The aim of the present study was to explore the role of group II and III metabotropic glutamate receptors (mGluRs) in carotid body plasticity induced by chronic intermittent hypoxia (CIH) in rats. Sprague Dawley (SD) rats were treated with CIH in Oxycycler A84 hypoxic chamber for 4 weeks, and the tail artery blood pressure was measured at the end of model preparation. RT-qPCR was performed to examine the mRNA expression levels of mGluR2/3/8 in rat carotid body. Carotid sinus nerve activity was detected by ex vivo carotid sinus nerve discharge recording technique, and acute intermittent hypoxia (AIH) was administered to induce carotid body sensory long-term facilitation (sLTF), in order to observe the role of group II and group III mGluRs in carotid body plasticity induced by CIH. The results showed that: 1) After 4 weeks of CIH exposure, the blood pressure of rats increased significantly; 2) CIH down-regulated the mRNA levels of mGluR2/3, and up-regulated the mRNA level of mGluR8 in the carotid body; 3) AIH induced sLTF in carotid body of CIH group. In the CIH group, activation of group II mGluRs had no effect on sLTF of carotid body, while activation of group III mGluRs completely inhibited sLTF. These results suggest that CIH increases blood pressure in rats, and group III mGluRs play an inhibitory role in CIH-induced carotid body plasticity in rats.
Rats ; Animals ; Carotid Body/metabolism* ; Rats, Sprague-Dawley ; Hypoxia ; Receptors, Metabotropic Glutamate/metabolism* ; RNA, Messenger/metabolism*

The purpose of the present study was to explore the role of carotid body metabotropic glutamate receptor 1 (mGluR1) in chronic intermittent hypoxia (CIH)-induced carotid body plasticity. Sprague Dawley (SD) rats were exposed to CIH (6%-21% O₂, 4 min/cycle, 8 h/day) for 4 weeks. The blood pressure of rats was monitored non-invasively by tail-cuff method under consciousness. RT-qPCR was used to examine the mRNA expression level of mGluR1 in rat carotid body. Western blot was used to detect the protein expression level of mGluR1 in rat carotid body. The role of mGluR1 in CIH-induced carotid body sensory long-term facilitation (sLTF) was investigated by ex vivo carotid sinus nerve discharge recording, and the carotid body sLTF was evoked by a 10-episode of repetitive acute intermittent hypoxia (AIH: 1 min of 5% O₂ interspersed with 5 min of 95% O₂). The results showed that: 1) CIH increased the systolic blood pressure (P < 0.001), diastolic blood pressure (P < 0.005) and mean arterial blood pressure (P < 0.001) of rats; 2) CIH decreased the mRNA and protein levels of mGluR1 in the rat carotid body (P < 0.01); 3) 4 weeks of CIH induced carotid body sLTF significantly, exhibiting as an increasing baseline sensory activity during post-AIH, which was inhibited by application of an agonist of group I metabotropic glutamate receptors, (S)-3,5-dihydroxyphenylglycine (DHPG), during sLTF induction (P < 0.005). In summary, these results suggest that activation of mGluR1 inhibits CIH-induced carotid body plasticity in rats.
Rats ; Animals ; Carotid Body/metabolism* ; Rats, Sprague-Dawley ; Hypoxia ; Receptors, Metabotropic Glutamate/metabolism* ; RNA, Messenger/metabolism*

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is the most abundant kinase within excitatory synapses in the mammalian brain. It interacts with and phosphorylates a large number of synaptic proteins, including major ionotropic glutamate receptors (iGluRs) and group I metabotropic glutamate receptors (mGluRs), to constitutively and/or activity-dependently regulate trafficking, subsynaptic localization, and function of the receptors. Among iGluRs, the N-methyl-D-aspartate receptor (NMDAR) is a direct target of CaMKII. By directly binding to an intracellular C-terminal (CT) region of NMDAR GluN2B subunits, CaMKII phosphorylates a serine residue (S1303) in the GluN2B CT. CaMKII also phosphorylates a serine site (S831) in the CT of α-amino-3-hydroxy-5- methylisoxazole-4-propionic acid receptors. This phosphorylation enhances channel conductance and is critical for synaptic plasticity. In addition to iGluRs, CaMKII binds to the proximal CT region of mGluR1a, which enables the kinase to phosphorylate threonine 871. Agonist stimulation of mGluR1a triggers a CaMKII-mediated negative feedback to facilitate endocytosis and desensitization of the receptor. CaMKII also binds to the mGluR5 CT. This binding seems to anchor and accumulate inactive CaMKII at synaptic sites. Active CaMKII dissociates from mGluR5 and may then bind to adjacent GluN2B to mediate the mGluR5-NMDAR coupling. Together, glutamate receptors serve as direct substrates of CaMKII. By phosphorylating these receptors, CaMKII plays a central role in controlling the number and activity of the modified receptors and determining the strength of excitatory synaptic transmission.
Calcium-Calmodulin-Dependent Protein Kinase Type 2 ; metabolism ; Neuronal Plasticity ; Phosphorylation ; Receptor, Metabotropic Glutamate 5 ; metabolism ; Receptors, Metabotropic Glutamate ; metabolism ; Receptors, N-Methyl-D-Aspartate ; metabolism ; Serine ; metabolism ; Synapses ; Synaptic Transmission

Disease Progression ; Humans ; Neoplasms ; diagnosis ; metabolism ; Receptors, Metabotropic Glutamate ; metabolism

OBJECTIVETo investigate the role of ventrolateral periaqueductal gray (VL-PAG) metabotropic glutamate receptors subtype 7 and 8 (mGluR 7/8) in descending modulation of cardiosomatic motor reflex (CMR) in rats.

METHODSAMN082 (agonist of mGluR 7) and DCPG (agonist of mGluR 8) were injected into the VL-PAG of a rat model of CMR to observe their effects in modulating CMR. The raphe magnus nucleus (NRM) or the gigantocellular reticular nucleus (Gi) was then damaged, and the changes in VL-PAG descending modulation were observed.

RESULTSSelective activation of mGluR 7 of the VL-PAG by AMN082 obviously facilitated capsaicin (CAP)-induced CMR (P<0.05), which was suppressed by DCPG-induced mGluR 8 activation (P<0.05). These facilitatory or inhibitory effects were completely reversed by group III mGluR antagonist MSOP. Damaging the NRM of VL-PAG main relay nucleus did not significantly affect the facilitatory effect produced by AMN082 microinjection (P>0.05), but partially attenuated the inhibitory effect of DCPG microinjection (P<0.05). Both the facilitatory effect of AMN082 and the inhibitory effect of DCPG were reduced obviously after bilateral Gi damage (P<0.05).

CONCLUSIONVL-PAG mGluR 7 and mGluR 8 mediate biphasic regulation of CMR in rats probably through activation of different sub-nuclei and different neurons in the rostroventral medulla.

Animals ; Benzhydryl Compounds ; pharmacology ; Benzoates ; pharmacology ; Glycine ; analogs & derivatives ; pharmacology ; Male ; Medulla Oblongata ; metabolism ; Periaqueductal Gray ; metabolism ; Physical Conditioning, Animal ; Rats ; Rats, Sprague-Dawley ; Receptors, Metabotropic Glutamate ; agonists ; metabolism ; Reflex ; physiology

The present study was to investigate the role of the quinolinic acid (QUIN) and its relationship with N-methyl-D-aspartic acid (NMDA) receptor and metabotropic glutamate receptor 1 (mGluR1) in depression induced by chronic unpredictable mild stress (CUMS) in hippocampus. CUMS-induced depression model was established in Sprague-Dawley rats. Intrahippocampal injections of QUIN, QUIN antagonist Ro61-8048, non-competitive NMDA receptor antagonist MK-801 and mGluR1 antagonist AIDA were respectively adopted by rat brain stereotaxic coordinates. The behavioral observations were conducted by measurement of weight changes, sucrose preference test, open-field test and tail suspension test. The concentration of glutamic acid (Glu) and the expression of its receptor subunits in hippocampus were detected by HPLC and Western blot, respectively. The QUIN content in hippocampus was determined by enzyme linked immunosorbent assay (ELISA). The result showed that CUMS significantly induced the depressive-like behaviors in rats, increased the contents of QUIN and Glu, and upregulated the expression of NMDA receptor subunits NR2B and mGluR1 in hippocampus. Microinjection of QUIN into hippocampus resulted in animal depressive-like behaviors, and increased the content of Glu and the expression of NR2B and mGluR1 significantly. QUIN antagonist Ro61-8048 effectively restrained the depression-like behaviors induced by CUMS, and decreased the content of Glu and the expression of NR2B and mGluR1 significantly. Intrahippocampal injections of MK-801 and AIDA effectively improved the depression-like behaviors induced by CUMS and decreased the Glu content. The results suggest that CUMS may contribute to the production and release of QUIN in hippocampal microglia. QUIN results in elevation of Glu level via NMDA receptor and mGluR1, and the increase of expression of NR2B and mGluR1 in hippocampus, which leads to depression-like behaviors in the end.
Animals ; Behavior, Animal ; Depression ; drug therapy ; Dizocilpine Maleate ; pharmacology ; Glutamic Acid ; metabolism ; Hippocampus ; drug effects ; metabolism ; Quinolinic Acid ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Metabotropic Glutamate ; metabolism ; Receptors, N-Methyl-D-Aspartate ; metabolism ; Stress, Psychological

OBJECTIVETo investigate the expression of metabotropic glutamate receptor 4 (mGluR4) in cardiomyocytes differentiated from mouse embryonic stem cells (ES cells).

METHODSES cells were differentiated into cardiomyocytes with hanging-drop cultures. Retinoic acid (RA) and dimethyl sulfoxide (DMSO) were used as positive and negative controls, respectively. The co-expression of cardiac sarcomeric protein (α-actinin or troponin-T) and mGluR4 were verified by immunocytochemistry and flow cytometry analysis. The mRNA and protein expressions of mGluR4 were verified by RT-PCR and Western blot analysis, respectively. Meanwhile, the expression of mGluR4 in prenatal mouse heart was also examined.

RESULTSmGluR4 was expressed in both mouse ES cells and ES cell-derived cardiomyocytes. The level of mGluR4 protein expression decreased during the maturation of the cardiomyocytes. The co-expression rate of mGluR4 and Troponin T in the beating embryoid bodies (EBs) was only (3.00 ±1.00)%. On the other hand, mGluR4 gene and protein expressions showed remarkable down-regulation in the development of mouse fetal heart, which was not detected in mouse adult heart.

CONCLUSIONThe expression of mGluR4 is down-regulated in the cardiomyocyte differentiation of ES cells. The trend of expression is consistent with that in the prenatal mouse heart development.

Animals ; Cell Differentiation ; physiology ; Cell Line ; Embryonic Stem Cells ; cytology ; metabolism ; Mice ; Mice, Inbred ICR ; Myocytes, Cardiac ; cytology ; metabolism ; RNA, Messenger ; genetics ; Receptors, Metabotropic Glutamate ; genetics ; metabolism

OBJECTIVETo investigate the expression of metabotropic glutamate receptor 5 (mGluR5) and its cellular distribution in the frontal cortex, ventricular zone (VZ) and subventricular zone (SVZ) in human fetuses.

METHODSAccording to the gestational age, the collected fetuses were divided into 4 groups, namely 9-11 weeks, 14-16 weeks, 22-24 weeks and 32-36 weeks. Brain tissue blocks including the frontal lobe or VZ/SVZ were prepared into slices, and the expression pattern and cellular distribution of mGluR5 in the frontal cortex and VZ/SVZ were observed by immunohistochemistry or immunofluorescence.

RESULTSmGluR5 immunoreactivity was present in the cell membrane in the frontal cortex, VZ and SVZ from the 9th to 36th weeks and the immunoreactivity in the marginal zone (MZ) and cortical plate (CP) was markedly stronger than that in VZ and SVZ. The cells expressing mGluR5 included neural stem/progenitor cells in the VZ and SVZ, immature neurons in the VZ and MZ, and numerous mature neurons in the CP.

CONCLUSIONmGluR5 is expressed by a variety of cells such as neural stem cells in the frontal cortex, VZ and SVZ in human fetus, suggesting a role of mGluR5 in the development of human cerebral cortex.

Cerebral Cortex ; cytology ; Cerebral Ventricles ; cytology ; metabolism ; Fetus ; cytology ; metabolism ; Frontal Lobe ; cytology ; metabolism ; Humans ; Neural Stem Cells ; cytology ; metabolism ; Receptor, Metabotropic Glutamate 5 ; Receptors, Metabotropic Glutamate ; metabolism

The study aims to identify the role of cAMP-PKA pathway in the group Ⅱ metabotropic glutamate receptors (mGluRs)-mediated regulation of respiratory rhythm from the brainstem slice. Neonatal (aged 0-3 d) Sprague-Dawley rats of either sex were used. The brainstem slice containing the medial region of the nucleus retrofacialis (mNRF) and the hypoglossal nerve rootlets was prepared, and the surgical procedure was performed in the modified Kreb's solution (MKS) with continuous carbogen (95% O2 and 5% CO2) bubbling, and ended in 3 min. Respiratory rhythmical discharge activity (RRDA) of the hypoglossal nerve rootlets was recorded by suction electrode. Eighteen brainstem slice preparations were divided into 3 groups. In group 1, group Ⅱ mGluRs specific antagonist (2S)-α-ethylglutamic acid (EGLU) was added into the perfusion solution for 10 min. In group 2, after application of Forskolin for 10 min, washout with MKS, the slice was perfused with Rp-cyclic 3', 5'-hydrogen phosphorothioate adenosine triethylammonium salt (Rp-cAMPS) alone for another 10 min. In group 3, after application of Rp-cAMPS for 10 min, additional EGLU was added into the perfusion for another 10 min. The results showed EGLU shortened respiratory cycle (RC), but the changes of integral amplitude (IA) and inspiratory time (TI) were not statistically significant. Forskolin induced significant decreases in RC, and increased TI, IA. Rp-cAMPS could make the opposite effect compared with the changes of RRDA with Forskolin. The effect of EGLU on the RRDA was inhibited after blocking the cAMP-PKA pathway. Taken together, cAMP-PKA pathway may play an important role in the group Ⅱ mGluRs-mediated regulation of RRDA in the brainstem slice of neonatal rats.
Animals ; Animals, Newborn ; Brain Stem ; physiology ; Cyclic AMP-Dependent Protein Kinases ; metabolism ; Female ; In Vitro Techniques ; Male ; Rats ; Rats, Sprague-Dawley ; Receptors, Metabotropic Glutamate ; physiology ; Respiration ; Signal Transduction ; physiology

The aim of this study is to investigate the effect of (S)-4-carboxy-3-hydroxy-phenylglycine [(S)-4C3HPG], a mixed group I glutamate metabotropic receptor antagonist and a group II agonist, on impairment in a cortical impact model of traumatic brain injury (TBI) in mice and to elucidate the possible mechanisms. Mice were injected (i.p.) with saline, 1 mg/kg (S)-4C3HPG, 5 mg/kg (S)-4C3HPG and 10 mg/kg (S)-4C3HPG (n=10 per group), respectively, at 30 min before moderate TBI. Neurological deficit scores, water content in injured brain and glutamate concentration in cerebral spinal fluid (CSF) were detected at 24 h after TBI. The expressions of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) mRNA in injured cortex were also detected by real-time RT-PCR. The results showed that the neurological deficits and cerebral edema were significantly attenuated in mice pretreated with (S)-4C3HPG (5 and 10 mg/kg respectively) compared with those in mice pretreated with saline. Furthermore, (S)-4C3HPG treatment also decreased the glutamate concentration in CSF and the expressions of TNF-α and IL-1β mRNA remarkably in a dose-dependent manner. These results suggest that (S)-4C3HPG treatment attenuates cortical impact-induced brain injury possibly via suppression of glutamate release and inhibition of excessive inflammatory cytokine production. These findings highlight the potential benefit of glutamate metabotropic receptor ligand for preventing TBI.
Animals ; Brain Injuries ; drug therapy ; metabolism ; physiopathology ; Cytokines ; metabolism ; Glutamic Acid ; cerebrospinal fluid ; Glycine ; analogs & derivatives ; therapeutic use ; Male ; Mice ; Mice, Inbred C57BL ; Receptors, Metabotropic Glutamate ; agonists ; antagonists & inhibitors