-hydroxytryptamine in enterochromaffin cells could alleviate depression symptoms through regulating the CREB-BDNF pathway in the brain.

The Role of G-proteins and G-protein Regulating Proteins in Depressive Disorders

Progress toward new antidepressant therapies has been relatively slow over the past few decades, with the result that individuals suffering from depression often struggle to find an effective treatment – a process often requiring months. Furthermore, the neural factors that contribute to depression remain poorly understood, and there are many open questions regarding the mechanism of action of existing antidepressants. A better understanding of the molecular processes that underlie depression and contribute to antidepressant efficacy is therefore badly needed. In this review we highlight research investigating the role of G-proteins and the regulators of G-protein signaling (RGS) proteins, two protein families that are intimately involved in both the genesis of depressive states and the action of antidepressant drugs. Many antidepressants are known to indirectly affect the function of these proteins. Conversely, dysfunction of the G-protein and RGS systems can affect antidepressant efficacy. However, a great deal remains unknown about how these proteins interact with antidepressants. Findings pertinent to each individual G-protein and RGS protein are summarized from in vitro, in vivo, and clinical studies.

5-HT1F receptor regulates mitochondrial homeostasis and its loss potentiates acute kidney injury and impairs renal recovery

Our laboratory previously reported that agonists of the 5-hydoxytryptamine 1F (5-HT1F) receptor induce renal mitochondrial biogenesis (MB) and that stimulation of the 5-HT1F receptor following ischemia/reperfusion (I/R)-induced acute kidney injury (AKI) accelerated the recovery of renal function in mice. The goal of this study was to examine the contribution of the 5-HT1F receptor in the regulation of renal mitochondrial homeostasis and renal function in naïve and injured mice. Although 5-HT1F receptor knockout (KO) mice were healthy and fertile, and did not exhibit renal dysfunction, renal mitochondrial DNA copy number and mitochondrial fission gene expression increased at 10 wk of age. The 5-HT1F receptor KO mice exhibited greater proximal tubular injury and diminished renal recovery after I/R-induced AKI compared with wild-type mice. These findings were associated with persistent suppression of renal cortical MB and ATP levels after injury. In summary, the 5-HT1F receptor is a component of physiological MB regulation in the kidney, and its absence potentiates renal injury and impedes recovery.

Cyanobacterial extract with serotonin receptor subtype 7 (5-HT7 R) affinity modulates depression and anxiety-like behavior in mice

Marine cyanobacteria represent a unique source in the field of drug discovery due to the secondary metabolites they produce and the structural similarity these compounds have to endogenous mammalian receptor ligands. A series of cyanobacteria were subjected to extraction, fractionation by column chromatography and screened for affinity against CNS targets with a focus on serotonin receptors (5-HTRs). Out of 276 fractions screened, 21% had activity at 5-HTRs and/or the 5-HT transporter (SERT). One sample, a cyanobacterium identified by 16S rRNA sequencing as Leptolyngbya from Las Perlas archipelago in Panama, contained a fraction with noted affinity for the 5-HT₇ receptor (5-HT₇ R). This fraction (DUQ0002I) was screened via intracerebroventricular (ICV) injections in mice using depression and anxiety assays including the forced swim, tail suspension, elevated zero maze, and light-dark preference tests. DUQ0002I decreased depression and anxiety-like behaviors in males and did not have effects in 5-HT₇ R knockout or female mice. Administration of DUQ0002I to the CA1 of the hippocampus induced antidepression-like, but not anxiolytic-like behaviors. Testing of further purified materials showed no behavioral effects, leading us to hypothesize that the behavioral effects are likely caused by a synergistic effect between multiple compounds in the fraction. Finally, DUQ0002I was used in a model of neuropathic pain with comorbid depression (spared nerve injury-SNI). DUQ0002I had a similar antidepressant effect in animals with SNI, suggesting a role for the 5-HT₇ R in the development of comorbid pain and depression. These results demonstrate the potential that cyanobacterial metabolites have in the field of neuropharmacognosy.

Structure-Activity Relationships and Therapeutic Potentials of 5-HT7 Receptor Ligands: An Update

Serotonin 5-HT₇ receptor (5-HT₇R) has been the subject of intense research efforts because of its presence in brain areas such as the hippocampus, hypothalamus, and cortex. Preclinical data link the 5-HT₇R to a variety of central nervous system processes including the regulation of circadian rhythms, mood, cognition, pain processing, and mechanisms of addiction. 5-HT₇R blockade has antidepressant effects and may ameliorate cognitive deficits associated with schizophrenia. 5-HT₇R has been recently shown to modulate neuronal morphology, excitability, and plasticity, thus contributing to shape brain networks during development and to remodel neuronal wiring in the mature brain. Therefore, the activation of 5-HT₇R has been proposed as a therapeutic approach for neurodevelopmental and neuropsychiatric disorders associated with abnormal neuronal connectivity. This Perspective celebrates the silver jubilee of the discovery of 5-HT₇R by providing a survey of recent studies on the medicinal chemistry of 5-HT₇R ligands and on the neuropharmacology of 5-HT₇R.

Pharmacophore Comparison and Development of Recently Discovered Long Chain Arylpiperazine and Sulfonamide Based 5-HT7 Ligands

The serotonin system exerts its effects on the CNS and many peripheral systems. Of the 14 serotonin receptors, the 5-HT7 receptor is the most recently discovered. The 5-HT7 receptor has been shown to be involved in stress reduction, depression, and nociceptive control. Despite the 20 years since the discovery of 5-HT7R, there are still few truly selective ligands. Two of the common scaffolds for 5-HT7R ligands are long chain arylpiperazines (LCAPs) and sulfonamide containing compounds. This review focuses on recently developed (2014-2016) 5-HT7R ligands, their selectivity for the receptor, and suggests the possible new pharmacophore models for these ligands.

Re-evaluation of Adrenocorticotropic Hormone and Melanocyte Stimulating Hormone Activation of GPR139 in Vitro

It is now well established that GPR139, a G-protein coupled receptor exclusively expressed in the brain and pituitary, is activated by the essential amino acids L-tryptophan (L-Trp) and L-phenylalanine (L-Phe) via G_αq-coupling. The in vitro affinity and potency values of L-Trp and L-Phe are within the physiological concentration ranges of L-Trp and L-Phe. A recent paper suggests that adrenocorticotropic hormone (ACTH), α and β melanocyte stimulating hormones (α-MSH and β-MSH) and derivatives α-MSH_1-9/α-MSH_1-10 can also activate GPR139 in vitro. We tested this hypothesis using guanosine 5′-O-(3-[³⁵S]thio)-triphosphate binding (GTPγS), calcium mobilization and [³H]JNJ-63533054 radioligand binding assays. In the GTPγS binding assay, α-MSH, α-MSH_1-9/α-MSH_1-10, and β-MSH had no effect on [³⁵S]GTPγS incorporation in cell membranes expressing GPR139 up to 30 μM in contrast to the concentration dependent activation produced by L-Trp, JNJ-63533054, and TC-09311 (two small molecule GPR139 agonists). ACTH slightly decreased the basal level of [³⁵S]GTPγS incorporation at 30 μM. In the GPR139 radioligand binding assay, a moderate displacement of [³H]JNJ-63533054 binding by ACTH and β-MSH was observed at 30 μM (40 and 30%, respectively); α-MSH, α-MSH_1-9/α-MSH_1-10 did not displace any specific binding at 30 μM. In three different host cell lines stably expressing GPR139, α-MSH, and β-MSH did not stimulate calcium mobilization in contrast to L-Trp, JNJ-63533054, and TC-09311. ACTH, α-MSH_1-9/α-MSH_1-10 only weakly stimulated calcium mobilization at 30 μM (<50% of EC₁₀₀). We then co-transfected GPR139 with the three melanocortin (MC) receptors (MC3R, MC4R, and MC5R) to test the hypothesis that ACTH, α-MSH, and β-MSH might stimulate calcium mobilization through a MCR/GPR139 interaction. All three MC peptides stimulated calcium response in cells co-transfected with GPR139 and MC3R, MC4R, or MC5R. The MC peptides did not stimulate calcium response in cells expressing MC3R or MC5R alone consistent with the G_s signaling transduction pathway of these receptors. In agreement with the previously reported multiple signaling pathways of MC4R, including G_q transduction pathway, the MC peptides produced a calcium response in cells expressing MC4R alone. Together, our findings do not support that GPR139 is activated by ACTH, α-MSH, and β-MSH at physiologically relevant concentration but we did unravel an in vitro interaction between GPR139 and the MCRs.

Design, physico-chemical and pre-clinical evaluation of a homo-bivalent 99mTc-(BTZ)2DTPA radioligand for targeting dimeric 5-HT1A/5-HT7 receptors

A ^99mTc-labelled bis-benzothiazolone-DTPA radio-complex as a SPECT neuroimaging agent.

Spotlight on once-monthly long-acting injectable aripiprazole and its potential as maintenance treatment for bipolar I disorder in adult patients

The lack of long-term medication adherence is a challenge in the treatment of bipolar disorder, particularly during the maintenance phase when symptoms are less prominent. The rate of nonadherence is ~20%-60% depending on how strict a definition is used. Nonadherence worsens the course of bipolar disorder and can add hundreds of thousands of dollars to the lifetime cost of treating the illness. Long-acting injectable (LAI) medication is an attractive alternative to daily dosing of oral medication, especially among patients who are ambivalent about treatment. The purpose of this paper is to review the evidence for the safety and efficacy of LAI aripiprazole, which was recently approved for the treatment of bipolar disorder. The approval was based on a single double-blind, placebo-controlled, multisite trial that recruited participants from 103 sites in 7 countries. A total of 731 participants with bipolar disorder were enrolled in the study. Out of that total, 266 were successfully stabilized on LAI aripiprazole and entered the randomization phase. Treatment-emergent adverse events were, for the most part, mild to moderate. Akathisia was the most common adverse event, which, combined with restlessness, was experienced by 23% of the sample. At the end of the 52-week study period, nearly twice as many LAI-treated participants remained stable compared to those treated with placebo. Stability during the maintenance phase is arguably the most important goal of treatment. It is during this period of relative freedom from symptoms that patients are able to build a meaningful and satisfying life. The availability of a new treatment agent, particularly one that has the potential to enhance long-term adherence, is a welcome development.

Frameworking memory and serotonergic markers

The evidence for neural markers and memory is continuously being revised, and as evidence continues to accumulate, herein, we frame earlier and new evidence. Hence, in this work, the aim is to provide an appropriate conceptual framework of serotonergic markers associated with neural activity and memory. Serotonin (5-hydroxytryptamine [5-HT]) has multiple pharmacological tools, well-characterized downstream signaling in mammals’ species, and established 5-HT neural markers showing new insights about memory functions and dysfunctions, including receptors (5-HT1A/1B/1D, 5-HT2A/2B/2C, and 5-HT3-7), transporter (serotonin transporter [SERT]) and volume transmission present in brain areas involved in memory. Bidirectional influence occurs between 5-HT markers and memory/amnesia. A growing number of researchers report that memory, amnesia, or forgetting modifies neural markers. Diverse approaches support the translatability of using neural markers and cerebral functions/dysfunctions, including memory formation and amnesia. At least, 5-HT1A, 5-HT4, 5-HT6, and 5-HT7receptors and SERT seem to be useful neural markers and therapeutic targets. Hence, several mechanisms cooperate to achieve synaptic plasticity or memory, including changes in the expression of neurotransmitter receptors and transporters.

Allosteric Inhibition of Serotonin 5-HT7 Receptors by Zinc Ions

The allosteric regulation of G protein-coupled receptors (GPCRs) is a well-known phenomenon, but there are only a few examples of allosteric modulation within the metabotropic serotonergic receptor family. Recently, we described zinc non-competitive interactions toward agonist binding at serotonin 5-HT_1A receptors, in which biphasic effects, involving potentiation at sub-micromolar concentrations (10 μM) and inhibition at sub-millimolar concentrations (500 μM) of Zn²⁺ in radioligand binding assays, were consistent with both the agonist and antagonist-like effects of zinc ions observed in in vivo studies. Here, we showed new data demonstrating zinc allosteric inhibition of both agonist and antagonist binding at human recombinant 5-HT₇ receptors stably expressed in HEK293 cells as observed by radioligand binding studies as well as zinc neutral antagonism displayed by the concentration of 10 μM in the functional LANCE assay. The allosteric nature of the effect of Zn on 5-HT₇ receptors was confirmed (1) in saturation studies in which zinc inhibited the binding of potent orthosteric 5-HT₇ receptor radioligands, the agonist [³H]5-CT, and the two antagonists [³H]SB-269970 and [³H]mesulergine, showing ceiling effect and differences in the magnitude of negative cooperativity (α = 0.15, 0.06, and 0.25, respectively); (2) in competition experiments in which 500 μM of zinc inhibited all radioligand displacements by non-labeled orthosteric ligands (5-CT, SB-269970, and clozapine), and the most significant reduction in affinity was observed for the 5-CT agonist (4.9–16.7-fold) compared with both antagonists (1.4–3.9-fold); and (3) in kinetic experiments in which 500 μM zinc increased the dissociation rate constants for [³H]5-CT and [³H]mesulergine but not for [³H]SB-269970. Additionally, in the functional LANCE test using the constitutively active HEK293 cell line expressing the 5-HT₇ receptor, 10 μM zinc had features of neutral antagonism and increased the EC₅₀ value of the 5-CT agonist by a factor of 3.2. Overall, these results showed that zinc can act as a negative allosteric inhibitor of 5-HT₇ receptors. Given that the inhibiting effects of low concentrations of zinc in the functional assay represent the most likely direction of zinc activity under physiological conditions, among numerous zinc-regulated proteins, the 5-HT₇ receptor can be considered a serotonergic target for zinc modulation in the CNS.

New N- and O-arylpiperazinylalkyl pyrimidines and 2-methylquinazolines derivatives as 5-HT7 and 5-HT1A receptor ligands: Synthesis, structure-activity relationships, and molecular modeling studies

Based on our earlier studies of structure activity relationships on 4-substituted piperazine derivatives, in this work we synthesized a novel set of long-chain arylpiperazines with the purpose of elucidating if some structural modifications in the terminal fragment could affect the binding affinity for the 5-HT₇ and 5-HT_1A receptors. In this new series, the quinazolinone system of the previous derivatives was replaced by a 6-phenylpyrimidine or a 2-methylquinazoline, which were used as versatile building blocks for the preparation of new compounds. A 4-arylpiperazine moiety through a five methylene chain was anchored at the nitrogen or oxygen atom of the heterocyclic scaffolds. The substituents borne by the piperazine nucleus were phenyl, phenylmethyl, 3- or 4-chlorophenyl, and 2-ethoxyphenyl. Binding tests, performed on human cloned 5-HT₇ and 5-HT_1A receptors, showed that, among the newly synthesized derivatives, 4-[5-[4-(2-ethoxyphenyl)-1-piperazinyl]pentoxy]-6-phenyl-pyrimidine (13) and 3-[5-[4-(2-ethoxyphenyl)-1-piperazinyl]pentyl]-2-methyl-4(3H)-quinazolinone (20) displayed the best affinity values, K_i=23.5 and 8.42nM for 5-HT₇ and 6.96 and 2.99nM for 5-HT_1A receptors, respectively. Moreover, the functional properties for both compounds were further evaluated using the cAMP assay. Finally, a molecular modeling study has been performed for 5-HT₇ and 5-HT_1A receptor homology models to investigate the binding mode of N- and O-alkylated pyrimidinones/pyrimidines 4-13, 2-methylquinazolinones/quinazolines 17-22, and previously reported 2- and 3-substituted quinazolinones 23-30.

An Algorithm to Identify Target-Selective Ligands - A Case Study of 5-HT7/5-HT1A Receptor Selectivity

A computational procedure to search for selective ligands for structurally related protein targets was developed and verified for serotonergic 5-HT7/5-HT1A receptor ligands. Starting from a set of compounds with annotated activity at both targets (grouped into four classes according to their activity: selective toward each target, not-selective and not-selective but active) and with an additional set of decoys (prepared using DUD methodology), the SVM (Support Vector Machines) models were constructed using a selective subset as positive examples and four remaining classes as negative training examples. Based on these four component models, the consensus classifier was then constructed using a data fusion approach. The combination of two approaches of data representation (molecular fingerprints vs. structural interaction fingerprints), different training set sizes and selection of the best SVM component models for consensus model generation, were evaluated to determine the optimal settings for the developed algorithm. The results showed that consensus models with molecular fingerprints, a larger training set and the selection of component models based on MCC maximization provided the best predictive performance.

Design and synthesis of dual 5-HT1A and 5-HT7 receptor ligands

5-HT1A and 5-HT7 receptors have been at the center of discussions recently due in part to their major role in the etiology of major central nervous system diseases such as depression, sleep disorders, and schizophrenia. As part of our search to identify dual targeting ligands for these receptors, we have carried out a systematic modification of a selective 5HT7 receptor ligand culminating in the identification of several dual 5-HT1A and 5-HT7 receptor ligands. Compound 16, a butyrophenone derivative of tetrahydroisoquinoline (THIQ), was identified as the most potent agent with low nanomolar binding affinities to both receptors. Interestingly, compound 16 also displayed moderate affinity to other clinically relevant dopamine receptors. Thus, it is anticipated that compound 16 may serve as a lead for further exploitation in our quest to identify new ligands with the potential to treat diseases of CNS origin.

5-HT1A receptor gene silencers Freud-1 and Freud-2 are differently expressed in the brain of rats with genetically determined high level of fear-induced aggression or its absence

Serotonin 5-HT1A receptor is known to play a crucial role in the mechanisms of genetically defined aggression. In its turn, 5-HT1A receptor functional state is under control of multiple factors. Among others, transcriptional factors Freud-1 and Freud-2 are known to be involved in the repression of 5-HT1A receptor gene expression. However, implication of these factors in the regulation of behavior is unclear. Here, we investigated the expression of 5-HT1A receptor and silencers Freud-1 and Freud-2 in the brain of rats selectively bred for 85 generations for either high level of fear-induced aggression or its absence. It was shown that Freud-1 and Freud-2 levels were different in aggressive and nonaggressive animals. Freud-1 protein level was decreased in the hippocampus, whereas Freud-2 protein level was increased in the frontal cortex of highly aggressive rats. There no differences in 5-HT1A receptor gene expression were found in the brains of highly aggressive and nonaggressive rats. However, 5-HT1A receptor protein level was decreased in the midbrain and increased in the hippocampus of highly aggressive rats. These data showed the involvement of Freud-1 and Freud-2 in the regulation of genetically defined fear-induced aggression. However, these silencers do not affect transcription of the 5-HT1A receptor gene in the investigated rats. Our data indicate the implication of posttranscriptional rather than transcriptional regulation of 5-HT1A receptor functional state in the mechanisms of genetically determined aggressive behavior. On the other hand, the implication of other transcriptional regulators for 5-HT1A receptor gene in the mechanisms of genetically defined aggression could be suggested.

Effects of serotonin in the hippocampus: how SSRIs and multimodal antidepressants might regulate pyramidal cell function

The hippocampus plays an important role in emotional and cognitive processing, and both of these domains are affected in patients with major depressive disorder (MDD). Extensive preclinical research and the notion that modulation of serotonin (5-HT) neurotransmission plays a key role in the therapeutic efficacy of selective serotonin reuptake inhibitors (SSRIs) support the view that 5-HT is important for hippocampal function in normal and disease-like conditions. The hippocampus is densely innervated by serotonergic fibers, and the majority of 5-HT receptor subtypes are expressed there. Furthermore, hippocampal cells often co-express multiple 5-HT receptor subtypes that can have either complementary or opposing effects on cell function, adding to the complexity of 5-HT neurotransmission. Here we review the current knowledge of how 5-HT, through its various receptor subtypes, modulates hippocampal output and the activity of hippocampal pyramidal cells in rodents. In addition, we discuss the relevance of 5-HT modulation for cognitive processing in rodents and possible clinical implications of these results in patients with MDD. Finally, we review the data on how SSRIs and vortioxetine, an antidepressant with multimodal activity, affect hippocampal function, including cognitive processing, from both a preclinical and clinical perspective.

Yokukansan Increases 5-HT1A Receptors in the Prefrontal Cortex and Enhances 5-HT1A Receptor Agonist-Induced Behavioral Responses in Socially Isolated Mice

The traditional Japanese medicine yokukansan has an anxiolytic effect, which occurs after repeated administration. In this study, to investigate the underlying mechanisms, we examined the effects of repeated yokukansan administration on serotonin 1A (5-HT_1A) receptor density and affinity and its expression at both mRNA and protein levels in the prefrontal cortex (PFC) of socially isolated mice. Moreover, we examined the effects of yokukansan on a 5-HT_1A receptor-mediated behavioral response. Male mice were subjected to social isolation stress for 6 weeks and simultaneously treated with yokukansan. Thereafter, the density and affinity of 5-HT_1A receptors were analyzed by a receptor-binding assay. Levels of 5-HT_1A receptor protein and mRNA were also measured. Furthermore, (±)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT; a 5-HT_1A receptor agonist) was injected intraperitoneally, and rearing behavior was examined. Social isolation stress alone did not affect 5-HT_1A receptor density or affinity. However, yokukansan significantly increased receptor density and decreased affinity concomitant with unchanged protein and mRNA levels. Yokukansan also enhanced the 8-OH-DPAT-induced decrease in rearing behavior. These results suggest that yokukansan increases 5-HT_1A receptors in the PFC of socially isolated mice and enhances their function, which might underlie its anxiolytic effects.

Antidepressant- and Anxiolytic-Like Effects of New Dual 5-HT₁A and 5-HT₇ Antagonists in Animal Models

The aim of this study was to further characterize pharmacological properties of two phenylpiperazine derivatives: 1-{2-[2-(2,6-dimethlphenoxy)ethoxy]ethyl}-4-(2-methoxyphenyl)piperazynine hydrochloride (HBK-14) and 2-[2-(2-chloro-6-methylphenoxy)ethoxy]ethyl-4-(2- methoxyphenyl)piperazynine dihydrochloride (HBK-15) in radioligand binding and functional in vitro assays as well as in vivo models. Antidepressant-like properties were investigated in the forced swim test (FST) in mice and rats. Anxiolytic-like activity was evaluated in the four-plate test in mice and elevated plus maze test (EPM) in rats. Imipramine and escitalopram were used as reference drugs in the FST, and diazepam was used as a standard anxiolytic drug in animal models of anxiety. Our results indicate that HBK-14 and HBK-15 possess high or moderate affinity for serotonergic 5-HT₂, adrenergic α₁, and dopaminergic D₂ receptors as well as being full 5-HT_1A and 5-HT₇ receptor antagonists. We also present their potent antidepressant-like activity (HBK-14—FST mice: 2.5 and 5 mg/kg; FST rats: 5 mg/kg) and (HBK-15—FST mice: 1.25, 2.5 and 5 mg/kg; FST rats: 1.25 and 2.5 mg/kg). We show that HBK-14 (four-plate test: 2.5 and 5 mg/kg; EPM: 2.5 mg/kg) and HBK-15 (four-plate test: 2.5 and 5 mg/kg; EPM: 5 mg/kg) possess anxiolytic-like properties. Among the two, HBK-15 has stronger antidepressant-like properties, and HBK-14 displays greater anxiolytic-like activity. Lastly, we demonstrate the involvement of serotonergic system, particularly 5-HT_1A receptor, in the antidepressant- and anxiolytic-like actions of investigated compounds.

Prenatal stress, regardless of concurrent escitalopram treatment, alters behavior and amygdala gene expression of adolescent female rats

Depression during pregnancy has been linked to in utero stress and is associated with long-lasting symptoms in offspring, including anxiety, helplessness, attentional deficits, and social withdrawal. Depression is diagnosed in 10-20% of expectant mothers, but the impact of antidepressant treatment on offspring development is not well documented, particularly for females. Here, we used a prenatal stress model of maternal depression to test the hypothesis that in utero antidepressant treatment could mitigate the effects of prenatal stress. We also investigated the effects of prenatal stress and antidepressant treatment on gene expression related to GABAergic and serotonergic neurotransmission in the amygdala, which may underlie behavioral effects of prenatal stress. Nulliparous female rats were implanted with osmotic minipumps delivering clinically-relevant concentrations of escitalopram and mated. Pregnant dams were exposed to 12 days of mixed-modality stressors, and offspring were behaviorally assessed in adolescence (postnatal day 28) and adulthood (beyond day 90) to determine the extent of behavioral change. We found that in utero stress exposure, regardless of escitalopram treatment, increased anxiety-like behavior in adolescent females and profoundly influenced amygdala expression of the chloride transporters KCC2 and NKCC1, which regulate GABAergic function. In contrast, prenatal escitalopram exposure alone elevated amygdala expression of 5-HT1A receptors. In adulthood, anxiety-like behavior returned to baseline and gene expression effects in the amygdala abated, whereas deficits emerged in novel object recognition for rats exposed to stress during gestation. These findings suggest prenatal stress causes age-dependent deficits in anxiety-like behavior and amygdala function in female offspring, regardless of antidepressant exposure.

Genotype-Dependent Difference in 5-HT2C Receptor-Induced Hypolocomotion: Comparison with 5-HT2A Receptor Functional Activity

In the present study behavioral effects of the 5-HT2C serotonin receptor were investigated in different mouse strains. The 5-HT2C receptor agonist MK-212 applied intraperitoneally induced significant dose-dependent reduction of distance traveled in the open field test in CBA/Lac mice. This effect was receptor-specific because it was inhibited by the 5-HT2C receptor antagonist RS102221. To study the role of genotype in 5-HT2C receptor-induced hypolocomotion, locomotor activity of seven inbred mouse strains was measured after MK-212 acute treatment. We found that the 5-HT2C receptor stimulation by MK-212 decreased distance traveled in the open field test in CBA/Lac, C57Bl/6, C3H/He, and ICR mice, whereas it failed to affect locomotor activity in DBA/2J, Asn, and Balb/c mice. We also compared the interstrain differences in functional response to 5-HT2C and 5-HT2A receptors activation measured by the quantification of receptor-mediated head-twitches. These experiments revealed significant positive correlation between 5-HT2C and 5-HT2A receptors functional responses for all investigated mouse strains. Moreover, we found that 5-HT2A receptor activation with DOI did not change locomotor activity in CBA/Lac mice. Taken together, our data indicate the implication of 5-HT2C receptors in regulation of locomotor activity and suggest the shared mechanism for functional responses mediated by 5-HT2C and 5-HT2A receptors.

The role of the serotonin receptor subtypes 5-HT1A and 5-HT7 and its interaction in emotional learning and memory

Serotonin [5-hydroxytryptamine (5-HT)] is a multifunctional neurotransmitter innervating cortical and limbic areas involved in cognition and emotional regulation. Dysregulation of serotonergic transmission is associated with emotional and cognitive deficits in psychiatric patients and animal models. Drugs targeting the 5-HT system are widely used to treat mood disorders and anxiety-like behaviors. Among the fourteen 5-HT receptor (5-HTR) subtypes, the 5-HT_1AR and 5-HT₇R are associated with the development of anxiety, depression and cognitive function linked to mechanisms of emotional learning and memory. In rodents fear conditioning and passive avoidance (PA) are associative learning paradigms to study emotional memory. This review assesses the role of 5-HT_1AR and 5-HT₇R as well as their interplay at the molecular, neurochemical and behavioral level. Activation of postsynaptic 5-HT_1ARs impairs emotional memory through attenuation of neuronal activity, whereas presynaptic 5-HT_1AR activation reduces 5-HT release and exerts pro-cognitive effects on PA retention. Antagonism of the 5-HT_1AR facilitates memory retention possibly via 5-HT₇R activation and evidence is provided that 5HT₇R can facilitate emotional memory upon reduced 5-HT_1AR transmission. These findings highlight the differential role of these 5-HTRs in cognitive/emotional domains of behavior. Moreover, the results indicate that tonic and phasic 5-HT release can exert different and potentially opposing effects on emotional memory, depending on the states of 5-HT_1ARs and 5-HT₇Rs and their interaction. Consequently, individual differences due to genetic and/or epigenetic mechanisms play an essential role for the responsiveness to drug treatment, e.g., by SSRIs which increase intrasynaptic 5-HT levels thereby activating multiple pre- and postsynaptic 5-HTR subtypes.

Orexin receptors exert a neuroprotective effect in Alzheimer's disease (AD) via heterodimerization with GPR103

Orexins are neuropeptides that regulate the sleep-wake cycle and feeding behaviour. QRFP is a newly discovered neuropeptide which exerts similar orexigenic activity, thus playing an important role in energy homeostasis and regulation of appetite. The exact expression and signalling characteristics and physiological actions of QRFP and its receptor GPR103 are poorly understood. Alzheimer's disease (AD) patients experience increased nocturnal activity, excessive daytime sleepiness, and weight loss. We hypothesised therefore that orexins and QRFP might be implicated in the pathophysiology of AD. We report that the down-regulation of hippocampal orexin receptors (OXRs) and GPR103 particularly in the cornu ammonis (CA) subfield from AD patients suffering from early onset familial AD (EOFAD) and late onset familial AD (LOAD). Using an in vitro model we demonstrate that this downregulation is due to to Aβ-plaque formation and tau hyper-phosphorylation. Transcriptomics revealed a neuroprotective role for both orexins and QRFP. Finally we provide conclusive evidence using BRET and FRET that OXRs and GPR103 form functional hetero-dimers to exert their effects involving activation of ERK1/2. Pharmacological intervention directed at the orexigenic system may prove to be an attractive avenue towards the discovery of novel therapeutics for diseases such as AD and improving neuroprotective signalling pathways.

IL-4 Knock Out Mice Display Anxiety-Like Behavior

Inflammation is a recognized antecedent and coincident factor when examining the biology of anxiety. Little is known, however, about how reductions in endogenous anti-inflammatory mediators impact anxiety. Therefore, mood- cognition- and anxiety-associated/like behaviors were examined in IL-4 knock out (KO) mice and wild-type (WT) mice. In comparison to WT mice, IL-4 KO mice demonstrated decreased burrowing and increased social exploration. No differences were seen in forced swim or saccharine preference testing. IL-4 KO mice had similar performance to WT mice in the Morris water maze and during object location and novel object recognition. In the elevated zero-maze, IL-4 KO mice, in comparison to WT mice, demonstrated anxiety-like behavior. Anxiety-like behavior in IL-4 KO mice was not observed, however, during open-field testing. Taken together, these data indicate that IL-4 KO mice display state, but not trait, anxiety suggesting that reductions in endogenous anti-inflammatory bioactives can engender subtypes of anxiety.

Patent Highlights

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.