Effect of lithium on behavioral disinhibition induced by electrolytic lesion of the median raphe nucleus

Proposing the sweet solution preference test as a screening assay for anti-manic effects of mood stabilizers

BACKGROUND

There is a desperate need for in-vivo behavioral screening tests for anti-manic effects. The frequently used psychostimulant-induced hyperactivity test appears to have lower validity than previously described, but other quick, simple and high throughput tests are currently unavailable.

NEW METHOD

In the context of modeling the behavioral facets of mania, we previously suggested that the sweet solution preference test (SSP) in naive mice might have predictive validity for screening anti-manic effects. The current study further examined this proposal by testing the effects of lithium, valproate and imipramine on SSP in three strains of mice (male mice from the black Swiss, ICR and C57bl/6 strains) and an exploratory test in females (black Swiss strain).

RESULTS

Data demonstrate that lithium and valproate at appropriate dosing schedules significantly and reliably reduce SSP in all three strains (including in females) but that the antidepressant imipramine has no effects.

COMPARISON WITH EXISTING METHODS

The results support the utilization of the SSP as mice screening model for anti-manic effects of drugs with stronger predictive validity compared with other methods.

CONCLUSIONS

The SSP is not a comprehensive model for bipolar disorder but it has good predictive validity and strong practical value that can be applied towards simple and fast screening of large numbers of animals, without the need for specialized equipment or complicated/prolonged procedures. We therefore propose that the SSP is an advantageous screening assay for testing novel mood stabilizing drugs for anti-manic properties.

A novel social fear conditioning procedure alters social behavior and mTOR signaling in differentially housed adolescent rats

Vulnerabilities to fear-related disorders can be enhanced following early life adversity. This study sought to determine whether post-weaning social isolation (PSI), an animal model of early life adversity, alters the development of social fear in an innovative model of conditioned social fear. Male and female Sprague-Dawley rats underwent either social rearing (SR) or PSI for 4 weeks following weaning. Rats were then assigned to groups consisting of either Footshock only, Social conditioned stimulus (CS) only, or Paired footshock with a social CS. Social behavior was assessed the next day. We observed a novel behavioral response in PSI rats, running in circles, that was rarely observed in SR rats; moreover, this behavior was augmented after Paired treatment in PSI rats. Other social behaviors were altered by both PSI and Paired footshock and social CS. The mammalian target of rapamycin (mTOR) pathway was assessed using immunohistochemistry for phosphorylated ribosomal protein S6 (pS6) in subregions of the prefrontal cortex (PFC) and amygdala. Paired treatment produced opposite effects in the PFC and amygdala in males, but no differences were observed in females. Conditioned social fear produced alterations in social behavior and the mTOR pathway that are dependent upon rearing condition and sex.

The GLP-1 receptor agonist liraglutide reverses mania-like alterations and memory deficits induced by D-amphetamine and augments lithium effects in mice: Relevance for bipolar disorder

Metabolic and psychiatric disorders present a bidirectional relationship. GLP-1 system, known for its insulinotropic effects, has also been associated with numerous regulatory effects in cognitive and emotional processing. GLP-1 receptors (GLP-1R) agonists present neuroprotective and antidepressant/anxiolytic properties. However, the effects of GLP-1R agonism in bipolar disorder (BD) mania and the related cognitive disturbances remains unknown. Here, we investigated the effects of the GLP-1R agonist liraglutide (LIRA) at monotherapy or combined with lithium (Li) against D-amphetamine (AMPH)-induced mania-like symptoms, brain oxidative and BDNF alterations in mice. Swiss mice received AMPH 2 mg/kg or saline for 14 days. Between days 8-14, they received LIRA 120 or 240 μg/kg, Li 47.5 mg/kg or the combination Li + LIRA, on both doses. After behavioral evaluation the brain areas prefrontal cortex (PFC), hippocampus and amygdala were collected. AMPH induced hyperlocomotion, risk-taking behavior and multiple cognitive deficits which resemble mania. LIRA reversed AMPH-induced hyperlocomotion, working and recognition memory impairments, while Li + LIRA240 rescued all behavioral changes induced by AMPH. LIRA reversed AMPH-induced hippocampal oxidative and neurotrophic changes. Li + LIRA240 augmented Li antioxidant effects and greatly reversed AMPH-induced BDNF changes in PFC and hippocampus. LIRA rescued the weight gain induced by Li in the course of mania model. Therefore, LIRA can reverse some mania-like behavioral alterations and combined with Li augmented the mood stabilizing and neuroprotective properties of Li. This study points to LIRA as a promising adjunctive tool for BD treatment and provides the first rationale for the design of clinical trials investigating its possible antimanic effect.

Neurobehavioral effects of lithium in the rat: Investigation of the effect/concentration relationships and the contribution of the poisoning pattern

Severity of lithium poisoning depends on the ingested dose, previous treatment duration and renal function. No animal study has investigated neurobehavioral differences in relation to the lithium poisoning pattern observed in humans, while differences in lithium pharmacokinetics have been reported in lithium-pretreated rats mimicking chronic poisonings with enhanced brain accumulation in rats with renal failure. Our objectives were: 1)-to investigate lithium-related effects in overdose on locomotor activity, anxiety-like behavior, spatial recognition memory and anhedonia in the rat; 2)-to model the relationships between lithium-induced effects on locomotion and plasma, erythrocyte, cerebrospinal fluid and brain concentrations previously obtained according to the poisoning pattern. Open-field, elevated plus-maze, Y-maze and sucrose consumption tests were used. In acutely lithium-poisoned rats, we observed horizontal (p<0.001) and vertical hypolocomotion (p<0.0001), increased anxiety-like behavior (p<0.05) and impaired memory (p<0.01) but no altered hedonic status. Horizontal (p<0.01) and vertical (p<0.001) hypolocomotion peaked more markedly 24h after lithium injection and was more prolonged in acute-on-chronically vs. acutely lithium-poisoned rats. Hypolocomotion in chronically lithium-poisoned rats with impaired renal function did not differ from acutely poisoned rats 24h after the last injection. Interestingly, hypolocomotion/concentration relationships best fitted a sigmoidal E_max model in acute poisoning and a linear regression model linked to brain lithium in acute-on-chronic poisoning. In conclusion, lithium overdose alters rat behavior and consistently induces hypolocomotion which is more marked and prolonged in repeatedly lithium-treated rats. Our data suggest that differences between poisoning patterns regarding lithium-induced hypolocomotion are better explained by the duration of lithium exposure than by its brain accumulation.

Combined treatment with subchronic lithium and acute intracerebral mirtazapine microinjection into the median raphe nucleus exerted an anxiolytic-like effect synergistically

Although preclinical and clinical studies have established the efficacy of lithium augmentation of antidepressant drugs, the mechanism of action of lithium augmentation is not fully understood. Our previous study reported that subchronic lithium treatment enhanced the anxiolytic-like effect of systemic mirtazapine. In the present study, we examined the effect of subchronic lithium in combination with acute local intracerebral injection of mirtazapine on fear-related behaviors in a contextual fear conditioning test in rats to clarify the target brain region of lithium augmentation of mirtazapine. After conditioning by footshock, diet (food pellets) containing Li2CO3 at a concentration of 0.2% was administered for 7 days. Ten min before testing and 7 days after conditioning, mirtazapine (3μg/site) in a volume of 0.5µl was acutely injected into the median raphe nucleus (MRN), hippocampus or amygdala. The combination of subchronic lithium and acute mirtazapine microinjection into the MRN but not the hippocampus or the amygdala reduced fear expression synergistically. These results suggest that intra-MRN mirtazapine treatment with subchronic lithium exerts the anxiolytic-like effect through the facilitation of the MRN-5HT pathway.

Chemogenetic inhibition of cells in the paramedian midbrain tegmentum increases locomotor activity in rats

Pronounced hyperactivity can be produced by lesions or pharmacological inhibition of cells in the median raphe nucleus (MR) located in the paramedian midbrain tegmentum. In the current study we examined whether a similar effect can be seen after chemogenetic inhibition of cells in this region using the DREADD (Designer Receptors Exclusively Activated by Designer Drugs) approach. We found that the DREADD ligand clozapine-N-oxide (CNO) increased locomotor activity in animals expressing the inhibitory DREADD hM4Di, but not those injected with a control virus in the MR. The effect was of rapid onset and short duration and persisted for at least four months after virus injections. Histological examination of the brains indicated that labeled fibers followed the known projection patterns of the MR to a variety of forebrain and midbrain structures. These findings confirm the role of the MR region in the control of locomotion and suggest that the DREADD technique may be a useful approach to the study of the functional architecture of this complex area. Methodological and interpretive aspects of DREADD studies are discussed.

Activity of Raphé Serotonergic Neurons Controls Emotional Behaviors

Despite the well-established role of serotonin signaling in mood regulation, causal relationships between serotonergic neuronal activity and behavior remain poorly understood. Using a pharmacogenetic approach, we find that selectively increasing serotonergic neuronal activity in wild-type mice is anxiogenic and reduces floating in the forced-swim test, whereas inhibition has no effect on the same measures. In a developmental mouse model of altered emotional behavior, increased anxiety and depression-like behaviors correlate with reduced dorsal raphé and increased median raphé serotonergic activity. These mice display blunted responses to serotonergic stimulation and behavioral rescues through serotonergic inhibition. Furthermore, we identify opposing consequences of dorsal versus median raphé serotonergic neuron inhibition on floating behavior, together suggesting that median raphé hyperactivity increases anxiety, whereas a low dorsal/median raphé serotonergic activity ratio increases depression-like behavior. Thus, we find a critical role of serotonergic neuronal activity in emotional regulation and uncover opposing roles of median and dorsal raphé function.

Chronic treatment with mood stabilizer lithium inhibits amphetamine-induced risk-taking manic-like behaviors

A lack of behavioral tests and animal models for manic-depressive bipolar disorder is recognized as an important factor limiting development of novel pharmaceutical treatments for the disorder. Repeated amphetamine-induced hyperactivity is a commonly used animal model for mania. However, hyperactivity represents only one facet of mania and is also seen in other disorders. Increased engagement in risk taking behavior is frequently observed in the manic phase of bipolar disorder. In the present study, we analyzed the effect of the most commonly used mood stabilizer lithium on repeated amphetamine treatment-induced risk-taking behaviors in rats using elevated plus maze and wire-beam bridge tests. We found that repeated amphetamine treatment not only increased locomotor activity, but also increased risk taking behaviors in rats, and further that chronic lithium treatment inhibited the amphetamine-increased risk taking behavior. Our studies suggest that these tests may be useful tools to analyze the pharmacological validity of new and improved anti-manic drugs in animals.