Acute intracerebroventricular inositol does not reverse the effect of chronic lithium treatment in the forced swim test

Questioning the predictive validity of the amphetamine-induced hyperactivity model for screening mood stabilizing drugs

Animal models are critical for the study of disease mechanisms and the screening of potential novel treatments. In the context of bipolar disorder, amphetamine-induced hyperactivity (AIH) is a frequently used screening model for antimanic effects. Yet, the utility of screening models depends on their predictive (or pharmacological) validity and it is expected that such models will respond to effective treatments. Lithium is the prototypic mood stabilizer but previous data regarding the effects of lithium in the AIH model are not clear and most data comes from studies using acute lithium administration that is not relevant to the therapeutic regimen in patients. To evaluate the pharmacological validity of AIH as a model for mania-like behavior we tested the interaction between chronic oral administration of lithium and amphetamine in ICR (CD-1®) mice and in black Swiss mice. We conducted 4 different experiments where chronic lithium was followed by an acute injection of amphetamine and one experiment where chronic amphetamine was combined with chronic lithium. The results show that amphetamine result in hyperactivity (experiments 1-4) and that lithium has no effects. Moreover, chronic amphetamine (experiment 5) result in sensitization that is not attenuated by lithium. The results clearly show that the predictive validity of the AIH model in ICR or black Swiss mice is problematic and possibly cast doubt on the utilization of the AIH as a screening model for novel mood stabilizers in other strains of mice.

Revisiting the validity of the mouse forced swim test: Systematic review and meta-analysis of the effects of prototypic antidepressants

One problem area regarding animal models for affective disorders is unclear reproducibility, including external validity or generalizability. One way to evaluate external validity is with systematic reviews and meta-analyses. The current study presents a meta-analysis of the effects of prototypic antidepressants in the mouse forced swim test (FST). We identified studies that examined effects of antidepressants in the FST in mice and used standard protocol, male mice and acute drug administration. We calculated Effect sizes using Cohen's d, homogeneity using Q statistic and correlations using Pearson's correlation. Results indicate that all drugs reduce immobility in the FST. However, effect sizes for most drugs are heterogeneous and do not show a consistent dose/response relationship across variability factors. Reducing variability by examining only one strain or data from individual laboratories partially increases dose response relationship. These findings suggest that whereas the FST is a valid tool to qualitatively screen antidepressant effects its validity in the context of hierarchical comparison between doses or compounds might be relevant only to single experiments.

Telomere length in bipolar disorder and lithium response

Telomeres consist of exanucleotide tandem repeats and proteins complexes at the end of chromosome ends. Telomeres shorten at each cell division, and as such telomere length is a marker of cellular age. Accelerated telomere shortening and cell senescence have been associated with a number of chronic medical conditions, including psychiatric disorders, where increased prevalence of age-related disorders and shorter telomere length have been reported. Shorter telomeres in psychiatric patients are thought to be the consequence of allostatic load, consisting in the overactivation of allostatic systems due to chronic exposure to severe medical conditions and failure to adapt to chronic stressful stimuli. Most of the studies on telomere length in psychiatry have focused on major depressive disorder, but recent findings have shown shorter leukocyte telomere length in bipolar disorder patients and suggested that lithium may counteract telomeres shortening. These findings provided new insights into the pathophysiology of bipolar disorder and the mechanism of action of lithium. In this review we will present findings from the literature on telomere length in bipolar disorder, with a specific focus on lithium. We will also discuss advances and limitations of published work as well as methodological issues and potential confounding factors that should be taken into account when designing research protocols to study telomere length.

IP3 accumulation and/or inositol depletion: two downstream lithium's effects that may mediate its behavioral and cellular changes

Lithium is the prototype mood stabilizer but its mechanism is still unresolved. Two hypotheses dominate-the consequences of lithium's inhibition of inositol monophosphatase at therapeutically relevant concentrations (the 'inositol depletion' hypothesis), and of glycogen-synthase kinase-3. To further elaborate the inositol depletion hypothesis that did not decisively determine whether inositol depletion per se, or phosphoinositols accumulation induces the beneficial effects, we utilized knockout mice of either of two inositol metabolism-related genes-IMPA1 or SMIT1, both mimic several lithium's behavioral and biochemical effects. We assessed in vivo, under non-agonist-stimulated conditions, ³H-inositol incorporation into brain phosphoinositols and phosphoinositides in wild-type, lithium-treated, IMPA1 and SMIT1 knockout mice. Lithium treatment increased frontal cortex and hippocampal phosphoinositols labeling by several fold, but decreased phosphoinositides labeling in the frontal cortex of the wild-type mice of the IMPA1 colony strain by ~50%. Inositol metabolites were differently affected by IMPA1 and SMIT1 knockout. Inositoltrisphosphate administered intracerebroventricularly affected bipolar-related behaviors and autophagy markers in a lithium-like manner. Namely, IP₃ but not IP₁ reduced the immobility time of wild-type mice in the forced swim test model of antidepressant action by 30%, an effect that was reversed by an antagonist of all three IP₃ receptors; amphetamine-induced hyperlocomotion of wild-type mice (distance traveled) was 35% reduced by IP₃ administration; IP₃ administration increased hippocampal messenger RNA levels of Beclin-1 (required for autophagy execution) and hippocampal and frontal cortex protein levels ratio of Beclin-1/p62 by about threefold (p62 is degraded by autophagy). To conclude, lithium affects the phosphatidylinositol signaling system in two ways: depleting inositol, consequently decreasing phosphoinositides; elevating inositol monophosphate levels followed by phosphoinositols accumulation. Each or both may mediate lithium-induced behavior.

Inositol-deficient food augments a behavioral effect of long-term lithium treatment mediated by inositol monophosphatase inhibition: an animal model with relevance for bipolar disorder

Lithium treatment in rodents markedly enhances cholinergic agonists such as pilocarpine. This effect can be reversed in a stereospecific manner by administration of inositol, suggesting that the effect of lithium is caused by inositol monophosphatase inhibition and consequent inositol depletion. If so, inositol-deficient food would be expected to enhance lithium effects. Inositol-deficient food was prepared from inositol-free ingredients. Mice with a homozygote knockout of the inositol monophosphatase 1 gene unable to synthesize inositol endogenously and mimicking lithium-treated animals were fed this diet or a control diet. Lithium-treated wild-type animals were also treated with the inositol-deficient diet or control diet. Pilocarpine was administered after 1 week of treatment, and behavior including seizures was assessed using rating scale. Inositol-deficient food-treated animals, both lithium treated and with inositol monophosphatase 1 knockout, had significantly elevated cholinergic behavior rating and significantly increased or earlier seizures compared with the controls. The effect of inositol-deficient food supports the role of inositol depletion in the effects of lithium on pilocarpine-induced behavior. However, the relevance of this behavior to other more mood-related effects of lithium is not clear.

Beware of your mouse strain; differential effects of lithium on behavioral and neurochemical phenotypes in Harlan ICR mice bred in Israel or the USA

Animal models are crucial components in the search for better understanding of the biological basis of psychiatric disorders and for the development of novel drugs. Research, in general, and research with animal models, in particular, relies on the consistency of effects of investigated drugs or manipulations across experiments. In that context, it had been noted that behavioral responses to lithium in ICR (CD-1) mice from Harlan Israel have changed across the last years. To examine this change, the present study compared the effect of lithium treatment in ICR mice from Harlan Israel with the ICR mice from Harlan USA. The mice were treated with chronic oral lithium. Their lithium serum levels were measured and their behavior in the forced swim test (FST) was evaluated. The mice were also treated with [(3)H]-inositol ICV and lithium injection and their frontal cortex [(3)H]-phosphoinositols accumulation was measured. Results show that lithium serum levels in Israeli mice were significantly lower compared with the USA mice, that lithium had no behavioral effect in the Israeli mice but significantly reduced FST immobility time of the USA mice, and that phosphoinositols accumulation was much more strongly affected by lithium in the USA mice compared with the Israeli mice. These results suggest that the Israeli Harlan colony of ICR mice changed significantly from the original ICR colony in Harlan USA and that the differences might be related to absorption or secretion of lithium.