Alona Shaldubina

The mechanism of lithium action: state of the art, ten years later

Lithium is an effective drug for both treatment and prophylaxis of bipolar disorder. However, the mechanism of lithium action is still unknown. The inositol depletion hypothesis is supported by biochemical and behavioral data in rats, but primate inositol levels are higher than in rodents and may obviate the effects of depletion. Inhibition of 5HT autoreceptors by lithium is supported by biochemical and behavioral data in rats but would seem more related to lithiums antidepressant than to its antimanic or prophylactic effects. Lithium induces increases in levels of the anti-apoptotic factor Bcl-2. This effect could be most relevant for treatment of neurodegenerative disorders. Lithium inhibits glycogen synthase kinase-3, which is involved in a wide range of signal transduction pathways. However, this lithium effect occurs at high concentrations and may be more relevant for its toxic effect. Lithium in low concentrations induces accumulation of PAP, which affects several cellular processes including RNA processing. However, PAP phosphatase is present more in peripheral tissues than in brain. This lithium effect could explain some of its peripheral side effects. Chronic lithium administration upregulates glutamate reuptake and thus decreases glutamate availability in synapse. Glutamate is an excitatory neurotransmitter and its reduction could exert an antimanic effect. Biochemical and clinical experiments are necessary to determine the key mechanism of lithium efficacy in treatment and prophylaxis of affective disorders.

The antidepressant activity of inositol in the forced swim test involves 5-HT2 receptors

The effect of inositol as an antidepressant was previously demonstrated in both animal models of depression-like behavior and in clinical trials. Unlike most antidepressant drugs, inositol does not have a clear target in the synapse and was not demonstrated to alter monoamine levels in the brain. The present study attempted to draw a psychopharmacological profile of inositols behavioral effects by exploring the interactions between the drug and specific receptor agonists and antagonists in the forced swim test. Rats received inositol treatment (or control) in combination with the serotonergic metabolism inhibitor PCPA or with the noradrenergic neurotoxin DSP-4. Results indicated that PCPA but not DSP-4 abolished the ability of inositol to cause a reduction in immobility time in the forced swim test. In mice, the specific 5-HT(2A)/5-HT(2C) antagonist ritanserin, but not the 5-HT(1A)/5-HT(1B)/beta adrenergic antagonist pindolol, abolished inositols effect in the forced swim test. The 5-HT(2A)/5-HT(2C) agonist DOI and the 5-HT(1A) agonist 8-OH-DPAT did not have any significant effects on inositols activity. The present data indicates that the antidepressant effect of inositol may involve 5-HT(2) receptors. It is thus possible that the effects of reuptake antidepressant drugs and the effects of inositol may have a common final pathway.

Preliminary evaluation of oral anticonvulsant treatment in the quinpirole model of bipolar disorder

Summary. A potential model for bipolar disorder, quinpirole-induced biphasic locomotion, was used for a preliminary evaluation of behavioral effects of oral anticonvulsant treatment. Quinpirole, a D2/D3 agonist, induces a biphasic locomotor response starting with inhibition and followed by excitation, resembling the oscillating nature of bipolar disorder. The present study developed a paradigm for oral administration of anticonvulsants that resulted in therapeutic blood levels and tested the effects of treatment on the quinpirole-induced response.Eleven days treatment with valproate (12 g/liter water), phenytoin (6 g/kg food), and carbamazepine (8 g/kg food) resulted in therapeutic blood levels and in a borderline significant reduction in quinpirole-induced hyperactivity without effects on the hypoactive phase. Valproate effects became more significant at the height of the hyperactivity response. Eleven days treatment with topiramate (30 mg/kg) resulted in a significant attenuation of quinpirole-induced hyperactivity, qualitatively similar to the effects of the other anticonvulsants.The results suggest that mood-stabilizing anticonvulsant drugs including topiramate may attenuate quinpirole-induced hyperactivity.

Glycogen synthase kinase-3?? heterozygote knockout mice as a model of findings in postmortem schizophrenia brain or as a model of behaviors mimicking lithium action: negative results

In mice glycogen synthase kinase (GSK)-3&bgr; heterozygote knockout status was reported to cause reduced immobility in the Porsolt forced swim test and reduced amphetamine-induced hyperactivity, behaviors that mimic the effects of lithium. GSK-3&bgr; protein and mRNA level and activity have been reported to be reduced in the postmortem brain of schizophrenia patients and this could suggest the involvement of GSK-3&bgr; in the etiology of schizophrenia. However, apomorphine-induced stereotyping was reported to be unchanged in GSK-3&bgr; heterozygote (HZ) knockout (KO) mice. As such behaviors are not always robust, study in another laboratory seemed indicated. Motor activity and coordination were assessed in the rotarod test. Behavior was studied in the following tests: pilocarpine-induced seizures model for lithium action, Porsolt forced swim test, tail suspension test, elevated plus-maze, large open field, startle response and prepulse inhibition of acoustic startle response, amphetamine-induced hyperactivity, and apomorphine-induced stereotypic climbing. We could not confirm the report that GSK-3&bgr; HZ KO mice exhibit reduced immobility in the Porsolt forced swim or reduced amphetamine-induced hyperactivity in a manner mimicking the behavioral effects of lithium. We did not find increased apomorphine-induced stereotypic climbing or disruption of prepulse inhibition, suggesting that human postmortem findings regarding GSK-3&bgr; in schizophrenia are not mediated by changes in dopamine receptors and are not the cause of prepulse inhibition deficits in schizophrenia. These data do not support the role of GSK-3&bgr; in schizophrenia or in the mechanism of therapeutic action of lithium. Although differences in the genetic background of the GSK-3&bgr; HZ KOs used in the present study compared with that of the previous study could be responsible, such results could suggest that the previously reported effects of GSK-3&bgr; knockout on behavior are not robust.

Homozygote inositol transporter knockout mice show a lithium-like phenotype

OBJECTIVE Lithium inhibits inositol monophosphatase and also reduces inositol transporter function. To determine if one or more of these mechanisms might underlie the behavioral effects of lithium, we studied inositol transporter knockout mice. We previously reported that heterozygous knockout mice with reduction of 15-37% in brain inositol had no abnormalities of pilocarpine sensitivity or antidepressant-like behavior in the Porsolt forced swim test. We now report on studies of homozygous inositol transporter knockout mice. METHODS Homozygote knockout mice were rescued by 2% inositol supplementation to the drinking water of the dam mice through pregnancy and lactation. Genotyping was carried out by polymerase chain reaction followed by agarose electrophoresis. Brain free myo-inositol levels were determined gas-chromatographically. Motor activity and coordination were assessed by the rotarod test. Behavior of the mice was studied in lithium-pilocarpine seizure models for lithium action and in the Porsolt forced swim test model for depression. RESULTS In homozygote knockout mice, free inositol levels were reduced by 55% in the frontal cortex and by 60% in the hippocampus. There were no differences in weight or motor coordination by the rotarod test. They behaved similarly to lithium-treated animals in the model of pilocarpine seizures and in the Porsolt forced swimming test model of depression. CONCLUSIONS Reduction of brain inositol more than 15-37% may be required to elicit lithium-like neurobehavioral effects.

Behavioural phenotyping of sodium-myo-inositol cotransporter heterozygous knockout mice with reduced brain inositol.

Inositol plays a key role in dopamine, serotonin, noradrenaline and acetylcholine neurotransmission, and inositol treatment is reported to have beneficial effects in depression and anxiety. Therefore, a reduction in brain intracellular inositol levels could be a cause of some psychiatric disorders, such as depression or anxiety. To determine the behavioural consequences of inositol depletion, we studied the behaviour of sodium‐dependent myo‐inositol cotransporter‐1 heterozygous knockout mice. In heterozygous mice, free inositol levels were reduced by 15% in the frontal cortex and by 25% in the hippocampus, but they did not differ from their wild‐type littermates in cholinergic‐mediated lithium–pilocarpine seizures, in the apomorphine‐induced stereotypic climbing model of dopaminergic system function, in the Porsolt forced‐swimming test model of depression, in amphetamine‐induced hyperactivity, or in the elevated plus‐maze model of anxiety. Reduction of brain inositol by more than 25% may be required to elicit neurobehavioural effects.

Lack of effect of eicosapentaenoic acid in the Porsolt forced swimming test model of depression

Background: Eicosapentaenoic acid (EPA) is one of the major components of fish oils. Omega-3 fatty acids, particularly EPA, have been hypothesized to play a role in the etiology, pathogenesis and treatment of mood disorders. Clinical studies have shown beneficial effects of omega-3 fatty acids in major depression, bipolar disorder and other psychiatric disorders. Objective: The present study design evaluates the effect of EPA in the Porsolt forced swimming test. Results: EPA alone did not reduce the immobility time and did not enhance the anti-immobility effect of a low dose of imipramine. Contrary to the hypothesis, EPA slightly increased the immobility time, and in some experiments tended to reduce the anti-despair effect of imipramine. Conclusion: The present results do not provide an animal model for the antidepressant effect of EPA as demonstrated in clinical experiments. The mechanism of EPA antidepressant action is unknown and the Porsolt forced swimming test could be non-sensitive for its antidepressant properties.

Discrimination and avoidance learning in adult mice following developmental exposure to diisopropylfluorophosphate

Exposure to acetylcholinesterase inhibitors during development was shown in the past to induce sex-dependent changes in locomotion and specific cognitive and emotional tests in rodents. Adult mice that had been treated with 0.5 mg/kg diisopropylfluorphosphate (DFP), on post-natal days 14-20 were tested on active avoidance and a set-shifting task. DFP pre-treatment did not affect the active avoidance task, but impaired performance on the extra-dimensional shift task. DFP-treated females showed more general deficits in the acquisition of simple discrimination, intra-dimensional shift, extra-dimensional shift and reversal learning. These data suggest that pre-weanling exposure to cholinesterase inhibitors may have long-term consequences on attentional capabilities.

Epi-inositol: A potential antidepressant

Inositol is a simple polyol precursor in a second messenger system important in the brain. A double‐blind controlled trial of 12 g daily of inositol in 28 patients with depression for 4 weeks found significant benefit for inositol compared to placebo on the Hamilton Depression Scale. Because many antidepressants are effective in panic disorder, 21 patients with this disorder completed a double‐blind, placebo‐controlled crossover treatment trial of inositol 12 g per day. Frequency and severity of panic attacks and severity of agoraphobia declined significantly with inositol treatment compared to placebo. Because serotonin reuptake inhibitors benefit obsessive‐compulsive disorder (OCD) and inositol is reported to reverse desensitization of serotonin receptors, 13 patients with OCD completed a double‐blind, controlled crossover trial of 18 g inositol or placebo for 6 weeks each. Inositol significantly reduced scores of OCD symptoms compared with placebo. Epi‐inositol, an artificial stereoisomer of myoinositol, was found to have effects similar to those of myoinositol in reversing lithium–pilocarpine seizures and in reversing lithium‐induced rises in cytidine monophosphorylphosphatidate in cultured cells as does myoinositol. We measured the behavior of rats in an elevated plus‐maze model of anxiety after chronic treatment of 11 daily ip injections of epi‐inositol, myoinositol, or control solution. Epi‐inositol reduced anxiety levels of rats compared with controls, and its effect was stronger than that of myoinositol. Epi‐inositol could be a more effective psychoactive drug than its natural analog. Drug Dev. Res. 50:309–315, 2000.