Prostaglandin E2 potentiates interferon-γ-induced nitric oxide production in cultured rat microglia.

Prostaglandin E2 (PGE2 ) plays crucial roles in managing microglial activation through the prostanoid EP2 receptor, a PGE2 receptor subtype. In this study, we report that PGE2 enhances interferon-γ (IFN-γ)-induced nitric oxide production in microglia. IFN-γ increased the release of nitrite, a metabolite of nitric oxide, which was augmented by PGE2 , although PGE2 by itself slightly affects nitrite release. The potentiating effect of PGE2 was positively associated with increased expression of inducible nitric oxide synthase. In contrast to nitrite release induced by IFN-γ, lipopolysaccharide-induced nitrite release was not affected by PGE2 . An EP2 agonist, ONO-AE1-259-01 also augmented IFN-γ-induced nitrite release, while an EP1 agonist, ONO-DI-004, an EP3 agonist, ONO-AE-248, or an EP4 agonist, ONO-AE1-329, did not. In addition, the potentiating effect of PGE2 was inhibited by an EP2 antagonist, PF-04418948, but not by an EP1 antagonist, ONO-8713, an EP3 antagonist, ONO-AE3-240, or an EP4 antagonist, ONO-AE3-208, at 10-6  M. Among the EP agonists, ONO-AE1-259-01 alone was able to accumulate cyclic adenosine monophosphate (AMP), and among the EP antagonists, PF-04418948 was the only one able to inhibit PGE2 -increased intracellular cyclic AMP accumulation. On the other hand, IFN-γ promoted phosphorylation of signal transducer and activator of transcription 1, which was not affected by PGE2 . Furthermore, other prostanoid receptor agonists, PGD2 , PGF2α , iloprost, and U-46119, slightly affected IFN-γ-induced nitrite release. These results indicate that PGE2 potentiates IFN-γ-induced nitric oxide production in microglia through the EP2 receptor, which may shed light on one of the pro-inflammatory aspects of PGE2 .

Agmatine attenuates methamphetamine-induced hyperlocomotion and stereotyped behavior in mice.

We investigated whether pretreatment with the neurotransmitter/neuromodulator agmatine (decarboxylated L-arginine) affected methamphetamine (METH)-induced hyperlocomotion and stereotypy in male ICR mice. Agmatine pretreatment alone had no effects on locomotion or stereotypy, but it produced a dose-dependent attenuation of locomotion and the total incidence of stereotyped behavior induced by a low dose of METH (5 mg/kg). The stereotypy induced by this dose was predominantly characterized by stereotyped sniffing. By contrast, agmatine did not affect the total incidence of stereotypy induced by a higher dose of METH (10 mg/kg). However, the nature of stereotypy induced by this dose of METH was substantially altered; agmatine pretreatment significantly reduced stereotyped biting but significantly increased stereotyped sniffing and persistent locomotion. Agmatine pretreatment therefore appears to produce a rightward shift in the dose-response curve for METH. Pretreatment of mice with piperazine-1-carboxamidine (a putative agmatinase inhibitor) had no effect on locomotion or stereotypy induced by a low dose of METH, suggesting that endogenous agmatine may not regulate the METH action.

Histamine H3 receptor agonists decrease hypothalamic histamine levels and increase stereotypical biting in mice challenged with methamphetamine.

The effects of the histamine H(3) receptor agonists (R)-α-methylhistamine, imetit and immepip on methamphetamine (METH)-induced stereotypical behavior were examined in mice. The administration of METH (10 mg/kg, i.p.) to male ddY mice induced behaviors including persistent locomotion and stereotypical behaviors, which were classified into four categories: stereotypical head-bobbing (1.9%), circling (1.7%), sniffing (14.3%), and biting (82.1%). Pretreatment with (R)-α-methylhistamine (3 and 10 mg/kg, i.p.) significantly decreased stereotypical sniffing, but increased stereotypical biting induced by METH, in a dose-dependent manner. This effect of (R)-α-methylhistamine on behavior was mimicked by imetit or immepip (brain-penetrating selective histamine H(3) receptor agonists; 10 mg/kg, i.p. for each drug). Hypothalamic histamine levels 1 h after METH challenge were significantly increased in mice pretreated with saline. These increases in histamine levels were significantly decreased by pretreatment with histamine H(3) receptor agonists, effects which would appear to underlie the shift from METH-induced stereotypical sniffing to biting.

Withdrawal from fixed-dose injection of methamphetamine decreases cerebral levels of 3-methoxy-4-hydroxyphenylglycol and induces the expression of anxiety-related behavior in mice.

A variety of drug treatment regimens have been proposed to model the dysphoric state observed during methamphetamine (METH) withdrawal in rats, but little has been established in experiments using mice. In male ICR mice, a fixed-dose injection regimen of METH (1.0 or 2.5 mg/kg, i.p., twice daily for 10 consecutive days) induced a significant decrease in the time spent in open arms in an elevated plus maze after 5 days of drug abstinence. Under an escalating-dose injection regimen (0.2-2.0 mg/kg, i.p., 3 times daily for 4 days, total: 15 mg/kg/animal) or continuous subcutaneous administration with osmotic mini-pumps (15 or 76 mg/kg of METH for 2 weeks), no significant behavioral change was observed after 5 days of drug abstinence, compared with control animals. Reduced gains in body weight were observed during repeated treatment with METH in the fixed-dose injection and mini-pump treatment regimens, but not the escalating-dose injection regimen. HPLC analysis revealed significant decreases in the level of cerebral 3-methoxy-4-hydroxyphenylglycol, a norepinephrine metabolite, and norepinephrine turnover, which may be attributed to the expression of anxiety-related behavior in the elevated plus maze. These observations suggest that the mice treated with a fixed-dose of METH may model the anxiety-related behavior observed in the dysphoric state induced by METH withdrawal in humans.

In vivo evaluation of effects of histamine H3 receptor antagonists on methamphetamine-induced hyperlocomotion in mice.

A single administration with METH (3 mg/kg) induced a hyperlocomotion in male ICR mice. Pretreatment of mice with pitolisant, a histamine H3 receptor antagonist (5 and 10 mg/kg), for 30 min showed a significant reduction of the hyperlocomotion induced by METH, as compared with vehicle (saline)-pretreated subjects. Pretreatment of mice with the histamine H3 receptor antagonists JNJ-10181457 (5 and 10 mg/kg) or conessine (20 mg/kg), also showed similar inhibitory effects on METH-induced hyperlocomotion, similar to pitolisant. No significant change in locomotion was observed in mice pretreated with pitolisant, JNJ-10181457, or conessine alone. The pitolisant (10 mg/kg) action on METH-induced hyperlocomotion was completely abolished by the histamine H1 receptor antagonist pyrilamine (10 mg/kg), but not by the peripherally acting histamine H1 receptor antagonist fexofenadine (20 mg/kg), the brain-penetrating histamine H2 receptor antagonist zolantidine (10 mg/kg), or the brain-penetrating histamine H4 receptor antagonist JNJ-7777120 (40 mg/kg). Pretreatment with a histamine H3 receptor agonist immepip (10 mg/kg) augmented METH--induced behavior, including hyperlocomotion and stereotyped biting, and combined pretreatment with pitolisant (10 mg/kg) significantly attenuated stereotyped biting. These observations suggest that pretreatment with histamine H3 receptor antagonists attenuate METH-induced hyperlocomotion via releasing histamine after blocking H3 receptors, which then bind to the post-synaptic histamine receptor H1 (but not H2 or H4). It is likely that activation of brain histamine systems may be a good strategy for the development of agents, which treat METH abuse and dependence.

Prostaglandin E2 reduces extracellular ATP-induced migration in cultured rat microglia.

Treatment with 100 microM adenosine triphosphate (ATP) for 120 min augmented migration of cultured rat microglia by about 4-fold. This augmentation was effectively reduced by 0.1-10 microM prostaglandin E(2) (PGE(2)). PGE(2)-mediated reduction was reversed by the EP2 antagonist AH6809 at 10 microM. The EP2 agonist butaprost also reduced ATP-induced migration at 10 microM, whereas the EP1 agonist 17-phenyl trinor PGE(2), the EP3 agonist sulprostone, and the EP4 agonist PGE(1) alcohol all had no effect at 10 microM. In addition, ATP-induced migration was reduced by the adenylate cyclase activator forskolin at 100 microM, whereas the adenylate cyclase inhibitor SQ22536 reversed the effect of PGE(2) on ATP-induced migration at 100 microM. Over the same experimental duration, PGE(2), butaprost, and forskolin had little effect on cell viability. These findings indicate that ATP-induced microglial migration is reduced by PGE(2) through EP2 and adenylate cyclase.

Tetrabenazine, a vesicular monoamine transporter-2 inhibitor, attenuates morphine-induced hyperlocomotion in mice through alteration of dopamine and 5-hydroxytryptamine turnover in the cerebral cortex.

A single administration with morphine (30 mg/kg, i.p.) induced long-lasting hyperlocomotion in male ICR mice. Pretreatment of mice with a benzoquinolizine derivative tetrabenazine (TBZ; a reversible vesicular monoamine transporter-2 inhibitor) (1 mg/kg, i.p.) for 30 min significantly attenuated the hyperlocomotion induced by morphine, as compared with vehicle (saline)-pretreated mice. No significant change in locomotion was observed in mice pretreated with TBZ (1 mg/kg) alone. Mice treated with TBZ (1 mg/kg) showed an increase in immobility time in a tail suspension test, as compared with saline-treated mice. Pretreatment with TBZ (1 mg/kg) had no effect on morphine (1-30 mg/kg)-induced antinociception. TBZ at a dose of 1 mg/kg inhibited dopamine turnover (the ratio of 3,4-dihydroxyphenylacetic acid/dopamine) and 5-hydroxytryptamine turnover (the ratio of 5-hydroxyindoleacetic acid/5-hydroxytryptamine) in the cerebral cortex of mice challenged with morphine, as compared with saline-pretreated mice challenged with morphine. No stereotypic behavior was observed in mice treated with morphine (30 mg/kg) in combination with TBZ (1 mg/kg), so the reduction in observed locomotion did not result from induction of stereotypical behavior. Moreover, TBZ (1 and 2 mg/kg) pretreatment had no effect on stereotyped behaviors observed in mice challenged with 10 mg/kg methamphetamine. These data support the potential antagonistic actions of TBZ on some opiate actions, and encourage further exploration of potential effects on morphine reinforcement.

Psychotomimetic-like behavioral effects of memantine in the mouse.

A single administration of mice with memantine (1-amino-3,5-dimethyladamantane), a glutamatergic N-methyl-d-aspartate (NMDA) receptor antagonist, induced stereotyped behaviors in dose- and time-dependent manners. The predominant behavioral component of the stereotypy was a continuous, exaggerated sniffing which was accompanied by persistent locomotion. In contrast, a psychostimulant methamphetamine (METH) predominantly induced a stereotyped biting and other forms of intense stationary stereotypical behaviors. Memantine-induced stereotyped sniffing was attenuated by pretreatment with haloperidol, a dopamine D2 receptor antagonist, in a dose-dependent manner. The memantine-induced stereotyped sniffing was also attenuated by pretreatment with betahistine (2-[2-(methylamino)ethyl]pyridine), an agent which increases histamine turnover and releases histamine in the brain. These observations suggest that memantine might induce stereotypies through neuronal mechanisms that are somewhat different from those of METH, but still overlap to a certain extent, since memantine-induced stereotypies can be attenuated by the mechanisms that also suppress METH-induced stereotypy. Importantly, these data suggests that the effects of memantine may be more limited to the ventral striatum including nucleus accumbens than those of METH, which is associated with dorsal striatal stimulation at high doses. In this respect memantine may also have pharmacological properties such as compartmentation (i.e. brain distribution) and neuronal mechanisms different from those of other NMDA receptor antagonists, such as ketamine, which may have important implications for therapeutic uses of these drugs.

Lack of effect of anticonvulsant topiramate on methamphetamine-induced stereotypy and rewarding property in mice.

The effects of topiramate, a structurally novel anticonvulsant, on the methamphetamine (METH)-induced expression of stereotypy and conditioned place preference (CPP) in male ICR mice were investigated. After a single administration of METH (10 mg/kg, i.p.), mice showed stereotyped behaviors with a plateau level 25 min after drug challenge. Pretreatment with topiramate (1, 10, and 100 mg/kg, i.p.) 30 min prior to METH challenge had no effect on the expression frequency of stereotypy, compared with saline challenge. No differential effects of topiramate on METH-induced stereotyped behavior (that is, head-bobbing, circling, continuous sniffing, nail and/or wood-chip biting, and vigorous and compulsive grooming) were observed. In saline-challenged groups, the doses of topiramate examined did not induce any stereotyped behaviors. Although mice showed a significant CPP for METH (0.5 mg/kg, i.p.), pretreatment with subchronic topiramate did not affect the magnitude of CPP. Locomotor activity was not affected by the doses of topiramate tested. Conditioned rewarding or aversive effects of topiramate were not observed as indexed by the place preference procedure. These results suggested the lack of effect of topiramate on METH-induced stereotypy and rewarding property in mice.

Brain Histamine N-Methyltransferase As a Possible Target of Treatment for Methamphetamine Overdose.

Stereotypical behaviors induced by methamphetamine (METH) overdose are one of the overt symptoms of METH abuse, which can be easily assessed in animal models. Currently, there is no successful treatment for METH overdose. There is increasing evidence that elevated levels of brain histamine can attenuate METH-induced behavioral abnormalities, which might therefore constitute a novel therapeutic treatment for METH abuse and METH overdose. In mammals, histamine N-methyltransferase (HMT) is the sole enzyme responsible for degrading histamine in the brain. Metoprine, one of the most potent HMT inhibitors, can cross the blood-brain barrier and increase brain histamine levels by inhibiting HMT. Consequently, this compound can be a candidate for a prototype of drugs for the treatment of METH overdose.

The absence of the SOD1 gene causes abnormal monoaminergic neurotransmission and motivational impairment-like behavior in mice.

Copper/zinc superoxide dismutase (SOD1), a primary anti-oxidative enzyme, protects cells against oxidative stress. We report herein on a comparison of behavioral and neurobiological changes between SOD1 knockout (KO) and wild-type mice, in an attempt to assess the role of SOD1 in brain functions. SOD1 KO mice exhibited impaired motivational behavior in both shuttle-box learning and three-chamber social interaction tests. High levels of dopamine transporter protein and an acceleration of serotonin turnover were also detected in the cerebrums of the SOD1 KO mice. These findings suggest that SOD1 deficiency disturbs monoaminergic neurotransmission leading to a decrease in motivational behavior.

SEA0400, a specific inhibitor of the Na+-Ca2+ exchanger, attenuates sodium nitroprusside-induced apoptosis in cultured rat microglia.

1. Using SEA0400, a potent and selective inhibitor of the Na+-Ca2+ exchanger (NCX), we examined whether NCX is involved in nitric oxide (NO)-induced disturbance of endoplasmic reticulum (ER) Ca2+ homeostasis followed by apoptosis in cultured rat microglia. 2. Sodium nitroprusside (SNP), an NO donor, decreased cell viability in a dose- and time-dependent manner with apoptotic cell death in cultured microglia. 3. Treatment with SNP decreased the ER Ca2+ levels as evaluated by measuring the increase in cytosolic Ca2+ level induced by exposing cells to thapsigargin, an irreversible inhibitor of ER Ca2+-ATPase. 4. The treatment with SNP also increased mRNA expression of CHOP and GPR78, makers of ER stress. 5. SEA0400 at 0.3-1.0 microM protected microglia against SNP-induced apoptosis. 6. SEA0400 blocked not only the SNP-induced decrease in ER Ca2+ levels but also SNP-induced increase in CHOP and GRP78 mRNAs. 7. SEA0400 did not affect capacitative Ca2+ entry in the presence and absence of SNP. 8. SNP increased Na+-dependent 45Ca2+ uptake and this increase was blocked by SEA0400. 9. These results suggest that SNP induces apoptosis via the ER stress pathway and SEA0400 attenuates SNP-induced apoptosis via suppression of the ER stress in cultured microglia. Our findings imply that NCX plays a role in ER Ca2+ depletion under pathological conditions.

2-Phenylethylamine in combination with l-deprenyl lowers the striatal level of dopamine and prolongs the duration of the stereotypy in mice.

2-Phenylethylamine (PEA)-induced stereotypy in rodents is suggested to model psychotic symptoms of schizophrenia. It is reported that PEA induces dopamine release in the striatum in vivo and in vitro. The present study analyzed the PEA-induced stereotypy and possible associated brain dopamine metabolism in mice. Using male ICR mice treated with a combination of PEA (100 mg/kg, i.p.) and increasing doses of l-deprenyl (0-10 mg/kg, s.c.), we examined (1) the behavioral profile of stereotypy (rating the scores), and (2) the tissue levels of dopamine and its metabolites by high-performance liquid chromatography. The stereotypic scores reached a plateau level at 10 min which lasted until 30 min after a single administration of 100 mg/kg PEA. The stereotyped behavior completely disappeared 45 min after PEA administration. Pretreatment with l-deprenyl (0.1, 1, and 10 mg/kg, s.c.) dose-dependently prolonged the duration of PEA-induced stereotypy. Notably, pretreatment with l-deprenyl dose-dependently increased the continuous sniffing. Treatment with PEA in combination of l-deprenyl (1 and 10 mg/kg) significantly reduced the level of dopamine in the region of the striatum and nucleus accumbens, compared with control animals. These results suggest that PEA in combination with l-deprenyl prolonged the duration of the stereotypy (particularly, continuous sniffing) while reducing the striatal level of dopamine.

Pretreatment or Posttreatment with Aripiprazole Attenuates Methamphetamine-induced Stereotyped Behavior in Mice.

Aripiprazole is a third-generation atypical antipsychotic and a dopamine D2 receptor partial agonist. In the present study, we investigated whether a single administration of aripiprazole to mice, either as a pretreatment or as a posttreatment, would affect stereotypy induced by methamphetamine (METH). Pretreatment of male ICR mice with aripiprazole (1 or 10 mg/kg, i.p.) attenuated the incidence of METH-induced stereotypical behavior in a dose-dependent manner. Pretreatment of mice with 1 mg/kg aripiprazole produced an increase in the locomotor activity in mice treated with METH compared with mice treated with vehicle plus METH and with 10 mg/kg aripiprazole plus METH. This increase in locomotion is indicative of a rightward shift in the dose-response curve for METH, consistent with a shift in the type of stereotypical behavior observed from biting to sniffing. Aripiprazole posttreatment, after METH-induced stereotypical behavior, was fully expressed and also significantly attenuated overall stereotypy in an aripiprazole dose-dependent manner. These data suggest that the antagonism of METH effects by aripiprazole should be investigated as a potential treatment for acute METH overdose.

Memory impairment and reduced exploratory behavior in mice after administration of systemic morphine.

In the present study, the effects of morphine were examined on tests of spatial memory, object exploration, locomotion, and anxiety in male ICR mice. Administration of morphine (15 or 30 mg/kg, intraperitoneally (i.p.)) induced a significant decrease in Y-maze alternations compared to saline vehicle-treated mice. The reduced Y-maze alternations induced by morphine were completely blocked by naloxone (15 mg/kg) or ß-funaltrexamine (5 mg/kg) but not by norbinaltorphimine (5 mg/kg) or naltrindole (5 mg/kg), suggesting that the morphine-induced spatial memory impairment was mediated predominantly by µ-opioid receptors (MOPs). Significant spatial memory retrieval impairments were observed in the Morris water maze (MWM) in mice treated with morphine (15 mg/kg) or scopolamine (1 mg/kg), but not with naloxone or morphine plus naloxone. Reduced exploratory time was observed in mice after administration of morphine (15 mg/kg), in a novel-object exploration test, without any changes in locomotor activity. No anxiolytic-like behavior was observed in morphine-treated mice in the elevated plus maze. A significant reduction in buried marbles was observed in morphine-treated mice measured in the marble-burying test, which was blocked by naloxone. These observations suggest that morphine induces impairments in spatial short-term memory and retrieval, and reduces exploratory behavior, but that these effects are not because of overall changes in locomotion or anxiety.

Behavioral sensitization and alteration in monoamine metabolism in mice after single versus repeated methamphetamine administration.

To address the functional alterations of monoaminergic neuronal systems in mice after single and repeated administration of methamphetamine, we examined the tissue contents of monoamines and their metabolites in addition to locomotor activity estimated by horizontal locomotion and rearing measurements. In male ICR mice, the repeated treatment regimen (intraperitoneal administration of 1.0 mg/kg methamphetamine once per day for five consecutive days) induced hyperlocomotion with a plateau level on test day 4. The initial behavioral response (within 5 min after injection) to the drug appeared to include context-dependent sensitization. Mice after the initial repeated treatment regimen showed behavioral sensitization to the same dose of methamphetamine 5 days after the final injection (test day 11). On test day 11, the first 150 min, but not the nocturnal behavior (during the dark hours), were significantly enhanced after the drug challenge. A marked reduction of the content of L-dihydroxyphenylalanine and the ratio of 3,4-dihydroxyphenylacetic acid to dopamine was observed in the striatum+accumbens of mice after single and repeated administration of methamphetamine. As for serotonin metabolism, the ratio of 5-hydroxyindolacetic acid to serotonin significantly increased in mice after single administration of methamphetamine, although it decreased in mice after repeated administration of methamphetamine. Norepinephrine metabolism (the ratio of 3-methoxy-4-hydroxyphenylglycol to norepinephrine) was not affected in the striatum+accumbens or thalamus+hypothalamus of the mice after repeated or single methamphetamine treatment. These results suggest that dopaminergic and serotonergic neuronal activities were altered during the development of behavioral sensitization. The ratio of 3-methoxytyramine to dopamine was not affected, suggesting that the methamphetamine treatment selectively inhibited the monoamine oxidase pathway for dopamine inactivation.

Expression of diamine oxidase (histaminase) in guinea-pig tissues.

The expression of mRNA for diamine oxidase (histaminase) and the enzyme activity in guinea-pig tissues were investigated. Reverse transcription-polymerase chain reaction analysis revealed that the message corresponding to the long form present in humans and rats was expressed abundantly in the small intestine and liver. Small but detectable amounts of diamine oxidase mRNA were observed in the kidney, stomach, cerebellum, thalamus+hypothalamus, and cerebral cortex. Northern blot analysis showed that the message (2.8 kb in size) was observed abundantly in the liver and small intestine and was detectable in the kidney and stomach but not in the brain or lung. In situ hybridization showed that diamine oxidase mRNA was localized throughout the liver and epithelial cells of the small intestine. Diamine oxidase activity was detected at various levels in different tissues of the guinea-pig at the following relative abundance: liver>small intestine>lung, kidney>stomach. Histamine dose-dependently induced the contraction of sections of the guinea-pig small intestine, and the pretreatment of the tissue section with aminoguanidine (100 microM), a diamine oxidase inhibitor, but not with S-[4-(N,N-dimethylamino)butyl]isothiourea (100 microM), an inhibitor of histamine N-methyltransferase, shifted the dose-response curve of histamine-induced contraction to lower concentrations. These results suggest that diamine oxidase has a crucial role in the degradation of histamine in the guinea-pig small intestine and probably in the liver.

Isolation and sequencing of a putative promoter region of the murine G protein beta 1 subunit (GNB1) gene.

The expression of the heterotrimeric GTP-binding protein beta 1 subunit gene (GNB1) is regulated by psychostimulants such as cocaine and amphetamines. Since the up-regulation appears to be one of the candidate processes of sensitization, it is necessary to elucidate the cellular and molecular mechanism of the GNB1 gene regulation for a better understanding the establishment of sensitization. In the present study, we describe the isolation and nucleotide sequence analysis of the GNB1 gene promoter region. We have isolated approximately 10 kb of the 5'-flanking region of the mouse of GNB1 gene and found potential elements involved in putative transcriptional control of the GNB1, such as AP1, AP2, Sp1, cyclic AMP response element, and nuclear factor kappa B recognition sites, within the sequences 0.3 kb upstream from the putative transcription start site. This region was highly rich in G + C content, but lacked TATA or CATT boxes. Comparing the nucleotide sequence of the cDNA clone with the human genome databases using the BLAST program a region containing putative exon 1 and promoter of the human GNB1 gene in chromosome 1 was found. The cloning and sequence analysis of an extensive portion of the 5'-flanking regulatory region of the GNB1 gene provides new insights into the factors involved in the regulation by psychostimulants of GNB1 expression.

Prostaglandin E2 induces apoptosis in cultured rat microglia.

Prostaglandin E2 (PGE2) plays a critical role in the modulation of microglial function including migration and phagocytosis through EP2, which increases intracellular cyclic adenosine monophosphate (AMP) concentration. In the present study, we found that PGE2 reduces cell viability in microglia. PGE2 decreased 3-(4,5-dimethylthiazol-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) reduction and increased lactate dehydrogenase release, deoxyribonucleic acid fragmentation, and poly(ADP-ribose) polymerase cleavage after 24h incubation, suggesting that PGE2 induces apoptosis in these cells. An EP2 agonist, butaprost, and an EP4 agonist, PGE1 alcohol, also induced apoptosis, while an EP1 agonist, 17-phenyl trinor PGE2, or an EP3 agonist, sulprostone, at 10(-6)M did not. On the other hand, EP1-EP4 antagonists, SC-51322, AH6809, L-798106, or GW627368X, up to 10(-5)M did not affect the decrease in MTT reduction by PGE2. Intracellular cyclic AMP accumulation was induced by butaprost, but not 17-phenyl trinor PGE2, sulprostone, or PGE1 alcohol at 10(-6)M. Additionally, we previously reported that PGE2-induced intracellular cyclic AMP accumulation was reversed by AH6809. Besides EP receptors, one of other targets was thought to be prostaglandin transporter, but its inhibitors, bromocresol green or U-46619 up to 10(-5)M did not affect the decrease in MTT reduction by PGE2. These results suggest that PGE2 induces apoptosis in microglia independent of intracellular cyclic AMP concentration, and there are different mechanisms between PGE2-induced apoptosis and the modulation of microglial function.

The selective µ opioid receptor antagonist ß-funaltrexamine attenuates methamphetamine-induced stereotypical biting in mice.

We investigated whether pretreatment with opioid receptor antagonists affected methamphetamine (METH)-induced stereotypy in mice. Pretreatment of male ICR mice with naloxone, a relatively non-selective opioid receptor antagonist, significantly attenuated the total incidence of METH-induced stereotypical behavior compared with saline vehicle-pretreated subjects. Furthermore, the distribution of METH-induced stereotypical behavior was affected by naloxone administration. Thus, METH-induced stereotypical sniffing and persistent locomotion were significantly increased by naloxone treatment while stereotypical biting was reduced. One way to interpret this pattern of effects is that pretreatment with naloxone appeared to produce a shift in the dose-response curve for METH. Thus, while the more intense forms of oral-facial stereotypies were reduced, increased persistent locomotion was observed in mice given naloxone followed by METH. The selective µ opioid receptor antagonist ß-funaltrexamine, but not nor-binaltorphimine (a κ-selective antagonist) nor naltrindole (a δ-selective antagonist), mimicked the effect of naloxone. These observations suggest that opioid receptor antagonists may attenuate METH-induced stereotypical biting in mice via µ opioid receptors, and suggest that antagonism of this system may be a potential therapeutic approach to reducing some deleterious effects of METH use and perhaps in the treatment of some forms of self-injurious behavior.