Identification of a small-molecule ligand that activates the neuropeptide receptor GPR171 and increases food intake

The role of orphan G protein-coupled receptors in pain

G protein-coupled receptors (GPCRs), which form the largest family of membrane protein receptors in humans, are highly complex signaling systems with intricate structures and dynamic conformations and locations. Among these receptors, a specific subset is referred to as orphan GPCRs (oGPCRs) and has garnered significant interest in pain research due to their role in both central and peripheral nervous system function. The diversity of GPCR functions is attributed to multiple factors, including allosteric modulators, signaling bias, oligomerization, constitutive signaling, and compartmentalized signaling. This review primarily focuses on the recent advances in oGPCR research on pain mechanisms, discussing the role of specific oGPCRs including GPR34, GPR37, GPR65, GPR83, GPR84, GPR85, GPR132, GPR151, GPR160, GPR171, GPR177, and GPR183. The orphan receptors among these receptors associated with central nervous system diseases are also briefly described. Understanding the functions of these oGPCRs can contribute not only to a deeper understanding of pain mechanisms but also offer a reference for discovering new targets for pain treatment.

Illuminating the understudied GPCR-ome

G-protein-coupled receptors (GPCRs) are the target of >30% of approved drugs. Despite their popularity, many of the >800 human GPCRs remain understudied. The Illuminating the Druggable Genome (IDG) project has generated many tools leading to important insights into the function and druggability of these so-called 'dark' receptors. These tools include assays, such as PRESTO-TANGO and TRUPATH, billions of small molecules made available via the ZINC virtual library, solved orphan GPCR structures, GPCR knock-in mice, and more. Together, these tools are illuminating the remaining 'dark' GPCRs.

The dark sides of the GPCR tree - research progress on understudied GPCRs

A large portion of the human GPCRome is still in the dark and understudied, consisting even of entire subfamilies of GPCRs such as odorant receptors, class A and C orphans, adhesion GPCRs, Frizzleds and taste receptors. However, it is undeniable that these GPCRs bring an untapped therapeutic potential that should be explored further. Open questions on these GPCRs span diverse topics such as deorphanisation, the development of tool compounds and tools for studying these GPCRs, as well as understanding basic signalling mechanisms. This review gives an overview of the current state of knowledge for each of the diverse subfamilies of understudied receptors regarding their physiological relevance, molecular mechanisms, endogenous ligands and pharmacological tools. Furthermore, it identifies some of the largest knowledge gaps that should be addressed in the foreseeable future and lists some general strategies that might be helpful in this process.

A small molecule ligand for the novel pain target, GPR171, produces minimal reward in mice

ProSAAS is one of the most abundant proteins in the brain and is processed into several smaller peptides. One of which, BigLEN, is an endogenous ligand for the G protein-coupled receptor, GPR171. Recent work in rodent models has shown that a small-molecule ligand for GPR171, MS15203, increases morphine antinociception and is effective in lessening chronic pain. While these studies provide evidence for GPR171 as a possible pain target, its abuse liability has not yet been assessed and was evaluated in the current study. We first mapped the distribution of GPR171 and ProSAAS throughout the reward circuit of the brain using immunohistochemistry and showed that GPR171 and ProSAAS are localized in the hippocampus, basolateral amygdala, nucleus accumbens, prefrontal cortex. In the major dopaminergic structure, the ventral tegmental area (VTA), GPR171 appeared to be primarily localized in dopamine neurons while ProSAAS is outside of dopamine neurons. Next, MS15203 was administered to mice with or without morphine, and VTA slices were stained for the immediate early gene c-Fos as a marker of neuronal activation. Quantification of c-Fos-positive cells revealed no statistical difference between MS15203 and saline, suggesting that MS15203 does not increase VTA activation and dopamine release. The results of a conditioned place preference experiment showed that treatment with MS15203 produced no place preference indicating a lack of reward-related behavior. Taken together this data provides evidence that the novel pain therapeutic, MS15203, has minimal reward liability. Therefore, GPR171 deserves further exploration as a pain target. SIGNIFICANCE STATEMENT: MS15203, a drug that activates the receptor GPR171, was previously shown to increase morphine analgesia. The authors use in vivo and histological techniques to show that it fails to activate the rodent reward circuitry, providing support for the continued exploration of MS15203 as a novel pain drug, and GPR171 a novel pain target.

Regulatory T cells suppress CD4+ effector T cell activation by controlling protein synthesis

Regulatory T cells (Tregs) suppress the activation and subsequent effector functions of CD4 effector T cells (Teffs). However, molecular mechanisms that enforce Treg-mediated suppression in CD4 Teff are unclear. We found that Tregs suppressed activation-induced global protein synthesis in CD4 Teffs prior to cell division. We analyzed genome-wide changes in the transcriptome and translatome of activated CD4 Teffs. We show that mRNAs encoding for the protein synthesis machinery are regulated at the level of translation in activated CD4 Teffs by Tregs. Tregs suppressed global protein synthesis of CD4 Teffs by specifically inhibiting mRNAs of the translation machinery at the level of mTORC1-mediated translation control through concerted action of immunosuppressive cytokines IL-10 and TGFβ. Lastly, we found that the therapeutic targeting of protein synthesis with the RNA helicase eIF4A inhibitor rocaglamide A can alleviate inflammatory CD4 Teff activation caused by acute Treg depletion in vivo. These data show that peripheral tolerance is enforced by Tregs through mRNA translational control in CD4 Teffs.

The oxytocin receptor represents a key hub in the GPCR heteroreceptor network: potential relevance for brain and behavior

In the last 10 years, it has become increasingly clear that large numbers of axon collaterals extend from the oxytocin (OXT) hypothalamic axons, especially the parvocellular components, to other brain regions. Consequently, the OXT signaling system forms, like other monoamine axons, a rich functional network across several brain regions. In this manuscript, we review the recently indicated higher order G-protein coupled heteroreceptor complexes of the oxytocin receptor (OXTR), and how these, via allosteric receptor-receptor interactions modulate the recognition, signaling, and trafficking of the participating receptor protomers and their potential impact for brain and behavior. The major focus will be on complexes of the OXTR protomer with the dopamine D2 receptor (D2R) protomer and the serotonin 2A (5-HT2AR) and 2C (5-HT2CR) receptor protomers. Specifically, the existence of D2R-OXTR heterocomplexes in the nucleus accumbens and the caudate putamen of rats has led to a postulated function for this heteromer in social behavior. Next, a physical interaction between OXTRs and the growth hormone secretagogue or ghrelin receptor (GHS-R1a) was demonstrated, which consequently was able to attenuate OXTR-mediated Gαq signaling. This highlights the potential of ghrelin-targeted therapies to modulate oxytocinergic signaling with relevance for appetite regulation, anxiety, depression, and schizophrenia. Similarly, evidence for 5-HT2AR-OXTR heteromerization in the pyramidal cell layer of CA2 and CA3 in the dorsal hippocampus and in the nucleus accumbens shell was demonstrated. This complex may offer new strategies for the treatment of both mental disease and social behavior. Finally, the 5-HT2CR-OXTR heterocomplexes were demonstrated in the CA1, CA2, and CA3 regions of the dorsal hippocampus. Future work should be done to investigate the precise functional consequence of region-specific OXTR heteromerization in the brain, as well across the periphery, and whether the integration of neuronal signals in the brain may also involve higher order OXTR-GHS-R1a heteroreceptor complexes including the dopamine (DA), noradrenaline (NA) or serotonin (5-HT) receptor protomers or other types of G-protein coupled receptors (GPCRs).

GPR171 activation regulates morphine tolerance but not withdrawal in a test-dependent manner in mice

A newly deorphanized G protein-coupled receptor, GPR171, is found to be highly expressed within the periaqueductal gray, a pain-modulating region in the brain. Our recent research has shown that a GPR171 agonist increases morphine antinociception in male mice and opioid signaling in vitro . The objective of this study was to evaluate the effects of combination treatment in females as well as whether chronic treatment can be used without exacerbating morphine-induced tolerance and withdrawal in female and male mice. Our results demonstrate that activation of GPR171 with an agonist attenuates morphine tolerance in both female and male mice on the tail-flick test, but not the hotplate test. Importantly, the GPR171 agonist in combination with morphine does not exacerbate morphine-induced tolerance and withdrawal during long-term morphine treatment. Taken together, these data suggest that the GPR171 agonist may be combined with morphine to maintain antinociception while reducing the dose of morphine and therefore reducing side effects and abuse liability. The outcome of this study is clearly an important step toward understanding the functional interactions between opioid receptors and GPR171 and developing safer therapeutics for long-term pain management.

GPR171 Agonist Reduces Chronic Neuropathic and Inflammatory Pain in Male, But Not Female Mice

Chronic pain is a growing public health crisis that requires exigent and efficacious therapeutics. GPR171 is a promising therapeutic target that is widely expressed through the brain, including within the descending pain modulatory regions. Here, we explore the therapeutic potential of the GPR171 agonist, MS15203, in its ability to alleviate chronic pain in male and female mice using a once-daily systemic dose (10 mg/kg, i.p.) of MS15203 over the course of 5 days. We found that in our models of Complete Freund's Adjuvant (CFA)-induced inflammatory pain and chemotherapy-induced peripheral neuropathy (CIPN), MS15203 did not alleviate thermal hypersensitivity and allodynia, respectively, in female mice. On the other hand, MS15203 treatment decreased the duration of thermal hypersensitivity in CFA-treated male mice following 3 days of once-daily administration. MS15203 treatment also produced an improvement in allodynia in male mice, but not female mice, in neuropathic pain after 5 days of treatment. Gene expression of GPR171 and that of its endogenous ligand BigLEN, encoded by the gene PCSK1N, were unaltered within the periaqueductal gray (PAG) in both male and female mice following inflammatory and neuropathic pain. However, following neuropathic pain in male mice, the protein levels of GPR171 were decreased in the PAG. Treatment with MS15203 then rescued the protein levels of GPR171 in the PAG of these mice. Taken together, our results identify GPR171 as a GPCR that displays sexual dimorphism in alleviation of chronic pain. Further, our results suggest that GPR171 and MS15203 have demonstrable therapeutic potential in the treatment of chronic pain.

GPR171 Activation Modulates Nociceptor Functions, Alleviating Pathologic Pain

Modulation of the function of somatosensory neurons is an important analgesic strategy, requiring the proposal of novel molecular targets. Many G-protein-coupled receptors (GPRs) have been deorphanized, but the receptor locations, outcomes due to their activations, and their signal transductions remain to be elucidated, regarding the somatosensory nociceptor function. Here we report that GPR171, expressed in a nociceptor subpopulation, attenuated pain signals via Gi/o-coupled modulation of the activities of nociceptive ion channels when activated by its newly found ligands. Administration of its natural peptide ligand and a synthetic chemical ligand alleviated nociceptor-mediated acute pain aggravations and also relieved pathologic pain at nanomolar and micromolar ranges. This study suggests that functional alteration of the nociceptor neurons by GPR171 signaling results in pain alleviation and indicates that GPR171 is a promising molecular target for peripheral pain modulation.

Advances in therapeutic peptides targeting G protein-coupled receptors

Dysregulation of peptide-activated pathways causes a range of diseases, fostering the discovery and clinical development of peptide drugs. Many endogenous peptides activate G protein-coupled receptors (GPCRs) - nearly 50 GPCR peptide drugs have been approved to date, most of them for metabolic disease or oncology, and more than 10 potentially first-in-class peptide therapeutics are in the pipeline. The majority of existing peptide therapeutics are agonists, which reflects the currently dominant strategy of modifying the endogenous peptide sequence of ligands for peptide-binding GPCRs. Increasingly, novel strategies are being employed to develop both agonists and antagonists, to both introduce chemical novelty and improve drug-like properties. Pharmacodynamic improvements are evolving to allow biasing ligands to activate specific downstream signalling pathways, in order to optimize efficacy and reduce side effects. In pharmacokinetics, modifications that increase plasma half-life have been revolutionary. Here, we discuss the current status of the peptide drugs targeting GPCRs, with a focus on evolving strategies to improve pharmacokinetic and pharmacodynamic properties.

Opioid-Induced Signaling and Antinociception Are Modulated by the Recently Deorphanized Receptor, GPR171

ProSAAS is one of the most widely expressed proteins throughout the brain and was recently found to be upregulated in chronic fibromyalgia patients. BigLEN is a neuropeptide that is derived from ProSAAS and was recently discovered to be the endogenous ligand for the orphan G protein-coupled receptor GPR171. Although BigLEN-GPR171 has been found to play a role in feeding and anxiety behaviors, it has not yet been explored in pain and opioid modulation. The purpose of this study was to evaluate this novel neuropeptide-receptor system in opioid-induced antinociception. We found that GPR171 is expressed in GABAergic neurons within the periaqueductal gray, which is a key brain area involved in pain modulation and opioid functions. We also found that, although the GPR171 agonist and antagonist do not have nociceptive effects on their own, they oppositely regulate morphine-induced antinociception with the agonist enhancing and antagonist reducing antinociception. Lastly, we showed that the GPR171 antagonist or receptor knockdown decreases signaling by the mu-opioid receptor, but not the delta-opioid receptor. Taken together, these results suggest that antagonism of the GPR171 receptor reduces mu opioid receptor signaling and morphine-induced antinociception, whereas the GPR171 agonist enhances morphine antinociception, suggesting that GPR171 may be a novel target toward the development of pain therapeutics. SIGNIFICANCE STATEMENT: GPR171 is a recently deorphanized receptor that is expressed within the periaqueductal gray and can regulate mu opioid receptor signaling and antinociception. This research may contribute to the development of new therapeutics to treat pain.

Hyperlipidemias and Obesity

The organs require oxygen and other types of nutrients (amino acids, sugars, and lipids) to function, the heart consuming large amounts of fatty acids for oxidation and adenosine triphosphate (ATP) generation.

From Synapse to Function: A Perspective on the Role of Neuroproteomics in Elucidating Mechanisms of Drug Addiction

Drug addiction is a complex disorder driven by dysregulation in molecular signaling across several different brain regions. Limited therapeutic options currently exist for treating drug addiction and related psychiatric disorders in clinical populations, largely due to our incomplete understanding of the molecular pathways that influence addiction pathology. Recent work provides strong evidence that addiction-related behaviors emerge from the convergence of many subtle changes in molecular signaling networks that include neuropeptides (neuropeptidome), protein-protein interactions (interactome) and post-translational modifications such as protein phosphorylation (phosphoproteome). Advancements in mass spectrometry methodology are well positioned to identify these novel molecular underpinnings of addiction and further translate these findings into druggable targets for therapeutic development. In this review, we provide a general perspective of the utility of novel mass spectrometry-based approaches for addressing critical questions in addiction neuroscience, highlighting recent innovative studies that exemplify how functional assessments of the neuroproteome can provide insight into the mechanisms of drug addiction.

Orphan neuropeptides and receptors: Novel therapeutic targets

Neuropeptides are the largest class of intercellular signaling molecules, contributing to a wide variety of physiological processes. Neuropeptide receptors are therapeutic targets for a broad range of drugs, including medications to treat pain, addiction, sleep disorders, and nausea. In addition to >100 peptides with known functions, many peptides have been identified in mammalian brain for which the cognate receptors have not been identified. Similarly, dozens of "orphan" G protein-coupled receptors have been identified in the mammalian genome. While it would seem straightforward to match the orphan peptides and receptors, this is not always easily accomplished. In this review we focus on peptides named PEN and big LEN, which are among the most abundant neuropeptides in mouse brain, and their recently identified receptors: GPR83 and GPR171. These receptors are co-expressed in some brain regions and are able to interact. Because PEN and big LEN are produced from the same precursor protein and co-secreted, the interaction of GPR83 and GPR171 is physiologically relevant. In addition to interactions of these two peptides/receptors, PEN and LEN are co-localized with neuropeptide Y and Agouti-related peptide in neurons that regulate feeding. In this review, using these peptide receptors as an example, we highlight the multiple modes of regulation of receptors and present the emerging view that neuropeptides function combinatorially to generate a network of signaling messages. The complexity of neuropeptides, receptors, and their signaling pathways is important to consider both in the initial deorphanization of peptides and receptors, and in the subsequent development of therapeutic applications.

To probe interaction of morphine and IBNtxA with 7TM and 6TM variants of the human μ-opioid receptor using all-atom molecular dynamics simulations with an explicit membrane

IBNtxA, a morphine derivative, is 10-fold more potent and has a better safety profile than morphine. Animal studies indicate that the analgesic effect of IBNtxA appears to be mediated by the activation of truncated splice variants (6TM) of the Mu opioid receptor (MOR-1) where transmembrane helix 1 (TM1) is removed. Interestingly, morphine is unable to activate 6TM variants. To date, a high resolution structure of 6TM variants is missing, and the interaction of 6TM variants with IBNtxA and morphine remains elusive. In this study we used homology modeling, docking and molecular dynamics (MD) simulations to study a representative 6TM variant (G1) and a full-length 7TM variant of human MOR-1 in complex with IBNtxA and morphine respectively. The structural models of human G1 and 7TM were obtained by homology modeling using the X-ray solved crystal structure of the active mouse 7TM bound to an agonist BU72 (PDB id: ) as the template. Our 6000 ns MD data show that either TM1 truncation (i.e. from 7TM to 6TM) or ligand modification (i.e. from morphine to IBNtxA) alone causes the loss of key morphine-7TM interactions that are well-known to be required for MOR-1 activation. Receptor disruptions are mainly located at TMs 2, 3, 6 and 7 in comparison with the active crystal complex. However, when both perturbations occur in the 6TM-IBNtxA complex, the key ligand-receptor interactions and the receptor conformation are recovered to resemble those in the active 7TM-morphine complex. Our molecular switch analysis further explains well why morphine is not able to activate 6TM variants. The close resemblance between 6TM-IBTtxA and 7TM in complex with PZM21, a G-protein biased 7TM agonist, suggests the possible biased agonism of IBNtxA on G1, which is consistent with its reduced side effects.

The BigLEN-GPR171 Peptide Receptor System Within the Basolateral Amygdala Regulates Anxiety-Like Behavior and Contextual Fear Conditioning

Studies show that neuropeptide-receptor systems in the basolateral amygdala (BLA) play an important role in the pathology of anxiety and other mood disorders. Since GPR171, a recently deorphanized receptor for the abundant neuropeptide BigLEN, is expressed in the BLA, we investigated its role in fear and anxiety-like behaviors. To carry out these studies we identified small molecule ligands using a homology model of GPR171 to virtually screen a library of compounds. One of the hits, MS0021570_1, was identified as a GPR171 antagonist based on its ability to block (i) BigLEN-mediated activation of GPR171 in heterologous cells, (ii) BigLEN-mediated hyperpolarization of BLA pyramidal neurons, and (iii) feeding induced by DREADD-mediated activation of BigLEN containing AgRP neurons in the arcuate nucleus. The role of GPR171 in anxiety-like behavior or fear conditioning was evaluated following systemic or intra-BLA administration of MS0021570_1, as well as following lentiviral-mediated knockdown of GPR171 in the BLA. We find that systemic administration of MS0021570_1 attenuates anxiety-like behavior while intra-BLA administration or knockdown of GPR171 in the BLA reduces anxiety-like behavior and fear conditioning. These results indicate that the BigLEN-GPR171 system plays an important role in these behaviors and could be a novel target to develop therapeutics to treat psychiatric disorders.

Carboxypeptidase E and the Identification of Novel Neuropeptides as Potential Therapeutic Targets

Peptides and small molecules that bind to peptide receptors are important classes of drugs that are used for a wide variety of different applications. The search for novel neuropeptides traditionally involved a time-consuming approach to purify each peptide to homogeneity and determine its amino acid sequence. The discovery in the 1980s of enkephalin convertase/carboxypeptidase E (CPE), and the observation that this enzyme was involved in the production of nearly every known neuropeptide led to the idea for a one-step affinity purification of CPE substrates. This approach was successfully used to isolate hundreds of known neuropeptides in mouse brain, as well as over a dozen novel peptides. Some of the novel peptides found using this approach are among the most abundant peptides present in brain, but had not been previously identified by traditional approaches. Recently, receptors for two of the novel peptides have been identified, confirming their role as neuropeptides that function in cell-cell signaling. Small molecules that bind to one of these receptors have been developed and found to significantly reduce food intake and anxiety-like behavior in an animal model. This review describes the entire project, from discovery of CPE to the novel peptides and their receptors.

Discovery of new GPCR ligands to illuminate new biology

Although a plurality of drugs target G-protein-coupled receptors (GPCRs), most have emerged from classical medicinal chemistry and pharmacology programs and resemble one another structurally and functionally. Though effective, these drugs are often promiscuous. With the realization that GPCRs signal via multiple pathways, and with the emergence of crystal structures for this family of proteins, there is an opportunity to target GPCRs with new chemotypes and confer new signaling modalities. We consider structure-based and physical screening methods that have led to the discovery of new reagents, focusing particularly on the former. We illustrate their use against previously untargeted or orphan GPCRs, against allosteric sites, and against classical orthosteric sites that selectively activate one downstream pathway over others. The ligands that emerge are often chemically novel, which can lead to new biological effects.

Quantitative Mass Spectrometry Reveals Food Intake-Induced Neuropeptide Level Changes in Rat Brain: Functional Assessment of Selected Neuropeptides as Feeding Regulators

Endogenous neuropeptides are important signaling molecules that function as regulators of food intake and body weight. Previous work has shown that neuropeptide gene expression levels in a forebrain reward site, the nucleus accumbens (NAc), were changed by feeding. To directly monitor feeding-induced changes in neuropeptide expression levels within the NAc, we employed a combination of cryostat dissection, heat stabilization, neuropeptide extraction and label-free quantitative neuropeptidomics via a liquid chromatography-high resolution mass spectrometry platform. Using this methodology, we described the first neuropeptidome in NAc and discovered that feeding caused the expression level changes of multiple neuropeptides derived from different precursors, especially proSAAS-derived peptides such as Big LEN, PEN and little SAAS. We further investigated the regulatory functions of these neuropeptides derived from the ProSAAS family by performing an intra-NAc microinjection experiment using the identified ProSAAS neuropeptides, 'Big-LEN' and 'PEN'. Big LEN significantly increased rats' food and water intake, whereas both big LEN and PEN affected other behaviors including locomotion, drinking and grooming. In addition, we quantified the feeding-induced changes of peptides from hippocampus, hypothalamus and striatum to reveal the neuropeptide interplay among different anatomical regions. In summary, our study demonstrated neuropeptidomic changes in response to food intake in the rat NAc and other key brain regions. Importantly, the microinfusion of ProSAAS peptides into NAc revealed that they are behaviorally active in this brain site, suggesting the potential use of these peptides as therapeutics for eating disorders.

How Ligands Illuminate GPCR Molecular Pharmacology

G protein-coupled receptors (GPCRs), which are modulated by a variety of endogenous and synthetic ligands, represent the largest family of druggable targets in the human genome. Recent structural and molecular studies have both transformed and expanded classical concepts of receptor pharmacology and have begun to illuminate the distinct mechanisms by which structurally, chemically, and functionally diverse ligands modulate GPCR function. These molecular insights into ligand engagement and action have enabled new computational methods and accelerated the discovery of novel ligands and tool compounds, especially for understudied and orphan GPCRs. These advances promise to streamline the development of GPCR-targeted medications.

Neuro-psychopharmacological perspective of Orphan receptors of Rhodopsin (class A) family of G protein-coupled receptors

BACKGROUND

In the central nervous system (CNS), G protein-coupled receptors (GPCRs) are the most fruitful targets for neuropsychopharmacological drug development. Rhodopsin (class A) is the most studied class of GPCR and includes orphan receptors for which the endogenous ligand is not known or is unclear. Characterization of orphan GPCRs has proven to be challenging, and the production pace of GPCR-based drugs has been incredibly slow.

OBJECTIVE

Determination of the functions of these receptors may provide unexpected insight into physiological and neuropathological processes. Advances in various methods and techniques to investigate orphan receptors including in situ hybridization and knockdown/knockout (KD/KO) showed extensive expression of these receptors in the mammalian brain and unmasked their physiological and neuropathological roles. Due to these rapid progress and development, orphan GPCRs are rising as a new and promising class of drug targets for neurodegenerative diseases and psychiatric disorders.

CONCLUSION

This review presents a neuropsychopharmacological perspective of 26 orphan receptors of rhodopsin (class A) family, namely GPR3, GPR6, GPR12, GPR17, GPR26, GPR35, GPR39, GPR48, GPR49, GPR50, GPR52, GPR55, GPR61, GPR62, GPR63, GPR68, GPR75, GPR78, GPR83, GPR84, GPR85, GPR88, GPR153, GPR162, GPR171, and TAAR6. We discussed the expression of these receptors in mammalian brain and their physiological roles. Furthermore, we have briefly highlighted their roles in neurodegenerative diseases and psychiatric disorders including Alzheimer's disease, Parkinson's disease, neuroinflammation, inflammatory pain, bipolar and schizophrenic disorders, epilepsy, anxiety, and depression.