Ultrasound of alternating frequencies and variable emotional impact evokes depressive syndrome in mice and rats.

Emotional stress is primarily triggered by the cognitive processing of negative input; it is regarded as a serious pathogenetic factor of depression that is challenging to model in animals. While available stress paradigms achieve considerable face and construct validity in modelling depressive disorders, broader use of naturalistic stressors instead of the more prevalent models with artificial challenges inducing physical discomfort or pain may substantially contribute to the development of novel antidepressants. Here, we investigated whether a 3-week exposure of Wistar rats and Balb/c mice to unpredictably alternating frequencies of ultrasound between the ranges of 20-25 and 25-45kHz, which are known to correspond with an emotionally negative and with a neutral emotional state, respectively, for small rodents in nature, can induce behavioural and molecular depressive-like changes. Both rats and mice displayed decreased sucrose preference, elevated "despair" behaviour in a swim test, reduced locomotion and social exploration. Rats showed an increased expression of SERT and 5-HT2A receptor, a decreased expression of 5-HT1A receptor in the prefrontal cortex and hippocampus, diminished BDNF on gene and protein levels in the hippocampus. Fluoxetine, administered to rats at the dose of 10mg/kg, largely precluded behavioural depressive-like changes. Thus, the here applied paradigm of emotional stress is generating an experimental depressive state in rodents, which is not related to any physical stressors or pain. In essence, this ultrasound stress model, besides enhancing animal welfare, is likely to provide improved validity in the modelling of clinical depression and may help advance translational research and drug discovery for this disorder.

Animal Models of Depression and Drug Delivery with Food as an Effective Dosing Method: Evidences from Studies with Celecoxib and Dicholine Succinate.

Multiple models of human neuropsychiatric pathologies have been generated during the last decades which frequently use chronic dosing. Unfortunately, some drug administration methods may result in undesirable effects creating analysis confounds hampering model validity and preclinical assay outcomes. Here, automated analysis of floating behaviour, a sign of a depressive-like state, revealed that mice, subjected to a three-week intraperitoneal injection regimen, had increased floating. In order to probe an alternative dosing design that would preclude this effect, we studied the efficacy of a low dose of the antidepressant imipramine (7 mg/kg/day) delivered via food pellets. Antidepressant action for this treatment was found while no other behavioural effects were observed. We further investigated the potential efficacy of chronic dosing via food pellets by testing the antidepressant activity of new drug candidates, celecoxib (30 mg/kg/day) and dicholine succinate (50 mg/kg/day), against standard antidepressants, imipramine (7 mg/kg/day) and citalopram (15 mg/kg/day), utilizing the forced swim and tail suspension tests. Antidepressant effects of these compounds were found in both assays. Thus, chronic dosing via food pellets is efficacious in small rodents, even with a low drug dose design, and can prevail against potential confounds in translational research within depression models applicable to adverse chronic invasive pharmacotherapies.

Dicholine succinate, the neuronal insulin sensitizer, normalizes behavior, REM sleep, hippocampal pGSK3 beta and mRNAs of NMDA receptor subunits in mouse models of depression.

Central insulin receptor-mediated signaling is attracting the growing attention of researchers because of rapidly accumulating evidence implicating it in the mechanisms of plasticity, stress response, and neuropsychiatric disorders including depression. Dicholine succinate (DS), a mitochondrial complex II substrate, was shown to enhance insulin-receptor mediated signaling in neurons and is regarded as a sensitizer of the neuronal insulin receptor. Compounds enhancing neuronal insulin receptor-mediated transmission exert an antidepressant-like effect in several pre-clinical paradigms of depression; similarly, such properties for DS were found with a stress-induced anhedonia model. Here, we additionally studied the effects of DS on several variables which were ameliorated by other insulin receptor sensitizers in mice. Pre-treatment with DS of chronically stressed C57BL6 mice rescued normal contextual fear conditioning, hippocampal gene expression of NMDA receptor subunit NR2A, the NR2A/NR2B ratio and increased REM sleep rebound after acute predation. In 18-month-old C57BL6 mice, a model of elderly depression, DS restored normal sucrose preference and activated the expression of neural plasticity factors in the hippocampus as shown by Illumina microarray. Finally, young naïve DS-treated C57BL6 mice had reduced depressive- and anxiety-like behaviors and, similarly to imipramine-treated mice, preserved hippocampal levels of the phosphorylated (inactive) form of GSK3 beta that was lowered by forced swimming in pharmacologically naïve animals. Thus, DS can ameliorate behavioral and molecular outcomes under a variety of stress- and depression-related conditions. This further highlights neuronal insulin signaling as a new factor of pathogenesis and a potential pharmacotherapy of affective pathologies.

Endotoxaemia resulting from decreased serotonin tranporter (5-HTT) function: a reciprocal risk factor for depression and insulin resistance?

Depression and diabetes are serious diseases with an increasing global prevalence. Intriguingly, recent meta-analyses have highlighted an asymmetrical relationship between the two conditions as depressed patients were found to display a higher risk of developing type 2 diabetes than those individuals suffering from diabetes are to become depressed. Based on recent findings, we favor a hypothesis where by decreased peripheral serotonin (5-HT) transporter (5-HTT) function is a reciprocal risk factor for the co-morbidity of depression and diabetes, as it can trigger inflammatory pathogenetic mechanisms of both conditions. Higher intestinal levels of 5-HT and 5-HT3 receptor stimulation lead to increased intestinal permeability in 5-HTT deficient mice, which is viewed one of the most relevant animal models of depression. We hypothesize that this leakage of bacterial endotoxins can activate both central and peripheral Toll-like receptor 4 (TLR4), which inhibits insulin signaling and IRS1/PI3K/Akt and thus, contribute to the pathogenesis of diabetes and depression that are associated with this pathway. Antidepressant therapies, which also suppress intestinal 5-HTT, may have potentiating effects on the association between depression and diabetes. It is also of interest that high carbohydrate and fat intake ("cafeteria-type diet") increases intestinal 5-HT leading to TLR4 activation. Thus, endotoxaemia and inflammation owing to increased intestinal 5-HT may underpin the depression and diabetes association, where the risk of the latter pathology becomes particularly preeminent after the onset of depression and not vice versa. The evidence presented here shows the further investigation into peripheral mechanisms that linked diabetes to depression is clearly warranted.

Lasting downregulation of the lipid peroxidation enzymes in the prefrontal cortex of mice susceptible to stress-induced anhedonia.

Antioxidant enzymes and lipid peroxidation in the brain are involved in neuropsychiatric pathologies, including depression. 14- or 28-day chronic stress model induced a depressive syndrome defined by lowered reward sensitivity in C57BL/6J mice and changed gene expression of peroxidation enzymes as shown in microarray assays. We studied how susceptibility or resilience to anhedonia is related to lipid peroxidation in the prefrontal cortex (PFC). With 14-day stress, a comparison of the activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX) and accumulation of malondialdehyde (MDA) revealed a decrease of the first two measures in susceptible, but not in resilient animals or in stressed mice chronically dosed with imipramine (7mg/kg/day). Acute stress elevated activity of CAT and SOD and dynamics of MDA accumulation in the PFC that was prevented by imipramine (30mg/kg). 28-day stress evoked anhedonia lasting two but not five weeks while behavioural invigoration was detected at the latter time point in anhedonic but not non-anhedonic mice; enhanced aggressive traits were observed in both groups. After two weeks of a stress-free period, CAT and SOD activity levels in the PFC were reduced in anhedonic animals; after five weeks, only CAT was diminished. Thus, in the present chronic stress depression paradigm, lasting alterations in brain peroxidation occur not only during anhedonia but also in the recovery period and are accompanied by behavioural abnormalities in mice. This mimics behavioural and neurochemical deficits observed in depressed patients during remission which could be used to develop remedies preventing their relapse.

Hypothalamic astroglial connexins are required for brain glucose sensing-induced insulin secretion.

Hypothalamic glucose detection participates in maintaining glycemic balance, food intake, and thermogenesis. Although hypothalamic neurons are the executive cells involved in these responses, there is increasing evidence that astrocytes participate in glucose sensing (GS); however, it is unknown whether astroglial networking is required for glucose sensitivity. Astroglial connexins 30 and 43 (Cx30 and Cx43) form hexameric channels, which are apposed in gap junctions, allowing for the intercellular transfer of small molecules such as glucose throughout the astroglial networks. Here, we hypothesized that hypothalamic glucose sensitivity requires these connexins. First, we showed that both Cxs are enriched in the rat hypothalamus, with highly concentrated Cx43 expression around blood vessels of the mediobasal hypothalamus (MBH). Both fasting and high glycemic levels rapidly altered the protein levels of MBH astroglial connexins, suggesting cross talk within the MBH between glycemic status and the connexins' ability to dispatch glucose. Finally, the inhibition of MBH Cx43 (by transient RNA interference) attenuated hypothalamic glucose sensitivity in rats, which was demonstrated by a pronounced decreased insulin secretion in response to a brain glucose challenge. These results illustrate that astroglial connexins contribute to hypothalamic GS.

The neuronal insulin sensitizer dicholine succinate reduces stress-induced depressive traits and memory deficit: possible role of insulin-like growth factor 2.

BACKGROUND: A number of epidemiological studies have established a link between insulin resistance and the prevalence of depression. The occurrence of depression was found to precede the onset of diabetes and was hypothesized to be associated with inherited inter-related insufficiency of the peripheral and central insulin receptors. Recently, dicholine succinate, a sensitizer of the neuronal insulin receptor, was shown to stimulate insulin-dependent H2O2 production of the mitochondrial respiratory chain leading to an enhancement of insulin receptor autophosphorylation in neurons. As such, this mechanism can be a novel target for the elevation of insulin signaling. RESULTS: Administration of DS (25 mg/kg/day, intraperitoneal) in CD1 mice for 7 days prior to the onset of stress procedure, diminished manifestations of anhedonia defined in a sucrose test and behavioral despair in the forced swim test. Treatment with dicholine succinate reduced the anxiety scores of stressed mice in the dark/light box paradigm, precluded stress-induced decreases of long-term contextual memory in the step-down avoidance test and hippocampal gene expression of IGF2. CONCLUSIONS: Our data suggest that dicholine succinate has an antidepressant-like effect, which might be mediated via the up-regulation of hippocampal expression of IGF2, and implicate the neuronal insulin receptor in the pathogenesis of stress-induced depressive syndrome.

Reduced sensitivity to reward in CB1 knockout mice.

RATIONALE: Previous studies have demonstrated that the activation and blockade of the cannabinoid type 1 receptor (CB1) leads to an enhancement and decrease of the consumption of food and other orally ingested reinforcers, respectively. OBJECTIVE: To gain further knowledge about the role of CB1 in sucrose/saccharin reinforcing efficacy and intake, we tested CB1 knockout (CB1-KO) and littermate wild-type (WT) control mice in several self-administration experimental protocols. METHODS: Operant (fixed or progressive ratio schedule) and non-operant conditioning procedures were used. In addition, a choice analysis based on the "matching law" as well as a microstructural analysis of the intra-session pattern of self-administration was performed. RESULTS: CB1-KO mice consume less sucrose under operant conditions or when using a two-bottle free choice procedure. Moreover, as revealed by additional behavioural analysis, CB1-KO mice exhibit a decreased sensitivity to the rewarding properties of sucrose. In agreement with this finding, the differences between WT and CB1-KO mice faded away when the palatability of sucrose was devaluated by adding quinine, but not when a non-caloric sweetener, saccharin, was available. CONCLUSIONS: These results demonstrate a modulatory role of CB1 in the determination of the rewarding properties of sucrose and probably, as suggested by previous studies, other reinforcers.