Effect of chronic treatment with typical and atypical neuroleptics on the expression of dopamine D2 and D3 receptors in rat brain

Oleanolic acid alleviates the extrapyramidal symptoms and cognitive impairment induced by haloperidol through the striatal PKA signaling pathway in mice

Haloperidol, one of the representative typical antipsychotics, is on the market for schizophrenia but shows severe adverse effects such as extrapyramidal symptoms (EPS) or cognitive impairments. Oleanolic acid (OA) is known to be effective for tardive dyskinesia which is induced by long-term treatment with L-DOPA. This study aimed to investigate whether OA could ameliorate EPS or cognitive impairment induced by haloperidol. The balance beam, catalepsy response, rotarod and vacuous chewing movement (VCM) tests were performed to measure EPS and the novel object recognition test was used to estimate haloperidol-induced cognitive impairment. Levels of dopamine and acetylcholine, the phosphorylation levels of c-AMP-dependent protein kinase A (PKA) and its downstream signaling molecules were measured in the striatum. OA significantly attenuated EPS and cognitive impairment induced by haloperidol without affecting its antipsychotic properties. Valbenazine only ameliorated VCM. Also, OA normalised the levels of dopamine and acetylcholine in the striatum which were increased by haloperidol. Furthermore, the increased phosphorylated PKA, extracellular signal-regulated kinase (ERK) and cAMP response element-binding protein (CREB) levels and c-FOS expression level induced by haloperidol were significantly decreased by OA in the striatum. In addition, cataleptic behaviour of haloperidol was reversed by sub-effective dose of H-89 with OA. These results suggest that OA can alleviate EPS and cognitive impairment induced by antipsychotics without interfering with antipsychotic properties via regulating neurotransmitter levels and the PKA signaling pathway in the striatum. Therefore, OA is a potential candidate for treating EPS and cognitive impairment induced by antipsychotics.

The relationship between excitement symptom severity and extrastriatal dopamine D2/3 receptor availability in patients with schizophrenia: a high-resolution PET study with [18F]fallypride

The purpose of this study was to investigate the relationship between specific symptom severity and D_2/3 receptor availability in extrastriatal regions in outpatients with schizophrenia to shed light on the role of extrastriatal dopaminergic neurotransmission in the pathophysiology of symptoms of schizophrenia. Sixteen schizophrenia patients receiving relatively low-dose maintenance atypical antipsychotics and seventeen healthy controls underwent 3-Tesla magnetic resonance imaging and high-resolution positron emission tomography with [¹⁸F]fallypride. For D_2/3 receptor availability, the binding potential with respect to non-displaceable compartment (BP_ND) was derived using the simplified reference tissue model. The BP_ND values were lower in patients on antipsychotic treatment than in controls across all regions with large effect sizes (1.03-1.42). The regions with the largest effect size were the substantia nigra, amygdala, and insula. Symptoms of schizophrenia were assessed using a five-factor model of the Positive and Negative Syndrome Scale (PANSS). The region of interest-based analysis showed that PANSS excitement factor score had a significant positive correlation with the [¹⁸F]fallypride BP_ND in the insula. The equivalent dose of antipsychotics was not significantly correlated with PANSS factor scores or regional BP_ND values. The voxel-based analysis also revealed a significant positive association between the PANSS excitement factor and the [¹⁸F]fallypride BP_ND in the insula. The present study revealed a significant association between excitement symptom severity and D_2/3 receptor availability in the insula in schizophrenia, suggesting a possible important role of D_2/3 receptor-mediated neurotransmission in the insula and related limbic system in the pathophysiology of this specific symptom cluster.

Calcium CaV1 channel subtype mRNA expression in Parkinson's disease examined by in situ hybridization

The factors which make some neurons vulnerable to neurodegeneration in Parkinson's disease while others remain resistant are not fully understood. Studies in animal models of Parkinson's disease suggest that preferential use of CaV1.3 subtypes by neurons may contribute to the neurodegenerative process by increasing mitochondrial oxidant stress. This study quantified the level of mRNA for the CaV1 subtypes found in the brain by in situ hybridization using CaV1 subtype-specific [(35)S]-radiolabelled oligonucleotide probes. In normal brain, the greatest amount of messenger RNA (mRNA) for each CaV1 subtype was found in the midbrain (substantia nigra), with a moderate level in the pons (locus coeruleus) and lower quantities in cerebral cortex (cingulate and primary motor). In Parkinson's disease, the level of CaV1 subtype mRNA was maintained in the midbrain and pons, despite cell loss in these areas. In cingulate cortex, CaV1.2 and CaV1.3 mRNA increased in cases with late-stage Parkinson's disease. In primary motor cortex, the level of CaV1.2 mRNA increased in late-stage Parkinson's disease. The level of CaV1.3 mRNA increased in primary motor cortex of cases with early-stage Parkinson's disease and normalized to near the control level in cases from late-stage Parkinson's disease. The finding of elevated CaV1 subtype expression in cortical brain regions supports the view that disturbed calcium homeostasis is a feature of Parkinson's disease throughout brain and not only a compensatory consequence to the neurodegenerative process in areas of cell loss.

Effects of antipsychotics on D3 receptors: a clinical PET study in first episode antipsychotic naive patients with schizophrenia using [11C]-(+)-PHNO

Most antipsychotics are thought to have an effect on D(2) and D(3) receptors, although their D(3), versus D(2) binding has not been clearly established in vivo in humans. However, the development of [(11)C]-(+)-PHNO now permits the differentiation of antipsychotic activity on these two receptor subtypes. In this study we examined the effects of antipsychotics on D(2) and D(3) receptors by comparing [(11)C]-(+)-PHNO in D(2)-rich (caudate, CAU and putamen, PUT), mixed (ventral striatum) and D(3)-rich (globus-pallidus, GP and substantia nigra, SN) regions before and after the initiation of antipsychotic medication. The investigation therefore represents a longitudinal within-subject follow-up design wherein antipsychotic-naive patients with schizophrenia spectrum disorders were first scanned in a drug-naïve state and then again after ~2.5 weeks of antipsychotic treatment (risperidone or olanzapine). Binding potential (non displaceable or BP(ND)) was obtained to derive estimates of drug occupancy in the identified brain regions. Antipsychotic treatment was associated with the expected occupancies in the D(2)-rich regions; unexpectedly though, patients showed a higher, rather than the expected lower, [(11)C]-(+)-PHNO BP(ND) in the GP and SN despite simultaneous evidence for ongoing D(2) blockade in the other regions (CAU and PUT). In conclusion, patients treated with atypical antipsychotics demonstrated no evidence of D(3) receptor occupancy, but instead possible D(3) up-regulation following short-term treatment. The present findings add to a very limited body of evidence related to D(3) binding in vivo. [(11)C]-(+)-PHNO offer new opportunities for exploring the potential therapeutic significance of the D(3) receptor in schizophrenia and the action of antipsychotics.

Blocking dopamine D2 receptors by haloperidol curtails the beneficial impact of calorie restriction on the metabolic phenotype of high-fat diet induced obese mice

Calorie restriction is the most effective way of expanding life-span and decreasing morbidity. It improves insulin sensitivity and delays the age-related loss of dopamine receptor D(2) (DRD2) expression in the brain. Conversely, high-fat feeding is associated with obesity, insulin resistance and a reduced number of DRD2 binding sites. We hypothesised that the metabolic benefit of calorie restriction involves the preservation of appropriate DRD2 transmission. The food intake of wild-type C57Bl6 male mice was restricted to 60% of ad lib. intake while they were treated with the DRD2 antagonist haloperidol or vehicle using s.c. implanted pellets. Mice with ad lib. access to food receiving vehicle treatment served as controls. All mice received high-fat food throughout the experiment. After 10 weeks, an i.p. glucose tolerance test was performed and, after 12 weeks, a hyperinsulinaemic euglycaemic clamp. Hypothalamic DRD2 binding was also determined after 12 weeks of treatment. Calorie-restricted (CR) vehicle mice were glucose tolerant and insulin sensitive compared to ad lib. (AL) fed vehicle mice. CR mice treated with haloperidol were slightly heavier than vehicle treated CR mice. Haloperidol completely abolished the beneficial impact of calorie restriction on glucose tolerance and partly reduced the insulin sensitivity observed in CR vehicle mice. The metabolic differences between AL and CR vehicle mice were not accompanied by alterations in hypothalamic DRD2 binding. In conclusion, blocking DRD2 curtails the metabolic effects of calorie restriction. Although this suggests that the dopaminergic system could be involved in the metabolic benefits of calorie restriction, restricting access to high-fat food does not increase (hypothalamic) DRD2 binding capacity, which argues against this inference.

Subchronic haloperidol increases CB(1) receptor binding and G protein coupling in discrete regions of the basal ganglia

The present study was designed to test whether chronic neuroleptic treatment, which is known to alter both expression and density of dopamine D(2) receptors in striatal regions, has effects upon function and binding level of the cannabinoid CB(1) receptor in the basal ganglia by using receptor autoradiography. As predicted, subchronic haloperidol treatment resulted in increased binding of (3)H-raclopride and quinpirole-induced guanosine 5'-O-(gamma-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) in the striatum when compared to that measured in control animals. This increased D(2) receptor binding and function after 3 days washout was normalized after a 2-week washout period. Effect of haloperidol treatment was studied for CB(1) receptor binding and CP55,940-stimulated [(35)S]GTPgammaS in the striatum, globus pallidus, and substantia nigra. (3)[H]CP55,940 binding levels were found in rank order from highest to lowest in substantia nigra > globus pallidus > striatum. Furthermore, subchronic haloperidol treatment resulted in elevated binding levels of (3)[H]CP55,940 in the striatum and the substantia nigra and CB(1) receptor-stimulated [(35)S]GTPgammaS bindings in the substantia nigra after 3 days washout. These increased binding levels were normalized at 1-4 weeks after termination of haloperidol treatment. Haloperidol treatment had no significant effect on CB(1) receptor or [(35)S]GTPgammaS binding levels in globus pallidus. The results help to elucidate the underlying biochemical mechanism of CB(1) receptor supersensitivity after haloperidol treatment.

Time-dependent changes in gene expression profiles of midbrain dopamine neurons following haloperidol administration

Antipsychotic drugs require a treatment regimen of several weeks before clinical efficacy is achieved in patient populations. While the biochemical mechanisms underlying the delayed temporal profile remain unclear, molecular adaptations in specific neuroanatomical loci are likely involved. Haloperidol-induced changes in gene expression in various brain regions have been observed; however, alterations in distinct neuronal populations have remained elusive. The present study examined changes in gene expression profiles of ventral tegmental area (VTA) and substantia nigra (SN) tyrosine hydroxylase immunopositive neurons following 1, 10 or 21 days of haloperidol administration (0.5 mg/kg/day). Macroarrays were used to study the expression of receptors, signaling proteins, transcription factors and pre- and post-synaptic proteins. Data were analyzed using conventional statistical procedures as well as self-organizing maps (SOM) to elucidate conserved patterns of expression changes. Results show statistically significant haloperidol-induced and time-dependent alterations in 17 genes in the VTA and 25 genes in the SN, including glutamate and GABA receptor subunits, signaling proteins and transcription factors. SOMs revealed distinct patterns of gene expression changes in response to haloperidol. Understanding how gene expression is altered over a clinically relevant time course of haloperidol administration may provide insight into the development of antipsychotic efficacy as well as the underlying pathology of schizophrenia.

Effects of acute citalopram treatment on the methamphetamine-induced locomotor activity

1. Previously the authors have shown that acute citalopram treatment increased the dopamine D2 receptor expression in rat brain striatum (Kameda et al., 2000). In the present study, the authors attempted to determine whether these effects of citalopram influence the methamphetamine-induced locomotor activity. 2. The pretreatment with a single administration of citalopram (10 mg/kg, i.p.) resulted in the significant enhancement of the locomoter activity induced by methamphetamine treatment (1 mg/kg, i.p.). The enhancement was observed 30 min, 12 hours, 24 hours, but not 7 days after withdrawal of citalopram administration. 3. Then the authors determined the methamphetamine concentration in rat brain striatum by gas chromatography-mass spectrometry (GC-MS) The results showed that the concentration of methamphetamine wars significantly higher in the rats 24 hours, and also 7 days after withdrawal of citalopram administration, compared to the control rats. 4. These results emphasized the involvement of the high methamphetamine concentration, caused by the pretreatment with citalopram, in the enhancement of the methamphetamine-induced locomotor activity. However high methamphetamine concentration alone could not account for this enhancement, since the high concentration of methamphetamine observed 7 days after withdrawal of citalopram administration did not appear to enhance the methamphetamine-induced locomotor activity. Another mechanism through which the pretreatment with citalopram enhanced the methamphetamine-induced locomotor activity, such as the increased expression of the dopamine D2 receptors, could not be excluded.

New dopamine receptor, D2(Longer), with unique TG splice site, in human brain

Brain dopamine receptor agonists alleviate the signs of Parkinson's disease, while dopamine receptor antagonists alleviate hallucinations and delusions in psychosis. The dopamine type 2 receptor (or D2) is blocked by antipsychotic drugs, including even the "atypical" drugs such as clozapine or remoxipride, in direct relation to their clinical potencies. Compared to the long form of the D2 receptor (D2(Long)), the short form (D2(Short)) may be three times more sensitive to benzamide antipsychotic drugs. Hence, it is essential to identify additional variants of dopamine receptors for which more selective antipsychotic drugs can be found. Although no family linkage has been found between the D2 receptor and schizophrenia, there can be brain region abnormalities in the RNA transcript expression of dopamine receptors. Therefore, in order to identify variant dopamine D2 receptors, we searched for mutations in the RNA transcripts for the dopamine D2 receptor in the striatum of post-mortem brains from individuals who died with psychosis, including schizophrenia. A new splice variant of the D2 receptor, D2(Longer), with a unique TG splice site, was found in one control brain and in two psychotic brains.

Differential behavioural effect of quinpirole in neuroleptic-pretreated rats - role of alpha(1)-adrenoceptor

This paper presents the effect of 14-day intraperitoneal (i.p.) neuroleptic treatment on the behavioural response of Wistar rats to (-)-quinpirole hydrochloride (3 mg/kg, i.p.) administered 24 h after the last neuroleptic dose. Chlorpromazine hydrochloride (10 mg/kg), haloperidol (2 mg/kg) or (+/-)-sulpiride (100 mg/kg) increased the effect of quinpirole; however, there were qualitative and quantitative differences between the neuroleptics. Chlorpromazine and haloperidol, but not sulpiride, pretreatment enhanced quinpirole-induced locomotor hyperactivity. Prazosin (0.5 mg/kg, i.p. ) given to chlorpromazine-treated rats 1 h before quinpirole attenuated the quinpirole-induced hyperlocomotion. In chlorpromazine-pretreated rats, quinpirole elicited defensive aggressive behaviour with vocalization, copulatory attempts, intense rearing and head-down sniffing. When prazosin was given before quinpirole, head-down sniffing and object-directed oral activity were mainly observed. In haloperidol-pretreated rats, quinpirole induced intense head-down sniffing, rearing, grooming and object-directed oral activity. In sulpiride-pretreated rats, quinpirole induced intense head-down sniffing, grooming and object-directed oral activity. The results of the study suggest that differences in the behavioural expression of dopamine D(2) receptor supersensitivity induced by neuroleptics may be, at least in part, caused by concurrent stimulation of alpha(1)-adrenoceptors.

Differential effects of treatment with typical and atypical antipsychotic drugs on adenylyl cyclase and G proteins

We examined the effects of chronic in vivo antipsychotic drug treatments on G protein function and regulation. Mice were treated with typical antipsychotic haloperidol (6 mg/kg per day) and atypical agent olanzapine (20 mg/kg per day) for 14 days via mini-osmotic pumps. G protein-activated adenylyl cyclase activity in brain tissues was measured in the presence of guanine nucleotide analogue guanosine-5'-O(3-thiotriphosphate) tetralithium salt, or GTPgammaS. In frontal cortex, haloperidol treatment produced 21% increases in the GTPgammaS -mediated adenylyl cyclase Emax value (vs. vehicle controls) while olanzapine produced 20% reductions in this value (vs. controls); these effects were significant. In striatum, olanzapine treatment produced significant 31 and 27% decreases in Emax values compared with vehicle and haloperidol treatment, respectively. Chronic haloperidol treatment produced significant 24% reductions in the immunoreactivity of cortical, but not striatal, Gialpha1,2 subunits. There were no effects of chronic olanzapine treatment on G(i)alpha1,2 levels and no effects of either antipsychotic on G(s)alpha, levels. Chronic haloperidol and olanzapine treatments differentially regulate G protein-mediated adenylyl cyclase responses in brain regions possibly relating to their unique effects on G protein-coupled receptors.

Differential effects of acute and chronic treatment with typical and atypical neuroleptics on c-fos mRNA expression in rat forebrain regions using non-radioactive in situ hybridization

The regional difference in the expression of c-fos mRNA in rat forebrain after either acute or chronic administration of typical (haloperidol and fluphenazine) and atypical neuroleptics (clozapine and (+/-)-sulpiride) was investigated. Rats were injected intraperitoneally with vehicle or neuroleptics daily for 14 days. Twenty-four hours after the last injection, the rats were challenged with vehicle or neuroleptics. C-fos mRNA expression was determined by non-radioactive in situ hybridization. Acute treatment with typical neuroleptics induced a remarkable induction of c-fos mRNA in the dorsolateral striatum, whereas this induction was greatly attenuated by chronic administration. All neuroleptics examined induced c-fos mRNA in the shell region of N. accumbens by acute administration and this expression was still elevated after chronic treatment. Since chronic neuroleptics do not induce tolerance to their antipsychotic activities, our study suggests that the shell region of N. accumbens is an important target site for antipsychotic effects of neuroleptics.

Effects of acute or long-term treatment with chlorpromazine, haloperidol or sulpiride on neuropeptide Y-like immunoreactivity concentrations in the nucleus accumbens of rat

The effects of acute, subchronic ( 14 days) or chronic (28 days) intraperitoneal (i.p.) administration of chlorpromazine (2 or 10 mg/kg), haloperidol (0.5 or 2 mg/kg) or sulpiride (50 or 100 mg/kg) on the neuropeptide Y (NPY) system in the rat nucleus accumbens were studied. NPY-like immunoreactivity (NPY-LI) decreased in a dose- and time-dependent manner, and was the lowest after haloperidol. NPY-LI levels increased 8 days after withdrawal of chronic drugs treatment. Acute administration of haloperidol reduced NPY mRNA, while Subchronic treatment did not change it. Subchronic i.p. administration of the dopamine D1-like antagonist SCH 23390 (1 mg/kg) reduced NPY-LI levels but the alpha1-adrenergic antagonist prazosin (0.2 mg/kg) had no effect. The effect of sulpiride coadministered with SCH 23390 was greater than that of SCH 23390 alone, while prazosin coadministered with sulpiride insignificantly reduced the effect of sulpiride. The dopamine D2/D3 agonist quinpirole given as a single injection (3 mg/kg) did not alter NPY-LI content by itself but antagonized the chlorpromazine-induced decrease and attenuated the haloperidol-induced decrease. Our findings indicate that the accumbens NPY system is markedly affected by the antipsychotics studied, and suggest that their effects may be in part mediated by blockade of D2-like (D2, D3) and D1 dopaminergic receptors.

Effect of chronic haloperidol treatment on synaptic protein mRNAs in the rat brain

Chronic haloperidol treatment caused significant decreases in the levels of synaptotagmin I and IV, synaptobrevin II, syntaxin 1A and Rab 3A mRNAs in the nucleus accumbens but not in the prefrontal cortex medial field, striatum, substantia nigra and ventral tegmental area. No significant changes in SNAP 25 and synaptophysin mRNA levels were observed in any brain region examined. The reduced expression of synaptic proteins may be related to haloperidol-induced depolarization block of mesolimbic dopamine neurons.

Influence of typical and atypical antipsychotics on neuropeptide Y-like immunoreactivity and NPY mRNA expression in rat striatum

Striatal neuropeptide Y-like immunoreactivity (NPY-LI) levels were investigated in naive rats after acute, subchronic (14 days) or chronic (28 days) intraperitoneal (i.p.) treatment with chlorpromazine (2 or 10mg/kg), haloperidol (0.5 or 2 mg/kg), (+/-)sulpiride (50 or 100 mg/kg) or clozapine (10 or 25 mg/kg), and in chronically treated rats after 8-day drug withdrawal. The most pronounced changes in NPY-LI levels were found 24 h after acute chlorpromazine or haloperidol administration (a decrease) and after withdrawal of chlorpromazine, haloperidol or sulpiride (an increase). The effect of clozapine on NPY-LI differed from those of the other antipsychotics: both single doses had no effect, the higher chronic dose increased NPY-LI levels, and its withdrawal resulted in their decrease. No significant alterations were detected in the hybridization signal of NPY mRNA in response to acute or subchronic administration of haloperidol or clozapine. Our results suggest that the effects of antipsychotics are in part mediated by blockade of dopamine D2-like (D2/D3) or serotonin 5HT2A receptors but not dopamine D1, D4 or alpha1-adrenergic receptors. The antipsychotic-induced changes in NPY system activity has been discussed in connection with adaptive alterations in the dopamine system.

Dopamine receptor mRNAs in the rat lymphocytes

It has been suggested that dopamine might play a role in the regulation of the immune system. In this study, reverse transcriptase-polymerase chain reaction (RT-PCR) was used to investigate the expression of mRNA for the different subtypes of dopamine receptors in the rat lymphocytes. D1, D3 and D5 receptor mRNAs were identified. These results provide further evidence for the interaction of dopamine systems and the immune system, and suggest to further investigate whether the immunosuppressive actions of dopamine and dopaminergic drugs might depend on a direct interaction with dopamine receptors on the lymphocyte membrane. Moreover, they suggest the suitability of this animal species to further investigate the correlation between changes in the expression of central and peripheral dopamine receptors produced by manipulations of the dopamine systems.