Małgorzata Hołuj

Effects of the Selective 5-HT7 Receptor Antagonist SB-269970 and Amisulpride on Ketamine-Induced Schizophrenia-like Deficits in Rats

A wide body of evidence suggests that 5-HT7 receptors are implicated in a variety of central nervous system functions, including control of learning and memory processes. According to recent preclinical data, the selective blockade of these receptors may be a potential target for cognitive improvement in schizophrenia. The first aim of the present study was to evaluate the effects of the selective 5-HT7 receptor antagonist, SB-269970, and the antipsychotic drug with a high affinity for 5-HT7 receptors, amisulpride, on ketamine-induced deficits in attentional set-shifting and novel object recognition tasks in rats. Because the role of 5-HT7 receptor blockade in ameliorating positive and negative symptoms of schizophrenia remains equivocal, the second aim of these experiments was to examine the effectiveness of SB-269970 and amisulpride in reversing ketamine-induced deficits in prepulse inhibition of the startle reflex and in social interaction test in rats. The study revealed that acute administration of SB-269970 (1 mg/kg) or amisulpride (3 mg/kg) ameliorated ketamine-induced cognitive inflexibility and novel object recognition deficit in rats. Both compounds were also effective in attenuating ketamine-evoked disruption of social interactions. In contrast, neither SB-269970 nor amisulpride affected ketamine-disrupted prepulse inhibition or 50 kHz USVs accompanying social behaviour. In conclusion, antagonism of 5-HT7 receptors may represent a useful pharmacological approach in the treatment of cognitive deficits and some negative symptoms of schizophrenia.

Zinc deficiency in rats is associated with up-regulation of hippocampal NMDA receptor

RATIONALE Data indicated that zinc deficiency may contribute to the development of depression; however changes induced by zinc deficiency are not fully described. OBJECTIVES In the present paper we tested whether the dietary zinc restriction in rats causes alterations in N-methyl-D-aspartate receptor (NMDAR) subunits in brain regions that are relevant to depression. METHODS Male Sprague Dawley rats were fed a zinc adequate diet (ZnA, 50 mg Zn/kg) or a zinc deficient diet (ZnD, 3 mg Zn/kg) for 4 or 6weeks. Then, the behavior of the rats was examined in the forced swim test, sucrose intake test and social interaction test. Western blot assays were used to study the alterations in NMDAR subunits GluN2A and GluN2B and proteins associated with NMDAR signaling in the hippocampus (Hp) and prefrontal cortex (PFC). RESULTS Following 4 or 6 weeks of zinc restriction, behavioral despair, anhedonia and a reduction of social behavior occurred in rats with concomitant increased expression of GluN2A and GluN2B and decreased expression of the PSD-95, p-CREB and BDNF protein levels in the Hp. The up-regulation of GluN2A protein was also found in the PFC, but only after prolonged (6 weeks) zinc deprivation. CONCLUSIONS The procedure of zinc restriction in rats causes behavioral changes that share some similarities to the pathophysiology of depression. Obtained data indicated that depressive-like behavior induced by zinc deficiency is associated with the changes in NMDAR signaling pathway.

Improvement of ketamine-induced social withdrawal in rats: the role of 5-HT7 receptors.

Social withdrawal, one of the core negative symptoms of schizophrenia, can be modelled in the social interaction (SI) test in rats using N-methyl-D-aspartate receptor glutamate receptor antagonists. We have recently shown that amisulpride, an antipsychotic with a high affinity for serotonin 5-HT7 receptors, reversed ketamine-induced SI deficits in rats. The aim of the present study was to further elucidate the potential involvement of 5-HT7 receptors in the prosocial action of amisulpride. Acute administration of amisulpride (3 mg/kg) and SB-269970 (1 mg/kg), a 5-HT7 receptor antagonist, reversed ketamine-induced social withdrawal, whereas sulpiride (20 or 30 mg/kg) and haloperidol (0.2 mg/kg) were ineffective. The 5-HT7 receptor agonist AS19 (10 mg/kg) abolished the prosocial efficacy of amisulpride (3 mg/kg). The coadministration of an inactive dose of SB-269970 (0.2 mg/kg) showed the prosocial effects of inactive doses of amisulpride (1 mg/kg) and sulpiride (20 mg/kg). The anxiolytic chlordiazepoxide (2.5 mg/kg) and the antidepressant fluoxetine (2.5 mg/kg) were ineffective in reversing ketamine-induced SI deficits. The present study suggests that the antagonism of 5-HT7 receptors may contribute towards the mechanisms underlying the prosocial action of amisulpride. These results may have therapeutic implications for the treatment of negative symptoms in schizophrenia and other disorders characterized by social withdrawal.

The effects of a 5-HT5A receptor antagonist in a ketamine-based rat model of cognitive dysfunction and the negative symptoms of schizophrenia.

Serotonin (5-HT) receptors still represent promising targets for the development of novel multireceptor or stand-alone antipsychotic drugs with a potential to ameliorate cognitive impairments and negative symptoms in schizophrenia. The 5-HT5A receptor, one of the least known members of the serotonin receptor family, has also drawn attention in this regard. Although the antipsychotic efficacy of 5-HT5A antagonists is still equivocal, recent experimental data suggest the cognitive-enhancing activity of this strategy. The aim of the present study was to evaluate pro-cognitive and pro-social efficacies of the 5-HT5A receptor antagonist in a rat pharmacological model of schizophrenia employing the administration of the NMDA receptor antagonist, ketamine. The ability of SB-699551 to reverse ketamine-induced cognitive deficits in the attentional set-shifting task (ASST) and novel object recognition task (NORT) was examined. The compounds efficacy against ketamine-induced social withdrawal was assessed in the social interaction test (SIT) and in the social choice test (SCT). The results demonstrated the efficacy of SB-699551 in ameliorating ketamine-induced impairments on the ASST and NORT. Moreover, the tested compound also enhanced set-shifting performance in cognitively unimpaired control rats and improved object recognition memory in conditions of delay-induced natural forgetting. The pro-social activity of SB-699551 was demonstrated on both employed paradigms, the SIT and SCT. The present study suggests the preclinical efficacy of a strategy based on the blockade of 5-HT5A receptors against schizophrenia-like cognitive deficits and negative symptoms. The utility of this receptor as a target for improvement of cognitive and social dysfunctions warrants further studies.

3-Furan-2-yl-N-p-tolyl-acrylamide, a positive allosteric modulator of the α7 nicotinic receptor, reverses schizophrenia-like cognitive and social deficits in rats

&NA; The cognitive impairments and negative symptoms experienced by schizophrenia patients still await effective treatment. Alpha7 nicotinic acetylcholine receptors (&agr;7 nAChRs) have gain considerable attention in this regard. It has been recently proposed that positive allosteric modulators (PAMs) of &agr;7 nAChRs may represent an alternative strategy to that based on orthosteric agonists. The aim of the present study is to evaluate the efficacy of PAM‐2 (3‐furan‐2‐yl‐N‐p‐tolyl‐acrylamide) against cognitive deficits and negative‐like symptoms in a rat model of schizophrenia based on administration of ketamine, a NMDAR antagonist. The activity of PAM‐2 was compared to that elicited by DMXBA, an &agr;7 nAChR partial agonist. For this purpose, the attentional set‐shifting task (ASST) and the novel object recognition task (NORT) were used. The efficacies of PAM‐2 and DMXBA against ketamine‐induced social withdrawal were assessed using the social interaction test (SIT). The results demonstrated that PAM‐2 and DMXBA ameliorated ketamine‐induced cognitive impairments on the ASST and NORT as well as produced pro‐social activities in the SIT. Moreover, the co‐administration of inactive doses of PAM‐2 and antipsychotic drugs, clozapine or risperidone, reversed ketamine‐induced deficits. The present findings provide further support for the concept that &agr;7‐PAMs could be used either alone or in combination with antipsychotics for schizophrenia therapy. HighlightsWe evaluated the pro‐cognitive and pro‐social efficacies of the &agr;7‐nAChRs PAM in rats.PAM‐2 reversed ketamine‐induced cognitive impairments and social withdrawal.The effects of PAM‐2 were comparable to those of the &agr;7‐nAChR agonist, DMXBA.Combination of PAM‐2 and antipsychotics reversed impaired object recognition.

Effects of the selective 5-HT7 receptor antagonist SB-269970 on premature responding in the five-choice serial reaction time test in rats

The antagonists of serotonin 5-HT7 receptors have been demonstrated to ameliorate cognitive impairments in pharmacological animal models of schizophrenia that involve blockade of N-methyl-D-aspartate receptors (NMDARs). The administration of NMDAR antagonists evokes a broad range of cognitive deficits, including a loss of impulse control. The involvement of 5-HT7 receptors in the modulation of impulsivity has been recently suggested but has not been studied in great detail. The aim of the present study was to examine the effect of a selective 5-HT7 receptor antagonist SB-269970 on a measure of impulsive action, i.e., premature responding on the five-choice serial reaction time task (5-CSRTT) in rats. The antagonist of 5-HT2A receptor M100,907 was used as a positive control. The efficacies of both compounds were assessed in conditions of increased impulsivity that were produced by the administration of the NMDAR antagonist MK-801 or/and non-drug stimuli, i.e., using variable inter-trial intervals (vITIs). To examine the general ability of SB-269970 to counteract the MK-801-induced impairments, a discrete paired-trial delayed alternation task in a T-maze was employed. MK-801 significantly increased the number of premature responses in 5-CSRTT, and this effect was abolished by the administration of M100,907 (0.5 mg/kg) and SB-269970 (1 mg/kg). In addition, M100,907, but not SB-269970, reduced premature responding in the prolonged ITI trials. Both M100,907 and SB-269970 attenuated MK-801-induced working memory impairment in a T-maze. The present study demonstrated the efficacy of SB-269970 against MK-801-induced premature responding in the 5-CSRTT. This anti-impulsive action may offer additional benefits to the cognitive-enhancing effects of pharmacological blockade of 5-HT7 receptors.

Conditioned rewarding effects of morphine and methadone in mice pre-exposed to cocaine

BACKGROUND Methadone is widely accepted as the most effective treatment of opioid dependence. However, clinical observations indicate that the medication is less effective in individuals abusing cocaine. Diminished therapeutic efficacy of methadone in cocaine users is intriguing, but its mechanism has not been studied. METHODS Here, the conditioned place preference (CPP) procedure was used to examine the effects of the dose, number of conditioning sessions and pre-exposure to cocaine on the rewarding effects of morphine and methadone. Vehicle-pre-exposed and cocaine-sensitized mice (five injections of 10 mg/kg over 16 days) were conditioned using methadone (0, 0.1, 0.5, 3, and 5 mg/kg) or morphine (0, 1, and 10 mg/kg). Place preference was measured after one and again after two additional conditioning sessions. RESULTS As expected, morphine at 10 mg/kg produced CPP following just one conditioning session. While a single conditioning session with 1 mg/kg of morphine produced no CPP, the rewarding effect became apparent following two additional conditioning sessions as well as in mice pre-exposed to cocaine. Methadone produced CPP following one conditioning session at doses of 0.5, 3 and 5 mg/kg. However, unlike with morphine, methadones rewarding effect was not enhanced by two additional conditioning sessions or by pre-exposure with cocaine. CONCLUSIONS Prior exposure to cocaine increases unconditioned motivational effects of morphine but not of methadone.

Stimulation of nicotinic acetylcholine alpha7 receptors rescue schizophrenia-like cognitive impairments in rats

Alpha7 nicotinic acetylcholine receptor (α7 nAChR) dysfunction plays an important role in schizophrenia. Positive allosteric modulators of α7 nAChR have emerged as a promising therapeutic approach to manage cognitive deficits that are inadequately treated in schizophrenic patients. The aim of the present study was to evaluate the ability of type I (CCMI) and type II (PNU120596) α7 nAChR positive allosteric modulators to counteract MK-801-induced cognitive and sensorimotor gating deficits. The activity of these compounds was compared with the action of the α7 nAChR agonist A582941. CCMI, PNU120596 and A582941 reversed the sensorimotor gating impairment evoked by MK-801 based on the prepulse inhibition of the startle response. Additionally, no MK-801-evoked working memory deficits were observed with α7 nAChR ligand pretreatment as assessed in a discrete paired-trial delayed alternation task. However, these compounds did not affect the rats’ attentional performances in the five-choice serial reaction time test. The α7 nAChR agents demonstrated a beneficial effect on sensorimotor gating and some aspects of cognition tested in a rat model of schizophrenia. Therefore, these results support the use of α7 nAChR positive allosteric modulators as a potential treatment strategy in schizophrenia.