Water maze learning and hippocampal synaptic plasticity in streptozotocin-diabetic rats: effects of insulin treatment

Intranasal insulin treatment ameliorates spatial memory, muscular strength, and frailty deficits in 5xFAD mice

The 5xFAD mouse model shows age-related weight loss as well as cognitive and motor deficits. Metabolic dysregulation, especially impaired insulin signaling, is also present in AD. This study examined whether intranasal delivery of insulin (INI) at low (0.875 U) or high (1.750 U) doses would ameliorate these deficits compared to saline in 10-month-old female 5xFAD and B6SJL wildtype (WT) mice. INI increased forelimb grip strength in the wire hang test in 5xFAD mice in a dose-dependent manner but did not improve the performance of 5xFAD mice on the balance beam. High INI doses reduced frailty scores in 5xFAD mice and improved spatial memory in both acquisition and reversal probe trials in the Morris water maze. INI increased swim speed in 5xFAD mice but had no effect on object recognition memory or working memory in the spontaneous alternation task, nor did it improve memory in the contextual or cued fear memory tasks. High doses of insulin increased the liver, spleen, and kidney weights and reduced brown adipose tissue weights. P-Akt signaling in the hippocampus was increased by insulin in a dose-dependent manner. Altogether, INI increased strength, reduced frailty scores, and improved visual spatial memory. Hypoglycemia was not present after INI, however alterations in tissue and organ weights were present. These results are novel and important as they indicate that intra-nasal insulin can reverse cognitive, motor and frailty deficits found in this mouse model of AD.

The administration of Cerebrolysin elicits neuroprotective and neurorepair effects in an animal model of type 1 diabetes mellitus

Diabetes mellitus (DM) is a metabolic disorder impacting cerebral function. The administration of Streptozotocin (STZ) is a well-known animal model of insulinopenic type 1 DM in rats. STZ-induced DM results in a myriad of alteration in the periphery and central nervous system (CNS). Cerebrolysin (CBL) is a neuropeptide preparation that promotes synaptic and neuronal plasticity in various animal models. In all cases, CBL was administered when the model was established. This research aims to investigate the neuroprotective and neurorepair effect of CBL on the cytoarchitecture of neurons and spine density in pyramidal neurons of the prefrontal (PFC) and the CA1 region of the dorsal hippocampus, as well as spheroidal neurons of the dentate gyrus (DG), in STZ-induced DM. In the first experimental condition, STZ and CBL are administered at the same time to evaluate the potential preventive effect of CBL. In the second experimental condition, CBL was administered two months after establishing the DM model to measure the potential neurorepair effect of CBL. STZ-induced hyperglycemia remained unaltered by the administration of CBL in both experimental conditions. In the first experimental condition, CBL treatment preserved the neuronal morphology in PFC layer 3, PFC layer 5 and the DG of the hippocampus, while also maintaining spine density in the PFC-3, DG and CA1 hippocampus. Furthermore, CBL induced neurorepair in neurons within the PFC-3, PFC-5 and CA1 regions of the hippocampus, along with an increase in spine density in the PFC-3, DG and CA1 hippocampus. These findings suggest that CBL´s effects on neuroplasticity could be observed before or after the damage was evident.

Temporal and region-specific tau hyperphosphorylation in the medulla and forebrain coincides with development of functional changes in male obese Zucker rats

Metabolic syndrome (MetS) is associated with development of tauopathies that contribute to cognitive decline. Without functional leptin receptors, male obese Zucker rats (OZRs) develop MetS, and they have increased phosphorylated tau (ptau) with impaired cognitive function. In addition to regulating energy balance, leptin enhances activation of the hippocampus, which is essential for spatial learning and memory. Whether spatial learning and memory are always impaired in OZRs or develop with MetS is unknown. We hypothesized that male OZRs develop MetS traits that promote regional increases in ptau and functional deficits associated with those brain regions. In the medulla and cortex, tau-pSer199,202 and tau-pSer396 were comparable in juvenile (7-8 wk old) lean Zucker rats (LZRs) and OZRs but increased in 18- to 19-wk-old OZRs. Elevated tau-pSer396 was concentrated in the dorsal vagal complex of the medulla, and by this age OZRs had hypertension with increased arterial pressure variability. In the hippocampus, tau-pSer199,202 and tau-pSer396 were still comparable in 18- to 19-wk-old OZRs and LZRs but elevated in 28- to 29-wk-old OZRs, with emergence of deficits in Morris water maze performance. Comparable escape latencies observed during acquisition in 18- to 19-wk-old OZRs and LZRs were increased in 28- to 29-wk-old OZRs, with greater use of nonspatial search strategies. Increased ptau developed with changes in the insulin/phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway in the hippocampus and cortex but not medulla, suggesting different underlying mechanisms. These data demonstrate that leptin is not required for spatial learning and memory in male OZRs. Furthermore, early development of MetS-associated autonomic dysfunction by the medulla may be predictive of later hippocampal dysfunction and cognitive impairment.NEW & NOTEWORTHY Male obese Zucker rats (OZRs) lack functional leptin receptors and develop metabolic syndrome (MetS). At 16-19 wk, OZRs are insulin resistant, with increased ptau in dorsal medulla and impaired autonomic regulation of AP. At 28-29 wk OZRs develop increased ptau in hippocampus with deficits in spatial learning and memory. Juvenile OZRs lack elevated ptau and these deficits, demonstrating that leptin is not essential for normal function. Elevated ptau and deficits emerge before the onset of diabetes in insulin-resistant OZRs.

Diabetes alters neuroeconomically dissociable forms of mental accounting

Those with diabetes mellitus are at high-risk of developing psychiatric disorders, yet the link between hyperglycemia and alterations in motivated behavior has not been explored in detail. We characterized value-based decision-making behavior of a streptozocin-induced diabetic mouse model on a naturalistic neuroeconomic foraging paradigm called Restaurant Row. Mice made self-paced choices while on a limited time-budget accepting or rejecting reward offers as a function of cost (delays cued by tone-pitch) and subjective value (flavors), tested daily in a closed-economy system across months. We found streptozocin-treated mice disproportionately undervalued less-preferred flavors and inverted their meal-consumption patterns shifted toward a more costly strategy that overprioritized high-value rewards. We discovered these foraging behaviors were driven by impairments in multiple decision-making systems, including the ability to deliberate when engaged in conflict and cache the value of the passage of time in the form of sunk costs. Surprisingly, diabetes-induced changes in behavior depended not only on the type of choice being made but also the salience of reward-scarcity in the environment. These findings suggest complex relationships between glycemic regulation and dissociable valuation algorithms underlying unique cognitive heuristics and sensitivity to opportunity costs can disrupt fundamentally distinct computational processes and could give rise to psychiatric vulnerabilities.

Effect of glycemic control on cognitive function in patients with type 1 diabetes mellitus: a systematic review and meta-analysis

BACKGROUND

It is controversial whether the level of glycemic control in patients with type 1 diabetes mellitus (T1DM) correlates with reduced cognitive function. This study explored the influence of glycemic management quality on cognitive function in T1DM patients by examining the association between glycemic control level and impaired cognitive function.

METHODS

The electronic databases PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure, China Science and Technology Journal database, Wanfang database, and China Biology Medicine disc database were systematically searched to identify eligible studies published before January 2023. Search, selection, and data extraction were performed by two independent reviewers. RevMan 5.4 software was used for meta-analysis, and standardized mean difference (SMD) between groups was calculated.

RESULTS

Six studies involving 351 patients with T1DM were included in this study. Compared with T1DM subjects with good glycemic control, those with poor glycemic control performed worse in full-scale intellectual quotient (P = 0.01, SMD = -0.79, 95%CI = -1.42 to -0.17), but no significant differences were observed in verbal intellectual quotient (P = 0.08, SMD = -1.03, 95%CI = -2.20 to 0.13), memory (P = 0.05, SMD = -0.41, 95%CI = -0.82 to 0.00), and attention (P = 0.23, SMD = -0.26, 95%CI = -0.69 to 0.16).

CONCLUSIONS

T1DM patients with suboptimal glycemic control may have a worse cognitive function, mainly focusing on the full-scale intellectual quotient. The current study highlights the significance of maintaining satisfactory glycemic control in T1DM patients to improve their health status and quality of life. Standardized tests should be employed in clinical neuropsychological practice to provide early and complete cognitive assessment of individuals with poor glycemic control.

SYSTEMATIC REVIEW REGISTRATION

The study protocol has been registered in the PROSPERO database (CRD42023390456).

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.

The extract of Sclerocarya birrea, Nauclea latifolia, and Piper longum mixture ameliorates diabetes-associated cognitive dysfunction

Diabetes-associated cognitive dysfunction is linked to chronic hyperglycemia, oxidative stress, inflammation, cholinergic dysfunction, and neuronal degeneration. We investigated the antidiabetic and neuroprotective activity of a mixture of Sclerocarya birrea, Nauclea latifolia, and Piper longum (SNP) in type 2 diabetic (T2D) rat model-induced memory impairment. Fructose (10%) and streptozotocin (35 mg/kg) were used to induce T2D in male Wistar rats. Diabetic animals received distilled water, metformin (200 mg/kg), or SNP mixture (75, 150, or 300 mg/kg). HPLC-MS profiling of the mixture was performed. Behavioral testing was conducted using the Y-maze, NORT, and Morris water mazes to assess learning and memory. Biochemical markers were evaluated, including carbohydrate metabolism, oxidative/nitrative stress, pro-inflammatory markers, and acetylcholinesterase activity. Histopathological examination of the pancreas and hippocampus was also performed. Fructose/STZ administration resulted in T2D, impaired short- and long-term memory, significantly increased oxidative/nitrative stress, pro-inflammatory cytokine levels, acetylcholinesterase activity (AChE), hippocampal neuronal loss and degeneration in CA1 and CA3 subfields, and neuronal vacuolation in DG. SNP mixture at 150 and 300 mg/kg significantly improved blood glucose and memory function in diabetic rats. The mixture reduced oxidative/nitrative stress and increased endogenous antioxidant levels. It also reduced serum IL-1β, INF-γ and TNF-α levels and ameliorated AChE activity. Histologically, SNP protected hippocampus neurons against T2D-induced neuronal necrosis and degeneration. We conclude that the aqueous extract of SNP mixture has antidiabetic and neuroprotective activities thanks to active metabolites identified in the plant mixture, which consequently normalized blood glucose, protected hippocampus neurons, and improved memory function in diabetic rats.

Investigating the effects of Citrullus colocynthis on cognitive performance and anxiety-like behaviors in STZ-induced diabetic rats

Background: Diabetes can impair cognitive performance and lead to dementia. Patients with type 1 diabetes mellitus (T1DM) are reported with different levels of cognitive dysfunctions in various cognitive domains ranging from general intellectual testing to specific deficits with visuospatial abilities, motor speed, writing, attention, reading, and psychomotor efficiency. The present study aimed to investigate the effect of Citrullus colocynthis on cognitive functions.Methods: A total of 42 male Wistar rats (3-4  months old and weighing 200-250  g) were tested in the current study. Rats were randomly allocated into 3 groups of control, Diabetes, and Diabetes + Drug. The diabetic rats received Citrullus colocynthis extraction orally. The behavioral tests included the open field, elevated plus maze (EPM), novel object recognition (NOR), passive avoidance tests, and Morris Water Maze (MWM) tests. Data were analyzed using student and paired t-tests via SPSS software version 16.Results: Our results showed the protective effects of Citrullus colocynthis administration against cognitive impairments. This is followed by STZ-induced diabetes in the MWM, novel object recognition, and passive avoidance tasks. Also, it was found that Citrullus colocynthis improved anxiety in diabetic rats.Conclusion According to the findings of this study, the administration of 200  mg/kg C. colocynthis once per day for 40  days can lead to ameliorated cognitive impairments and antidiabetic effects such as increasing body weight and decreasing FBS.

Myrtenal improves memory deficits in mice exposed to radiofrequency-electromagnetic radiation during gestational and neonatal development via enhancing oxido-inflammatory, and neurotransmitter functions

Objective

Radiofrequency-electromagnetic radiation (RF-EMR) exposure during gestational and neonatal development may interact with the foetus and neonate considered hypersensitive to RF-EMR, consequently resulting in developmental defects associated with neuropsychological and neurobehavioral disorders, including learning and memory impairment. This study assessed the potential of Myrtenal (Myrt) to improve memory deficits in C57BL/6 mice exposed to RF-EMR during gestational and neonatal development.

Method

Thirty-five male mice were randomly allocated into 5 cohorts, each comprising of 7 mice. Group I was administered vehicle, Group II: RF-EMR (900 MHz); Group III: RF-EMR (900 MHz) + 100 mg/kg Myrt; Group IV: RF-EMR (900 MHz) + 200 mg/kg Myrt; and Group V: RF-EMR (900 MHz) + donepezil 0.5 mg/kg.

Results

Myrt treatment improved short-term memory performance in RF-EMR (900 MHz)-exposed mice by augmenting activities of endogenous antioxidant enzymes and proinflammatory cytokines, thereby protecting the brain from oxido-inflammatory stress. Additionally, Myrt restored the homeostasis of neurotransmitters in RF-EMR-exposed animals.

Conclusion

Results from the present study shows that exposure to RF-EMR impaired short-term memory in animals and altered the response of markers of oxido-inflammatory stress, and neurotransmitters. It is therefore conceivable that the recommendation of Myrt-enriched fruits may offer protective benefits for foeti and neonates prone to RF-EMR exposure.

Assessment of executive function in a rodent model of Type 1 diabetes

This study examined the impact of Type 1 Diabetes Mellitus (T1DM) on executive function using a series of operant conditioning-based tasks in rats. Sprague Dawley rats were randomized to either non-diabetic (n = 12; 6 male) or diabetic (n = 14; 6 male) groups. Diabetes was induced using multiple low-dose streptozotocin injections. All diabetic rodents were insulin-treated using subcutaneous insulin pellet implants (9-15 mM). At week 14 of the study, rats were placed on a food restricted diet to induce 5-10 % weight loss. Rodents were familiarized and their set-shifting ability was tested on a series of tasks that required continuous adjustments to novel stimulus-reward paradigms in order to receive food rewards. Results showed no differences in the number of trials, nor number and type of errors made to successfully complete each task between groups. Therefore, we report no differences in executive function, or more specifically set-shifting abilities between non-diabetic and diabetic rodents that receive insulin.

Regional high iron deposition on quantitative susceptibility mapping correlates with cognitive decline in type 2 diabetes mellitus

Objective

To quantitatively evaluate the iron deposition and volume changes in deep gray nuclei according to threshold-method of quantitative susceptibility mapping (QSM) acquired by strategically acquired gradient echo (STAGE) sequence, and to analyze the correlation between the magnetic susceptibility values (MSV) and cognitive scores in type 2 diabetes mellitus (T2DM) patients.

Methods

Twenty-nine patients with T2DM and 24 healthy controls (HC) matched by age and gender were recruited in this prospective study. QSM images were used to evaluate whole-structural volumes (V_wh), regional magnetic susceptibility values (MSV_RII), and volumes (V_RII) in high-iron regions in nine gray nuclei. All QSM data were compared between groups. Receiver operating characteristic (ROC) analysis was used to assess the discriminating ability between groups. The predictive model from single and combined QSM parameters was also established using logistic regression analysis. The correlation between MSV_RII and cognitive scores was further analyzed. Multiple comparisons of all statistical values were corrected by false discovery rate (FDR). A statistically significant P-value was set at 0.05.

Results

Compared with HC group, the MSV_RII of all gray matter nuclei in T2DM were increased by 5.1-14.8%, with significant differences found in bilateral head of caudate nucleus (HCN), right putamen (PUT), right globus pallidus (GP), and left dentate nucleus (DN) (P < 0.05). The V_wh of most gray nucleus in T2DM group were decreased by 1.5-16.9% except bilateral subthalamic nucleus (STN). Significant differences were found in bilateral HCN, bilateral red nucleus (RN), and bilateral substantia nigra (SN) (P < 0.05). V_RII was increased in bilateral GP, bilateral PUT (P < 0.05). V_RII/V_wh was also increased in bilateral GP, bilateral PUT, bilateral SN, left HCN and right STN (P < 0.05). Compared with the single QSM parameter, the combined parameter showed the largest area under curve (AUC) of 0.86, with a sensitivity of 87.5% and specificity of 75.9%. The MSV_RII in the right GP was strongly associated with List A Long-delay free recall (List A LDFR) scores (r = -0.590, P = 0.009).

Conclusion

In T2DM patients, excessive and heterogeneous iron deposition as well as volume loss occurs in deep gray nuclei. The MSV in high iron regions can better evaluate the distribution of iron, which is related to the decline of cognitive function.

Diabetic Encephalopathy in a Preclinical Experimental Model of Type 1 Diabetes Mellitus: Observations in Adult Female Rat

Patients affected by diabetes mellitus (DM) show diabetic encephalopathy with an increased risk of cognitive deficits, dementia and Alzheimer's disease, but the mechanisms are not fully explored. In the male animal models of DM, the development of cognitive impairment seems to be the result of the concomitance of different processes such as neuroinflammation, oxidative stress, mitochondrial dysfunction, and aberrant synaptogenesis. However, even if diabetic encephalopathy shows some sex-dimorphic features, no observations in female rats have been so far reported on these aspects. Therefore, in an experimental model of type 1 DM (T1DM), we explored the impact of one month of pathology on memory abilities by the novel object recognition test and on neuroinflammation, synaptogenesis and mitochondrial functionality. Moreover, given that steroids are involved in memory and learning, we also analysed their levels and receptors. We reported that memory dysfunction can be associated with different features in the female hippocampus and cerebral cortex. Indeed, in the hippocampus, we observed aberrant synaptogenesis and neuroinflammation but not mitochondrial dysfunction and oxidative stress, possibly due to the results of locally increased levels of progesterone metabolites (i.e., dihydroprogesterone and allopregnanolone). These observations suggest specific brain-area effects of T1DM since different alterations are observed in the cerebral cortex.

Diabetes and associated cognitive disorders: Role of the Hypothalamic-Pituitary Adrenal axis

Both diabetes types, types 1 and 2, are associated with cognitive impairments. Each period of life is concerned, and this is an increasing public health problem. Animal models have been developed to investigate the biological actors involved in such impairments. Many levels of the brain function (structure, volume, neurogenesis, neurotransmission, behavior) are involved. In this review, we detailed the part potentially played by the Hypothalamic-Pituitary Adrenal axis in these dysfunctions. Notably, regulating glucocorticoid levels, their receptors and their bioavailability appear to be relevant for future research studies, and treatment development.

Type 2 diabetes mellitus-associated cognitive dysfunction: Advances in potential mechanisms and therapies

Type 2 diabetes (T2D) and its target organ injuries cause distressing impacts on personal health and put an enormous burden on the healthcare system, and increasing attention has been paid to T2D-associated cognitive dysfunction (TDACD). TDACD is characterized by cognitive dysfunction, delayed executive ability, and impeded information-processing speed. Brain imaging data suggest that extensive brain regions are affected in patients with T2D. Based on current findings, a wide spectrum of non-specific neurodegenerative mechanisms that partially overlap with the mechanisms of neurodegenerative diseases is hypothesized to be associated with TDACD. However, it remains unclear whether TDACD is a consequence of T2D or a complication that co-occurs with T2D. Theoretically, anti-diabetes methods are promising neuromodulatory approaches to reduce brain injury in patients with T2D. In this review, we summarize potential mechanisms underlying TDACD and promising neurotropic effects of anti-diabetes methods and some neuroprotective natural compounds. Constructing screening or diagnostic tools and developing targeted treatment and preventive strategies would be expected to reduce the burden of TDACD.

Brain insulin resistance as a mechanistic mediator links peripheral metabolic disorders with declining cognition

BACKGROUND AND AIMS

Studies continue to investigate the underlying mechanism of the association between the increased risk of different types of cognitive decline and metabolic dysregulation. Brain insulin resistance (BIR) has been suggested to explain this association. The vital role of insulin in the body has been examined intensively and extensively; however, its role in the brain requires further investigation. Herein, we confined our focus to summarize the role of brain insulin signaling and the negative effect of dysmetabolism on insulin functioning in the brain.

METHODS

Published scientific manuscripts between 1998 and 2020 that discussed the effect of selected metabolic disorder conditions such as obesity, type 2 diabetes mellitus (T2DM), and high-fat diet (HFD) on brain functions were reviewed. The main keywords used were insulin resistance, brain insulin resistance, obesity, T2DM, and cognition.

RESULTS

Various metabolic disorders were linked to the increased risk of BIR, and was suggested to increase the probability of cognition impairment occurrence. Several proposed mechanisms explain this association among which insulin resistance and hyperinsulinemia were primary factors attributed to an increased risk of BIR among various metabolic disorders.

CONCLUSIONS

Understanding the trajectory of the association between metabolic disorders and alternation in cognition status could expand our vision of those overlapping conditions and pave the road to both treatment and preventative strategies for cognitive disorders.

Enhancement of Mitochondrial Function by the Neurogenic Molecule NSI-189 Accompanies Reversal of Peripheral Neuropathy and Memory Impairment in a Rat Model of Type 2 Diabetes

AIMS

Mitochondrial dysfunction contributes to many forms of peripheral and central nervous system degeneration. Therapies that protect mitochondrial number and function have the potential to impact the progression of conditions such as diabetic neuropathy. We therefore assessed indices of mitochondrial function in dorsal root ganglia (DRG) and brain cortex of the Zucker diabetic fatty (ZDF) rat model of type 2 diabetes and tested the therapeutic impact of a neurogenic compound, NSI-189, on both mitochondrial function and indices of peripheral and central neurological dysfunction.

MATERIALS AND METHODS

ZDF rats were maintained for 16 weeks of untreated diabetes before the start of oral treatment with NSI-189 for an additional 16 weeks. Nerve conduction velocity, sensitivity to tactile and thermal stimuli, and behavioral assays of cognitive function were assessed monthly. AMP-activated protein kinase (AMPK) phosphorylation, mitochondrial protein levels, and respiratory complex activities were assessed in the DRG and brain cortex after 16 weeks of treatment with NSI-189.

RESULTS

Treatment with NSI-189 selectively elevated the expression of protein subunits of complexes III and V and activities of respiratory complexes I and IV in the brain cortex, and this was accompanied by amelioration of impaired memory function and plasticity. In the sensory ganglia of ZDF rats, loss of AMPK activity was ameliorated by NSI-189, and this was accompanied by reversal of multiple indices of peripheral neuropathy.

CONCLUSIONS

Efficacy of NSI-189 against dysfunction of the CNS and PNS function in type 2 diabetic rats was accompanied by improvement of mitochondrial function. NSI-189 exhibited actions at different levels of mitochondrial regulation in central and peripheral tissues.

Myrtenal mitigates streptozotocin-induced spatial memory deficit via improving oxido inflammatory, cholinergic and neurotransmitter functions in mice

The occurrence of chronic neurodegenerative disorders is on the rise, but with no effective treatment due to the paucity of information on the pathological mechanism underlying these disorders. Thus, this study investigated the role of oral administration of myrtenal in mitigating memory deficits and neuro-biochemical alterations in streptozotocin-demented mice model. Mice (n ​= ​35) were randomly allocated into five cohorts consisting of 7 mice each; Group I: Control mice received vehicle alone; Group II: streptozotocin; Group III: streptozotocin + 100 ​mg/kg myrtenal; Group IV: streptozotocin +200 ​mg/kg myrtenal; and Group V: streptozotocin ​+ ​donepezil 0.5 ​mg/kg. Data from this study demonstrated that the administration of streptozotocin (STZ) impaired spatial memory and induced alterations in markers of oxido-inflammatory response, cholinergic function, cytoarchitecture, and neurotransmitter levels in mice hippocampus. Notably, administration of myrtenal enhanced spatial memory performance in STZ-demented mice by improving the activities of endogenous antioxidant enzymes to protect the brain from oxido-inflammatory stress. Treatment with myrtenal also restored cholinergic function and stabilized the homeostasis of neurotransmitters in STZ-demented mice. The authors infer that fruits rich in myrtenal may be beneficial for treating patients living with dementia associated with Alzheimer's disease.

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Data from the present study demonstrates that the administration of streptozotocin impairs spatial memory in mice and induces alterations in markers of oxido-inflammatory response, cholinergic function, histoarchitecture, and neurotransmitter levels in the hippocampus.

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The administration of myrtenal enhances spatial memory performance in streptozotocin-demented mice by improving the activities of endogenous antioxidant enzymes to protect the brain from oxido-inflammatory stress.

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Treatment with myrtenal restores cholinergic function and stabilizes the homeostasis of neurotransmitters in streptozotocin-demented mice.

Fustin Inhibits Oxidative Free Radicals and Inflammatory Cytokines in Cerebral Cortex and Hippocampus and Protects Cognitive Impairment in Streptozotocin-Induced Diabetic Rats

The phytogenic flavanol component of the plant Rhus verniciflua Stokes is fustin which is implicated in various disease aliments and has promising therapeutic efficacy and a long history of its uses in the Indian medicinal system. The present study investigated the ameliorative effect of fustin in streptozotocin (STZ) induced cognitive impairments in the diabetic animal paradigm. A total of five different animal groups were used for the present study.The preclinical efficacy of fustin at 50 mg/kg and 100 mg/kg was studied in diabetic male rats by employing a 35-day study design. In the present investigation the Morris water maze test (MWM) and elevated plus maze (EPM) test were employed as behavioral paradigms for the assessment of memory impairments. The study design also carried out certain biochemical parameters which include glutathione (GSH), superoxide dismutase (SOD), catalase activity (CAT), malondialdehyde (MDA), nitric oxide (NO), relative interleukin-6 (IL-6), and IL-1B in samples obtained from cerebral cortex and hippocampus. The behavioral parameters with MWM and EPM were significant restored in fustin treatment groups as compared to elevated levels in the diabetic control group. Furthermore, fustin significantly improved the altered levels of several biochemical parameters for cognitive dysfunction such as GSH, SOD, CAT, MDA, NO, and relative IL-6 and IL-1B compared to a diabetic control group. The present investigation highlights certain preclinical pieces of evidence that strongly indicate that fustin might restore the normal cognitive function in the experimental animal paradigm.

Alleviative Effect of Alpha-Lipoic Acid on Cognitive Impairment in High-Fat Diet and Streptozotocin-Induced Type 2 Diabetic Rats

Background: The intricate relationship between type 2 diabetes mellitus (T2DM) and Alzheimer’s disease (AD) suggests that insulin is involved in modulating AD-related proteins. Alpha-lipoic acid (ALA) can improve insulin resistance (IR) in diabetic rats. However, the role of ALA in alleviating the cognitive decline of T2DM is not yet clear. This study examined the ameliorative effect of ALA on cognitive impairment, cerebral IR, and synaptic plasticity abnormalities in high-fat diet (HFD) plus streptozotocin (STZ) induced diabetic rats.

Methods: The HFD/STZ-induced T2DM male Wistar rats were orally administered with ALA (50, 100, or 200 mg/kg BW) once a day for 13 weeks. Abilities of cognition were measured with a passive avoidance test and Morris water maze. Specimens of blood and brain were collected for biochemical analysis after the rats were sacrificed. Western blotting was used to determine protein expressions in the hippocampus and cortex in the insulin signaling pathways, long-term potentiation (LTP), and synaptic plasticity-related protein expressions.

Results: Alpha-lipoic acid improved hyperinsulinemia and the higher levels of free fatty acids of the T2DM rats. Behavioral experiments showed that the administration of ALA improved cognitive impairment in HFD/STZ-induced T2DM rats. ALA ameliorated insulin-related pathway proteins [phosphoinositide 3-kinase (PI3K), phospho-protein kinase B (pAkt)/Akt, and insulin-degrading enzyme (IDE)] and the LTP pathway, as well as synaptic plasticity proteins (calmodulin-dependent protein kinase II, cyclic AMP response element-binding protein, and postsynaptic density protein-95) of the cerebral cortex or hippocampus in HFD/STZ-induced T2DM rats.

Conclusion: Our findings suggested that ALA may ameliorate cognition impairment via alleviating cerebral IR improvement and cerebral synaptic plasticity in diabetic rats.

Peripheral versus central insulin and leptin resistance: Role in metabolic disorders, cognition, and neuropsychiatric diseases

Insulin and leptin are classically regarded as peptide hormones that play key roles in metabolism. In actuality, they serve several functions in both the periphery and central nervous system (CNS). Likewise, insulin and leptin resistance can occur both peripherally and centrally. Metabolic disorders such as diabetes and obesity share several key features including insulin and leptin resistance. While the peripheral effects of these disorders are well-known (i.e. cardiovascular disease, hypertension, stroke, dyslipidemia, etc.), the CNS complications of leptin and insulin resistance have come into sharper focus. Both preclinical and clinical findings have indicated that insulin and leptin resistance are associated with cognitive deficits and neuropsychiatric diseases such as depression. Importantly, these studies also suggest that these deficits in neuroplasticity can be reversed by restoration of insulin and leptin sensitivity. In view of these observations, this review will describe, in detail, the peripheral and central functions of insulin and leptin and explain the role of insulin and leptin resistance in various metabolic disorders, cognition, and neuropsychiatric diseases.

Microvascular basis of cognitive impairment in type 1 diabetes

The complex computations of the brain require a constant supply of blood flow to meet its immense metabolic needs. Perturbations in blood supply, even in the smallest vascular networks, can have a profound effect on neuronal function and cognition. Type 1 diabetes is a prevalent and insidious metabolic disorder that progressively and heterogeneously disrupts vascular signalling and function in the brain. As a result, it is associated with an array of adverse vascular changes such as impaired regulation of vascular tone, pathological neovascularization and vasoregression, capillary plugging and blood brain barrier disruption. In this review, we highlight the link between microvascular dysfunction and cognitive impairment that is commonly associated with type 1 diabetes, with the aim of synthesizing current knowledge in this field.

Investigation of glycaemic traits in psychiatric disorders using Mendelian randomisation revealed a causal relationship with anorexia nervosa

Data from observational studies have suggested an involvement of abnormal glycaemic regulation in the pathophysiology of psychiatric illness. This may be an attractive target for clinical intervention as glycaemia can be modulated by both lifestyle factors and pharmacological agents. However, observational studies are inherently confounded, and therefore, causal relationships cannot be reliably established. We employed genetic variants rigorously associated with three glycaemic traits (fasting glucose, fasting insulin, and glycated haemoglobin) as instrumental variables in a two-sample Mendelian randomisation analysis to investigate the causal effect of these measures on the risk for eight psychiatric disorders. A significant protective effect of a natural log transformed pmol/L increase in fasting insulin levels was observed for anorexia nervosa after the application of multiple testing correction (OR = 0.48 [95% CI: 0.33-0.71]-inverse-variance weighted estimate). There was no consistently strong evidence for a causal effect of glycaemic factors on the other seven psychiatric disorders considered. The relationship between fasting insulin and anorexia nervosa was supported by a suite of sensitivity analyses, with no statistical evidence of instrument heterogeneity or horizontal pleiotropy. Further investigation is required to explore the relationship between insulin levels and anorexia.

Insulin action on astrocytes: From energy homeostasis to behaviour

Astrocytes are specialised glial cells that integrate distinct inputs arising from neurones, other glial cells and the microcirculation to regulate diverse aspects of brain function. A growing body of emerging evidence supports that astrocytes, similar to neurones, also play active roles in the neuroendocrine control of metabolism by responding to afferent nutritional and hormonal cues and translating these metabolic cues into neuronal inputs. Specifically, insulin action in astrocytes has received special emphasis given its newly discovered regulatory role in brain glucose uptake, which until recently was assumed to be an insulin independent process. We now know that insulin signalling in astrocytes regulates metabolic processes and behavioural responses through coupling brain glucose uptake with nutrient availability to maintain energy balance and systemic glucose homeostasis. Moreover, genetic ablation of the insulin receptor in astrocytes is associated with anxiety- and depressive-like behaviours, confirming that these glial cells are involved in the regulation of cognition and mood via insulin action. Here, we provide a comprehensive review of the most relevant findings that have been made over the course of the last few years linking insulin signalling in astrocytes with the pathogenesis of brain metabolic and neurodegenerative diseases; a still unexplored field, but with a high translational potential for developing therapies.

Mechanisms of Insulin Resistance at the Crossroad of Obesity with Associated Metabolic Abnormalities and Cognitive Dysfunction

Obesity mediates most of its direct medical sequelae through the development of insulin resistance (IR). The cellular effects of insulin occur through two main postreceptor pathways that are the phosphatidylinositol 3-kinase (PI3-K) and the mitogen-activated protein kinase (MAP-K) pathways. Obesity-related IR implicates the PI3-K pathway that confers the metabolic effects of insulin. Numerous and complex pathogenic pathways link obesity with the development of IR, including chronic inflammation, mitochondrial dysfunction (with the associated production of reactive oxygen species and endoplasmic reticulum stress), gut microbiota dysbiosis and adipose extracellular matrix remodelling. IR itself plays a key role in the development of metabolic dysfunction, including hypertension, dyslipidaemia and dysglycaemia. Furthermore, IR promotes weight gain related to secondary hyperinsulinaemia, with a resulting vicious cycle of worsening IR and its metabolic sequelae. Ultimately, IR underlies obesity-related conditions such as type 2 diabetes mellitus (T2D) and polycystic ovary syndrome (PCOS). IR also underlies many obesity-related malignancies, through the effects of compensatory hyperinsulinaemia on the relatively intact MAP-K insulin pathway, which controls cellular growth processes and mitoses. Furthermore, the emergent data over recent decades support an important role of obesity- and T2D-related central IR in the development of cognitive dysfunction, including effects on hippocampal synaptic plasticity. Importantly, IR is largely reversible through the optimisation of lifestyle factors that include regular engagement in physical activity with the avoidance of sedentariness, improved diet including increased fibre intake and sleep sufficiency. IR lies at the key crossroad between obesity and both metabolic and cognitive dysfunction. Given the importance of IR in the pathogenesis of many 21st century chronic diseases and its eminent reversibility, it is important that we all embrace and facilitate optimised lifestyles to improve the future health and wellbeing of the populace.

Hyperglycemia induces RAGE-dependent hippocampal spatial memory impairments

Diabetes is a prevalent metabolic disorder that has long been associated with changes in different regions of the brain, including the hippocampus. Changes in hippocampal synaptic plasticity and subsequent impairment in cognitive functions such as learning and memory, are well documented in animal models of type 1 and type 2 diabetes. It is known that RAGE contributes to peripheral micro- and macro-vascular complications of diabetes. However, it is still unknown if RAGE plays a similar role in the development of CNS complications of diabetes. Therefore, we hypothesize that RAGE contributes to cognitive dysfunction, such as learning and memory impairments, in a mouse model of STZ-induced hyperglycemia. Control and STZ-induced hyperglycemic mice from WT and RAGE-KO groups were used for the behavioral experiments. While STZ-induced hyperglycemia decreased locomotor activity in the open field (OF) test, it did not affect the recognition memory in the novel object recognition (NOR) test in either genotype. Spatial memory, however, was impaired in STZ-induced hyperglycemic mice in WT but not in RAGE-KO group in both the Barnes maze (BM) and the Morris water maze (MWM) tests. Consistently, the RAGE antagonist FPS-ZM1 protected WT STZ-induced hyperglycemic mice from spatial memory impairment in the BM test. Our findings indicate that the parameters associated with locomotor activity and recognition memory were independent of RAGE in STZ-induced hyperglycemic mice. In contrast, the parameters associated with hippocampal-dependent spatial memory were dependent on RAGE expression.

RAGE signaling is required for AMPA receptor dysfunction in the hippocampus of hyperglycemic mice

Diabetes in humans has been associated for a long time with cognitive dysfunction. In rodent animal models, cognitive dysfunction can manifest as impaired hippocampal synaptic plasticity. Particular attention has been concentrated on the receptor for advanced glycation end products (RAGE), which is implicated in multiple diabetic complications involving the development of vascular and peripheral nerve abnormalities. In this study, we hypothesize that RAGE signaling alters glutamate receptor function and expression, impairing synaptic transmission in the hippocampus. Using preparations of hippocampal slices from male mice, we show a RAGE-dependent decrease in long-term potentiation (LTP) and an increase in paired-pulse facilitation (PPF) following streptozotocin (STZ)-induced diabetes. Consistently, in hippocampal cultures from male and female neonatal mice, high glucose caused a RAGE-dependent reduction of AMPA- but not NMDA-evoked currents, and an increase in cytosolic reactive oxygen species (ROS). Consistently, when cultures were co-treated with high glucose and the RAGE antagonist FPS-ZM1, AMPA-evoked currents were unchanged. Hippocampi from STZ-induced hyperglycemic wild type (WT) mice showed increased RAGE expression concomitant with a decrease of both expression and phosphorylation (Ser 831 and 845) of the AMPA GluA1 subunit. We found these changes correlated to activation of the MAPK pathway, consistent with decreased pJNK/JNK ratio and the JNK kinase, pMEK7. As no changes in expression or phosphorylation of regulatory proteins were observed in hippocampi from STZ-induced hyperglycemic RAGE-KO mice, we report a RAGE-dependent impairment in the hippocampi of hyperglycemic WT mice, with reduced AMPA receptor expression/function and LTP deficits.

Glucose transporters in brain in health and disease

Energy demand of neurons in brain that is covered by glucose supply from the blood is ensured by glucose transporters in capillaries and brain cells. In brain, the facilitative diffusion glucose transporters GLUT1-6 and GLUT8, and the Na⁺-d-glucose cotransporters SGLT1 are expressed. The glucose transporters mediate uptake of d-glucose across the blood-brain barrier and delivery of d-glucose to astrocytes and neurons. They are critically involved in regulatory adaptations to varying energy demands in response to differing neuronal activities and glucose supply. In this review, a comprehensive overview about verified and proposed roles of cerebral glucose transporters during health and diseases is presented. Our current knowledge is mainly based on experiments performed in rodents. First, the functional properties of human glucose transporters expressed in brain and their cerebral locations are described. Thereafter, proposed physiological functions of GLUT1, GLUT2, GLUT3, GLUT4, and SGLT1 for energy supply to neurons, glucose sensing, central regulation of glucohomeostasis, and feeding behavior are compiled, and their roles in learning and memory formation are discussed. In addition, diseases are described in which functional changes of cerebral glucose transporters are relevant. These are GLUT1 deficiency syndrome (GLUT1-SD), diabetes mellitus, Alzheimer’s disease (AD), stroke, and traumatic brain injury (TBI). GLUT1-SD is caused by defect mutations in GLUT1. Diabetes and AD are associated with changed expression of glucose transporters in brain, and transporter-related energy deficiency of neurons may contribute to pathogenesis of AD. Stroke and TBI are associated with changes of glucose transporter expression that influence clinical outcome.

Elevating Insulin Signaling Using a Constitutively Active Insulin Receptor Increases Glucose Metabolism and Expression of GLUT3 in Hippocampal Neurons

Insulin signaling is an integral component of healthy brain function, with evidence of positive insulin-mediated alterations in synaptic integrity, cerebral blood flow, inflammation, and memory. However, the specific pathways targeted by this peptide remain unclear. Previously, our lab used a molecular approach to characterize the impact of insulin signaling on voltage-gated calcium channels and has also shown that acute insulin administration reduces calcium-induced calcium release in hippocampal neurons. Here, we explore the relationship between insulin receptor signaling and glucose metabolism using similar methods. Mixed, primary hippocampal cultures were infected with either a control lentivirus or one containing a constitutively active human insulin receptor (IRβ). 2-NBDG imaging was used to obtain indirect measures of glucose uptake and utilization. Other outcome measures include Western immunoblots of GLUT3 and GLUT4 on total membrane and cytosolic subcellular fractions. Glucose imaging data indicate that neurons expressing IRβ show significant elevations in uptake and rates of utilization compared to controls. As expected, astrocytes did not respond to the IRβ treatment. Quantification of Western immunoblots show that IRβ is associated with significant elevations in GLUT3 expression, particularly in the total membrane subcellular fraction, but did not alter GLUT4 expression in either fraction. Our work suggests that insulin plays a significant role in mediating neuronal glucose metabolism, potentially through an upregulation in the expression of GLUT3. This provides further evidence for a potential therapeutic mechanism underlying the beneficial impact of intranasal insulin in the clinic.

Altered Effective Connectivity of Bilateral Hippocampus in Type 2 Diabetes Mellitus

Patients with type 2 diabetes mellitus (T2DM) experience cognitive deficits but the underlying pathophysiologic mechanisms are not known. We therefore applied Granger causality analysis of resting-state functional magnetic resonance imaging to study the effective connectivity (EC) of the hippocampus in patients with T2DM. Eighty six patients with T2DM and 84 matched healthy controls (HC) were recruited. The directional EC between anatomically defined seeds in left hippocampus (LHIP) and right hippocampus (RHIP) and other brain regions was compared between T2DM and HC and Pearson correlation analysis was performed to determine whether alterations in EC were related to clinical characteristics of diabetes. Compared with HC, patients with T2DM had altered EC between LHIP and RHIP and the default mode network (DMN), occipital cortex and cerebellum. In addition, for LHIP only duration of diabetes positively correlated with decreased inflow from right postcentral gyrus and right parietal lobe, glycosylated hemoglobin (HbA1c) negatively correlated with decreased inflow from right thalamus (r = -0.255, p = 0.018) and Montreal Cognitive Assessment (MoCA) negatively correlated with decreased inflow from left inferior parietal lobe (r = -0.206, p = 0.05). The altered EC between hippocampus and DMN is interpreted to be related to cognitive deficits in patients with T2DM particularly affecting memory and learning.

Neuroprotective and memory-enhancing effects of methanolic leaf extract of Peristrophe bicalyculata in rat model of type 2 diabetes mellitus

This study investigated the effect of methanolic leaf extract of Peristrophe Bicalyculata (MEPb) on type 2 diabetes mellitus (T2DM) associated cognitive decline in Wistar rats.

36 male rats weighing 130–200 g were assigned into 6 groups (n = 6) as follows: normal control, diabetic control, pioglitazone-treated diabetic and three MEPb-treated diabetic groups, type 2 diabetes mellitus was induced with low dose streptozocin (STZ) injection following 3 weeks of high fat diet (HFD) intake. Thirty days after diabetes induction, rats exhibited marked and persistent hyperglycemia, animals were treated with MEPb (50, 100 and 200 mg/kg) and pioglitazone (10 mg/kg) as standard. Morris water maze (MWM) test and Novel object recognition test (NORT) were used to assess learning and memory. Blood glucose level, oxidative stress makers, pro-inflammatory marker and acetylcholinestarase activities were analysed.

Both MEPb and pioglitazone significantly (P < 0.05) reduced escape latency in treated animals compared to the diabetic control group in the MWM test. Methanolic leaf extract of Peristrophe bicalyculata and pioglitazone also significantly (P < 0.05) increased discrimination index in treated animals compared to the diabetic control group in the novel object recognition test. Serum, brain and liver MDA levels were significantly (P < 0.05) decreased in MEPb and pioglitazone treated rats compared to diabetic control. Serum and liver GSH as well as CAT levels were significantly (P < 0.05) increased while brain GSH and CAT levels shows apparent increase in MEPb and pioglitazone treated rats compared with diabetic control. Treatment with MEPb caused a significant (P < 0.05) decrease in brain nitrite level, interleukin 6 and acetylcholinesterase activity compared to diabetic control group.

We conclude that Methanolic leaf extract of Peristrophe bicalyculata enhanced antioxidant capacity and prevented neuroinflammation, consequently improving brain neuronal cholinergic function in experimental animals.

Functions of adiponectin signaling in regulating neural plasticity and its application as the therapeutic target to neurological and psychiatric diseases

Convergent lines of evidence indicate the critical roles of adiponectin in regulating neural functions on different levels. Because of the importance in maintaining neural plasticity including adult neurogenesis and synaptic plasticity, adiponectin has the potential to serve as the treatment targets in therapies of neurological and psychiatric disorders. Hence, systematic review is needed to summarize how adiponectin works in the brain, and how the adiponectin pathway is employed as the treatment method needs to be determined. Moreover, the benefits of adiponectin as the regulator for neural plasticity such as synaptic plasticity and neurogenesis have been supported by many literatures. In the current article, we reviewed the functions of adiponectin in different types of neural plasticity. We also demonstrated the potential value of adiponectin as the treatment target for different types of neurodegenerative and psychiatric disorders. Taken together, this review offers a new insight about adiponectin as the ideal target to develop the new treatment methods against neurodegeneration or psychiatric diseases.

MicroRNA-29b Modulates β-Secretase Activity in SH-SY5Y Cell Line and Diabetic Mouse Brain

Hyperglycemia is one of the major risk factors responsible for memory impairment in diabetes which may lead to Alzheimer's disease (AD) at a later stage. MicroRNAs are a class of non-coding RNAs that are found to play a role in diabetes. Downregulation of microRNA-29b in diabetes is well reported. Moreover, microRNA-29b is also reported to target the 3' UTR of β-secretase (BACE-1) enzyme which is involved in the formation of amyloid-beta (Aβ) in AD via cleavage of amyloid precursor protein (APP). Therefore, the present study was designed to elucidate whether microRNA-29b could be a link between diabetes and dementia. In the in vitro and in vivo diabetic model, we found downregulation of microRNA-29b due to hyperglycemia. After human microRNA-29b treatment, there was a significant improvement in the short-term and spatial memory in diabetic mice. Also, the human microRNA-29b treatment decreased oxidative stress and BACE-1 activity in diabetes. The present findings revealed that the downregulation of microRNA-29b in diabetes could be associated with memory impairment and increased BACE-1 activity. These results would give a future direction to study the role played by microRNAs in diabetes-associated memory impairment and hence aid in the development of therapeutics to treat the same.

Decreased striatal vesicular monoamine transporter 2 (VMAT2) expression in a type 1 diabetic rat model: A longitudinal study using micro-PET/CT

AIMS

Diabetes mellitus is a risk factor for Parkinson's disease. These diseases share similar pathogenic pathways, such as mitochondrial dysfunction, inflammation, and altered metabolism. Despite these similarities, the pathogenic relationship between these two diseases is unclear. [¹⁸F]FP-(+)-DTBZ is a promising radiotracer targeting VMAT2, which has been used to measure β-cell mass and to diagnose Parkinson's disease. The aim of this study was to examine the effect of type 1 diabetes on VMAT2 expression in the striatum using [¹⁸F]FP-(+)-DTBZ.

MATERIALS AND METHODS

A longitudinal study of type 1 diabetic rats was established by intraperitoneally injecting male Wistar rats with streptozotocin. Rats injected with saline were used as the control group. Glucose level, body weight, and [¹⁸F]FP-(+)-DTBZ uptake in the striatum and pancreas were evaluated at 0.5, 1, 4, 6 and 12 months after STZ or saline injection.

RESULTS

At one-half month post-STZ injection, the glucose levels in these rats increased and then returned to a normal level at 6 months. Along with increased glucose levels, body weight was also decreased significantly and returned slowly to a normal level. β-Cell mass and striatal [¹⁸F]FP-(+)-DTBZ uptake were impaired significantly at 2 weeks post-STZ injection in type 1 diabetic rats and returned to a normal level at 6 and 4 months post-STZ injection.

CONCLUSIONS

Due to increased glucose levels and decreased β-cell mass, decreased [¹⁸F]FP-(+)-DTBZ uptake in the striatum was observed in type 1 diabetic rats. Decreased BCM and increased glucose levels were correlated with VMAT2 expression in the striatum which indicated DM is a risk factor for PD.

Time-dependent impairments in learning and memory in Streptozotocin-induced hyperglycemic rats

The sedentary lifestyle is responsible for the high prevalence of diabetes which also impairs cognition including learning and memory. Various studies have highlighted the learning and memory impairments in rodent models but data regarding the timeline of their development and their correlation to biochemical parameters are scarce. So, the present study was designed to investigate the type of memory which is more susceptible to hyperglycemia and its correlation with biochemical parameters such as inflammatory cytokines, cAMP response element binding (CREB) and protein kinase B (Akt) activation. Hyperglycemia was induced using streptozotocin (STZ, 45 mg/kg i.p.) and confirmed by measuring fasting blood glucose levels after 1 week of STZ injection. Learning and memory deficits were evaluated using the Novel Object Recognition Test (NORT) and Morris water maze (MWM), and correlated with biochemical parameters (TNF-α, IL-1β, and dopamine) at 3, 6 and 9 weeks. STZ-injected rats after 3 weeks of injection demonstrated moderate hyperglycemia (blood glucose = 7.99 ± 0.62 mM) with intact learning and reference memory; however, their working memory was impaired in MWM. Severe hyperglycemia (blood glucose = 11.51 ± 0.69 mM) accompanied by impaired short, long, and working memory was evident after 6 weeks whereas learning was intact. After 9 weeks of STZ injection, hyperglycemia was more pronounced (13.69 ± 1.43 mM) and accompanied by a learning deficit in addition to short, long, and working memory impairments. The extent of hyperglycemia either in terms of duration or severity resulted in enhanced inflammation, down-regulation of the level of dopamine, protein expression of AKT and CREB, which possibly affected learning and memory negatively.

Trigonella foenum-graceum seed (Fenugreek) hydroalcoholic extract improved the oxidative stress status in a rat model of diabetes-induced memory impairment

Background

The antidiabetic and antioxidant effects of Trigonella foenum-graceum have been suggested. The effects of hydroalcoholic extract of the plant seeds and metformin against the diabetes-induced memory impairment were investigated.

Materials and methods

The rats were treated: (1) control, (2) diabetic (3–6) and diabetic rats treated by 50, 100 and 200 mg/kg of the plant extract or metformin. The rats were diabetic by streptozotocin (STZ, 55 mg/kg). After the passive avoidance test, malondialdehyde (MDA), nitric oxide (NO) metabolites, total thiol (SH), catalase (CAT) and superoxide dismutase (SOD) were determined in the brain.

Results

In the diabetic group, at 3, 24 and 48 h after receiving a shock, the latency to enter the dark room was lower than for the controls (p < 0.001). All doses of the extract and metformin increased the latencies to enter the dark at 3 and 24 h after the shock treatment (p < 0.05–p < 0.001). Additionally, the two higher doses of the extract and metformin increased the latency at 48 h after the shock (p < 0.05–p < 0.001). Diabetes also elevated MDA and NO metabolites, while it reduced thiol, SOD and CAT in the hippocampal and cortical tissues (p < 0.001). Treatment of the diabetic animals by the highest dose of the extract and also metformin reduced the MDA and NO metabolites, while it improved thiols, SOD and CAT (p < 0.01–p < 0.001).

Conclusions

Based on our findings, metformin and the hydro-alcoholic extract from the T. foenum-graceum seed prevented memory deficits resulting from diabetes. Preventing oxidative damage in the brain may at least, in part, be responsible for the positive effects of the extract and metformin.

The role of APOE4 in Alzheimer's disease: strategies for future therapeutic interventions

Alzheimer’s disease (AD) is the leading cause of dementia affecting almost 50 million people worldwide. The ε4 allele of Apolipoprotein E (APOE) is the strongest known genetic risk factor for late-onset AD cases, with homozygous APOE4 carriers being approximately 15-times more likely to develop the disease. With 25% of the population being APOE4 carriers, understanding the role of this allele in AD pathogenesis and pathophysiology is crucial. Though the exact mechanism by which ε4 allele increases the risk for AD is unknown, the processes mediated by APOE, including cholesterol transport, synapse formation, modulation of neurite outgrowth, synaptic plasticity, destabilization of microtubules, and β-amyloid clearance, suggest potential therapeutic targets. This review will summarize the impact of APOE on neurons and neuronal signaling, the interactions between APOE and AD pathology, and the association with memory decline. We will then describe current treatments targeting APOE4, complications associated with the current therapies, and suggestions for future areas of research and treatment.

Involvement of IL-6 and GSK3β in impaired sensorimotor gating induced by high-fat diet

Increased levels of proinflammatory cytokines have been implicated in schizophrenia; however, their pathophysiological roles in abnormal brain dysfunctions remain unclear. We evaluated the effect of proinflammatory cytokines on a high-fat diet (HFD)-induced prepulse inhibition (PPI) deficits in the acoustic startle response. Eight-week-old male C57BL/6J mice were fed a HFD for 3 weeks and then PPI was examined. HFD significantly induced PPI deficits and increased plasma IL-6, but not TNFα, levels. Interestingly, MR16-1 administration during the HFD period ameliorated PPI deficits. Further, in the striatum of HFD-fed mice, phosphorylation of GSK3β, but not GSK3α, was significantly increased; this increase was attenuated by MR16-1, although the protein levels of GSK3α and β were not altered. There were no significant differences in either phosphorylation or protein levels of GSK3α, β in the PFC during the HFD period. These results suggest that increased IL-6 levels during HFD may induce sensorimotor gating deficits, likely through the alteration of striatal GSK3β phosphorylation. MR16-1 might have a beneficial effect on such HFD-induced sensorimotor gating deficits.

Effect of quercetin-conjugated superparamagnetic iron oxide nanoparticles on diabetes-induced learning and memory impairment in rats

Background

Diabetes mellitus plays a causative role in cognitive decline. Newly, neuroprotective effects of flavonoids have been widely investigated in neurodegenerative diseases. Quercetin (QC) is a phyto-derived bioactive flavone with numerous beneficial activities. However, its limited permeability to cross the blood–brain barrier, low oral bioavailability, poor aqueous solubility, and rapid gastrointestinal digestion lead to the administration of high dose of QC in clinical application.

Materials and methods

In order to overcome these limitations, we conjugated QC with superparamagnetic iron oxide nanoparticles (QCSPIONs) and supplemented streptozotocin-induced diabetic rats with it to improve diabetes-related memory impairment. In this regard, 40 rats were distributed into five groups with eight animals: control, diabetes, and diabetes treated with SPIONs, QC, and QCSPIONs. All treatments (at the dose of 25 mg/kg) were dissolved in deionized water and gavaged for 35 consecutive days.

Results

At the end of the study, QCSPIONs possessed significantly better efficacy than free QC on the improvement of memory performance. In the Morris water maze test, QCSPIONs compared to free QC reduced much better the escape latency over training trials (P<0.01) and increased the time spent in the target quadrant in probe trial (P<0.001). In the passive avoidance test, it increased step-through latency (P<0.05) and reduced the time spent in the dark compartment (P<0.01). In addition, both free QC and QCSPIONs were able to prevent the changes in body weight and decrease blood glucose levels in diabetic rats (P<0.05).

Conclusion

Overall, according to these results, we conclude that QC in the conjugated state with lower dose offers significantly higher potency in ameliorating diabetes-related memory impairment. Thus, this study offers an effective combined therapy for improving learning and memory.

Neuroactive Steroids and Sex-Dimorphic Nervous Damage Induced by Diabetes Mellitus

Diabetes mellitus is a metabolic disease where improper glycaemic control may induce severe complications in different organs. In this review, we will discuss alterations occurring in peripheral and central nervous system of patients with type 1 (i.e., insulin dependent diabetes mellitus,) or type 2 diabetes (i.e., non-insulin dependent diabetes mellitus), as well as related experimental models. A particular focus will be on the role exerted by neuroactive steroids (i.e., important regulators of nervous functions) in the nervous damage induced by diabetes. Indeed, the nervous levels of these molecules are affected by the pathology and, in agreement, their neuroprotective effects have been reported. Interestingly, the sex is another important variable. As discussed, nervous diabetic complications show sex dimorphic features in term of incidence, functional outcomes and neuroactive steroid levels. Therefore, these features represent an interesting background for possible sex-oriented therapies with neuroactive steroids aimed to counteract nervous damage observed in diabetic pathology.

Hyperglycemia Alters Astrocyte Metabolism and Inhibits Astrocyte Proliferation

Diabetes milieu is a complex metabolic disease that has been known to associate with high risk of various neurological disorders. Hyperglycemia in diabetes could dramatically increase neuronal glucose levels which leads to neuronal damage, a phenomenon referred to as glucose neurotoxicity. On the other hand, the impact of hyperglycemia on astrocytes has been less explored. Astrocytes play important roles in brain energy metabolism through neuron-astrocyte coupling. As the component of blood brain barrier, glucose might be primarily transported into astrocytes, hence, impose direct impact on astrocyte metabolism and function. In the present study, we determined the effect of high glucose on the energy metabolism and function of primary astrocytes. Hyperglycemia level glucose (25 mM) induced cell cycle arrest and inhibited proliferation and migration of primary astrocytes. Consistently, high glucose decreased cyclin D1 and D3 expression. High glucose enhanced glycolytic metabolism, increased ATP and glycogen content in primary astrocytes. In addition, high glucose activated AMP-activated protein kinase (AMPK) signaling pathway in astrocytes. In summary, our in vitro study indicated that hyperglycemia might impact astrocyte energy metabolism and function phenotype. Our study provides a potential mechanism which may underlie the diabetic cerebral neuropathy and warrant further in vivo study to determine the effect of hyperglycemia on astrocyte metabolism and function.

Effect of insulin-coated trimethyl chitosan nanoparticles on IGF-1, IGF-2, and apoptosis in the hippocampus of diabetic male rats

BACKGROUND

Subcutaneous injection of insulin can lead to problems such as hypoglycemia and edema.

OBJECTIVE

The purpose of this research was to evaluate the effect of oral insulin-coated trimethyl chitosan nanoparticles on control of glycemic status, IGF-1 and IGF-2 levels, and apoptosis in the hippocampus of rats with diabetes mellitus.

METHODS

Insulin-coated trimethyl chitosan nanoparticles were prepared by the polyelectrolyte complex method (PEC) method. Insulin loading content, loading efficiency, quantity and quality of particle size were evaluated. In vivo study was performed in different treatment groups of male Wistar rats with diabetes mellitus by insulin-coated trimethyl chitosan nanoparticles or subcutaneous injection of trade insulin. The duration of diabetes was eight weeks and the treatment was started after that time and continued for another two weeks. Body weight, fasting blood glucose (FBS), hippocampal apoptosis, and immunohistochemical (IHC) protein levels of IGF-1 and IGF-2 were assessed at the end of the experiments.

RESULTS

The size and polydispersity indexes were 533 nanometers and 0.533, respectively. Insulin coated trimethyl chitosan nanoparticles showed high loading efficiency (97.67% ) and loading content (48.83% ). The spherical shape of nanoparticle was confirmed by transmission electron microscopic (TEM). The amine, amide, ether and aliphatic groups were evaluated using FT-IR spectrophotometer which represented the correctness of the insulin coated trimethyl chitosan nanoparticles. Although the apoptotic index was not changed either by insulin-coated nano-particles or commercial insulin, in vivo results showed the efficacy of insulin-coated nanoparticles as well as commercial insulin in compensated weight loss, FBS and protein levels of IGF-1 and IGF-2.

CONCLUSIONS

The present study showed the efficacy of insulin coated nanoparticle in oral route manner that can be tested in Phase I- III clinical trials. However, a behavioral study could reveal the efficacy of insulin-loaded nanoparticles in the improvement of cognitive changes through the modulation of IGF-1 and IGF-2 levels in the hippocampus.

An inhibitor of soluble epoxide hydrolase ameliorates diabetes-induced learning and memory impairment in rats

BACKGROUND

Pharmacological inhibition of soluble epoxide hydrolase (sEH) enhances the synaptic function in the CNS and has a protective role in cognitive decline. We hypothesized that the sEH inhibitor TPPU might prevent the diabetes-induced decline in learning and memory which is associated with an alteration in the level of neurotransmitters and oxidative stress.

METHODS

Type 1 diabetes was induced in rats and the animals were treated with TPPU for 8 weeks. The learning and memory functions were assessed by the Barnes maze and a step-down test. Indicators of oxidative stress, levels of neurotransmitters, and activity of acetylcholinesterase were measured in the discrete regions of the brain.

RESULTS

Our results revealed that treatment with TPPU significantly improves learning and memory performance in diabetic rats along with decreasing the level of blood sugar. Moreover, treatment with TPPU significantly prevented the diabetes-induced alteration in levels of neurotransmitters, the activity of acetylcholinesterase and preserved anti-oxidant defence system.

CONCLUSION

Inhibition of the sEH alleviates diabetes-induced decline in learning and memory.

Mitochondrial Chaperones in the Brain: Safeguarding Brain Health and Metabolism?

The brain orchestrates organ function and regulates whole body metabolism by the concerted action of neurons and glia cells in the central nervous system. To do so, the brain has tremendously high energy consumption and relies mainly on glucose utilization and mitochondrial function in order to exert its function. As a consequence of high rate metabolism, mitochondria in the brain accumulate errors over time, such as mitochondrial DNA (mtDNA) mutations, reactive oxygen species, and misfolded and aggregated proteins. Thus, mitochondria need to employ specific mechanisms to avoid or ameliorate the rise of damaged proteins that contribute to aberrant mitochondrial function and oxidative stress. To maintain mitochondria homeostasis (mitostasis), cells evolved molecular chaperones that shuttle, refold, or in coordination with proteolytic systems, help to maintain a low steady-state level of misfolded/aggregated proteins. Their importance is exemplified by the occurrence of various brain diseases which exhibit reduced action of chaperones. Chaperone loss (expression and/or function) has been observed during aging, metabolic diseases such as type 2 diabetes and in neurodegenerative diseases such as Alzheimer's (AD), Parkinson's (PD) or even Huntington's (HD) diseases, where the accumulation of damage proteins is evidenced. Within this perspective, we propose that proper brain function is maintained by the joint action of mitochondrial chaperones to ensure and maintain mitostasis contributing to brain health, and that upon failure, alter brain function which can cause metabolic diseases.