NMDA receptor antagonists inhibit apomorphine-induced climbing behavior not only in intact mice but also in reserpine-treated mice

Neurobehavioural evaluation of resveratrol in murine models of anxiety and schizophrenia

Resveratrol, a caloric restriction mimetic, is a naturally occurring polyphenolic compound with antioxidant and anti-inflammatory properties. Oxidative stress has been implicated in the etiology of a number of neuropsychiatric disorders including generalized anxiety and schizophrenia. This study investigated the anxiolytic and antipsychotic potentials of resveratrol in murine models of anxiety and schizophrenia. Mice were pretreated with resveratrol (200 and 400 mg/kg) in 1% carboxymethyl cellulose for 14 days and subjected to behavioural tests on the 15th day. Anxiolytic activity of resveratrol was determined using the hole board and staircase tests while its anti-psychotic property was evaluated via apormorphine induced stereotypy and swim-induced grooming tests. Although resveratrol did not significantly reduce the mean number of head dips at doses used in the hole board test, it significantly (p < 0.01) decreased the mean episodes of rearing without significantly altering the total number of upward steps climbed in the staircase test. Resveratrol significantly (p < 0.05) reduced the mean climbing scores in the first ten minutes of the apormorphine induced stereotypic climbing and significantly decreased (p < 0.01) episodes and total duration of swim induced grooming in mice. Administration of resveratrol at doses used in this study produced anxiolysis and anti-psychotic effects in mice.

Synthesis and evaluation of amide, sulfonamide and urea – benzisoxazole derivatives as potential atypical antipsychotics

A series of amide derivatives of benzisoxazole has been synthesized and the target compounds evaluated for atypical antipsychotic activity in vitro and vivo.

L-tetrahydropalmatine inhibits methamphetamine-induced locomotor activity via regulation of 5-HT neuronal activity and dopamine D3 receptor expression

Methamphetamine (METH) is a psychomotor stimulant that produces hyperlocomotion in rodents. l-tetrahydropalmatine (l-THP) is an active ingredient found in Corydalis ternata which has been used as a traditional herbal preparation in Asian countries for centuries, however, the effect of l-THP on METH-induced phenotypes largely unknown. In this study, to evaluate the effect of l-THP on METH-induced psychotropic effects, rats were pretreated with l-THP (10 and 15 mg/kg) before acute METH injection, following which the total distance the rats moved in an hour was measured. To clarify a possible mechanism underlying the effect of l-THP on METH-induced behavioral changes, dopamine receptor mRNA expression levels in the striatum of the rats was measured following the locomotor activity study. In addition, the effect of l-THP (10 and 15 mg/kg) on serotonergic (5-HTergic) neuronal pathway activation was studied by measurement of 5-HT (80 μg/10μl/mouse)-induced head twitch response (HTR) in mice. l-THP administration significantly inhibited both hyperlocomotion in rats and HTR in mice. l-THP inhibited climbing behavior-induced by dopaminergic (DAergic) neuronal activation in mice. Furthermore, l-THP attenuated the decrease in dopamine D3 receptor mRNA expression levels in the striatum of the rats induced by METH. These results suggest that l-THP can ameliorate behavioral phenotype induced by METH through regulation of 5-HT neuronal activity and dopamine D3 receptor expression.

Synthesis and evaluation of new coumarin derivatives as potential atypical antipsychotics

In this paper, we report the synthesis of novel, potential antipsychotic coumarin derivatives combining potent dopamine D₂, D₃ and serotonin 5-HT(1A), 5-HT(2A) receptors properties. We describe the structure activity relationship that leads us to the promising derivative: 7-(4-(4-(6-fluorobenzo[d]isoxazol-3-yl)piperidin-1-yl)butoxy)-6-methyl-2,3-dihydrocyclopenta[c]chromen-4(1H)-one 27. The unique pharmacological features of compound 27 are a high affinity for dopamine D₂, D₃ and serotonin 5-HT(1A), 5-HT(2A) receptors, together with a low affinity for H₁ receptor (to reduce the risk of obesity under chronic treatment). In animal models, compound 27 inhibited apomorphine-induced climbing and MK-801-induced hyperactivity without observable catalepsy at the highest dose tested. In particular, compound 27 was more potent than clozapine.

The role of nitric oxide on glutaminergic modulation of dopaminergic activation

Biochemical studies have been demonstrated that N-methyl-D-aspartate (NMDA)-evoked dopaminergic (DAergic) activation can be modulated by nitric oxide (NO) systems. Therefore, behavioral study was performed to characterize the role of NO on NMDA modulation of DAergic activation. It is well known that apomorphine induces climbing behaviors in mice by the activation of DAergic receptors. Our previous studies showed that NMDA receptor antagonists reduced apomorphine-induced climbing behaviors. It was reported that nitric oxide synthase (NOS) inhibitors reduced the apomorphine-induced climbing behaviors. In this experiment, NO donor restored the apomorphine-induced climbing behavior, which was inhibited by NMDA receptor antagonist. NOS inhibitor inhibited the apomorphine-induced climbing behavior, which was enhanced by NMDA receptor agonist. These results suggest that DAergic activation is regulated by both NMDA receptors and NO systems, and NO in the down-stream of NMDA receptors play an important role on the glutaminergic NMDA modulation of DAergic function.

NMDA-receptor antagonism via dextromethorphan and ifenprodil modulates graded anxiety test performance of C57BL/6 mice

The majority of N-methyl-D-aspartate receptors (NMDA-R) in the adult forebrain are di- or triheteromers composed of NR1, NR2A and NR2B subunits. Subunit non-selective NMDA-R antagonists produce anxiolytic-like effects together with motor and sensory side-effects. The graded anxiety test (GAT), permits the within-task distinction of drug effects on anxiety from those on activity and perception. By testing NMDA-R subunit selective agents in the GAT it might be possible to determine whether their effects on anxiety, activity and perception are interrelated, and whether separate NMDA-R subtypes are involved. Dextromethorphan (weakly NR2A-selective) (10 and 30 mg/kg, i.p.) and ifenprodil (highly NR2B-selective) (1, 3 and 5 mg/kg, i.p.) were tested in the GAT. Both drugs failed to induce anxiolysis devoid of side-effects. However, the 10 mg/kg dose of dextromethorpan showed an anxiolytic, whereas the 30 mg/kg dose showed an anxiogenic, behavioral profile. Since the selective blockade of the NR2B subunit by ifenprodil had no clear anxiolytic effect, the anxiolytic potential of NMDA subunit non-selective agents might involve NR2A-containing receptors.

Inhibitory effects of MK-801 on contextual sensitization to climbing behavior and on development of tolerance to hypothermia induced by a single high dose of apomorphine

A single high dose of apomorphine (10 mg x kg(-1)) produced not only contextual sensitization to and conditioning of climbing behavior, but also context-independent tolerance to hypothermia. MK-801 (0.15 and 0.3 mg x kg(-1)) inhibited contextual sensitization to and conditioning of climbing behavior. Development of tolerance to hypothermia was also inhibited by MK-801. Dopamine D1 antagonist, SCH23390 (0.5 mg x kg(-1)), but not D2 antagonist, sulpiride, inhibited sensitization to and conditioning of climbing behavior. D2 antagonist, sulpiride (50 mg x kg(-1)), but not D1 antagonist, SCH23390, inhibited development of tolerance to hypothermia. These results suggest that MK-801 inhibited contextual sensitization to climbing behavior and development of tolerance to hypothermia through glutamatergic modulation of dopaminergic functions at dopamine receptors.

N-Methyl-D-aspartate receptor antagonists enhance the head-twitch response, a 5-hydroxytryptamine2 receptor-mediated behaviour, in reserpine-treated mice

In this study, N-methyl-D-aspartate (NMDA)-receptor antagonists enhanced the head-twitch response induced by 5-hydroxytryptamine (5-HT) in reserpine-treated mice. To minimize the risk of any indirect involvement of NMDA-receptor antagonists (D(-)-2-amino-5-phosphonopentanoic acid (AP-5), D(-)-3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP), (+)-5-methyl-10,11-dihydroxy-5H-dibenzo-[a,d]-cyclohepten-5,10-imi ne (MK-801), ketamine, dextrorphan and dextromethorphan) with 5-HT neurones, vesicle stores of monoamines, especially 5-HT, were depleted with reserpine. In addition, the enhancement of 5-HT-induced head-twitch response was inhibited by apomorphine and NMDA as well as ritanserin in reserpine-treated mice. These results support our previous conclusion that NMDA receptors play important roles in the glutamatergic modulation of 5-HTergic function at the postsynaptic 5-HT2 receptors in mice.

NMDA receptor antagonists enhance 5-HT2 receptor-mediated behavior, head-twitch response, in PCPA-treated mice

Previous work in our laboratory has shown that the N-methyl-D-aspartate (NMDA) receptor antagonists, AP-5, CPP, MK-801, ketamine, dextrorphan and dextromethorphan cause a pronounced enhancement of 5-hydroxytryptamine (5-HT)-induced head-twitch response (HTR) in intact mice, suggesting the involvement of NMDA receptors in the glutamatergic modulation of serotonergic function at the postsynaptic 5-HT2 receptors. The purpose of this study was to extend our previous work on the behavioral interaction between glutamatergic and serotonergic receptors. In the present study, both competitive (AP-5 and CPP) and noncompetitive (MK-801, ketamine, dextrorphan and dextromethorphan) NMDA receptor antagonists markedly enhanced 5-HT-induced selective serotonergic behavior, HTR, in p-chlorophenylalanine (PCPA)-treated mice which were devoid of any involvement of indirect serotonergic function, to establish the involvement of the NMDA receptor in 5-HT-induced HTR at the postsynaptic 5-HT2 receptors. In addition, the enhancement of 5-HT-induced HTR was inhibited by a dopamine agonist, apomorphine, NMDA receptor antagonist, NMDA and a serotonin 5-HT2 receptor antagonist, cyproheptadine, in PCPA-treated mice. Therefore, the present results support our previous conclusion that the NMDA receptors play an important role in the glutamatergic modulation of serotonergic function at the postsynaptic 5-HT2 receptors.