Chronic phencyclidine (PCP)-induced modulation of muscarinic receptor mRNAs in rat brain : Impact of antipsychotic drug treatment

Effects of Antipsychotics on the Hypothalamus-Pituitary-Adrenal Axis in a Phencyclidine Animal Model of Schizophrenia

Schizophrenia (SCH) is a mental disorder that requires long-term antipsychotic treatment. SCH patients are thought to have an increased sensitivity to stress. The dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, observed in SCH, could include altered levels of glucocorticoids, glucocorticoid receptors (GRs), and associated proteins. The perinatal administration of phencyclidine (PCP) to rodents represents an animal model of SCH. This study investigated the effects of perinatal PCP exposure and subsequent haloperidol/clozapine treatment on corticosterone levels measured by ELISA and the expression of GR-related proteins (GR, pGR, HSP70, HSP90, FKBP51, and 11β-Hydroxysteroid dehydrogenase-11β-HSD) determined by Western blot, in different brain regions of adult rats. Six groups of male rats were treated on the 2nd, 6th, 9th, and 12th postnatal days (PN), with either PCP or saline. Subsequently, one saline and one PCP group received haloperidol/clozapine from PN day 35 to PN day 100. The results showed altered GR sensitivity in the rat brain after PCP exposure, which decreased after haloperidol/clozapine treatment. These findings highlight disturbances in the HPA axis in a PCP-induced model of SCH and the potential protective effects of antipsychotics. To the best of our knowledge, this is the first study to investigate the effects of antipsychotic drugs on the HPA axis in a PCP animal model of SCH.

Muscarinic receptor signaling contributes to atypical antipsychotic drug reversal of the phencyclidine-induced deficit in novel object recognition in rats

Enhancement of cholinergic function via muscarinic acetylcholine receptor M₁ agonism improves cognition in some schizophrenia patients. Most atypical antipsychotic drugs, including clozapine and its active metabolite, N-desmethylclozapine, and lurasidone, enhance the release of acetylcholine in key brain regions involved in cognition (e.g. hippocampus). We determined the effect of muscarinic acetylcholine receptor M₁ stimulation on novel object recognition and its contribution to the ability of atypical antipsychotic drugs to reverse the novel object recognition deficit in rats withdrawn from subchronic phencyclidine, a rodent model of cognitive impairment in schizophrenia. In control rats, the non-specific muscarinic acetylcholine receptor antagonist, scopolamine, and the M₁ selective antagonist, VU0255035, induced a novel object recognition deficit, which was reversed by the M₁ agonist, AC260584. Scopolamine fully blocked the effect of clozapine and N-desmethylclozapine, but not lurasidone, to restore novel object recognition in subchronic phencyclidine-treated rats. VU0255035 also blocked these effects of clozapine and N-desmethylclozapine, but not lurasidone; however, the blockade was not as complete as that achieved with scopolamine. Furthermore, subchronic phencyclidine increased hippocampal M₁ mRNA expression. These data suggest that M₁ agonism is required for clozapine and N-desmethylclozapine to ameliorate the phencyclidine-induced deficit in novel object recognition, additional evidence that M₁ agonism is a potential target for treating cognitive impairment in schizophrenia.

Haloperidol affects bones while clozapine alters metabolic parameters - sex specific effects in rats perinatally treated with phencyclidine

Background

The presentation of schizophrenia (SCH) symptoms differs between the sexes. Long-term treatment with antipsychotics is frequently associated with decreased bone mineral density, increased fracture risk and metabolic side effects. Perinatal phencyclidine (PCP) administration to rodents represents an animal model of SCH. The aim of this study was to assess the effects of chronic haloperidol and clozapine treatment on bone mass, body composition, corticosterone, IL-6 and TNF-α concentrations and metabolic parameters in male and female rats perinatally treated with PCP.

Methods

Six groups of male and six groups of female rats (n = 6-12 per group) were subcutaneously treated on 2nd, 6th, 9th and 12th postnatal day (PN), with either PCP (10 mg/kg) or saline. At PN35, one NaCl and PCP group (NaCl-H and PCP-H) started receiving haloperidol (1 mg/kg/day) and one NaCl and PCP group (NaCl-C and PCP-C) started receiving clozapine (20 mg/kg/day) dissolved in drinking water. The remaining NaCl and PCP groups received water. Dual X-ray absorptiometry measurements were performed on PN60 and PN98. Animals were sacrificed on PN100. Femur was analysed by light microscopy. Concentrations of corticosterone, TNF-α and IL-6 were measured in serum samples using enzyme-linked immunosorbent assay (ELISA) commercially available kits. Glucose, cholesterol and triacylglycerol concentrations were measured in serum spectrophotometrically.

Results

Our results showed that perinatal PCP administration causes a significant decrease in bone mass and deterioration in bone quality in male and female rats. Haloperidol had deleterious, while clozapine had protective effect on bones. The effects of haloperidol on bones were more pronounced in male rats. It seems that the observed changes are not the consequence of the alterations of corticosterone, IL-6 and TNF-α concentration since no change of these factors was observed. Clozapine induced increase of body weight and retroperitoneal fat in male rats regardless of perinatal treatment. Furthermore, clozapine treatment caused sex specific increase in pro-inflammatory cytokines.

Conclusion

Taken together our findings confirm that antipsychotics have complex influence on bone and metabolism. Evaluation of potential markers for individual risk of antipsychotics induced adverse effects could be valuable for improvement of therapy of this life-long lasting disease.

Electronic supplementary material

The online version of this article (10.1186/s40360-017-0171-4) contains supplementary material, which is available to authorized users.

The subchronic phencyclidine rat model: relevance for the assessment of novel therapeutics for cognitive impairment associated with schizophrenia

RATIONALE

Current treatments for schizophrenia have modest, if any, efficacy on cognitive dysfunction, creating a need for novel therapies. Their development requires predictive animal models. The N-methyl-D-aspartate (NMDA) hypothesis of schizophrenia indicates the use of NMDA antagonists, like subchronic phencyclidine (scPCP) to model cognitive dysfunction in adult animals.

OBJECTIVES

The objective of this study was to assess the scPCP model by (1) reviewing published findings of scPCP-induced neurochemical changes and effects on cognitive tasks in adult rats and (2) comparing findings from a multi-site study to determine scPCP effects on standard and touchscreen cognitive tasks.

METHODS

Across four research sites, the effects of scPCP (typically 5 mg/kg twice daily for 7 days, followed by at least 7-day washout) in adult male Lister Hooded rats were studied on novel object recognition (NOR) with 1-h delay, acquisition and reversal learning in Morris water maze and touchscreen-based visual discrimination.

RESULTS

Literature findings showed that scPCP impaired attentional set-shifting (ASST) and NOR in several labs and induced a variety of neurochemical changes across different labs. In the multi-site study, scPCP impaired NOR, but not acquisition or reversal learning in touchscreen or water maze. Yet, this treatment regimen induced locomotor hypersensitivity to acute PCP until 13-week post-cessation.

CONCLUSIONS

The multi-site study confirmed that scPCP impaired NOR and ASST only and demonstrated the reproducibility and usefulness of the touchscreen approach. Our recommendation, prior to testing novel therapeutics in the scPCP model, is to be aware that further work is required to understand the neurochemical changes and specificity of the cognitive deficits.

Chronic phencyclidine treatment induces long-lasting glutamatergic activation of VTA dopamine neurons

Use of phencyclidine (PCP) can mimic some aspects of schizophrenia. However, the underlying mechanism is unclear. Administration of PCP is known to activate mesolimbic dopamine pathway. In this study, we focused on ventral tegmental area (VTA) of mesolimbic dopamine pathway as target of PCP for inducing schizophrenia-like symptoms. Single VTA neuron was isolated and its neural activity was monitored by measuring cytosolic Ca(2+) concentration ([Ca(2+)]i) followed by immunocytochemical identification of dopamine neurons. Administration of glutamate increased [Ca(2+)]i in dopamine neurons from control rats, and the [Ca(2+)]i increase was inhibited in the presence of PCP. In contrast, in VTA dopamine neurons from rats chronically treated with PCP for 7 days, administration of glutamate was able to induce [Ca(2+)]i increase in the presence of PCP. Furthermore, this glutamate-induced [Ca(2+)]i increase in the presence of PCP continued even after washout of glutamate and this effect lasted as long as PCP was present. This long-lasting glutamate-induced [Ca(2+)]i increase in the presence of PCP was not observed or significantly attenuated under Ca(2+) free condition and by N-type Ca(2+) channel blocker ω-conotoxin. The results indicate that chronic treatment with PCP reverses the acute PCP effect on VTA dopamine neurons from inhibitory to stimulatory tone, and consequently induces long-lasting activation of dopamine neurons by glutamate.

Second generation antipsychotic-induced type 2 diabetes: a role for the muscarinic M3 receptor

Second generation antipsychotics (SGAs) are widely prescribed to treat various disorders, most notably schizophrenia and bipolar disorder; however, SGAs can cause abnormal glucose metabolism that can lead to insulin-resistance and type 2 diabetes mellitus side-effects by largely unknown mechanisms. This review explores the potential candidature of the acetylcholine (ACh) muscarinic M3 receptor (M3R) as a prime mechanistic and possible therapeutic target of interest in SGA-induced insulin dysregulation. Studies have identified that SGA binding affinity to the M3R is a predictor of diabetes risk; indeed, olanzapine and clozapine, SGAs with the highest clinical incidence of diabetes side-effects, are potent M3R antagonists. Pancreatic M3Rs regulate the glucose-stimulated cholinergic pathway of insulin secretion; their activation on β-cells stimulates insulin secretion, while M3R blockade decreases insulin secretion. Genetic modification of M3Rs causes robust alterations in insulin levels and glucose tolerance in mice. Olanzapine alters M3R density in discrete nuclei of the hypothalamus and caudal brainstem, regions that regulate glucose homeostasis and insulin secretion through vagal innervation of the pancreas. Furthermore, studies have demonstrated a dynamic sensitivity of hypothalamic and brainstem M3Rs to altered glucometabolic status of the body. Therefore, the M3R is in a prime position to influence glucose homeostasis through direct effects on pancreatic β-cells and by potentially altering signalling in the hypothalamus and brainstem. SGA-induced insulin dysregulation may be partly due to blockade of central and peripheral M3Rs, causing an initial disruption to insulin secretion and glucose homeostasis that can progressively lead to insulin resistance and diabetes during chronic treatment.