Screening of antipsychotic drugs in animal models

Extract of Synedrella nodiflora (L) Gaertn exhibits antipsychotic properties in murine models of psychosis

BACKGROUND

The hydro-ethanolic whole plant extract of Synedrella nodiflora (SNE) has demonstrated anticonvulsant, sedative and analgesic effects. Preliminary studies conducted in animals, SNE significantly decreased stereotypic behaviours suggesting antipsychotic potential. Coupled with the central nervous system depressant effects of SNE, we hypothesized that it may have utility in the management of psychosis. The present study therefore investigated the antipsychotic potential of the SNE in several murine models of psychosis.

METHOD

The primary central nervous system activities of SNE (30-3000 mg/kg, p.o) were investigated using the Irwin's test. The novelty-induced rearing, locomotion and stereotypy counts provoked by SNE (100-1000 mg/kg, p.o) were conducted using the open-field paradigm. The antipsychotic test models used in the screening of SNE (100-1000 mg/kg, p.o) included apomorphine-induced stereotypy, rearing, locomotion and cage climbing activities. The combined effects of a low dose of SNE (100 mg/kg) with various doses of haloperidol and chlorpromazine were analysed using the apomorphine-induced cage climbing and stereotypy, respectively. The ability of SNE to cause catalepsy in naïve mice as well as its effect on haloperidol-induced catalepsy was assessed.

RESULTS

SNE showed acetylcholine-like and serotonin-like activities in the Irwin test, with sedation occurring at high doses. SNE significantly reduced the frequencies of novelty- and apomorphine-induced rearing and locomotion; stereotypy behaviour and the frequency and duration of apomorphine-induced cage climbing in mice. In all the tests performed, SNE was less potent than the reference drugs used (chlorpromazine and haloperidol). In addition, SNE potentiated the effects of haloperidol and chlorpromazine on apomorphine-induced cage climbing and stereotypy activities in mice.

CONCLUSION

SNE, while exhibiting antipsychotic properties itself, can also potentiate the antipsychotic effects of chlorpromazine and haloperidol.

The need for new approaches in CNS drug discovery: Why drugs have failed, and what can be done to improve outcomes

An important goal of biomedical research is to translate basic research findings into useful medical advances. In the field of neuropharmacology this requires understanding disease mechanisms as well as the effects of drugs and other compounds on neuronal function. Our hope is that this information will result in new or improved treatment for CNS disease. Despite great progress in our understanding of the structure and functions of the CNS, the discovery of new drugs and their clinical development for many CNS disorders has been problematic. As a result, CNS drug discovery and development programs have been subjected to significant cutbacks and eliminations over the last decade. While there has been recent resurgence of interest in CNS targets, these past changes in priority of the pharmaceutical and biotech industries reflect several well-documented realities. CNS drugs in general have higher failure rates than non-CNS drugs, both preclinically and clinically, and in some areas, such as the major neurodegenerative diseases, the clinical failure rate for disease-modifying treatments has been 100%. The development times for CNS drugs are significantly longer for those drugs that are approved, and post-development regulatory review is longer. In this introduction we review some of the reasons for failure, delineating both scientific and technical realities, some unique to the CNS, that have contributed to this. We will focus on major neurodegenerative disorders, which affect millions, attract most of the headlines, and yet have witnessed the fewest successes. We will suggest some changes that, when coupled with the approaches discussed in the rest of this special volume, may improve outcomes in future CNS-targeted drug discovery and development efforts. This article is part of the Special Issue entitled "Beyond small molecules for neurological disorders".

A rat-like robot for interacting with real rats

We developed a novel small rat-like robot calledWasedaRat No.4(WR-4) to interact with real rats. WR-4 can perform both rearing (rising up on its hind limbs) and rotating (body bending during movement) actions faster than live mature rats. After robot–rat interaction involving rearing and body grooming (body cuddling and head curling) actions of WR-4, real rats showed more activity and greater interest in the robot. Similar results evident from rat–rat interaction suggest that a rat-like robot is able to interact with rats in the same way as real rats. Furthermore, lower variances between the rat subjects in robot–rat interaction reveals that a rat-like robot can more effectively impact rat's behavior in a controllable, predictable way.

Preclinical behavioral models for predicting antipsychotic activity

Schizophrenia is a major psychiatric disease that is characterized by three distinct symptom domains: positive symptoms, negative symptoms, and cognitive impairment. Additionally, treatment with classical antipsychotic medication can be accompanied by important side effects that involve extrapyramidal symptoms (EPS). The discovery of clozapine in the 1970s, which is efficacious in all three symptom domains and has a reduced propensity to induce EPS, has driven research for new antipsychotic agents with a wider spectrum of activity and a lower propensity to induce EPS. The following chapter reviews existing behavioral procedures in animals for their ability to predict compound efficacy against schizophrenia symptoms and liability to induce EPS. Rodent models of positive symptoms include procedures related to hyperfunction in central dopamine and serotonin (5-hydroxytryptamine) systems and hypofunction of central glutamatergic (N-methyl-d-aspartate) neurotransmission. Procedures for evaluating negative symptoms include rodent models of anhedonia, affective flattening, and diminished social interaction. Cognitive deficits can be assessed in rodent models of attention (prepulse inhibition (PPI), latent inhibition) and of learning and memory (passive avoidance, object and social recognition, Morris water maze, and operant-delayed alternation). The relevance of the conditioned avoidance response (CAR) is also discussed. A final section reviews animal procedures for assessing EPS liability, in particular parkinsonism (catalepsy), acute dystonia (purposeless chewing in rodents, dystonia in monkeys), akathisia (defecation in rodents), and tardive dyskinesia (long-term antipsychotic treatment in rodents and monkeys).

The d-amphetamine-treated Göttingen miniature pig: an animal model for assessing behavioral effects of antipsychotics

RATIONALE

Rodents are usually used to assess the ability of antipsychotic drugs to antagonize hyperlocomotion induced by dopamine agonists, such as the psychostimulant d-amphetamine. However, the substantial differences between rodents and humans may hinder extrapolation of experimental results to humans. For this reason, we speculated that Göttingen miniature pigs, which show strong physiological and genetic homology with humans, might be a better model for investigating the effects of antipsychotics. To investigate this, we determined whether d-amphetamine induced hyperlocomotion in miniature pigs and whether this effect was reversible by antipsychotics.

MATERIALS AND METHODS

d-amphetamine was tested in the dose range of 0.2 to 2.0 mg kg(-1) for its ability to induce hyperactivity in the open field, and the effects of two antipsychotics, haloperidol and risperidone, on amphetamine-induced hyperactivity were examined.

RESULTS

d-amphetamine increased open-field activity at 0.2, 0.4, and 0.7 mg kg(-1) s.c. but not at higher doses. The stimulation of open-field activity induced by 0.4 mg kg(-1) s.c. d-amphetamine was antagonized by haloperidol and risperidone (0.01 and 0.04 mg kg(-1) s.c.).

CONCLUSION

d-amphetamine-induced hyperlocomotion in miniature pigs may be a useful model for studying the effect of putative antipsychotics.

Evaluation of animal models of neurobehavioral disorders

Animal models play a central role in all areas of biomedical research. The process of animal model building, development and evaluation has rarely been addressed systematically, despite the long history of using animal models in the investigation of neuropsychiatric disorders and behavioral dysfunctions. An iterative, multi-stage trajectory for developing animal models and assessing their quality is proposed. The process starts with defining the purpose(s) of the model, preferentially based on hypotheses about brain-behavior relationships. Then, the model is developed and tested. The evaluation of the model takes scientific and ethical criteria into consideration.Model development requires a multidisciplinary approach. Preclinical and clinical experts should establish a set of scientific criteria, which a model must meet. The scientific evaluation consists of assessing the replicability/reliability, predictive, construct and external validity/generalizability, and relevance of the model. We emphasize the role of (systematic and extended) replications in the course of the validation process. One may apply a multiple-tiered 'replication battery' to estimate the reliability/replicability, validity, and generalizability of result.Compromised welfare is inherent in many deficiency models in animals. Unfortunately, 'animal welfare' is a vaguely defined concept, making it difficult to establish exact evaluation criteria. Weighing the animal's welfare and considerations as to whether action is indicated to reduce the discomfort must accompany the scientific evaluation at any stage of the model building and evaluation process. Animal model building should be discontinued if the model does not meet the preset scientific criteria, or when animal welfare is severely compromised. The application of the evaluation procedure is exemplified using the rat with neonatal hippocampal lesion as a proposed model of schizophrenia.In a manner congruent to that for improving animal models, guided by the procedure expounded upon in this paper, the developmental and evaluation procedure itself may be improved by careful definition of the purpose(s) of a model and by defining better evaluation criteria, based on the proposed use of the model.

Acute and subacute effects of risperidone and cocaine on accumbens dopamine and serotonin release using in vivo microvoltammetry on line with open-field behavior

In vivo microvoltammetry was used to detect dopamine (DA) and serotonin (5-HT) release from nucleus accumbens (NAcc) of freely moving, male, Sprague-Dawley laboratory rats, while animals' locomotor (forward ambulations) and stereotypic behavior (fine movements of sniffing and grooming) were monitored at the same time with infrared photobeams. Monoamine release mechanisms were determined by using a depolarization blocker (gamma-butyrolactone, gamma BL). Miniature carbon sensors (BRODERICK PROBES microelectrodes) smaller than a human hair were used in conjunction with a semidifferential electrochemical circuit to detect release of each monoamine in separate signals and within seconds. The purpose was to evaluate the neuropharmacology of the 5-HT(2)/DA(2) antagonist risperidone in its current therapeutic role as an atypical antipsychotic medication as well as in its potential role as pharmacotherapy for cocaine psychosis and withdrawal symptoms. Acute (single drug dose) and subacute (24-h follow-up studies in the same animal, no drug administration) studies were performed for each treatment group. The hypothesis for the present studies is derived from a growing body of evidence that cocaine-induced psychosis and schizophrenic psychosis share similar neurochemical and behavioral manifestations. Results showed that (1) Acute administration of risperidone (2 mg/kg sc) significantly increased DA and 5-HT release in NAcc above baseline (habituation) values (P<.001) while locomotion and stereotypy were virtually unaffected. In subacute studies, DA release did not differ from baseline (P>.05), whereas 5-HT release was significantly increased above baseline (P<.001). Locomotion increased over baseline but not to a significant degree, while stereotypy was significantly increased above baseline (P<.05). (2) Acute administration of cocaine (10 mg/kg ip) significantly increased both DA and 5-HT release above baseline (P<.001), while locomotion and stereotypy were significantly increased over baseline (P<.001). In subacute studies, DA decreased significantly below baseline (P<.001) and significant decreases in 5-HT release occurred at 15, 20, 50 and 55 min (P<.05). Behavior increased above baseline but did not reach a statistically significant degree. (3) Acute administration of risperidone/cocaine (2 mg/kg sc and 10 mg/kg ip, respectively) showed a significant block of the cocaine-induced increase in DA release in the first hour (P<.001) and 5-HT release in both hours of study (P<.001). Cocaine-induced locomotion and stereotypy were blocked simultaneously with the monoamines (P<.001). In subacute studies, DA and 5-HT release returned to baseline while locomotion and stereotypy increased insignificantly above baseline. Thus, (a) these studies were able to tease out pharmacologically the critical differences between presynaptic and postsynaptic responses to drug treatment(s) and these differences may lead to more effective therapies for schizophrenic and/or cocaine psychosis. (b) Taken together with other data, these acute studies suggest that risperidone may possibly act via inhibition of presynaptic autoreceptors to produce the observed increases in accumbens DA and 5-HT release, whereas cocaine may be acting at least in part via serotoninergic modulation of DA postsynaptically. The subacute data suggest that pharmacokinetics may play a role in risperidone's action and that neuroadaptation may play a role in the mechanism of action of cocaine. Finally, the ability of risperidone to block cocaine-induced psychostimulant neurochemistry and behavior during acute studies while diminishing the withdrawal symptoms of cocaine during subacute studies suggests that risperidone may be a viable pharmacotherapy for cocaine psychosis and withdrawal.

Ketamine-induced changes in rat behaviour: A possible animal model of schizophrenia

It was investigated whether subchronic application of 30 mg/kg ketamine (Ket) induces reliable changes in behaviour and parameters of dopaminergic, glutamatergic, and serotonergic neurotransmissions, which might be the basis of an animal model in schizophrenia research. To test this, rats were injected with 30 mg/kg ip Ket daily for five consecutive days. In response to the first Ket injection, there was a decrease in activity time representing an acute Ket effect. Following the fifth injection, there were no differences between Ket- and saline (sal)-injected control rats in activity time, which might be a tolerance reaction. The following experiments were performed 2 or 4 weeks after Ket treatment. There were no effects on anxiety in either vehicle or Ket-treated rats using either low or high illumination levels in the elevated plus-maze. In the social interaction test, both groups of rats spent comparable times in social contact. The percentage of nonaggressive behaviour was decreased in Ket-treated rats. Two weeks after completion of the treatment, there was no effect on prepulse inhibition (PPI). Four weeks after the final Ket injection, latent inhibition (LI) was disrupted. There was no difference in the animals' activity in reaction to apomorphine (Apo) administration. Ket-treated rats injected with 0.1 mg/kg MK-801 showed an enhancement in locomotor activity. Ket treatment leads to an increase in D2 receptor binding in the hippocampus and a decrease in glutamate receptor binding in the frontal cortex. The authors did not find any changes in D1 receptor binding. The density of dopamine transporters was increased in the striatum. The density of 5-HT transporters was increased in the striatum, the hippocampus, and the frontal cortex. The results suggest that subchronic treatment with subanaesthetic doses of Ket induce schizophrenia-related alterations, which might be a useful animal model in the study of this disease.

A comparison of drug effects in latent inhibition and the forced swim test differentiates between the typical antipsychotic haloperidol, the atypical antipsychotics clozapine and olanzapine, and the antidepressants imipramine and paroxetine

Current animal models of antipsychotic activity that have the capacity to dissociate between typical and atypical antipsychotic drugs (APDs) have two drawbacks: they require previous administration of a psychotomimetic drug, and they achieve the dissociation by demonstrating effectiveness of atypical but not typical APDs, thus losing specificity and selectivity for APDs. The present experiments were designed to solve these problems by using two non-pharmacological tests: latent inhibition (LI), in which potentiation of the deleterious effects of non-reinforced stimulus pre-exposure on its subsequent conditioning served as a behavioral index for a common action of typical and atypical APDs (antipsychotic), and the forced swim test (FST), in which reduction of immobility served as a behavioral index for a dissimilar action of these drugs (antidepressant). The typical APD haloperidol (0.1 mg/kg), the atypical APDs clozapine (2.5 mg/kg) and olanzapine (0.6 mg/kg), and the antidepressants imipramine (10 mg/kg) and paroxetine (7.0 mg/kg), produced distinct patterns of action in the two tests: haloperidol potentiated LI and increased immobility in the FST, clozapine and olanzapine potentiated LI and decreased immobility in the FST, and imipramine and paroxetine decreased immobility in the FST and did not potentiate LI. Thus, the comparison of drug effects in LI and FST enabled a discrimination between typical and atypical APDs without losing selectivity for APDs.

Disruption and potentiation of latent inhibition by risperidone: the latent inhibition model of atypical antipsychotic action

Latent inhibition (LI), that is, retarded conditioning to a stimulus following its nonreinforced pre-exposure, is impaired in some subsets of schizophrenia patients and in amphetamine-treated rats. Potentiation of LI by antipsychotic drugs (APDs) given in conditioning, under conditions that do not lead to LI in controls, is a well-established index of antipsychotic activity. Recently, we have shown that the atypical APD, clozapine, in addition disrupts LI if administered in pre-exposure, under conditions that lead to LI in controls. This study demonstrates the same behavioral profile for the atypical APD risperidone. LI was measured in a thirst-motivated conditioned emotional response procedure by comparing suppression of drinking in response to a tone previously paired with a foot shock in rats that received nonreinforced exposure to the tone prior to conditioning (pre-exposed (PE)) and rats for whom the tone was novel (non-pre-exposed (NPE)). We show that under conditions that did not yield LI in vehicle controls (40 pre-exposures and five conditioning trials), risperidone (0.25, 0.5, and 1.2 mg/kg) led to LI when administered in conditioning. Under conditions that led to LI in vehicle controls (40 pre-exposures and two conditioning trials), risperidone (0.25, 0.5, and 2.5 mg/kg) abolished LI when administered in pre-exposure; the latter effect was not evident with haloperidol. In addition, the effects of risperidone administered in both the pre-exposure and conditioning stages were dose-dependent so that the pre-exposure-based action was manifested at lower but not at higher doses. It is concluded that atypical APDs exert in the LI model a dual pattern of effects, which enables detection of their 'typical' action (conditioning-based LI potentiation) as well as a dissociation from typical APDs by their 'atypical' action (pre-exposure-based LI disruption). It is suggested that the former and latter effects are subserved by D2 and 5HT2A antagonism, respectively.