A simple procedure for assessing ataxia in rats: effects of phencyclidine

Phencyclidine increased while isolation rearing did not affect progressive ratio responding in rats: Investigating potential models of amotivation in schizophrenia

BACKGROUND

Schizophrenia is a debilitating neurodevelopmental disorder affecting 1% of the global population with heterogeneous symptoms including positive, negative, and cognitive. While treatment for positive symptoms exists, none have been developed to treat negative symptoms. Animal models of schizophrenia are required to test targeted treatments and since patients exhibit reduced effort (breakpoints) for reward in a progressive ratio (PR) task, we examined the PR breakpoints of rats treated with the NMDA receptor antagonist phencyclidine or those reared in isolation - two common manipulations used to induce schizophrenia-relevant behaviors in rodents.

METHODS

In two cohorts, the PR breakpoint for a palatable food reward was examined in Long Evans rats after: 1) a repeated phencyclidine regimen; 2) A subchronic phencyclidine regimen followed by drug washout; and 3) post-weaning social isolation.

RESULTS

Rats treated with repeated phencyclidine and those following washout from phencyclidine exhibited higher PR breakpoints than vehicle-treated rats. The breakpoint of isolation reared rats did not differ from those socially reared, despite abnormalities of these rats in other schizophrenia-relevant behaviors.

CONCLUSION

Despite their common use for modeling other schizophrenia-relevant behaviors neither phencyclidine treatment nor isolation rearing recreated the motivational deficits observed in patients with schizophrenia, as measured by PR breakpoint. Other manipulations, and negative symptom-relevant behaviors, require investigation prior to testing putative therapeutics.

Global quantitative analysis of phosphorylation underlying phencyclidine signaling and sensorimotor gating in the prefrontal cortex

Prepulse inhibition (PPI) is an example of sensorimotor gating and deficits in PPI have been demonstrated in schizophrenia patients. Phencyclidine (PCP) suppression of PPI in animals has been studied to elucidate the pathological elements of schizophrenia. However, the molecular mechanisms underlying PCP treatment or PPI in the brain are still poorly understood. In this study, quantitative phosphoproteomic analysis was performed on the prefrontal cortex from rats that were subjected to PPI after being systemically injected with PCP or saline. PCP downregulated phosphorylation events were significantly enriched in proteins associated with long-term potentiation (LTP). Importantly, this data set identifies functionally novel phosphorylation sites on known LTP-associated signaling molecules. In addition, mutagenesis of a significantly altered phosphorylation site on xCT (SLC7A11), the light chain of system xc-, the cystine/glutamate antiporter, suggests that PCP also regulates the activity of this protein. Finally, new insights were also derived on PPI signaling independent of PCP treatment. This is the first quantitative phosphorylation proteomic analysis providing new molecular insights into sensorimotor gating.

Repeated phencyclidine administration alters glutamate release and decreases GABA markers in the prefrontal cortex of rats

Repeated phencyclidine (PCP) administration induces cognitive disruptions resembling those seen in schizophrenia. Alterations in glutamate transmission and γ-aminobutyric acid (GABA) function in the prefrontal cortex (PFC) have been implicated in these PCP-induced deficits, as well as in cognitive symptoms of schizophrenia. PCP-induced cognitive deficits are reversed by chronic treatment with the atypical antipsychotic clozapine in rats. We investigated the effects of a single injection vs. repeated administration of PCP on glutamate levels in the PFC using in vivo microdialysis. Furthermore, we examined how these PCP regimens affect GABA neuronal markers in the PFC. Finally, we investigated the effects of clozapine on disruptions in glutamate levels and GABA neuronal markers induced by repeated PCP administration. Acute PCP administration (2 mg/kg) increased extracellular PFC glutamate; this increase appeared blunted, but was not eliminated, after repeated PCP pretreatment. PCP administration also strongly decreased levels of parvalbumin and glutamic acid decarboxylase-67 (two markers of GABA function) in the PFC, an effect that was maintained after a 10 day drug-free washout period and unaltered by the resumption of repeated PCP injections. All of the observed PCP effects were attenuated by chronic treatment with clozapine, an atypical antipsychotic that has partial effectiveness on cognitive impairment in schizophrenia. These findings suggest that abnormal cortical glutamate transmission, possibly driven by pathological changes in GABA function in parvalbumin-positive fast-spiking interneurons, may underlie some of the cognitive deficits in schizophrenia. A better understanding of glutamate and GABA dysregulation in schizophrenia may uncover new treatment targets for schizophrenia-related cognitive dysfunction.

Disruption of performance in the five-choice serial reaction time task induced by administration of N-methyl-D-aspartate receptor antagonists: relevance to cognitive dysfunction in schizophrenia

Schizophrenia patients suffer from cognitive impairments that are not satisfactorily treated by currently available medications. Cognitive dysfunction in schizophrenia encompasses deficits in several cognitive modalities that can be differentially responsive to different medications and are likely to be mediated by different neurobiological substrates. Translational animal models of cognitive deficits with relevance to schizophrenia are critical for gaining insights into the mechanisms underlying these impairments and developing more effective treatments. The five-choice serial reaction time task (5-CSRTT) is a cognitive task used in rodents that allows simultaneous assessment of several cognitive modalities, including attention, response inhibition, cognitive flexibility, and processing speed. Administration of N-methyl-D-aspartate (NMDA) glutamate receptor antagonists disrupts multiple 5-CSRTT performance measures in a way that mirrors various cognitive deficits exhibited by schizophrenia patients. Some of these disruptions are partially attenuated by antipsychotic medications that exhibit partial effectiveness on cognitive dysfunction in schizophrenia, suggesting that the model has predictive validity. Examination of the effects of pharmacological manipulations on 5-CSRTT performance disruptions induced by NMDA antagonists have implicated a range of brain regions, neurotransmitter systems, and specific receptor subtypes in schizophrenia-like impairment of different cognitive modalities. Thus, disruption of 5-CSRTT performance by NMDA antagonists represents a valuable tool for exploring the neurobiological bases of cognitive dysfunction in schizophrenia.

Effects of metabotropic glutamate receptor 2/3 agonism and antagonism on schizophrenia-like cognitive deficits induced by phencyclidine in rats

Dysregulation of glutamate neurotransmission may play a role in cognitive deficits in schizophrenia. Manipulation of glutamate signaling using drugs acting at metabotropic glutamate receptors has been suggested as a novel approach to treating schizophrenia-related cognitive dysfunction. We examined how the metabotropic glutamate receptor 2/3 agonist LY379268 and the metabotropic glutamate receptor 2/3 antagonist LY341495 altered phencyclidine-induced disruptions in performance in the 5-choice serial reaction time task. This test assesses multiple cognitive modalities characteristically impaired in schizophrenia that are disrupted by phencyclidine administration. Acute LY379268 alone did not affect 5-choice serial reaction time task performance, except for nonspecific response suppression at high doses. Acute LY379268 administration exacerbated phencyclidine-induced disruption of attentional performance in this task, while acute LY341495 did not alter 5-choice serial reaction time task performance during phencyclidine exposure. Chronic LY341495 impaired attentional performance in the 5-choice serial reaction time task by itself, but attenuated phencyclidine-induced excessive timeout responding. The mixed effects of metabotropic glutamate receptor 2/3 agonism and antagonism on cognitive performance under baseline conditions and after disruption with phencyclidine demonstrate that different aspects of cognition may respond differently to a given pharmacological manipulation, indicating that potential antipsychotic or pro-cognitive medications need to be tested for their effects on a range of cognitive modalities. Our findings also suggest that additional mechanisms, besides cortical glutamatergic transmission, may be involved in certain cognitive dysfunctions in schizophrenia.

Repeated low dose of phencyclidine administration impairs spatial learning in mice: blockade by clozapine but not by haloperidol

The effect of phencyclidine (PCP), a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, was examined in the water maze, a spatial learning and memory task dependent on hippocampal functions. Male adult C57Bl/6J mice received daily (s.c.) injections of either saline or PCP (0.25-4.0 mg/kg) for 12 days. During the last 5 days, the injections were followed by water maze training. Repeated PCP treatments disrupted spatial learning and memory in the 0.5-4.0 mg/kg dose range. Severe sensorimotor disturbances, observed at the 2.0 and 4.0 mg/kg doses of PCP, precluded further swim maze testing. The 0.5 mg/kg but not the 1.0 mg/kg dose of PCP impaired spatial learning and memory without any apparent sensorimotor deficits. PCP, at 1.0 mg/kg, produced impairment in non-spatial learning in the swim maze task and motor disturbances in the rotarod test. Repeated daily treatment with either the "atypical" antipsychotic drug clozapine (0.5 mg/kg i.p.) or the "typical" antipsychotic drug haloperidol (0.05 mg/kg i.p.) failed to influence spatial performances. The spatial impairment caused by the 0.5 mg/kg dose of PCP was blocked by concomitant treatment with clozapine (0.5 mg/kg), but not with haloperidol (0.05 mg/kg). The results suggest that it is possible, at low doses of PCP, to dissociate the spatial learning impairment in the water maze from the adverse behavioral effects of NMDA receptor blockade. This model may provide a basis for the analysis of the mechanisms underlying declarative memory disturbances in schizophrenia and the differences in mechanisms between typical and atypical antipsychotic drugs.

Novel discriminative stimulus effects of TPA023B, subtype-selective gamma-aminobutyric-acid(A)/benzodiazepine modulator: comparisons with zolpidem, lorazepam, and TPA023

Anxiolytics with fewer unwanted effects may be created by varying GABAergic efficacy at the BZ binding site across GABA(A) receptor subtypes. TPA023 and TPA023B have in vitro antagonist efficacy at alpha(1) subtypes and partial-agonist efficacy at alpha(2/3) subtypes. TPA023B has partial-agonist efficacy at alpha(5); TPA023 has none. Drug discrimination procedures were used to determine whether the novel GABA(A) receptor efficacy profiles would be reflected in a model of subjective effects of BZ-site ligands. Rats were trained to discriminate TPA023, TPA023B, the nonselective BZ anxiolytic lorazepam, or the alpha(1)-selective hypnotic zolpidem. The lorazepam, zolpidem, and TPA023 discriminations were learned in < 50 sessions. The TPA023B training group showed no evidence of acquiring the TPA023B discrimination after 160 sessions despite various procedural manipulations. Neither zolpidem- nor lorazepam-trained rats generalized to TPA023B. Within the same dose range, however, TPA023-trained rats generalized fully and dose-dependently to TPA023B. Number of training sessions to regain criterion discrimination performance following TPA023B tests in the lorazepam, zolpidem, and TPA023 groups increased as a function of dose, likely due to effects of residual TPA023B. Together with previous data, the present results suggest that elimination of alpha(1) efficacy plus reductions in alpha(2/3) efficacy permits anxiolysis but decreases BZ-like interoceptive stimulus effects.

Increased response to ketamine following treatment at long intervals: implications for intermittent use

BACKGROUND

Ketamine has been used for many years as a dissociative anesthetic; however, there is evidence of increasing abuse, especially at dance clubs and raves. In addition, there is increasing interest in the use of subanesthetic doses of ketamine for the treatment of pain and depression, as well as for clinical research on schizophrenia. Despite growing use, relatively little is known about the consequences of repeated administration of low doses of ketamine.

METHODS

To determine the changes in response to repeated administration, ketamine (20 mg/kg or 50 mg/kg intraperitoneal [IP]) was administered once weekly to laboratory rats and the locomotor response was assessed following each injection.

RESULTS

Repeated administration of ketamine led to an escalation in the stimulant effects of the drug, characteristic of behavioral sensitization. The development of sensitization was greater when ketamine was repeatedly administered in the presence of distinct environmental cues.

CONCLUSIONS

Intermittent administration of ketamine at weekly intervals leads to the development of locomotor sensitization. These results suggest caution in the repeated use of ketamine for recreational or clinical purposes.

Cognitive-disruptive effects of the psychotomimetic phencyclidine and attenuation by atypical antipsychotic medications in rats

BACKGROUND

Cognitive deficits in schizophrenia are severe and do not respond well to available treatments. The development and validation of animal models of cognitive deficits characterizing schizophrenia are crucial for clarifying the underlying neuropathology and discovery of improved treatments for such deficits.

MATERIALS AND METHODS

We investigated whether single and repeated administrations of the psychotomimetic phencyclidine (PCP) disrupt performance in the five-choice serial reaction time task (5-CSRTT), a test of attention and impulsivity. We also examined whether PCP-induced disruptions in this task are attenuated by atypical antipsychotic medications.

RESULTS

A single injection of PCP (1.5-3 mg/kg, s.c., 30-min pre-injection time) had nonspecific response-depressing effects. Repeated PCP administration (2 mg/kg for two consecutive days followed by five consecutive days, s.c., 30-min pre-injection time) resulted in decreased accuracy, increased premature and timeout responding, and increased response latencies. The atypical antipsychotic medications clozapine, risperidone, quetiapine, and olanzapine and the typical antipsychotic medication haloperidol did not disrupt 5-CSRTT performance under baseline conditions except at high doses. The response depression induced by a single PCP administration was exacerbated by acute clozapine or risperidone and was unaffected by chronic clozapine. Importantly, chronic clozapine partially attenuated the performance disruptions induced by repeated PCP administration, significantly reducing both the accuracy impairment and the increase in premature responding.

CONCLUSIONS

Disruptions in 5-CSRTT performance induced by repeated PCP administration are prevented by chronic clozapine treatment and may constitute a useful animal model of some cognitive symptoms of schizophrenia.

The parallel rod floor test: a measure of ataxia in mice

The parallel rod floor test is a new model of ataxia in mice. It allows the simultaneous measurement of ataxia and locomotor activity. This protocol is designed for researchers examining ethanol-induced motor incoordination in mice, but it should be applicable to other sedative/hypnotic drugs and to testing cerebellar mutant mice or mice with engineered genetic defects. This protocol takes 3 d, with the time per day depending on how many animals are tested. The test allows researchers to quantify differences in motor coordination among genotypes of mice that may differ in locomotor activity. Unlike many other methods for assessing incoordination, the parallel rod floor test yields similar patterns of genetic sensitivity across a range of variant forms of the apparatus.

Characterization of the parallel rod floor apparatus to test motor incoordination in mice

Impairment of motor coordination, or ataxia, is a prominent effect of alcohol ingestion in humans. To date, many models have been created to examine this phenomenon in animals. Evidence suggests that the tasks thought to measure this behavior in mice actually measure different components of this complex trait. We have characterized the parallel rod floor apparatus to quantify ethanol-induced motor incoordination. Using genetically heterogeneous mice, we evaluated the influence of rod diameter and inter-rod distance on dose-related ethanol-induced motor incoordination to select parameters that optimized testing procedures. We then used the DBA/2J and C57BL/6J inbred strains of mice to examine the effect of 2 g/kg of ethanol, by serially testing mice on two floor types, separated by 1 week. Finally, we tested eight inbred strains of mice on four floor types to examine patterns of strain sensitivity to 2 g/kg of intraperitoneal ethanol and determined the test parameters that maximized strain effect size. Motor incoordination varied depending on the floor type and strain. When data from strain 129S1/SvlmJ were removed from the analyses because of their extreme behavior, the greatest strain effect size was observed on one floor type during the first 10 min of testing after 2 g/kg of intraperitoneal ethanol. These findings suggest that the parallel rod floor apparatus provides a useful means for examining ethanol-induced motor incoordination in mice but that specific testing procedures are important for optimizing detection of motor incoordination and genetic influences.

Performance of male C57BL/6J mice and Wistar rats in the water maze following various schedules of phencyclidine treatment

In order to establish an animal model of cognitive impairments relevant to schizophrenia, we set out to obtain an optimal treatment protocol with phencyclidine (PCP) that would lead to robust cognitive impairment with minimal PCP-related adverse effects. Effects of various doses (0.63-5 mg/kg), pre-treatment period (0, 3, 7 and 10 days before the beginning of acquisition) and treatment schedules (before the first or immediately after the last trial on each day) of PCP on the performance of male C57BL/6J mice and Wistar rats in the spatial version of the water maze were studied. In mice, a 10-day pre-treatment period was required to prevent PCP-induced motor impairments, whereas a 3-day pre-treatment was sufficient in rats. PCP impaired spatial learning in both rats and mice, if animals were administered PCP prior to the first trial. The optimal dose was 2.5 mg/kg. In contrast, animals given PCP immediately after the daily training sessions performed as well as controls. Thus, PCP impairs spatial learning in the water maze only when present in the organism. It can be concluded that PCP interferes with learning, and perhaps retrieval, but not consolidation of newly acquired information.