Computerized measurement of MK-801-elicited popping and hyperactivity in mice

From Mouse to Man: N-Methyl-d-Aspartic Acid Receptor Activation as a Promising Pharmacotherapeutic Strategy for Autism Spectrum Disorders

The BALB/c mouse displays hypersensitivity to behavioral effects of MK-801 (dizocilpine), a noncompetitive N-methyl-d-aspartic acid (NMDA) receptor "open-channel" blocker, and shows both no preference for an enclosed stimulus mouse over an inanimate object and reduced social interaction with a freely behaving stimulus mouse. NMDA receptor agonist interventions improved measures of social preference and social interaction of the BALB/c mouse model of autism spectrum disorder (ASD). A "proof of principle/proof of concept" translational 10-week clinical trial with 8-week of active medication administration was conducted comparing 20 DSM-IV-TR-diagnosed older adolescent/young adult patients with ASD randomized to once-weekly pulsed administration (50 mg/d) versus daily administration of d-cycloserine (50 mg/d). The results showed that d-cycloserine, a partial glycine agonist, was well tolerated, the 2 dosing strategies did not differ, and improvement was noted on the "lethargy/social withdrawal" and "stereotypic behavior" subscales of the Aberrant Behavior Checklist. NMDA receptor activation contributes to the regulation of mTOR signaling, a pathologic point of convergence in several monogenic syndromic forms of ASD. Furthermore, both NMDA receptor hypofunction and imbalance between NMDA receptor activation mediated by GluN2B and GluN2A-containing NMDA receptors occur as "downstream" consequences of several genetically unrelated abnormalities associated with ASD. NMDA receptor-subtype selective "positive allosteric modulators (PAMs)" are particularly appealing medication candidates for future translational trials.

Sensorimotor gating deficits and effects of antipsychotics on the hyperactivity in VGF-overexpressing mice

BACKGROUND

VGF nerve growth factor inducible (VGF) is a neuropeptide which is expressed in neuronal cells and endocrine cells. VGF is induced by several neurotrophic factors. The expression level of VGF in patients with schizophrenia is increased in cerebrospinal fluid (CSF) and prefrontal cortex. In our previous study, we generated mice in which the expression level of VGF in the brain was increased. VGF-overexpressing mice exhibited abnormal behaviors including hyperactivity. However, it remains unknown whether VGF-overexpressing mice exhibit the endophenotype of schizophrenia and whether abnormal behaviors in these mice can be improved by antipsychotics.

METHODS

In the present study, we investigated schizophrenia-like behaviors and the responsiveness to antipsychotics in transgenic mice.

RESULTS

VGF-overexpressing mice (1) exhibited prepulse inhibition (PPI) impairment, (2) showed normalized hyperactivity following antipsychotic drug treatment, and (3) showed abnormal responsiveness to haloperidol.

CONCLUSION

Upregulation of VGF may be implicated in the pathophysiology of schizophrenia and abnormalities of dopaminergic signaling.

Examination of clozapine and haloperidol in improving ketamine-induced deficits in an incremental repeated acquisition procedure in BALB/c mice

RATIONALE

Ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist, causes locomotor hyperactivity, aberrant prepulse inhibition and impaired reversal learning among other deficits. There are numerous clinical and pre-clinically uses of NMDAR antagonists and a growing need to characterize their neurobehavioral effects.

OBJECTIVES

The present study was designed to characterize 1) ketamine's effect on incremental repeated acquisition (IRA), a procedure that taps multiple neurobehavioral functions and has performance measures correlated with IQ in humans, and 2) the extent to which clozapine (CLZ) and haloperidol (HAL) block ketamine's detrimental effects.

METHODS AND RESULTS

In experiment 1 (Exp. 1), BALB/c mice nose-poked under an IRA procedure for sucrose pellets. Systemic ketamine (1-30 mg/kg) dose-dependently decreased measures of cognitive and motor function. CLZ pretreatment (CLZ 0.1-4.0 mg/kg) dose-dependently attenuated ketamine-induced (30 mg/kg) deficits; the effective dose range of CLZ was 0.3-1.0 mg/kg. HAL pretreatment (0.01-0.1 mg/kg) did not attenuate any ketamine-induced deficits. In experiment 2 (Exp. 2), BALB/c mice lever-pressed under an IRA procedure for sweetened condensed milk. Ketamine (30 mg/kg) produced a global impairment in the IRA procedure and CLZ pretreatment (0.3-1.0 mg/kg) dose-dependently attenuated that impairment; motor-based performance recovered to a greater extent than cognitive performance. When tested alone, these doses of CLZ had little effect on IRA performance.

CONCLUSIONS

These findings support the notion that CLZ is more effective than HAL at blocking ketamine-induced deficits. The IRA procedure may be beneficial for distinguishing the efficacy of drugs that seek to alleviate deficits in complex behavior that result from acute NMDAR antagonism.

NMDA NR2B subtype-selective receptor antagonists fail to antagonize electrically-precipitated seizures and elicit popping in mice

NR2B-subtype-selective antagonists differ from MK-801, a nonselective NMDA receptor antagonist. MK-801 antagonizes electrical seizures at doses as low as 0.1 to 0.18mg/kg and elicits popping at doses as low as 0.5mg/kg, whereas ifenprodil and Ro 8-4304 were unable to do so at the doses tested. Ro 25-6981, however, was able to antagonize electrically-precipitated tonic hindlimb extension at 100mg/kg, but was not able to elicit popping behavior at this dose.

Effects of CDP-choline and the combination of CDP-choline and galantamine differ in an animal model of schizophrenia: development of a selective alpha7 nicotinic acetylcholine receptor agonist strategy

The regionally selective reduction of expression of the alpha7 nicotinic acetylcholine receptor (alpha7 nAChR) in schizophrenia underlies impaired sensory inhibition, a possible endophenotype of the disorder. This ligand-gated ion channel receptor has been proposed as a pharmacotherapeutic target in schizophrenia. The current study examined the effect of CDP-choline alone and the combination of CDP-choline and galantamine, administered acutely and once-daily for five consecutive days, in an animal model of NMDA receptor hypofunction that is relevant to schizophrenia. The results support the allosteric modulatory influence of galantamine on CDP-choline; however, individual doses of CDP-choline and galantamine must be carefully titrated in order to achieve optimal levels of alpha7 nAChR "agonism" that may be necessary for the desired therapeutic effect.

Phencyclidine and dizocilpine induced behaviors reduced by N-acetylaspartylglutamate peptidase inhibition via metabotropic glutamate receptors

BACKGROUND

N-methyl-D-aspartate (NMDA) receptor open channel blockers phencyclidine (PCP) and dizocilpine (MK-801) elicit schizophrenia-like symptoms in humans and in animal models. Group II metabotropic glutamate receptor agonists reverse the behavioral effects of PCP and MK-801 in animal models. N-acetylaspartylglutamate (NAAG), the third most prevalent neurotransmitter in the mammalian nervous system, is a selective group II metabotropic glutamate receptor agonist. We previously reported that ZJ43, a potent inhibitor of the enzymes that inactivate synaptically released NAAG, reduced motor and stereotypic effects of PCP in the rat.

METHODS

To confirm the efficacy of NAAG peptidase inhibition in decreasing motor behaviors induced by PCP and MK-801, ZJ43 was tested in additional schizophrenia models.

RESULTS

ZJ43 reduced MK-801-induced motor activation in a mouse model that has been used to characterize the efficacy of a wide range of pharmacotherapies for this human disorder. In a second mouse strain, the peptidase inhibitor reduced PCP-induced stereotypic movements. ZJ43 also reduced PCP-induced negative symptoms in a resident-intruder assay. The group II metabotropic glutamate receptor antagonist, LY341495, blocked the effect of NAAG peptidase inhibition in these mouse models of positive and negative PCP- and MK-801-induced behaviors. Additionally, LY341495 alone increased some PCP-induced behaviors suggesting that normal levels of NAAG act to moderate the effect of PCP via a group II mGluR.

CONCLUSIONS

These data support the proposal that NAAG peptidase inhibition and elevation of synaptic NAAG levels represent a new therapeutic approach to treating the positive and negative symptoms of schizophrenia that are modeled by open channel NMDA receptor antagonists.

Thechakragati mouse: A mouse model for rapidin vivo screening of antipsychotic drug candidates

The chakragati (ckr) mouse is a serendipitously discovered insertional transgenic mutant that exhibits circling and hyperactivity. Studies of social behavior, sensorimotor gating and ventricular anatomy suggest that the ckr mouse models aspects of schizophrenia. The underlying genetic and neurodevelopmental mechanisms remain to be elucidated but appear to result in a hemispheric asymmetry in striatal D(2)-like dopamine receptors. The circling is inhibited by administration of antipsychotic drugs and so lends itself to in vivo prospective screening for novel molecules with antipsychotic-like activity. Using the ckr mouse we have applied an in vivo first approach to screening for antipsychotic drug candidates. This offers the advantage of early indication of central nervous system bioavailability and potential toxicological concerns. Additionally, in vivo first screening in the ckr mouse is not biased by any particular neurotransmitter hypothesis of the disease, and so has the potential to identify compounds modifying the behavioral output by novel mechanisms of interaction with the underlying brain circuitry. Thus, in contrast to the classical strategy of hypothesis-driven in vitro screening for drugs fitting a "receptor model" of the disease, the ckr mouse screen has greater potential to identify lead molecules for a new generation antipsychotics with novel mechanisms of action.

Use of a force-plate actometer for detecting and quantifying vertical leaping induced by amphetamine in BALB/cJ mice, but not in C57BL/6J, DBA/2J, 129X1/SvJ, C3H/HeJ, and CD-1 mice

The force-plate actometer is a relatively new computer-based instrument with high temporal and spatial resolution that has been used to measure the behavioral effects of genetic restriction (e.g., inbred mice) and drugs (e.g., dopaminergic agonists and antagonists) on a variety of behaviors in rodents, including locomotor activity, stereotypies, tremor, and wall rearing. In the present study, the force-plate actometer was used to measure the differential effects of amphetamine-induced (10.0mg/kg) vertical leaping in five inbred mouse strains (BALB/cJ, C57BL/6J, DBA/2J, 129X1/SvJ, and C3H/HeJ) and one outbred stock (CD-1). Across a 13-day, five-injection procedure, mice of the BALB/cJ strain leaped an average of 82 times per 60-min session; the C57BL/6J, DBA/2J, 129X1/SvJ, C3H/HeJ strains and CD-1 stock always showed zero or near zero levels of vertical leaping following amphetamine treatment. The quantitative precision afforded by the force-plate actometer revealed that the mean duration of the leaps by the BALB/cJ strain was 0.18 second, and the corresponding peak force averaged 87.4 gram per leap, which was more than 400% of the average body weight of this strain. Although no evidence of behavioral sensitization was indicated for amphetamine's effects on vertical leaping, sensitization to amphetamine's effects on spatial confinement (i.e., bouts of low mobility) was observed in all mouse types. Results indicate that the force-plate actometer is an instrument well suited for detecting and quantifying both vertical leaping and collateral behaviors induced by amphetamine in mice.

Anabasine, a selective nicotinic acetylcholine receptor agonist, antagonizes MK-801-elicited mouse popping behavior, an animal model of schizophrenia

The expression of the alpha7-nicotinic acetylcholine receptor is diminished in selected brain areas of patients with schizophrenia. This diminished expression may account for the pathophysiological deficits of sensory inhibition and smooth pursuit eye movement performance in these patients. Furthermore, the deficits in sensory inhibition and smooth pursuit eye movement performance in schizophrenia appear to be inherited in an autosomal dominant fashion; thus, the "alpha7-nicotinic acetylcholine receptor-deficiency" may be a necessary condition for expression of schizophrenia. This deficit has encouraged speculation about the possible therapeutic benefit of selective alpha7-nicotinic acetylcholine receptor agonist interventions in this disorder. In view of this, we sought to examine the effect of anabasine, a selective alpha7-nicotinic acetylcholine receptor agonist, on popping behavior in mice elicited by MK-801. MK-801, a high affinity analogue of phencyclidine (PCP), is a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist that binds to the hydrophobic domain of this ligand-gated channel. PCP is known to precipitate a schizophreniform psychosis in susceptible individuals, causing productive (e.g. hallucinations) deficit (e.g. affective blunting, amotivation, and social withdrawal), cognitive and motor symptoms similar to those seen in naturally-occurring schizophrenia. Behaviors elicited by MK-801 in mice reflect a pharmacologically-induced state of NMDA receptor hypofunction (NRH), which has been proposed to exist in schizophrenia. Compounds that attenuate MK-801-elicited behaviors, which are identified in this animal model, may have the potential to treat schizophrenia, including deficit and cognitive symptoms. In the current study, anabasine attenuated MK-801-elicited popping at a dose that did not cause clonic seizures. The development of alpha7-nicotinic acetylcholine receptor agonist interventions for schizophrenia must consider their potential liability to elicit seizure activity.

NMDA receptor blockade attenuates locomotion elicited by intrastriatal dopamine D1-receptor stimulation

Previous behavioral studies suggest that the striatum mediates a hyperactive response to systemic NMDA receptor antagonism in combination with systemic D1 receptor stimulation. However, many experiments conducted at the cellular level suggest that inhibition of NMDA receptors should block D1 receptor-mediated locomotor activity. Therefore, we investigated the consequences of NMDA receptor blockade on the ability of striatal D1 receptors to elicit locomotor activity using systemic and intrastriatal injections of the NMDA antagonist MK-801 combined with intrastriatal injections of the D1 full agonist SKF 82958. Following drug treatment locomotor activity was measured via computerized activity monitors designed to quantify multiple parameters of rodent open-field behavior. Both systemic (0.1 mg/kg) and intrastriatal (1.0 microg) MK-801 pretreatments completely blocked locomotor and stereotypic activity elicited by 10 microg of SKF 82958 directly infused into the striatum. Further, increased activity triggered by intrastriatal SKF 82958 was attenuated by a posttreatment with intrastriatal infusion of 1 microg MK-801. These data suggest that D1-stimulated locomotor behaviors controlled by the striatum require functional NMDA channels.

[Altered higher brain function in PACAP-knockout mice]

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that functions as not only a neurotransmitter/neuromodulator but also a neurotrophic factor. To assess the roles of endogenous PACAP, several groups including ours have independently produced mice with targeted mutations in the PACAP gene. The phenotypes of the mutant mice both confirm and extend our knowledge of the physiological roles of PACAP in the central nervous system as well as many peripheral organs. In this review, we briefly summarize the roles of PACAP in higher brain function, which have been proposed by the studies using the mutant mice as well as histological and pharmacological approaches.

Modulation of MK-801-elicited mouse popping behavior by galantamine is complex and dose-dependent

The ability of phencyclidine (PCP), a noncompetitive antagonist of NMDA receptor-mediated neurotransmission, to precipitate a schizophreniform psychosis in susceptible individuals is consistent with the hypothesized pathologic occurrence of NMDA receptor hypofunction in this disorder. Because the psychosis caused by PCP resembles schizophrenia in all of the relevant domains of psychopathology, investigators have sought to characterize animal models of NMDA receptor hypofunction. MK-801 (dizocilpine) binds to the same hydrophobic channel domain in the NMDA receptor-associated ionophore as PCP, and has been shown to elicit intense irregular episodes of jumping behavior in mice, termed "popping." MK-801-elicited mouse popping is an animal model of NMDA receptor hypofunction that has been used to screen novel candidate compounds for the treatment of schizophrenia. Recently, a selective abnormality in the transduction of the acetylcholine signal at the level of the alpha 7 nicotinic receptor has been described in schizophrenia. The existence of a nicotinic cholinergic abnormality in schizophrenia has stimulated interest in a potential therapeutic role for positive allosteric modulation of nicotinic receptors. Galantamine is a compound that possesses two interesting properties: inhibition of acetylcholinesterase and positive allosteric modulation of nicotinic neurotransmission. Theoretically, galantamine would be expected to increase the efficiency or likelihood that acetylcholine will promote channel opening and ionic conductance at nicotinic receptors. As expected, in the current investigation statistically significant popping behavior was elicited by MK-801 in mice (T(22) = 2.16, P < 0.05). This MK-801-elicited popping was significantly attenuated by 100 mg/kg of galantamine (T(22) = 2.24, P < 0.05). The data show that nicotinic interventions can influence NMDA receptor-mediated neurotransmission in the intact mouse.

Interaction of stress and strain on glutamatergic neurotransmission: relevance to schizophrenia

Psychosis caused by phencyclidine (PCP) stimulated interest in characterizing rodent behaviors elicited by PCP and its analogues. We have shown that MK-801 antagonizes electrically precipitated seizures (defined as tonic hindlimb extension) and elicits episodes of intense jumping behavior, referred to as "popping," in mice. Moreover, 24 h after stress, MK-801's ability to antagonize electrically precipitated seizures is reduced in outbred NIH Swiss mice. Inbred BALBc mice are more resistant to electrically precipitated seizures than the NIH Swiss strain, and are more sensitive to both MK-801's anticonvulsant effect and ability to elicit popping. In the current experiments, we examined the influence of stress and genetic mouse strain on both MK-801's ability to antagonize electrically precipitated seizures and elicit popping. Stress significantly reduced the threshold voltage for precipitation of seizures in BALBc mice and the anticonvulsant properties of MK-801 in both strains. These data show that factors relevant to schizophrenia and its exacerbation (i.e., acute stress and genetics) influence N-methyl-D-aspartic acid (NMDA) receptor-mediated neurotransmission in intact mice. The BALBc inbred strain of mouse may possess advantages in preclinical screening paradigms designed to assess NMDA receptor agonist interventions for disorders such as schizophrenia. Specifically, stressed BALBc mice showed the greatest behavioral sensitivity to MK-801 with regard to electrically precipitated seizures in the incremental electroconvulsive shock (IECS) paradigm, whereas unstressed BALBc showed the greatest behavioral sensitivity to MK-801 in the "popping" paradigm, relative to BALBc and NIH Swiss mice in the appropriate comparison conditions.

Topiramate antagonizes MK-801 in an animal model of schizophrenia

The phencyclidine (PCP) model of schizophrenia suggests that N-methyl-D-aspartate (NMDA) receptor hypofunction and its consequences may play an important role in the pathophysiology of this psychiatric disorder. Moreover, the schizophreniform psychosis caused by PCP resembles schizophrenia in all of the relevant domains of psychopathology, especially negative symptoms and cognitive dysfunction. Because of interest in the PCP model and possible NMDA receptor hypofunction in schizophrenia, animal behaviors elicited by PCP and its analogues have been characterized. These preclinical models may serve to identify candidate compounds that possess therapeutic efficacy in schizophrenia. Ideally, negative symptoms and cognitive dysfunction would also serve as therapeutic targets for these novel medications. In the current study, the ability of topiramate to attenuate the severity of a specific behavior elicited by MK-801 (dizocilpine), a high affinity analogue of PCP was studied in mice. Topiramate was chosen because it addresses two of the predicted pathological consequences of NMDA receptor hypofunction. Specifically, topiramate potentiates GABAergic neurotransmission and antagonizes the excitotoxic actions of glutamate at the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate (KA) classes of glutamate-gated channels. Topiramate was shown to inhibit MK-801-elicited "popping" behavior in a complex dose-dependent manner.

Altered psychomotor behaviors in mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP)

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been conserved remarkably during evolution and is widely expressed in the mammalian brain. In Drosophila, mutation of the PACAP homologue results in behavioral defects, including impaired olfaction-associated learning and changes in ethanol sensitivity. Here, we report the generation of mice lacking the PACAP gene (PACAP(-/-)). PACAP(-/-) mice were born in the expected Mendelian ratios but had a high early-mortality rate. The surviving adult PACAP(-/-) mice displayed remarkable behavioral changes; they exhibited hyperactive and explosive jumping behaviors in an open field, increased exploratory behavior, and less anxiety in the elevated plus maze, emergence, and novel-object tests. Analysis of PACAP(-/-) mice brains revealed that the serotonin metabolite 5-hydroxyindoleacetic acid was slightly decreased in the cortex and striatum compared with wild-type mice. The present study provides evidence that PACAP plays a previously uncharacterized role in the regulation of psychomotor behaviors.

A force-plate actometer for quantitating rodent behaviors: illustrative data on locomotion, rotation, spatial patterning, stereotypies, and tremor

This report describes a new kind of actometer for recording the behavior of rodents or other small animals. The instrument, a force-plate actometer, uses a stiff, low-mass horizontal plate coupled to four supporting force transducers positioned at the corners of the plate. When an animal moves on the plate, its movements are sensed by the transducers whose signals are processed by computer to yield measurements of a wide range of behaviors or behavioral attributes, such as locomotor activity, rotation around the center, whole-body tremor, and amphetamine-induced stereotypies. Spatial resolution is less than 1 mm, and temporal resolution is 0.02 s. Sample data were presented comparing the locomotor activity of CD-1, BALB/c, and C57BL/6 mice before and after treatment with D-amphetamine sulfate. Rotational behavior was recorded in an amphetamine-treated rat that had sustained a unilateral 6-hydroxydopamine-induced lesion of the nigrostriatal system. In the C57BL/6 mouse, harmaline-induced tremor was quantified. With rats as subjects, the force-plate actometer was used to quantify amphetamine-induced stereotypies, to demonstrate the development of sensitization to amphetamine's effects, and to quantitate the consistent 11-12 Hz rhythmicities that underlie the sterotypies. The performance of the force-plate actometer was compared with that of a variety of instruments reported in the literature on behavioral instrumentation. Finally, potential applications in neuroscience research other than those illustrated in this report were discussed.

Stress and a glycinergic intervention interact in the modulation of MK-801-elicited mouse popping behavior

The ability of D-cycloserine, a partial glycine agonist, to modulate mouse popping behavior elicited by MK-801, a noncompetitive NMDA receptor antagonist, was studied in unstressed and stressed mice. In unstressed animals, D-cycloserine (5.6 and 10 mg/kg) attenuated the ability of MK-801 (1.0 mg/kg) to elicit this behavior. However, the ability of D-cycloserine to attenuate MK-801-elicited mouse-popping behavior was not evident in stressed mice, 24 h after they were forced to swim for up to 10 min in cold water. Thus, the therapeutic value of glycinergic interventions may be limited by environmental factors, such as stress.

Inbred mouse strains differ in sensitivity to "popping" behavior elicited by MK-801

We examined possible genetic contributions to MK-801-elicited "popping" behavior in mice. MK-801-elicited "popping" behavior may represent a preclinical screening paradigm for identifying novel antipsychotic medications. Specifically, we studied the sensitivity of four inbred strains of mice (BALB/c, C57BL/6, AKR, and DBA/2) to MK-801-elicited "popping" behavior and compared their response to the outbred NIH Swiss strain in which the behavior was first characterized. The BALB/c strain was most sensitive to the elicitation of MK-801 induced popping behavior, whereas the other inbred strains were less sensitive than the outbred strain. The identification of strain differences in MK-801-elicited "popping" behavior suggests an important role for genetic factors in the elicitation of MK-801 "popping" behavior in mice.