Lurasidone inhibits NMDA receptor antagonist-induced functional abnormality of thalamocortical glutamatergic transmission via 5-HT7 receptor blockade.

BACKGROUND AND PURPOSE: Lurasidone is an atypical mood-stabilizing antipsychotic with a unique receptor-binding profile, including 5-HT7 receptor antagonism; however, the detailed effects of 5-HT7 receptor antagonism on various transmitter systems relevant to schizophrenia, particularly the thalamo-insular glutamatergic system and the underlying mechanisms, are yet to be clarified. EXPERIMENTAL APPROACH: We examined the mechanisms underlying the clinical effects of lurasidone by measuring the release of l-glutamate, GABA, dopamine, and noradrenaline in the reticular thalamic nucleus (RTN), mediodorsal thalamic nucleus (MDTN) and insula of freely moving rats in response to systemic injection or local infusion of lurasidone or MK-801 using multiprobe microdialysis with ultra-HPLC. KEY RESULTS: Systemic MK-801 (0.5 mg·kg-1 ) administration increased insular release of l-glutamate, dopamine, and noradrenaline but decreased GABA release. Systemic lurasidone (1 mg·kg-1 ) administration also increased insular release of l-glutamate, dopamine, and noradrenaline but without affecting GABA. Local lurasidone administration into the insula (3 µM) did not affect MK-801-induced insular release of l-glutamate or catecholamine, whereas local lurasidone administration into the MDTN (1 µM) inhibited MK-801-induced insular release of l-glutamate and catecholamine, similar to the 5-HT7 receptor antagonist SB269970. CONCLUSIONS AND IMPLICATIONS: The present results indicate that MK-801-induced insular l-glutamate release is generated by activation of thalamo-insular glutamatergic transmission via MDTN GABAergic disinhibition resulting from NMDA receptor inhibition in the MDTN and RTN. Lurasidone inhibited this MK-801-evoked insular l-glutamate release through inhibition of excitatory 5-HT7 receptor in the MDTN. These effects on thalamo-insular glutamatergic transmission may contribute to the antipsychotic and mood-stabilizing actions of lurasidone.

CB2 receptor agonism reverses MK-801-induced disruptions of prepulse inhibition in mice.

RATIONALE: Whilst cannabinoid CB2 receptors were thought to exist predominantly in immune cells in the periphery, the recent discovery of CB2 receptors in the brain has led to an increased interest in the role of these central CB2 receptors. Several studies have reported an association with CB2 receptors and schizophrenia. Sensorimotor gating deficits occur in schizophrenia patients and can be induced in animals using psychotomimetic drugs such as N-methyl-D-aspartate (NMDA) receptor antagonists. OBJECTIVES: The aim of this study was to investigate the effect of CB2 ligands on sensorimotor gating, either alone, or on sensorimotor gating deficits induced by the NMDA receptor antagonist MK-801 in mice. METHOD: The effects of CB2 receptor ligands on prepulse inhibition (PPI), an operational measure of sensorimotor gating, alone or when administrated in combination with MK-801, in Balb-C mice were evaluated. RESULTS: The CB2 receptor agonist JWH015 had no significant effect on PPI alone but reversed disruptions in PPI induced by MK-801. This effect was blocked by co-administration of the CB2 receptor antagonist AM630, but not by co-administration of the CB1 receptor antagonist AM251, indicating a CB2-mediated effect. The mixed CB1/CB2 receptor agonist JWH203 was partially able to reverse MK-801-induced PPI disruptions. Neither the CB2 receptor antagonist AM630 nor the CB1 receptor antagonist AM251 had any significant effect alone or on MK-801-induced disruptions in PPI. CONCLUSIONS: CB2 receptor agonism reversed MK-801 disruptions in sensorimotor gating deficits in mice, indicating that CB2 agonism may have a protective effect against aspects of drug-induced psychosis.

CRF1 receptor antagonists do not reverse pharmacological disruption of prepulse inhibition in rodents.

RATIONALE: As enhanced corticotropin-releasing factor (CRF) transmission is associated with induction of sensorimotor gating deficits, CRF1 receptor antagonists may reverse disrupted prepulse inhibition (PPI), an operational measure of sensorimotor gating. OBJECTIVES: To determine the effects of CRF1 receptor antagonists in pharmacological models of disrupted PPI and to determine if long-term elevated central CRF levels alter sensitivity towards PPI disrupting drugs. METHODS: CP154,526 (10-40 mg/kg), SSR125543 (3-30 mg/kg) and DMP695 (40 mg/kg) were tested on PPI disruption provoked by D-amphetamine (2.5, 3 mg/kg), ketamine (5, 30 mg/kg) and MK801 (0.2, 0.5 mg/kg) in Wistar rats, C57Bl/6J and CD1 mice, and on spontaneously low PPI in Iffa Credo rats and DBA/2J mice. PPI-disrupting effects of D-amphetamine (2.5-5 mg/kg) and MK801 (0.3-1 mg/kg) were examined in CRF-overexpressing (CRFtg) mice, which display PPI deficits. Finally, we determined the influence of CP154,526 on D-amphetamine-induced dopamine outflow in nucleus accumbens and prefrontal cortex of CRFtg mice using in vivo microdialysis. RESULTS: No CRF1-antagonists improved PPI deficits in any test. CRFtg mice showed blunted PPI disruption in response to MK801, but not D-amphetamine. Further, D-amphetamine-induced dopamine release was less pronounced in CRFtg versus wild-type mice, a response normalized by pretreatment with CP154,526. CONCLUSION: The inability of CRF1 receptor antagonists to block pharmacological disruption of sensorimotor gating suggests that the involvement of CRF1 receptors in the modulation of dopaminergic and glutamatergic neurotransmission relevant for sensory gating is limited. Furthermore, the alterations observed in CRFtg mice support the notion that long-term elevated central CRF levels induce changes in these neurotransmitter systems.

MK-801 disrupts and nicotine augments 40 Hz auditory steady state responses in the auditory cortex of the urethane-anesthetized rat.

Patients with schizophrenia show marked deficits in processing sensory inputs including a reduction in the generation and synchronization of 40 Hz gamma oscillations in response to steady-state auditory stimulation. Such deficits are not readily demonstrable at other input frequencies. Acute administration of NMDA antagonists to healthy human subjects or laboratory animals is known to reproduce many sensory and cognitive deficits seen in schizophrenia patients. In the following study, we tested the hypothesis that the NMDA antagonist MK-801 would selectively disrupt steady-state gamma entrainment in the auditory cortex of urethane-anesthetized rat. Moreover, we further hypothesized that nicotinic receptor activation would alleviate this disruption. Auditory steady state responses were recorded in response to auditory stimuli delivered over a range of frequencies (10-80 Hz) and averaged over 50 trials. Evoked power was computed under baseline condition and after vehicle or MK-801 (0.03 mg/kg, iv). MK-801 produced a significant attenuation in response to 40 Hz auditory stimuli while entrainment to other frequencies was not affected. Time-frequency analysis revealed deficits in both power and phase-locking to 40 Hz. Nicotine (0.1 mg/kg, iv) administered after MK-801 reversed the attenuation of the 40 Hz response. Administered alone, nicotine augmented 40 Hz steady state power and phase-locking. Nicotine's effects were blocked by simultaneous administration of the α4ß2 antagonist DHßE. Thus we report for the first time, a rodent model that mimics a core neurophysiological deficit seen in patients with schizophrenia and a pharmacological approach to alleviate it.

Differential effects of the antidepressant mirtazapine on amphetamine- and dizocilpine-induced PPI deficits.

Prepulse inhibition (PPI) refers to the decrease in motor startle response to salient sensory stimuli (pulses) when they are closely preceded in time by another more modest sensory stimulus (prepulse). PPI deficits can be induced by stimulation of dopamine receptors (e.g., amphetamine or apomorphine) or blockade of NMDA glutamate receptors (e.g., dizocilpine or PCP). Previously we found that antagonists of α(2)-noradrenergic and H(1)-histaminergic receptors significantly attenuate PPI impairments caused by amphetamine or dizocilpine. In the current study we assessed the effects of the antidepressant mirtazapine, which has combined antagonist effects at α(2)-noradrenergic, H(1)-histaminergic and 5-HT serotonergic receptors, on amphetamine- and dizocilpine-induced PPI deficits. In Experiment 1, rats were tested for PPI of the startle response to a tactile air-puff stimulus after auditory prepulses of three different intensities. Drug treatments consisted of combinations of amphetamine (0 and 1mg/kg) and mirtazapine (0, 0.5, 1, 2, and 5mg/kg), with all rats receiving all drug doses and combinations with different counterbalanced orders. In Experiment 2, a different group of rats was tested with drug treatments consisting of combinations of dizocilpine (0 and 0.05 mg/kg) and mirtazapine (0, 0.5, 1, 2, and 5 mg/kg). In Experiment 1 amphetamine (1 mg/kg) significantly reduced PPI whereas mirtazapine caused the opposite effect, with the highest dose of mirtazapine (5 mg/kg) effectively reversing the amphetamine-induced PPI deficit. In Experiment 2 dizocilpine (0.05 mg/kg) significantly reduced PPI, but mirtazapine did not have a significant effect on the inhibition of the startle response. These results indicate that the potential beneficial effects of combined α-adrenergic, 5-HT, and H(1) receptor blockade in counteracting PPI deficits may be associated to cases of sensorimotor gating disorders mediated by dopamine, but not necessarily to NMDA glutamate-induced PPI impairments.

Reversal of oxidative stress by histamine H3 receptor-ligands in experimental models of schizophrenia.

Schizophrenia (SCZ) is a debilitating disorder afflicting around 1% of the world population. Recent literature reveals oxidative injuries contribute enormously to the pathophysiology of SCZ alongside other psychopathological disturbances. Histamine H3R-antagonists have shown dual mechanism of action in experimental models of SCZ. Firstly it prevents oxidative stress and secondly alleviates schizophrenic symptoms, particularly the negative symptoms and cognitive deficits. In the present study, histamine H3R-antagonists used were ciproxifan (3.0 mg/kg, ip) and clobenpropit (15 mg/kg, ip) markedly controlled the elevated levels of various oxidative stress markers, for example, thiobarbituric acid reactive substance (TBARS), glutathione (GSH), superoxide dismutase, catalase, etc., as a result of augmented oxidative stress in the experimental models of SCZ such as amphetamine (0.5 mg/kg, sc) and dizocilpine (MK-801) (0.2 mg/kg, ip) induced locomotor hyperactivity, apomorphine (1.5 mg/kg, sc) induced climbing behavior and haloperidol (2.0 mg/kg, po) induced catalepsy. The results of the present study revealed that H3R-antagonists possess antioxidant activity and could serve with dual mechanism by supplementing antioxidant needs of SCZ and at the same time controlling symptoms of SCZ.

Preclinical profile of a novel metabotropic glutamate receptor 5 positive allosteric modulator.

Recent reports have indicated that patients with schizophrenia have a profound hypo-functionality of glutamatergic signaling pathways. Positive allosteric modulation of mGlu(5) receptor has been postulated to augment NMDA function and thereby alleviate the glutamatergic hypo-function observed in schizophrenic patients. Here we report the in vitro and in vivo characterization of CPPZ (1-(4-(2-chloro-4-fluorophenyl)piperazin-1-yl)-2-(pyridin-4-ylmethoxy)ethanone), a structurally novel positive allosteric modulator selective for mGlu(5) receptor. In HEK293 cells stably over-expressing human mGlu(5) receptor, CPPZ potentiates the intracellular calcium response elicited by a suboptimal concentration of the endogenous agonist glutamate. CPPZ does not have any intrinsic agonist activity and behaves functionally as a positive allosteric modulator. This is further supported by binding data, which demonstrate that CPPZ is able to displace the negative allosteric modulator MPEP but does not compete with the orthosteric ligand quisqualic acid. Instead, CPPZ enhances the binding of the orthosteric ligand. In native preparations, CPPZ potentiates calcium flux in rat cortical neurons stimulated with the group I agonist dihydroxyphenylglycine (DHPG). In addition, CPPZ modulates long-term potentiation in rat hippocampal slices, a process known to be NMDA dependent. In vivo, CPPZ reverses hyper locomotion triggered by the NMDA open channel blocker MK801 in CD1 mice. CPPZ was also able to reduce rat conditioned avoidance responding to electric shock. Both in vitro and in vivo data demonstrate that this novel compound acts as an mGlu(5) receptor positive allosteric modulator, which modulates NMDA dependent responses and suggests that the enhancement of mGlu(5) receptor activity may prove useful in the treatment of schizophrenia.

Effects of postnatal dietary choline manipulation against MK-801 neurotoxicity in pre- and postadolescent rats.

Prenatal supplementation of rat dams with dietary choline has been shown to provide their offspring with neuroprotection against N-methyl-d-aspartate (NMDA) antagonist-mediated neurotoxicity. This study investigated whether postnatal dietary choline supplementation exposure for 30 and 60 days of rats starting in a pre-puberty age would also induce neuroprotection (without prenatal exposure). Male and female Sprague-Dawley rats (postnatal day 30 of age) were reared for 30 or 60 concurrent days on one of the four dietary levels of choline: 1) fully deficient choline, 2) 1/3 the normal level, 3) the normal level, or 4) seven times the normal level. After diet treatment, the rats received one injection of MK-801 (dizocilpine 3mg/kg) or saline control. Seventy-two hours later, the rats were anesthetized and transcardially perfused. Their brains were then postfixed for histology with Fluorojade-C (FJ-C) staining. Serial coronal sections were prepared from a rostrocaudal direction from 1.80 to 4.2mm posterior to the bregma to examine cell degeneration in the retrosplenial and piriform regions. MK-801, but not control saline, produced significant numbers of FJ-C positive neurons, indicating considerable neuronal degeneration. Dietary choline supplementation or deprivation in young animals reared for 30-60days did not alter NMDA antagonist-induced neurodegeneration in the retrosplenial region. An interesting finding is the absence of the piriform cortex involvement in young male rats and the complete absence of neurotoxicity in both hippocampus regions and DG. However, neurotoxicity in the piriform cortex of immature females treated for 60days appeared to be suppressed by low levels of dietary choline.

Co-administration of a D-amino acid oxidase inhibitor potentiates the efficacy of D-serine in attenuating prepulse inhibition deficits after administration of dizocilpine.

BACKGROUND: D-Serine, an endogenous agonist of the N-methyl-D-aspartate (NMDA) receptors, is effective in the treatment of schizophrenia. However, orally administered D-serine is metabolized substantially by D-amino acid oxidase (DAAO), diminishing its oral bioavailability. In this study, we examined the effects of oral D-serine administration with or without a DAAO inhibitor, 5-chloro-benzo[d]isoxazol-3-ol (CBIO), on the prepulse inhibition (PPI) deficits after administration of the NMDA receptor antagonist dizocilpine. METHODS: Vehicle or D-serine (30, 300, or 900 mg/kg) with or without CBIO (30 mg/kg) was orally administered to mice 1 hour before administration of dizocilpine (.1 mg/kg), and then the PPI of the acoustic startle response was measured. We measured the extracellular levels of D-serine in the frontal cortex after oral administration of D-serine with or without CBIO. RESULTS: Coadministration of CBIO with D-serine (30 mg/kg), but not D-serine (30 mg/kg) alone, significantly attenuated dizocilpine-induced PPI deficits. Furthermore, coadministration of CBIO significantly increased the extracellular levels of D-serine in the frontal cortex after administration of D-serine. CONCLUSIONS: These findings suggest that coadministration of CBIO significantly enhanced the efficacy of D-serine in attenuating PPI deficits by administration of dizocilpine. Therefore, coadministration of D-serine and a DAAO inhibitor has therapeutic potential for the treatment of schizophrenia.

The effect of zotepine, risperidone, clozapine and olanzapine on MK-801-disrupted sensorimotor gating.

Dizocilpine (MK-801; 0.3 mg/kg i.p.)-induced disruption in prepulse inhibition of the acoustic startle response (PPI) can be preferentially restored by "atypical" antipsychotics. In contrast, some findings indicate that not all of the "atypical" antipsychotics, such as clozapine and risperidone, are effective in restoring the NMDA antagonist-induced deficits in PPI. In our study, we evaluated the effect of four different "atypical" antipsychotic drugs on deficits in PPI induced by MK-801. Zotepine and risperidone have high affinities to D2-like and 5-HT2A receptors, while clozapine and olanzapine have multipharmacological profiles with the highest affinities to serotonin 5-HT1A,2A/2C receptors and muscarinic receptors. Results have shown that MK-801 disrupted PPI and increased the ASR in rats. Our results showed no effect of zotepine (1 and 2 mg/kg) and risperidone (0.1 and 1 mg/kg) on disrupted PPI by MK-801. Administration of clozapine (5 and 10 mg/kg) and olanzapine (2.5 and 5 mg/kg) restored the deficits in PPI induced by MK-801. Additionally, we found a decrease of approximately 46% in PPI after administration of clozapine (5 mg/kg) and olanzapine (2.5 and 5 mg/kg) without MK-801 treatment. In summary, the four "atypical" antipsychotics had different efficacies to restore the disrupted PPI by MK-801. Only clozapine and olanzapin restored the MK-801-induced deficits in PPI.

Atypical antipsychotic profile of flunarizine in animal models.

RATIONALE: Flunarizine is known as a calcium channel blocker commonly used in many countries to treat migraine and vertigo. Parkinsonism has been described as one of its side-effects in the elderly, which is in agreement with its recently characterized moderate D2 receptor antagonism. OBJECTIVES: To perform a pre-clinical evaluation of flunarizine as a potential antipsychotic. METHODS: We evaluated the action of orally administered flunarizine in mice against hyperlocomotion induced by amphetamine and dizocilpine (MK-801) as pharmacological models of schizophrenia, induction of catalepsy as a measure for extrapyramidal symptoms and impairment induced by dizocilpine on the delayed alternation task for working memory. RESULTS: Flunarizine robustly inhibited hyperlocomotion induced by both amphetamine and dizocilpine at doses that do not reduce spontaneous locomotion (3-30 mg/kg). Mild catalepsy was observed at 30 mg/kg, being more pronounced at 50 mg/kg and 100 mg/kg. Flunarizine (30 mg/kg) improved dizocilpine-induced impairment on the delayed alternation test. CONCLUSIONS: These results suggest a profile comparable to atypical antipsychotics. The low cost, good tolerability and long half-life (over 2 weeks) of flunarizine are possible advantages for its use as an atypical antipsychotic. These results warrant clinical trials with flunarizine for the treatment of schizophrenia.

A competitive antagonist of NMDA receptors CGP 40116 attenuates experimental symptoms of schizophrenia evoked by MK-801.

In the present study, the interaction between a noncompetitive [(+)-MK-801] and a competitive (CGP 40116) NMDA receptor antagonists was tested in two different behavioral paradigms: locomotor activity test and prepulse inhibition of the acoustic startle reflex. Additionally, their effects on working memory and selective attention were evaluated in the delayed alternation task. All above paradigms served to model the symptoms of schizophrenia. It was found that locomotor stimulatory effect of (+)-MK-801 (0.4 mg/kg) was antagonized by prior administration of CGP 40116 (5 mg/kg). Lower doses of CGP 40116 (1.25 and 2.5 mg/kg) were ineffective. CGP 40116 given alone did not influence locomotor activity in rats. It was also shown that CGP 40116 antagonized the disruption of the process of sensorimotor gating evoked by (+)-MK-801. On the contrary, both CGP 40116 and (+)-MK-801 increased a number of errors in the delayed alternation test revealing detrimental effect of CGP 40116 on spatial working memory and selective attention even at a lower dose than that required to antagonize the effects of (+)-MK-801. The presented results indicate that noncompetitive and competitive NMDA receptor antagonists, when used at relatively low doses, may produce qualitatively different behavioral effects, as evidenced by the experiments with locomotor activity and prepulse inhibition. Moreover, the competitive NMDA receptor antagonists may even inhibit some psychotomimetic effects related to the noncompetitive blockade of this receptor. However, therapeutic potential of CGP 40116, a competitive NMDA receptor antagonist, should be considered with caution since in the range of doses effective against the psychotomimetic effects of (+)-MK-801, it impairs rats' performance in the delayed alternation paradigm, i.e. it worsens efficacy of working memory.

Does MK-801 discrimination constitute an animal model of schizophrenia useful for detecting atypical antipsychotics?

Two groups of female Wistar rats were trained to discriminate two doses (0.075 and 0.0375 mg/kg) of the noncompetitive NMDA antagonist MK-801 (dizocilpine) in a food-rewarded operant FR30 drug discrimination task. The atypical neuroleptic clozapine (2-6 mg/kg) produced only minimal antagonism (max. 32%) of the MK-801 cue at either training dose, and the "antagonist" effects were not clearly dose related. Furthermore, in the 0.075 mg/kg trained animals clozapine at 3 mg/kg failed to shift the MK-801 dose-response curve to the right. The alpha1-adrenoceptor antagonist prazosin (1-8 mg/kg) was also tested for antagonism of the 0.0375 mg/kg MK-801 cue, and again, only partial antagonism was seen (maximum 36%). Recently, it was suggested [4] that as the discriminative stimulus produced by MK-801 (0.075 mg/kg) was fully antagonized by clozapine at 3 mg/kg, but not by the typical neuroleptic haloperidol, this assay may be a useful screen for detecting atypical neuroleptics. It would seem, however, that this is not necessarily the case, and that the MK-801 discriminative cue may not be psychotomimetic. However, as this was a food rewarded rather than an avoidance paradigm that was used in the prior study [4], it may be that the drug discrimination procedure itself is a critical factor, although this hypothesis requires empirical testing.

Dopaminergic basis for the facilitation of brain stimulation reward by the NMDA receptor antagonist, MK-801.

MK-801 (dizocilpine maleate), an antagonist of the NMDA receptor, was given alone or in combination with dopamine D1 and D2 receptor antagonists to rats self-stimulating in lateral hypothalamus to determine whether the dopamine neurons play a role in mediating the effects of MK-801. MK-801 given at a dose of 0.1 mg/kg i.p. to self-stimulators induced a prolonged facilitation of lever-pressing, but given to non-self-stimulators, the drug had no effects. Pretreatment of self-stimulators with the dopamine D1 receptor antagonist Schering 23390 (SCH 23390), 0.2 mg/kg given i.p. 15 min before MK-801, prevented the facilitation seen with MK-801, but did not suppress self-stimulation. SCH 23390 given alone suppressed self-stimulation. Pretreatment of self-stimulators with the dopamine D1/D2 receptor antagonist, haloperidol, 0.2 mg/kg given i.p. 15 min before MK-801, also prevented the facilitation of self-stimulation induced by MK-801 yet did not suppress self-stimulation. Haloperidol given alone suppressed self-stimulation. Pretreatment of self-stimulators with both SCH 23390 and haloperidol 15 min before MK-801 prevented the facilitation seen with MK-801 and suppressed self-stimulation. The combined treatment with SCH 23390 and haloperidol (without MK-801) suppressed self-stimulation, and the suppression lasted longer than the suppression seen when the two dopamine receptor antagonists were given as pretreatment, before MK-801. Pretreating self-stimulators with the combination of SCH 23390 and haloperidol 15 min before amphetamine (2 mg/kg) prevented the facilitatory response and suppressed responding for the brain reward. The suppression was of shorter duration than the suppression seen after the injection of SCH 23390 plus haloperidol. The treatment of self-stimulators with both MK-801 and amphetamine resulted in a greater and longer-lasting facilitation than the increase in responding produced by either drug alone. The similarity between the effects of MK-801 and those of amphetamine and between the effects of pretreatment with the dopamine receptor antagonists before MK-801 and before amphetamine suggests that dopaminergic activity played a significant role in the action underlying the effects of MK-801 on brain stimulation reward.

Antagonism of phencyclidine-induced deficits in prepulse inhibition by the putative atypical antipsychotic olanzapine.

Prepulse inhibition (PPI) of the startle reflex provides an operational measure of sensorimotor gating. Deficits in PPI are observed in schizophrenia patients and can be modelled in animals by administration of noncompetitive NMDA antagonists such as phencyclidine (PCP) or dizocilpine (MK-801). Previous studies indicate that the atypical antipsychotic clozapine restores PPI in PCP-treated animals while the typical antipsychotic haloperidol does not. Olanzapine (LY170053) is a novel putative atypical antipsychotic that shares many pharmacological and behavioral properties with clozapine. The present study assessed the ability of olanzapine (0, 1.25, 2.5, 5.0 or 10.0 mg/kg) to antagonize deficits in PPI produced by PCP (1.5 mg/kg) and dizocilpine (0.1 mg/kg). At the two highest doses, olanzapine significantly increased PPI in PCP- and dizocilpine-treated animals without affecting PPI or baseline startle reactivity by itself. These results support the notion that olanzapine is functionally similar to clozapine and may have utility as an atypical antipsychotic agent.