Activation of GIPR Exerts Analgesic and Anxiolytic-Like Effects in the Anterior Cingulate Cortex of Mice.

Background: Chronic pain is defined as pain that persists typically for a period of over six months. Chronic pain is often accompanied by an anxiety disorder, and these two tend to exacerbate each other. This can make the treatment of these conditions more difficult. Glucose-dependent insulinotropic polypeptide (GIP) is a member of the incretin hormone family and plays a critical role in glucose metabolism. Previous research has demonstrated the multiple roles of GIP in both physiological and pathological processes. In the central nervous system (CNS), studies of GIP are mainly focused on neurodegenerative diseases; hence, little is known about the functions of GIP in chronic pain and pain-related anxiety disorders. Methods: The chronic inflammatory pain model was established by hind paw injection with complete Freund's adjuvant (CFA) in C57BL/6 mice. GIP receptor (GIPR) agonist (D-Ala2-GIP) and antagonist (Pro3-GIP) were given by intraperitoneal injection or anterior cingulate cortex (ACC) local microinjection. Von Frey filaments and radiant heat were employed to assess the mechanical and thermal hypersensitivity. Anxiety-like behaviors were detected by open field and elevated plus maze tests. The underlying mechanisms in the peripheral nervous system and CNS were explored by GIPR shRNA knockdown in the ACC, enzyme-linked immunosorbent assay, western blot analysis, whole-cell patch-clamp recording, immunofluorescence staining and quantitative real-time PCR. Results: In the present study, we found that hind paw injection with CFA induced pain sensitization and anxiety-like behaviors in mice. The expression of GIPR in the ACC was significantly higher in CFA-injected mice. D-Ala2-GIP administration by intraperitoneal or ACC local microinjection produced analgesic and anxiolytic effects; these were blocked by Pro3-GIP and GIPR shRNA knockdown in the ACC. Activation of GIPR inhibited neuroinflammation and activation of microglia, reversed the upregulation of NMDA and AMPA receptors, and suppressed the enhancement of excitatory neurotransmission in the ACC of model mice. Conclusions: GIPR activation was found to produce analgesic and anxiolytic effects, which were partially due to attenuation of neuroinflammation and inhibition of excitatory transmission in the ACC. GIPR may be a suitable target for treatment of chronic inflammatory pain and pain-related anxiety.

CB1 agonism prolongs therapeutic window for hormone replacement in ovariectomized mice.

Hormone therapy (HT) is reported to be deficient in improving learning and memory in older postmenopausal women according to recent clinical studies; however, the reason for failure is unknown. A "window of opportunity" for estrogen treatment is proposed to explain this deficiency. Here, we found that facilitation of memory extinction and long-term depression by 17ß-estradiol (E2) was normal in mice 1 week after ovariectomy (OVXST), but it was impaired in mice 3 months after ovariectomy (OVXLT). High-throughput sequencing revealed a decrease of miR-221-5p, which promoted cannabinoid receptor 1 (CB1) ubiquitination by upregulation of Neurl1a/b in E2-treated OVXLT mice. Blood samples from postmenopausal women aged 56-65 indicated decreases of miR-221-5p and 2-arachidonoylglycerol compared with samples from perimenopausal women aged 46-55. Replenishing of miR-221-5p or treatment with a CB1 agonist rescued the impairment of fear extinction in E2-treated OVXLT mice. The present study demonstrates that an HT time window in mice can be prolonged by cotreatment with a CB1 agonist, implying a potential strategy for HT in long-term menopausal women.

Anxiolytic effects of Formononetin in an inflammatory pain mouse model.

Chronic pain is commonly accompanied with anxiety disorder, which complicates treatment. In this study, we investigated the analgesic and anxiolytic effects of Formononetin (FMNT), an active component of traditional Chinese medicine red clover (Trifolium pratense L.) that is capable of protecting neurons from N-methyl-D-aspartate (NMDA)-evoked excitotoxic injury, on mice suffering from complete Freund's adjuvant (CFA)-induced chronic inflammatory pain. The results show that FMNT administration significantly reduces anxiety-like behavior but does not affect the nociceptive threshold in CFA-injected mice. The treatment reverses the upregulation of NMDA, GluA1, and GABAA receptors, as well as PSD95 and CREB in the basolateral amygdala (BLA). The effects of FMNT on NMDA receptors and CREB binding protein (CBP) were further confirmed by the potential structure combination between these compounds, which was analyzed by in silico docking technology. FMNT also inhibits the activation of the NF-κB signaling pathway and microglia in the BLA of mice suffering from chronic inflammatory pain. Therefore, the anxiolytic effects of FMNT are partially due to the attenuation of inflammation and neuronal hyperexcitability through the inhibition of NMDA receptor and CBP in the BLA.

Tetrahydroxystilbene glucoside relieves the chronic inflammatory pain by inhibiting neuronal apoptosis, microglia activation, and GluN2B overexpression in anterior cingulate cortex.

Tetrahydroxystilbene glucoside (THSG) is one of the active ingredients of Polygonum multiflorum. It has been shown to exert a variety of pharmacological effects, including antioxidant, anti-aging, and anti-atherosclerosis. Because of its prominent anti-inflammatory effect, we explored whether THSG had analgesic effect. In this study, we used a model of chronic inflammatory pain caused by injecting complete Freund's adjuvant into the hind paw of mice. We found THSG relieved swelling and pain in the hind paw of mice on a dose-dependent manner. In the anterior cingulate cortex, THSG suppressed the upregulation of GluN2B-containing N-methyl-D-aspartate receptors and the downregulation of GluN2A-containing N-methyl-D-aspartate receptors caused by chronic inflammation. In addition, THSG increased Bcl-2 and decreased Bax and Caspase-3 expression by protecting neuronal survival. Furthermore, THSG inhibited the phosphorylation of p38 and the increase of nuclear factor κB (NF-κB) and tumor necrosis factor α (TNF-α). Immunohistochemical staining revealed that THSG blocked the activation of microglia and reduced the release of proinflammatory cytokines TNF-α, interleukin 1ß (IL-1ß), and interleukin 6 (IL-6). In conclusion, this study demonstrated that THSG had a certain effect on alleviating complete Freund's adjuvant-induced chronic inflammatory pain.

The novel cannabinoid receptor GPR55 mediates anxiolytic-like effects in the medial orbital cortex of mice with acute stress.

The G protein-coupled receptor 55 (GPR55) is a novel cannabinoid receptor, whose exact role in anxiety remains unknown. The present study was conducted to explore the possible mechanisms by which GPR55 regulates anxiety and to evaluate the effectiveness of O-1602 in the treatment of anxiety-like symptoms. Mice were exposed to two types of acute stressors: restraint and forced swimming. Anxiety behavior was evaluated using the elevated plus maze and the open field test. We found that O-1602 alleviated anxiety-like behavior in acutely stressed mice. We used lentiviral shRNA to selective ly knockdown GPR55 in the medial orbital cortex and found that knockdown of GPR55 abolished the anxiolytic effect of O-1602. We also used Y-27632, a specific inhibitor of ROCK, and U73122, an inhibitor of PLC, and found that both inhibitors attenuated the effectiveness of O-1602. Western blot analysis revealed that O-1602 downregulated the expression of GluA1 and GluN2A in mice. Taken together, these results suggest that GPR55 plays an important role in anxiety and O-1602 may have therapeutic potential in treating anxiety-like symptoms.

Cucurbitacin IIa exerts antidepressant-like effects on mice exposed to chronic unpredictable mild stress.

Cucurbitacin IIa (CuIIa) is the major active component of the Helmseya amabilis root and is known to have antiviral and anti-inflammatory effects. In this study, we examined the antidepressant-like effects of CuIIa in a mouse model of chronic unpredictable mild stress (CUMS) and investigated the possible underlying mechanisms. To evaluate the antidepressant-like effects of CuIIa on depression-like behaviors, mice were subjected to the open-field test, the elevated plus-maze test, the forced-swimming test, and the tail-suspension test. We found that CuIIa treatment reversed the CUMS-induced behavioral abnormalities. Western blot analyses showed that CUMS significantly decreased brain-derived neurotrophic factor (BDNF) levels, cAMP-response element binding protein (CREB), and calcium/calmodulin-dependent protein kinase II (CaMKII) phosphorylation, and N-methyl-D-aspartate receptor subtype GluN2B and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor GluA1 expression in the amygdala; in addition, the expression of gamma-aminobutyric acid receptor A subunit α2 was upregulated in CUMS mice. These CUMS-induced changes were all normalized by CuIIa treatment and administration of the BDNF antagonist ANA-12 can block the antidepressant effect of CuIIa. Our findings suggest that the antidepressant-like effects of CuIIa may be exerted by regulation of the CaMKIIα-CREB-BDNF pathway and the balance between excitatory and inhibitory synaptic transmission in the amygdala.

Effect of Praeruptorin C on 3-nitropropionic acid induced Huntington's disease-like symptoms in mice.

Huntington's disease (HD) is an autosomal dominant inherited disease characterized by movement, psychiatric, and cognitive disorders. Previous research suggests that Praeruptorin C (Pra-C), an effective component in the root of Peucedanum praeruptorum dunn, a traditional Chinese medicine, may function in neuroprotection. The present study was conducted to evaluate the effectiveness of Pra-C in the treatment of HD-like symptoms in a 3-nitropropionic acid (3-NP) mouse model, and to explore the possible mechanism of the drug's activity. We treated 3-NP-injected mice with two different doses of Pra-C (1.5 and 3.0mg/kg) for 3 days. Motor behavior was tested using the open field test (OFT) and rotarod test, while psychiatric symptoms were tested using the forced swimming test (FST) and tail suspension test (TST). We found that Pra-C alleviated the motor deficits and depression-like behavior in the 3-NP-treated mice, and protected neurons from excitotoxicity. Western blot analysis revealed that Pra-C upregulated BDNF, DARPP32, and huntingtin protein in the striatum of 3-NP mice. These results taken together suggest that Pra-C may have therapeutic potential with respect to the movement, psychiatric, and cognitive symptoms of HD.