A review of the biochemical and neuropharmacological actions of lithium

Old drug, new data

New data have emerged over the past 10 years regarding the efficacy and mechanisms of action of lithium. This article briefly summarises the evidence for the use of lithium to treat affective disorders and psychosis, reviews its putative anti-suicidal effect, highlights new research on its mechanism of action and provides an update on some important side-effects and consequences of its use.

Hyperprolactinemia and medications for bipolar disorder: systematic review of a neglected issue in clinical practice

Drug-induced changes in serum prolactin (sPrl) levels constitute a relevant issue due to the potentially severe consequences on physical health of psychiatric patients such as sexual dysfunctions, osteoporosis and Prl-sensitive tumors. Several drugs have been associated to sPrl changes. Only antipsychotics have been extensively studied as sPrl-elevating agents in schizophrenia, but the extent to which bipolar disorder (BD) treatments affect sPrl levels is much less known. The objective of this systematic review is to summarize the evidence of the effects of drugs used in BD on Prl. This review followed the PRISMA statement. The MEDLINE/PubMed/Index Medicus, EMBASE, and Cochrane Library databases were systematically searched for articles in English appearing from any time to May 30, 2014. Twenty-six studies were included. These suggest that treatments for BD are less likely to be associated with Prl elevations, with valproate, quetiapine, lurasidone, mirtazapine, and bupropion reported not to change PRL levels significantly and lithium and aripiprazole to lower them in some studies. Taking into account the effects of the different classes of drugs on Prl may improve the care of BD patients requiring long-term pharmacotherapy. Based on the results of this review, lithium and valproate appear to be safer due to their low potential to elevate sPrL; among antipsychotics, quetiapine, lurasidone and aripiprazole appear to be similarly safe.

Antimanic potency of typical neuroleptic drugs and affinity for dopamine D2 and serotonin 5-HT2A receptors--a new analysis of data from the archives and implications for improved antimanic treatments

Datasets of antimanic potency ratings and receptor-binding affinities [inhibition constants (K(i))] at dopamine D2 and serotonin 5-HT2A brain receptors were accessed from published literature for a large series (n = 24) of typical neuroleptic drugs, many of which are now obsolete and unobtainable. There was a strong positive association between antimanic potency and affinity for D2 receptors, in support of a 'dopamine-blockade hypothesis' of antimanic drug action. Taking the series of neuroleptics as a whole, there was no association between antimanic potency and affinity for 5-HT2A receptors. Despite this, within a subsample of typical neuroleptics with low affinity for D2 receptors resembling new generation atypical antipsychotics, a positive association between antimanic potency and affinity for 5-HT2A receptors emerged. This suggests that blockade of brain 5-HT2A receptors plays at least a subsidiary role in the antimanic effects of some typical neuroleptics. Other considerations also suggest that combining drugs to achieve high affinity for and blockade of both dopamine D2 receptors and serotonin 5-HT2A receptors, possibly with additional direct or indirect stimulation of postsynaptic 5-HT1A receptors, might maximize antimanic efficacy.

Effect of lithium on endothelium-dependent and neurogenic relaxation of rat corpus cavernosum: Role of nitric oxide pathway

INTRODUCTION

Some studies have reported erectile dysfunction in patients receiving lithium through a mechanism that has not yet been defined. The aim of the present study was to verify the effect of acute lithium administration on the nonadrenergic noncholinergic (NANC)- and endothelium-mediated relaxation of rat isolated corpus cavernosum.

MATERIALS AND METHODS

The isolated rat corporeal strips were precontracted with phenylephrine hydrochloride (7.5 microM) and electrical field stimulation (EFS) was applied at different frequencies (2, 5, 10, and 15 Hz) to obtain NANC-mediated relaxation or relaxed by adding cumulative doses of acetylcholine (10nM-1mM) to obtain endothelium-dependent relaxation in the presence or absence of lithium (0.3, 0.5, 1, and 5mM). Also, effects of combining lithium (0.3mM) with 30 nM and 0.1 nM L-NAME (an NO synthase inhibitor) on NANC- and acetylcholine-mediated relaxation was investigated, respectively. Moreover, effects of combining lithium (1mM) with 0.1mM and 10 microM L-arginine (a precursor of NO) on NANC- and endothelium-mediated relaxation was assessed, respectively. Also, the effect of lithium (1mM) on relaxation to sodium nitroprusside (SNP; 1nM-1mM), an NO donor, was investigated.

RESULTS

The NANC-mediated relaxation was significantly (P<0.001) reduced by 1 and 5mM, but not by 0.3 and 0.5mM lithium. Lithium significantly (P<0.001) attenuated the maximum response to acetylcholine in a concentration-dependent manner. Combination of lithium (0.3mM) with 30 and 0.1 nM L-NAME, which separately had a minimum effect on NANC- and endothelium-mediated relaxation, significantly (P<0.001) reduced the NANC- and endothelium-mediated relaxation, respectively. Although L-arginine at 10 microM and 0.1mM did not alter the relaxant responses to acetylcholine and EFS, it improved the inhibition by lithium (1mM) of relaxant responses to acetylcholine and EFS, respectively. Also, SNP produced similar concentration-dependent relaxations from both groups.

DISCUSSION

Our experiments indicated that lithium likely by interfering with NO pathway in both endothelium and nitrergic nerve can result in impairment of both the endothelium- and NANC-mediated relaxation of rat corpus cavernosum.

The role of mood stabilisers in the treatment of the depressive facet of bipolar disorders

It was previously shown that available mood stabilisers are used to treat bipolar depression. As part of the natural course of illness, patients with bipolar disorder often suffer from episodes of depression more frequently and for longer durations than mania. A major challenge in the treatment of bipolar depression is the tendency for antidepressant medications, particularly tricyclic antidepressants, to precipitate episodes of mania, or to increase cycle frequency or symptom intensity. Thus, exploring the utility of mood stabilisers as monotherapy for bipolar depression is important. The aim of this review it to collate data involving the effects of some mood stabilisers like lithium, carbamazepine, valproate and lamotrigine in depressive aspects of bipolar disorder, but as well using an animal model of depression, to understand their mechanism of action.

Lithium inhibits the modulatory effects of morphine on susceptibility to pentylenetetrazole-induced clonic seizure in mice: involvement of a nitric oxide pathway

Lithium has been reported to inhibit opioid-induced properties. The present study examined the effect of acute and chronic administration of lithium chloride (LiCl) on morphine's biphasic modulation of susceptibility to pentylenetetrazole (PTZ)-induced clonic seizure in mice. We also examined the possible involvement of nitric oxide (NO) pathway in lithium effect. Both acute (0.1 and 1 mg/kg) and chronic (same doses, 21 consecutive days) administration of LiCl completely inhibited the anticonvulsant and proconvulsant effects of morphine (at doses 1 and 30 mg/kg, respectively). A very low and per se noneffective dose of LiCl (0.05 mg/kg) significantly inhibited both phases of morphine effect when administered concomitant with a noneffective low dose of naloxone (0.1 mg/kg). The NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME) at a per se noneffective dose of 0.3 mg/kg potentiated the inhibitory effects of low doses of LiCl (0.01 and 0.05 mg/kg) on both phases of morphine effect. l-arginine, a NO synthase substrate, at a per se noneffective dose of 30 mg/kg reversed the inhibitory effects of lithium (1 mg/kg). Lithium is capable of antagonizing both modulatory effects of morphine on seizure susceptibility even at relatively low doses. These inhibitory effects of lithium may also involve NO synthesis.

Chronic lithium administration enhances noradrenergic responses to intravenous administration of the alpha2 antagonist idazoxan in healthy volunteers

The acute and chronic effects of lithium carbonate administration at therapeutic blood levels on peripheral noradrenergic activity and sympathetic responses to alpha2 adrenoceptor blockade were examined in 10 medically and psychiatrically healthy volunteers. Supine resting levels of plasma norepinephrine and the increases in norepinephrine following intravenous infusion of 200 microg/kg of idazoxan, a selective alpha2 adrenoceptor antagonist, were determined before lithium (Li+) administration and after 5 days and after 4 weeks of daily Li+ treatment. Chronic Li+ treatment significantly increased mean resting plasma norepinephrine levels by 53.6%. The noradrenergic responses to infusions of idazoxan were slightly enhanced after 5 days of Li+ administration and significantly increased following 4 weeks of Li+ treatment. The possibility that Li+ produces functional alpha2 subsensitivity causing enhanced peripheral noradrenergic activity in humans is supported by the findings of increased mean resting plasma norepinephrine and increased response to idazoxan following chronic Li+ administration. Alteration of regulatory mechanisms in the noradrenergic system may be relevant to understanding the clinical effects of Li+ in manic-depressive illness.

Predicting response to lithium in mood disorders: role of genetic polymorphisms

Lithium is considered to be the first choice mood stabilizer in recurrent mood disorders. Its widespread and large-scale use is the result of its proven efficacy. In spite of this fact, patients have been observed to show a variable response to lithium treatment: in some cases it is completely effective in preventing manic or depressive relapses, while in other cases it appears to show no influence on the disease course. The possible definition of a genetic liability profile for adverse effects and efficacy will be of great help, as lithium therapy needs at least 6 months to be effective in stabilizing mood disorders. During the last few years, a number of groups have reported possible liability genes. Lithium long-term prophylactic efficacy has been associated with serotonin transporter protein, tryptophan hydroxylase and inositol polyphosphate 1-phosphatase variants. A number of other candidate genes and anonymous markers did not yield positive associations. Therefore, even if some positive results have been reported, no unequivocal susceptibility gene for lithium efficacy has been identified. Although the available data may not currently allow a meaningful prediction of lithium response, future research is aimed at the development of individualized treament of mood disorders, including the possibility of 'pharmacological genetic counseling'.

Epi-inositol regulates expression of the yeast INO1 gene encoding inositol-1-P synthase

Myo-inositol exerts behavioral effects in animal models of psychiatric disorders and is effective in clinical trials in psychiatric patients. Interestingly, epi-inositol exerts behavioral effects similar to myo-inositol, even though epi-inositol is not a substrate for synthesis of phosphatidylinositol. We postulated that the behavioral effects of epi-inositol may be due to its effects on gene expression. Yeast INO1expression was measured in northern blots. INM1 was determined by beta-galactosidase activity in a strain containing the fusion gene INM1-lacZintegrated into the genome. Epi-inositol affects regulation of expression of the INO1 gene (encoding inositol-1-P synthase), even though it cannot support growth of an inositol auxotroph (suggesting that, as in mammalian cells, it is not incorporated into phosphatidylinositol). Like myo-inositol, although to a lesser extent, epi-inositol causes a significant reduction in INO1 expression, and reverses the lithium- or valproate-induced increase in INO1 expression. However, it does not affect regulation of INM1 (encoding inositol monophosphatase), the expression of which is up-regulated by myo-inositol. The observed regulatory effects of epi-inositol on expression of the most highly regulated gene in the inositol biosynthetic pathway may help to explain how this inositol isomer can exert behavioral effects without being incorporated into phosphatidylinositol.

Lithium long-term treatment in mood disorders: clinical and genetic predictors

Lithium is the most widely used long-term treatment for recurrent mood disorders. Despite its proven efficacy, patients show a variable response, ranging from complete efficacy to no influence at all. This paper reviews possible predictors of response focusing on molecular genetic studies. The functional polymorphism in the upstream regulatory region of the serotonin transporter gene (5-HTTLPR) has been associated with lithium long-term efficacy in two independent studies, marginal associations have been reported for tryptophan hydroxylase and inositol polyphosphate 1-phosphatase (INPP1). A number of other candidate genes and anonymous markers did not yield positive associations. Therefore, even though some positive results have been reported, no unequivocal susceptibility gene for lithium efficacy has been identified.

Effects of subchronic lithium chloride treatment on G-protein subunits (Golf, Ggamma7) and adenylyl cyclase expressed specifically in the rat striatum

Lithium salt has been widely used as a treatment for mania, but the mechanism of its effect remains unknown. Previously, by studying c-fos expression, we showed that the striatum was a possible target region for the antimanic effects of lithium salt. The present study focused on the effect of subchronic lithium chloride treatment on G-proteins (Golf, Ggamma7) and adenylyl cyclase type V, which are expressed specifically in the rat striatum. Subchronic lithium chloride treatment significantly increased the level of Golf protein, a stimulant alpha-subunit of G-protein, by 53.5% (P<0.01), but the levels of Ggamma7 and adenylyl cyclase type V did not change. This increased level of Golf protein was found after 2 weeks of lithium chloride treatment, but not after 1 week, and the level returned to the basal level 1 week after withdrawal of lithium chloride. This result suggests that the level of Golf protein increases to compensate for the suppression of the adenylyl cyclase system by lithium, and that this increase may account for the "rebound" phenomenon, which is the relapse observed after abrupt discontinuation of lithium salt treatment.

7Li 2D CSI of human brain on a clinical scanner

Lithium salts have been widely used in the treatment of mood disorders, but the mechanism of action is still not clear. In this work, a methodology for two-dimensional Lithium-7 imaging on clinical systems is presented. The data were acquired using a phosphorus volume head coil that was re-tuned for the Lithium-7 frequency. A spectroscopic sequence was used to acquire the free induction decay (FID) after volume excitation using a hard pulse. The results obtained on the head of patients undergoing lithium treatment (n = 7, 0.6 mEq/l average serum level) demonstrate that images of adequate signal to noise ratio (100:1) can be obtained in acceptable imaging times (55 min) using the proposed methodology. The distribution of 7Li appears uniform in the brains of the patients studied.

Effects of short and long-term lithium treatment on serum prolactin levels in patients with bipolar affective disorder

1. In this study, the authors sought to test the hypothesis that Li (lithium) treatment can induce alterations in PRL (prolactin) secretion in euthymic bipolar patients compared to controls and that short and long-term administration can lead to prolactin changes different from each other. 2. Twenty euthymic bipolar male patients on long-term lithium carbonate treatment for more than 6 months and 15 euthymic male bipolar patients on short-term Li treatment for shorter than 6 months who met DSM-IV criteria for bipolar affective disorder were included in the study. Seventeen age-matched healthy control males were chosen among the hospital staff. The mean +/- SD duration of Li use was 68.93+/-46.31 months in the long-term lithium-treated group and 4+/-3.42 months in the short-term lithium-treated group. 3. Serum PRL values in the long-term Li-treated group were significantly lower than those of the control group, while there was no significant difference in PRL values between the short-term Li-treated group and the control group. 4. Our study documents that short-term (<6 months) Li treatment does not induce any significant changes in PRL release in bipolar patients compared to normal control subjects while long-term Li treatment (>6 months) leads to lower PRL release compared to the controls. Furthermore, PRL has wide intra-interindividual and circadian variations Li-PRL relationship seems to be very complex and probably depends on various interactions among dopamine, serotonin and PRL. Therefore, further studies are needed to confirm the data.

Effects of acute tryptophan depletion on mood and suicidal ideation in bipolar patients symptomatically stable on lithium

BACKGROUND

Previous studies suggest that brain serotonin neurotransmission may mediate the actions of lithium carbonate. Acute tryptophan depletion reduces brain serotonin and allows the study of this neurotransmitter in patient groups.

AIMS

To examine the effects of acute tryptophan depletion on mood and suicidal ideation in bipolar patients who were symptomatically stable on lithium.

METHOD

Nineteen subjects satisfying DSM-IV criteria for bipolar I disorder participated in a within-subject, double-blind, placebo-controlled random-order crossover study. Symptoms were evaluated following acute tryptophan depletion, which was induced by a 100 g amino acid drink following an overnight fast.

RESULTS

Plasma tryptophan fell significantly after the depleting drink, but not after the control drink (P < 0.05, paired t-test, mean reduction 83%). No significant changes in mood or suicidality scores were recorded after acute tryptophan depletion.

CONCLUSIONS

Acute tryptophan depletion does not reverse lithium's effects on mood and suicidality in bipolar disorder.

Role played by sodium in activity-dependent secretion of neurotrophins - revisited

In previous experiments, a causal relationship between sodium influx and secretion of nerve growth factor (NGF) was deduced from the observation that the sodium substitute N-methyl-D-glucamine (NMDG) abolished any activity-mediated NGF secretion that depends on intact internal calcium stores. However, all available experimental evidence speaks against sodium-mediated calcium mobilization from these stores under physiological conditions. We now report that rapid sodium influx initiated by monensin or ouabain did not induce brain-derived neurotrophic factor (BDNF) secretion from either native hippocampal slices or BDNF-transduced hippocampal neuronal cultures. Additionally, we found marked differences between the replacement of sodium by NMDG and sucrose on the one hand, and choline and lithium on the other. Replacement of 100% (and as little as 10%) sodium by NMDG or sucrose not only blocked the activity-mediated neurotrophin secretion, but itself led to a rapid and substantial increase of neurotrophin secretion. In contrast, the replacement of sodium (10% and 100%) by lithium and choline did not result in a release of neurotrophins, and only 100% replacement blocked the activity-mediated neurotrophin secretion. We conclude that the blocking effects of NMDG and sucrose on neurotrophin secretion do not reflect the sodium replacement, but instead represent an independent blocking effect. These differences were also reflected in part by electrophysiological investigations in individually patched hippocampal neurons. The importance of the present observations lies not only in the reevaluation of the involvement of sodium in activity-dependent neurotrophin secretion, but also in the demonstration that sodium replacement may initiate 'side effects' that are unrelated to sodium replacement.

Brain 5-HT function in bipolar affective disorder

BACKGROUND

Previous studies suggest that brain serotonin neurotransmission may mediate the actions of lithium carbonate. Acute tryptophan depletion (ATD) reduces brain serotonin and allows the study of this neurotransmitter in patient groups. Serotonin modulates electroencephalographic (EEG) activity, which is abnormal in bipolar disorder, and EEG abnormalities persist in euthymic bipolar patients. The EEG may therefore be a sensitive marker of 5-HT function in bipolar disorder.

AIMS

This study examined the effects of ATD on mood, suicidal ideation and EEG activity in bipolar patients who were symptomatically stable on lithium.

METHODS

19 subjects satisfying DSM-IV criteria for bipolar I disorder participated in a within-subject, double-blind, placebo-controlled random-order crossover study. Following acute tryptophan depletion (induced by a 100g amino acid drink following an overnight fast) symptoms were evaluated, quantitative power spectrum brain mapping and measurement of auditory evoked potentials were carried out.

RESULTS

ATD produced a significant fall in the amplitude of N1P2 and P300 components of the auditory evoked potential, but no significant changes in the power spectrum. There was an 83% reduction in plasma tryptophan (p<0.05, paired t-test) after the depleting but not the control drink. No significant changes in mood or suicidally scores were recorded after ATD.

CONCLUSIONS

ATD attenuates auditory evoked potentials in bipolar disorder but does not reverse lithium's effects on mood and suicidally in bipolar disorder.

Serotonin in mania and in the mechanism of action of mood stabilizers: a review of clinical studies

OBJECTIVES

Serotonin (5-hydroxytryptamine, 5-HT) was implicated in the pathophysiology of manic-depressive illness as early as 1958. Although extensive evidence has accumulated since then to support 5-HT's role in depression, relatively fewer studies examined its role in mania. The purpose of this paper was to review and summarize the current state of knowledge on the role of 5-HT in mania and its treatment.

METHODS

We systemically reviewed clinical studies of 1) 5-HT function in mania and 2) 5-HT in the mechanism of action of mood stabilizers, including lithium and anticonvulsants.

RESULTS

Review showed that cerebrospinal fluid, postmortem, platelet, neuroendocrine challenge, and tryptophan depletion studies provided some evidence to support the hypothesis that a 5-HT deficit is involved in mania and that enhancement of 5-HT neurotransmission exerts a mood-stabilizing effect.

CONCLUSIONS

There is some evidence from clinical studies for the contribution of 5-HT in mania and in the mechanism of action of mood stabilizers. However, it is very likely that other neurotransmitters also play important roles. Future directions for research include 1) in vivo study of 5-HT receptor subtypes using positron emission tomography, 2) investigation of the interaction between 5-HT and other neurotransmitter systems, and 3) determination of the relationships between diagnostic subtypes of mania and 5-HT function and other neurotransmitter systems.

Intrathecal lithium reduces neuropathic pain responses in a rat model of peripheral neuropathy

We tested the ability of lithium (Li(+)) to block heat hyperalgesia, cold allodynia, mechanical allodynia and mechanical hyperalgesia in rats experimentally subjected to painful peripheral neuropathy. Chronic constrictive injury (CCI) to the sciatic nerve induced persistent hyperalgesia and allodynia. Intrathecal injection of Li(+) (2.5-40 micromol) into the region of lumbar enlargement dose-dependently reduced heat hyperalgesia, cold allodynia and mechanical allodynia for 2-6 h after injection, but had no effect on mechanical hyperalgesia. Li(+) had no significant effect on responses from control and sham-operated animals. Intrathecal injection of myo-inositol (2.5 mg) significantly reversed both the anti-hyperalgesic and anti-allodynic effect of Li(+). These findings suggest that intrathecal Li(+) suppresses neuropathic pain response in CCI rats through the intracellular phosphatidylinositol (PI) second messenger system in spinal cord neurons. Lithium (Li(+)) has already found widespread clinical application; these results suggest that its therapeutic utility may be extended to include treatment of neuropathic pain syndromes resulting from peripheral nerve injury.

Applications of (7)Li NMR in biomedicine

The applications of (7)Li NMR spectroscopy and imaging in biology and experimental medicine have been progressing steadily. The interest derives primarily from the clinical use of Li salts to treat mania and manic-depressive illness. One area of investigation is ionic transport across the cellular membrane and compartmentation, so as to elucidate the mechanism(s) of therapeutic action and toxicity in clinical practice. The second is the development of a noninvasive, in vivo analytical tool to measure brain Li concentrations in humans, both as an adjunct to treatment and as a mechanistic probe. Here we review progress to date in this area.

Interactions of lithium and drugs that affect signal transduction on behaviour in rats

The therapeutic mechanism of the action of lithium in the treatment of bipolar affective disorder is not known, in spite of a burgeoning number of biochemical studies linking lithium to signal transduction processes. This article reviews a decade of studies examining the behavioural manifestations of manipulating inositol, cyclic adenosine monophosphate (cAMP) and G proteins in rats. Inositol, forskolin, dibutyryl cAMP and pertussis toxin all interacted with lithium when rearing behavior was measured. Lithium potentiated the increase in locomotion induced by injections of cholera toxin into the nucleus accumbens, consistent with the hypothesis that it inactivates inhibitory G proteins. More specific interactions were found between lithium and inositol following cholinergic and serotonergic stimulation. Inositol, but not forskolin, attenuated lithium-pilocarpine seizures and the enhancement of the serotonin syndrome; however, inositol had no effect on lithium-induced attenuation of wet dog shakes following an injection of 5-hydroxytryptophan. Behavioural evidence supports biochemical findings suggesting that lithium's interactions with the phoshphatidyl inositol and cyclic AMP signal transduction systems may be relevant to its therapeutic effects in bipolar disorder. Further research on more specific behaviours may elucidate the relevant pharmacological mechanisms underlying the therapeutic effect of lithium.

Is it time to have another look at lithium maintenance therapy in bipolar disorder?

1. Bipolar disorder is typically a chronic disease entailing an episodes course, whereby psychiatric status alternates between periods of normal functioning and periods of illness. Lithium is well established and approved for the treatment of bipolar disorder. However, its efficacy in practice is not as great as expected. This retrospective record study was undertaken to determine the efficacy of lithium in bipolar disorders. 2. 48 patients who met DSM-III-R diagnostic criteria for bipolar I disorder and had been admitted once before lithium therapy and twice or more after that, were included in this study. 3. No significant difference in length between episode (frequency) was observed before and after lithium maintenance therapy. In addition, the percentages of manic episode after lithium therapy were much greater than before that. 4. The results indicate that it is worth re-examining the efficacy of lithium in bipolar disorders.

Effects of chronic lithium on ototoxicity induced by gentamicin and amikacin in guinea-pigs

The effects of chronic lithium co-therapy on the expression of gentamicin and amikacin ototoxicity were tested in guinea-pigs. Intramuscular injection of different doses of gentamicin (5, 10 mg/kg/day) and amikacin (150, 300 mg/kg/day) for three weeks, induced hearing loss consistent with the established pattern of aminoglycoside ototoxicity. Lithium salts remains one of the most widely used treatment for depressive illness. Administration of lithium chloride (600 mg/l, 35 days) in drinking water changed auditory brainstem response in a time-dependent manner. Pretreatment of animals with lithium chloride after seven days induced significant alterations in wave latency and interval. The present study assesses the protective effects of chronic lithium on gentamicin-induced ototoxicity in guinea pig. The results suggest that duration of lithium administration may be involved in auditory brainstem response changes and the observations could be accounted for, at least partially, by lithium- and aminoglycosides-induced perturbations of the phosphoinositide cascade within the inner ear.

Paradoxical effects of lithium on serotonergic receptor function: an immunocytochemical, behavioural and autoradiographic study

Lithium is the preferred treatment for bipolar affective disorder, yet its mechanism of action is poorly understood. Our study was designed to investigate the effect of lithium on the 5-HT2A or 5-HT2C (5-HT2A/2C) receptor subtypes, by comparing the consequences of chronic pre-treatment of rats with lithium on 5-HT2A/2C receptor-mediated behavioural responses, Fos expression, and the density of these receptors in the brain. In addition, the time-course and persistence of the effect of chronic lithium on 5-HT2A/2C receptor-mediated Fos expression was examined. Furthermore, the acute action of lithium on Fos expression was also examined. In an investigation of the dose response of Fos to the 5-HT2A/2C agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), rats received saline or 1, 2, 4, 8, 12, 16, 24 or 32 mg/kg DOI, then were sacrificed 3 h later for immunocytochemical localisation of Fos. In a chronic lithium study, rats received either control or lithium-containing (0.1% LiCO3) chow for 3 weeks prior to challenge with 8 mg/kg DOI. DOI-induced locomotor activity was measured for 30 min immediately following the drug challenge, then 150 min later, the animals were sacrificed for Fos immunocytochemistry. The brains of another group of rats, also receiving either control or lithium-containing diet for 3 weeks, were analysed for the distribution and density of 5-HT2A receptor binding sites by quantitative [3H]ketanserin autoradiography. One group of chronic lithium treated rats received ritanserin (0.4 mg/kg), a 5-HT2A/2C receptor antagonist, 40 min before DOI challenge and were sacrificed 3 h later for Fos localisation. In the time-course experiment, rats received lithium-containing diet for 3 weeks followed by normal, control diet for 48 h, 1, 2 or 4 weeks prior to DOI or saline challenge. A further group of animals received an injection of LiCl (3 mM/kg) before being challenged with DOI or saline 12, 24, 36 or 48 h later. The dose-response experiment revealed that little Fos-like immunoreactivity was evident above basal levels following administration of 1 mg/kg DOI. However, at all other doses examined, Fos-like immunoreactivity was elevated in a number of brain areas, particularly in cerebral cortex, olfactory tubercle and amygdala. Following 24 mg/kg DOI, the number of Fos-positive nuclei appeared to have reached a plateau level. Treatment of rats with chronic lithium significantly enhanced DOI-induced locomotor activity and Fos-like immunoreactivity throughout the cerebral cortex. This elevation in Fos-like immunoreactivity was completely abolished by prior treatment with ritanserin. In contrast, chronic lithium treatment had no effect on the density of [3H]ketanserin binding to 5-HT2A receptors in any brain region examined. The results of the time-course experiment demonstrated that the enhancing effect of lithium on 5-HT2A/2C receptor-mediated Fos expression was short-lived such that Fos-like immunoreactivity returned to untreated levels within 48 h. In the acute lithium experiment, administration of lithium to rats 12 or 24 h before DOI resulted in a similar elevation of Fos-like immunoreactivity to that seen in chronically treated animals. Administration of acute lithium 36 or 48 h before DOI had no effect. The effects of lithium on 5-HT2A/2C receptor function thus appear to be complex. In particular, the results of this study indicate that the enhancing effects of lithium on DOI-induced locomotor activity and Fos-like immunoreactivity are not accompanied by any alteration in the density of 5-HT2A receptor binding sites. If changes in receptor numbers therefore do not account for the physiological effect of chronic lithium, other explanations must be sought. The study also suggests that the inositol depletion hypothesis of lithium's therapeutic action does not adequately explain the mechanism of action of lithium in man.

Lithium does not attenuate the effects of D-amphetamine in healthy volunteers

It has previously been suggested that an acute dose of 20 mg D-amphetamine can be a good model of mania. In the present study we attempted to validate this model by determining if subacute administration of lithium (for 7 days) would attenuate the effects of 20 mg D-amphetamine in human volunteers. Sixteen healthy volunteers were enrolled in this double-blind, placebo-controlled study. Subjects received either oral lithium at night for 7 nights (1200 mg) (n = 10) or matching placebo (n = 6). On day 8, subjects were assessed at baseline and then once each hour for 3 h following an oral dose of D-amphetamine (20 mg). Subjective states were measured with visual analog scales, and pulse, systolic and diastolic blood pressure were also repeatedly assessed. The results showed that D-amphetamine alone produced a number of subjective and cardiovascular changes, as expected. However, lithium did not attenuate any of these subjective or cardiovascular changes, as would be predicted if D-amphetamine were a valid model of mania. It is suggested that whilst D-amphetamine may produce effects similar to mania, its mechanism of action is different from that which occurs in mania, and therefore the usefulness of the amphetamine model of mania is called into question.

Action potential broadening induced by lithium may cause a presynaptic enhancement of excitatory synaptic transmission in neonatal rat hippocampus

Lithium enhances excitatory synaptic transmission in CA1 pyramidal cells, but the mechanisms remain unclear. The present study demonstrates that lithium enhances the N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-isoxazole propionic acid (AMPA) receptor-mediated components of the excitatory postsynaptic current (EPSC). Lithium decreased the magnitude of paired-pulse facilitation and presented an inverse correlation between the lithium-induced enhancement of synaptic transmission and initial paired-pulse facilitation, which is consistent with a presynaptic mode of action. The enhancement of synaptic strength is likely to act, at least in part, by increasing the amplitude of the presynaptic Ca2+ transient. One mechanism which could account for this change of the presynaptic Ca2+ transient is an increase in the duration of the action potential. We investigated action potential in hippocampal pyramidal neurons and found that lithium (0.5-6 mM) increased the half-amplitude duration and reduced the rate of repolarization, whereas the rate of depolarization remained similar. To find out whether the lithium synaptic effects might be explained by spike broadening, we investigated the field recording of the excitatory postsynaptic potential (EPSP) in hippocampal slices and found three lines of evidence. First, the prolongation of the presynaptic action potential with 4-aminopyridine and tetraethylammonium blocked or reduced the synaptic effects of lithium. Second, the lithium-induced synaptic enhancement was modulated when presynaptic Ca2+ influx was varied by changing the external Ca2+ concentration. Finally, both effects, the synaptic transmission increment and the action potential broadening, were independent of inositol depletion. These results suggest that lithium enhances synaptic transmission in the hippocampus via a presynaptic site of action: the mechanism underlying the potentiating effect may be attributable to an increased Ca2+ influx consequent to the broadening effect of lithium on the action potential.

The effect of acute lithium and rubidium pretreatment on apomorphine-induced pecking in pigeons

The effects of different doses of lithium (5-320 mg/kg intramuscularly) and rubidium (0.25 32 mg/kg intramuscularly) on apomorphine-induced pecking were investigated in pigeons. These two cations did not induce pecking by itself. Intramuscular administration of apomorphine (a mixed D1/D2 dopamine receptors agonist, 0.1-1.6 mg/kg) induced pecking in a dose-dependent manner. SCH 23390 (D1 dopamine receptor antagonist, 0.02-0.08 mg/kg) and sulpiride (D2 dopamine receptor antagonist, 25-100 mg/kg) decreased apomorphine-induced pecking dose-dependently. Combination of SCH 23390 (0.04 mg/kg) with sulpiride (50 mg/kg) caused a stronger inhibitory effect on apomorphine response. This indicates that both D1 and D2 dopamine receptors are involved in apomorphine-induced pecking. The response induced by apomorphine (0.2-0.8 mg/kg) was decreased in animals pretreated with lithium and rubidium. In these conditions, SCH 23390 and sulpiride produced a larger inhibitory effect on the apomorphine response, suggesting that acute lithium and rubidium pretreatment inhibit pecking by interfering with dopaminergic mechanisms.

Tryptophan depletion in recently manic patients treated with lithium

BACKGROUND

Serotonin has been repeatedly implicated in the mechanism of action of lithium against acute mania. Its role, however, has never been directly confirmed.

METHODS

We studied recently manic patients successfully treated with lithium using a tryptophan depletion methodology.

RESULTS

Patients remained euthymic despite a confirmed decrease in serum tryptophan levels.

CONCLUSIONS

These data do not suggest that serotonin plays a critical role in the acute antimanic effect of lithium.

5-HT brain function in affective disorder: d,l-fenfluramine-induced hormone release and clinical outcome in long-term lithium/carbamazepine prophylaxis

Prolactin (PRL) and Cortisol (CORT) responses to d,l-fenfluramine (FEN) challenge (60 mg) were examined in patients with affective disorders on two occasions under euthymic conditions: drug-free before admission to prophylactic treatment and after about 9 months of medication with lithium or carbamazepine. Response to treatment was assessed by a complex algorithm using continuous ratings in outpatient clinic over a period of 2 years. In general, treatment resulted in a delayed and diminished CORT release (n.s.); subgroup analysis revealed an attenuated CORT response (P < 0.05) in responders, whereas nonresponders showed no change in CORT secretion pattern except an enhanced CORT baseline value (P < 0.05). Cross-sectional comparison of responders with nonresponders under medication yielded a trend for greater CORT stimulation in nonresponders. This result was not affected by FEN/NorFEN or lithium/carbamazepine serum levels, baseline CORT values, age, sex, diagnostic distribution, number of appointments to the outpatient clinic or duration of medication at the time of FEN test session. Before onset of prophylactic medication responders and nonresponders could not be discriminated significantly regarding stimulated hormone release, probably due to the small sample size (n = 17). CORT response to FEN was increased in drugfree unipolar patients compared to bipolar (P < 0.05) and to schizoaffective patients (P < 0.1). In accordance with its well-documented presynaptic 5-HT-agonistic action lithium medication resulted in a significantly greater increase in CORT release than carbamazepine (P < 0.05). Evaluation of PRL stimulation showed patterns of secretion quite similar to those of CORT, without reaching statistical significance in most cases. Perhaps due to methodological differences in assessing treatment response, these data do not confirm former results, which supposed an enhanced 5-HT net activity in long-term prophylactic lithium treatment. Because of high interindividual variances of hormone parameters, the FEN-test procedure is not a useful tool for the prediction of therapeutical outcome in terms of clinical routine use. Relations of stimulated hormone response as a marker of central serotoninergic activity and clinical outcome are discussed.

Alterations of physostigmine-induced yawning by chronic lithium administration in rats

The effect of chronic lithium pretreatment on physostigmine-induced yawning was investigated in male rats. Intraperitoneal administration of physostigmine to rats induced yawning in a biphasic manner. However the maximum response was obtained by 0.2 mg/kg of the drug. Intracerebroventricular administrations of a putative M1 and M2 muscarinic receptor antagonists, pirenzepine and methoctramine decreased physostigmine-induced yawning. Intraperitoneal administration of a non-selective muscarinic receptor antagonist, atropine, also decreased the physostigmine-induced yawning significantly. Chronic lithium pretreatment (30 days) reduced yawning induced by physostigmine. The inhibitory effect of pirenzepine, methoctramine and atropine on physostigmine-induced yawning increased in rats pretreated with chronic lithium. These findings indicate that yawning is induced by a central cholinergic mechanism and that chronic pretreatment of lithium may interact with the cholinergic-induced behaviour.

Lithium enhances synaptic transmission in neonatal rat hippocampus

The effects of lithium on excitatory synaptic transmission were studied in the CA1 region of hippocampal slices taken from 14- to 30-day-old rats using extracellular recording techniques. Lithium (2-18 mM) reversibly increased the field excitatory postsynaptic potentials in a concentration-dependent manner. Application of lithium for 6-15 min had no effect on the synaptic input-output function, while application of lithium for 20-35 min shifted this curve to the left. Lithium reversibly increased the amplitude of the presynaptic fibre volley in a concentration- and calcium-dependent manner. Lithium decreased paired-pulse facilitation measured at 50-ms interstimulus intervals. The results indicate that lithium enhances excitatory synaptic transmission in CA1 pyramidal cells by at least two different actions.

The effect of chronic lithium treatment on the calibre of axons and nerve fibres in the rat sural nerve

Cases of peripheral neuropathy have been reported in humans receiving lithium therapy. However, no previous studies have addressed the question of whether chronic lithium treatment causes morphological changes in the peripheral nervous system in experimental animals. The present study used stereological methods to determine whether long-term administration of lithium affected the calibre of the axons or of the nerve fibres in the rat sural nerve. Twenty-two rats were divided into 2 groups and given either no treatment or lithium, with serum levels averaging from 0.5 to 0.7 mmol/l. After 30 weeks of treatment, the animals were killed and the sural nerve was isolated at the level of the knee and was removed. The cross-sectional area of axons and of nerve fibres was estimated by point counting. Compared with the controls, a strong tendency towards a reduced nerve fibre area in the lithium-treated animals was found, with a between-group difference of 1.79 microns 2 (P = 0.06). For the axon area, the difference was 0.73 micron 2 (P = 0.20).

On the functions of lithium: the mood stabilizer

Lithium, despite its simple structure, has numerous biological effects. It also has a remarkable therapeutic effect in the prophylactic treatment of manic depression, and is finding a role in controlling aggressive and self-mutilating behavior. The special feature of lithium is that it only acts on overactive systems to bring them back to normal, without affecting the stable system. The mechanisms of action of this simple cation are still largely unknown although the inositol depletion theory is the most widely accepted model. A recent paper described a different molecular mechanism for its effect on development, which may also explain its action in manic depression.

Chronic lithium does not alter human myo-inositol or phosphomonoester concentrations as measured by 1H and 31P MRS

Lithium may act by decreasing intracellular concentrations of myo-inositol. The present study measured the effects of chronic lithium on myo-inositol concentrations in volunteers. Eleven subjects received either lithium (n = 7) or placebo (n = 4) for 7 days in a double-blind study. Myo-inositol concentrations at baseline and day 8 were measured in vivo using 1H magnetic resonance spectroscopy (MRS). The results showed that lithium did not alter brain myo-inositol concentrations compared to placebo. In 5 other subjects we used 1H MRS and 31P MRS to measure changes in both myo-inositol and phosphomonoester concentrations. This second study showed that lithium did not alter myo-inositol or phosphomonoester concentrations. Thus, the present studies do not support the hypothesis that lithium significantly affects the brain concentrations of myo-inositol or phosphomonoesters; however, it is possible these findings represent an inability to detect the changes in myo-inositol and phosphomonoester concentrations that may have occurred following lithium administration.

Additive effects of glyburide and antidepressants in the forced swimming test: evidence for the involvement of potassium channel blockade

Evidence in the literature suggests that the modulatory effects of antidepressant drugs (ADS) on neuronal excitability, via the inhibition of K+ channels, may be the final common pathway of pharmacological action. Therefore, we tested the hypothesis that combining the ATP-sensitive K+ channel blocker glyburide with a variety of ADS would produce an additive effect and decrease the immobility time of mice in the forced swimming test (FST). Glyburide (GLY, IP, 30 and 50 mg/kg) and subactive doses of ADS were administered 45 and 30 min, respectively, prior to behavioral testing. Results showed that when combined with GLY, ADS whose main pharmacological effect is one of 5-HT uptake blockade (imipramine, amitriptyline, citalopram, paroxetine, fluoxetine, and fluvoxamine) were more effective in decreasing the amount of time mice were immobile, than when these drugs were administered alone. Some noradrenaline uptake inhibiting ADS (desipramine and viloxazine, but not maprotiline) were also significantly more effective in decreasing immobility time when combined with GLY than when administered alone. Pretreatment with GLY was found to have no effect on the dopamine uptake inhibitor bupropion, and out of the atypical ADS tested (trazodone, mianserine and iprindole), only coadministration with iprindole decreased the immobility time. Only the specific MAO-A inhibitor moclobemide was observed to have an antiimmobility effect when combined with GLY. Neither MAO-B specific (RO 16 6491) nor mixed MAO inhibitors (nialamide and pargyline) interacted with GLY to produce antiimmobility effects. These results corroborate and extend our previous report of the ADS enhancing effects of quinine in the same behavioral model, and suggest that the additive effects of quinine and GLY on ADS in FST are a result of K+ channel blockade.

Inhibition of noradrenaline stimulated increase in [Ca2+]i in cultured astrocytes by chronic treatment with a therapeutically relevant lithium concentration

Chronic treatment of mouse astrocytes in primary cultures with 1 mM lithium chloride for 7-14 days decreased the basal level of free cytosolic calcium concentration ([Ca2+]i) from 50-70 nM to approximately 70% of this value and reduced the increase in [Ca2+]i caused by exposure to 1 microM noradrenaline (normally to 500-700 nM) by almost one half. A similar, but much smaller, response to serotonin was unaffected by chronic treatment with lithium. Acute exposure to lithium (30 min) had no effect on either basal or noradrenaline stimulated [Ca2+]i. The dependence on chronic, versus acute treatment suggests that this effect may be related to the therapeutic effect of lithium as a mood-stabilizing drug, which likewise requires chronic treatment. Since good evidence is found that noradrenaline increases [Ca2+]i by activation of the phosphoinositol second messenger system the present findings are also consistent with literature data that lithium acts by interfering with this system.

Acute effect of 17 beta-estradiol and lithium on ovariectomized rat brain biogenic amines metabolism

The effect of 17 beta-estradiol (E2) on the response of dopamine (DA) and serotonin (5-HT) to acute lithium in the brains of ovariectomized rats was investigated. An E2 injection (100 ng/s.c.) to ovariectomized rats did not change striatal DA levels, whereas the levels of its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), increased 30 min later; concentrations of 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), also remained unchanged. In the frontal cortex, DA, 5-HT, HVA and 5-HIAA levels remained unchanged after the E2 injection, whereas DOPAC levels and DOPAC/DA and HVA/DA ratios increased 30 min later. Injection of LiCl (10 mEq) decreased striatal DA levels, increased DOPAC levels and slightly decreased HVA levels; by contrast, frontal cortex DA and HVA levels increased but DOPAC levels were unchanged. A biphasic response of striatal 5-HT levels occurred, increasing shortly after injection of LiCl, followed by a decrease; 5-HIAA levels, however, increased. In the frontal cortex, injection of rats with LiCl led to a gradual increase in 5-HT levels, whereas 5-HIAA concentrations decreased. In the presence of E2, LiCl effected a greater decrease in striatal DA than injection of LiCl alone, advanced the DOPAC peak by 30 min and increased HVA levels; E2 had less effect on the 5-HT response to LiCl, except the decreases in 5-HT and 5-HIAA at 60 min were greater. Furthermore, in the striatum, the increased DA turnover caused by LiCl, estimated by the DOPAC/DA and HVA/DA ratios, was advanced in rats treated with E2. In the presence of E2, LiCl slightly increased frontal cortex DA, DOPAC and HVA levels compared with treatment with LiCl alone, whereas DOPAC levels decreased in rats treated with LiCl + E2 compared with levels in E2-treated rats. Generally, higher levels of 5-HT and 5-HIAA were measured in the frontal cortices of rats treated with LiCl + Ex compared with rats injected with LiCl. These results indicate that E2 potentiates the acute effect of lithium on striatal and frontal cortex DA and 5-HT levels and metabolism, suggesting a role of the hormonal state on this drug response.

Alterations of bromocriptine-induced penile erection by chronic lithium in rats

In the present study, the effects of chronic lithium pre-treatment (30 days) on penile erection (PE) induced by bromocriptine were investigated in rats. Intraperitoneal administration of the dopamine receptor agonist, bromocriptine (4-32 mg/kg) induced PE in a biphasic manner. The maximum response was obtained with 8 mg/kg of bromocriptine and the effect was decreased with increasing doses of the drug from 8 to 32 mg/kg. When animals were pre-treated with different doses of the D-1 dopamine receptor antagonist, SCH 23390, or the D-2 dopamine receptor antagonist, sulpiride, the PE response was decreased. The response induced by bromocriptine (4-32mg/kg) was reduced in animals pre-treated with chronic lithium. SCH 23390 did not produce a larger inhibitory effect on the bromocriptine response in animals pre-treated with chronic lithium, but the inhibitory effect of sulpiride was increased in this condition. It is concluded that chronic lithium treatment may alter the D-1/D-2 receptor activity and inhibit bromocriptine-induced PE.

Effects of chronic lithium pretreatment on apomorphine-induced penile erection

1. The effects of chronic lithium pretreatment (600 mg/l in drinking rats, 30 days) on penile erection (PE) induced by apomorphine were investigated in rats. This treatment resulted in a serum Li concentration after 30 days of 0.31 +/- 0.01 mmol/l. 2. Subcutaneous (s.c.) administration of mixed D1/D2 dopamine receptor agonist apomorphine (0.05-0.5 mg/kg) induced PE in a biphasic manner. The maximum effect was obtained with 0.1 mg/kg of the drug while the response decreased with increasing doses of apomorphine from 0.1 to 0.5 mg/kg. 3. Pretreatment of animals with 0.0125-0.1 mg/kg of D1 dopamine receptor antagonist SCH 23390 or D2 dopamine receptor antagonist sulpiride (12.5-100 mg/kg) decreased apomorphine-induced PE. Combination of SCH 23390 (0.025 mg/ kg) with sulpiride (12.5 mg/kg) caused a stronger inhibitory effect on apomorphine response. This indicates that both D1 and D2 dopamine receptors may be involved in PE induced by apomorphine. 4. The response induced by apomorphine (0.05-0.05 mg/kg) was decreased in animals pretreated with chronic lithium. The inhibitory effect of sulpiride on apomorphine response, increased in animals pretreated with lithium, in contrast the inhibitory effect of SCH 23390 did not change in this condition. However, a combination of SCH 23390 with sulpiride increased inhibitory effect on apomorphine response in lithium pretreated rats. 5. It is concluded that chronic lithium inhibits PE induced by dopaminergic mechanism(s).

Inositol monophosphatase--a putative target for Li+ in the treatment of bipolar disorder

Attenuation of the phosphatidylinositol (PI) signal transduction pathway as a consequence of inhibition of inositol monophosphatase (IMPase) has been proposed as the mechanism for the efficacy of Li+ in the treatment of bipolar disorder. Nevertheless, Li+ also affects other aspects of PI signal transduction, and it is therefore not clear whether modulation of PI responses by Li+ can be attributed solely to inhibition of IMPase. However, inhibitors of IMPase mimic the effects of Li+ on some aspects of PI cell signalling, thus highlighting the potential of IMPase as a target for the treatment of bipolar disorder. The recent description of the three-dimensional structure of IMPase in conjunction with site-directed mutagenesis and kinetic studies has led to the elucidation of the enzyme mechanism. These structural and mechanistic data should prove useful in the development of novel inhibitors of IMPase that might ultimately prove useful clinically.

Lithium treatment in affective disorders: The significance of strongly elevated erythrocyte choline levels

In manic-depressive patients treated with lithium salts the transport of choline over the erythrocyte membrane is strongly inhibited, resulting in dramatically increased erythrocyte choline levels (for review see ref. 1). Whether or not there is a relationship between this effect and treatment response is not clear. Data on this issue are scarce possibly because the measurement of treatment response in lithium prophylaxis is very difficult and time consuming. Also the effect on erythrocyte choline is specific for lithium and not for manic-depressive illness. We will address here the question of a possible relation between erythrocyte choline and clinical effects of lithium.

Structure and mechanism of inositol monophosphatase

Since lithium inhibits IMPase and modulates phosphatidylinositol (PtdIns) cell signalling at therapeutically relevant concentrations (0.5-1.0 mM), IMPase has attracted attention as a putative molecular target for lithium in the treatment of manic depression. IMPase is a homodimer, with each subunit organised in an alpha beta alpha beta alpha arrangement of alpha-helices and beta-sheets, and this type of structure seems crucial to the two-metal catalysed mechanism in which an activated water molecule serves as a nucleophile. Lithium appears to inhibit the enzyme following substrate hydrolysis by occupying the second metal binding site before the phosphate group can dissociate from its interaction with the site 1 metal. The understanding of IMPase structure and the mechanism of substrate hydrolysis and lithium inhibition should be useful in the development of novel inhibitors which may prove clinically useful in the treatment of manic depression.

Myo-inositol attenuates the enhancement of the serotonin syndrome by lithium

Lithium elicits opposite effects on two behavioural syndromes in rats: enhancement of the 5-HT1A-linked serotonin syndrome and attenuation of the 5-HT2-linked wet dog shakes. The ability of intracerebroventricular (ICV) myo-inositol or forskolin to reverse the enhancement of the serotonin syndrome by lithium was tested in rats that were fed chronic dietary lithium or control diet and injected with the serotonin agonist 5-MeODMT (5-methoxy-N, N-dimethyltryptamine). Lithium enhanced the total serotonin syndrome score and particularly flat posture and tremor. Inositol, but not forskolin, mitigated the effects of lithium. Inositol was also injected in the lateral ventricle of rats pretreated with chronic dietary lithium or regular rat chow for 3 weeks and injected with carbidopa and L-5-hydroxytryptophan (5-HTP). Lithium attenuated wet dog shakes, but inositol had no significant effect on lithium-treated or control rats. These findings suggest that the enhancement of the serotonin syndrome by lithium may be related to lithium-induced inositol depletion.

Inhibition of the morphine withdrawal syndrome and the development of physical dependence by lithium in mice

Due to the claim that lithium (Li+) reduces morphine self-administration in dependent rats, the effects of acute and chronic Li+ treatments on naloxone-precipitated withdrawal syndrome and physical dependence development to morphine in mice chronically treated with morphine, were evaluated. Morphine dependency was induced by the ingestion of morphine through drinking water in increasing doses for 10 days. Physical dependence to morphine was observed by precipitating an abstinence syndrome with naloxone (2 mg/kg, i.p.). In the acute experiments, Li+ (1 and 10 mg/kg, i.p.) was administered 1 hr prior to challenge with naloxone to morphine-dependent mice whereas for chronic studies, mice received morphine concomitant with Li+ (1200 mg/l) as drinking fluid for 10 days. Results obtained indicate that acute Li+ administration significantly reduced the withdrawal signs, and we were unable to induce some degree of morphine dependency in co-administration of Li+ to mice receiving chronic morphine treatment as compared to chronic morphine administration alone. The present study revealed that even in mice with very much lower serum Li+ levels than the commonly accepted therapeutic range there was a significant reduction in the withdrawal signs. It has been shown that Li+ and morphine have diverse effects on the transmembrane signal control systems. The interaction of Li+ and morphine might be through these systems.

24-hour lithium concentration in human brain studied by Li-7 magnetic resonance spectroscopy

Brain and serum lithium concentrations were measured every second hour during a 24-hr period following lithium intake, and again 48-hr later in two normal subjects in steady state lithium treatment receiving lithium carbonate (Priadel Synthelabo) once every evening. The brain-lithium concentration was measured by 7Li magnetic resonance spectroscopy (MRS). The brain lithium level was found to undulate in a peak-trough pattern that followed the serum lithium profile, although in an attenuated form. The brain/serum lithium concentration ratio varied considerably during the 48-hr period, ranging from 0.5 to 1.3, but the ratio was independent of the serum-lithium concentration. The median half-life for lithium was 28 hr in the brain, and 16 hr in serum. The brain lithium concentration in the morning was about 75% of the clinically relevant standard 12-hr serum lithium concentration. The finding that brain lithium undulates during the day means that MRS measurements of brain lithium can only be compared if carried out under standard conditions that include a fixed interval following lithium intake and an identical treatment regimen.

Lithium-induced decrease in spontaneous Ca2+ oscillations in single GH3 rat pituitary cells

1. Measurement of [Ca2+]i in single rat pituitary GH3 cells by dynamic single cell imaging techniques demonstrated that under basal conditions there is a large variation in the temporal pattern of [Ca2+]i signalling between individual cells ranging from high frequency asynchronous oscillations to quiescence. 2. We have reported previously that treatment of GH3 cells with 1 mM Li+ (a concentration used therapeutically in the treatment of manic depression) for 7 days reduces basal and thyrotrophin-releasing hormone (TRH)-stimulated levels of mass inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. In the present study, we show that this is associated with a reduction in the number of cells exhibiting basal Ca2+ oscillations over a sampling period of 60 s, whereas the maximum amplitude of oscillations is unaffected. 3. The pattern of [Ca2+]i responses to the agonist TRH varied considerably between individual cells, making quantitation of the responses difficult; however, data obtained from measurements made on a population of cells showed that increases in peak [Ca2+]i induced by high concentrations of TRH were reduced in cells treated with 1 mM Li+ for 7 days relative to control cells. 4. The sensitivity of the phosphoinositide pathway to [Ca2+]i was investigated by loading GH3 cells with BAPTA/AM at a concentration sufficient to lower 'basal' [Ca2+]i in a population of cells and to inhibit agonist-stimulated increases in [Ca2+]i. Under these conditions, basal and TRH-stimulated mass Ins(1,4,5)P3 levels were unaffected. 5. These results demonstrate that a 7-day Li+ treatment leads to an alteration in Ca2+ signalling, in particular by reducing the number of cells exhibiting high frequency Ca2+ oscillations under basal conditions. The significance of these results to the clinical effectiveness of Li+ in the treatment of manic depression is discussed.

LiCl promotes survival of GABAergic neurons from cerebellum and cerebral cortex: LiCl induces survival of GABAergic neurons

Previous studies showed that LiCl promotes short-term survival of PC12 cells after NGF or serum deprivation. In the present work, we investigate the survival effect of lithium on cerebellar granule primary cultures. While the total population of cerebellar neurons, mainly granule cells, showed only a short-term survival (about 20 h) in the presence of LiCl, the survival of 65-100% of the GABAergic interneurons originating from cerebellum and cerebral cortex at two different developmental stages was prolonged by 1-2 weeks. Optimal activity was elicited between 5 and 7 mM LiCl. The action of lithium required the presence of serum and persisted also after medium renewal. By direct visual inspection, LiCl promoted neuronal survival without apparently altering the morphological differentiation of the cells. Our studies thereby suggest a means to obtaining enriched populations of GABAergic neurons.

Lithium maintenance therapy for bipolar I patients: possible refractoriness to reinstitution after discontinuation

Recent reports of negative responsiveness in some bipolar I patients to attempts to reinstitute lithium treatment once discontinued are reviewed.