The competitive NMDA antagonist CPP blocks MK-801-elicited popping behavior in mice

In the current investigation, the ability of CPP (3-(2-carboxypiperazine-4-yl) propyl-1-phosphate) to elicit mouse popping behavior in a manner similar to that of MK-801 was studied. Unlike MK-801, CPP (3.2-32 mg/kg) did not elicit any popping. The data show that a reduction in NMDA-mediated neural transmission alone is not sufficient to elicit popping behavior in mice. Moreover, pretreatment of mice with CPP attenuated MK-801's ability to elicit popping. These results suggest that popping requires the channel to be in the "active", or open, configuration and that it depends on MK-801's access and binding to its unique site in the hydrophobic channel domain.

An open-label study of the therapeutic efficacy of high-dose famotidine adjuvant pharmacotherapy in schizophrenia: preliminary evidence for treatment efficacy

Histaminergic projections innervate brain areas implicated in the pathophysiology of schizophrenia. In a previous open-label study, there was the suggestion that famotidine, and H2 histamine-receptor antagonist, possessed adjuvant therapeutic properties when added to the stable neuroleptic medications regimens of 10 treatment-refractory patients. In that study, the maximal dosage of famotidine was limited to 40 mg/day, the recommended maximal dosage for the treatment of peptic ulcer disease. In this study, we examined 18 patients fulfilling DSM-III-R criteria for schizophrenia and schizoaffective disorder who had famotidine (100 mg/day) added to their stable neuroleptic medication regimen. Patients were rated on baseline, weekly thereafter, and 1 week after famotidine discontinuation, by using the Brief Psychiatric Rating Scale (BPRS), Schedule for the Assessment of Negative Symptoms (SANS), and the Clinical Global Impression (CGI). On all of these outcome measures, statistically significant improvements suggestive of a beneficial adjunctive effect of famotidine were found. Famotidine (100 mg/day) was well tolerated by the study subjects. There was a wide range of famotidine blood levels achieved at the end of 3 weeks of famotidine adjunctive treatment, but these blood levels did not correlate with BPRS or SANS score changes. However, the patients with the greatest improvement in BPRS scores (and without concomitant deterioration in SAND scores) had some of the higher famotidine levels found in the study. Double-blind studies further assessing the potential adjunctive benefit of famotidine in the treatment of schizophrenia are indicated.

7-Nitroindazole and methylene blue, inhibitors of neuronal nitric oxide synthase and NO-stimulated guanylate cyclase, block MK-801-elicited behaviors in mice

We examined the abilities of 7-nitroindazole and methylene blue, inhibitors of the neuronal isoform of nitric oxide synthase (NOS) and nitric oxide-stimulated guanylate cyclase activity respectively, to attenuate explosive episodic jumping behavior(s) ("popping") elicited by MK-801 in mice. MK-801, like phencyclidine (PCP), is a high-affinity, noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. We have postulated that MK-801-elicited popping behavior in mice represents an animal model of schizophrenia, because popping behavior is markedly inhibited/antagonized by both typical and atypical antipsychotic drugs. In the present study, popping behavior induced by MK-801 was measured using an automated detection system that quantifies vertical displacements on the testing platform. 7-Nitroindazole (100 mg/kg) and methylene blue (32 and 100 mg/kg) significantly reduced the number and force of MK-801-elicited popping behavior. Mouse rotorod performance did not differ between animals receiving 7-nitroindazole, methylene blue, or their respective vehicles, suggesting that attenuation of MK-801-elicited popping behavior was not due to either sedation or ataxia caused by 7-nitroindazole or methylene blue. Our findings suggest that nitric oxide may, in part, mediate behaviors induced by NMDA receptor antagonists, like MK-801, and that inhibitors of NOS may have antipsychotic actions.

Smooth pursuit eye movements in the evaluation of famotidine adjunctive therapy of schizophrenia: a preliminary report

Smooth pursuit eye movements (SPEM) are often abnormal in schizophrenic patients and have been proposed as a trait marker of the disorder. We explored the use of SPEM as an outcome measure in an open-label clinical trial of famotidine, an H-2 antagonist, in patients with schizophrenia; famotidine has been proposed as an adjunctive medication, particularly for negative symptoms. Prior studies using SPEM as an outcome measure have not found a significant effect with "typical" neuroleptic medication, and one study found greater SPEM dysfunction with clozapine treatment. In this study, 19 schizophrenic subjects were stabilized for at least 1 week on conventional neuroleptic medications and then administered oral famotidine, 100 mg daily, for an additional 3 weeks. SPEM and clinical measures were assessed. Whereas Brief Psychiatric Rating Scale (BPRS) and Schedule for Assessment of Negative Symptoms (SANS) scores decreased significantly with famotidine administration, there was no significant change in SPEM performance over the course of the study. Two subjects (11%) doubled their signal/noise ratio and maintained this increase after famotidine discontinuation, whereas three subjects (17%) approximately halved this ratio and returned to baseline after famotidine discontinuation. SPEM changes were not found to correlate significantly with changes in BPRS or SANS scores. These findings suggest that SPEM dysfunction reflects a "trait" rather than clinical "state" in schizophrenia, and changes in SPEM performance might not be expected always to parallel changes in clinical ratings.

Selective cyclodextrin inhibition of alfaxolone-induced ataxia

The effect of the use of a number of popular solubility treatments was examined on alfaxolone- and diazepam-induced ataxia. The effects of diazepam were not significantly altered by solution in cyclodextrin, Alkamuls EL-620 or a mixture of propylene glycol and ethanol. The effects of alfaxolone were not altered by solution in Alkamuls EL-620, but were significantly lessened by solution in cyclodextrin. In a dose-response experiment, the ED50 of alfaxolone increased from 15.3 mg kg-1 (in Alkamuls EL-620) to 25.6 mg kg-1 (in hydroxypropyl-beta-cyclodextrin). The results suggest that although cyclodextrins are popular and effective solubilizers, their use must be considered carefully in the context of the experiments in which they are to be used.

Impaired motor skill learning in schizophrenia: implications for corticostriatal dysfunction

We assessed skill learning in young and older schizophrenic patients using the rotary pursuit task. Schizophrenic patients displayed impaired learning on this task compared with normal control subjects, but older patients were not more impaired than young ones. The patients' rotary pursuit learning was not correlated to the severity of abnormal movements or to their treatment with medication, but it was associated to conceptual abilities assessed on the Dementia Rating Scale (Mattis 1988). An impairment in acquiring motor procedures in this task might reflect neuropsychological deficits associated with corticostriatal pathology.

Lack of neurotoxic effect of diethylpropion in crack-cocaine abusers

Dopamine agonists have been used with some success in treating cocaine addiction. However, both cocaine and psychostimulants have been reported to produce neurotoxic effects. We evaluated the effect of the stimulant diethylpropion on cognitive performance in a double-blind, placebo-controlled trial. Forty-six abstinent crack-cocaine users received either placebo, 25-mg, 50-mg, or 75-mg doses of diethylpropion. Patients were tested at baseline and again after 9-14 days of medication. There were no differences between placebo and medication groups on any test, indicating that, within the time frame studied, diethylpropion does not produce neurotoxic effects that can be detected with standardized neuropsychological tests.

d-Cycloserine enhances implicit memory in Alzheimer patients

We tested the ability of d-cycloserine, a partial glycine agonist acting at the N-methyl-D-aspartate (NMDA) receptor complex, to improve implicit memory in Alzheimer patients in a parallel-group, placebo-controlled, double-blind study. One-hundred eight patients with probable Alzheimer's disease of mild to moderate severity received d-cycloserine (5, 15, or 50 mg) or placebo twice daily for 10 weeks. We then evaluated their ability to identify perceptually degraded words, some of which were repeated over multiple trials across 3 days. Implicit memory performance of words repeated across trials was significantly enhanced for the patients who received 15 mg d-cycloserine compared with those who received placebo. These findings support development of NMDA receptor-mediated glutamatergic interventions for the treatment of Alzheimer-related memory disorders.

A measure of pupillary oscillation as a marker of cocaine-induced paranoia

Cocaine-induced paranoia (CIP) remains an important drug-induced model of idiopathic paranoia for which no psychophysiologic marker has yet emerged. Measures of pupillary oscillation were able to significantly distinguish a group of abstinent crack cocaine abusers endorsing past CIP (n = 32) from another group of crack addicts who denied past CIP (n = 29).

The nitric oxide pathway: potential implications for treatment of neuropsychiatric disorders

The freely diffusible gaseous compound nitric oxide (NO) has recently been discovered to be an important cellular messenger in many organ systems throughout the body. The importance of NO as an intermediary in cell communication in the brain is highlighted by the fact that the excitatory amino acid glutamate, the most abundant central neurotransmitter, is an initiator of the reaction that forms NO. In this article, background information about the discovery of NO, its biochemistry, and a brief summary of some of its peripheral and central actions are given to provide a complete picture of this remarkable novel second messenger. We also discuss how an improved understanding of NO pathway may lead to the identification of novel medications for the treatment of a number of neuropsychiatric conditions, including memory deficits, pain, drug addiction, seizures, bipolar disorder, psychosis, eating disorders, and the treatment of the sequelae of various brain injuries.

Predicting premorbid functioning in crack-cocaine abusers

The Wide Range Achievement Test (Revised) (WRAT-R) reading test, demographic variables and drug use severity were used to develop prediction equations to estimate premorbid ability in 92 cocaine abusers. WRAT-R reading was correlated significantly with full scale, verbal and performance IQ. Stepwise regression indicated that only WRAT-R reading score and age accounted for 23% of the variance in Full Scale IQ (FSIQ) and 28% in Verbal IQ (VIQ). Abstinence and severity of use variables did not correlate with nor predict IQ. Actual and predicted IQ scores were correlated significantly and did not differ based on within group t-tests. Thus, these formulas accurately estimate premorbid functioning in cocaine-dependent research patients with FSIQs in the average to low average range, replicating the results in normal adults with average IQs.

Facilitating role of m-chlorophenylbiguanide in a cocaine discrimination

To examine the interaction between serotonergic systems and the discriminative stimulus effects of cocaine, the effects of the selective 5-HT3 agonist mCPBG were examined in 46 Sprague-Dawley rats trained to discriminate 10 mg/kg cocaine from saline. mCPBG substitution tests showed partial substitution for the cocaine stimulus. In interaction tests, the combination of mCPBG and low doses of cocaine resulted in increased cocaine lever selection. mCPBG treatment reduced response rates, but not below a 50% criterion. These results point toward a limited modulatory role of serotonergic systems in the cocaine discriminative stimulus.

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

MK-801, a high-affinity phencyclidine (PCP) analogue, is a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) subclass of glutamate receptor that elicits hyperactivity, stereotypic behaviors, and "popping," an explosive episodic jumping behavior, in mice. The schizophreniform psychosis precipitated by PCP in humans has stimulated interest in studying MK-801-elicited mouse behaviors for their potential development as animal models of idiopathic psychosis. We describe a computerized method for measuring popping and hyperactivity elicited by MK-801 in mice, based on vertical displacements of a platform. This computerized procedure allows for the automatic measurement of discrete "pops" per individual episode of popping behavior, the force of each one of the explosive jumps, and the duration of discrete episodes of popping; these latter measures could not be easily ascertained by visual inspection alone. Moreover, the computerized measurements facilitate quantitative evaluation of the effects of pharmacological manipulations on MK-801-elicited popping. For example, the antipsychotic haloperidol was shown to reduce significantly both MK-801-induced popping and hyperactivity. Ideally, MK-801-elicited mouse popping and hyperactivity will serve as a useful preclinical screening paradigm for potential antipsychotic medications. Additionally, it is hoped that the use of this automated system will contribute to a greater understanding of the mechanisms of MK-801-induced popping and hyperactivity.

Famotidine adjunctive pharmacotherapy of schizophrenia: a case report

Recent reports suggest some utility for famotidine, a histamine type 2 (H2) antagonist, in the treatment of schizophrenia. The current report describes a treatment-resistant patient with chronic undifferentiated schizophrenia whose most dramatic symptomatic improvements were temporarily related to the open-label addition of famotidine (40-100 mg/day) to conventional neuroleptic treatment (molindone 150-200 mg/day) over the course of approximately 10 months. During one 2-week interval, his symptoms were controlled with famotidine (40 mg/day) alone. The case suggests that some adjuvant efficacy exists for famotidine in at least some patients with schizophrenia. Placebo-controlled trials are needed to more fully evaluate the utility of famotidine in the treatment of schizophrenia.

MK-801 alters the GABAA receptor complex and potentiates flurazepam's antiseizure efficacy

MK-801 is an uncompetitive allosteric antagonist that interferes with glutamate-gated calcium ion conductance through the NMDA receptor-associated ionophore. In an outbred strain of mouse, MK-801 elicits episodes of explosive "popping" behaviors that may serve as a preclinical screening paradigm for novel antipsychotic medications. This investigation examined the effects of MK-801, at doses associated with the elicitation of popping, on the GABAA receptor complex in cerebral cortex, and flurazepam's ability to antagonize electrically precipitated seizures. Twenty four hours after MK-801 administration, there was an increased density of the radiolabeled antagonist-preferring conformation of the central benzodiazepine binding site and a potentiation of flurazepam's antiseizure efficacy. The data show that interference with NMDA receptor-mediated calcium ion conductance is associated with a relatively selective change in the GABAA receptor complex in cerebral cortex, and has functional behavioral consequences. Moreover, the data provide additional evidence for a delicate balance between GABAergic and glutamatergic transmission. Disturbance of this balance can have behavioral consequences for the animal.

Anxiety and pupil reactivity in cocaine dependent subjects endorsing cocaine-induced paranoia: preliminary report

There has been the clinical impression that people with higher levels of anxiety and central arousal are more prone to develop cocaine-induced paranoia (CIP), but this notion has not been formally studied. In the current study, we examined the differences between 28 CIP-endorsing and 16 CIP-denying chronic cocaine users in their levels of state and trait anxiety as measured by the Spielberger State-Tait Anxiety Inventory. We also studied levels of central arousal and reactivity using pupil size measures both during exposure to neutral, abstract, non-drug cues, and after exposure to a cocaine cue. Levels of trait (but not state) anxiety were significantly higher in the CIP group than in the non-CIP group. Moreover, while there were no significant pupil size differences or changes between the two groups while viewing neutral, abstract video images, the CIP group had significantly greater pupillary dilation in response to a video image of crack cocaine than did the non-CIP group. These significant differences remained even after covarying for anxiety scores. The study findings seem relevant to studies of autonomic reactivity in response to drug cues in cocaine-dependent patients; such studies might remain attentive to potential cue reactivity differences between patients endorsing and those denying CIP. Finally, this is the first study showing higher trait anxiety in patients with CIP.

Interference with nitric oxide production and action potentiates the antiseizure efficacy of flurazepam

The effect of inhibiting "downstream" consequences of NMDA receptor stimulation with 7-nitroindazole, an inhibitor of the neuronal form of nitric oxide synthase (NOS), and methylene blue, an inhibitor of the nitric oxide (NO)-sensitive soluble guanylyl cyclase, on electrically precipitated tonic hindlimb extension in mice was studied. Moreover, the abilities of these compounds to potentiate the antiseizure efficacy of flurazepam were also examined. When administered alone, 7-nitroindazole (10.0-100 mg/kg) and methylene blue (1.0-100 mg/kg) did not share the ability of MK-801 (0.1 to 1.0 mg/kg) to antagonize electrically precipitated tonic hindlimb extension. However, doses of MK-801 (0.18 mg/kg), 7-nitroindazole (100 mg/kg), and methylene blue (10.0 and 100 mg/kg) that were devoid of apparent antiseizure efficacy by themselves potentiated the ability of flurazepam to antagonize electrically precipitated seizures. NMDA receptor antagonists cause neuronal toxicity, interfere with acquisition of spatial memory and induction of long-term potentiation in the hippocampal CA1 region, and precipitate psychoses in susceptible individuals. Thus, the development of both open-channel blockers of the NMDA receptor complex that can be administered in lower doses, and inhibitors of the "downstream" consequences of NMDA receptor-gated transient elevations of intraneuronal calcium ions as potential adjunctive antiseizure medications should be considered. Moreover, administration of these compounds with benzodiazepines may attenuate some of the neurotoxicity that may result from NMDA receptor antagonism.

Diethylpropion pharmacotherapeutic adjuvant therapy for inpatient treatment of cocaine dependence: a test of the cocaine-agonist hypothesis

Fifty cocaine-dependent patients completed a 2-week double-blind, double-dummy, parallel-group comparison of four dosage levels of diethylpropion and placebo. This clinical trial was designed to evaluate both diethylpropion's ability to attenuate cocaine cue-induced craving and its potential for development as a medication with cocaine-agonist properties. The results indicated that diethylpropion was not superior to placebo and confirmed earlier reports that craving for cocaine diminishes over the course of an inpatient hospitalization. Moreover, the results showed that the cocaine cue-induced craving paradigm employed is effective in stimulating craving for cocaine. Medications that are effective in attenuating this type of "conditioned" craving may have relevance to the breaking of the cycle of relapse and long-term treatment of cocaine dependence. Diethylpropion may not be an appropriate candidate for future medication development because of its lack of obvious therapeutic efficacy and the emergence of a significant number of side effects. However, a cocaine-agonist medication strategy may be appropriate for a subgroup of cocaine-dependent patients with coexisting attention deficit-hyperactivity disorder.

The effects of adenosine A3 receptor stimulation on seizures in mice

We have previously shown that acute preischemic adenosine A3 receptor stimulation results in an increased postischemic damage, while chronic stimulation of this receptor diminishes it. Since several pathophysiological phenomena are common for both ischemia and seizures, we have explored the effect of acute and chronic administration of the adenosine A3 receptor selective agonist IB-MECA (N6-(3-iodobenzyl) adenosine-5'-N-methylcarboxamide) prior to seizures induced by N-methyl-D-aspartate (NMDA), pentamethylenetetrazole, or electric shock. At 100 micrograms/kg, acutely injected IB-MECA was protective in chemically but not electrically induced seizures. In chronic administration of IB-MECA, significant protection against chemically induced seizures was obtained in all studied measures, i.e., seizure latency, neurological impairment, and survival. Although threshold voltage was unchanged in electrically induced seizures, a chronic regimen of IB-MECA significantly reduced postepileptic mortality. Since the combination of an arteriole-constricting compound 48/80 and hypotension-inducing clonidine injected prior to NMDA results in a significant protection against seizures, and since acute stimulation of adenosine A3 receptor causes both arteriolar constriction and severe hypotension, there is a possibility that the protection obtained by the acutely administered drug may result from inadequate delivery of chemoconvulsants to the brain. It is, however, unknown whether the protective effect of chronically administered IB-MECA is related to the effect of the drug on blood flow, neuronal mechanisms, or both.

The relationship between cocaine-induced paranoia and compulsive foraging: a preliminary report

Two prominent behavioral syndromes associated with chronic cocaine use that have been described in the literature are cocaine-induced paranoia (CIP) and cocaine-induced compulsive foraging (CICF) for cocaine. To help to clarify the relationship between the two cocaine-induced syndromes, the concordance and sequence of onset of the two cocaine-induced behaviors over the course of the patients' lifetime use of cocaine and during the course of a binge was examined in 62 crack cocaine-dependent men. Thirty-four (54.8%) reported experiencing both CIP and CICF. In 18 (29%) of the patients, only one of these cocaine-induced behavioral syndromes was reported. Ten (16.1%) of the subjects reported neither CIP nor CICF. Patterns of cocaine or other substance use and degrees of tolerance to cocaine were not significantly different between the groups endorsing different patterns of cocaine-induced behaviors. CIP typically preceded the onset of CICF both over the course of the patients' lifetime use of cocaine and over the course of a binge. The study results suggest varying thresholds for the expression of these behaviors in chronic cocaine-abusing individuals.

Phenomenologic comparison of the idiopathic psychosis of schizophrenia and drug-induced cocaine and phencyclidine psychoses: a retrospective study

Both stimulant-induced and phencyclidine (PCP)-induced psychoses have been proposed as models of the idiopathic psychosis of schizopherenia. In this two-part study, the phenomenology of the psychosis associated with a period of cocaine intoxication was evaluated retrospectively in 34 male crack cocaine-dependent patients without concomitant psychiatric disorder and then was compared with the psychosis of 16 actively psychotic schizophrenic men (without a history of drug or alcohol abuse in the past year). Certain First Rank Schneiderian Symptoms (FRSS) were more commonly observed in the schizophrenic patients (e.g., thought broadcasting, thought withdrawal) than in the cocaine addicts. In the second part of this study, we retrospectively examined the cocaine and PCP experiences of an additional 22 cocaine addicts who had a past history of separate periods of cocaine and PCP use. Overall, the frequency of FRSS recalled during periods of cocaine and PCP intoxication was similar. However, the psychosis related to cocaine intoxication was more associated with an intense suspiciousness and paranoia related to a fear of being discovered or harmed while using cocaine. PCP-induced psychosis was less associated with suspiciousness and more associated with delusions of physical power, altered sensations, and unusual experiences [e.g., out of body experiences, experiencing religious figures or events directly (e.g., being with Noah at the time of the Arc)]. As elements of both cocaine and PCP psychosis can be found in schizophrenia, a model integrating the mechanisms of several psychotogenic drugs may be more informative. Such an integrative model might better capture the heterogeneity of psychotic symptoms that can be seen in schizophrenia. Furthermore, different pharmacologic interventions (e.g., "anti-stimulant" versus "anti-PCP") might address different aspects of the positive symptom picture in schizophrenia.

Nimodipine pharmacotherapeutic adjuvant therapy for inpatient treatment of cocaine dependence

Recent preclinical studies suggest utility for voltage-sensitive calcium channel blockers (VSCCBs) in the treatment of cocaine addiction. The following double-blind placebo-controlled study examined the role of the VSCCB nimodipine in attenuating cocaine craving in 66 recently abstinent cocaine-dependent patients on an inpatient substance abuse treatment unit utilizing an intensive 12-step milieu-oriented psychosocial therapy. While the medication was well tolerated, the dose of nimodipine used in this study (90 mg q.d.) was not superior to placebo in reducing background or cue-induced cocaine craving over the 3 weeks of the study. There was the suggestion that nimodipine might attenuate the severity of some cocaine-induced brain deficits, as detected by evaluation of smooth pursuit eye movement function. A rationale for evaluating higher doses of nimodipine for the treatment of cocaine addiction is presented. As nimodipine might have anticraving and mood-stabilizing properties and cardio- and neuroprotective properties in the face of cocaine intoxication and might possibly even reverse some cocaine-induced brain deficits, further investigation of the role of nimodipine (and other VSCCBs) in cocaine addiction appears an attractive avenue of future medication development.

Gaze discrimination in patients with schizophrenia: preliminary report

The authors administered a gaze discrimination task to 24 patients with chronic schizophrenia and 25 subjects with no psychiatric history. Each subject was shown slides and asked, "Is the person in the slide looking directly at you?" Patients with schizophrenia were more likely than comparison subjects to perceive the person in the slide as looking at them when the person was looking away. Because there is evidence that gaze discrimination performance involves the superior temporal sulcus region of the brain and this region has been implicated in theories about the pathogenesis of schizophrenia, further study of the gaze discrimination task seems indicated.