Activation of 5-HT1A postsynaptic receptors by NLX-101 results in functional recovery and an increase in neuroplasticity in mice with brain ischemia

The antidepressant-like effect and proposed mechanism of action of TPN672MA, a novel serotonin-dopamine receptor modulator for the treatment of schizophrenia

TPN672MA, an innovative antipsychotic drug candidate currently in clinical trials, acts as a dopamine D2/D3 receptor partial agonist, serotonin 5-HT1A receptor agonist, and serotonin 5-HT2A receptor antagonist. Preclinical investigations have demonstrated its potential in treating the core symptoms of schizophrenia. The present study highlights TPN672MA's significant antidepressant-like effects in classical behavioral models, such as the chronic social defeat stress paradigm. The pronounced 5-HT1A receptor agonism and D2/D3 receptor partial agonism of TPN672MA likely contribute to its therapeutic effects in depression. Additionally, TPN672MA's antidepressant-like efficacy may be linked to its ability to enhance the expression levels of brain-derived neurotrophic factor (BDNF) and postsynaptic density protein-95 (PSD95) in the hippocampus. Furthermore, TPN672MA displayed a more rapid onset of antidepressant-like action. In conclusion, TPN672MA represents a promising new drug candidate for the treatment of symptoms of schizophrenia and depression.

Pesticide-Induced Alterations in Locomotor Activity, Anxiety, and Depression-like Behavior Are Mediated through Oxidative Stress-Related Autophagy: A Persistent Developmental Study in Mice

Chlorpyrifos (CPF), dichlorvos (DDV), and cypermethrin (CP), as commonly used pesticides, have been implicated in inducing neuropsychiatric disorders, such as anxiety, depression-like behaviors, and locomotor activity impairment. However, the exact molecular mechanisms of these adverse effects, particularly in both sexes and their next-generation effects, remain unclear. In this study, we conducted behavioral analysis, along with cellular assays (monodansylcadaverine staining) and molecular investigations (qRT-PCR and western blotting of mTOR, P62, and Beclin-1) to clear the potential role of autophagy in pesticide-induced behavioral alterations. For this purpose, 42 adult female and 21 male inbred ICR mice (F0) were distributed into seven groups. Maternal mice (F0) and 112 F1 offspring were exposed to 0.5 and 1 ppm of CPF, DDV, and CP through drinking water. F1 male and female animals were studied to assess the sex-specific effects of pesticides on brain tissue. Our findings revealed pronounced anxiogenic effects and impaired locomotor activity in mice. F1 males exposed to CPF (1 ppm) exhibited significantly elevated depression-like behaviors compared to other groups. Moreover, pesticide exposure reduced mTOR and P62 levels, while enhancing the Beclin-1 gene and protein expression. These changes in autophagy signaling pathways, coupled with oxidative and neurogenic damage in the cerebral cortex and hippocampus, potentially contribute to heightened locomotor activity, anxiety, and depression-like behaviors following pesticide exposure. This study underscores the substantial impact of pesticides on both physiological and behavioral aspects, emphasizing the necessity for comprehensive assessments and regulatory considerations for pesticide use. Additionally, the identification of sex-specific responses presents a crucial dimension for pharmaceutical sciences, highlighting the need for tailored therapeutic interventions and further research in this field.

Mitochondrial antioxidant elamipretide improves learning and memory impairment induced by chronic sleep deprivation in mice

BACKGROUND

The inflammation and synaptic dysfunction induced by mitochondrial dysfunction play essential roles in the learning and memory impairment associated with sleep dysfunction. Elamipretide (SS-31), a novel mitochondrion-targeted antioxidant, was proven to improve mitochondrial dysfunction, the inflammatory response, synaptic dysfunction, and cognitive impairment in models of cerebral ischemia, sepsis, and type 2 diabetes. However, the potential for SS-31 to improve the cognitive impairment induced by chronic sleep deprivation (CSD) and its underlying mechanisms is unknown.

METHODS

Adult c57BL/6J mice were subjected to CSD for 21 days using an activity wheel accompanied by daily intraperitoneal injection of SS-31 (5 mg/kg). The novel object recognition and Morris water maze test were used to evaluate hippocampus-dependent cognitive function. Western blotting and reverse transcription-quantitative polymerase chain reaction assays were used to determine the effects of CSD and SS-31 on markers of mitochondria, inflammation response, and synaptic function. Enzyme-linked immunosorbent assays were used to examine the levels of proinflammatory cytokines.

RESULTS

SS-31 could improve the cognitive impairment induced by CSD. In particular, SS-31 treatment restored the CSD-induced decrease in sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor γ coactivator alpha levels and the increase in levels nuclear factor kappa-B and inflammatory cytokines, including interleukin (IL)-1β, IL-6, and tumor necrosis factor-alpha. Furthermore, SS-31 significantly increased the levels of brain-derived neurotrophic factor, postsynaptic density protein-95, and synaptophysin in CSD mice.

CONCLUSION

Taken together, these results suggest that SS-31 could improve CSD-induced mitochondrial biogenesis dysfunction, inflammatory response, synaptic dysfunction, and cognitive impairment by increasing SIRT1 expression levels.

Sleep deprivation aggravates lipopolysaccharide-induced anxiety, depression and cognitive impairment: The role of pro-inflammatory cytokines and synaptic plasticity-associated proteins

Growing evidence indicates that neuroinflammation plays a critical role in anxiety, depression, and cognitive impairment. Sleep loss disrupts the host's immune balance and increases neuroinflammation. This study explored whether chronic sleep deprivation aggravates lipopolysaccharide-induced anxiety, depression, and cognitive impairment and assessed the underlying mechanisms. Lipopolysaccharide (250 μg/kg) was administered to adult mice for 9 days, accompanied with daily intermittent sleep deprivation from 12:00 to 18:00 by using an activity wheel. Anxiety, depression, and cognitive function were evaluated using a task battery consisting of an open field, elevated plus maze, tail suspension, forced swimming, and Morris water maze tests. The levels of pro-inflammatory cytokines and synaptic plasticity-associated proteins were examined by enzyme-linked immunosorbent assay and western blot, respectively. The results showed that lipopolysaccharide increased anxiety- and depression-like behaviors, impaired cognitive function, uprelated interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α), and decreased brain-derived neurotrophic factor (BDNF), postsynaptic density-95 (PSD-95), and synaptophysin (SYN), which were aggravated by chronic sleep deprivation. These results suggest that chronic sleep deprivation exerted adverse effects on lipopolysaccharide-induced anxiety, depression, and cognitive impairment, which was associated with changes in pro-inflammatory cytokines and synaptic plasticity associated proteins.

The antidepressant-like effects of escitalopram in mice require salt-inducible kinase 1 and CREB-regulated transcription co-activator 1 in the paraventricular nucleus of the hypothalamus

BACKGROUND

The salt-inducible kinase 1 (SIK1)-CREB-regulated transcription co-activator 1 (CRTC1) system in the paraventricular nucleus (PVN) of the hypothalamus has been demonstrated to participate in not only depression neurobiology but also the antidepressant mechanisms of fluoxetine, paroxetine, venlafaxine, and duloxetine. Like fluoxetine and paroxetine, escitalopram is also a well-known selective serotonin (5-HT) reuptake inhibitor (SSRI). However, recently it has been found that escitalopram can modulate a lot of targets other than the 5-HT system. Here, we speculate that escitalopram produces effects on the SIK1-CRTC1 system in the PVN.

METHODS

Two mice models of depression (chronic social defeat stress (CSDS) and chronic unpredictable mild stress (CUMS)), various behavioral tests, enzyme linked immunosorbent assay (ELISA), western blotting, co-immunoprecipitation (Co-IP), quantitative real-time reverse transcription PCR (qRT-PCR), immunofluorescence, and adeno-associated virus (AAV)-mediated gene transfer were used together in the present study.

RESULTS

It was found that escitalopram administration not only significantly prevented the hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis induced by CSDS and CUMS, but also notably reversed the effects of CSDS and CUMS on SIK1, CRTC1, and CRTC1-CREB binding in the PVN of mice. AAV-based genetic knock-down of SIK1 in PVN neurons evidently abolished the antidepressant-like effects of escitalopram in mice.

LIMITATION

A shortage of this study is that only rodent models of depression were used, while human samples were not included.

CONCLUSIONS

In summary, regulating the SIK1-CRTC1 system in the PVN participates in the antidepressant mechanism of escitalopram, which extends the knowledge of the pharmacological actions of escitalopram.

A new perspective on hippocampal synaptic plasticity and post-stroke depression

Post-stroke depression, a common complication after stroke, severely affects the recovery and quality of life of patients with stroke. Owing to its complex mechanisms, post-stroke depression treatment remains highly challenging. Hippocampal synaptic plasticity is one of the key factors leading to post-stroke depression; however, the precise molecular mechanisms remain unclear. Numerous studies have found that neurotrophic factors, protein kinases and neurotransmitters influence depressive behaviour by modulating hippocampal synaptic plasticity. This review further elaborates on the role of hippocampal synaptic plasticity in post-stroke depression by summarizing recent research and analysing possible molecular mechanisms. Evidence for the correlation between hippocampal mechanisms and post-stroke depression helps to better understand the pathological process of post-stroke depression and improve its treatment.

Arsenic exposure induced anxiety-like behaviors in male mice via influencing the GABAergic Signaling in the prefrontal cortex

Arsenic contamination in drinking water causes a global public health problem. Emerging evidence suggests that arsenic may act as an environmental risk factor for anxiety disorders. However, the exact mechanism underlying the adverse effects has not been fully elucidated. This study aimed to evaluate the anxiety-like behaviors of mice exposed to arsenic trioxide (As2O3), to observe the neuropathological changes, and to explore the link between the GABAergic system and behavioral manifestations. For this purpose, male C57BL/6 mice were exposed to various doses of As2O3 (0, 0.15, 1.5, and 15 mg/L) through drinking water for 12 weeks. Anxiety-like behaviors were assessed using the open field test (OFT), light/dark choice test, and elevated zero maze (EZM). Neuronal injuries in the cerebral cortex and hippocampus were assessed by light microscopy with H&E and Nissl staining. Ultrastructural alteration in the cerebral cortex was assessed by transmission electron microscope (TEM). The expression levels of GABAergic system-related molecules (i.e., glutamate decarboxylase, GABA transporter, and GABAB receptor subunits) in the prefrontal cortex (PFC) were determined by qRT-PCR and western blotting. Arsenic exposure showed a striking anxiogenic effect on mice, especially in the group exposed to 15 mg/L As2O3. Light microscopy showed neuron necrosis and reduced cell counts. TEM revealed marked ultrastructural changes, including the vacuolated mitochondria, disrupted Nissl bodies, an indentation in the nucleus membrane, and delamination of myelin sheath in the cortex. In addition, As2O3 influenced the GABAergic system in the PFC by decreasing the expression of the glutamate decarboxylase 1 (GAD1) and the GABAB2 receptor subunit, but not the GABAB1 receptor subunit. To sum up, sub-chronic exposure to As2O3 is associated with increased anxiety-like behaviors, which may be mediated by altered GABAergic signaling in the PFC. These findings shed light on the mechanisms responsible for the neurotoxic effects of arsenic and therefore more cautions should be taken.

A pilot controlled trial of a combination of electroacupuncture and psychological intervention for post-stroke depression

OBJECTIVE

This study was to investigate effects of a combination of electroacupuncture (EA) and psychological intervention (PI) for post-stroke depression (PSD) and provide treatment suggestions METHODS: In a single-blind, randomized controlled trial, 49 patients with PSD were randomly divided into two groups, PI group (n = 23) and PI+EA group (n = 26). PI group received PI 2 times a week by a professional psychologist. In addition to PI treatment, PI+EA group was treated with EA at GB13 and HT7, 30 min, 5 times a week, 4 weeks as a course of treatment, a total of 12 weeks. The 17-item Hamilton Rating Scale for Depression (HAMD-17) and Lo Knapp Ron J's sleep score table were measured before treatment, 4 weeks, 8 weeks and 12 weeks after treatment.

RESULTS

After 12 weeks of PI or PI+EA therapy, 42 of 49 patients were effective and 7 were ineffective, with an effective rate of 85.7 %. Among them, the effective rate of PI group alone was 78.3 %, and the effective rate of PI+EA group was 92.3 %. Compared with values of PI, HAMD-17 values at 8 weeks of PI+EA treatment were significantly decreased (P < 0.01). At the same time, Sleep Score table was significantly decreased after PI+EA treatment (P < 0.05). Incidence of adverse events was not different in the two groups CONCLUSION: A combination of EA and PI maybe an effective and safe treatment option for PSD, which is statistically more significant than PI treatment alone. Due to small samples involved in this pilot study, further research is needed to see whether a combination of EA and PI will match the results of this pilot study.

Congenital anomalies and spontaneous abortion in mice resulting from the use of escitalopram

CONTEXT

Escitalopram (ESC) use during pregnancy has not been associated with teratogenic effects in fetuses.

AIMS

To investigate whether ESC administered during pregnancy in mice induces maternal toxicity and teratogenicity in offspring.

METHODS

Treated mice groups G1 and control G0 (n =15 per group). Administration of ESC (G1) and saline solution (G0) during pregnancy and euthanasia on the 18thday. Pregnant female mice were treated with ESC (20mg/kg, via gavage) or saline solution (control group) from the 5th to the 17thday of gestation, when implantation was consolidated. During intraembryonic development until the day before delivery, the drug had an influence on the development of alterations from its maintenance in the uterine environment and its development to the disturbance causing skeletal or visceral malformations.

KEY RESULTS

The intrauterine development parameters that were altered by ESC treatment were: number of resorptions (G0: [0.93±0.24]); G1: [3.33±0.51]), post-implantation loss (G0: [3.95±1.34], G1: [13.75±3.62]) and reduced fetal viability: [97.30±1.00]; G1: [81.09±6.22]). Regarding fetal formation, the treated group had visceral malformations with a significant frequency: cleft palate (G0: [1.0%], G1: [11.86%]) and reduced kidneys (G0: [0%]; G1: [10.17%]). Regarding skeletal malformations, a higher frequency was observed in the following parameters: incomplete supraoccipital ossification (G0: [0%], G1: [15.25]), absence of ribs (G0: [0%], G1 (G0: [0%], G1 [15.25%]) and absence of one or more of the foot phalanges (G0: [1.0%]; 64%]).

CONCLUSION

Results indicate that ESC is an embryotoxic and teratogenic drug.

IMPLICATIONS

Until further studies are performed, greater caution is necessary in prescribing the drug to pregnant women.

The role of serotonin neurotransmission in rapid antidepressant actions

RATIONALE

Ketamine has rapid antidepressant effects that represent a significant advance in treating depression, but its poor safety and tolerability limit its clinical utility. Accreting evidence suggests that serotonergic neurotransmission participates in the rapid antidepressant effects of ketamine and hallucinogens. Thus, understanding how serotonin contributes to these effects may allow identification of novel rapid antidepressant mechanisms with improved tolerability.

OBJECTIVE

The goal of this paper is to understand how serotonergic mechanisms participate in rapid antidepressant mechanisms.

METHODS

We review the relevance of serotonergic neurotransmission for rapid antidepressant effects and evaluate the role of 5-HT_1A, 5-HT_1B, 5-HT_2A, and 5-HT₄ receptors in synaptic plasticity, BDNF signaling, and GSK-3β activity. Subsequently, we develop hypotheses on the relationship of these receptor systems to rapid antidepressant effects.

RESULTS

We found that 5-HT_1A and 5-HT_1B receptors may participate in ketamine's rapid antidepressant mechanisms, while agonists at 5-HT_2A and 5-HT₄ receptors may independently behave as rapid antidepressants. 5-HT_1A, 5-HT_2A, and 5-HT₄ receptors increase synaptic plasticity in the cortex or hippocampus but do not consistently increase BDNF signaling. We found that 5-HT_1A and 5-HT_1B receptors may participate in rapid antidepressant mechanisms as a consequence of increased BDNF signaling, rather than a cause. 5-HT_2A and 5-HT₄ receptor agonists may increase BDNF signaling, but these relationships are tenuous and need more study. Finally, we found that ketamine and several serotonergic receptor systems may mechanistically converge on reduced GSK-3β activity.

CONCLUSIONS

We find it plausible that serotonergic neurotransmission participates in rapid antidepressant mechanisms by increasing synaptic plasticity, perhaps through GSK-3β inhibition.

Molecular Signaling Mechanisms for the Antidepressant Effects of NLX-101, a Selective Cortical 5-HT1A Receptor Biased Agonist

Depression is the most prevalent of the mental illnesses and serotonin (5-hydroxytryptamine, 5-HT) is considered to be the major neurotransmitter involved in its etiology and treatment. In this context, 5-HT_1A receptors have attracted interest as targets for therapeutic intervention. Notably the activation of presynaptic 5-HT_1A autoreceptors delays antidepressant effects whereas the stimulation of postsynaptic 5-HT_1A heteroreceptors is needed for an antidepressant action. NLX-101 (also known as F15599) is a selective biased agonist which exhibits preferred activation of cortical over brain stem 5-HT_1A receptors. Here, we used behavioral, neurochemical and molecular methods to examine the antidepressant-like effects in rats of a single dose of NLX-101 (0.16 mg/kg, i.p.). NLX-101 reduced immobility in the forced swim test when measured 30 min but not 24 h after drug administration. NLX-101 increased extracellular concentrations of glutamate and dopamine in the medial prefrontal cortex, but no changes were detected in the efflux of noradrenaline or 5-HT. NLX-101 also produced an increase in the activation of pmTOR, pERK1/2 and pAkt, and the expression of PSD95 and GluA1, which may contribute to its rapid antidepressant action.

Biased 5-HT1A receptor agonists F13714 and NLX-101 differentially affect pattern separation and neuronal plasticity in rats after acute and chronic treatment

Pattern separation is a hippocampal process in which highly similar stimuli are recognized as separate representations, and deficits could lead to memory impairments in neuropsychiatric disorders such as schizophrenia. The 5-HT_1A receptor (5-HT_1AR) is believed to be involved in these hippocampal pattern separation processes. However, in the dorsal raphe nucleus (DRN), the 5-HT_1AR is expressed as a somatodendritic autoreceptor, negatively regulates serotonergic signaling, and could thereby counteract the effects of hippocampal postsynaptic 5-HT_1A receptors. Therefore, this study aims to identify how pre- and post-synaptic 5-HT_1AR activity affects pattern separation. Object pattern separation (OPS) performance was measured in male Wistar rats after both acute and chronic treatment (i.p.) with 5-HT_1AR biased agonists F13714 (0.0025 mg/kg acutely, 0.02 mg/kg/day chronically) or NLX-101 (0.08 mg/kg acutely, 0.32 mg/kg/day chronically), which preferentially activate autoreceptors or postsynaptic receptors respectively, for 14 days. Body temperature - a functional correlate of hypothalamic 5-HT_1AR stimulation - was measured daily. Additionally, 5-HT_1AR density (DRN) and plasticity markers (hippocampus) were assessed. Acute treatment with F13714 impaired OPS performance, whereas chronic treatment normalized this, and a drop in body temperature was found from day 4 onwards. NLX-101 enhanced OPS performance acutely and chronically, and caused an acute drop in body temperature. Chronic NLX-101 treatment increased doublecortin positive neurons in the dorsal hippocampus, while chronic treatment with F13714 resulted in a downregulation of 5-HT_1A autoreceptors, which likely reversed the acute impairment in OPS performance. Chronic treatment with NLX-101 appears to have therapeutic potential to improve brain plasticity and OPS performance.

Positive effects of roflumilast on behavior, neuroinflammation, and white matter injury in mice with global cerebral ischemia

Inhibition of phosphodiesterase 4 (PDE4) is a promising pharmacological strategy for the treatment of cerebral ischemic conditions. To increase the relevance and increase the translational value of preclinical studies, it is important to conduct experiments using different animal species and strains, different animal models, and to evaluate long-term functional outcomes after cerebral ischemia. In the present study, the effects of the selective PDE4 inhibitor roflumilast were evaluated in vivo and in vitro. Balb/c mice were subjected to bilateral common carotid artery occlusion (BCCAO) and tested during 21 days in multiple behavioral tasks to investigate the long-term effects of roflumilast on functional recovery. The effects of roflumilast were also investigated on hippocampal cell loss, white matter injury, and expression of neuroinflammatory markers. Roflumilast prevented cognitive and emotional deficits induced by BCCAO in mice. Roflumilast also prevented neurodegeneration and reduced the white matter damage in the brain of ischemic animals. Besides, roflumilast decreased Iba-1 (microglia marker) levels and increased Arginase-1 (Arg-1; microglia M2 phenotype marker) levels in the hippocampus of these mice. Likewise, roflumilast suppressed inducible nitric oxide synthase (microglia M1 phenotype marker) expression and increased Arg-1 levels in a primary mouse microglia culture. These findings support evidence that PDE4 inhibition by roflumilast might be beneficial in cerebral ischemic conditions. The neuroprotective effects of roflumilast appear to be mediated by a decrease in neuroinflammation.

Differential effects of memory enhancing and impairing doses of methylphenidate on serotonin metabolism and 5-HT1A, GABA, glutamate receptor expression in the rat prefrontal cortex

Methylphenidate (MPD), a psychostimulant, is a prescription medicine for treating attention deficit hyperactivity disorder (ADHD). Previously we have shown that moderate doses of MPD enhanced learning and memory while higher doses impaired it. To understand neurochemical mechanisms and receptors involved in memory enhancing and impairing effects of MPD, the present study concerns the effects of these doses of MPD on serotonin, 5-HT1A, GABA, and NMDA receptor mRNA expression in the prefrontal cortex (PFC). We found that low doses (2.5 mg/kg) of MPD improved performance in the water-maze test but higher doses (5 mg/kg) impaired memory retention. Animals showing improved performance had high 5-HT metabolism in the PFC while these levels were not affected in the group treated with higher MPD doses and exhibiting impaired memory. There was downregulation of 5-HT1A receptors in the PFC of rats treated with higher dose MPD, which didn't occur in low dose of MPD treated animals. Further, a decrease in GABA_Areceptor mRNA expression occurred in low doses of MPD treated animals and GluN2A expression was reduced in higher doses of MPD treated animals. The findings suggest that memory enhancing doses of MPD increase 5-HT and reduce GABA_A receptor mRNA expression in the PFC to release excitatory glutamate neurons from the inhibitory influence of GABA. Conversely, higher dose of MPD downregulates 5-HT1A receptor mRNA expression to enhance inhibitory GABA influence on glutamate neurons and impair cognitive performance. The findings show an important role of 5-HT1A heteroreceptors in the PFC for improving therapeutic use of MPD and developing novel cognitive enhancers.

Cannabidiol Confers Neuroprotection in Rats in a Model of Transient Global Cerebral Ischemia: Impact of Hippocampal Synaptic Neuroplasticity

Evidence for the clinical use of neuroprotective drugs for the treatment of cerebral ischemia (CI) is still greatly limited. Spatial/temporal disorientation and cognitive dysfunction are among the most prominent long-term sequelae of CI. Cannabidiol (CBD) is a non-psychotomimetic constituent of Cannabis sativa that exerts neuroprotective effects against experimental CI. The present study investigated possible neuroprotective mechanisms of action of CBD on spatial memory impairments that are caused by transient global cerebral ischemia (TGCI) in rats. Hippocampal synaptic plasticity is a fundamental mechanism of learning and memory. Thus, we also evaluated the impact of CBD on neuroplastic changes in the hippocampus after TGCI. Wistar rats were trained to learn an eight-arm aversive radial maze (AvRM) task and underwent either sham or TGCI surgery. The animals received vehicle or 10 mg/kg CBD (i.p.) 30 min before surgery, 3 h after surgery, and then once daily for 14 days. On days 7 and 14, we performed a retention memory test. Another group of rats that received the same pharmacological treatment was tested in the object location test (OLT). Brains were removed and processed to assess neuronal degeneration, synaptic protein levels, and dendritic remodeling in the hippocampus. Cannabidiol treatment attenuated ischemia-induced memory deficits. In rats that were subjected to TGCI, CBD attenuated hippocampal CA1 neurodegeneration and increased brain-derived neurotrophic factor levels. Additionally, CBD protected neurons against the deleterious effects of TGCI on dendritic spine number and the length of dendritic arborization. These results suggest that the neuroprotective effects of CBD against TGCI-induced memory impairments involve changes in synaptic plasticity in the hippocampus.

Knockout of NPFFR2 Prevents LPS-Induced Depressive-Like Responses in Mice

The precise neural mechanisms underlying the pathogenesis of depression are largely unknown, though stress-induced brain inflammation and serotonergic plasticity are thought to be centrally involved. Moreover, we previously demonstrated that neuropeptide FF receptor 2 (NPFFR2) overexpression provokes depressive-like behaviors in mice. Here, we assess whether NPFFR2 is involved in priming of depressive-like behaviors and downregulation of serotonergic 1A receptor (5HT1AR) after lipopolysaccharide (LPS) treatment. The forced swimming test (FST) and sucrose preference test (SPT) were used to quantify depressive-like phenotypes in wild-type (WT) and NPFFR2-knockout (KO) mice. A single dose of LPS (i.p. 1 mg/kg) readily caused increases in toll-like receptor 4 and tumor necrosis factor-α along with decreases in 5-HT1AR mRNA in the ventral hippocampus of WT mice. Furthermore, LPS treatment of WT mice increased immobility time in FST and decreased sucrose preference in SPT. In contrast, none of these effects were observed in NPFFR2-KO mice. While WT mice injected with lentiviral 5-HT1AR shRNA in the ventral hippocampus displayed an unaltered response after LPS challenge, LPS-challenged NPFFR2-KO mice displayed a profound decrease in sucrose preference when pretreated with 5-HT1AR shRNA. Taken together, these results suggest that NPFFR2 modulates LPS-induced depressive-like behavioral phenotypes by downregulating 5HT1AR in the ventral hippocampus.

The 5-HT1A receptor as a serotonergic target for neuroprotection in cerebral ischemia

Cerebral ischemia due to stroke or cardiac arrest greatly affects daily functioning and the quality of life of patients and has a high socioeconomic impact due to the surge in their prevalence. Advances in the identification of an effective pharmacotherapy to promote neuroprotection and recovery after a cerebral ischemic insult are, however, limited. The serotonin 1A (5-HT_1A) receptor has been implicated in the regulation of several brain functions, including mood, emotions, memory, and neuroplasticity, all of which are deleteriously affected by cerebral ischemia. This review focuses on the specific roles and mechanisms of 5-HT_1A receptors in neuroprotection in experimental models of cerebral ischemia. We present experimental evidence that 5-HT_1A receptor agonists can prevent neuronal damage and promote functional recovery induced by focal and transient global ischemia in rodents. However, indiscriminate activation of pre-and postsynaptic by non-biased 5-HT_1A receptor agonists may be a limiting factor in the anti-ischemic clinical efficacy of these compounds since 5-HT_1A receptors in different brain regions can mediate diverging or even contradictory responses. Current insights are presented into the 'biased' 5-HT_1A post-synaptic heteroreceptor agonist NLX-101 (also known as F15599), a compound that preferentially and potently stimulates postsynaptic cortical pyramidal neurons without inhibiting firing of serotoninergic neurons, as a potential strategy providing neuroprotection in cerebral ischemic conditions.

Translating biased agonists from molecules to medications: Serotonin 5-HT1A receptor functional selectivity for CNS disorders

Biased agonism (or "functional selectivity") at G-protein-coupled receptors has attracted rapidly increasing interest as a means to improve discovery of more efficacious and safer pharmacotherapeutics. However, most studies are limited to in vitro tests of cellular signaling and few biased agonists have progressed to in vivo testing. As concerns 5-HT_1A receptors, which exert a major control of serotonergic signaling in diverse CNS regions, study of biased agonism has previously been limited by the poor target selectivity and/or partial agonism of classically available ligands. However, a new generation of highly selective, efficacious and druggable agonists has advanced the study of biased agonism at this receptor and created new therapeutic opportunities. These novel agonists show differential properties for G-protein signaling, cellular signaling (particularly pERK), electrophysiological effects, neurotransmitter release, neuroimaging by PET and pharmacoMRI, and behavioral tests of mood, motor activity and side effects. Overall, NLX-101 (a.k.a. F15599) exhibits preferential activation of cortical and brain stem 5-HT_1A receptors, whereas NLX-112 (a.k.a. befiradol or F13640) shows prominent activation of 5-HT_1A autoreceptors in Raphe nuclei and in regions associated with motor control. Accordingly, NLX-101 is potently active in rodent models of depression and respiratory control, whereas NLX-112 shows promising activity in models of Parkinson's disease across several species - rat, marmoset and macaque. Moreover, NLX-112 has also been labeled with ¹⁸F to produce the first agonist PET radiopharmaceutical (known as [¹⁸F]-F13640) for investigation of the active state of 5-HT_1A receptors in rodent, primate and human. The structure-functional activity relationships of biased agonists have been investigated by receptor modeling and novel compounds have been identified which exhibit increased affinity at 5-HT_1A receptors and new profiles of cellular signaling bias, notably for β-arrestin recruitment versus pERK. Taken together, the data suggest that 5-HT_1A receptor biased agonists constitute potentially superior pharmacological agents for treatment of CNS disorders involving serotonergic mechanisms.

Perspectives for therapy of treatment-resistant depression

A high proportion of depressed patients fail to respond to antidepressant drug treatment. Treatment-resistant depression (TRD) is a major challenge for the psychopharmacology of mood disorders. Only in the past decade have novel treatments, including deep brain stimulation (DBS) and ketamine, been discovered that provide rapid and sometimes prolonged relief to a high proportion of TRD sufferers. In this review, we consider the current status of TRD from four perspectives: the challenge of developing an appropriate regulatory framework for novel rapidly acting antidepressants; the efficacy of non-pharmacological somatic therapies; the development of an animal model of TRD and its use to understand the neural basis of antidepressant non-response; and the potential for rapid antidepressant action from targets (such as 5-HT_1A receptors) beyond the glutamate receptor.

G-Protein-Coupled Receptors and Ischemic Stroke: a Focus on Molecular Function and Therapeutic Potential

In ischemic stroke, there is only one approved drug, tissue plasminogen activator, to be used in clinical conditions for thrombolysis. New neuroprotective therapies for ischemic stroke are desperately needed. Several targets and pathways have been shown to confer neuroprotective effects in ischemic stroke. G-protein-coupled receptors (GPCRs) are one of the most frequently targeted receptors for developing novel therapeutics for central nervous system disorders. GPCRs are a large family of cell surface receptors that response to a wide variety of extracellular stimuli. GPCRs are involved in a wide range of physiological and pathological processes. More than 90% of the identified non-sensory GPCRs are expressed in the brain, where they play important roles in regulating mood, pain, vision, immune responses, cognition, and synaptic transmission. There is also good evidence that GPCRs are implicated in the pathogenesis of stroke. This review narrates the pathophysiological role and possible targeted therapy of GPCRs in ischemic stroke.

Distinct association of plasma BDNF concentration and cognitive function in depressed patients treated with vortioxetine or escitalopram

RATIONALE

Cognitive dysfunction is frequent in major depressive disorder (MDD), and brain-derived neurotrophic factor (BDNF) is involved both in regulation of cognition and in therapeutic response in MDD.

OBJECTIVES

The aim of this study was to determine if baseline plasma BDNF might predict change in cognitive function in MDD patients treated with vortioxetine or escitalopram, and whether the alterations in BDNF levels correlate with changes in cognitive performance during treatment.

METHODS

Drug-naive or drug-free patients with MDD (N=121) were sampled and evaluated at baseline and 4 weeks after treatment initiation with vortioxetine or escitalopram. Cognitive function was evaluated using the F-A-S test, Digit Span test, and Digit Symbol Coding test. Plasma BDNF was determined using ELISA.

RESULTS

The results of the study indicate that both vortioxetine (V) and escitalopram (E) improved cognitive functions evaluated with F-A-S test (V: p<0.001; r=-0.427, E: p<0.001; r=-0.370), Digit Symbol Coding test (V: p<0.001; r=-0.706, E: p<0.001; r=-0.435), and Digit Span test-backward span (V: p=0.001; r=-0.311, E: p=0.042; r=-0.185), while only vortioxetine (p<0.001; r=-0.325) improved cognition evaluated with the Digit Span test-forward span. A moderate positive correlation between pretreatment plasma BDNF levels and improvement in cognitive performance was only detected in patients treated with vortioxetine (delta F-A-S test: p=0.011; r=0.325, delta Digit Span test-forward span: p=0.010, r=0.326).

CONCLUSIONS

These results suggest that higher baseline plasma BDNF levels might be associated with improvements in verbal fluency and working memory in vortioxetine, but not escitalopram treated patients. Vortioxetine treatment was superior in simple attention efficiency.

Biased agonism in drug discovery: Is there a future for biased 5-HT1A receptor agonists in the treatment of neuropsychiatric diseases?

Serotonin (5-HT) is one of the fundamental neurotransmitters that contribute to the information essential for an organism's normal, physiological function. Serotonin acts centrally and systemically. The 5-HT_1A receptor is the most widespread serotonin receptor, and participates in many brain-related disorders, including anxiety, depression, and cognitive impairments. The 5-HT_1A receptor can activate several different biochemical pathways and signals through both G protein-dependent and G protein-independent pathways. Preclinical experiments indicate that distinct signaling pathways in specific brain regions may be crucial for antidepressant-like, anxiolytic-like, and procognitive responses. Therefore, the development of new ligands that selectively target a particular signaling pathway(s) could open new possibilities for more effective and safer pharmacotherapy. This review discusses the current state of preclinical studies focusing on the concept of functional selectivity (biased agonism) regarding the 5-HT_1A receptor and its role in antidepressant-like, anxiolytic-like, and procognitive regulation. Such work highlights not only the differential effects of targeted autoreceptors, vs. heteroreceptors, but also the importance of targeting specific downstream intracellular signaling processes, thereby enhancing favorable over unfavorable signaling activation.

Effect of vortioxetine vs. escitalopram on plasma BDNF and platelet serotonin in depressed patients

Escitalopram and vortioxetine are efficacious antidepressants. They directly target serotonin (5-HT) system, but vortioxetine mechanism of action is distinct from the one of selective serotonin reuptake inhibitors (SSRIs). Treatment with SSRIs decrease platelet 5-HT concentration and increase peripheral brain-derived neurotrophic factor (BDNF) levels. Since vortioxetine has a multimodal mechanism of action, it is expected to have a greater effect on circulatory BDNF concentration, compared to conventional antidepressants. This longitudinal study aimed to explore and compare the effects of 4-weeks of treatment with vortioxetine and escitalopram on plasma BDNF and platelet 5-HT concentration in patients with major depressive disorder (MDD). The results revealed that vortioxetine significantly increased plasma BDNF concentration (p = .018) and significantly decreased platelet 5-HT concentration (p < .001). Treatment with escitalopram significantly decreased platelet 5-HT concentration (p < .001), but it did not affect plasma BDNF concentration (p = .379). Response to vortioxetine was not predicted by baseline plasma BDNF or platelet 5-HT concentration, but response to escitalopram was predicted by baseline platelet 5-HT concentration. These effects might be due to vortioxetine unique mechanism of action, but the clinical implications are unclear. It remains to be determined whether this finding extends during long-term vortioxetine treatment, and which, if any, clinical effects emerge from BDNF increase.

Identification of 14-3-3 epsilon as a regulator of the neural apoptotic pathway for chronic-stress-induced depression

Major depression is a prevalent and long-lasting psychiatric illness with severe functional impairment and high suicide rate. We have previously shown that the ventrolateral orbital cortex (VLO) plays a key role in the stress responses in mice, but the underlying mechanisms remains unclear. Here, we used proteomic method to identify differentially expressed proteins in VLO of chronic unpredictable mild stress (CUMS) mice. Of 4,953 quantified proteins, 45 proteins were differentially expressed following CUMS. The integrated pathway analyses identified 14-3-3ε and TrkB signaling as differentially downregulated in association with stress-induced depressive-like behaviors. 14-3-3ε overexpression in VLO relieved the depressive-like behaviors by rescue of Bad-mediated apoptosis. Moreover, treatment with the 14-3-3ε stabilizer FC-A precluded neuronal apoptotic signaling in VLO of depressed mice. Because 14-3-3ε provides significant protection against chronic stress, boosting 14-3-3ε expression, pharmacological stabilization of 14-3-3s (e.g. with FC-A) is identified as an exciting therapeutic target for major depression.

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Novel screening of chronic mild stress-induced depression phenotypes in mice

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Proteomics identify 14-3-3ε as a key modulator of depressive behaviors in VLO

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14-3-3ε partially reversed depressive behaviors through neural apoptotic pathway

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14-3-3ε stabilizer FC-A ameliorates depression phenotypes after chronic mild stress

Neuroprotective Effects Against Cerebral Ischemic Injury Exerted by Dexmedetomidine via the HDAC5/NPAS4/MDM2/PSD-95 Axis

Numerous evidences have highlighted the efficient role of dexmedetomidine (DEX) in multi-organ protection. In the present study, the neuroprotective role of DEX on cerebral ischemic injury and the underlining signaling mechanisms were explored. In order to simulate cerebral ischemic injury, we performed middle cerebral artery occlusion in mice and oxygen-glucose deprivation in neurons. Immunohistochemistry, Western blot analysis, and RT-qPCR were used to examine expression of HDAC5, NPAS4, MDM2, and PSD-95 in hippocampus tissues of MCAO mice and OGD-treated neurons. MCAO mice received treatment with DEX and sh-PSD-95, followed by neurological function evaluation, behavioral test, infarct volume detection by TTC staining, and apoptosis by TUNEL staining. Additionally, gain- and loss-of-function approaches were conducted in OGD-treated neuron after DEX treatment. Cell viability and apoptosis were assessed with the application of CCK-8 and flow cytometry. The interaction between MDM2 and PSD-95 was evaluated using Co-IP assay, followed by ubiquitination of PSD-95 detection. As per the results, HDAC5 and MDM2 were abundantly expressed, while NPAS4 and PSD-95 were poorly expressed in hippocampus tissues of MCAO mice and OGD-treated neurons. DEX elevated viability, and reduced LDH leakage rate and apoptosis rate of OGD-treated neurons, which was reversed following the overexpression of HDAC5. Moreover, HDAC5 augmented MDM2 expression via NPAS4 inhibition. MDM2 induced PSD-95 ubiquitination and degradation. In MCAO mice, DEX improved neurological function and behaviors and decreased infarct volume and apoptosis, which was negated as a result of PSD-95 silencing. DEX plays a neuroprotective role against cerebral ischemic injury by disrupting MDM2-induced PSD-95 ubiquitination and degradation via HDAC5 and NPAS4.

Solid lipid nanoparticles loading with curcumin and dexanabinol to treat major depressive disorder

Dexanabinol (HU-211) is an artificially synthesized cannabinoid derivative that exerts neuroprotective effects through anti-inflammatory and antioxidant effects. Curcumin exhibits antidepressant effects in the treatment of major depressive disorder. To investigate the antidepressant effects of solid lipid nanoparticles loaded with both curcumin and dexanabinol, and the underlying mechanisms associated with this combination, we established wild-type (CBR1^+/+) and cannabinoid receptor 1 (CBR1) knockout (CBR1^–/–) mouse models of major depressive disorder, through the intraperitoneal injection of corticosterone, for 3 successive days, followed by treatment with intraperitoneal injections of solid lipid nanoparticles loading with curcumin (20 mg/kg) and dexanabinol (0.85 mg/kg), for 2 successive days. Our results revealed that solid lipid nanoparticle loading with curcumin and dexanabinol increased the mRNA and protein expression levels of the mature neuronal markers neuronal nuclei, mitogen-activated protein 2, and neuron-specific beta-tubulin III, promoted the release of dopamine and norepinephrine, and increased the mRNA expression of CBR1 and the downstream genes Rasgef1c and Egr1, and simultaneously improved rat locomotor function. However, solid lipid nanoparticles loaded with curcumin and dexanabinol had no antidepressant effects on the CBR1^–/– mouse models of major depressive disorder. This study was approved by the Institutional Ethics Committee of Tongji Hospital of Tongji University, China (approval No. 2017-DW-020) on May 24, 2017.

Fluoxetine-induced recovery of serotonin and norepinephrine projections in a mouse model of post-stroke depression

Chronic treatment with fluoxetine (FLX) is required for its antidepressant effects, but the role of serotonin (5-HT) axonal plasticity in FLX action is unknown. To address this, we examined mice with a stroke in the left medial prefrontal cortex (mPFC) resulting in persistent anxiety-like and depression-like behaviors and memory deficits as a model of post-stroke depression. Chronic treatment with FLX (but not exercise) completely reversed the behavioral phenotype and partially reversed changes in FosB-labeled cells in the mPFC, nucleus accumbens, septum, hippocampus, basolateral amygdala (BLA), and dorsal raphe. In these regions, 5-HT or norepinephrine (NE) innervation was quantified by staining for 5-HT or NE transporters, respectively. 5-HT synapses and synaptic triads were identified as synaptophysin-stained sites on 5-HT axons located proximal to gephyrin-stained or PSD95-stained spines. A week after stroke, 5-HT innervation was greatly reduced at the stroke site (left cingulate gyrus (CG) of the mPFC) and the left BLA. Chronically, 5-HT and NE innervation was reduced at the left CG, nucleus accumbens, and BLA, with no changes in other regions. In these areas, pre-synaptic and post-synaptic 5-HT synapses and triads to inhibitory (gephyrin+) sites were reduced, while 5-HT contacts at excitatory (PSD95+) sites were reduced in the CG and prelimbic mPFC. Chronic FLX, but not exercise, reversed these reductions in 5-HT innervation but incompletely restored NE projections. Changes in 5-HT innervation were verified using YFP staining in mice expressing YFP-tagged channelrhodopsin in 5-HT neurons. Thus, FLX-induced 5-HT axonal neuroplasticity of forebrain projections may help mediate recovery from brain injury.

Central 5-HT receptors and their function; present and future

Since our review of central 5-HT receptors and their function twenty years ago, no new 5-HT receptor has been discovered and there is little evidence that this situation will change in the near future. Nevertheless, over this time significant progress has been made in our understanding of the properties of these receptors and in the clinical translation of this information, and some of these developments are highlighted herein. Such highlights include extensive mapping of 5-HT receptors in both animal and human brain, culminating in readily-accessible brain atlases of 5-HT receptor distribution, as well as emerging data on how 5-HT receptors are distributed within complex neural circuits. Also, a range of important pharmacological and genetic tools have been developed that allow selective 5-HT receptor manipulation, in cells through to whole organism models. Moreover, unexpected complexity in 5-HT receptor function has been identified including agonist-dependent signalling that goes beyond the pharmacology of canonical 5-HT receptor signalling pathways set down in the 1980s and 1990s. This new knowledge of 5-HT signalling has been extended by the discovery of combined signalling of 5-HT and co-released neurotransmitters, especially glutamate. Another important advance has been the progression of a large number of 5-HT ligands through to experimental medicine studies and clinical trials, and some such agents have already become prescribed therapeutic drugs. Much more needs to be discovered and understood by 5-HT neuropharmacologists, not least how the diverse signalling effects of so many 5-HT receptor types interact with complex neural circuits to generate neurophysiological changes which ultimately lead to altered cognitions and behaviour. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Challenges and Improvements of Developing an Ischemia Mouse Model Through Bilateral Common Carotid Artery Occlusion

Brain ischemia is one of the principal causes of death and disability worldwide in which prevention or an effective treatment does not exist. In order to develop successful treatments, an adequate and useful ischemia model is essential. Transient global cerebral ischemia is one of the most interesting pathological conditions in stroke studies because of the observed degeneration of forebrain and delayed neuronal cell death in selective vulnerable regions such as hippocampus. Transient occlusion of both common carotid arteries is the most convenient model to induce tGCI. Although there are effective rat and gerbil models using this method, the induction of a reproducible and reliable injury after global ischemia in mouse has presented higher variations, mainly because of its size and the necessary monitoring skills in order to accomplish homogeneous and reproducible results. Further, great variability among cerebral vasculature and susceptibility of the different strains and sub-strains is observed. In recent years, some modifications have been made to the model in order to normalize the heterogenic effects. Analysis of posterior communicating artery patency has been proposed as an exclusion parameter due to the direct relationship reported with the reduction of cerebral blood flow. Another method used to significantly reduce blood flow is the induction of hypotension with isoflurane. Each protocol produces distinct injury outcomes. Further improvements are needed to attain a general, simpler, reproducible and globally accepted model that allows comparisons between research groups, progress in understanding ischemia and the consequent development of therapeutic alternatives for ischemic injury.