Inositol trisphosphate, cyclic AMP, and cyclic GMP in rat brain regions after lithium and seizures

The neuropsychiatric manifestations of COVID-19: Interactions with psychiatric illness and pharmacological treatment

The recent outbreak of the corona virus disease (COVID-19) has had major global impact. The relationship between severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection and psychiatric diseases is of great concern, with an evident link between corona virus infections and various central and peripheral nervous system manifestations. Unmitigated neuro-inflammation has been noted to underlie not only the severe respiratory complications of the disease but is also present in a range of neuro-psychiatric illnesses. Several neurological and psychiatric disorders are characterized by immune-inflammatory states, while treatments for these disorders have distinct anti-inflammatory properties and effects. With inflammation being a common contributing factor in SARS-CoV-2, as well as psychiatric disorders, treatment of either condition may affect disease progression of the other or alter response to pharmacological treatment. In this review, we elucidate how viral infections could affect pre-existing psychiatric conditions and how pharmacological treatments of these conditions may affect overall progress and outcome in the treatment of SARS-CoV-2. We address whether any treatment-induced benefits and potential adverse effects may ultimately affect the overall treatment approach, considering the underlying dysregulated neuro-inflammatory processes and potential drug interactions. Finally, we suggest adjunctive treatment options for SARS-CoV-2-associated neuro-psychiatric symptoms.

The ratio of 'deleted in colorectal cancer' to 'uncoordinated-5A' netrin-1 receptors on the growth cone regulates mossy fibre directionality

Proper axonal targeting is fundamental to the establishment of functional neural circuits. The hippocampal mossy fibres normally project towards the CA3 region. In the hippocampi of patients with temporal lobe epilepsy and related animal models, however, mossy fibres project towards the molecular layer and produce the hyperexcitable recurrent networks. The cellular and molecular mechanisms underlying this aberrant axonal targeting, known as mossy fibre sprouting, remain unclear. Netrin-1 attracts or repels axons depending on the composition of its attraction-mediating receptor, deleted in colorectal cancer, and its repulsion-mediating receptor, uncoordinated-5, on the growth cone; but the roles of netrin-1-dependent guidance in pathological conditions are largely unknown. In this study, we examined the role of netrin-1 and its receptors in mossy fibre guidance and report that enhanced neuronal activity changes netrin-1-mediated cell targeting by the axons under hyperexcitable conditions. Netrin-1 antibody or Dcc ribonucleic acid interference attenuated mossy fibre growth towards CA3 in slice overlay assays. The axons were repelled from CA3 and ultimately innervated the molecular layer when hyperactivity was pharmacologically introduced. We first hypothesized that a reduction in netrin-1 expression in CA3 underlies the phenomenon, but found that its expression was increased. We then examined two possible activity-dependent changes in netrin-1 receptor expression: a reduction in the deleted in colorectal cancer receptor and induction of uncoordinated-5 receptor. Hyperactivity did not affect the surface expression of the deleted in colorectal cancer receptor on the growth cone, but it increased that of uncoordinated-5A, which was suppressed by blocking cyclic adenosine monophosphate signalling. In addition, Dcc knockdown did not affect hyperactivity-induced mossy fibre sprouting in the slice cultures, whereas Unc5a knockdown rescued the mistargeting. Thus, netrin-1 appears to attract mossy fibres via the deleted in colorectal cancer receptor, while it repels them via cyclic adenosine monophosphate-induced uncoordinated-5A under hyperexcitable conditions, resulting in mossy fibre sprouting.

lazaro encodes a lipid phosphate phosphohydrolase that regulates phosphatidylinositol turnover during Drosophila phototransduction

An essential step in Drosophila phototransduction is the hydrolysis of phosphatidylinositol 4,5 bisphosphate PI(4,5)P2 by phospholipase Cbeta (PLCbeta) to generate a second messenger that opens the light-activated channels TRP and TRPL. Although the identity of this messenger remains unknown, recent evidence has implicated diacylglycerol kinase (DGK), encoded by rdgA, as a key enzyme that regulates its levels, mediating both amplification and response termination. In this study, we demonstrate that lazaro (laza) encodes a lipid phosphate phosphohydrolase (LPP) that functions during phototransduction. We demonstrate that the synergistic activity of laza and rdgA regulates response termination during phototransduction. Analysis of retinal phospholipids revealed a reduction in phosphatidic acid (PA) levels and an associated reduction in phosphatidylinositol (PI) levels. Together our results demonstrate the contribution of PI depletion to the rdgA phenotype and provide evidence that depletion of PI and its metabolites might be a key signal for TRP channel activation in vivo.

Effect of chronic lithium treatment on the turnover of alpha2-adrenoceptors after chemical inactivation in rats

One of the most effective psychotherapeutic agents in the treatment of bipolar disease is lithium. Chronic lithium treatment affects some signal transduction mechanisms such as cAMP, cGMP, inositol 1,4,5 P(3), Gi protein, protein kinase C and can also modify gene expression in rat brain. In a previous study, we observed a greater inhibitory effect of lithium on cAMP production after blockade of alpha(2)-adrenoceptors in rat cerebral cortex. Here we examine the influence of chronic lithium treatment on turnover of alpha(2)-adrenoceptors after their inactivation by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) in rat cerebral cortex. After treatment with lithium for 10 days (120 mg/kg/day, i.p.), there was a significant increase in the appearance and disappearance rate constants of these adrenoceptors and a significant reduction of their half-life. These results suggest that chronic lithium administration alters the alpha(2)-adrenoceptor turnover in rat brain.

Pharmacological plasticity of GABA(A) receptors at dentate gyrus synapses in a rat model of temporal lobe epilepsy

In the lithium-pilocarpine model (Li-pilocarpine) of temporal lobe epilepsy, GABA(A) receptor-mediated inhibitory postsynaptic currents (GABA(A) IPSCs) were recorded in dentate gyrus granule cells (GCs) from adult rat hippocampal slices. The properties of GABA(A) IPSCs were compared before and after superfusion of modulators in control conditions (Li-saline rats) and in Li-pilocarpine rats 24-48 h and 3-5 months (epileptic rats) after status epilepticus (SE). The mean peak amplitude of GABA(A) IPSCs increased by about 40% over Li-saline values in GCs 24-48 h after SE and remained higher in epileptic rats. In Li-pilocarpine rats, studied at 24-48 h after SE, diazepam (1 microm) lost 65% of its effectiveness at increasing the half-decay time (T(50%)) of GABA(A) miniature IPSCs (mIPSCs). Diazepam had no effects on mIPSC T(50%) in epileptic rats. The benzodiazepine ligand flumazenil (1 microm), acting as an antagonist in Li-saline rats, exhibited a potent inverse agonistic effect on GABA(A) mIPSCs of GCs from Li-pilocarpine rats 24-48 h and 3-5 months after SE. The neurosteroid allopregnanolone (100 nm), which considerably prolonged GABA(A) mIPSCs in Li-saline rats, totally lost its effect in rats studied 24-48 h after SE. However, this decrease in effectiveness was transient and was totally restored in epileptic rats. In addition to the up-regulation in the number of receptors at individual GC synapses, we propose that these 'epileptic' GABA(A) receptors possess benzodiazepine binding sites with altered allosteric properties. The failure of benzodiazepine and neurosteroid to potentiate inhibition early after SE may be a critical factor in the development of epileptogenesis and occurrence of seizures.

Neuroprotection and epilepsy

During the last years it has become obvious that the current way of treating epilepsy with antiepeileptic drugs is insufficient concerning the modification of the underlying disesease and provides merely a symptomatic treatment, without clear influence on the course of the disease. There is a pressing need to find alternative strategies and to find possibilities to intervene either into the basic processes determining the development of epilepsies or to promote compensatory processes in repairing these dysfunctions. The increasing knowledge about the basic neuronal changes underlying epilepsies allows now to analyse the potential role of neuroprotective agents in in epileptogenesis. In epilepsy the most frequent constellation is the presence of damage and overexcitation together. Increase in excitability may develop after a primary damage as in posttraumatic epilepsy, or outburst of epileptic excitability may cause neuronal damage as in cell loss after status epilepticus or in any case of the so called cytotoxic damage from extensive glutamatergic involvement. Epilepsy in certain forms is a progressive disease. The factors determining the progressive course and the possibe prevention of it is obviously an overlaping field with neuroprotection. Therefore although neuroprotection works only against certain aspects of a complex cascade of pathological events, might be a promising option in several stadiums during the development and course of epilepsy. We provide evidences that some of the new antiepileptic drugs have neuroprotective effect on different animal models of chronic partial epilepsies, and how this effect is fitting to the antiepileptogenic, and seizure supressing effect of the same drugs.

Lithium detaches hexokinase from mitochondria and inhibits proliferation of B16 melanoma cells

Glycolysis is known to be the primary energy source in cancer cells. Hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1), the only glycolytic enzyme which binds to mitochondria, is exceptionally high in cancer cells, and believed to play a key role in regulating cell energy metabolism and cancer cell growth rate. We show here that lithium induces a detachment of hexokinase from mitochondria of B16 melanoma cells. This effect eventually leads to inhibition of cell proliferation. These results reveal a novel, additional, mechanism of action of lithium and suggest that lithium may be promising drug in treatment of melanoma.

The high affinity inositol transport system--implications for the pathophysiology and treatment of bipolar disorder

The 'inositol-depletion hypothesis' postulates that the therapeutic effects of lithium are due to inhibition of inositol monophosphatase, which leads to depletion of brain cells of myo-inositol and consequently to dampening of phosphoinositide (PI) signaling. This article examines the potential relevance of an alternative mechanism for inositol depletion: inhibition of myo-inositol uptake that proceeds via the sodium/myo-inositol cotransport (SMIT). We discuss recent in vitro experiments that show a pronounced downregulation of SMIT after chronic treatment with lithium, carbamazepine, and valproate at therapeutically relevant concentrations. It is concluded that downregulation of SMIT could represent a common mechanism of action of mood stabilizers.

Acute cellular alterations in the hippocampus after status epilepticus

The critical, fundamental mechanisms that determine the emergence of status epilepticus from a single seizure and the prolonged duration of status epilepticus are uncertain. However, several general concepts of the pathophysiology of status epilepticus have emerged: (a) the hippocampus is consistently activated during status epilepticus; (b) loss of GABA-mediated inhibitory synaptic transmission in the hippocampus is critical for emergence of status epilepticus; and, finally (c) glutamatergic excitatory synaptic transmission is important in sustaining status epilepticus. This review focuses on the alteration of GABAergic inhibition in the hippocampus that occurs during the prolonged seizures of status epilepticus. If reduction in GABAergic inhibition leads to development of status epilepticus, enhancement of GABAergic inhibition would be expected to interrupt status epilepticus. Benzodiazepines and barbiturates are both used in the treatment of status epilepticus and both drugs enhance GABA(A) receptor-mediated inhibition. However, patients often become refractory to benzodiazepines when seizures are prolonged, and barbiturates are often then used for these refractory cases of status epilepticus. Recent evidence suggests the presence of multiple GABA(A) receptor isoforms in the hippocampus with different sensitivity to benzodiazepines but similar sensitivity to barbiturates, thus explaining why the two drug classes might have different clinical effects. In addition, rapid functional plasticity of GABA(A) receptors has been demonstrated to occur during status epilepticus in rats. During status epilepticus, there was a substantial reduction of diazepam potency for termination of the seizures. The loss of sensitivity of the animals to diazepam during status epilepticus was accompanied by an alteration in the functional properties of hippocampal dentate granule cell GABA(A) receptors. Dentate granule cell GABA(A) receptor currents from rats undergoing status epilepticus had reduced sensitivity to diazepam and zinc but normal sensitivity to GABA and pentobarbital. Therefore, the prolonged seizures of status epilepticus rapidly altered the functional properties of hippocampal dentate granule cell GABA(A) receptors, possibly explaining why benzodiazepines and barbiturates may not be equally effective during treatment of the prolonged seizures of status epilepticus. A comprehensive understanding of the cellular and molecular events leading to the development, maintenance, and cytotoxicity of status epilepticus should permit development of more effective treatment strategies and reduction in the mortality and morbidity of status epilepticus.

Li+ and muscarine cooperatively enhance the cationic tail current in rat cortical pyramidal cells

Li+ is known to facilitate the onset of status epilepticus induced by cholinergic stimulation, although the underlying mechanisms are not clear. Under whole-cell current clamp conditions with a CsCl-based internal solution, cortical pyramidal cells display a single plateau-spike followed by a slow depolarizing afterpotential (DAP) in response to injection of a short current pulse. However, the same current pulse generated a burst of plateau-spikes after application of Li+ (2 mM) and muscarine (10 microM). As similar bursts of plateau-spikes were generated through an enhancement of the slow DAP when [K+]o was raised (Kang et al. 1998), we have investigated the effects of Li+ and muscarine on the Ca2+-dependent cationic current underlying the slow DAP, measured as the slow tail current evoked after the offset of depolarizing voltage pulses. Muscarine enhanced the amplitudes of both early and late components of the slow tail current. This effect of muscarine was markedly potentiated by Li+, while Li+ by itself affected the slow tail current only slightly. Intracellular application of heparin (0.5-1 mg/mL) suppressed the effect of muscarine in the presence of Li+. These results suggest that inositol-trisphosphate-induced Ca2+ release is involved in the cooperative enhancement of the slow tail current, and this cooperation may be one of the mechanisms underlying facilitation of the onset of epilepsy induced by these agents.

Lithium reduces tau phosphorylation: effects in living cells and in neurons at therapeutic concentrations

BACKGROUND

The mechanism of action of lithium remains to be determined satisfactorily. Recent studies suggested a possible role in inhibiting glycogen synthase kinase-3 (GSK-3), previously shown to phosphorylate the protein tau. Tau is expressed mainly in neurons, where it functions to stabilize microtubules in a phosphorylation-dependent manner.

METHODS

Neurons and transfected non-neuronal cells were treated with lithium and the phosphorylation of tau at multiple epitopes examined by western blotting and by immunocytochemistry. Using green fluorescent protein as a tag we examined the effects of lithium on phosphorylated tau in living cells.

RESULTS

Lithium reversibly reduced tau phosphorylation at therapeutic concentrations, and even at high concentrations did not alter neuronal morphology. Green fluorescent protein tagged-tau when phosphorylated by GSK-3 was diffusely distributed; treatment with lithium resulted in association with microtubules and then bundle formation. Removing lithium allowed observation of the dissolution of bundles and gradual dissociation of tau from microtubules in living cells.

CONCLUSIONS

Lithium may have multiple effects in brain, but at least one action is demonstrated to be a relative inhibition of GSK-3-induced tau phosphorylation. These results carry implications for future studies of the actions of mood-stabilizing drugs and indeed of the molecular mechanisms of affective disorders.

Effects of lithium treatment on extracellular serotonin levels in the dorsal hippocampus and wet-dog shakes in the rat

In the present study wet-dog shakes in rats were induced by local potassium (K+) depolarization in the dorsal hippocampus. Concurrently, changes in extracellular concentrations of cyclic AMP (cAMP) and serotonin (5-HT) were assessed by microdialysis. It has been well-established that lithium influences the synthesis of cAMP in the brain via effects on adenylate cyclases. In this study, the effect of chronic lithium treatment on the number of wet-dog shakes and the release of 5-HT was investigated. Wet-dog shakes, formation of cAMP and release of 5-HT were induced by perfusing a Ringer solution containing 60 mM K+ through the microdialysis probe for 20 min. Under some conditions, this high K+ solution also contained 20 microM forskolin. The number of wet-dog shakes and the formation of cAMP induced by K+ depolarization were enhanced by forskolin, while the K+ -stimulated release of 5-HT was unaffected by forskolin. Chronic lithium treatment, yielding a plasma lithium level of 0.78+/-0.09 mmol/l, decreased the number of wet-dog shakes but did not affect the extracellular level of 5-HT in the dorsal hippocampus. Chronic lithium treatment may affect the serotonergic wet-dog shake syndrome in the rat partly via the cAMP signalling system but does not seem to influence this syndrome by changing the release of 5-HT from nerve terminals in the dorsal hippocampus.

Effects of lithium, alone or associated with pilocarpine, on muscarinic and dopaminergic receptors and on phosphoinositide metabolism in rat hippocampus and striatum

The mechanism of action of lithium (Li) alone or with pilocarpine (Pilo), focusing on muscarinic and dopaminergic systems and also on phosphoinositide metabolism was studied. Li (3 mEq/kg) administered to rats once (1 d) or daily for 7 days (7 d), 24 h before Pilo (15 mg/kg), exacerbated cholinergic signs, leading to tremors. convulsions and brain lesions. Increases in muscarinic receptors (MR) of 29 and 49% were observed in the hippocampus after atropine (Atro) and Li-Atro-Pilo treatments, respectively, as compared to controls (Atro) and the Li-Pilo group (Li-Atro-Pilo). In the striatum, except for the 37% increase in the Li-Atro (50 mg/kg)-Pilo group as compared to the Li-Pilo one, no other changes were observed in MR. A decrease of 32% on average in D2-like receptors (D2R) was detected in the hippocampus in the group Li-7d. On the contrary, in the striatum an increase (25%) in the Li-7d group was observed and this effect was blocked by Li-Pilo. As far as inositol phosphates (IP) and phosphatidylinositol-4,5-biphosphate (PIP2) metabolism is concerned, Li caused a decrease (28%) and an increase (60%) in IP and PIP2 accumulations, respectively, in hippocampus slices while Pilo only altered IP accumulation (32% decrease). In this area the association of Li-Atro (10 mg/kg)-Pilo also caused a decrease (36%) in PIP2 as compared to the Li-Pilo group. In striatal slices, except for the Li, Atro (10 mg/kg) and Li-Atro (10 mg/kg)-Pilo groups which showed a decrease (33 40%) in IP accumulation, no other alteration was detected. The potentiation of the effect of Pilo by Li does not seem to depend on the PI metabolism, but instead on its involvement with muscarinic and dopaminergic systems.

Selective effects of long-term lithium and carbamazepine administration on G-protein subunit expression in rat brain

The efficacy of lithium and carbamazepine in treatment of bipolar affective disorder is well established. Although a number of biochemical effects have been found the exact molecular mechanisms underlying their therapeutic actions have not been elucidated. Nor have the target regions in the brain been located. The objectives of the present investigation were to identify the selective effects and target regions of long-term treatment, with either lithium or carbamazepine, on G-protein subunit expression in rat brain. Effects were measured in hippocampus, hypothalamus, amygdala, frontal cortex, neostriatum, thalamus, raphe nuclei and cerebellum. At the protein level amounts of Galphao decreased significantly (P < 0.01) in neostriatum and Gbeta increased in frontal cortex in response to both drug treatments. At the mRNA level amounts of Galphai1 increased significantly (P < 0.01) in neostriatum. Galphas messenger amounts decreased in frontal cortex and increased in thalamus. These effects were common for both drugs, however, in addition also some differential effects, specific for either of the two drugs, were observed. We conclude frontal cortex and neostriatum are important target regions of long-term treatment with either lithium or carbamazepine and suggest Galphao, Galphas, Galphai1 and Gbeta to be selective target molecules.

Rapid seizure-induced reduction of benzodiazepine and Zn2+ sensitivity of hippocampal dentate granule cell GABAA receptors

Fast synaptic inhibition in the forebrain is mediated primarily by GABA acting on GABAA receptors (GABARs). GABARs are regulated by numerous positive (barbiturates, benzodiazepines, and neurosteroids) and negative (picrotoxin, bicuculline, and Zn2+) allosteric modulators. The sensitivity of GABARs to GABA and to allosteric modulators changes gradually during normal development, during development of chronic epilepsy, and after prolonged exposure to GABAR agonists. Here we report the development of rapid functional plasticity of GABARs occurring over 45 min of continuous seizures (status epilepticus) in rats. Seizures induced in rats by administration of lithium followed by pilocarpine were readily terminated by the benzodiazepine diazepam when administered early during the seizures (after 10 min of seizures). However, during status epilepticus, there was a substantial reduction of diazepam potency for termination of the seizures. To determine whether the loss of sensitivity of the animals to diazepam was caused by an alteration of GABAR functional properties, we obtained whole-cell GABAR currents from hippocampal dentate granule cells isolated acutely from control rats and from rats undergoing status epilepticus. GABAR properties were characterized by determining GABA sensitivity and the sensitivity of GABARs to regulation by benzodiazepines, barbiturates, and Zn2+. When compared with those from naive controls, GABAR currents from rats undergoing status epilepticus were less sensitive to diazepam and Zn2+ but retained their sensitivity to GABA and pentobarbital. We conclude that the prolonged seizures of status epilepticus rapidly altered the functional properties of hippocampal dentate granule cell GABARs.

Chronic treatment with antidepressants, verapamil, or lithium inhibits the serotonin-induced intracellular calcium response in individual C6 rat glioma cells

The effects of chronic treatment with antidepressants, verapamil, or lithium on serotonin (5-HT)-induced Ca2+ increase were investigated in single C6BU-1 glioma cells with digital imaging microscopy. Clomipramine and citalopram, at a concentration of 100 nM, decreased the peak values of 5-HT-induced [Ca2+]i changes. Verapamil (100 nM), a calcium antagonist, and lithium (1 mM) also inhibited the peak amplitudes in the same way. The present findings suggest that chronic treatment with antidepressants, verapamil, or lithium, at therapeutic concentrations, have the common action of inhibiting 5-HT-mediated [Ca2+]i increase.

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.

Modulation by inositol of cholinergic- and serotonergic-induced seizures in lithium-treated rats

Hippocampal and cortical EEG recordings in rats were used to monitor the in vivo modulation by lithium of responses to agonists for 5HT2/5HT1c serotonergic (DOI) and cholinergic (pilocarpine) receptors and the influence of inositol administration. Administration of DOI (8 mg/kg) or pilocarpine (30 mg/kg) to rats pretreated with lithium acutely (3 mmol/kg) or chronically (dietary, 4 weeks) resulted in seizures, whereas these doses did not cause seizures without lithium pretreatment. This indicated that lithium most likely affects a signal transduction process common to both systems, which is the phosphoinositide second messenger system. To examine the potential influence of altered inositol levels on these responses, we tested the effects of infusions (10 mg, i.c.v.) of myo-inositol, a precursor of phosphoinositide synthesis, and of epi-inositol, an isomer not used for phosphoinositide synthesis. Administration of myo-inositol (10 mg) slightly reduced the incidence of seizures induced by acute lithium plus DOI but almost completely blocked seizures induced by acute lithium plus pilocarpine. This was surprising since seizures induced by acute lithium plus DOI were less severe than those after acute lithium plus pilocarpine, but myo-inositol was more effective in blocking the latter. Epi-inositol also blocked seizures under both conditions but it was less effective than myo-inositol after treatment with acute lithium plus pilocarpine. The latencies to seizures and/or severity of seizures were potentiated more by chronic than acute lithium pretreatment with both DOI and pilocarpine, but attenuation by myo-inositol was less with each agonist after chronic lithium compared with acute lithium treatment. Peripheral administration of a high dose of myo-inositol blocked seizures induced by acute lithium plus pilocarpine, but the inositol treatment itself was toxic and caused seizures prior to pilocarpine administration, so the mechanism of action cannot simply be attributed to increased brain inositol levels. These results demonstrate that lithium modulates the in vivo responses to DOI and pilocarpine, most probably through an effect on the phosphoinositide signal transduction system. They also show that centrally administered myo-inositol modifies responses to these agents, but the effectiveness of epi-inositol and other results leave unclear the mechanistic basis of its actions.

Lithium stimulates accumulation of second-messenger inositol 1,4,5-trisphosphate and other inositol phosphates in mouse pancreatic minilobules without inositol supplementation

Previous studies showed that lithium, beginning at therapeutic plasma concentrations in the treatment of manic depression, increased the accumulation of second-messenger inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] in cerebral cortex slices of guinea pig and rhesus monkey [Lee, Dixon, Reichman, Moummi, Los and Hokin (1992) Biochem. J. 282, 377-385; Dixon, Lee, Los and Hokin (1992) J. Neurochem. 59, 2332-2335; Dixon, Los and Hokin (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 8358-8362]. These studies have now been extended to a peripheral tissue, mouse pancreatic minilobules. In the presence of carbachol, concentrations of lithium from 1 to 20 mM sharply and progressively increased the accumulation of Ins(1,4,5)P3 and inositol 1,3,4,5-tetrakisphosphate, followed by a decrease. Assay of these inositol polyphosphates by either the prelabelling technique or mass assay gave similar results. Atropine quenching of cholinergically stimulated pancreatic minilobules led to a rapid disappearance of Ins(1,4,5)P3. This disappearance was impeded by lithium. This suggested that the lithium-induced elevation in Ins(1,4,5)P3 was due to inhibition of the 5-phosphatase and, on the basis of the markedly elevated concentrations of inositol 1,3,4-trisphosphate [Ins(1,3,4)P3] and inositol 1,4-bisphosphate in the presence of lithium, probably by feedback inhibition by these latter two compounds. An additional mechanism, i.e. a stimulatory effect of lithium on phospholipase C, cannot, however, be ruled out. The other reaction product of phospholipase C, inositol cyclic 1:2,4,5-trisphosphate, also increased in the presence of lithium. This may also be due to inhibition of the 5-phosphatase, which is the exclusive mechanism for removal of this compound. The effects of lithium on the accumulation of other inositol phosphates paralleled that of Ins(1,4,5)P3, with the exception of inositol 3,4-bisphosphate, which decreased. This was presumably due to the inhibition of Ins(1,3,4)P3 1-phosphatase by lithium. Unlike mouse cerebral cortex slices [Lee, Dixon, Reichman, Moummi, Los and Hokin (1992) Biochem. J. 282, 377-385], inositol supplementation was not required to demonstrate lithium-stimulated Ins(1,4,5)P3 accumulation in mouse pancreatic minilobules. This indicates that inositol depletion sufficient to impair lithium-stimulated Ins(1,4,5)P3 accumulation does not occur in mouse pancreatic minilobules, even though an elevation of cytidine diphosphodiacylglycerol occurred, indicating some inositol depletion due to lithium. Elevation of Ins(1,4,5)P3 by lithium may be a general phenomenon in the central nervous system and peripheral tissues under non-rate-limiting concentrations of inositol.

Distinctive rat brain immediate early gene responses to seizures induced by lithium plus pilocarpine

The mRNA levels of four immediate early genes (IEG) were measured in rat brain regions 60 min after administration of pilocarpine (30 mg/kg) to lithium-treated (3 mmol/kg) rats, during generalized convulsive status epilepticus. Northern blots demonstrated induction of the genes in the order of c-fos = jun-B > c-jun > jun-D with large increases in the cerebral cortex, hippocampus, and striatum, a smaller increase in the cerebellum, and less in the brainstem. The mRNA levels of these four IEG were measured in rat cerebral cortex and hippocampus at several times after administration of the cholinergic agonist pilocarpine (5 or 30 mg/kg) with or without lithium pretreatment (3 mmol/kg, 16 h prior, or chronic 4 week dietary administration). Treatment with pilocarpine (30 mg/kg) alone increased mRNA levels in the order of c-fos > jun-B > c-jun but did not change the jun-D mRNA level, and maximal c-fos and jun-B mRNA levels occurred earlier (30 min) in the cortex than in the hippocampus. Treatment with the lower dose of pilocarpine (5 mg/kg) alone caused only small increases in c-fos and jun-B mRNA levels and these responses were unaffected by lithium pretreatment. Lithium pretreatment potentiated IEG expression induced by 30 mg/kg pilocarpine, likely as a result of the seizures caused by this combination of drugs because pretreatment with anticonvulsants (diazepam or MK-801) blocked seizures and the enhanced IEG mRNA levels. The mRNA levels were increased during seizures in the order of c-fos > jun-B > c-jun > jun-D in the hippocampus and jun-B > c-fos > c-jun > jun-D in the cortex, and were increased for a longer duration as well as to a greater extent than after administration of pilocarpine alone. Administration of pilocarpine (30 mg/kg) to rats treated chronically with lithium caused increases similar to those measured with acute lithium pretreatment. Thus the induction of IEG by cholinergic stimulation varied with dose, time, and brain region, and unique responses were observed for each of the IEG. Lithium pretreatment did not impair IEG expression induced by the lower dose of pilocarpine and greatly enhanced expression of IEG after administration of the higher dose of pilocarpine concomitant with seizure activity.

Protective effect of lithium on the stress-induced depression of cell-mediated immunity in mice

The effect of lithium chloride (LiCl) administration on the stress-induced depression of cell-mediated immunity was studied in mice. Two models of stress-induced depression of immunity were used: (1) keeping the animals at a temperature of 4 degrees C twice for 24 h at a 24-h interval, and (2) keeping them in the dark for 96 h. Both kinds of stress significantly decreased the reactivity of cell donors in the graft-versus-host (GVH) reaction and recipients in the host-versus-graft (HVG) reaction. Treatment with LiCl of the cell donors in GVH reaction or the recipients in HVG reaction daily for three weeks before stress application completely abolished the immunosuppressive effect of "cooling" stress, but not "darkness" stress. The LiCl is thus shown as a potential immunomodulator protecting mice from some forms of the stress-induced depression of cell-mediated immunity.

Intracellular calcium signalling in peripheral cells of patients with bipolar affective disorder

Consistent with previous studies, elevated free intracellular calcium ion concentrations ([Ca2+]i) were found in blood platelets and lymphocytes of patients with mania and bipolar depression. Incubation with an ultrafiltrate of plasma from patients with bipolar illness had no effect on intracellular calcium ion concentration in platelets from normal subjects, suggesting that elevated [Ca2+]i is not due to a circulating factor. As was true in an earlier study of the effect of lithium on platelets, incubation with therapeutic levels of carbamazepine lowered [Ca2+]i in lymphocytes from affectively ill patients but not controls. Increased [Ca2+]i in peripheral cells may reflect a diffuse change in cellular homeostasis and may contribute to mixtures as well as rapid alternations of activity of affective, behavioral and physiologic systems in bipolar illness. Correction of the abnormality may at least be a marker of a relevant therapeutic action if it is not the action itself.

Lithium modulation of phosphoinositide signaling system in rat cortex: selective effect on phorbol ester binding

Recent work indicates that the therapeutic action of lithium may be mediated through perturbation of postreceptor second messenger systems. To elucidate further the postreceptor cellular sites of action(s) of lithium, the effect of chronic lithium treatment on various components of the receptor-activated phosphoinositide pathway was investigated. We found that chronic administration of lithium (0.2% LiCl, 21 days) to adult male rats did not significantly affect phosphoinositide hydrolysis in cerebral cortical slices induced by carbachol (1 mM) or NaF (10 mM). Nor did the same treatment alter the carbachol (1 mM) potentiation of guanosine 5'-(gamma-thio)triphosphate (30 microM) stimulation of phosphoinositide hydrolysis (an index of receptor/G protein coupling) in cortical membranes. Immunoblotting studies revealed no changes in the levels of G alpha q/11 immunoreactivity in the cortex after chronic lithium treatment. The levels of protein kinase C, as revealed by specific binding of [3H]phorbol dibutyrate ([3H]PDBu), were significantly reduced in the cytosolic fraction and increased in the particulate fraction of rat cortex after chronic lithium, whereas the KD of [3H]PDBu binding remained relatively constant. A small and insignificant decrease in the density of [3H]inositol 1,4,5-trisphosphate binding was also found in the cortex. The above data suggest that chronic lithium treatment affects neither the muscarinic cholinergic-linked phosphoinositide turnover nor the putative G protein alpha subunit (G alpha q/11) responsible for phospholipase C activation. However, a possible translocation and activation of protein kinase C activity may be significant in the therapeutic effect of this mood-stabilizing agent.

Characterization of the effects of lithium on phosphatidylinositol (PI) cycle activity in human muscarinic m1 receptor-transfected CHO cells

1. The effects of lithium on [3H]-inositol and [3H]-cytidine incorporation into [3H]-inositol monophosphates ([3H]-InsP1) and [3H]-cytidine monophosphorylphosphatidate ([3H]-CMP-PA), respectively, and inositol 1,4,5-trisphosphate (InsP3) and inositol 1,3,4,5-tetrakisphosphate (InsP4) mass were studied in carbachol-stimulated human m1 muscarinic receptor-transfected Chinese hamster ovary cells (m1 CHO cells). 2. Lithium alone (10 mM) had no appreciable effects on any of the four parameters measured; it was only in carbachol-stimulated cells that the effects of lithium became apparent. 3. In the presence of carbachol (1 mM), lithium (10 mM) caused a relatively rapid (within 5 min) accumulation of [3H]-InsP1 and [3H]-CMP-PA which continued up to about 20-30 min, after which accumulation slowed down. On the other hand, the elevation in InsP3 and InsP4 levels produced by carbachol was not altered by lithium in the short-term and only at later times (> 20-30 min) was the response attenuated, with InsP3 and InsP4 levels approaching basal. 4. The effects of lithium on carbachol-stimulated [3H]-InsP1 and [3H]-CMP-PA accumulation and the attenuation of the carbachol-induced elevation of InsP3 and InsP4 were all dose-dependent, with EC50s in the region of 1 mM. 5. The lithium-induced effects on [3H]-CMP-PA and InsP3 and InsP4 in carbachol-stimulated cells could be reversed, in a dose-dependent manner, by preincubation with exogenous myo-inositol (EC50 = 2-3 mM) but not by the inactive analogue scyllo-inositol, indicating that these effects occur as a consequence of depletion of inositol. 6. The temporal effects of lithium are consistent with lithium inhibiting inositol monophosphatase,causing accumulation of InsP1, resulting in lower free inositol levels. This leads to accumulation of CMP-PA and reduced PI synthesis which, once agonist-linked membrane inositol phospholipids are depleted, produces attenuated InsP3 and InsP4 responses.7. These results in ml CHO cells support the hypothesis that lithium affects the PI cycle cell signalling pathway by depletion of inositol due to inhibition of inositol monophosphatase.

The cholinergic receptor-linked phosphoinositide metabolism in mouse cerebrum and cerebellum in vivo

The cholinergic receptor-linked poly-phosphoinositide hydrolysis was studied in mouse cerebrum and cerebellum after prelabeling the brain with [3H]inositol. I.p. injection of Li (8 meq/kg) to C57Bl/6J mice for 4 h resulted in 14- and five-fold increases in [3H]inositol-labeled inositol monophosphate (IP1) in cerebrum and cerebellum, respectively. The labeled inositol bisphosphate (IP2) was also increased 83 and 19% in cerebrum and cerebellum, respectively. Prior injection of atropine (100 mg/kg) resulted in inhibition of Li-induced increases in labeled IP1 by 74 and 56% in cerebrum and cerebellum, respectively. Administration of pilocarpine (20 mg/kg) to the Li-treated mice for 30 min resulted in further increases in labeled IP1 and IP2 and a concomitant decrease in labeled inositol in cerebrum but not in cerebellum. Mass measurements of IP1 and IP2 isomers by HPLC revealed that inositol 1-monophosphate (Ins(1)P), inositol 4-monophosphate (Ins(4)P) and inositol 1,4-bisphosphate (Ins(1,4)P2) were all increased by pilocarpine administration in the Li-treated mouse cerebrum. The effects of pilocarpine administration in mouse cerebrum (increases in IP1 and IP2) could be completely inhibited by preinjection of atropine. Atropine injection also decreased the levels of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. Surprisingly, a decrease in Ins(1,4,5)P3 level was also found in non-Li-treated mice after pilocarpine administration (30 mg/kg, 10-40 min). Except for the increase (20%) in [32P]-labeled PIP in the cerebrum, Li or Li together with pilocarpine administration did not alter the levels of [3H]inositol or [32P]phosphate-labeled phosphoinositides.(ABSTRACT TRUNCATED AT 250 WORDS)

Lithium enhances accumulation of [3H]inositol radioactivity and mass of second messenger inositol 1,4,5-trisphosphate in monkey cerebral cortex slices

We previously reported that lithium, in the presence of acetylcholine, increased accumulations of inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate in brain cortex slices from the guinea pig, rabbit, rat, and mouse. In the mouse and rat, the Li(+)-induced increases required supplementation of the medium with inositol. This probably relates to the following facts: (a) Brain cortices of the mouse and rat contain in vivo concentrations of inositol half of that of the guinea pig. (b) Incubated rat brain cortex slices are depleted of inositol by 80%. (c) The slices require 10 mM inositol supplementation to restore in vivo concentrations. We now show that in monkey brain cortex slices, therapeutic concentrations of Li+ increase accumulation of inositol 1,4,5-trisphosphate. The inositol 1,3,4,5-tetrakisphosphate level is not increased. Neither inositol nor an agonist is required. The same effects are seen whether inositol 1,4,5-trisphosphate is quantified by the [3H]inositol prelabeling technique or by mass assay, although mass includes a pool of inositol 1,4,5-trisphosphate that is metabolically inactive. Thus, in a therapeutically relevant model for humans, Li+ increases inositol 1,4,5-trisphosphate levels in brain cortex slices, as was previously seen in lower mammals at non-rate-limiting concentrations of inositol.