Motor behavior induced by bergamot essential oil in experimental tasks is differentially modulated by pretreatment with metabotropic glutamate receptor 2/3 or 5 antagonists.

Bergamot essential oil shows anxiolytic-relaxant effects devoid of sedative action and motor impairment typical of benzodiazepines. Considering the potential for clinical of these effects, it is important to understand the underlying mechanisms of the phytocomplex. Modulation of glutamate group I and II metabotropic receptors is involved in stress and anxiety disorders, in cognition and emotions and increases locomotor activity and wakefulness. Interestingly, early data indicate that bergamot essential oil modulates glutamatergic transmission in specific manifestations of the central nervous system. The aim of this work is to investigate if selective antagonists of metabotropic glutamate 2/3 and 5 receptors affect behavioral parameters modulated by the phytocomplex. Male Wistar rats were used to measure behavioral parameters to correlate anxiety and motor activity using elevated plus maze (EPM), open field (OF), and rotarod tasks. Bergamot essential oil increases in EPM the time spent in open/closed arms and reduces total number of entries. The essential oil also increases immobility in EPM and OF and not affect motor coordination in rotarod. Pretreatment with the metabotropic glutamate antagonists does not affect the time spent in open/close arms, however, differently affects motor behavior measured after administration of phytocomplex. Particularly, glutamate 2/3 antagonist reverts immobility and glutamate 5 antagonist potentiates this parameter induced by the phytocomplex. Our data show that modulation of both metabotropic glutamate receptors is likely involved in some of behavioral effects of bergamot essential oil.

Graded heterogeneity of metabotropic signaling underlies a continuum of cell-intrinsic temporal responses in unipolar brush cells.

Many neuron types consist of populations with continuously varying molecular properties. Here, we show a continuum of postsynaptic molecular properties in three types of neurons and assess the functional correlates in cerebellar unipolar brush cells (UBCs). While UBCs are generally thought to form discrete functional subtypes, with mossy fiber (MF) activation increasing firing in ON-UBCs and suppressing firing in OFF-UBCs, recent work also points to a heterogeneity of response profiles. Indeed, we find a continuum of response profiles that reflect the graded and inversely correlated expression of excitatory mGluR1 and inhibitory mGluR2/3 pathways. MFs coactivate mGluR2/3 and mGluR1 in many UBCs, leading to sequential inhibition-excitation because mGluR2/3-currents are faster. Additionally, we show that DAG-kinase controls mGluR1 response duration, and that graded DAG kinase levels correlate with systematic variation of response duration over two orders of magnitude. These results demonstrate that continuous variations in metabotropic signaling can generate a stable cell-autonomous basis for temporal integration and learning over multiple time scales.

Protocol for interfering peptide injection into adult mouse hippocampus and spatial memory testing.

Metabotropic glutamate receptor-dependent long-term depression (mGluR-LTD) occurs in diverse brain regions and contributes to the plasticity of behavior, learning, and memory. mGluR-LTD relies on rapid (in minutes) local protein synthesis. Here, we describe a detailed protocol for delivering an interfering peptide into the adult mouse hippocampus. The delivered peptide disrupts the interaction between polyglutamine binding protein 1 and eukaryotic elongation factor 2, resulting in impaired hippocampal mGluR-LTD and mGluR-LTD-associated behaviors. For complete details on the use and execution of this protocol, please refer to Shen et al. (2021).

Inhibition of metabotropic glutamate receptor III facilitates sensitization to alkylating chemotherapeutics in glioblastoma.

Glioblastoma (GBM), the most malignant tumor of the central nervous system, is marked by its dynamic response to microenvironmental niches. In particular, this cellular plasticity contributes to the development of an immediate resistance during tumor treatment. Novel insights into the developmental trajectory exhibited by GBM show a strong capability to respond to its microenvironment by clonal selection of specific phenotypes. Using the same mechanisms, malignant GBM do develop intrinsic mechanisms to resist chemotherapeutic treatments. This resistance was reported to be sustained by the paracrine and autocrine glutamate signaling via ionotropic and metabotropic receptors. However, the extent to which glutamatergic signaling modulates the chemoresistance and transcriptional profile of the GBM remains unexplored. In this study we aimed to map the manifold effects of glutamate signaling in GBM as the basis to further discover the regulatory role and interactions of specific receptors, within the GBM microenvironment. Our work provides insights into glutamate release dynamics, representing its importance for GBM growth, viability, and migration. Based on newly published multi-omic datasets, we explored the and characterized the functions of different ionotropic and metabotropic glutamate receptors, of which the metabotropic receptor 3 (GRM3) is highlighted through its modulatory role in maintaining the ability of GBM cells to evade standard alkylating chemotherapeutics. We addressed the clinical relevance of GRM3 receptor expression in GBM and provide a proof of concept where we manipulate intrinsic mechanisms of chemoresistance, driving GBM towards chemo-sensitization through GRM3 receptor inhibition. Finally, we validated our findings in our novel human organotypic section-based tumor model, where GBM growth and proliferation was significantly reduced when GRM3 inhibition was combined with temozolomide application. Our findings present a new picture of how glutamate signaling via mGluR3 interacts with the phenotypical GBM transcriptional programs in light of recently published GBM cell-state discoveries.

mGlu2/3 receptor in the prelimbic cortex is implicated in stress resilience and vulnerability in mice.

Resilience, referring to "achieving a positive outcome in the face of adversity", is a common phenomenon in daily life. Elucidating the mechanisms of stress resilience is instrumental to developing more effective treatments for stress-related psychiatric disorders such as depression. Metabotropic glutamate receptors (mGlu2/3 and mGlu5) within the medial prefrontal cortex (mPFC) have been recently recognized as promising therapeutic targets for rapid-acting antidepressant treatment. In this study, we assessed the functional roles of the mGlu2/3 and mGlu5 within different subregions of the mPFC in modulating stress resilience and vulnerability by using chronic social defeat stress (CSDS) paradigms in mice. Our results showed that approximately 51.6% of the subjects exhibited depression- or anxiety-like behaviors after exposure to CSDS. When a susceptible mouse was confronted with an attacker, c-Fos expression in the prelimbic cortex (PrL) subregion of the mPFC substantially increased. Compared with the resilient and control groups, the expression of mGlu2/3 was elevated in the PrL of the susceptible group. The expression of mGlu5 showed no significant difference among the three groups in the whole mPFC. Finally, we found that the social avoidance symptoms of the susceptible mice were rapidly relieved by intra-PrL administration of LY341495-an mGluR2/3 antagonists. The above results indicate that mGluR2/3 within the PrL may play an important regulatory role in stress-related psychiatric disorders. Our results are meaningful, as they expand our understanding of stress resilience and vulnerability which may open an avenue to develop novel, personalized approaches to mitigate depression and promote stress resilience.

Targeting metabotropic glutamate receptors for the treatment of depression and other stress-related disorders.

The discovery of robust antidepressant effects of ketamine in refractory patients has led to increasing focus on agents targeting glutamatergic signaling as potential novel antidepressant strategy. Among the agents targeting the glutamatergic system, compounds acting at metabotropic glutamate (mGlu) receptors are among the most promising agents under studies for depressive disorders. Further, the receptor diversity, distinct distribution in the CNS, and ability to modulate the glutamatergic neurotransmission in the brain areas implicated in mood disorders make them an exciting target for stress-related disorders. In preclinical models, antidepressant and anxiolytic effects of mGlu5 negative allosteric modulators (NAMs) have been reported. Interestingly, mGlu2/3 receptor antagonists show fast and sustained antidepressant-like effects similar to that of ketamine in rodents. Excitingly, they can also induce antidepressant effects in the animal models of treatment-resistant depression and are devoid of the side-effects associated with ketamine. Unfortunately, clinical trials of both mGlu5 and mGlu2/3 receptor NAMs have been inconclusive, and additional trials using other compounds with suitable preclinical and clinical properties are needed. Although group III mGlu receptors have gained less attention, mGlu7 receptor ligands have been shown to induce antidepressant-like effects in rodents. Collectively, compounds targeting mGlu receptors provide an alternative approach to fill the outstanding clinical need for safer and more efficacious antidepressants. This article is part of the special Issue on "Glutamate Receptors - mGluRs".

Novel thienopyrimidine analogues as potential metabotropic glutamate receptors inhibitors and anticancer activity: Synthesis, In-vitro, In-silico, and SAR approaches.

There is a continuous need in drug development approach for synthetic anticancer analogues with new therapeutic targets to diminish chemotherapeutic resistance of cancer cells. This study presents new group of synthetic thienopyrimidine analogues (1-9) aims as mGluR-1 inhibitors with anticancer activity. In-vitro antiproliferative assessment was carried out using viability assay against cancer cell lines (MCF-7, A-549 and PC-3) compared to WI-38 normal cell line. Analogues showed variable anticancer activity with IC50 ranging from 6.60 to 121 µg/mL with compound 7b is the most potent analogue against the three cancer cell lines (MCF-7; 6.57 ± 0.200, A-549; 6.31 ± 0.400, PC-3;7.39 ± 0.500 µg/mL) compared to Doxorubicin, 5-Flurouracil and Riluzole controls. Selected compounds were tested as mGluR-1 inhibitors in MCF-7 cell line and results revealed compound 7b induced significant reduction in extracellular glutamate release (IC50; 4.96 ± 0.700 µM) compared to other analogues and next to Riluzole (IC50; 2.80 ± 0.500 µM) of the same suggested mode of action. Furthermore, both cell cycle and apoptosis assays confirmed the potency of compound 7b for early apoptosis of MCF-7 at G2/M phase and apoptotic positive cell shift to (91.4%) compared to untreated control (19.6%) and Raptinal positive control (51.4%). On gene expression level, compound 7b induced over-expression of extrinsic (FasL, TNF-α and Casp-8), intrinsic (Cyt-C, Casp-3, Bax) apoptotic genes with down-regulation of anti-apoptotic Bcl-2 gene with boosted Bax/Bcl-2 ratio to 2.6-fold increase. Molecular docking and dynamic studies confirmed the biological potency through strong binding and stability modes of 7b where it was faster in reaching the equilibrium point and achieving the stability than Riluzole over 20 ns MD. These results suggest compound 7b as a promising mGluR inhibitory scaffold with anticancer activity that deserves further optimization and in-depth In-vivo and clinical investigations.

Metabotropic Glutamate Receptor Blockade Reduces Preservation Damage in Livers from Donors after Cardiac Death.

We previously demonstrated that the blockade of mGluR5 by 2-methyl-6(phenylethynyl)pyridine (MPEP) reduces both cold and warm ischemia/reperfusion injury. Here we evaluated whether MPEP reduces the hepatic preservation injury in rat livers from cardiac-death-donors (DCDs). Livers from DCD rats were isolated after an in situ warm ischemia (30 min) and preserved for 22 h at 4 °C with UW solution. Next, 10 mg/Kg MPEP or vehicle were administered 30 min before the portal clamping and added to the UW solution (3 µM). LDH released during washout was quantified. Liver samples were collected for iNOS, eNOS, NO, TNF-α, ICAM-1, caspase-3 and caspase-9 protein expression and nuclear factor-erythroid-2-related factor-2 (Nrf2) gene analysis. Lower LDH levels were detected in control grafts versus DCD groups. An increase in eNOS and NO content occurred after MPEP treatment; iNOS and TNF-α content was unchanged. ICAM-1 expression was reduced in the MPEP-treated livers as well as the levels of caspase-3 and caspase-9. Nrf2, oxidative stress-sensitive gene, was recovered to control value by MPEP. These results suggest that MPEP can be used to reclaim DCD livers subjected to an additional period of cold ischemia during hypothermic storage. MPEP protects against apoptosis and increased eNOS, whose overexpression has been previously demonstrated to be protective in hepatic ischemia/reperfusion damage.

A fine-tuned azobenzene for enhanced photopharmacology in vivo.

Despite the power of photopharmacology for interrogating signaling proteins, many photopharmacological systems are limited by their efficiency, speed, or spectral properties. Here, we screen a library of azobenzene photoswitches and identify a urea-substituted "azobenzene-400" core that offers bistable switching between cis and trans with improved kinetics, light sensitivity, and a red-shift. We then focus on the metabotropic glutamate receptors (mGluRs), neuromodulatory receptors that are major pharmacological targets. Synthesis of "BGAG12,400," a photoswitchable orthogonal, remotely tethered ligand (PORTL), enables highly efficient, rapid optical agonism following conjugation to SNAP-tagged mGluR2 and permits robust optical control of mGluR1 and mGluR5 signaling. We then produce fluorophore-conjugated branched PORTLs to enable dual imaging and manipulation of mGluRs and highlight their power in ex vivo slice and in vivo behavioral experiments in the mouse prefrontal cortex. Finally, we demonstrate the generalizability of our strategy by developing an improved soluble, photoswitchable pore blocker for potassium channels.

Discovery and optimization of a novel CNS penetrant series of mGlu4 PAMs based on a 1,4-thiazepane core with in vivo efficacy in a preclinical Parkinsonian model.

A high throughput screen (HTS) identified a novel, but weak (EC50 = 6.2 µM, 97% Glu Max) mGlu4 PAM chemotype based on a 1,4-thiazepane core, VU0544412. Reaction development and chemical optimization delivered a potent mGlu4 PAM VU6022296 (EC50 = 32.8 nM, 108% Glu Max) with good CNS penetration (Kp = 0.45, Kp,uu = 0.70) and enantiopreference. Finally, VU6022296 displayed robust, dose-dependent efficacy in reversing Haloperidol-Induced Catalepsy (HIC), a rodent preclinical Parkinson's disease model.

Regulation of mGluR1 on the Expression of PKC and NMDAR in Aluminum-Exposed PC12 Cells.

Aluminum demonstrates clear neurotoxicity and can cause Alzheimer's disease (AD)-like symptoms, including cognitive impairment. One toxic effect of aluminum is a decrease in synaptic plasticity, but the specific mechanism remains unclear. In this study, PC12 cells were treated with Al(mal)3 to construct a toxic cell model. (S)-3,5-Dihydroxyphenylglycine (DHPG), α-methyl-4-carboxyphenylglycine (MCPG), and mGluR1-siRNA were used to interfere with the expression of metabotropic glutamate receptor subtype 1 (mGluR1). Polymerase chain reaction and western blotting were used to investigate the expression of mGluR1, protein kinase C (PKC), and N-methyl-D-aspartate receptor (NMDAR) subunits. ELISA was used to detect PKC enzyme activity. In PC12 cells, mRNA and protein expressions of PKC and NMDAR subunits were inhibited by Al(mal)3. Aluminum may further regulate the expression of NMDAR1 and NMDAR2B through mGluR1 to regulate PKC enzyme activity, thereby affecting learning and memory functions. Furthermore, the results implied that the mGluR1-PKC-NMDAR signaling pathway may predominately involve positive regulation. These findings provide new targets for studying the neurotoxic mechanism of aluminum.

The group II mGlu receptor antagonist LY341495 induces a rapid antidepressant-like effect and enhances the effect of ketamine in the chronic unpredictable mild stress model of depression in C57BL/6J mice.

Ketamine produces a rapid antidepressant effect, but its use can be associated with serious side effects. Hence, other therapeutic options that will allow us to obtain a quick and safe antidepressant effect by modulating glutamatergic transmission are needed. Antagonists of mGlu2/3 receptors, which share some mechanisms of action with ketamine, may be good candidates to obtain this effect. Here, we show that the metabotropic glutamate (mGlu) 2/3 receptor antagonist LY341495 induced a dose-dependent antidepressant-like effect in the chronic unpredictable mild stress (CUMS) model of depression in C57BL/6J mice after both single and subchronic (three-day) administration. Furthermore, a noneffective dose of LY341495 (0.3 mg/kg) given jointly with a noneffective dose of ketamine (3 mg/kg) reversed the CUMS-induced behavioral effects, indicating that coadministration of ketamine with an mGlu2/3 receptor antagonist might allow its therapeutically effective dose to be lowered. Western blot results indicate that mTOR pathway activation might be involved in the mechanism of action of this drug combination. Moreover, the combined doses of both substances did not produce undesirable behavioral effects characteristic of a higher dose of ketamine (10 mg/kg) commonly used in rodent studies to induce antidepressant effects. Coadministration of low doses of ketamine and LY341495 did not induce the hyperactivity typical of NMDA channel blockers, did not disturb short-term memory in the novel object recognition (NOR) test, and did not disturb motor coordination in the rotarod test. Our research not only confirmed the earlier data on the rapid antidepressant effect of mGlu2/3 receptor antagonists but also indicated that such compounds can safely lower the effective dose of ketamine.

mGlu3 receptor regulates microglial cell reactivity in neonatal rats.

BACKGROUND: Perinatal inflammation is a key factor of brain vulnerability in neonates born preterm or with intra-uterine growth restriction (IUGR), two leading conditions associated with brain injury and responsible for neurocognitive and behavioral disorders. Systemic inflammation is recognized to activate microglia, known to be the critical modulators of brain vulnerability. Although some evidence supports a role for metabotropic glutamate receptor 3 (mGlu3 receptor) in modulation of neuroinflammation, its functions are still unknown in the developing microglia. METHODS: We used a double-hit rat model of perinatal brain injury induced by a gestational low-protein diet combined with interleukin-1ß injections (LPD/IL-1ß), mimicking both IUGR and prematurity-related inflammation. The effect of LPD/IL-1ß on mGlu3 receptor expression and the effect of mGlu3 receptor modulation on microglial reactivity were investigated using a combination of pharmacological, histological, and molecular and genetic approaches. RESULTS: Exposure to LPD/IL-1ß significantly downregulated Grm3 gene expression in the developing microglia. Both transcriptomic analyses and pharmacological modulation of mGlu3 receptor demonstrated its central role in the control of inflammation in resting and activated microglia. Microglia reactivity to inflammatory challenge induced by LPD/IL-1ß exposure was reduced by an mGlu3 receptor agonist. Conversely, both specific pharmacological blockade, siRNA knock-down, and genetic knock-out of mGlu3 receptors mimicked the pro-inflammatory phenotype observed in microglial cells exposed to LPD/IL-1ß. CONCLUSIONS: Overall, these data show that Grm3 plays a central role in the regulation of microglial reactivity in the immature brain. Selective pharmacological activation of mGlu3 receptors may prevent inflammatory-induced perinatal brain injury.

Modulation by chronic stress and ketamine of ionotropic AMPA/NMDA and metabotropic glutamate receptors in the rat hippocampus.

Converging clinical and preclinical evidence has shown that dysfunction of the glutamate system is a core feature of major depressive disorder. In this context, the N-methyl-d-aspartate (NMDA) receptor antagonist ketamine has raised growing interest as fast acting antidepressant. Using the chronic mild stress (CMS) rat model of depression, performed in male rats, we aimed at analyzing whether hippocampal specific changes in subunit expression and regulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or NMDA ionotropic receptors and in metabotropic glutamate receptors could be associated with behavioral vulnerability/resilience to CMS. We also assessed whether acute ketamine (10 mg/kg) was able to dampen the alterations in CMS vulnerable animals. Although chronic stress and ketamine had no effect on ionotropic glutamate receptors mRNAs (expression, RNA editing and splicing), we found selective modulations in their protein expression, phosphorylation and localization at synaptic membranes. AMPA GluA2 expression at synaptic membranes was significantly increased only in CMS resilient rats (although a trend was found also in vulnerable animals), while its phosphorylation at Ser880 was higher in both CMS resilient and vulnerable rats, a change partially dampened by ketamine. In the hippocampus from all stressed groups, despite NMDA receptor expression levels were reduced in total extract, the levels of GluN2B-containing NMDA receptors were remarkably increased in synaptic membranes. Finally, mGlu2 underwent a selective downregulation in stress vulnerable animals, which was completely restored by acute ketamine. Overall, these results are in line with a hypofunction of activity-dependent glutamatergic synaptic transmission induced by chronic stress exposure in all the animals, as suggested by the alterations of ionotropic glutamate receptors expression and localization at synaptic level. At the same time, the selective modulation of mGlu2 receptor, confirms its previously hypothesized functional role in regulating stress vulnerability and, for the first time here, suggests a mGlu2 involvement in the fast antidepressant effect of ketamine.

Subtype-selective mechanisms of negative allosteric modulators binding to group I metabotropic glutamate receptors.

Group I metabotropic glutamate receptors (mGlu1 and mGlu5) are promising targets for multiple psychiatric and neurodegenerative disorders. Understanding the subtype selectivity of mGlu1 and mGlu5 allosteric sites is essential for the rational design of novel modulators with single- or dual-target mechanism of action. In this study, starting from the deposited mGlu1 and mGlu5 crystal structures, we utilized computational modeling approaches integrating docking, molecular dynamics simulation, and efficient post-trajectory analysis to reveal the subtype-selective mechanism of mGlu1 and mGlu5 to 10 diverse drug scaffolds representing known negative allosteric modulators (NAMs) in the literature. The results of modeling identified six pairs of non-conserved residues and four pairs of conserved ones as critical features to distinguish the selective NAMs binding to the corresponding receptors. In addition, nine pairs of residues are beneficial to the development of novel dual-target NAMs of group I metabotropic glutamate receptors. Furthermore, the binding modes of a reported dual-target NAM (VU0467558) in mGlu1 and mGlu5 were predicted to verify the identified residues that play key roles in the receptor selectivity and the dual-target binding. The results of this study can guide rational structure-based design of novel NAMs, and the approach can be generally applicable to characterize the features of selectivity for other G-protein-coupled receptors.

Regulation of Glutamatergic Activity via Bidirectional Activation of Two Select Receptors as a Novel Approach in Antipsychotic Drug Discovery.

Schizophrenia is a mental disorder that affects approximately 1-2% of the population and develops in early adulthood. The disease is characterized by positive, negative, and cognitive symptoms. A large percentage of patients with schizophrenia have a treatment-resistant disease, and the risk of developing adverse effects is high. Many researchers have attempted to introduce new antipsychotic drugs to the clinic, but most of these treatments failed, and the diversity of schizophrenic symptoms is one of the causes of disappointing results. The present review summarizes the results of our latest papers, showing that the simultaneous activation of two receptors with sub-effective doses of their ligands induces similar effects as the highest dose of each compound alone. The treatments were focused on inhibiting the increased glutamate release responsible for schizophrenia arousal, without interacting with dopamine (D2) receptors. Ligands activating metabotropic receptors for glutamate, GABAB or muscarinic receptors were used, and the compounds were administered in several different combinations. Some combinations reversed all schizophrenia-related deficits in animal models, but others were active only in select models of schizophrenia symptoms (i.e., cognitive or negative symptoms).

Synthesis and SAR of a series of mGlu7 NAMs based on an ethyl-8-methoxy-4-(4-phenylpiperazin-1-yl)quinoline carboxylate core.

A High-Throughput Screening (HTS) campaign identified a fundamentally new mGlu7 NAM chemotype, based on an ethyl-8-methoxy-4-(4-phenylpiperazin-1-yl)quinolone carboxylate core. The initial hit, VU0226390, was a potent mGlu7 NAM (IC50 = 647 nM, 6% L-AP4 min) with selectivity versus the other group III mGlu receptors (>30 µM vs. mGlu4 and mGlu8). A multi-dimensional optimization effort surveyed all regions of this new chemotype, and found very steep SAR, reminiscent of allosteric modulators, and unexpected piperazine mimetics (whereas classical bioisosteres failed). While mGlu7 NAM potency could be improved (IC50s ~ 350 nM), the necessity of the ethyl ester moiety and poor physiochemical and DMPK properties precluded optimization towards in vivo tool compounds or clinical candidates. Still, this hit-to-lead campaign afforded key medicinal chemistry insights and new opportunities.

Metabotropic Glutamate Receptor Subtype 7 Is Essential for Ejaculation.

Metabotropic glutamate receptor subtype 7 (mGluR7) is a member of the group III mGluRs, which are negatively coupled to adenylate cyclase via Gi/Go proteins and localized to presynaptic active zones of the mammalian central nervous system (CNS). To elucidate the mechanism of impaired reproductivity of mGluR7 knockout (KO) mice, we investigated sexual behavior in this line, which exhibits ejaculatory disorder, although with normal sexual motivation and erectile function. To identify the site of action within the CNS responsible for the effect of mGluR7 on ejaculation, we then used a para-chloroamphetamine (PCA)-induced ejaculation model. Intrathecal administration of the mGluR7-selective antagonist 6-(4-methoxyphenyl)-5-methyl-3-pyridin-4-ylisoxazolo[4,5-c]pyridin-4(5H)-one (MMPIP) into the lumbosacral spinal cord inhibited PCA-induced ejaculation. Immunohistochemistry revealed mGluR7-like immunoreactivity (LI) expressed in the same area where lumbar spinothalamic (LSt) cells regulate the parasympathetic ejaculatory pathway. At high magnification, the apposition of mGluR7-LI puncta and neuronal nitric oxide synthase (nNOS)-LI-positive putative parasympathetic preganglionic neurons was evident. These results indicate that mGluR7 in the lumbosacral spinal cord regulates ejaculation by potentiating the excitability of parasympathetic preganglionic neurons. The ejaculatory disorder is a major issue in the field of male reproductive function. Erectile dysfunction (ED) can be treated by phosphodiesterase type 5 inhibitors like sildenafil (Viagra®), but the ejaculatory disorder cannot. Lack of understanding of the ejaculatory mechanism hinders the development of therapies for ejaculatory problems. This study is the first to demonstrate that mGluR7 regulates ejaculation and the results provide insight into the mechanism of ejaculation as well as a strategy for future therapies to treat ejaculatory disorders in humans.

dmPFC-vlPAG projection neurons contribute to pain threshold maintenance and antianxiety behaviors.

The dorsal medial prefrontal cortex (dmPFC) has been recognized as a key cortical area for nociceptive modulation. However, the underlying neural pathway and the function of specific cell types remain largely unclear. Here, we show that lesions in the dmPFC induced an algesic and anxious state. Using multiple tracing methods including a rabies-based transsynaptic tracing method, we outlined an excitatory descending neural pathway from the dmPFC to the ventrolateral periaqueductal gray (vlPAG). Specific activation of the dmPFC/vlPAG neural pathway by optogenetic manipulation produced analgesic and antianxiety effects in a mouse model of chronic pain. Inhibitory neurons in the dmPFC were specifically activated using a chemogenetic approach, which logically produced an algesic and anxious state under both normal and chronic pain conditions. Antagonists of the GABAA receptor (GABAAR) or mGluR1 were applied to the dmPFC, which produced analgesic and antianxiety effects. In summary, the results of our study suggest that the dmPFC/vlPAG neural pathway might participate in the maintenance of pain thresholds and antianxiety behaviors under normal conditions, while silencing or suppressing the dmPFC/vlPAG pathway might be involved in the initial stages and maintenance of chronic pain and the emergence of anxiety-like behaviors.

mGlu2/3 receptor as a novel target for rapid acting antidepressants.

Given that ketamine, a noncompetitive N-methyl-d-aspartate receptor antagonist that exerts rapid antidepressant effects in patients with treatment-resistant depression, also has undesirable adverse effects, agents that can be used as alternatives to ketamine have been actively pursued. Group II metabotropic glutamate (mGlu) receptors, consisting of mGlu2 and mGlu3 receptors, have emerged as one of the most promising targets in the development of ketamine-like antidepressants. Indeed, mGlu2/3 receptor antagonists have been demonstrated to exert rapid antidepressant effects in animal models and to be efficacious in animal models refractory to conventional antidepressants. Moreover, there are striking similarities between mGlu2/3 receptor antagonists and ketamine in terms of not only their antidepressant profiles, but also the underlying mechanisms of their antidepressant effects. Nonetheless, studies in rodents have shown that mGlu2/3 receptor antagonists do not cause ketamine-like adverse events, such as psychotomimetic-like behavior, abuse potential or neurotoxicity, supporting the usefulness of mGlu2/3 receptor antagonists as alternatives to ketamine. In this chapter, the past and recent research on the antidepressant effects of mGlu2/3 receptor antagonists will be reviewed. In particular, the potential of mGlu2/3 receptor antagonists as novel ketamine-like antidepressants will be emphasized.