Effects of haloperidol, lithium, and valproate on phosphoinositide turnover in rat brain

Chronic administration of valproic acid reduces brain NMDA signaling via arachidonic acid in unanesthetized rats

Evidence that brain glutamatergic activity is pathologically elevated in bipolar disorder suggests that mood stabilizers are therapeutic in the disease in part by downregulating glutamatergic activity. Such activity can involve the second messenger, arachidonic acid (AA, 20:4n - 6). We tested this hypothesis with regard to valproic acid (VPA), when stimulating glutamatergic N-methyl-D: -aspartate (NMDA) receptors in rat brain and measuring AA and related responses. An acute subconvulsant dose of NMDA (25 mg/kg i.p.) or saline was administered to unanesthetized rats that had been treated i.p. daily with VPA (200 mg/kg) or vehicle for 30 days. Quantitative autoradiography following intravenous [1-(14)C]AA infusion was used to image regional brain AA incorporation coefficients k*, markers of AA signaling. In chronic vehicle-pretreated rats, NMDA compared with saline significantly increased k* in 41 of 82 examined brain regions, many of which have high NMDA receptor densities, and also increased brain concentrations of the AA metabolites, prostaglandin E(2) (PGE(2)) and thromboxane B(2) (TXB(2)). VPA pretreatment reduced baseline concentrations of PGE(2) and TXB(2), and blocked the NMDA induced increases in k* and in eicosanoid concentrations. These results, taken with evidence that carbamazepine and lithium also block k* responses to NMDA in rat brain, suggest that mood stabilizers act in bipolar disorder in part by downregulating glutamatergic signaling involving AA.

Mimicking human bipolar ion dysregulation models mania in rats

Psychiatric diseases in general, and bipolar illness in particular, are difficult to model in animals since the subjective nature of the core symptoms appears to preclude objective observation of behavioral changes. An adequate animal model of a psychiatric condition must fulfill three core criteria: share pathophysiological characteristics of the human condition (face validity), have similar behavioral manifestations as the human disease (construct validity), and improve with medications that improve the symptoms seen in afflicted humans (predictive validity). The ouabain model for bipolar illness mimics a widely reproduced biologic abnormality in mania: reduced sodium pump activity. An intracerebroventricular (ICV) administration of 5microL 10(-3)M ouabain induces motoric hyperactivity preventable by lithium, carbamazepine, and haloperidol. ICV ouabain may also produce environmentally dependent hypoactivity. The model, however, has not yet been examined for other potential manic behavior in rats such as reduced need for sleep, increased sexual activity, or increased irritability. While additional characterization of the model is required, the ouabain model for bipolar illness is the only available animal model that fulfills the three criteria for an adequate animal model for bipolar illness.

Efficacy of olanzapine and haloperidol in an animal model of mania

PURPOSE

Intracerebroventricular (ICV) administration of ouabain, a potent sodium pump inhibitor, has been used to model mania. Antipsychotic agents have demonstrated efficacy in the management of acute mania. This study was undertaken to determine the prophylactic efficacy of olanzapine and haloperidol in the ouabain mania model.

METHODS

Male Sprague-Dawley rats (4-8/group) were treated with two haloperidol decanoate intramuscular shots one week apart (21 mg/kg) or twice daily olanzapine intraperitoneal injections at low dose (1 mg/kg/day) or high dose (6 mg/kg/day) for 7 days prior to ICV administration of ouabain. Open field locomotion was quantified at baseline and after ouabain administration.

RESULTS

Ouabain caused a significant increase in open field locomotion (253.7+/-SEM 55.12 vs control 53.1+/-12.13 squares traversed in 30 min in the olanzapine experiments, P<0.05; and 236.5+/-41.42 vs 129.3+/-38.23, P<0.05 in the haloperidol experiments). Olanzapine alone at low dose (102.2+/-37.7) or high dose (151.2+/-49.2) did not alter open field activity. Low dose olanzapine (176.6+/-73.27) but not high dose (307.5+/-167.32) caused a modest reduction of the ouabain effect. Haloperidol alone significantly reduced motoric activity compared to control (55.6+/-18.0, P<0.05), and prevented ouabain-induced hyperactivity (60.3+/-33.1, P<0.05).

CONCLUSION

Haloperidol, but not olanzapine, demonstrated efficacy in this mania model, but methodological details may have reduced the effect of olanzapine.

Lithium and valproate attenuate dextroamphetamine-induced changes in brain activation

BACKGROUND

Previous studies have suggested that both lithium and valproate may decrease phosphoinositol second messenger system (PI-cycle) activity. There is also evidence that dextroamphetamine may increase PI cycle activity. It was previously demonstrated that dextroamphetamine administration in volunteers causes a region and task dependent decrease in brain activation in healthy volunteers. The current study assessed the effect of 14 days pretreatment with lithium and valproate on these dextroamphetamine-induced changes in regional brain activity in healthy volunteers.

METHODS

This was a double-blind, placebo-controlled, study in which volunteers received either 1000 mg sodium valproate (n = 12), 900 mg lithium (n = 9) or placebo (n = 12). Functional images were acquired using functional magnetic resonance imaging (fMRI) while subjects performed three cognitive tasks, a word generation paradigm, a spatial attention task and a working memory task. fMRI was carried out both before and after administration of dextroamphetamine (25 mg). Changes in the number of activated pixels and changes in the magnitude of the blood-oxygen-level-dependent (BOLD) signal after dextroamphetamine administration were then determined.

RESULTS

In keeping with previous findings dextroamphetamine administration decreased regional brain activation in all three tasks. Pretreatment with lithium attenuated changes in the word generation paradigm and the spatial attention task, while pretreatment with valproate attenuated the changes in the working memory task.

CONCLUSIONS

These results suggest that both lithium and valproate can significantly attenuate dextroamphetamine-induced changes in brain activity in a task dependent and region specific manner. This is the first human evidence to suggest that both lithium and valproate may have a similar effect on regional brain activation, conceivably via similar effects on PI-cycle activity.

Bipolar disorder and myo-inositol: a review of the magnetic resonance spectroscopy findings

OBJECTIVES

Myo-inositol is an important component of the phosphatidylinositol second messenger system (PI-cycle). Alterations in PI-cycle activity have been suggested to be involved in the pathophysiology and/or treatment of bipolar disorder. More specifically, lithium has been suggested to act primarily by lowering myo-inositol concentrations, the so-called inositol-depletion hypothesis. myo-Inositol concentrations can be measured in vivo with magnetic resonance spectroscopy (MRS).

METHODS

The current review primarily examines animal and human MRS studies that evaluated the role of myo-inositol in bipolar illness and treatment.

RESULTS

Studies have been carried out in patients who are manic, depressed, and euthymic, both on and off treatment. However, there are several limitations of these studies.

CONCLUSIONS

The preclinical and clinical MRS findings were generally supportive of the involvement of myo-inositol in bipolar disorder and its treatment. Overall, in bipolar patients who are manic or depressed there are abnormalities in brain myo-inositol concentrations, with changes in frontal and temporal lobes, as well as the cingulate gyrus and basal ganglia. These abnormalities are not seen in either euthymic patients or healthy controls, possibly due to a normalizing effect of treatment with either lithium or sodium valproate. There is also increasing evidence that sodium valproate may also act upon the PI-cycle. Nonetheless, it remains uncertain if these changes in myo-inositol concentration are primary or secondary. Findings regarding the specific inositol-depletion hypothesis are also generally supportive in acutely ill patients, although it is not yet possible to definitively confirm or refute this hypothesis based on the current MRS evidence.

Effects of valproic acid derivatives on inositol trisphosphate depletion, teratogenicity, glycogen synthase kinase-3beta inhibition, and viral replication: a screening approach for new bipolar disorder drugs derived from the valproic acid core structure

Inositol-1,4,5-trisphosphate (InsP3) depletion has been implicated in the therapeutic action of bipolar disorder drugs, including valproic acid (VPA). It is not currently known whether the effect of VPA on InsP3 depletion is related to the deleterious effects of teratogenicity or elevated viral replication, or if it occurs via putative inhibitory effects on glycogen synthase kinase-3beta (GSK-3beta). In addition, the structural requirements of VPA-related compounds to cause InsP3 depletion are unknown. In the current study, we selected a set of 10 VPA congeners to examine their effects on InsP3 depletion, in vivo teratogenic potency, HIV replication, and GSK-3beta activity in vitro. We found four compounds that function to deplete InsP3 in the model eukaryote Dictyostelium discoideum, and these drugs all cause growth-cone enlargement in mammalian primary neurons, consistent with the effect of InsP3 depletion. No relationship was found between InsP3 depletion and teratogenic or elevated viral replication effects, and none of the VPA congeners were found to affect GSK-3beta activity. Structural requirements of VPA congers to maintain InsP3 depletion efficacy greater than that of lithium are a carboxylic-acid function without dependence on side-chain length, branching, or saturation. Noteworthy is the enantiomeric differentiation if a chiral center exists, suggesting that InsP3 depletion is mediated by a stereoselective mode of action. Thus, the effect of InsP3 depletion can be separated from that of teratogenic potency and elevated viral replication effect. We have used this to identify two VPA derivatives that share the common InsP3-depleting action of VPA, lithium and carbamazepine, but do not show the side effects of VPA, thus providing promising novel candidates for bipolar disorder treatment.

Antipsychotic drug treatment alters expression of mRNAs encoding lipid metabolism-related proteins

Using an automated PCR-based genomics approach, TOtal Gene expression Analysis (TOGA), we have examined gene expression profiles of mouse striatum and frontal cortex in response to clozapine and haloperidol drug treatment. Of 17 315 mRNAs observed, TOGA identified several groups of related molecules that were regulated by drug treatment. The expression of some genes encoding proteins involved in neurotransmission, signal transduction, oxidative stress, cell adhesion, apoptosis and proteolysis were altered in the brains of both clozapine- and haloperidol-treated mice as recognized by TOGA. Most notable was the differential expression of those genes whose products are associated with lipid metabolism. These include apolipoprotein D (apoD), the mouse homolog of oxysterol-binding protein-like protein 8 (OSBPL8), a diacylglycerol receptor (n-chimerin), and lysophosphatidic acid (LPA) acyltransferase. Real-time PCR analysis confirmed increases in the RNA expression of apoD (1.6-2.2-fold) and OSBPL8 (1.7-2.6-fold), and decreases in the RNA expression of n-chimerin (1.5-2.2-fold) and LPA acyltransferase (1.5-fold) in response to haloperidol and/or clozapine treatment. Additional molecules related to calcium homeostasis and signal transduction, as well as four sequences of previously unidentified mRNAs, were also confirmed by real-time PCR to be regulated by drug treatment. While antipsychotic drugs may affect several metabolic pathways, lipid metabolism/signaling pathways may be of particular importance in the mechanisms of antipsychotic drug action and in the pathophysiology of psychiatric disorders.

Lithium and valproate decrease inositol mass and increase expression of the yeast INO1 and INO2 genes for inositol biosynthesis

Bipolar affective disorder (manic-depressive illness) is a chronic, severe, debilitating illness affecting 1-2% of the population. The Food and Drug Administration-approved drugs lithium and valproate are not completely effective in the treatment of this disorder, and the mechanisms underlying their therapeutic effects have not been established. We are employing genetic and molecular approaches to identify common targets of lithium and valproate in the yeast Saccharomyces cerevisiae. We show that both drugs affect molecular targets in the inositol metabolic pathway. Lithium and valproate cause a decrease in intracellular myo-inositol mass and an increase in expression of both a structural (INO1) and a regulatory (INO2) gene required for inositol biosynthesis. The opi1 mutant, which exhibits constitutive expression of INO1, is more resistant to inhibition of growth by lithium but not by valproate, suggesting that valproate may inhibit the Ino1p-catalyzed synthesis of inositol 1-phosphate. Consistent with this possibility, growth in valproate leads to decreased synthesis of inositol monophosphate. Thus, both lithium and valproate perturb regulation of the inositol biosynthetic pathway, albeit via different mechanisms. This is the first demonstration of increased expression of genes in the inositol biosynthetic pathway by both lithium and valproate. Because inositol is a key regulator of many cellular processes, the effects of lithium and valproate on inositol synthesis have far-reaching implications for predicting genetic determinants of responsiveness and resistance to these agents.

Chronic valproate treatment decreases the in vivo turnover of arachidonic acid in brain phospholipids: a possible common effect of mood stabilizers

Both (Li(+)) and valproic acid (VPA) are effective in treating bipolar disorder, but the pathway by which either works, and whether it is common to both drugs, is not agreed upon. We recently reported, using an in vivo fatty acid model, that Li(+) reduces the turnover rate of the second messenger arachidonic acid (AA) by 80% in brain phospholipids of the awake rat, without changing turnover rates of docosahexaenoic or palmitic acid. Reduced AA turnover was accompanied by down-regulation of gene expression and protein levels of an AA-specific cytosolic phospholipase A(2) (cPLA(2)). To see if VPA had the same effect on AA turnover, we used our in vivo fatty acid model in rats chronically administered VPA (200 mg/kg, i.p. for 30 days). Like Li(+), VPA treatment significantly decreased AA turnover within brain phospholipids (by 28-33%), although it had no effect on cPLA(2) protein levels. Thus, both mood stabilizers, Li(+) and VPA have a common action in reducing AA turnover in brain phospholipids, albeit by different mechanisms.

A novel evidence of different mechanisms of lithium and valproate neuroprotective action on human SY5Y neuroblastoma cells: caspase-3 dependency

Both lithium and valproate have been used in the treatment of manic-depressive illness with very limited understanding of their therapeutic mechanism of action. Recent literature suggests that blocking of potassium channels may be a common therapeutic mechanism of many antidepressant agents. To determine whether the commonly used antimanic agents could prevent potassium efflux-induced cell damage and apoptosis and the underlying mechanisms, we treated SH-SY5Y human neuroblastoma cells with the potassium ionophore, valinomycin (2-100 microM) and observed cell shrinkage, mitochondria damage, a significant increase in of lactate dehydrogenase (LDH) activity and caspase-3 protein expression. Cells treated with lithium (0.5-3 mM) or valproate (0.07-1.4 mM) alone produced no apoptotic morphological and biochemical changes while both mood stabilizers pretreatment reduced or prevented the apoptotic morphological changes. However, valinomycin-induced caspase-3 elevation was only prevented by lithium pretreatment while both lithium and valproate attenuated valinomycin-induced LDH release. Our results suggest that lithium and valproate share a common neuroprotective action against potassium efflux-induced cell apoptosis with different mechanisms.

Chronic lithium and sodium valproate both decrease the concentration of myo-inositol and increase the concentration of inositol monophosphates in rat brain

One of the mechanisms underlying lithium's efficacy as a mood stabilizer in bipolar disorder has been proposed to be via its effects on the phosphoinositol cycle (PI-cycle), where it is an inhibitor of the enzyme converting inositol monophosphates to myo-inositol. In contrast, sodium valproate, another commonly used mood stabilizer, appears to have no direct effects on this enzyme and was thus believed to have a different mechanism of action. In the present study, high resolution nuclear magnetic resonance (NMR) spectroscopy was used to study the chronic effects of both lithium and sodium valproate on the concentrations of myo-inositol and inositol monophosphates in rat brain. As predicted, lithium-treated rats exhibited a significant increase in the concentration of inositol monophosphates and a significant decrease in myo-inositol concentration compared to saline-treated controls. However, unexpectedly, sodium valproate administration produced exactly the same results as lithium administration. These novel findings suggest that both lithium and sodium valproate may share a common mechanism of action in the treatment of bipolar disorder via actions on the PI-cycle.

Ouabain induction of cycling of multiple spike responses in hippocampal slices is delayed by lithium

Alterations in sodium- and potassium-activated adenosine triphosphatase (Na,K-ATPase) activity have been associated with changes of mood states and lithium treatment in bipolar illness. We examined the effects of ouabain and lithium on evoked population responses in rat hippocampal slices. In vitro 3.3 microM ouabain induced cycling between epliptiform activity and unresponsiveness in 18.5% of slices. In vitro ouabain, at 1-10 microM, induced epileptiform multiple spike responses. In vivo lithium pretreatment for 10-21 days produced a significant delay in the onset of this ouabain-induced epileptiform activity compared to control animals. These findings are consistent with other work which suggests that Na, K-ATPase inhibition can both activate and suppress excitable tissues and that lithium pretreatment can mitigate these effects. The implications of these results and others regarding the pathophysiology of bipolar illness are discussed.

Regulation of signal transduction pathways and gene expression by mood stabilizers and antidepressants

OBJECTIVE

To determine whether the currently available evidence supports the hypothesis that antidepressants and mood stabilizers may bring about some of their long-term therapeutic effects by regulating signal transduction pathways and gene expression in the central nervous system.

METHODS

To address this question, we reviewed the evidence showing that chronic administration of antidepressants and mood stabilizers involves alterations in signaling pathways and gene expression in the central nervous system.

RESULTS

A large body of data has shown that lithium and valproate exert effects on the protein kinase C signaling pathway and the activator protein 1 family of transcription factors; in contrast, antidepressants affect the cyclic adenosine monophosphate pathway and may bring about their therapeutic effects by modulating cyclic adenosine monophosphate-regulated gene expression in the central nervous system.

CONCLUSIONS

Given the key roles of these signaling cascades in the amplification and integration of signals in the central nervous system, the findings have clear implications not only for research into the etiology and pathophysiology of the severe mood disorders but also for the development of novel and innovative treatment strategies.

Lithium prevents ouabain-induced behavioral changes. Toward an animal model for manic depression

Both mania and bipolar depression have been associated with decrements in the activity of the sodium and potassium-activated adenosine triphosphatase (Na,K-ATPase) membrane pump. Although the role of this observation in the pathophysiology of bipolar illness is unclear, it has been proposed that this defect could be central to the pathogenesis of the illness. In an effort to test this hypothesis, the authors examined the efficacy of lithium pretreatment in attenuating behavioral changes secondary to acute administration of a single intracerebroventricular (i.c.v.) dose of the Na,K-ATPase-inhibiting compound, ouabain, in the Sprague-Dawley rat. Ouabain (10(-3)M) significantly decreased motor activity in automated activity monitors. Lithium pretreatment for 7 d totally prevented this effect. These preliminary data suggest that i.c.v. ouabain administration in the rat may prove to be a viable animal model for bipolar illness.

Effect of chronic haloperidol treatment on dopamine-induced inositol phosphate formation in rat brain slices

The effects of chronic haloperidol administration on the accumulation of inositol phosphates were examined in rat brain slices pre-labeled with [3H]myo-inositol and incubated with various dopaminergic drugs. Rats were treated with haloperidol-decanoate or its vehicle (sesame oil) for two, four or six weeks. Dopamine and the selective D1 agonist, SKF38393, induced a significant increase in lithium-dependent accumulation of [3H]inositol monophosphate (IP1) in the frontal cortex, hippocampus and striatum of vehicle-treated animals, while the selective D2 agonist quinpirole did not show any effect on IP1 accumulation. The actions of dopamine and SKF38393 were blocked by the D1 antagonist, SCH23390, but not by the D2 antagonist, spiperone, in all three brain regions. Haloperidol treatment did not affect basal phosphoinositide turnover in the three brain regions. Four or six weeks of haloperidol treatment significantly decreased dopamine-induced IP1 accumulation in the striatum (by 30% and 25%, respectively), but not in the frontal cortex and the hippocampus. Four weeks of treatment with haloperidol significantly decreased IP1 levels in the striatal slices when measured in the presence of quinpirole. However, the accumulation of IP1 measured in the presence of SKF38393 was not significantly altered after haloperidol treatment. The loss of dopamine-sensitive IP accumulation was not observed in the presence of spiperone after haloperidol treatment. The number, but not the affinity, of [3H]sulpiride binding sites in the striatum was significantly increased (by 34-46%) after chronic haloperidol treatment.(ABSTRACT TRUNCATED AT 250 WORDS)