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The use of atypical antipsychotic drugs like olanzapine is associated with side effects such as sedation and depression-like symptoms, especially during the initial period of the use. It is believed that the occurrence of these undesirable effectsis mainly the result of the histamine H1receptors blockade by olanzapine. In addition, use of olanzapine increases the level of triglycerides in the blood, which correlates with growing obesity. The aim of this study was to investigate the influence of pitolisant - H3 histamine antagonist - on subchronic olanzapine-induced depresion-like symptoms, sedation and hypertriglicerydemia. Forced swim test was conducted to determinate depressive-like effect of olanzapine and antidepressive-like activity during the co-administered pitolisant. The test was performed after the first and fifteenth day of the treatment of the mice. The spontaneous activity of the mice was measured on the fourteenth day of the treatment with a special, innovative RFID-system (Radio-frequency identification system) - TraffiCage (TSE-Systems, Germany). Triglyceride levels were determined on the sixteenth day of the experiment after 15 cycles of drug administration. Daily olanzapine treatment (4 mg/kg b.w., i.p., d.p.d) for 15 days significantly induces sedation (p < 0.05) and prolongs immobility time in forced swim tests (FST) in mice (p < 0.05); and also elevates the level of triglycerides (p < 0.05). Administration of pitolisant (10 mg/kg b.w., i.p.) subsequentto olanzapine normalizes these adverse effects. This study presents a promising alternative for counteracting some behavioral changes and metabolic disturbances which occur in the early period of treatment with antipsychotic drugs.

Cognitive deficits associated with schizophrenia (CDS) are implicated as a core symptom cluster of the disease and are associated with poor daily life functioning. Unfortunately, current antipsychotic agents provide little alleviation of CDS, representing a critical unmet therapeutic need. Here we investigated the effects of ABT-239 and A-431404, non-imidazole histamine H(3) receptor (H(3)R) antagonists, in animal models with relevance to CDS. As N-methyl-d-aspartate receptor hypofunction is considered an important factor in the pathogenesis of schizophrenia, acute administration of ketamine or MK-801 was used to induce cognitive impairments. The assays employed in the current studies were spontaneous alternation in cross-maze, used as an indication of working memory, and inhibitory avoidance (IA), used to assess long-term memory retention. Risperidone and olanzapine were also tested to directly compare the effects of H(3)R antagonists to two widely used antipsychotics. ABT-239 and A-431404, but not risperidone and olanzapine, attenuated ketamine-induced deficits on spontaneous alternation in cross-maze, while none of these compounds affected alternation performance on their own. ABT-239 and A-431404 also attenuated MK-801-induced impairments in IA; no effects were observed when given alone. Risperidone and olanzapine, however, failed to attenuate MK-801-induced deficits in IA and produced dose-dependent impairments when given alone. ABT-239 was also investigated in methylazoxymethanol acetate (MAM) treated rats, a neurodevelopmental model for schizophrenia. Chronic, but not acute, treatment with ABT-239 significantly improved spontaneous alternation impairments in MAM rats tested in cross-maze. In summary, these results suggest H(3)R antagonists may have the potential to ameliorate CDS.

Olanzapine is effective at treating multiple domains of schizophrenia symptoms. However, it induces serious metabolic side effects. Antipsychotic drug's antagonistic affinity to histamine H₁ receptors has been identified as a main contributor for weight gain/obesity side effects. This study therefore investigated whether a combined treatment of betahistine (a H₁ receptor agonist and H₃ receptor antagonist) could reduce the body weight/obesity induced by olanzapine. Female Sprague Dawley rats were treated orally with olanzapine (1 mg/kg, t.i.d.) and/or betahistine (2.67 mg/kg, t.i.d.), or vehicle for two weeks. Rats treated with olanzapine exhibited significant body weight gain and increased food intake. Co-treatment of olanzapine with betahistine significantly prevented (-45%) weight gain and reduced feeding efficiency compared to sole olanzapine treatment. Betahistine treatment alone had no effect on weight gain and food intake. Olanzapine reduced locomotor activity, but not betahistine. These findings demonstrate that olanzapine-induced body weight gain can partially be reduced by co-treatment with betahistine. Betahistine has H₃ receptor antagonistic effects to increase histamine release, which may augment its direct agonistic effects on H₁ receptors. These findings have important implications for clinical trials using betahistine to control antipsychotic-induced obesity side effects.

Schizophrenia (SZ) that is resistant to treatment with dopamine (DA) D2 antagonists may involve changes other than those in the dopaminergic system. Recently, histamine (HA), which regulates arousal and cognitive functions, has been suggested to act as a neurotransmitter in the central nervous system. Four HA receptors-H1, H2, H3, and H4-have been identified. Our recent basic and clinical studies revealed that brain HA improved the symptoms of SZ. The H3 receptor is primarily localized in the central nervous system, and it acts not only as a presynaptic autoreceptor that modulates the HA release but also as a presynaptic heteroreceptor that regulates the release of other neurotransmitters such as monoamines and amino acids. H3-receptor inverse agonists have been considered to improve cognitive functions. Many atypical antipsychotics are H3-receptor antagonists. Imidazole-containing H3-receptor inverse agonists inhibit not only cytochrome P450 but also hERG potassium channels (encoded by the human ether-a-go-go-related gene). Several imidazole H3-receptor inverse agonists also have high affinity for H4 receptors, which are expressed at high levels in mast cells and leukocytes. Clozapine is an H4-receptor agonist; this agonist activity may be related to the serious side effect of agranulocytosis caused by clozapine. Therefore, selective non-imidazole H3-receptor inverse agonists can be considered as novel antipsychotics that may improve refractory SZ.