Antidepressant effects of insulin in streptozotocin induced diabetic mice: Modulation of brain serotonin system

Depression and type 2 diabetes: A causal relationship and mechanistic pathway

Depression is a mood disorder that may increase risk for the development of insulin resistance (IR) and type 2 diabetes (T2D), and vice versa. However, the mechanistic pathway linking depression and T2D is not fully elucidated. The aim of this narrative review, therefore, was to discuss the possible link between depression and T2D. The coexistence of T2D and depression is twice as great compared to the occurrence of either condition independently. Hyperglycaemia and dyslipidaemia promote the incidence of depression by enhancing inflammation and reducing brain serotonin (5-hydroxytryptamine [5HT]). Dysregulation of insulin signalling in T2D impairs brain 5HT signalling, leading to the development of depression. Furthermore, depression is associated with the development of hyperglycaemia and poor glycaemic control. Psychological stress and depression promote the development of T2D. In conclusion, T2D could be a potential risk factor for the development of depression through the induction of inflammatory reactions and oxidative stress that affect brain neurotransmission. In addition, chronic stress in depression may induce the development of T2D through dysregulation of the hypothalamic-pituitary-adrenal axis and increase circulating cortisol levels, which triggers IR and T2D.

The analgesic effects of insulin and its disorders in streptozotocin-induced short-term diabetes

Evidence suggests that insulin resistance plays an important role in developing diabetes complications. The association between insulin resistance and pain perception is less well understood. This study aimed to investigate the effects of peripheral insulin deficiency on pain pathways in the brain. Diabetes was induced in 60 male rats with streptozotocin (STZ). Insulin was injected into the left ventricle of the brain by intracerebroventricular (ICV) injection, then pain was induced by subcutaneous injection of 2.5% formalin. Samples were collected at 4 weeks after STZ injection. Dopamine (DA), serotonin, reactive oxygen species (ROS), and mitochondrial glutathione (mGSH) were measured by ELISA, and gene factors were assessed by RT-qPCR. In diabetic rats, the levels of DA, serotonin, and mGSH decreased in the nuclei of the thalamus, raphe magnus, and periaqueductal gray, and the levels of ROS increased. In addition, the levels of expression of the neuron-specific enolase and receptor for advanced glycation end genes increased, but the expression of glial fibrillary acidic protein expression was reduced. These results support the findings that insulin has an analgesic effect in non-diabetic rats, as demonstrated by the formalin test. ICV injection of insulin reduces pain sensation, but this was not observed in diabetic rats, which may be due to cell damage ameliorated by insulin.

Affective and Cognitive Impairments in Rodent Models of Diabetes

Diabetes and related acute and long-term complications have a profound impact on cognitive, emotional, and social behavior, suggesting that the central nervous system (CNS) is a crucial substrate for diabetic complications. When anxiety, depression, and cognitive deficits occur in diabetic patients, the symptoms and complications related to the disease worsen, contributing to lower quality of life while increasing health care costs and mortality. Experimental models of diabetes in rodents are a fundamental and valuable tool for improving our understanding of the mechanisms underlying the close and reciprocal link between diabetes and CNS alterations, including the development of affective and cognitive disorders. Such models must reproduce the different components of this pathological condition in humans and, therefore, must be associated with affective and cognitive behavioral alterations. Beyond tight glycemic control, there are currently no specific therapies for neuropsychiatric comorbidities associated with diabetes; animal models are, therefore, essential for the development of adequate therapies. To our knowledge, there is currently no review article that summarizes changes in affective and cognitive behavior in the most common models of diabetes in rodents. Therefore, in this review, we have reported the main evidence on the alterations of affective and cognitive behavior in the different models of diabetes in rodents, the main mechanisms underlying these comorbidities, and the applicable therapeutic strategy.

Insulin and fluoxetine produce opposite actions on lateral septal nucleus-infralimbic region connection responsivity

Some diabetes patients develop depression, the main treatment for which is antidepressants. Pharmacological interactions between insulin and antidepressants (e.g., fluoxetine) are controversial in the literature. Some authors reported hypoglycemic actions of fluoxetine, whereas others reported antidepressant-like actions. In healthy rats, insulin produces an antidespair-like action in rats through an increase in locomotor and exploratory activity, but differences in actions of insulin and fluoxetine on neuronal activity are unknown. The present study evaluated Wistar healthy rats that were treated with saline, insulin, fluoxetine, or fluoxetine + insulin for 3 days (short-term) or 21 days (long-term). The model consisted of electrical stimulation of the lateral septal nucleus (LSN) while we performed single-unit extracellular response recordings in the prelimbic cortex (PL) and infralimbic cortex (IL) subregions of the medial prefrontal cortex (mPFC). Stimulation of the LSN produced an initial brief excitatory paucisynaptic response and then a long-lasting inhibitory afterdischarge in the PL and IL. Treatment with saline and fluoxetine, but not insulin, minimally affected the paucisynaptic response. Differences were found in LSN-IL responsivity. The inhibitory afterdischarge was clearly enhanced in the long-term fluoxetine group but not by insulin alone or fluoxetine + insulin. These findings suggest that insulin produces some actions that are opposite to fluoxetine on LSN-mPFC connection responsivity, with no synergistic actions between the actions of insulin and fluoxetine.

Apelin controls emotional behavior in age- and metabolic state-dependent manner

Apelin is a small peptide secreted by the adipose tissue notably in conditions of obesity-induced hyper-insulinemia. Apelin exerts a range of physiological functions at the periphery including the improvement of insulin sensitivity and the increase of muscle strength or cardiac contractibility. Interestingly, the brain is endowed with a high density of APJ, the single target of apelin, and growing evidence suggests various central actions of this adipokine. Recent studies reported that the intracerebroventricular infusion of apelin modulates emotional states in middle age stressed animals. However, results are so far been mixed and have not allowed for definitive conclusions about the impact of apelin on anxio-depressive-like phenotype. This study aims 1) to evaluate whether serum apelin levels are associated with mood in older adults and 2) to determine the impact of the genetic apelin inactivation in 12-month old mice fed a standard diet (STD) or in 6-month old mice fed a high fat diet (HFD). A higher plasma apelin level was associated with higher depressive symptoms in older adults. In line with these clinical findings, 12-month old apelin knock-out (Ap^-/-) mice displayed a spontaneous antidepressant-like phenotype. In a marked contrast, 6-month old Ap^-/- mice harbored a higher degree of peripheral insulin resistance than wild-types in response to HFD and were more prone to develop anxiety while the depressive-like state was not modified. We also provided evidence that such anxious behavior was associated with an impairment of central serotonergic and dopaminergic neuronal activities. Finally, although the insulin sensitizing drug metformin failed to reverse HFD-induced insulin resistance in 6-month old Ap^-/- mice, it reversed their anxious phenotype. These results emphasize a complex contribution of apelin in the regulation of emotional state that might depend on the age and the metabolic status of the animals. Further investigations are warranted to highlight the therapeutic potential of manipulating the apelinergic system in mood-related disorders.

Low-Frequency Oscillations of In Vivo Ambient Extracellular Brain Serotonin

Serotonin is an important neurotransmitter that plays a major role in many aspects of neuroscience. Fast-scan cyclic voltammetry measures fast in vivo serotonin dynamics using carbon fiber microelectrodes. More recently, fast-scan controlled-adsorption voltammetry (FSCAV) has been developed to measure slower, minute-to-minute changes in ambient extracellular serotonin. We have previously demonstrated that FSCAV measurements of basal serotonin levels give critical information regarding brain physiology and disease. In this work, we revealed the presence of low-periodicity fluctuations in serotonin levels in mouse hippocampi, measured in vivo with FSCAV. Using correlation analyses, we found robust evidence of oscillations in the basal serotonin levels, which had a period of 10 min and were not present in vitro. Under control conditions, the oscillations did not differ between male and female mice, nor do they differ between mice that underwent a chronic stress paradigm and those in the control group. After the acute administration of a selective serotonin reuptake inhibitor, we observed a shift in the frequency of the oscillations, leading us to hypothesize that the newly observed fluctuations were transporter regulated. Finally, we optimized the experimental parameters of the FSCAV to measure at a higher temporal resolution and found more pronounced shifts in the oscillation frequency, along with a decreased oscillation amplitude. We postulate that this work may serve as a potential bridge for studying serotonin/endocrine interactions that occur on the same time scale.

The Therapeutic Role of Ketogenic Diet in Neurological Disorders

The ketogenic diet (KD) is a high-fat, low-carbohydrate and adequate-protein diet that has gained popularity in recent years in the context of neurological diseases (NDs). The complexity of the pathogenesis of these diseases means that effective forms of treatment are still lacking. Conventional therapy is often associated with increasing tolerance and/or drug resistance. Consequently, more effective therapeutic strategies are being sought to increase the effectiveness of available forms of therapy and improve the quality of life of patients. For the moment, it seems that KD can provide therapeutic benefits in patients with neurological problems by effectively controlling the balance between pro- and antioxidant processes and pro-excitatory and inhibitory neurotransmitters, and modulating inflammation or changing the composition of the gut microbiome. In this review we evaluated the potential therapeutic efficacy of KD in epilepsy, depression, migraine, Alzheimer’s disease and Parkinson’s disease. In our opinion, KD should be considered as an adjuvant therapeutic option for some neurological diseases.

BRAIN ACTIVITIES OF STREPTOZOTOCIN-INDUCED DIABETIC WISTAR RATS TREATED WITH GLICLAZIDE: BEHAVIOURAL, BIOCHEMICAL AND HISTOMORPHOLOGY STUDIES

Gliclazide (GLD), a sulphonylurea is efficacious in the treatment of diabetes type-2. However, there is limited information on its activity in the brain, especially in diabetics. This research investigated the brain activities of GLD following streptozotocin-induced diabetes in Wistar rats. Twenty five adult male Wistar rats (200–250 g) were grouped (n = 5) as: Control (distilled water, 5 mL/kg) and GLD (150 mg/kg) groups; and the diabetic groups, untreated streptozotocin (STZ, 35 mg/kg), and STZ (35 mg/kg) treated with GLD (150 mg/kg) for two and four weeks, and already on high fat diet. The animals’ body weights and blood glucose levels were checked weekly. After the experimental duration, spontaneous alternation and novel object recognition tests were carried out and the animals sacrificed. Perfusion with phosphate buffered saline preceded brain excision for biochemical analyses, with halves fixed in 10% neutral buffered formalin for histology. Compared with the control, results showed (p < 0.05) declined spontaneous alternation and exploratory activities with no preference for familiar or novel objects, body weights loss, raised blood glucose, increased malondialdehyde with decreased superoxide dismutase concentrations, and no apparent adverse effect on hippocampal and prefrontal cortical Nissl substance in the untreated diabetic group. The adverse observations were attenuated in the GLD treated diabetic groups; although the spontaneous alternation in the four weeks GLD treated diabetic group improved (p < 0.05), exploration of objects increased (p < 0.05) without preference. The present results showed that treatment with GLD for two and four weeks mitigated STZ activities, even though there was less improvement in neurocognitive activities.

Putative Anti-Immobility Action of Acute Insulin Is Attributable to an Increase in Locomotor Activity in Healthy Wistar Rats

BACKGROUND/AIMS

Anti-immobility actions of insulin in diabetic rats that are subjected to the forced swim test (FST) have been reported. In this test, low doses of antidepressants exert actions after long-term treatment, without affecting locomotor activity in healthy rats. Few studies have compared acute and chronic actions of insulin with antidepressants in healthy rats.

METHODS

We hypothesized that if insulin exerts a true anti-immobility action, then its effects must be comparable to fluoxetine in both a 1-day treatment regimen and a 21-day treatment regimen in healthy, gonadally intact female Wistar rats.

RESULTS

The results showed that low levels of glycemia were produced by all treatments, including fluoxetine, and glycemia was lower in proestrus-estrus than in diestrus-metestrus. None of the treatments or regimens produced actions on indicators of anxiety in the elevated plus maze. Insulin in the 1-day regimen increased the number of crossings and rearings in the open field test and caused a low cumulative immobility time in the FST. These actions disappeared in the 21-day regimen. Compared with the other treatments, fluoxetine treatment alone or combined with insulin produced a longer latency to the first period of immobility and a shorter immobility time in the chronic regimen in the FST, without affecting locomotor activity, and more pronounced actions were observed in proestrus-estrus (i.e., a true anti-immobility effect).

CONCLUSION

These results indicate that insulin does not produce a true antidepressant action in healthy rats. The purported antidepressant effects that were observed were instead attributable to an increase in locomotor activity only in the 1-day regimen.

A new experimental design to study inflammation-related versus non-inflammation-related depression in mice

Background

Major depressive disorder (MDD) represents a major public health concern, particularly due to its steadily rising prevalence and the poor responsiveness to standard antidepressants notably in patients afflicted with chronic inflammatory conditions, such as obesity. This highlights the need to improve current therapeutic strategies, including by targeting inflammation based on its role in the pathophysiology and treatment responsiveness of MDD. Nevertheless, dissecting the relative contribution of inflammation in the development and treatment of MDD remains a major issue, further complicated by the lack of preclinical depression models suitable to experimentally dissociate inflammation-related vs. inflammation-unrelated depression.

Methods

While current models usually focus on one particular MDD risk factor, we compared in male C57BL/6J mice the behavioral, inflammatory and neurobiological impact of chronic exposure to high-fat diet (HFD), a procedure known to induce inflammation-related depressive-like behaviors, and unpredictable chronic mild stress (UCMS), a stress-induced depression model notably renowned for its responsivity to antidepressants.

Results

While both paradigms induced neurovegetative, depressive-like and anxiety-like behaviors, inflammation and downstream neurobiological pathways contributing to inflammation-driven depression were specifically activated in HFD mice, as revealed by increased circulating levels of inflammatory factors, as well as brain expression of microglial activation markers and enzymes from the kynurenine and tetrahydrobiopterin (BH4) pathways. In addition, serotoninergic and dopaminergic systems were differentially impacted, depending on the experimental condition.

Conclusions

These data validate an experimental design suitable to deeply study the mechanisms underlying inflammation-driven depression comparatively to non-inflammatory depression. This design could help to better understand the pathophysiology of treatment resistant depression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02330-9.

Impaired mitochondrial functions and energy metabolism in MPTP-induced Parkinson's disease: comparison of mice strains and dose regimens

Heterogenous diseases such as Parkinson's disease (PD) needs an efficient animal model to enhance understanding of the underlying mechanisms and to develop therapeutics. MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), a neurotoxin, has been widely used to replicate the pathophysiology of PD in rodents, however, the knowledge about its effects on energy metabolism is limited. Moreover, susceptibility to different dose regimens of MPTP also varies among mice strains. Thus, the present study compares the effect of acute and sub-acute MPTP administration on mitochondrial functions in C57BL/6 and BALB/c mice. In addition, activity of enzymes involved in energy metabolism was also studied along with behavioural alterations. The findings show that acute dose of MPTP in C57BL/6 mice had more profound effect on the activity of electron transport chain complexes. Further, the activity of MAO-B was increased following acute and sub-acute MPTP administration in C57BL/6 mice. However, no significant change was observed in BALB/c mice. Acute MPTP treatment resulted in decreased mitochondrial membrane potential along with increased swelling of mitochondria in C57BL/6 mice. In addition, perturbations were observed in hexokinase, the rate limiting enzyme of glycolysis and pyruvate dehydrogenase, the enzymes that connects glycolysis and TCA cycle. The activity of TCA cycle enzymes; citrate synthase, aconitase, isocitrate dehydrogenase and fumarase were also altered following MPTP intoxication. Furthermore, acute MPTP administration led to drastic reduction in dopamine levels in striatum of C57BL/6 as compared to BALB/c mice. Behavioral tests such as open field, narrow beam walk and footprint analysis revealed severe impairment in locomotor activity in C57BL/6 mice. These results clearly demonstrate that C57BL/6 strain is more vulnerable to MPTP-induced mitochondrial dysfunctions, perturbations in energy metabolism and motor defects as compared to BALB/c strain. Thus, the findings suggest that the dose and strain of mice need to be considered for pre-clinical studies using MPTP-induced model of Parkinson's disease.

Glycogen Synthase Kinase-3: A Focal Point for Advancing Pathogenic Inflammation in Depression

Increasing evidence indicates that the host immune response has a monumental role in the etiology of major depressive disorder (MDD), motivating the development of the inflammatory hypothesis of depression. Central to the involvement of chronic inflammation in MDD is a wide range of signaling deficits induced by the excessive secretion of pro-inflammatory cytokines and imbalanced T cell differentiation. Such signaling deficits include the glutamatergic, cholinergic, insulin, and neurotrophin systems, which work in concert to initiate and advance the neuropathology. Fundamental to the communication between such systems is the protein kinase glycogen synthase kinase-3 (GSK-3), a multifaceted protein critically linked to the etiology of MDD and an emerging target to treat pathogenic inflammation. Here, a consolidated overview of the widespread multi-system involvement of GSK-3 in contributing to the neuropathology of MDD will be discussed, with the feed-forward mechanistic links between all major neuronal signaling pathways highlighted.

Bixin attenuates mechanical allodynia, anxious and depressive-like behaviors associated with experimental diabetes counteracting oxidative stress and glycated hemoglobin

Neuropathic pain, depression, and anxiety are common comorbidities in diabetic patients, whose pathophysiology involves hyperglycemia-induced increased oxidative stress. Bixin (BIX), an apocarotenoid extracted from the seeds of Bixa orellana, has been used in traditional medicine to treat diabetes and has been recognized by its antioxidant profile. We aimed to investigate the effect of the BIX over the mechanical allodynia, depressive, and anxious-like behaviors associated with experimental diabetes, along with its involved mechanisms. Streptozotocin-induced diabetic rats were treated for 17 days (starting 14 days after diabetes induction) with the corresponding vehicle, BIX (10, 30 or 90 mg/kg; p.o), or INS (6 IU; s.c.). Mechanical allodynia, depressive, and anxious-like behavior were assessed by electronic Von Frey, forced swimming, and elevated plus-maze tests, respectively. Locomotor activity was assessed by the open field test. Blood glycated hemoglobin (HbA1) and the levels of lipid peroxidation (LPO) and reduced glutathione (GSH) were evaluated on the hippocampus, pre-frontal cortex, lumbar spinal cord, and sciatic nerve. Diabetic animals developed mechanical allodynia, depressive and anxious-like behavior, increased plasma HbA1, increased LPO, and decreased GSH levels in tissues analyzed. Repeated BIX-treatment (at all tested doses) significantly attenuated mechanical allodynia, the depressive (30 and 90 mg/kg) and, anxious-like behaviors (all doses) in diabetic rats, without changing the locomotor performance. BIX (at all tested doses) restored the oxidative parameters in tissues analyzed and reduced the plasma HbA1. Thereby, bixin may represent an alternative for the treatment of comorbidities associated with diabetes, counteracting oxidative stress and plasma HbA1.

Hydroxytyrosol as anti-parkinsonian molecule: Assessment using in-silico and MPTP-induced Parkinson's disease model

3-Hydroxytyrosol (HXT) is a natural polyphenol present in extra virgin olive oil. It is a key component of Mediterranean diet and is known for its strong antioxidant activity. The present study evaluated the potential of HXT as an anti-parkinsonian molecule in terms of its ability to inhibit MAO-B and thereby maintaining dopamine (DA) levels in Parkinson's disease (PD). In-silico molecular docking study followed by MMGBSA binding free energy calculation revealed that HXT has a strong binding affinity for MAO-B in comparison to MAO-A. Moreover, rasagiline and HXT interacted with the similar binding sites and modes of interactions. Additionally, molecular dynamics simulation studies revealed stable nature of HXT-MAO-B interaction and also provided information about the amino acid residues involved in binding. Moreover, in vitro studies revealed that HXT inhibited MAO-B in human platelets with IC₅₀ value of 7.78 μM. In vivo studies using MPTP-induced mouse model of PD revealed increase in DA levels with concomitant decrease in DA metabolites (DOPAC and HVA) on HXT treatment. Furthermore, MAO-B activity was also inhibited on HXT administration to PD mice. In addition, HXT treatment prevented MPTP-induced loss of DA neurons in substantia nigra and their nerve terminals in the striatum. HXT also attenuated motor impairments in PD mice assessed by catalepsy bar, narrow beam walk and open field tests. Thus, the present findings reveal HXT as a potential inhibitor of MAO-B, which may be used as a lead molecule for the development of therapeutics for PD.

Effects of date seeds administration on anxiety and depressive symptoms in streptozotocin-induced diabetic rats: biochemical and behavioral evidences

OBJECTIVES

Several epidemiological data indicate that chronic hyperglycemia is associated with behavioral changes such as anxiety and depressive symptoms. Date seeds, one of the most potent products with potential antioxidant activities and possess many benefits against hyperglycemia and its complication. The aim of the current study was to explore the potential effect of date seeds extract on biochemical and behavioral changes (anxiety and depression) in streptozotocin (STZ)-diabetic rats.

METHODS

Rats were divided into four groups as follows: normal control, diabetic control, diabetic treated with the lyophilized aqueous extract of the date seed (2,000 mg/kg) (LAE-DS) and diabetics treated with insulin (4 UI/day). Experimental diabetes was induced by a single intraperitoneal injection of STZ (60 mg/kg). After 24 days treatment period, anxiety and depressive behaviors were evaluated using four behavioral tests. After sacrifice, blood samples were collected to evaluate lipid parameters. In addition, rat organs (kidney, liver and brain) were dissected out in order to estimate lipid peroxidation levels as oxidative stress marker.

RESULTS

Oral administration of the lyophilized aqueous extract of date seeds and insulin injection for 30 days significantly decreased blood glucose levels in STZ-diabetic rats and protected them against undesirable changes in lipid parameters, including cholesterol, triglycerides, LDL cholesterol, VLDL cholesterol and atherosclerosis index. Compared to untreated diabetic rat, a significant decrease in lipid peroxidation levels in kidney, liver and brain (Hippocampus and prefrontal cortex) were observed after treatment with insulin or LAE-DS in diabetic rats. Furthermore, insulin and LAE-DS administration prevented anxiety-related behaviors in STZ-diabetic rats.

CONCLUSIONS

Therefore, it would be possible to combine this extract with insulin and use it as an antioxidant supplement for type 1 diabetic patients.

Neuroprotective effects of carbenoxolone against amyloid-beta 1-42 oligomer-induced neuroinflammation and cognitive decline in rats

The aggregation of Aβ plays a major role in the progression of Alzheimer's disease (AD) and induces neuroinflammation, neurodegeneration and cognitive decline. Recent studies have shown that the soluble aggregates of Aβ are the major culprits in the development of these aberrations inside the brain. In this study, we investigated the neuroprotective potential of carbenoxolone (Cbx), which has been found to possess anti-inflammatory and nootropic properties. Male SD rats (250-300 g) were divided into the four groups (n = 8 per group): (1) sham control rats injected with vehicles, (2) Aβ 1-42 group rats injected i.c.v. with Aβ 42 oligomers (10 μl/rat), (3) Aβ 1-42+Cbx group rats injected i.c.v. with Aβ 42 oligomers (10 μl/rat) and i.p. with carbenoxolone disodium (20 mg/kg body weight) for six-weeks and (4) Cbx group rats injected i.p. with carbenoxolone disodium (20 mg/kg body weight) for six-weeks. Progressive learning and memory deficits were seen through a battery of behavioral tests and a significant increase in the expressions of GFAP and Iba-1 was observed which resulted in the release of pro-inflammatory cytokines post Aβ oligomer injection. The levels of BDNF, Bcl-2 and pCREB were decreased while Bax, caspase-3, caspase-9 and cytochrome c levels were induced. Also, neurotransmitter levels were altered and neuronal damage was observed through histopathological studies. After Cbx supplementation, the expressions of GFAP, IBA-1, pro-inflammatory cytokines, iNOS, nNOS and nitric oxide levels were normalized. The expression levels of pro-apoptotic markers were decreased and neurotrophin levels were restored. Also, neurotransmitter levels and neuronal profile were improved and progressive improvements in behavioural performance were observed. Our results demonstrated that Cbx might have prevented the Aβ induced neurodegeneration and cognitive decline by inhibiting the neuroinflammation and inducing BDNF/CREB signalling. These findings suggest that Cbx can be explored as a potential therapeutic agent against the progression of AD.

Pathophysiology linking depression and type 2 diabetes: Psychotherapy, physical exercise, and fecal microbiome transplantation as damage control

Diabetes increases the likelihood of developing depression and vice versa. Research on this bidirectional association has somewhat managed to delineate the interplay among implicated physiological processes. Still, further exploration is required in this context. This review addresses the comorbidity by investigating suspected common pathophysiological mechanisms. One such factor is psychological stress which disturbs the hypothalamic-pituitary-adrenal axis causing hormonal imbalance. This includes elevated cortisol levels, a common biomarker of both depression and diabetes. Disrupted insulin signaling drives the hampered neurotransmission of serotonin, dopamine, and norepinephrine. Also, adipokine hormones such as adiponectin, leptin, and resistin and the orexigenic hormone, ghrelin, are involved in both depression and T2DM. This disarray further interferes with physiological processes encompassing sleep, the gut-brain axis, metabolism, and mood stability. Behavioral coping mechanisms, such as unhealthy eating, mediate disturbed glucose homeostasis, and neuroinflammation. This is intricately linked to oxidative stress, redox imbalance, and mitochondrial dysfunction. However, interventions such as psychotherapy, physical exercise, fecal microbiota transplantation, and insulin-sensitizing agents can help to manage the distressing condition. The possibility of glucagon-like peptide 1 possessing a therapeutic role has also been discussed. Nonetheless, there stands an urgent need for unraveling new correlating targets and biological markers for efficient treatment.

The impact of insulin on the serotonergic system and consequences on diabetes-associated mood disorders

The idea that insulin could influence emotional behaviours has long been suggested. However, the underlying mechanisms have yet to be solved and there is no direct and clear-cut evidence demonstrating that such action involves brain serotonergic neurones. Indeed, initial arguments in favour of the association between insulin, serotonin and mood arise from clinical or animal studies showing that impaired insulin action in type 1 or type 2 diabetes causes anxiety- and depressive symptoms along with blunted plasma and brain serotonin levels. The present review synthesises the main mechanistic hypotheses that might explain the comorbidity between diabetes and depression. It also provides a state of knowledge of the direct and indirect experimental evidence that insulin modulates brain serotonergic neurones. Finally, it highlights the literature suggesting that antidiabetic drugs present antidepressant-like effects and, conversely, that serotonergic antidepressants impact glucose homeostasis. Overall, this review provides mechanistic insights into how insulin signalling alters serotonergic neurotransmission and related behaviours bringing new targets for therapeutic options.

Depression with Comorbid Diabetes: What Evidence Exists for Treatments Using Traditional Chinese Medicine and Natural Products?

Comorbidity between diabetes mellitus (DM) and depression, two chronic and devastating diseases spreading worldwide, has been confirmed by a large body of epidemiological and clinical studies. Due to the bidirectional relationship between DM and depression, this comorbidity leads to poorer outcomes in both conditions. Given the adverse effects and limited effectiveness of the existing therapies for depression associated with diabetes, the development of novel therapeutic drugs with more potency and fewer side effects is still the most important goal. Hence, many researchers have made great efforts to investigate the potential usefulness of traditional Chinese medicine (TCM) and natural products, including natural extracts and purified compounds, in the treatment of comorbid depression in diabetes. Here, we reviewed the related literature on TCM and natural products that can remedy the comorbidity of diabetes and depression and presented them on the basis of their mechanism of action, focusing on shared risk factors, including insulin resistance, oxidative stress and inflammation, and nervous disturbances. In short, this review suggests that TCM and natural products could expand the therapeutic alternatives to ameliorate the association between DM and depressive disorders.

Bibliometrics Analysis of the Research Status and Trends of the Association Between Depression and Insulin From 2010 to 2020

Depression is one of the common mental illnesses. Because it is an important complication of diabetes, its association with changes in insulin levels and insulin resistance, the causative factors of diabetes, has attracted widespread attention. However, the association between insulin and depression has not been systematically studied through bibliometric and visual analysis. This study is based on 3131 publications of Web of Science to identify the current research status and research trends in this field. The results show that since 2010, the number of publications has been growing rapidly. Cooperative network analysis shows that the United States, the University of Toronto and Roger S Mcintyre are the most influential countries, research institutes and scholars, respectively. Insulin resistance, obesity, and metabolic syndrome are hot topics in this field. Analysis of keywords and references reveals that "sex hormones," is new research area that constantly emerging. As far as we know, this study is the first one to visualize the association between depression and insulin and predict potential future research trends through bibliometric and visual analysis.

Clinical Evidence of Antidepressant Effects of Insulin and Anti-Hyperglycemic Agents and Implications for the Pathophysiology of Depression-A Literature Review

Close connections between depression and type 2 diabetes (T2DM) have been suggested by many epidemiological and experimental studies. Disturbances in insulin sensitivity due to the disruption of various molecular pathways cause insulin resistance, which underpins many metabolic disorders, including diabetes, as well as depression. Several anti-hyperglycemic agents have demonstrated antidepressant properties in clinical trials, probably due to their action on brain targets based on the shared pathophysiology of depression and T2DM. In this article, we review reports of clinical trials examining the antidepressant effect of these medications, including insulin, metformin, glucagon like peptide-1 receptor agonists (GLP-1RA), and peroxisome proliferator-activated receptor (PPAR)-γ agonists, and briefly consider possible molecular mechanisms underlying the associations between amelioration of insulin resistance and improvement of depressive symptoms. In doing so, we intend to suggest an integrative perspective for understanding the pathophysiology of depression.

Antidepressant activity of anti-hyperglycemic agents in experimental models: A review

BACKGROUND AND AIMS

Diabetes Mellitus (DM) and depression occur comorbidly and share some pathophysiological mechanisms. The course of depression in patients with the two conditions is severe. Treatment of depression in diabetic patients requires special attention because most of psychopharmacological agents can worsen glycemic control. This article aims to review studies evaluating the antidepressant effect of anti-hyperglycemic agents from preclinical perspective.

METHODS

A literature search was performed with PubMed and Google Scholar using relevant keywords (antidiabetic; diabetes; depression; antidepressant; animals) to extract relevant studies evaluating the antidepressant activity of anti-hyperglycemic agents in experimental models.

RESULTS

Several studies have reported that some traditional anti-hyperglycemic agents reduce depression-like behavior in the absence or presence of diabetes. These drugs include insulin, glyburide, metformin, pioglitazone, vildagliptin, liraglutide, and exenatide. The antidepressant activity of anti-hyperglycemic agents may be mediated by reducing the blood glucose level, ameliorating the central oxidative stress and inflammation, and regulating the hypothalamic-pituitary-adrenal axis (HPAA).

CONCLUSIONS

Drugs which have both antidiabetic and antidepressant activities can provide better treatment strategy for patients with diabetes-associated depression. However, further research studies are still required in human subjects.

Potential role of insulin on the pathogenesis of depression

The regulation of insulin on depression and depression-like behaviour has been widely reported. Insulin and activation of its receptor can promote learning and memory, affect the hypothalamic-pituitary-adrenal axis (HPA) balance, regulate the secretion of neurotrophic factors and neurotransmitters, interact with gastrointestinal microbiome, exert neuroprotective effects and have an impact on depression. However, the role of insulin on depression remains largely unclear. Therefore, in this review, we summarized the potential role of insulin on depression. It may provide new insight for clarifying role of insulin on the pathogenesis of depression.

Modulatory Effects of Ginkgo biloba Against Amyloid Aggregation Through Induction of Heat Shock Proteins in Aluminium Induced Neurotoxicity

Protein misfolding and aggregation of amyloid beta (Aβ) peptide, as well as formation of neurofibrillary tangles (NFTs) are the signature hallmarks of Alzheimer's disease (AD) pathology. To prevent this, molecular chaperones come into play as they facilitate the refolding of the misfolded proteins and cell protection under stress. Here, we have evaluated the possible effects of Ginkgo biloba (GBE) against aggregation of the Aβ through activation of heat shock proteins (HSPs) in the Aluminium (Al) induced AD based model. GBE (100 mg/kg body weight) was administered per oral to the female SD rats in conjunction with intraperitoneal (i.p.) injection of Al lactate (10 mg/kg body weight) for six weeks. Pretreated animals were administered GBE for additional two weeks prior to any exposure of Al. GBE administration resulted in decrease in Aβ aggregation, ubiquitin deposition, accompanying a significant decline in APP & Tau protein hyperphosphorylation which can be attributed to activation of Heat shock factor (HSF-1) and upregulation in the protein expression of HSPs. Histopathological investigation studies have also shown the decrease in aggregation of Aβ peptide by GBE administration. Additionally, the decrease in ROS levels and Aβ aggregation by GBE administration prohibited the decline in the neurotransmitter levels and monoamine oxidase levels in hippocampus and cortex. This further caused improvement in learning and memory of the animals. In conclusion, our results indicate that GBE prevents the symptoms of Al induced AD like pathophysiology by upregulating the HSPs levels and decreasing the aggregation load.

Depression-like behavior, hyperglycemia, oxidative stress, and neuroinflammation presented in diabetic mice are reversed by the administration of 1-methyl-3-(phenylselanyl)-1H-indole

Oxidative stress and neuroinflammation are found both in diabetes mellitus and major depressive disorder (MDD). In addition to damage in peripheral organs, such as liver and kidney, diabetic patients have a higher risk of developing depression. In this sense, the objective of the present study was to characterize the antidepressant-like effect of a selenium-containing compound, the 1-methyl-3-(phenylselanyl)-1H-indole (MFSeI), in streptozotocin (STZ)-induced diabetic mice. STZ (200 mg/kg, i.p.) was used to induce diabetes mellitus type I, and after seven days, the administration of MFSeI (10 mg/kg, i.g.) was initiated and followed for the next 14 days. Twenty-four hours after the last administration of MFSeI, the behavioral tests were performed, followed by euthanasia. The treatment with MFSeI was able to reverse the hyperglycemia induced by STZ. MFSeI also decreased the plasma levels of biomarkers of liver and kidney damage. Importantly, MFSeI reversed the depression-like behavior induced by STZ in the tail suspension test and forced swimming test without promoting locomotor alterations. Furthermore, MFSeI reversed the increased levels of reactive species and lipid peroxidation in the prefrontal cortex (PFC), hippocampus (HC), liver, and kidney of STZ-treated mice. Treatment with MFSeI also decreased the expression of tumor necrosis factor-alpha, inducible nitric oxide synthase and indoleamine 2,3-dioxygenase, while increasing the expression of interleukin-10, insulin receptor substrate-1 and glucose transport-4 in the PFC and HC of mice. Taken together, the results indicate the effectiveness of MFSeI against depression-like behavior and central and peripheral complications caused by diabetes in mice.

Sucrose and saccharin differentially modulate depression and anxiety-like behavior in diabetic mice: exposures and withdrawal effects

RATIONALE

Sugar has addictive potential owing to increase in monoaminergic-transmission at pleasure and reward centers of brain. Insulin dysfunction triggered synaptic monoamine deficit is associated with sugar overeating and craving-related psychological changes in diabetic patients. Sugar-substitute (saccharin) is non-caloric artificial sweetener that may alleviate brain disorders in diabetes.

OBJECTIVES

In present study, effects of sucrose and sugar-substitute (saccharin) exposures and withdrawal on depression and anxiety-like behavior in type 2 diabetic mice were assessed.

METHODS

Swiss albino mice were injected with streptozotocin (135 mg/kg). After induction of diabetes, mice were exposed to a two-bottle water-water, 10% sucrose-water, or 10% saccharin-water choice paradigm for 28 days. Separate groups were employed to assess withdrawal effect of sucrose or saccharin in diabetic mice. Monoamine oxidase (MAO), corticosterone, thiobarbituric acid reactive substances (TBARS), and reduced glutathione (GSH) were quantified after behavioral tests.

RESULTS

Diabetic mice manifested preference towards 10% sucrose or saccharin over water. Sucrose-overeating by diabetic mice amplified symptoms of depression and anxiety; however, withdrawal further exaggerated these behavioral abnormalities. Substitution of sucrose by 10% saccharin attenuated the depressive and anxiety-like behavior in comparison to diabetic mice that were exposed separately to water-water or sucrose-water alone, and with respect to normal mice. Although withdrawal from saccharin resurfaced behavioral anomalies in diabetic mice, however, these were significantly low in comparison with withdrawal from sucrose or normal group. Reinstatement of exposure to saccharin mitigated symptoms of depression and anxiety in diabetic mice.

CONCLUSION

Preference of sucrose overeating augments while saccharin mitigates depressive and anxiety behavior during diabetes.

Responsivity of lateral septum-mPFC connections in alloxan-induced hyperglycemia

The lateral septal nucleus (LSN) is related to the actions of antidepressants, and the prelimbic cortex (PL) and infralimbic cortex (IL) modulate responses to fear. However, unknown is whether experimental diabetes that is induced by alloxan alters the responsivity of these regions. We used a method in which one forebrain region (LSN) was electrically stimulated while single-unit extracellular recordings were performed in another mPFC region (PL and IL). Several experimental groups were tested: (a) animals that were subjected to long-term (42-day) alloxan-hyperglycemia and protected with insulin, (b) healthy animals that received a low dose of insulin that does not produce changes in glycemia, and (c) animals that received long-term treatment with fluoxetine. Additional healthy groups of animals received insulin or fluoxetine and underwent the forced swim test. Biological measurements indicated the induction of diabetes in alloxan-treated rats. In this group, a shift toward an inhibitory response to LSN stimulation was observed in the PL and IL compared with the control group. A low dose of insulin or fluoxetine produced similar changes in LSN-PL and LSN-IL responsivity. Long-term hyperglycemia increased inhibitory responsivity in the LSN-PL and LSN-IL, but this action was less pronounced than the action that was exerted by insulin and fluoxetine, which produced similar actions. Such similar actions were confirmed in the forced swim test, in which the antidepressant-like effects of insulin partially resembled the effects of fluoxetine. The changes that were observed in the alloxan group appeared to be related to neuronal damage, and a low dose of insulin exerted some antidepressant-like actions.

Learned helplessness reveals a population at risk for depressive-like behaviour after myocardial infarction in mice

Aims

Myocardial infarction (MI) and heart failure (HF) are risk factors for the development of depression, additionally worsening the quality of life and patient outcome. How HF causes depression and how depression promotes HF remain mechanistically unclear, which is at least partly caused by the difficulty of in vivo modelling of psychosomatic co‐morbidity. We aimed to study the potential sequence of events with respect to different depression aspects upon HF.

Methods and results

Male C57BL6 mice underwent MI, followed by behavioural and echocardiographic characterization. Motility, exploration, and anxiety‐like behaviour were unaffected in mice after MI. We did not observe increased depressive‐like behaviour in the sucrose preference, tail suspension, or Porsolt forced swim test. Mice did not display signs of learned helplessness (LH) when compared to sham. Accordingly, cluster analysis revealed only a slightly higher quota of LH in HF (38%) vs. sham mice (32%). But strikingly, three‐group cluster analysis revealed an additional intermediate subpopulation at risk for LH after HF (29%). Interestingly, this population featured elevated cardiac expression of nr4a1.

Conclusions

The LH paradigm uncovered a subtle predisposition to depressive‐like behaviour after MI, whereas testing for anhedonia and despair was insufficient to show a behavioural shift in mice. Therefore, we suggest an accumulating risk profile and a multiple‐hits hypothesis regarding the pathogenesis of co‐morbid depression after MI. Symptoms of LH may present a marker of subclinical depression after MI, the impact of which remains to be investigated. The proposed sequence of behavioural testing enables the mechanistic dissection of cardio‐psychogenic signalling in the future.

Brain tumor necrosis factor-α mediates anxiety-like behavior in a mouse model of severe obesity

Although the high prevalence of anxiety in obesity increasingly emerges as significant risk factor for related severe health complications, the underlying pathophysiological mechanisms remain poorly understood. Considering that chronic inflammation is a key component of obesity and is well known to impact brain function and emotional behavior, we hypothesized that it may similarly contribute to the development of obesity-related anxiety. This hypothesis was experimentally tested by measuring whether chronic food restriction, a procedure known to reduce inflammation, or chronic anti-inflammatory treatment with ibuprofen improved anxiety-like behavior and concomitantly decreased peripheral and/or hippocampal inflammation characterizing a model of severe obesity, the db/db mice. In both experiments, reduced anxiety-like behaviors in the open-field and/or elevated plus-maze were selectively associated with decreased hippocampal tumor necrosis factor-α (TNF-α) mRNA expression. Highlighting the causality of both events, chronic central infusion of the TNF-α blocker etanercept was then shown to be sufficient to improve anxiety-like behavior in db/db mice. Lastly, by measuring the impact of ex-vivo etanercept on hippocampal synaptic processes underlying anxiety-like behaviors, we showed that the anxiolytic effect of central TNF-α blockade likely involved modulation of synaptic transmission within the ventral hippocampus. Altogether, these results uphold the role of brain TNF-α in mediating obesity-related anxiety and provide important clues about how it may modulate brain function and behavior. They may therefore help to introduce novel therapeutic strategies to reduce anxiety associated with inflammatory conditions.

The antioxidant gallic acid induces anxiolytic-, but not antidepressant-like effect, in streptozotocin-induced diabetes

The physiopathology of anxiety or depression related to diabetes is still poorly understood. The treatment with antidepressant drugs is a huge challenge due to theirs adherence low rate and many adverse effects. Thus, the seeking for a better treatment for these associated diseases is of utmost importance. Given that the oxidative stress in different tissues occurs in diabetes and anxiety or depression as well, the antioxidant gallic acid becomes an interesting compound to be investigated. Thus, the effects of long-term treatment with gallic acid (0, 10, 20 and 40 mg/kg; gavage) were evaluated in diabetic (DBT) animals submitted to the elevated plus-maze (EPM), the light-dark transition (LDT) tests and modified forced swim test (mFST). Also, indirect parameters of oxidative stress, lipid peroxidation (LPO) and reduced glutathione (GSH) levels were evaluated in the hippocampus (HIP) and prefrontal cortex (PFC). The results showed that DBT animals presented a decrease in the spent time in the open arms, in the end arm exploration and head dips when evaluated in the EPM test; moreover, a decrease in the spent time in the lit compartment of LDT test was observed, suggesting an anxiogenic-like behavior. During the mFST, an increase in the mean counts of immobility and a decrease in the mean counts of swimming and climbing were observed, indicating a depressive-like behavior. These aversive behaviors were more pronounced when compared to normoglycemic (NGL) animals and streptozotocin-treated animals that not become DBT. In addition, DBT rats showed an increase in the oxidative stress parameters in the HIP and PFC that was reversed by the gallic acid treatment (lowest dose - 10 mg/kg), i.e., the treatment decreased the elevated LPO levels and increased the reduced GSH in the HIP and PFC. Also, gallic acid treatment was able to produce an anxiolytic-like effect in the EPM and LDT tests, but not antidepressant-like effect in the FST. Taken together, the results suggest that the antioxidant/neuroprotective effect of gallic acid treatment in HIP and PFC of DBT animals may be essential to the anxiolytic-like effect.

Insulin regulates astrocyte gliotransmission and modulates behavior

Complications of diabetes affect tissues throughout the body, including the central nervous system. Epidemiological studies show that diabetic patients have an increased risk of depression, anxiety, age-related cognitive decline, and Alzheimer's disease. Mice lacking insulin receptor (IR) in the brain or on hypothalamic neurons display an array of metabolic abnormalities; however, the role of insulin action on astrocytes and neurobehaviors remains less well studied. Here, we demonstrate that astrocytes are a direct insulin target in the brain and that knockout of IR on astrocytes causes increased anxiety- and depressive-like behaviors in mice. This can be reproduced in part by deletion of IR on astrocytes in the nucleus accumbens. At a molecular level, loss of insulin signaling in astrocytes impaired tyrosine phosphorylation of Munc18c. This led to decreased exocytosis of ATP from astrocytes, resulting in decreased purinergic signaling on dopaminergic neurons. These reductions contributed to decreased dopamine release from brain slices. Central administration of ATP analogs could reverse depressive-like behaviors in mice with astrocyte IR knockout. Thus, astrocytic insulin signaling plays an important role in dopaminergic signaling, providing a potential mechanism by which astrocytic insulin action may contribute to increased rates of depression in people with diabetes, obesity, and other insulin-resistant states.

A serotonergic deficit in the dorsal periaqueductal gray matter may underpin enhanced panic-like behavior in diabetic rats

It is known that diabetic (DBT) animals present dysregulation on the serotonergic system in several brain areas associated with anxiety-like responses. The aim of this study was to investigate the involvement of 5-HT1A receptors on dorsal periaqueductal gray (dPAG) in the behavioral response related to panic disorder in type-1 DBT animals. For this, the escape response by electric stimulation (ES) of dPAG in DBT and normoglycemic (NGL) animals was assessed. Both NGL and DBT animals were exposed to an open-field test (OFT) 28 days after DBT confirmation. The current threshold to induce escape behavior in DBT animals was reduced compared with NGL animals. No impairment in locomotor activity was observed when DBT animals were compared with NGL animals. An intra-dPAG injection of the 5-HT1A receptor agonist (±)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) increased the [INCREMENT] threshold in both DBT and NGL, suggesting a panicolytic-like effect. DBT animals presented a more pronounced panicolytic-like response compared with NGL as a higher [INCREMENT] threshold was observed after 8-OH-DPAT treatment, which could be a consequence of the increased expression of the 5-HT1A receptor in the dPAG from DBT animals. Our results are in line with the proposal that a deficiency in serotonergic modulation of the dPAG is involved in triggering the panic attack and the 5-HT1A receptors might be essential for the panicolytic-like response.

Study of the Role of Dopamine Receptors in Streptozotocin-Induced Depressive-Like Behavior Using the Forced Swim Test Model

Background:

Diabetes is one of the most common endocrine diseases characterized by hyperglycemia. It is caused by an absolute or relative insulin deficiency or an insulin function deficiency. It is one of the major risk factors of depression, with the rate of depression in diabetic patients amounting to as high as 30%. This study examined the role of dopamine receptors in streptozotocin (STZ)-induced depressive-like behavior using the forced swim test (FST).

Materials and Methods:

This study was performed on 56 Wistar male rats. STZ at doses of 30 and 60 mg/kg body weight was administered via intraperitoneal (IP) route to induce diabetes and depression in rats. Thereafter, by using halobenzazepine (SCH23390) (D1 dopamine receptor antagonist) and sulpiride (D2 receptor dopamine receptor antagonist), the role of dopamine receptors in STZ-induced depression was studied. The one-way analysis of variance technique, Tukey’s range test, and t-test were used to analyze the data. The P-value less than 0.05 was regarded as statistically significant.

Results:

Our study showed that STZ at doses of 30 and 60 mg/kg, two weeks after injection, caused prolonged immobility in FST, indicating depressive-like behavior (P<0.05 and P<0.01, respectively). SCH23390 (0.001 mg/mL/kg) and sulpiride (0.1 mg/mL/kg) did not change the variables of depression in animals that received STZ (at doses of 30 and 60 mg/mL/kg) two weeks before (P>0.05).

Conclusion:

According to our study, STZ has a depressive-like behavior two weeks after injection, and dopamine receptors do not play a role in depression associated with STZ use.

Crossing the Worm-Brain Barrier by Using Caenorhabditis elegans to Explore Fundamentals of Human Psychiatric Illness

Endophenotypes and Research Domain Criteria (RDoC) represent recent efforts to deconvolute psychiatric illnesses into fundamental symptom clusters or biological markers more closely linked to genetic influences. By taking this one step farther, these biomarkers can be reduced to protophenotypes - endophenotypes conserved during evolution - with counterparts in lower organisms including Caenorhabditis elegans and Drosophila. Striking conservation in C. elegans of genes that increase the risk for mental illness bolsters the relevance of this model system for psychiatric research. Here, I review the characterization of several protophenotypes that are relevant for asociality, avolition/anhedonia, prepulse inhibition, and anorexia. Interestingly, the analogous behavioral defects in C. elegans are also corrected by psychotropic drugs used to treat the corresponding symptoms in man and/or are mediated by the same neurotransmitters. Overall, there is much we can learn about the complex human brain by studying simpler nervous systems directing evolutionarily conserved behaviors. The potential for generating important new insights from model organisms appears limitless when we begin to recognize the vestiges of evolution in ourselves.

Cytokine alterations and cognitive impairment in major depressive disorder: From putative mechanisms to novel treatment targets

Overwhelming evidence indicates the involvement of immune-inflammatory processes in the pathophysiology of major depressive disorder (MDD). Peripheral cytokine alterations serve as one of most consistently reported indices of subthreshold inflammatory state observed in MDD. Although cytokines cannot pass directly through the blood-brain barrier, a number of transport mechanisms have been reported. In addition, peripheral cytokines may impact central nervous system via downstream effectors of their biological activity. Animal model studies have provided evidence that cytokines might impact cognitive performance through direct and indirect effects on long-term potentiation, neurogenesis and synaptic plasticity. Therefore, it has been hypothesized that cytokine alterations might contribute to cognitive impairment that is widely observed in MDD and persists beyond episodes of acute relapse in the majority of patients. Although several studies have provided that peripheral cytokine alterations might be related to cognitive deficits in patients with MDD, the quality of evidence still leaves much to be desired due to methodological heterogeneity and limitations. In this article, we provide an overview of studies investigating the association between peripheral cytokine alterations and cognitive performance in MDD, discuss underlying mechanisms and neural substrates. Finally, we propose possible treatment targets related to cytokine alterations taking into account existing evidence for antidepressant efficacy of anti-inflammatory pharmacological treatment modalities.

Insulin Signaling Deficiency Produces Immobility in Caenorhabditis elegans That Models Diminished Motivation States in Man and Responds to Antidepressants

Defects in insulin signaling have been reported in schizophrenia and major depressive disorder, which also share certain negative symptoms such as avolition, anhedonia, and apathy. These symptoms reflect diminished motivational states, which have been modeled in rodents as increased immobility in the forced swimming test. We have discovered that loss-of-function mutations in the insulin receptor (daf-2) and syntaxin (unc-64) genes in Caenorhabditis elegans, brief food deprivation, and exposure to DMSO produce immobility and avolition in non-dauer adults. The animals remain responsive to external stimuli; however, they fail to forage and will remain in place for >12 days or until they die. Their immobility can be prevented with drugs used to treat depression and schizophrenia and that reduce immobility in the forced swimming test. This includes amitriptyline, amoxapine, clozapine, and olanzapine, but not benzodiazepines and haloperidol. Recovery experiments confirm that immobility is induced and maintained by excessive signaling via serotonergic and muscarinic cholinergic pathways. The immobility response described here represents a potential protophenotype for avolition/anhedonia in man. This work may provide clues about why there is a significant increase in depression in patients with diabetes and suggest new therapeutic pathways for disorders featuring diminished motivation as a prominent symptom.

Hydrogen sulfide attenuates homocysteine-induced cognitive deficits and neurochemical alterations by improving endogenous hydrogen sulfide levels

Hyperomocysteinemia (HHcy) has been associated with mild cognitive impairment and dementia. Hydrogen sulfide (H₂ S) has been suggested to be an endogenous modulator of neuronal functions. However, the effect and mechanisms involved in beneficial effect of H₂ S has not been investigated in homocysteine (Hcy)-induced cognitive deficits. This study has been designed to evaluate the effect of exogenous H₂ S on behavioral deficits and neurochemical alterations in HHcy animals. Hcy levels were significantly elevated in plasma, cortex, and hippocampus of Hcy administered animals. A progressive decline in memory functions and increased anxiolytic behavior was observed in HHcy animals. This was accompanied by decrease in endogenous H₂ S levels along with decreased activity of cystathionase (CSE) and cystathionine β-synthase (CBS). However, a significant increase in CSE and CBS mRNAs was observed. In addition, the catecholamine and serotonin levels were reduced and the activity of monoamine oxidase A and B were increased in brain regions of HHcy animals. Haematoxylin and eosin staining revealed higher number of pyknotic cells in brain regions of HHcy animals. H₂ S administration was found to lower elevated plasma and brain Hcy levels. The activities of CBS, CSE, and levels of H₂ S were restored in HHcy animals administered H₂ S. Exogenous H₂ S also ameliorated behavioral deficits accompanied by significant increase in catecholamines. Histological analysis revealed normal cell morphology in Hcy-treated animals supplemented with H₂ S. These results clearly demonstrate that the protective effect of H₂ S on Hcy-induced cognitive deficits is mediated through increased catecholamine and H₂ S levels thereby suggesting its beneficial role in preventing HHcy-induced neurodegeneration. © 2016 BioFactors, 43(3):434-450, 2017.

Synthetic matrix of polyether-polyurethane as a biological platform for pancreatic regeneration

AIMS

Several alternative cellular approaches using biomaterials to host insulin-producing cells derived from stem cells have been developed to overcome the limitations of type 1 diabetes treatment (exogenous insulin injection). However, none seem to fulfill all requirements needed to induce pancreatic cells successful colonization of the scaffolds. Here, we report a polymeric platform adherent to the native mice pancreas filled with human adipose stem cells (hASCs) that was able to induce growth of pancreatic parenchyma.

MAIN METHODS

Synthetic polyether-polyurethane discs were placed adjacent to pancreas of normoglycemic and streptozotocin-induced diabetic mice. At day 4 post implantation, 1×10⁶ hASCs were injected intra-implant in groups of normoglycemic and diabetic mice. Immunohistochemistry analysis of the implants was performed to identify insulin positive cells in the newly formed tissue. In addition, metabolic, inflammatory and angiogenic parameters were carried out in those mice.

KEY FINDINGS

This study provides evidence of the ability of a biohybrid device to induce the growth of differentiated pancreas parenchyma in both normoglycemic and streptozotocin-induced diabetic mice as detected by histological analysis. Glucose metabolism and body weight of hyperglycemic mice bearing hASCs implants improved.

SIGNIFICANCE

The synthetic porous scaffold bearing hASC cells placed adjacent to the native animal pancreas exhibits the potential to be exploited in future cell-based type 1 diabetes therapies.

Liraglutide prevents cognitive decline in a rat model of streptozotocin-induced diabetes independently from its peripheral metabolic effects

Diabetes has been identified as a risk factor for cognitive dysfunctions. Glucagone like peptide 1 (GLP-1) receptor agonists have neuroprotective effects in preclinical animal models. We evaluated the effects of GLP-1 receptor agonist, liraglutide (LIR), on cognitive decline associated with diabetes. Furthermore, we studied LIR effects against hippocampal neurodegeneration induced by streptozotocin (STZ), a well-validated animal model of diabetes and neurodegeneration associated with cognitive decline. Diabetes and/or cognitive decline were induced in Wistar rats by intraperitoneal or intracerebroventricular injection of STZ and then rats were treated with LIR (300μg/kg daily subcutaneously) for 6 weeks. Rats underwent behavioral tests: Morris water maze, passive avoidance, forced swimming (FST), open field, elevated plus maze, rotarod tests. Furthermore, LIR effects on hippocampal neurodegeneration and mTOR pathway (AKT, AMPK, ERK and p70S6K) were assessed. LIR improved learning and memory only in STZ-treated animals. Anxiolytic effects were observed in all LIR-treated groups but pro-depressant effects in CTRL rats were observed. At a cellular/molecular level, intracerebroventricular STZ induced hippocampal neurodegeneration accompanied by decreased phosphorylation of AMPK, AKT, ERK and p70S6K. LIR reduced hippocampal neuronal death and prevented the decreased phosphorylation of AKT and p70S6K; AMPK was hyper-phosphorylated in comparison to CTRL group, while LIR had no effects on ERK. LIR reduced animal endurance in the rotarod test and this effect might be also linked to a reduction in locomotor activity during only the last two minutes of the FST. LIR had protective effects on cognitive functions in addition to its effects on blood glucose levels. LIR effects in the brain also comprised anxiolytic and pro-depressant actions (although influenced by reduced endurance). Finally, LIR protected from diabetes-dependent hippocampal neurodegeneration likely through an effect on mTOR pathway.

Chronic Administration of Rosa canina Hydro-Alcoholic Extract Attenuates Depressive-Like Behavior and Recognition Memory Impairment in Diabetic Mice: A Possible Role of Oxidative Stress

OBJECTIVE

This study was designed to evaluate whether chronic Rosa canina (RC) extract administration could improve recognition memory and depressive-like behavior in diabetic mice.

MATERIALS AND METHODS

Seventy-five male albino mice (25-30 g) were randomly divided into 5 groups (15 in each group). A single intraperitoneal injection of 200 mg/kg streptozotocin (STZ) was administered to the mice to induce diabetes. The control group received normal saline, and the diabetic groups received normal saline or 50, 250, and 500 mg/kg of RC extract for 28 days. The mice were weighed each week. Recognition memory and depressive-like behavior were assessed using forced swimming and novel object recognition (NOR) tests, respectively. Malondialdehyde (MDA) levels and total antioxidant capacity (TAC) were measured in the mouse brain homogenate to evaluate oxidative stress. Statistical analysis was conducted using SPSS, version 22.

RESULTS

The groups receiving 250 or 500 mg/kg RC had significantly lower immobility time (159.4 ± 4.7 and 150.1 ± 3.1 s) compared to the sham control group (192.1 ± 7.8 s) in the forced swimming test, and a higher discrimination index (0.39 ± 0.02 and 0.48 ± 0.03) was seen in diabetic animals in the NOR task compared to the sham control group (0.2 ± 0.01). Also, the groups receiving treatment with RC (250 and 500 mg/kg) had significantly higher TAC (0.92 ± 0.04 and 0.96 ± 0.05 mmol/L) and lower MDA (0.76 ± 0.02 and 0.67 ± 0.03 nmol/mg protein) levels in the brains in comparison to the model group. In the 3rd and 4th weeks of study, the RC-treated mice (250 and 500 mg/kg) gained more weight (31.2 ± 0.3 and 32.4 ± 0.3 g, and 31.3 ± 0.2 and 33.7 ± 0.3 g, respectively) than the diabetic group (30 ± 0.2 and 29.6 ± 0.3 g).

CONCLUSION

This study showed that RC attenuated impairment of recognition memory and depressive-like behavior probably through modulation of oxidative stress in an STZ model of diabetes in mouse brains.

Role of Adiposity-Driven Inflammation in Depressive Morbidity

Depression and metabolic disorders, including overweight and obesity, appear tightly interrelated. The prevalence of these conditions is concurrently growing worldwide, and both depression and overweight/obesity represent substantial risk factors for multiple medical complications. Moreover, there is now multiple evidence for a bidirectional relationship between depression and increased adiposity, with overweight/obesity being associated with an increased prevalence of depression, and in turn, depression augmenting the risk of weight gain and obesity. Although the reasons for this intricate link between depression and increased adiposity remain unclear, converging clinical and preclinical evidence points to a critical role for inflammatory processes and related alterations of brain functions. In support of this notion, increased adiposity leads to a chronic low-grade activation of inflammatory processes, which have been shown elsewhere to have a potent role in the pathophysiology of depression. It is therefore highly possible that adiposity-driven inflammation contributes to the development of depressive disorders and their growing prevalence worldwide. This review will present recent evidence in support of this hypothesis and will discuss the underlying mechanisms and potential therapeutic targets. Altogether, findings presented here should help to better understand the mechanisms linking adiposity to depression and facilitate the identification of new preventive and/or therapeutic strategies.

Geniposide alleviates depression-like behavior via enhancing BDNF expression in hippocampus of streptozotocin-evoked mice

Clinical and preclinical data suggest that diabetes is often psychological complications such as depression. Geniposide (GP), a major compound in Gardenia jasminoides Ellis with both medicinal and nutritional values, has been previously confirmed to exert anti-diabetic and anti-depressive activities. The present study attempted to observe anti-depressive mechanisms of GP in streptozotocin (STZ) evoked diabetic mice by involving brain-derived neurotrophic factor (BDNF), for the first time. Mice were given GP daily (50, and 100 mg/kg, ig) or reference drugs FHMH [fluoxetine hydrochloride (FH, 10 mg/kg, ig) combined with metformin hydrochloride (MH, 100 mg/kg, ig)] for 3 weeks. The forced swimming test (FST) was performed to observe depression-like behavior, and serum and brain tissues were used for neurochemical and fluorescent quantitative reverse transcription PCR analyses. STZ induced excessively increased blood sugar and immobility time in FST, in a manner attenuated by GP and FHMH administration. GP administration further elevated BDNF levels, and up-regulated the mRNA expression of BDNF and tropomyosin-related kinase B (TrkB) in hippocampus of diabetic mice. In addition, STZ induced the excessive level of serum corticosterone (CORT), while GP did not influence on it in diabetic mice. Taken together, these findings indicate that GP can alleviate depression-like behavior in STZ-evoked diabetic mice, and suggest its mechanisms may partially be ascribed to up-regulating BDNF expression in brain.

Metabolic pathways in the periphery and brain: Contribution to mental disorders?

The association between mental disorders and diabetes has a long history. Recent large-scale, well-controlled epidemiological studies confirmed a link between diabetes and psychiatric illnesses. The scope of this review is to summarize our current understanding of this relationship from a molecular perspective. We first discuss the potential contribution of diabetes-associated metabolic impairments to the etiology of mental conditions. Then, we focus on possible shared molecular risk factors and mechanisms. Simple comorbidity, shared susceptibility loci, and common pathophysiological processes in diabetes and mental illnesses have changed our traditional way of thinking about mental illness. We conclude that schizophrenia and affective disorders are not limited to an imbalance in dopaminergic and serotoninergic neurotransmission in the brain. They are also systemic disorders that can be considered, to some extent, as metabolic disorders.

Reestablishment of the hyperglycemia to the normal levels seems not to be essential to the anxiolytic-like effect induced by insulin

Diabetes is a chronic metabolic disease accompanied by several comorbidities, including neuropsychiatric conditions. Since the hyperglycemia appears to be the primary factor involved in diabetic conditions, we examined the effect of insulin treatment in diabetic rats on behavioral responses related to anxiety and aversive memory extinction. For this, normoglycemic (NGL) or streptozotocin-diabetic (DBT) rats were submitted to the elevated T maze (ETM) and the contextual conditioned fear (CCF) tests. Therefore, animals were subjected to the prolonged treatment with insulin (6 IU/day, s.c.) to investigate the effect of the treatment on distinct behaviors. When anxiety-like responses such as the inhibitory avoidance (IA) on the ETM and the time of freezing in the first session of the CCF test were evaluated, our data showed a more pronounced anxiogenic-like behavior in DBT animals when compared to NGL ones. In addition, an increased freezing time was observed in DBT animals exposed to the CCF test (sessions 2 and 3) when compared to the NGL group, suggestive of an impairment in the extinction of aversive memory. Insulin treatment induced an anxiolytic-like effect when IA and freezing time (session 1) was evaluated, but did not alter the impaired extinction of aversive memory (sessions 2 and 3). To better understand the involvement of a rigorous control of glycaemia, we also investigated the effect of a lower dose of insulin (3 IU/day, s.c.), unable to reestablish the hyperglycemia to the normal levels, on the same behavioral parameters. Our data show that independent of the dose of insulin, the same effects were observed when animals were evaluated in the ETM and CCF tests. However, only the highest dose of insulin was able to reduce the hyperglycemia to the normal levels. To conclude, our data suggest that a severe glycemic control by insulin treatment seems to be important, but not essential in improving diabetes-induced anxiety.

Evidence for the involvement of neuropeptide Y in the antidepressant effect of imipramine in type 2 diabetes

Depression is a major comorbidity factor of diabetes and the outcome of one disorder influences the other. Our aim is to scrutinize the link between the two, if any. Since neuropeptide Y (NPY) system plays an important role in regulating central glucose sensing mechanisms, and also depression-related behavior, we test the involvement of NPY in the modulation of depression in type 2 diabetic mice. The mice were fed on high-fat diet and administered with low dose of streptozotocin to induce type 2 diabetes. These animals showed augmented plasma glucose and increased immobility time in tail suspension test (TST) suggesting induction of diabetes and depression. Intracerebroventricular (icv) treatment with NPY or NPY Y1 receptor agonist [Leu(31), Pro(34)]-NPY and intraperitoneal treatment with imipramine decreased immobility time. However, opposite effect was produced by NPY Y1 receptor antagonist BIBP3226 (icv). Moreover, reduced immobility time by imipramine was potentiated by NPY and [Leu(31), Pro(34)]-NPY, but attenuated by BIBP3226. Immunohistochemical analysis of the different nuclei of the extended amygdala, the region primarily involved in affective disorders, was undertaken. A significant reduction in NPY immunoreactivity in the central nucleus of amygdala, nucleus accumbens shell and lateral division of bed nucleus of stria terminalis of the diabetic mice was noticed; the response was ameliorated in imipramine treated animals. The results suggest that decreased NPY expression in the extended amygdala might be causally linked with the depression induced following type 2 diabetes and that the antidepressant action of imipramine in diabetic mice might be mediated by NPY-NPY Y1 receptor system.

Insulin receptor sensitizer, dicholine succinate, prevents both Toll-like receptor 4 (TLR4) upregulation and affective changes induced by a high-cholesterol diet in mice

BACKGROUND

High cholesterol intake in mice induces hepatic lipid dystrophy and inflammation, signs of non-alcoholic fatty liver disease (NAFLD), depressive- and anxiety-like behaviors, and the up-regulation of brain and liver Toll-like receptor 4 (Tlr4). Here, we investigated whether dicholine succinate (DS), an insulin receptor sensitizer and mitochondrial complex II substrate would interact with these effects.

METHODS

C57BL/6J mice were given a 0.2%-cholesterol diet for 3 weeks, alone or along with oral DS administration, or a control feed. Outcomes included behavioral measures of anxiety/depression, and Tlr4 and peroxisome-proliferator-activated-receptor-gamma coactivator-1b (PPARGC1b) expression.

RESULTS

50mg/kg DS treatment for 3 weeks partially ameliorated the cholesterol-induced anxiety- and depressive-like changes. Mice were next treated at the higher dose (180mg/kg), either for the 3-week period of dietary intervention, or for the last two weeks. Three-week DS administration normalized behaviors in the forced swim and O-maze tests and abolished the Tlr4 up-regulation in the brain and liver. The delayed, 2-week DS treatment had similar effects on Tlr4 expression and largely rescued the above-mentioned behaviors. Suppression of PPARGC1b, a master regulator of mitochondrial biogenesis, by the high cholesterol diet, was prevented with the 3-week administration, and markedly diminished by the a 2-week administration of DS. None of treatments prevented hepatic dystrophy and triglyceride accumulation.

LIMITATIONS

Other conditions have to be tested to define possible limitations of reported effects of DS.

CONCLUSIONS

DS treatment did not alter the patho-morphological substrates of NAFLD syndrome in mice, but ameliorated its molecular and behavioral consequences, likely by activating mitochondrial functions and anti-inflammatory mechanisms.