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

Olanzapine's effects on hypothalamic transcriptomics and kinase activity

Olanzapine is a second-generation antipsychotic that disrupts metabolism and is associated with an increased risk of type 2 diabetes. The hypothalamus is a key region in the control of whole-body metabolic homeostasis. The objective of the current study was to determine how acute peripheral olanzapine administration affects transcription and serine/threonine kinase activity in the hypothalamus. Hypothalamus samples from rats were collected following the pancreatic euglycemic clamp, thereby allowing us to study endpoints under steady state conditions for plasma glucose and insulin. Olanzapine stimulated pathways associated with inflammation, but diminished pathways associated with the capacity to combat endoplasmic reticulum stress and G protein-coupled receptor activity. These pathways represent potential targets to reduce the incidence of type 2 diabetes in patients taking antipsychotics.

Effects of the antipsychotic drug haloperidol on the somastostatinergic system in SH-SY5Y neuroblastoma cells

Antipsychotics are established drugs in schizophrenia treatment which, however, are not free of side effects. Lipid rafts are critical for normal brain function. Several G protein-coupled receptors, such as somatostatin (SRIF) receptors, have been shown to localize to lipid rafts. The aim of this study was to investigate whether haloperidol treatment affects the composition and functionality of lipid rafts in SH-SY5Y neuroblastoma cells. Haloperidol inhibited cholesterol biosynthesis, leading to a marked reduction in cell cholesterol content and to an accumulation of sterol intermediates, particularly cholesta-8,14-dien-3beta-ol. These changes were accompanied by a loss of flotillin-1 and Fyn from the lipid rafts. We next studied the functionality of the SRIF receptor. Treatment with haloperidol reduced the inhibitory effect of SRIF on adenylyl cyclase (AC) activity. On the other side, haloperidol decreased basal AC activity but increased forskolin-stimulated AC activity. Addition of free cholesterol to the culture medium abrogated the effects of haloperidol on lipid raft composition and SRIF signaling whereas the AC response to forskolin remained elevated. The results show that haloperidol, by affecting cholesterol homeostasis, ultimately alters SRIF signaling and AC activity, which might have physiological consequences.

Antipsychotic drugs: comparison in animal models of efficacy, neurotransmitter regulation, and neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D(2) receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

Antipsychotic-induced alterations in CB1 receptor-mediated G-protein signaling and in vivo pharmacology in rats

Dysregulation of the endocannabinoid and dopamine systems has been implicated in schizophrenia. The purpose of this study was to examine the effects of sub-chronic treatment with two antipsychotics on CB1 receptor-mediated in vitro and in vivo effects. Adult and adolescent male and female rats were injected twice daily with haloperidol (0.3 mg/kg), clozapine (10 mg/kg), or saline for 10 days. Subsequently, CB1 receptor number and function were assessed by [3H]SR141716 and WIN55,212-2-stimulated [35S]GTPgammaS binding, respectively. The effects of sub-chronic antipsychotic treatment on the in vivo actions of Delta9-tetrahydrocannabinol (Delta9-THC) were also evaluated. In adult female rats, antipsychotic treatment attenuated maximal stimulation of CB1 receptor-mediated G-protein activity in the striatum (clozapine) and prefrontal cortex (both antipsychotics), but not in the ventral midbrain. Associated changes in CB1 receptor number were not observed, suggesting that this attenuation was not due to downregulation. In vivo, sub-chronic treatment with clozapine, but not haloperidol, attenuated Delta9-THC-induced suppression of activity in adult females, whereas neither drug altered hypothermia or catalepsy. In contrast, antipsychotic treatment did not change CB1 receptor-mediated G-protein activation in any brain region in adult male rats and in adolescents of either sex. In vivo, haloperidol, but not clozapine, enhanced Delta9-THC-mediated suppression of activity and hypothermia in adult male rats whereas neither antipsychotic affected Delta9-THC-induced in vivo effects in adolescent rats. These findings suggest that modulation of the endocannabinoid system might contribute in a sex- and age-selective manner to differences in motor side effects of clozapine versus haloperidol.

Gene expression changes in peripheral mononuclear cells from schizophrenic patients treated with a combination of antipsychotic with fluvoxamine

Antipsychotic treatment combined with Selective Serotonin Reuptake Inhibitor (SSRI) antidepressant can improve negative symptoms in schizophrenic patients that are unresponsive to antipsychotic drugs alone. The mechanism of this therapeutic effect is not clear. The current study examined molecular changes induced by the combined treatment in human peripheral mononuclear cells (PMC) in order to get insight into its mechanism of action. Gene expression profile of PMC from antipsychotic-treated patients was examined before addition of the SSRI fluvoxamine, and 3 and 6 weeks after. Gene expression patterns screened with a cDNA array, comprising 1176 genes, revealed homologous changes in a range of transcripts related to G-protein coupled receptors (GPCR). Genes related to GPCR-family were assayed using customized cDNA array and the results verified by real-time RT-PCR. The mRNA expression of chemokine receptors, IL8RA and CCR1, and of RGS7 was significantly down-regulated following fluvoxamine augmentation. The clinical assessments showed improvement in negative symptoms following the combined treatment. The transcriptional analysis suggests that the therapeutic mechanism of the combined antipsychotic-fluvoxamine treatment may involve genes associated with G-protein coupled receptors (GPCR). Our findings suggest that gene expression changes in PMC may be useful in investigating the mechanism of drug action in schizophrenia.

Differential effects of spinal 5-HT1A receptor activation and 5-HT2A/2C receptor desensitization by chronic haloperidol

The effects of 7- and 21-day haloperidol treatment on the spinal serotonergic system were examined in vivo in acutely spinalized adult rats. Intravenous administration of a selective 5-HT(2A/2C) receptor agonist, (+/-)-2,5-Dimethoxy-4-iodoamphetamine hydrochloride (0.1 mg/kg) significantly increased the excitability of spinal motoneurones as reflected by increased monosynaptic mass reflex amplitude. This was significantly reduced in rats treated with haloperidol (1 mg/kg/day, i.p.) for 7 and 21 days. Administration of a 5-HT(1A/7) receptor agonist, (+/-)-8-Hydroxy dipropylaminotetraline hydrobromide (0.1 mg/kg, i.v.) significantly inhibited the monosynaptic mass reflex. This inhibition was greatly prolonged in haloperidol treated animals. These results demonstrate that the effects of haloperidol on the activation and desensitization of 5-HT(1A) and 5-HT(2A/2C) receptors respectively, may be mediated via intracellular mechanisms shared by these receptors with dopamine D(2) receptors in the mammalian spinal cord. The above serotonergic mechanisms may be partly responsible for haloperidol-induced extrapyramidal motor dysfunction.

Constitutive activation of Galphas within forebrain neurons causes deficits in sensorimotor gating because of PKA-dependent decreases in cAMP

Sensorimotor gating, the ability to automatically filter sensory information, is deficient in a number of psychiatric disorders, yet little is known of the biochemical mechanisms underlying this critical neural process. Previously, we reported that mice expressing a constitutively active isoform of the G-protein subunit Galphas (Galphas(*)) within forebrain neurons exhibit decreased gating, as measured by prepulse inhibition of acoustic startle (PPI). Here, to elucidate the biochemistry regulating sensorimotor gating and to identify novel therapeutic targets, we test the hypothesis that Galphas(*) causes PPI deficits via brain region-specific changes in cyclic AMP (cAMP) signaling. As predicted from its ability to stimulate adenylyl cyclase, we find here that Galphas(*) increases cAMP levels in the striatum. Suprisingly, however, Galphas(*) mice exhibit reduced cAMP levels in the cortex and hippocampus because of increased cAMP phosphodiesterase (cPDE) activity. It is this decrease in cAMP that appears to mediate the effect of Galphas(*) on PPI because Rp-cAMPS decreases PPI in C57BL/6J mice. Furthermore, the antipsychotic haloperidol increases both PPI and cAMP levels specifically in Galphas(*) mice and the cPDE inhibitor rolipram also rescues PPI deficits of Galphas(*) mice. Finally, to block potentially the pathway that leads to cPDE upregulation in Galphas(*) mice, we coexpressed the R(AB) transgene (a dominant-negative regulatory subunit of protein kinase A (PKA)), which fully rescues the reductions in PPI and cAMP caused by Galphas(*). We conclude that expression of Galphas(*) within forebrain neurons causes PPI deficits because of a PKA-dependent decrease in cAMP and suggest that cAMP PDE inhibitors may exhibit antipsychotic-like therapeutic effects.

Serotonin 1a receptor and associated G-protein activation in schizophrenia and bipolar disorder

Abnormalities in the serotonergic signalling system, including the serotonin 1a receptor, have been implicated in the pathogenesis of schizophrenia and bipolar 1 disorder. However, there is no consensus on whether the density of the serotonin 1a receptor and/or the activity of the G-proteins linking the receptor to the intracellular cascade are altered in these disease states. To address these issues, tissue obtained postmortem from four cortical regions was used to measure [3H] 8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT) binding and 8-OH-DPAT-stimulated guanosine 5'-[gamma-thio]triphosphate (GTPgammaS) binding to determine if either parameter is altered in schizophrenia or bipolar I disorder. There was an effect of diagnosis on the level of [3H] 8-OH-DPAT binding that may indicate a global change in the density of serotonin 1a receptors, although this effect did not reach significance in any individual brain region. The activation of serotonin 1a receptors did not differ significantly with diagnoses. However, in the outer cortical layers, there appeared to be a dissociation between the number of receptors available and the extent of ligand-induced GTPgammaS binding, suggesting considerable receptor reserve. In addition, comparing gender independent of diagnoses, a decrease in the levels of serotonin 1a receptors was observed in the cortex of female subjects. These data indicates that there may be subtle changes in serotonin 1a receptors across the cortex in schizophrenia or bipolar I disorder and suggests a gender discordance in receptor levels.

Antipsychotic-induced alterations in D2 dopamine receptor interacting proteins within the cortex

Current antipsychotic treatment involves the regulation of D2 dopamine receptor activity in the brain. Here, we examined the effects of chronic haloperidol and clozapine on cortical D2 dopamine receptors and six different dopamine receptor interacting proteins. Using comparative immunoblot analysis, we found that treatment with either haloperidol or clozapine increased D2 dopamine receptors, calcium activator protein for secretion, protein 4.1N, and neuronal calcium sensor-1 expression. Treatment with clozapine increased calmodulin and spinophilin expression, while treatment with haloperidol decreased expression of these two dopamine receptor interacting proteins. Neither antipsychotic drug was found to have an effect on filamin-A expression. These findings underscore a role for cortical D2 dopamine receptor in the mechanism of antipsychotic drug action, and suggest dopamine receptor interacting proteins as novel targets in antipsychotic drug development.

Effects of chronic olanzapine and haloperidol differ on the mouse N1 auditory evoked potential

Auditory evoked potentials have been used in a variety of animal models to assess information-processing impairments in schizophrenia. Previous mouse models have primarily employed a paired click paradigm to assess the transient measures of auditory gating. The current study uses stimulus trains at varied interstimulus intervals (ISI) between 0.25 and 8 s in mice to assess the effects of chronic olanzapine and haloperidol on auditory processing. Data indicate that olanzapine increases the amplitude of the N40, P80, and P20/N40 components of the auditory evoked potential, whereas haloperidol had no such effect. The ISI paradigm also allowed for an evaluation of several components of the mouse evoked potential to assess those that display response properties similar to the human P50 and N100. Data suggest that the mouse N40 displays an ISI response relationship that shares characteristics with the human N100, whereas the P20 appears more consistent with the human P50 across the ISI range evaluated in this task. This study suggests that olanzapine may help improve N100 impairments seen in schizophrenia, while haloperidol does not.

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.

Differential effects of haloperidol and clozapine on [(3)H]cAMP binding, protein kinase A (PKA) activity, and mRNA and protein expression of selective regulatory and catalytic subunit isoforms of PKA in rat brain

The present study was undertaken to examine whether the mechanism of action of typical and atypical antipsychotics is related in their ability to regulate key phosphorylating enzyme of adenylyl cyclase-cAMP pathway, i.e., protein kinase A (PKA). For this purpose, regulatory (R) and catalytic (Cat) activities of PKA and expression of various isoforms of regulatory and catalytic subunits were examined in rat brain after single or chronic (21-day) treatment with haloperidol (HAL, 1 mg/kg) or clozapine (CLOZ, 20 mg/kg). It was observed that chronic but not acute treatment of CLOZ significantly decreased [(3)H]cAMP binding to the regulatory subunit of PKA as well as catalytic activity of PKA in particulate and cytosol fractions of the rat cortex, hippocampus, and striatum. In these fractions, CLOZ significantly decreased protein levels of selective RII alpha-, RII beta-, and Cat beta-subunit isoforms of PKA. These decreases were accompanied by decreases in their respective mRNA expression. In contrast, chronic but not acute treatment of HAL significantly increased [(3)H]cAMP binding and the catalytic activity of PKA in particulate and cytosol fractions of only the striatum brain area. In addition, chronic treatment of HAL significantly increased mRNA and protein levels of RII alpha- and RII beta-subunit isoforms in the striatum. None of the antipsychotics caused any change in the expression of the Cat alpha-, RI alpha-, or RI beta-subunit isoform. These results, thus, suggest that HAL and CLOZ differentially regulate PKA catalytic and regulatory activities and the expression of selective catalytic and regulatory subunit isoforms of PKA, which may be associated with their mechanisms of action.

Decrease of adenylyl cyclase activity and expression by a sigma1 receptor ligand and putative atypical antipsychotic

We examined whether changes in the adenylyl cyclase system could be induced by the administration of the sigma1 receptor ligand and putative atypical antipsychotic 4-[4-fluorophenyl]-1,2,3,6-tetrahydro-1-[4-[1,-2,4-triazol-1-il]butyl]pyridine citrate) (E-5842). Repeated (21 days) but not acute (2 h) treatment with E-5842 induced a significant decrease in adenylyl cyclase type I immunoreactivity and adenylyl cyclase activity in rat frontal cortex membranes, with less or no effect in other brain regions such as the hippocampus or the striatum. Changes in immunoreactivity were not observed in other adenylyl cyclases (type V/VI). The reported changes, observed only after a chronic treatment, could be related to the mechanism of action of sigma receptor ligands in general or to that of E-5842 in particular and should be taken into account, given the long duration of treatment in psychiatric patients.

Stimulation of high-affinity GTPase activity through group II metabotropic glutamate receptors in rat hippocampal and striatal membranes

The stimulation of high-affinity GTPase activity through metabotropic glutamate receptors (mGluRs) was pharmacologically characterized with the use of a series of agonists for mGluRs in rat hippocampal and striatal membranes. The pharmacological profile of the response was almost identical to each other between both brain regions. Thus, the high-affinity GTPase activities were stimulated by several mGluR-related compounds with the following rank order of potency: (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) = (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine (L-CCG-I) > L-glutamate = 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate [(2R,4R)-APDC] > (S)-4-carboxy-3-hydroxyphenylglycine [(S)-4C3HPG] = 1S,3R-1-aminocyclopentane-1,3-dicarboxylate [(1S,3R)-ACPD] > (S)-3-carboxy-4-hydroxyphenylglycine [(S)-3C4HPG] = ibotenate. The negative logarithmically transformed EC50 (pEC50) values of these compounds in both brain regions were significantly correlated with those reported previously in the cerebral cortical membranes (N. Nishi et al., Br. J. Pharmacol., 130, 1664-1670, 2000). On the contrary, other reagents including a selective group I mGluRs agonist, (RS)-3,5-dihydroxyphenylglycine [(RS)-3,5-DHPG], and selective group III mGluRs agonists such as L(+)-2-amino-4-phosphonobutylate (L-AP4) and L-serine-O-phosphate (L-SOP) had little or no effects even at the highest concentration examined. Quisqualate was also a very weak agonist in both regions. These results indicate that mGluR-mediated high-affinity GTPase activity derives from the Gi proteins associated with adenylyl cyclase inhibition through group II mGluRs, in particular the mGluR2 subtype, in rat hippocampal and striatal membranes.