Intracellular calcium elevation induced by extracellular application of cyclic-ADP-ribose or oxytocin is temperature-sensitive in rodent NG108-15 neuronal cells with or without exogenous expression of human oxytocin receptors

Development of a Highly Potent Analogue and a Long-Acting Analogue of Oxytocin for the Treatment of Social Impairment-Like Behaviors

The nonapeptide hormone oxytocin (OT) has pivotal brain roles in social recognition and interaction and is thus a promising therapeutic drug for social deficits. Because of its peptide structure, however, OT is rapidly eliminated from the bloodstream, which decreases its potential therapeutic effects in the brain. We found that newly synthesized OT analogues in which the Pro⁷ of OT was replaced with N-( p-fluorobenzyl)glycine (2) or N-(3-hydroxypropyl)glycine (5) exhibited highly potent binding affinities for OT receptors and Ca²⁺ mobilization effects by selectively activating OT receptors over vasopressin receptors in HEK cells, where 2 was identified as a superagonist ( E_Max = 131%) for OT receptors. Furthermore, the two OT analogues had a remarkably long-acting effect, up to 16-24 h, on recovery from impaired social behaviors in two strains of CD38 knockout mice that exhibit autism spectrum disorder-like social behavioral deficits, whereas the effect of OT itself rapidly diminished.

New mechanisms of phenytoin in calcium homeostasis: competitive inhibition of CD38 in hippocampal cells

Purpose

Phenytoin is a major anticonvulsant drug that is effective to improve arrhythmia and neuropathic pain. According to early works, phenytoin affected cell membrane depolarization by sodium channel blocking, guanylyl and adenylyl cyclase suppression that cause to intracellular Na⁺ and Ca²⁺ downregulation. This study was aimed to clarify some ambiguities in pathophysiological action of phenytoin by in vitro and molecular docking analyses.

Methods

In this study intracellular free Ca²⁺ of primary culture of embryonic mouse hippocampus evaluated via Fura 2 as fluorescent probe. The effects of phenytoin on ADP ribosyl cyclase activity was assessed by recently developed fluorometric assay. Molecular docking simulation was also implemented to investigate the possible interaction between phenytoin and CD38.

Results

Our results confirmed phenytoin competitively inhibits cyclase activity of CD38 (IC₅₀ = 8.1 μM) and reduces cADPR content. cADPR is a Ca²⁺-mobilising second messenger which binds to L-type calcium channel and ryanodine receptors in cell and ER membrane and increases cytosolic free Ca²⁺. Ca²⁺ content of cells decreased significantly in the presence of phenytoin in a dose dependent manner (IC₅₀ = 12.74 µM). Based on molecular docking analysis, phenytoin binds to deeper site of CD38 active site, mainly via hydrophobic interactions and consequently inhibits proper contact of substrate with catalytic residues specially Glu 226, Trp 186, Thr221.

Conclusion

Taken together, one of the anticonvulsant mechanisms of phenytoin is Ca²⁺ inhibition from CD38 pathway, therefore could be used in disorders that accompanied by CD38 over production or activation such as heart disease, depression, brain sepsis, airway disease, oxidative stress and inflammation.

Graphical abstract

Transient receptor potential melastatin-2 and temperature participate in the process of CD38-regulated oxytocin secretion

In recent studies, oxytocin showed potential for the treatment of mental diseases. CD38 is essential for oxytocin release, and hence plays a critical role in social behavior. CD38 catalyzes β-NAD into cyclic ADP ribose (cADPR), which could elevate the intracellular Ca by Ca-permeable channels for oxytocin secretion. The temperature-sensitive cation channel, transient receptor potential melastatin-2 (TRPM2), is a cation-nonselective cation and has been shown to affect oxytocin indirectly. The aim of the present study was to verify the participation of temperature and TRPM2 in CD38-regulated oxytocin release. The crude membranes were prepared to isolate the nerve terminals from the posterior pituitary. At 34°C, 37°C, and 39°C, agonists (β-NAD, ADPR, cADPR) and antagonists (8-Br-cADPR, 2-APB) were used to stimulate the nerve terminals. Oxytocin releases were investigated by enzyme-linked immunosorbent assay. In addition, the expression of TRPM2 and CD38 in the hypothalamus and pituitary was detected by western blotting and quantitative PCR. CD38 agonists (β-NAD, cADPR) and antagonist (8-Br-cADPR) could increase or reduce the oxytocin release, respectively. TRPM2 agonist (ADPR) and antagonist (2-APB) alone could also regulate oxytocin release. Furthermore, temperature could increase agonist stimulation and attenuate the antagonist inhibition on oxytocin release. In addition, CD38 and TRPM2 were expressed in the hypothalamus and pituitary at both the mRNA and the protein level. TRPM2 in pituitary nerve terminals plays a role in oxytocin release. Temperature- enhanced oxytocin release by CD38 and TRPM2. TRPM2 might be involved in the process of CD38-regulated oxytocin release.

Communication Impairment in Ultrasonic Vocal Repertoire during the Suckling Period of Cd157 Knockout Mice: Transient Improvement by Oxytocin

Communication consists of social interaction, recognition, and information transmission. Communication ability is the most affected component in children with autism spectrum disorder (ASD). Recently, we reported that the CD157/BST1 gene is associated with ASD, and that CD157 knockout (Cd157^−/−) mice display severe impairments in social behavior that are improved by oxytocin (OXT) treatment. Here, we sought to determine whether Cd157^−/− mice can be used as a suitable model for communication deficits by measuring ultrasonic vocalizations (USVs), especially in the early developmental stage. Call number produced in pups due to isolation from dams was higher at postnatal day (PND) 3 in knockout pups than wild-type mice, but was lower at PNDs 7 and 10. Pups of both genotypes had similarly limited voice repertoires at PND 3. Later on, at PNDs 7 and 10, while wild-type pups emitted USVs consisting of six different syllable types, knockout pups vocalized with only two types. This developmental impairment in USV emission was rescued within 30 min by intraperitoneal OXT treatment, but quickly returned to control levels after 120 min, showing a transient effect of OXT. USV impairment was partially observed in Cd157^+/− heterozygous mice, but not in Cd157^−/− adult male mice examined while under courtship. These results demonstrate that CD157 gene deletion results in social communication insufficiencies, and suggests that CD157 is likely involved in acoustic communication. This unique OXT-sensitive developmental delay in Cd157^−/− pups may be a useful model of communicative interaction impairment in ASD.

Structure-specific effects of lipidated oxytocin analogs on intracellular calcium levels, parental behavior, and oxytocin concentrations in the plasma and cerebrospinal fluid in mice

Oxytocin (OT) is a neuroendocrine nonapeptide that plays an important role in social memory and behavior. Nasal administration of OT has been shown to improve trust in healthy humans and social interaction in autistic subjects in some clinical trials. As a central nervous system (CNS) drug, however, OT has two unfavorable characteristics: OT is short‐acting and shows poor permeability across the blood–brain barrier, because it exists in charged form in the plasma and has short half‐life. To overcome these drawbacks, an analog with long‐lasting effects is required. We previously synthesized the analog, lipo‐oxytocin‐1 (LOT‐1), in which two palmitoyl groups are conjugated to the cysteine and tyrosine residues. In this study, we synthesized and evaluated the analogs lipo‐oxytocin‐2 (LOT‐2) and lipo‐oxytocin‐3 (LOT‐3), which feature the conjugation of one palmitoyl group at the cysteine and tyrosine residues, respectively. In human embryonic kidney‐293 cells overexpressing human OT receptors, these three LOTs demonstrated comparably weak effects on the elevation of intracellular free calcium concentrations after OT receptor activation, compared to the effects of OT. The three LOTs and OT exhibited different time‐dependent effects on recovery from impaired pup retrieval behavior in sires of CD38‐knockout mice. Sires treated with LOT‐1 showed the strongest effect, whereas others had no or little effects at 24 h after injection. These results indicated that LOTs have structure‐specific agonistic effects, and suggest that lipidation of OT might have therapeutic benefits for social impairment.

Cyclic ADP-Ribose and Heat Regulate Oxytocin Release via CD38 and TRPM2 in the Hypothalamus during Social or Psychological Stress in Mice

Hypothalamic oxytocin (OT) is released into the brain by cyclic ADP-ribose (cADPR) with or without depolarizing stimulation. Previously, we showed that the intracellular free calcium concentration ([Ca²⁺]_i) that seems to trigger OT release can be elevated by β-NAD⁺, cADPR, and ADP in mouse oxytocinergic neurons. As these β-NAD⁺ metabolites activate warm-sensitive TRPM2 cation channels, when the incubation temperature is increased, the [Ca²⁺]_i in hypothalamic neurons is elevated. However, it has not been determined whether OT release is facilitated by heat in vitro or hyperthermia in vivo in combination with cADPR. Furthermore, it has not been examined whether CD38 and TRPM2 exert their functions on OT release during stress or stress-induced hyperthermia in relation to the anxiolytic roles and social behaviors of OT under stress conditions. Here, we report that OT release from the isolated hypothalami of male mice in culture was enhanced by extracellular application of cADPR or increasing the incubation temperature from 35°C to 38.5°C, and simultaneous stimulation showed a greater effect. This release was inhibited by a cADPR-dependent ryanodine receptor inhibitor and a nonspecific TRPM2 inhibitor. The facilitated release by heat and cADPR was suppressed in the hypothalamus isolated from CD38 knockout mice and CD38- or TRPM2-knockdown mice. In the course of these experiments, we noted that OT release differed markedly between individual mice under stress with group housing. That is, when male mice received cage-switch stress and eliminated due to their social subclass, significantly higher levels of OT release were found in subordinates compared with ordinates. In mice exposed to anxiety stress in an open field, the cerebrospinal fluid (CSF) OT level increased transiently at 5 min after exposure, and the rectal temperature also increased from 36.6°C to 37.8°C. OT levels in the CSF of mice with lipopolysaccharide-induced fever (+0.8°C) were higher than those of control mice. The TRPM2 mRNA levels and immunoreactivities increased in the subordinate group with cage-switch stress. These results showed that cADPR/CD38 and heat/TRPM2 are co-regulators of OT secretion and suggested that CD38 and TRPM2 are potential therapeutic targets for OT release in psychiatric diseases caused by social stress.

Calcium Entry Through Thermosensory Channels

ThermoTRPs are unique channels that mediate Na(+) and Ca(2+) currents in response to changes in ambient temperature. In combination with their activation by other physical and chemical stimuli, they are considered key integrators of environmental cues into neuronal excitability. Furthermore, roles of thermoTRPs in non-neuronal tissues are currently emerging such as insulin secretion in pancreatic β-cells, and links to cancer. Calcium permeability through thermoTRPs appears a central hallmark for their physiological and pathological activities. Moreover, it is currently being proposed that beyond working as a second messenger, Ca(2+) can function locally by acting on protein complexes near the membrane. Interestingly, thermoTRPs can enhance and expand the inherent plasticity of signalplexes by conferring them temperature, pH and lipid regulation through Ca(2+) signalling. Thus, unveiling the local role of Ca(2+) fluxes induced by thermoTRPs on the dynamics of membrane-attached signalling complexes as well as their significance in cellular processes, are central issues that will expand the opportunities for therapeutic intervention in disorders involving dysfunction of thermoTRP channels.

Somato-axodendritic release of oxytocin into the brain due to calcium amplification is essential for social memory

Oxytocin (OT) is released into the brain from the cell soma, axons, and dendrites of neurosecretory cells in the hypothalamus. Locally released OT can activate OT receptors, form inositol-1,4,5-trisphosphate and elevate intracellular free calcium (Ca²⁺) concentrations [(Ca²⁺)_i] in self and neighboring neurons in the hypothalamus, resulting in further OT release: i.e., autocrine or paracrine systems of OT-induced OT release. CD38-dependent cyclic ADP-ribose (cADPR) is also involved in this autoregulation by elevating [Ca²⁺]_i via Ca²⁺ mobilization through ryanodine receptors on intracellular Ca²⁺ pools that are sensitive to both Ca²⁺ and cADPR. In addition, it has recently been reported that heat stimulation and hyperthermia enhance [Ca²⁺]_i increases by Ca²⁺ influx, probably through TRPM2 cation channels, suggesting that cADPR and TRPM2 molecules act as Ca²⁺ signal amplifiers. Thus, OT release is not simply due to depolarization–secretion coupling. Both of these molecules play critical roles not only during labor and milk ejection in reproductive females, but also during social behavior in daily life in both genders. This was clearly demonstrated in CD38 knockout mice in that social behavior was impaired by reduction of [Ca²⁺]_i elevation and subsequent OT secretion. Evidence for the associations of CD38 with social behavior and psychiatric disorder is discussed, especially in subjects with autism spectrum disorder.

Design, Synthesis, and Chemical and Biological Properties of Cyclic ADP-4-Thioribose as a Stable Equivalent of Cyclic ADP-Ribose

Here we describe the successful synthesis of cyclic ADP-4-thioribose (cADPtR, 3), designed as a stable mimic of cyclic ADP-ribose (cADPR, 1), a Ca2+-mobilizing second messenger, in which the key N1-β-thioribosyladenosine structure was stereoselectively constructed by condensation between the imidazole nucleoside derivative 8 and the 4-thioribosylamine 7 via equilibrium in 7 between the α-anomer (7α) and the β-anomer (7β) during the reaction course. cADPtR is, unlike cADPR, chemically and biologically stable, while it effectively mobilizes intracellular Ca2+ like cADPR in various biological systems, such as sea urchin homogenate, NG108-15 neuronal cells, and Jurkat T-lymphocytes. Thus, cADPtR is a stable equivalent of cADPR, which can be useful as a biological tool for investigating cADPR-mediated Ca2+-mobilizing pathways.

TRPM2

TRPM2 is the second member of the transient receptor potential melastatin-related (TRPM) family of cation channels. The protein is widely expressed including in the brain, immune system, endocrine cells, and endothelia. It embodies both ion channel functionality and enzymatic ADP-ribose (ADPr) hydrolase activity. TRPM2 is a Ca(2+)-permeable nonselective cation channel embedded in the plasma membrane and/or lysosomal compartments that is primarily activated in a synergistic fashion by intracellular ADP-ribose (ADPr) and Ca(2+). It is also activated by reactive oxygen and nitrogen species (ROS/NOS) and enhanced by additional factors, such as cyclic ADPr and NAADP, while inhibited by permeating protons (acidic pH) and adenosine monophosphate (AMP). Activation of TRPM2 leads to increases in intracellular Ca(2+) levels, which can serve signaling roles in inflammatory and secretory cells through release of vesicular mediators (e.g., cytokines, neurotransmitters, insulin) and in extreme cases can induce apoptotic and necrotic cell death under oxidative stress.

Non-synonymous single-nucleotide variations of the human oxytocin receptor gene and autism spectrum disorders: a case-control study in a Japanese population and functional analysis

Background

The human oxytocin receptor (hOXTR) is implicated in the etiology of autism spectrum disorders (ASDs) and is a potential target for therapeutic intervention. Several studies have reported single-nucleotide polymorphisms (SNPs) of the OXTR gene associated with ASDs. These SNPs, however, reside outside the protein-coding region. Not much is known about genetic variations that cause amino acid substitutions that alter receptor functions.

Methods

Variations in the OXTR gene were analyzed in 132 ASD patients at Kanazawa University Hospital in Japan and 248 unrelated healthy Japanese volunteers by re-sequencing and real-time polymerase chain reaction-based genotyping. Functional changes in variant OXTRs were assessed by radioligand binding assay and measurements of intracellular free calcium concentrations ([Ca²⁺]_i) and inositol 1,4,5-trisphosphate (IP₃) levels.

Results

Six subjects (4.5%) in the ASD group and two in the control group (0.8%) were identified as heterozygotes carrying the R376G variation (rs35062132; c.1126C>G); one individual from the ASD group (0.8%) and three members of the control group (1.2%) were found to be carrying R376C (c.1126C>T). The C/G genotype significantly correlated with an increased risk of ASDs (odds ratio (OR) = 5.83; 95% confidence interval (CI) = 1.16 to 29.33; P = 0.024, Fisher’s exact test). Consistently, the G allele showed a correlation with an increased likelihood of ASDs (OR = 5.73; 95% CI = 1.15 to 28.61; P = 0.024, Fisher’s exact test). The frequencies of the C/T genotype and the T allele in the ASD and control groups did not differ significantly. We also examined changes in agonist-induced cellular responses mediated by the variant receptors hOXTR-376G and hOXTR-376C. OXT-induced receptor internalization and recycling were faster in hOXTR-376G-expressing HEK-293 cells than in cells expressing hOXTR-376R or hOXTR-376C. In addition, the elevation in [Ca²⁺]_i and IP₃ formation decreased in the cells expressing hOXTR-376G and hOXTR-376C tagged with enhanced green fluorescent protein (EGFP), in comparison with the cells expressing the common-type hOXTR-376R tagged with EGFP.

Conclusions

These results suggest that the rare genetic variation rs35062132 might contribute to the pathogenesis of ASDs, and could provide a molecular basis of individual differences in OXTR-mediated modulation of social behavior.

The roles of oxytocin and CD38 in social or parental behaviors

The nine amino acid peptide oxytocin (OXT) has been directly associated with different types of behavioral reactions. The formation and maintenance of social relationships in youth and middle age are important components of human mental health. A deficit in healthy behavioral formation leads to social isolation and limitation of well-being. Mice are social animals and are therefore useful for investigating the neurobiological mechanisms of cognitive process control, including the development of social relationships and social skills. Studies in mice may broaden our understanding of the human condition. The multifunctional protein CD38/ADP-ribosyl cyclase is highly expressed in the brain, plays an important role in central OXT release, and regulates social memory. In this review article, we discuss the mechanisms of social behavior affected by the dysregulation of brain OXT function as a consequence of a lack of CD38. OXT bound to OXT receptors initiates autoregulatory positive feedback of OXT release in the hypothalamus and posterior pituitary. OXT bio-behavioral positive feedback is usually implicated in female reproductive systems, but can also be observed in social behavior. Exogenous stimuli (OXT treatment in vitro, OXT intravenous or intraventricular administration, and nasal OXT delivery) initiate activation of OXT neurons via PKC-CD38/ADP-ribosyl cyclase cascades and result in the modulation of social behavior in humans and mice. Based on these findings, we reviewed the functions of OXT and its properties with respect to the development of therapies for human social behavior impairments in psychological diseases. In addition, preliminary studies of continuous nasal OXT administration on subjects with autism spectrum disorders are described.

CD38 and its role in oxytocin secretion and social behavior

Here, we review the functional roles of cyclic ADP-ribose and CD38, a transmembrane protein with ADP-ribosyl cyclase activity, in mouse social behavior via the regulation of oxytocin (OXT) release, an essential component of social cognition. Herein we describe data detailing the molecular mechanism of CD38-dependent OXT secretion in CD38 knockout mice. We also review studies that used OXT, OXT receptor (OXTR), or CD38 knockout mice. Additionally, we compare the behavioral impairments that occur in these knockout mice in relation to the OXT system and CD38. This review also examines autism spectrum disorder (ASD), which is characterized by social and communication impairments, in relation to defects in the OXT system. Two single nucleotide polymorphisms (SNPs) in the human CD38 gene are possible risk factors for ASD via inhibition of OXT function. Further analysis of CD38 in relation to the OXT system may provide a better understanding of the neuroendocrinological roles of OXT and CD38 in the hypothalamus and of the pathophysiology of ASD. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Social memory, amnesia, and autism: brain oxytocin secretion is regulated by NAD+ metabolites and single nucleotide polymorphisms of CD38

Previously, we demonstrated that CD38, a transmembrane protein with ADP-ribosyl cyclase activity, plays a critical role in mouse social behavior by regulating the release of oxytocin (OXT), which is essential for mutual recognition. When CD38 was disrupted, social amnesia was observed in Cd38 knockout mice. The autism spectrum disorders (ASDs), characterized by defects in reciprocal social interaction and communication, occur either sporadically or in a familial pattern. However, the etiology of ASDs remains largely unknown. Therefore, the theoretical basis for pharmacological treatments has not been established. Hence, there is a rationale for investigating single nucleotide polymorphisms (SNPs) in the human CD38 gene in ASD subjects. We found several SNPs in this gene. The SNP rs3796863 (C>A) was associated with high-functioning autism (HFA) in American samples from the Autism Gene Resource Exchange. Although this finding was partially confirmed in low-functioning autism subjects in Israel, it has not been replicated in Japanese HFA subjects. The second SNP of interest, rs1800561 (4693C>T), leads to the substitution of an arginine (R) at codon 140 by tryptophan (W; R140W) in CD38. This mutation was found in four probands of ASD and in family members of three pedigrees with variable levels of ASD or ASD traits. The plasma levels of OXT in ASD subjects with the R140W allele were lower than those in ASD subjects lacking this allele. The OXT levels were unchanged in healthy subjects with or without this mutation. One proband with the R140W allele receiving intranasal OXT for approximately 3years showed improvement in areas of social approach, eye contact and communication behaviors, emotion, irritability, and aggression. Five other ASD subjects with mental deficits received nasal OXT for various periods; three subjects showed improved symptoms, while two showed little or no effect. These results suggest that SNPs in CD38 may be possible risk factors for ASD by abrogating OXT function and that some ASD subjects can be treated with OXT in preliminary clinical trials.

Cyclic ADP-ribose requires CD38 to regulate the release of ATP in visceral smooth muscle

It is well established that the intracellular second messenger cADP-ribose (cADPR) activates Ca(2+) release from the sarcoplasmic reticulum through ryanodine receptors. CD38 is a multifunctional enzyme involved in the formation of cADPR in mammals. CD38 has also been reported to transport cADPR in several cell lines. Here, we demonstrate a role for extracellular cADPR and CD38 in modulating the spontaneous, but not the electrical field stimulation-evoked, release of ATP in visceral smooth muscle. Using a small-volume superfusion assay and an HPLC technique with fluorescence detection, we measured the spontaneous and evoked release of ATP in bladder detrusor smooth muscles isolated from CD38(+/+) and CD38(-/-) mice. cADPR (1 nM) enhanced the spontaneous overflow of ATP in bladders isolated from CD38(+/+) mice. This effect was abolished by the inhibitor of cADPR receptors on sarcoplasmic reticulum 8-bromo-cADPR (80 μM) and by ryanodine (50 μm), but not by the nonselective P2 purinergic receptor antagonist pyridoxal phosphate 6-azophenyl-2',4'-disulfonate (30 μM). cADPR failed to facilitate the spontaneous ATP overflow in bladders isolated from CD38(-/-) mice, indicating that CD38 is crucial for the enhancing effects of extracellular cADPR on spontaneous ATP release. Contractile responses to ATP were potentiated by cADPR, suggesting that the two adenine nucleotides may work in synergy to maintain the resting tone of the bladder. In conclusion, extracellular cADPR enhances the spontaneous release of ATP in the bladder by influx via CD38 and subsequent activation of intracellular cADPR receptors, probably causing an increase in intracellular Ca(2+) in neuronal cells.

Cyclic ADP-ribose and NAADP: fraternal twin messengers for calcium signaling

The concept advanced by Berridge and colleagues that intracellular Ca(2+)-stores can be mobilized in an agonist-dependent and messenger (IP(3))-mediated manner has put Ca(2+)-mobilization at the center stage of signal transduction mechanisms. During the late 1980s, we showed that Ca(2+)-stores can be mobilized by two other messengers unrelated to inositol trisphosphate (IP(3)) and identified them as cyclic ADP-ribose (cADPR), a novel cyclic nucleotide from NAD, and nicotinic acid adenine dinucleotide phosphate (NAADP), a linear metabolite of NADP. Their messenger functions have now been documented in a wide range of systems spanning three biological kingdoms. Accumulated evidence indicates that the target of cADPR is the ryanodine receptor in the sarco/endoplasmic reticulum, while that of NAADP is the two pore channel in endolysosomes.As cADPR and NAADP are structurally and functionally distinct, it is remarkable that they are synthesized by the same enzyme. They are thus fraternal twin messengers. We first identified the Aplysia ADP-ribosyl cyclase as one such enzyme and, through homology, found its mammalian homolog, CD38. Gene knockout in mice confirms the important roles of CD38 in diverse physiological functions from insulin secretion, susceptibility to bacterial infection, to social behavior of mice through modulating neuronal oxytocin secretion. We have elucidated the catalytic mechanisms of the Aplysia cyclase and CD38 to atomic resolution by crystallography and site-directed mutagenesis. This article gives a historical account of the cADPR/NAADP/CD38-signaling pathway and describes current efforts in elucidating the structure and function of its components.

TRPM2 cation channels, oxidative stress and neurological diseases: where are we now?

The Na+ and Ca(2+)-permeable melastatin related transient receptor potential 2 (TRPM2) channels can be gated either by ADP-ribose (ADPR) in concert with Ca(2+) or by hydrogen peroxide (H(2)O(2)), an experimental model for oxidative stress, binding to the channel's enzymatic Nudix domain. Since the mechanisms that lead to TRPM2 gating in response to ADPR and H(2)O(2) are not understood in neuronal cells, I summarized previous findings and important recent advances in the understanding of Ca(2+) influx via TRPM2 channels in different neuronal cell types and disease processes. Considering that TRPM2 is activated by oxidative stress, mediated cell death and inflammation, and is highly expressed in brain, the channel has been investigated in the context of central nervous system. TRPM2 plays a role in H(2)O(2) and amyloid β-peptide induced striatal cell death. Genetic variants of the TRPM2 gene confer a risk of developing Western Pacific amyotropic lateral sclerosis and parkinsonism-dementia complex and bipolar disorders. TRPM2 also contributes to traumatic brain injury processes such as oxidative stress, inflammation and neuronal death. There are a limited number of TRPM2 channel blockers and they seem to be cell specific. For example, ADPR-induced Ca(2+) influx in rat hippocampal cells was not blocked by N-(p-amylcinnomoyl)anthralic acid (ACA), the IP(3) receptor inhibitor 2-aminoethoxydiphenyl borate or PLC inhibitor flufenamic acid (FFA). However, the Ca(2+) entry in rat primary striatal cells was blocked by ACA and FFA. In conclusion TRPM2 channels in neuronal cells can be gated by either ADPR or H(2)O(2). It seems to that the exact relationship between TRPM2 channels activation and neuronal cell death still remains to be determined.