Juvenile treatment with mGluR2/3 agonist prevents schizophrenia-like phenotypes in adult by acting through GSK3ß.

Prodromal memory deficits represent an important marker for the development of schizophrenia (SZ), in which glutamatergic hypofunction occurs in the prefrontal cortex (PFC). The mGluR2/3 agonist LY379268 (LY37) attenuates excitatory N-methyl-D-aspartate receptor (NMDAR)-induced neurotoxicity, a central pathological characteristic of glutamatergic hypofunction. We therefore hypothesized that early treatment with LY37 would rescue cognitive deficits and confer benefits for SZ-like behaviors in adults. To test this, we assessed whether early intervention with LY37 would improve learning outcomes in the Morris Water Maze for rats prenatally exposed to methylazoxymethanol acetate (MAM), a neurodevelopmental SZ model. We found that a medium dose of LY37 prevents learning deficits in MAM rats. These effects were mediated through postsynaptic mGluR2/3 via improving GluN2B-NMDAR function by inhibiting glycogen synthase kinase-3ß (GSK3ß). Furthermore, dendritic spine loss and learning and memory deficits observed in adult MAM rats were restored by juvenile LY37 treatment, which did not change prefrontal neuronal excitability and glutamatergic synaptic transmission in adult normal rats. Our results provide a mechanism for mGluR2/3 agonists against NMDAR hypofunction, which may prove to be beneficial in the prophylactic treatment of SZ.

Group II metabotropic glutamate receptor agonist LY379268 regulates AMPA receptor trafficking in prefrontal cortical neurons.

Group II metabotropic glutamate receptor (mGluR) agonists have emerged as potential treatment drugs for schizophrenia and other neurological disorders, whereas the mechanisms involved remain elusive. Here we examined the effects of LY379268 (LY37) on the expression and trafficking of the α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor subunits GluA1 and GluA2 in prefrontal neurons. We show that LY37 significantly increased the surface and total expression of both GluA1 and GluA2 subunits in cultured prefrontal neurons and in vivo. This effect was mimicked by the selective mGluR2 agonist LY395756 and was blocked by mGluR2/3 antagonist LY341495. Moreover, we found that both GluA1 and GluA2 subunits were colocalized with PSD95 but not synapsin I, suggesting a postsynaptic localization. Consistently, treatment with LY37 significantly increased the amplitude, but not frequency, of miniature excitatory postsynaptic currents. Further, actinomycin-D blocked LY37's effects, suggesting a transcriptional regulation. In addition, application of glycogen synthase kinase-3beta (GSK-3ß) inhibitor completely blocked LY37's effect on GluA2 surface expression, whereas GSK-3ß inhibitor itself induced decreases in the surface and total protein levels of GluA1, but not GluA2 subunits. This suggests that GSK-3ß differentially mediates GluA1 and GluA2 trafficking. Further, LY37 significantly increased the phosphorylation, but not total protein, of extracellular signal-regulated kinase 1/2 (ERK1/2). Neither ERK1/2 inhibitor PD98059 alone nor PD98059 combined with LY37 treatment induced changes in GluA1 or GluA2 surface expression or total protein levels. Our data thus suggest that mGluR2/3 agonist regulates postsynaptic AMPA receptors by affecting the synaptic trafficking of both GluA1 and GluA2 subunits and that the regulation is likely through ERK1/2 signaling in GluA1 and/or both ERK1/2 and GSK-3ß signaling pathways in the GluA2 subunit.

Hyperdopaminergic modulation of inhibitory transmission is dependent on GSK-3ß signaling-mediated trafficking of GABAA receptors.

Cortical dopamine (DA) modulation of the gamma-amino butyric acid (GABA) system is closely associated with cognitive function and psychiatric disorders. We recently reported that the glycogen synthase kinase 3ß (GSK-3ß) pathway is required for hyperdopamine/D2 receptor-mediated inhibition of NMDA receptors in the prefrontal cortex. Here we explore whether or not GSK-3ß is also involved in dopaminergic modulation of GABAA receptor-mediated inhibitory transmission. We confirmed that DA induces a dose-dependent, bidirectional regulatory effect on inhibitory postsynaptic currents (IPSCs) in prefrontal neurons. The modulatory effects of DA were differentially affected by co-application of GSK-3ß inhibitors and different doses of DA. GSK-3ß inhibitors completely blocked high-dose (20 µM) DA-induced depressive effects on IPSCs but exhibited limited effects on the facilitating regulation of IPSC in low-dose DA (200 nM). We also confirmed that surface expressions of GABAA receptor ß2/3 subunits were significantly decreased by DA applied in cultured prefrontal neurons and in vivo administration of DA reuptake inhibitor. These effects were blocked by prior administration of GSK-3ß inhibitors. We explored DA-mediated regulation of GABAA receptor trafficking and exhibited the participation of brefeldin A-inhibited GDP/GTP exchange factor 2 (BIG2) or dynamin-dependent trafficking of GABAA receptors. Together, these data suggest that DA may act through different signaling pathways to affect synaptic inhibition, depending on the concentration. The GSK-3ß signaling pathway is involved in DA-induced decrease in BIG2-dependent insertion and an increase in the dynamin-dependent internalization of GABAA receptors, which results in suppression of inhibitory synaptic transmission.

Effect of total glycosides from Eucommia ulmoides seed on bone microarchitecture in rats.

Du-Zhong is one of the most important tonic herbs in traditional Chinese medicine for the treatment of bone fractures and other bone diseases. The present study examined whether Du-Zhong seed extract named total glycosides from Eucommia ulmoides seed (TGEUS) could display an increased effect on bone density and bone strength of the femur in rats. Sprague-Dawley rats were used and randomly assigned to the normal group and the TGEUS group (400 mg/kg body weight/day). Daily oral administration of TGEUS was found to increase significantly the biomechanical quality of the femur. The mechanical changes were associated with a bone mineral density (BMD) increase or even with some improvements in microarchitecture. Micro-CT analysis of the distal femur showed that TGEUS significantly increased the bone volume/tissue volume (BV/TV), connectivity density (Conn.D), trabecular number (Tb.N) and trabecular thickness (Tb.Th), and decreased trabecular separation (Tb.Sp) and the structure model index (SMI) in normal rats. To conclude, TGEUS taken orally increased bone density and altered bone histomorphology, suggesting that TGEUS might be a potential alternative medicine for the treatment of postmenopausal osteoporosis.

X-ray crystallographic study of ranaconitine.

The crystal structure of natural diterpenoid alkaloid ranaconitine isolated from Aconitum sinomontanum Nakai has been determined by single crystal X-ray diffraction analysis. The crystal presents a monoclinic system, space group C2 with Z = 4, unit cell dimensions a = 30.972(19) angstrom, b = 7.688(5) angstrom, and c = 19.632(12) angstrom. Moreover, the intermolecular O-H...O hydrogen bonds and weak pi-pi interactions play a critical role in expanding the dimensionality.

X-ray crystal structure of iridoid glucoside aucubin and its aglycone.

X-ray diffraction analyses of iridoid glycoside aucubin (1) and its aglycone aucubigenin (2) are reported. It was found that crystals of 1 are orthorhombic, with P2(1)2(1)2(1) space group, both cyclopentane ring and pyran ring adopt envelope conformations, and the Glc moiety is in the (4)C(1) conformation. Crystals of 2 are monoclinic, with space group P2(1), the cyclopentane and pyran rings also adopt the envelope conformation. The absolute configurations of 1 and 2 were also determined. Intensive O-H . . . O hydrogen bonds in both crystal lattices were observed.