Aerobic exercise improves memory and prevents cognitive deficits of relevance to schizophrenia in an animal model.

INTRODUCTION AND OBJECTIVES: Cognitive impairment associated with schizophrenia (CIAS) greatly reduces patients' functionality, and remains an unmet clinical need. The sub-chronic phencyclidine (scPCP) rat model is commonly employed in studying CIAS. We have previously shown that voluntary exercise reverses impairments in novel object recognition (NOR) induced by scPCP. However, there has not been a longitudinal study investigating the potential protective effects of exercise in a model of CIAS. This study aimed to investigate the pro-cognitive and protective effects of exercise on CIAS using the translational NOR and attentional set-shifting tasks (ASST). METHODS: Female Lister Hooded rats were either exercised (wheel running for one hour per day, five days per week, for six weeks; n=20) or not (n=20) and then tested in a natural-forgetting NOR test. Rats in each group were then administered either PCP (2 mg/kg intraperitoneally (i.p.)) or saline solution (1 mL/kg i.p.) for seven days, followed by seven days washout. Three NOR tests were conducted immediately and two and nine weeks after washout, and a natural-forgetting NOR test was carried out again eight weeks post washout. Rats were trained and tested in ASST from week 6 to week 10 post washout. RESULTS: Non-exercised rats displayed a deficit in both of the natural-forgetting NOR tests, whereas exercised rats did not. The scPCP exercise group did not show the expected deficit in NOR at any time point, and had a significantly ameliorated deficit in the ASST compared to the scPCP control group. CONCLUSION: Voluntary exercise has long-lasting pro-cognitive and protective effects in two cognitive domains. Exercise improves cognition and could provide protection against CIAS.

Deficits in social behavioral tests in a mouse model of alternating hemiplegia of childhood.

Social behavioral deficits have been observed in patients diagnosed with alternating hemiplegia of childhood (AHC), rapid-onset dystonia-parkinsonism and CAPOS syndrome, in which specific missense mutations in ATP1A3, encoding the Na(+), K(+)-ATPase α3 subunit, have been identified. To test the hypothesis that social behavioral deficits represent part of the phenotype of Na(+), K(+)-ATPase α3 mutations, we assessed the social behavior of the Myshkin mouse model of AHC, which has an I810N mutation identical to that found in an AHC patient with co-morbid autism. Myshkin mice displayed deficits in three tests of social behavior: nest building, pup retrieval and the three-chamber social approach test. Chronic treatment with the mood stabilizer lithium enhanced nest building in wild-type but not Myshkin mice. In light of previous studies revealing a broad profile of neurobehavioral deficits in the Myshkin model - consistent with the complex clinical profile of AHC - our results suggest that Na(+), K(+)-ATPase α3 dysfunction has a deleterious, but nonspecific, effect on social behavior. By better defining the behavioral profile of Myshkin mice, we identify additional ATP1A3-related symptoms for which the Myshkin model could be used as a tool to advance understanding of the underlying neural mechanisms and develop novel therapeutic strategies.

PNU-120596, a positive allosteric modulator of α7 nicotinic acetylcholine receptors, reverses a sub-chronic phencyclidine-induced cognitive deficit in the attentional set-shifting task in female rats.

The α7 nicotinic acetylcholine receptors (nAChRs) have been highlighted as a target for cognitive enhancement in schizophrenia. Adult female hooded Lister rats received sub-chronic phencyclidine (PCP) (2 mg/kg) or vehicle i.p. twice daily for 7 days, followed by 7 days' washout. PCP-treated rats then received PNU-120596 (10 mg/kg; s.c.) or saline and were tested in the attentional set-shifting task. Sub-chronic PCP produced a significant cognitive deficit in the extra-dimensional shift (EDS) phase of the task (p < 0.001, compared with vehicle). PNU-120596 significantly improved performance of PCP-treated rats in the EDS phase of the attentional set-shifting task (p < 0.001). In conclusion, these data demonstrate that PNU-120596 improves cognitive dysfunction in our animal model of cognitive dysfunction in schizophrenia, most likely via modulation of α7 nACh receptors.

The efficacy of sodium channel blockers to prevent phencyclidine-induced cognitive dysfunction in the rat: potential for novel treatments for schizophrenia.

Sodium channel inhibition is a well precedented mechanism used to treat epilepsy and other hyperexcitability disorders. The established sodium channel blocker and broad-spectrum anticonvulsant lamotrigine is also effective in the treatment of bipolar disorder and has been evaluated in patients with schizophrenia. Double-blind placebo-controlled clinical trials found that the drug has potential to reduce cognitive symptoms of the disorder. However, because of compound-related side-effects and the need for dose titration, a conclusive evaluation of the drug's efficacy in patients with schizophrenia has not been possible. (5R)-5-(4-{[(2-Fluorophenyl)methyl]oxy}phenyl)-l-prolinamide (GSK2) and (2R,5R)-2-(4-{[(2-fluorophenyl)methyl]oxy}phenyl)-7-methyl-1,7-diazaspiro[4.4]nonan-6-one (GSK3) are two new structurally diverse sodium channel blockers with potent anticonvulsant activity. In this series of studies in the rat, we compared the efficacy of the two new molecules to prevent a cognitive deficit induced by the N-methyl-d-aspartic acid receptor antagonist phencyclidine (PCP) in the reversal-learning paradigm in the rat. We also explored the effects of the drugs to prevent brain activation and neurochemical effects of PCP. We found that, like lamotrigine, both GSK2 and GSK3 were able to prevent the deficit in reversal learning produced by PCP, thus confirming their potential in the treatment of cognitive symptoms of schizophrenia. However, higher doses than those required for anticonvulsant efficacy of the drugs were needed for activity in the reversal-learning model, suggesting a lower therapeutic window relative to mechanism-dependent central side effects for this indication.

Asenapine improves phencyclidine-induced object recognition deficits in the rat: evidence for engagement of a dopamine D1 receptor mechanism.

RATIONALE: Cognitive deficits are common in schizophrenia. Asenapine is an atypical antipsychotic approved by the US Food and Drug Administration in adults for treatment of schizophrenia or acute treatment, as monotherapy or adjunct therapy to lithium or valproate, of manic or mixed episodes of bipolar I disorder. OBJECTIVES: Based on the receptor pharmacology of asenapine, the current study assessed the efficacy and mechanism of action of asenapine to improve a subchronic phencyclidine (PCP)-induced deficit in visual recognition memory using the novel object recognition (NOR) paradigm in the rat, a paradigm of relevance to cognition in schizophrenia. METHODS: Female-hooded Lister rats received vehicle or PCP (2 mg/kg, i.p.) for 7 days, followed by a 7-day washout. On the test day, rats were given asenapine (0.001-0.1 mg/kg, s.c.) alone or in combination with the D(1) receptor antagonist SCH-23390 (0.05 mg/kg, i.p.) or 5-HT(1A) receptor antagonist WAY100635 (1 mg/kg, i.p.). Time spent exploring two identical objects during a 3-min acquisition trial (followed by a 1-min intertrial interval) and then a familiar and a novel object for another 3 min (retention trial) were recorded onto videotape and scored blind. RESULTS: In the retention trial, vehicle- but not PCP-treated animals explored the novel object significantly more than the familiar object (p < 0.001). Asenapine (0.01-0.075 mg/kg) reversed PCP-induced deficits in NOR (p < 0.01-0.001) in a dose-related manner. This effect was antagonised by SCH-23390 but not by WAY100635. CONCLUSIONS: These results demonstrate a role for D(1) but not 5-HT(1A) receptor mechanisms in mediating the cognitive effects of asenapine in this rodent model.

PD168077, a D(4) receptor agonist, reverses object recognition deficits in rats: potential role for D(4) receptor mechanisms in improving cognitive dysfunction in schizophrenia.

This study investigated the effects of the dopamine D(4) receptor agonist, PD168077, on recognition memory using a novel object recognition task, which detects disruption and improvement of recognition memory in rats by measuring their ability to discriminate between familiar and novel objects. When acquisition and test were 6 h apart (experiment 1), control rats failed to discriminate between familiar and novel objects at test. Rats given low doses of PD168077 (0.3; 1.0 mg/kg) also failed to discriminate between the objects, while rats given higher doses (3.0; 10.0 mg/kg) explored the novel object more than the familiar object, indicating retained memory of the familiar object. Thus, at higher doses, PD168077 improved recognition memory in rats. Experiment 2 tested whether PD168077 would attenuate deficits in novel object recognition induced by sub-chronic phencyclidine. Testing was 1 min after acquisition, such that vehicle pre-treated rats differentiated between the novel and familiar objects: however, sub-chronic phencyclidine-treated rats failed to discriminate between the two, indicating disruption of recognition memory. PD168077 (10 mg/kg) restored the ability of phencyclidine-treated rats to differentiate between the novel and familiar objects, indicating improved recognition memory. The results suggest that D(4) receptor activation can improve cognitive dysfunction in an animal model relevant to schizophrenia.

Activation of α7 nicotinic receptors improves phencyclidine-induced deficits in cognitive tasks in rats: implications for therapy of cognitive dysfunction in schizophrenia.

RATIONALE: Nicotinic α7 acetylcholine receptors (nAChRs) have been highlighted as a target for cognitive enhancement in schizophrenia. AIM: To investigate whether the deficits induced by sub-chronic phencyclidine (PCP) in reversal learning and novel object recognition could be attenuated by the selective α7 nAChR full agonist, PNU-282987. METHODS: Adult female hooded-Lister rats received sub-chronic PCP (2mg/kg) or vehicle i.p. twice daily for 7days, followed by 7 days washout. In cohort 1, PCP-treated rats then received PNU-282987 (5, 10, 20mg/kg; s.c.) or vehicle and were tested in the reversal-learning task. In cohort 2, PCP-treated rats received PNU-282987 (10mg/kg; s.c.) or saline for 15days and were tested in the novel object recognition test on day 1 and on day 15, to test for tolerance. RESULTS: Sub-chronic PCP produced significant deficits in both cognitive tasks (P<0.01-0.001). PNU-282987 attenuated the PCP-induced deficits in reversal learning at 10mg/kg (P<0.01) and 20mg/kg (P<0.001), and in novel object recognition at 10mg/kg on day 1 (P<0.01) and on day 15 (P<0.001). CONCLUSIONS: These data show that PNU-282987 has efficacy to reverse PCP-induced deficits in two paradigms of relevance to schizophrenia. Results further suggest that 15-day once daily dosing of PNU-282987 (10mg/kg s.c.) does not cause tolerance in the rat. This study suggests that activation of α7 nAChRs, may represent a suitable strategy for improving cognitive deficits of relevance to schizophrenia.

Animal models of cognitive dysfunction and negative symptoms of schizophrenia: focus on NMDA receptor antagonism.

Cognitive deficits in schizophrenia remain an unmet clinical need. Improved understanding of the neuro- and psychopathology of these deficits depends on the availability of carefully validated animal models which will assist the development of novel therapies. There is much evidence that at least some of the pathology and symptomatology (particularly cognitive and negative symptoms) of schizophrenia results from a dysfunction of the glutamatergic system which may be modelled in animals through the use of NMDA receptor antagonists. The current review examines the validity of this model in rodents. We review the ability of acute and sub-chronic treatment with three non-competitive NMDA antagonists; phencyclidine (PCP), ketamine and MK801 (dizocilpine) to produce cognitive deficits of relevance to schizophrenia in rodents and their subsequent reversal by first- and second-generation antipsychotic drugs. Effects of NMDA receptor antagonists on the performance of rodents in behavioural tests assessing the various domains of cognition and negative symptoms are examined: novel object recognition for visual memory, reversal learning and attentional set shifting for problem solving and reasoning, 5-Choice Serial Reaction Time for attention and speed of processing; in addition to effects on social behaviour and neuropathology. The evidence strongly supports the use of NMDA receptor antagonists to model cognitive deficit and negative symptoms of schizophrenia as well as certain pathological disturbances seen in the illness. This will facilitate the evaluation of much-needed novel pharmacological agents for improved therapy of cognitive deficits and negative symptoms in schizophrenia.

Effects of asenapine, olanzapine, and risperidone on psychotomimetic-induced reversal-learning deficits in the rat.

BACKGROUND: Asenapine is a new pharmacological agent for the acute treatment of schizophrenia and bipolar disorder. It has relatively higher affinity for serotonergic and alpha(2)-adrenergic than dopaminergic D(2) receptors. We evaluated the effects of asenapine, risperidone, and olanzapine on acute and subchronic psychotomimetic-induced disruption of cued reversal learning in rats. METHODS: After operant training, rats were treated acutely with d-amphetamine (0.75 mg/kg intraperitoneally [i.p.]) or phencyclidine (PCP; 1.5mg/kg i.p.) or subchronically with PCP (2mg/kg i.p. for 7 days). We assessed the effects of acute coadministration of asenapine, risperidone, or olanzapine on acute d-amphetamine- and PCP-induced deficits and the effects of long-term coadministration of these agents (for 28 additional days) on the deficits induced by subchronic PCP. RESULTS: Deficits in reversal learning induced by acute d-amphetamine were attenuated by risperidone (0.2mg/kg i.p.). Acute PCP-induced impairment of reversal learning was attenuated by acute asenapine (0.025 mg/kg subcutaneously [s.c.]), risperidone (0.2mg/kg i.p.), and olanzapine (1.0mg/kg i.p.). Subchronic PCP administration induced an enduring deficit that was attenuated by acute asenapine (0.075 mg/kg s.c.) and by olanzapine (1.5mg/kg i.p.). Asenapine (0.075 mg/kg s.c.), risperidone (0.2mg/kg i.p.), and olanzapine (1.0mg/kg i.p.) all showed sustained efficacy with chronic (29 days) treatment to improve subchronic PCP-induced impairments. CONCLUSION: These data suggest that asenapine may have beneficial effects in the treatment of cognitive symptoms in schizophrenia. However, this remains to be validated by further clinical evaluation.

Sertindole improves sub-chronic PCP-induced reversal learning and episodic memory deficits in rodents: involvement of 5-HT(6) and 5-HT (2A) receptor mechanisms.

AIM: This study examined the efficacy of sertindole in comparison with a selective 5-HT(6) and a 5-HT(2A) receptor antagonist to reverse sub-chronic phencyclidine (PCP)-induced cognitive deficits in female rats. METHODS: In the first test, adult female hooded Lister rats were trained to perform an operant reversal learning task to 90% criterion. After training, rats were treated with PCP at 2 mg/kg (i.p.) or vehicle twice daily for 7 days, followed by 7 days washout. For the second test, novel object recognition (NOR), a separate batch of rats, had the same sub-chronic PCP dosing regime and washout period. In reversal learning, rats were treated acutely with sertindole, the selective 5-HT(2A) receptor antagonist M100.907 or the selective 5-HT(6) receptor antagonist SB-742457. RESULTS: The PCP-induced selective reversal learning deficit was significantly improved by sertindole, M100.907 and SB-742457. Sertindole also significantly improved the sub-chronic PCP-induced deficit in NOR, a test of episodic memory following a 1 min and 1 h inter-trial interval. In vivo binding studies showed that the dose-response relationship for sertindole in this study most closely correlates with affinity for 5-HT(6) receptor in vivo binding in striatum, although contribution from binding to 5-HT(2A) receptors in vivo in cortex may also provide an important mechanism. CONCLUSION: The efficacies of selective 5-HT(2A) and 5-HT(6) receptor antagonists suggest potential mechanisms mediating the effects of sertindole, which has high affinity for these 5-HT receptor subtypes. The sertindole-induced improvement in cognitive function in this animal model suggests relevance for the management of cognitive deficit symptoms in schizophrenia.

Comparison of the efficacy of two anticonvulsants, phenytoin and valproate to improve PCP and d-amphetamine induced deficits in a reversal learning task in the rat.

Recent studies in our laboratory have shown that PCP (phencyclidine) and d-amphetamine induce a cognitive deficit in rats, in a paradigm of potential relevance for the pathology of schizophrenia. Atypical, but not classical antipsychotics and the anticonvulsant, lamotrigine have been shown to prevent a selective reversal learning deficit induced by PCP. In contrast, only haloperidol reversed the d-amphetamine-induced deficit. The present study aimed to explore the ability of two anticonvulsants with differing mechanism of action, valproate and phenytoin to attenuate the cognitive deficits induced by PCP and d-amphetamine in the reversal learning paradigm. PCP at 1.5 mg/kg and d-amphetamine at 0.5 mg/kg both produced a selective and significant reduction in performance of the reversal phase with no effect on the initial phase of the task in female-hooded Lister rats. Valproate (25-200 mg/kg) and phenytoin (25-50 mg/kg) had no effect on performance when administered alone. Valproate (100-200 mg/kg), whose principle action is thought to be the enhancement of GABA transmission, was unable to prevent the cognitive deficit induced by either PCP or d-amphetamine. Conversely, phenytoin (50 mg/kg), a use-dependent sodium channel inhibitor, significantly prevented the deficit induced by PCP, but not d-amphetamine. These results add to our earlier work with lamotrigine, and suggest that sodium channel blockade may be a mechanism by which some anticonvulsant drugs can prevent the PCP-induced deficit. These data have implications for the use of anticonvulsant drugs in the treatment of cognitive or psychotic disorders.

D(1)-like receptor activation improves PCP-induced cognitive deficits in animal models: Implications for mechanisms of improved cognitive function in schizophrenia.

Phencyclidine (PCP) produces cognitive deficits of relevance to schizophrenia in animal models. The aim was to investigate the efficacy of the D(1)-like receptor agonist, SKF-38393, to improve PCP-induced deficits in the novel object recognition (NOR) and operant reversal learning (RL) tasks. Rats received either sub-chronic PCP (2 mg/kg) or vehicle for 7 days, followed by a 7-day washout. Rats were either tested in NOR or the RL tasks. In NOR, vehicle rats successfully discriminated between novel and familiar objects, an effect abolished in PCP-treated rats. SKF-38393 (6 mg/kg) significantly ameliorated the PCP-induced deficit (P<0.01) an effect significantly antagonised by SCH-23390 (0.05 mg/kg), a D(1)-like receptor antagonist (P<0.01). In the RL task sub-chronic PCP significantly reduced performance in the reversal phase (P<0.001); SKF-38393 (6.0 mg/kg) improved this PCP-induced deficit, an effect antagonised by SCH-23390 (P<0.05). These results suggest a role for D(1)-like receptors in improvement of cognitive function in paradigms of relevance to schizophrenia.