The role of the excitation:inhibition functional balance in the mPFC in the onset of antidepressants.

Currently available antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs), generally require weeks to months to produce a therapeutic response, but the mechanism of action underlying the delayed onset of antidepressant-like action remains to be elucidated. The balance between excitatory glutamatergic pyramidal neurons and inhibitory γ-aminobutyric acid (GABA) interneurons, i.e., the excitation:inhibition functional (E:I) balance, in the medial prefrontal cortex (mPFC) is critical in regulating several behaviors and might play an important mediating role in the mechanism of rapid antidepressant-like action reported by several studies. In the present study, the multichannel electrophysiological technique was used to record the firing activities of pyramidal neurons and interneurons and investigate the effects of a single dose of fluoxetine and ketamine (both 10 mg/kg, i.p.) on the E:I functional balance in the rat mPFC after 90 min or 24 h, and the forced swimming test (FST) was used to evaluate the antidepressant-like effects of fluoxetine and ketamine. The present study also explored the effects of chronic treatment with fluoxetine (10 mg/kg, i.g.) for 7 d or 21 d on the E:I functional balance in the mPFC. The present results suggested that a single dose of ketamine could both significantly increase the firing activities of pyramidal neurons and significantly decrease the firing activities of interneurons in the mPFC and exerted significant antidepressant-like action on the FST after 90 min and 24 h, but fluoxetine had no such effects under the same conditions. However, chronic treatment with fluoxetine for 21 d (but not 7 d) could significantly affect the firing activities of pyramidal neurons and interneurons in the mPFC. Taken together, the present results indicated that rapid regulation of the E:I functional balance in the mPFC might be an important common mechanism of rapid-acting antidepressants and the delayed onset of SSRIs might be partly attributed to their inability to rapidly regulate the E:I functional balance in the mPFC. The present study provided a new entry point to the development of rapid-acting antidepressants.

Serotonergic transmission is required for the anxiolytic-like behavioral effects of YL-IPA08, a selective ligand targeting TSPO.

Anxiety disorders are the most prevalent group of mental disorders globally, leading to considerable losses in health, functioning and increase of medical costs. Till now, the search for novel pharmacological treatments is driven by the growing medical need to improve on the effectiveness and the side effect profile of existing drugs. In central nervous system, the mitochondrially located translocator protein (18 kDa, TSPO) serves as the rate-limiting step for neurosteroidogenesis and influences GABAergic transmission. Since 5-HT is one of the most comprehensively studied neurotransmitter systems in the anxiety field, in the present study, we want to investigate whether 5-HT system is involved in the anxiolytic-like effects of YL-IPA08, a novel TSPO ligand designed and synthesized at our institute. Our data showed that YL-IPA08 could potentiate the 5-HTP-induced head-twitch response, and the anxiolytic-like effect of YL-IPA08 was abolished by pCPA or 5,7-DHT pretreatment in mice. Furthermore, we found that YL-IPA08 increased the extracellular levels of 5-HT in the rat ventral hippocampus in freely moving rat using the rapid and validated HPLC coupled with microdialysis. In addition, 5-HT level was positively correlated with the level of allopregnanolone. The above results suggest that 5-HT neurotransmission may play a critical role in the anxiolytic-like effects of YL-IPA08.

Translocator protein-mediated fast-onset antidepressant-like and memory-enhancing effects in chronically stressed mice.

BACKGROUND: Fast-acting and cognitive-enhancing antidepressants are desperately needed. Activation of translocator protein (18 kDa, TSPO) is a novel strategy for developing potential antidepressants, but there are no data available on the onset time of TSPO ligands. This study aimed to investigate the fast-onset antidepressant actions of AC-5216, a selective TSPO ligand, in TSPO knock-out (KO) mice. METHODS: TSPO wild-type (WT) and KO mice were subjected to a six-week chronic unpredicted stress (CUS) paradigm. Then, the mice were treated with AC-5216 and tested with depressive and cognitive behaviours. RESULTS: A single dose of AC-5216 (0.3 mg/kg) exerted anxiolytic- and antidepressant-like actions in TSPO WT mice. Moreover, in chronically stressed WT mice, two to four days of AC-5216 treatment (0.3 mg/kg, once per day) produced fast-onset antidepressant-like effects in the novelty-suppressed feeding and sucrose preference tests, as well as memory-enhancing effects in the novel object recognition test. In addition, a rapid (with five days of treatment) restoration of serum corticosterone levels and prefrontal cortex (PFC) allopregnanolone levels was found. Further studies showed that in these stress-exposed WT mice, AC-5216 significantly increased the levels of mTOR signalling-related proteins (mBDNF, p-mTOR, PSD-95, synapsin-1, GluR1), as well as the total dendritic length and branching points of pyramidal neurons in the PFC. CONCLUSIONS: These results suggest that TSPO mediates the fast-onset antidepressant-like and memory-enhancing effects of AC-5216, possibly through the rapid activation of mTOR signalling and restoration of dendritic complexity in the PFC.

Rapid anti-PTSD-like activity of the TSPO agonist YL-IPA08: Emphasis on brain GABA, neurosteroids and HPA axis function.

There is a serious need for fast-acting drugs to treat post-traumatic stress disorder (PTSD). Our previous studies revealed that YL-IPA08, a novel small-molecule TSPO agonist, exerted significant anti-PTSD effects in various animal models. However, the onset time of YL-IPA08 and its underlying mechanisms remain unclear. In the present study, we first investigated the time course of YL-IPA08 compared to selective serotonin reuptake inhibitors (SSRIs) in the well-known time-dependent sensitization model of PTSD. YL-IPA08 required only 2-4 days of treatment to take effect in behavioural models of PTSD, whereas sertraline required 7-8 days. Furthermore, the mechanism study revealed that YL-IPA08 elicited anti-PTSD-like effects associated with increased GABA levels and allopregnanolone efflux in the hippocampus and prefrontal cortex and increased corticosterone levels in the serum after only 5 days of treatment, whereas sertraline required 9 days. Our results demonstrate that YL-IPA08 can exert fast-onset anti-PTSD-like effects, and its mechanisms may be related to the increased GABA levels, allopregnanolone efflux and the hypothalamic-pituitary-adrenal (HPA) axis function.

Ammoxetine attenuates diabetic neuropathic pain through inhibiting microglial activation and neuroinflammation in the spinal cord.

BACKGROUND: Diabetic neuropathic pain (DNP) is a common and distressing complication in patients with diabetes, and the underlying mechanism remains unclear. Tricyclic antidepressants (TCAs) and serotonin and norepinephrine reuptake inhibitors (SNRIs) are recommended as first-line drugs for DNP. Ammoxetine is a novel and potent SNRI that exhibited a strong analgesic effect on models of neuropathic pain, fibromyalgia-related pain, and inflammatory pain in our primary study. The present study was undertaken to investigate the chronic treatment properties of ammoxetine on DNP and the underlying mechanisms for its effects. METHODS: The rat model of DNP was established by a single streptozocin (STZ) injection (60 mg/kg). Two weeks after STZ injection, the DNP rats were treated with ammoxetine (2.5, 5, and 10 mg/kg/day) for 4 weeks. The mechanical allodynia and locomotor activity were assayed to evaluate the therapeutic effect of ammoxetine. In mechanism study, the activation of microglia, astrocytes, the protein levels of pro-inflammatory cytokines, the mitogen-activated protein kinases (MAPK), and NF-κB were evaluated. Also, microglia culture was used to assess the direct effects of ammoxetine on microglial activation and the signal transduction mechanism. RESULTS: Treatment with ammoxetine for 4 weeks significantly relieved the mechanical allodynia and ameliorated depressive-like behavior in DNP rats. In addition, DNP rats displayed increased activation of microglia in the spinal cord, but not astrocytes. Ammoxetine reduced the microglial activation, accumulation of pro-inflammatory cytokines, and activation of p38 and c-Jun N-terminal kinase (JNK) in the spinal cord of DNP rats. Furthermore, ammoxetine displayed anti-inflammatory effects upon challenge with LPS in BV-2 microglia cells. CONCLUSION: Our results suggest that ammoxetine may be an effective treatment for relieving DNP symptoms. Moreover, a reduction in microglial activation and pro-inflammatory release by inhibiting the p-p38 and p-JNK pathways is involved in the mechanism.

5-HT6 receptor agonist and memory-enhancing properties of hypidone hydrochloride (YL-0919), a novel 5-HT1A receptor partial agonist and SSRI.

Most current antidepressants are lacking a pro-cognition effect or even impair cognition as a side effect, and there are few effective psychopharmacological options that improve cognitive dysfunction in depression. Our previous studies revealed that hypidone hydrochloride (YL-0919), a novel 5-HT1A receptor partial agonist and SSRI, has antidepressant- and anxiolytic-like effects. Here, further studies found that YL-0919, but not vilazodone (a 5-HT1A receptor partial agonist and SSRI), exerted a significant memory-enhancing effect in the Morris water maze, object recognition test and step-down passive avoidance task. Because the 5-HT6 receptor has emerged as an interesting drug target to improve cognition, we investigated the target profile of YL-0919 using radioligand binding assays, [35S]-GTPγS binding and cAMP stimulation assays. YL-0919 was found to act as a highly effective, full agonist of 5-HT6 receptors. Finally, we observed that the memory-enhancing activities of YL-0919 were completely reversed after co-administration of SB271046 (a selective 5-HT6 receptor antagonist) at a dose that does not alter cognition. In summary, the findings of the current study suggest that YL-0919 has clear memory-enhancing effects, which might be at least partially mediated by 5-HT6 receptor activation.

YL-0919, a dual 5-HT1A partial agonist and SSRI, produces antidepressant- and anxiolytic-like effects in rats subjected to chronic unpredictable stress.

YL-0919 has been identified as a novel dual 5-HT1A partial agonist and serotonin reuptake inhibitor. In the current study, we demonstrated that YL-0919 produced prominent antidepressant-like and anxiolytic-like effects in a chronic unpredictable stress (CUS) rat model. Male SD rats were exposed to CUS for 5 weeks; YL-0919 (1.25 and 2.5 mg/kg) or a positive control fluoxetine (Flx, 10 mg/kg) was orally administered daily. YL-0919 or Flx treatment significantly increased the sucrose preference rate, the locomotor activity in an open field test (OFT), the latency to feed in a novelty-suppressed feeding test (NSFT), and both the percentage of time spent in the open arms and the number of entries into the open arms in an elevated plus-maze test. YL-0919 or Flx treatment significantly suppressed the serum levels of ACTH and corticosterone in CUS-exposed rats. Additionally, YL-0919 or Flx treatment significantly enhanced the levels of cAMP, the expression of phosphorylated cAMP response element-binding protein (pCREB) and brain-derived neurotrophic factor (BDNF) in the hippocampus of CUS-exposed rats. Similar to Flx, YL-0919 treatment significantly enhanced the dendritic complexity, and increased the number of dendritic nodes as well as the spine length and number of branch nodes in the hippocampal pyramidal neurons of CUS-exposed rats. Overall, our results reveal that YL-0919 suppresses the HPA axis and exerts antidepressant-like and anxiolytic-like effects in CUS-exposed rats, which are associated with the enhanced cAMP signaling and hippocampal dendritic complexity.

Mouse strain differences in SSRI sensitivity correlate with serotonin transporter binding and function.

Selective serotonin reuptake inhibitors (SSRIs) bind 5-HT transporters, leading to the accumulation of 5-HT and amelioration of depression. Although different mouse strains show varying sensitivity to SSRIs in mouse models of depression, the underlying mechanism of these strain differences remains unclear. Here, the SSRI citalopram dose-dependently reduced immobility time in both the FST and TST in DBA/2J mice but not C57BL/6J mice, whereas fluoxetine showed the opposite results. Paroxetine similarly reduced immobility time in both strains. The affinity of citalopram for the 5-HT transporter was 700-fold higher in DBA/2J mice than in C57BL/6J mice, whereas the affinity of fluoxetine was 100-fold higher in C57BL/6J mice than in DBA/2J mice. Furthermore, high citalopram concentrations were required for [3H]5-HT uptake in C57BL/6J but not in DBA/2J mouse cortical synaptosomes, whereas fluoxetine showed the opposite results. The effects of paroxetine on 5-HT transporter binding and synaptosomal 5-HT uptake were similar in the two strains. These results suggest that immobility duration depends on 5-HT transporter binding levels, which lead to apparent strain differences in immobility time in the FST and TST. Furthermore, differences in 5-HT transporter binding may cause variations in SSRI effects on behaviors.

Neurochemical and behavioural effects of hypidone hydrochloride (YL-0919): a novel combined selective 5-HT reuptake inhibitor and partial 5-HT1A agonist.

BACKGROUND AND PURPOSE: Our previous studies revealed that hypidone hydrochloride (YL-0919), which acts as a selective 5-HT (serotonin) reuptake inhibitor (SSRI) and displays partial 5-HT1A receptor agonist properties, exerts a significant antidepressant effect in various animal models. The aim of present research was to further investigate the pharmacology of YL-0919. EXPERIMENTAL APPROACH: We first investigated the target profile of YL-0919 using [35 S]-GTPγS binding and microdialysis. To determine whether the 5-HT or noradrenergic systems are involved in the antidepressant-like effect of YL-0919, the 5-hydroxytryptophan (5-HTP)-induced head-twitch test and antagonism with a high dose of apomorphine were performed. Using the learned helplessness paradigm, the novelty suppressed feeding test, the Vogel-type conflict and elevated plus-maze test, we further verified the antidepressant-like and anxiolytic-like effects of YL-0919. The effects of YL-0919 on hippocampal long-term potentiation (LTP) and sexual behaviour were also evaluated. KEY RESULTS: Data from the present study demonstrated that YL-0919 displays partial 5-HT1A receptor agonist properties, producing a greater impact on extracellular 5-HT levels than a conventional SSRI (fluoxetine), as well as significant antidepressant and anxiolytic effects. Furthermore, YL-0919 treatment rapidly influenced the synaptic plasticity (enhancing LTP) of rats. Finally, at doses close to those producing antidepressant-like effects, YL-0919 did not result in a marked inhibition of sexual function. CONCLUSIONS AND IMPLICATIONS: These data suggest that YL-0919 is probably a fast-onset potent antidepressant with few side effects.

Anxiolytic effects of GLYX-13 in animal models of posttraumatic stress disorder-like behavior.

In the present study, we investigated the effectiveness of GLYX-13, an NMDA receptor glycine site functional partial agonist, to alleviate the enhanced anxiety and fear response in both a mouse and rat model of stress-induced behavioral changes that might be relevant to posttraumatic stress disorder (PTSD). Studies over the last decades have suggested that the hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis is one of the most consistent findings in stress-related disease. Herein, we used these animal models to further investigate the effect of GLYX-13 on the stress hormone levels and glucocorticoid receptor (GR) expression. We found that exposure to foot shock induced long-lasting behavioral deficiencies in mice, including freezing and anxiety-like behaviors, that were significantly ameliorated by the long-term administration of GLYX-13 (5 or 10 mg/kg). Our enzyme-linked immunosorbent assay results showed that long-term administration of GLYX-13 at behaviorally effective doses (5 or 10 mg/kg) significantly decreased the elevated serum levels of both corticosterone and its upstream stress hormone adrenocorticotropic hormone in rats subjected to the TDS procedure. These results suggest that GLYX-13 exerts a therapeutic effect on PTSD-like stress responding that is accompanied by (or associated with) modulation of the HPA axis, including inhibition of stress hormone levels and upregulation of hippocampal GR expression.

Iptakalim, an ATP-sensitive potassium channel opener, confers neuroprotection against cerebral ischemia/reperfusion injury in rats by protecting neurovascular unit cells.

OBJECTIVE: To investigate the role of iptakalim, an ATP-sensitive potassium channel opener, in transient cerebral ischemia/reperfusion (I/R) injury and its involved mechanisms. METHODS: Intraluminal occlusion of middle cerebral artery (MCAO) in a rat model was used to investigate the effect of iptakalim at different time points. Infarct volume was measured by staining with 2,3,5-triphenyltetrazolium chloride, and immunohistochemistry was used to evaluate the expressions of Bcl-2 and Bax. In vitro, neurovascular unit (NVU) cells, including rat primary cortical neurons, astrocytes, and cerebral microvascular endothelial cells, were cultured and underwent oxygen-glucose deprivation (OGD). The protective effect of iptakalim on NVU cells was investigated by cell viability and injury assessments, which were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and release of lactate dehydrogenase. Caspase-3, Bcl-2 and Bax mRNA expressions were evaluated by real-time polymerase chain reaction (PCR). RESULTS: Administration of iptakalim 0 or 1 h after reperfusion significantly reduced infarct volumes, improved neurological scores, and attenuated brain edema after cerebral I/R injury. Iptakalim treatment (0 h after reperfusion) also reduced caspase-3 expression and increased the ratio of Bcl-2 to Bax by immunohistochemistry. Iptakalim inhibited OGD-induced cell death in cultured neurons and astrocytes, and lactate dehydrogenase release from cerebral microvascular endothelial cells. Iptakalim reduced mRNA expression of caspase-3 and increased the ratio of Bcl-2 to Bax in NVU cells. CONCLUSIONS: Iptakalim confers neuroprotection against cerebral I/R injury by protecting NVU cells via inhibiting of apoptosis.

[Changes of VEGF, TNF-alpha, IL-6 and NO in serum of patients with HAPE].

OBJECTIVE: To explore the possible pathophysiological process and mechanisms underlying the development and formation of high altitude pulmonary edema(HAPE) by observing the changes in contents of VEGF, TNF-alpha, IL-6 and NO in serum from the initiated and recovery of HAPE patients. METHODS: We studied 10 HAPE patients in a Chinese population. The patients were divided into two groups including HAPE initiate group and the recovery group. Contents of VEGF, TNF-alpha, IL-6 and NO in serum of the two groups were determined to study the process of HAPE. RESULTS: VEGF levels in the HAPE initiate one and the recovery groups were (167.9 +/- 26.5 and 53.1 +/- 17.0 pg/ ml), respectively. There was a significant decrease of VEGF content in recovery one compared to the HAPE group. The same results for TNF-alpha were gained. The levels of TNF-alpha in recovery group was much lower than that in the HAPE initiate one. They were (29.2 +/- 6.8) pg/ml and (86.2 +/- 24.1) pg/ml, respectively. The contents of IL-6 in HAPE initiate group and the recovery group were (32.3 +/- 16.5) pg/ml and (12. 5 +/- 8.0) pg/ml, respectively. But no significance existed. The level of NO in HAPE initiate group was (33.8 +/- 3.3) micromol/L, and it remarkably increased to (74.1 +/- 6.2) micromol/L in recovery one. CONCLUSION: VEGF, TNF-alpha, IL-6 and NO participated in the different aspects of the pathophysiological process and might have influence on HAPE.

Cellular absorption of anthraquinones emodin and chrysophanol in human intestinal Caco-2 cells.

The intestinal absorption characteristics of anthraquinones emodin and chrysophanol were observed by measuring the intracellular accumulation across Caco-2 cells by the reverse-phase high performance liquid chromatography. The intracellular accumulation of chrysophanol was much greater than that of emodin, the maximum absorption of emodin and chrysophanol being 414.02+/-15.28 and 105.56+/-11.57 nmol/l x mg x protein, respectively. The absorption of each anthraquinone was significantly lower at 4 degrees C than that of 37 degrees C. The effects of the transport inhibitors, verapamil, cyclosporine and phloridzin, on the intracellular accumulation were also examined. Verapamil and cyclosporine increased the absorption of emodin and chrysophanol, while phloridzin inhibited their absorption, all in a dose-dependent manner. These results suggest that the absorption characteristics of emodin and chrysophanol were closely related to their special structure with the hydroxy groups. It is also likely that a specific transport system mediated the intracellular accumulation of emodin and chrysophanol across the Caco-2 cells.