The influence of N-desmethylclozapine and clozapine on recognition memory and BDNF expression in hippocampus

Cognitive Deficit in Schizophrenia: From Etiology to Novel Treatments

Schizophrenia is a major mental illness characterized by positive and negative symptoms, and by cognitive deficit. Although cognitive impairment is disabling for patients, it has been largely neglected in the treatment of schizophrenia. There are several reasons for this lack of treatments for cognitive deficit, but the complexity of its etiology-in which neuroanatomic, biochemical and genetic factors concur-has contributed to the lack of effective treatments. In the last few years, there have been several attempts to develop novel drugs for the treatment of cognitive impairment in schizophrenia. Despite these efforts, little progress has been made. The latest findings point to the importance of developing personalized treatments for schizophrenia which enhance neuroplasticity, and of combining pharmacological treatments with non-pharmacological measures.

N-3 polyunsaturated fatty acids and clozapine abrogates poly I: C-induced immune alterations in primary hippocampal neurons

The viral mimetic polyinosinic:polycytidylic acid (poly I:C) is an important tool to study the consequences of viral infection to the development of neuropsychiatric disorders. Here, based on the premise of omega-3 polyunsaturated fatty acids (n3 PUFAs) as supplemental treatment to antipsychotics in schizophrenia, we investigated the involvement of NFkB pathway in the effects of n3 PUFAs or of the atypical antipsychotic clozapine in hippocampal poly I:C-challenged neurons. Primary hippocampal neuronal cultures were exposed to n3 PUFAs (DHA4.35 μM/EPA7.10 μM, DHA 8.7 μM/EPA14.21 μM or DHA17.4 μM/EPA28.42 μM) or clozapine (1.5 or 3 μM) in the presence or absence of poly I:C. MTT assay revealed that poly I:C-induced reduction in cell viability was prevented by n3 PUFAs or clozapine. N3 PUFAs (DHA 8.7 μM/EPA14.21 μM) or clozapine (3 μM) significantly reduced poly I:C-induced increase in iNOS, NFkB (p50/p65), IL-6 and nitrite when compared to non-treated cells. Only n3 PUFAs prevented poly I:C-induced deficits in BDNF. On the other hand, poly I:C caused a marked reduction in DCX immunoexpression, which was prevented only by clozapine. Thus, n3 PUFAs and clozapine exert in vitro neuroprotective effects against poly I:C immune challenge in hippocampal neurons, by mechanisms possibly involving the inhibition of canonical NFkB pathway. The present study adds further evidences to the mechanisms underlying n3 PUFAs and clozapine neuroprotective effects against viral immune challenges. Since n3 PUFAs is a safe strategy for use during pregnancy, our results also add further evidence for the use of this supplement in order to prevent alterations induced by viral hits during this developmental period.

Effect of clozapine on locomotor activity and anxiety-related behavior in the neonatal mice administered MK-801

Atypical antipsychotics have been used to treat fear and anxiety disturbance that are highly common in schizophrenic patients. It is suggested that disruptions of N-methyl-d-aspartate (NMDA)-mediated transmission of glutamate may underlie the pathophysiology of schizophrenia. The present study was conducted to analyze the effectiveness of clozapine on the anxiety-related behavior and locomotor function of the adult brain, which had previously undergone NMDA receptor blockade during a developmental period. In order to block the NMDA receptor, male mice were administered 0.25 mg/kg of MK-801 on days 7 to 10 postnatal. In adulthood, they were administered intraperitoneally 0.5 mg/kg of clozapine and tested with open-field and elevated plus maze test, to assess their emotional behavior and locomotor activity. In the group receiving MK-801 in the early developmental period the elevated plus maze test revealed a reduction in the anxiety-related behavior (p<0.05), while the open-field test indicated a decrease in locomotor activity (p<0.01). Despite these reductions, clozapine could not reverse the NMDA receptor blockade. Also, as an atypical antipsychotic agent, clozapine could not reverse impairment in the locomotor activity and anxiety-related behavior, induced by administration of the MK-801 in neonatal period.

Presynaptic D2 dopamine receptors control long-term depression expression and memory processes in the temporal hippocampus

BACKGROUND

Dysfunctional mesocorticolimbic dopamine signaling has been linked to alterations in motor and reward-based functions associated with psychiatric disorders. Converging evidence from patients with psychiatric disorders and use of antipsychotics suggests that imbalance of dopamine signaling deeply alters hippocampal functions. However, given the lack of full characterization of a functional mesohippocampal pathway, the precise role of dopamine transmission in memory deficits associated with these disorders and their dedicated therapies is unknown. In particular, the positive outcome of antipsychotic treatments, commonly antagonizing D2 dopamine receptors (D2Rs), on cognitive deficits and memory impairments remains questionable.

METHODS

Following pharmacologic and genetic manipulation of dopamine transmission, we performed anatomic, neurochemical, electrophysiologic, and behavioral investigations to uncover the role of D2Rs in hippocampal-dependent plasticity and learning. Naïve mice (n = 4-21) were used in the different procedures.

RESULTS

Dopamine modulated both long-term potentiation and long-term depression in the temporal hippocampus as well as spatial and recognition learning and memory in mice through D2Rs. Although genetic deletion or pharmacologic blockade of D2Rs led to the loss of long-term potentiation expression, the specific genetic removal of presynaptic D2Rs impaired long-term depression and performances on spatial memory tasks.

CONCLUSIONS

Presynaptic D2Rs in dopamine fibers of the temporal hippocampus tightly modulate long-term depression expression and play a major role in the regulation of hippocampal learning and memory. This direct role of mesohippocampal dopamine input as uncovered here adds a new dimension to dopamine involvement in the physiology underlying deficits associated with neuropsychiatric disorders.

Differential effects of antipsychotics on hippocampal presynaptic protein expressions and recognition memory in a schizophrenia model in mice

We compared the effects of subchronic clozapine and haloperidol administration on the expression of SNAP-25 and synaptophysin in an animal model of schizophrenia based on the glutamatergic hypothesis. Mice were first treated with a non-competitive NMDA antagonist MK-801 (0.3 mg/kg/day) or saline for 5 days, and then clozapine (5 mg/kg/day), haloperidol (1 mg/kg/day) or saline was administered for two weeks. The locomotion test, as a behavioral model of the positive symptoms of schizophrenia, was applied after MK-801/saline administration on day 6 for acute effects and after antipsychotic/saline administration on day 19 for enduring effects on mice activity. Memory function was assessed by the Novel Object Recognition (NOR) test, one day after the last day of antipsychotic/saline administration (day 20). Western Blotting technique was used to determine SNAP-25 and synaptophysin expressions in the hippocampus and frontal cortex. Both antipsychotics reversed the enhanced locomotion effects of MK-801. MK-801 and haloperidol decreased recognition memory performance. On the other hand, clozapine did not compromise memory. It also did not reverse the negative effects of MK-801 on memory performance. MK-801 did not change SNAP-25 and synaptophysin expressions in the hippocampus and frontal cortex. Clozapine increased hippocampal SNAP-25, decreased hippocampal synaptophysin expression, whereas frontal SNAP-25 and synaptophysin expressions remained unchanged. Haloperidol had no effects on levels of SNAP-25 and synaptophysin in the frontal cortex and hippocampus. These findings support the idea that the differential effects of clozapine might be related to its plastic effects and synaptic reorganization of the hippocampus.

Ameliorative effect of N-desmethylclozapine in animal models of social deficits and cognitive functions

One of the major circulating metabolites of clozapine, N-desmethylclozapine (NDMC), has been demonstrated to exhibit partial agonistic activity at M(1) muscarinic receptors. Some of the unique therapeutic effects of clozapine might involve the pharmacological effects of this metabolite. The purpose of the present study was therefore to examine whether NDMC improved behavioral abnormalities in animal models of social deficits and cognitive deficits of schizophrenia. NDMC (3mg/kg) and clozapine (1-3mg/kg) each improved the reduction of social interaction caused by a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, 5R,10S-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) (0.1mg/kg), without affecting locomotor activity in rats. NDMC (3-10mg/kg) and clozapine (1-3mg/kg) each also resulted in better discrimination of a novel from a familiar object 24h after a training trial in a rat object recognition test. These findings suggest that NDMC can improve behavior in animal models of social deficits and cognitive deficits of schizophrenia as well as clozapine.