Neuronal and astroglial alterations in the hippocampus of a mouse model for type 1 diabetes

Isoform-specific distribution of 14-3-3 proteins in the hippocampus of streptozotocin-induced diabetic rats

Diabetes mellitus is associated with cognitive deficits in humans and animal models. These deficits are paralleled by neurophysiological and structural changes in the central nervous system, particularly in the hippocampus, which plays an important role in memory formation. We previously reported that the magnitude of long-term potentiation at hippocampal Schaffer collateral-CA1 synapses was significantly impaired in streptozotocin (STZ)-induced type 1 diabetic rats (STZ rats). The present study investigated the mechanisms underlying morphological changes in the hippocampus of STZ rats. We performed a proteomic analysis of the hippocampus of STZ rats using two-dimensional gel electrophoresis followed by mass spectrometry. The distribution of 14-3-3 proteins identified by the proteomic analysis was then examined using immunohistochemistry. The results obtained revealed that 14-3-3 η immunoreactivity in the dorsal hippocampus was weaker in STZ rats than in age-matched control rats. Moreover, the density of glial fibrillary acidic protein-immunoreactive astrocytes in the dorsal hippocampus of STZ rats was increased, whereas 14-3-3 η immunoreactivity in astrocytes and neurons in the dentate gyrus was significantly decreased. These results suggest that changes in 14-3-3 η expression are involved in hippocampal astrogliosis or/and neurogenesis in STZ rats.

Glucocorticoid feedback paradox: a homage to Mary Dallman

As the end product of the hypothalamus-pituitary-adrenal (HPA) axis, the glucocorticoid hormones cortisol and corticosterone coordinate circadian activities, stress-coping, and adaptation to change. For this purpose, the hormone promotes energy metabolism and controls defense reactions in the body and brain. This life-sustaining action exerted by glucocorticoids occurs in concert with the autonomic nervous and immune systems, transmitters, growth factors/cytokines, and neuropeptides. The current contribution will focus on the glucocorticoid feedback paradox in the HPA-axis: the phenomenon that stress responsivity remains resilient if preceded by stress-induced secretion of glucocorticoid hormone, but not if this hormone is previously administered. Furthermore, in animal studies, the mixed progesterone/glucocorticoid antagonist RU486 or mifepristone switches to an apparent partial agonist upon repeated administration. To address these enigmas several interesting phenomena are highlighted. These include the conditional nature of the excitation/inhibition balance in feedback regulation, the role of glucose as a determinant of stress responsivity, and the potential of glucocorticoids in resetting the stress response system. The analysis of the feedback paradox provides also a golden opportunity to review the progress in understanding the role of glucocorticoid hormone in resilience and vulnerability during stress, the science that was burned deeply in Mary Dallman's emotions.

Function and therapeutic value of astrocytes in diabetic cognitive impairment

Diabetic cognitive impairment (DCI) is a complex complication of diabetes in the central nervous system, and its pathological mechanism is still being explored. Astrocytes are abundant glial cells in central nervous system that perform diverse functions in health and disease. Accumulating excellent research has identified astrocyte dysfunction in many neurodegenerative diseases (such as Alzheimer's disease, aging and Parkinson's disease), and summarized and discussed its pathological mechanisms and potential therapeutic value. However, the contribution of astrocytes to DCI has been largely overlooked. In this review, we first systematically summarized the effects and mechanisms of diabetes on brain astrocytes, and found that the diabetic environment (such as hyperglycemia, advanced glycation end products and cerebral insulin resistance) mediated brain reactive astrogliosis, which was specifically reflected in the changes of cell morphology and the remodeling of signature molecules. Secondly, we emphasized the contribution and potential targets of reactive astrogliosis to DCI, and found that reactive astrogliosis-induced increased blood-brain barrier permeability, glymphatic system dysfunction, neuroinflammation, abnormal cell communication and cholesterol metabolism dysregulation worsened cognitive function. In addition, we summarized effective strategies for treating DCI by targeting astrocytes. Finally, we discuss the application of new techniques in astrocytes, including single-cell transcriptome, in situ sequencing, and prospected new functions, new subsets and new targets of astrocytes in DCI.

Effects of liraglutide on astrocyte polarization and neuroinflammation in db/db mice: focus on iron overload and oxidative stress

Neuroinflammation plays a crucial role in the occurrence and development of cognitive impairment in type 2 diabetes mellitus (T2DM), but the specific injury mechanism is not fully understood. Astrocyte polarization has attracted new attention and has been shown to be directly and indirectly involved in neuroinflammation. Liraglutide has been shown to have beneficial effects on neurons and astrocytes. However, the specific protection mechanism still needs to be clarified. In this study, we assessed the levels of neuroinflammation and A1/A2-responsive astrocytes in the hippocampus of db/db mice and examined their relationships with iron overload and oxidative stress. First, in db/db mice, liraglutide alleviated the disturbance of glucose and lipid metabolism, increased the postsynaptic density, regulated the expression of NeuN and BDNF, and partially restored impaired cognitive function. Second, liraglutide upregulated the expression of S100A10 and downregulated the expression of GFAP and C3, and decreased the secretion of IL-1β, IL-18, and TNF-α, which may confirm that it regulates the proliferation of reactive astrocytes and A1/A2 phenotypes polarize and attenuate neuroinflammation. In addition, liraglutide reduced iron deposition in the hippocampus by reducing the expression of TfR1 and DMT1 and increasing the expression of FPN1; at the same time, liraglutide by up-regulating the levels of SOD, GSH, and SOD2 expression, as well as downregulation of MDA levels and NOX2 and NOX4 expression to reduce oxidative stress and lipid peroxidation. The above may attenuate A1 astrocyte activation. This study preliminarily explored the effect of liraglutide on the activation of different astrocyte phenotypes and neuroinflammation in the hippocampus of a T2DM model and further revealed its intervention effect on cognitive impairment in diabetes. Focusing on the pathological consequences of astrocytes may have important implications for the treatment of diabetic cognitive impairment.

Arrangement of the photoreceptor mosaic in a diabetic rat model imaged with multiphoton microscopy

Diabetic retinopathy (DR) is defined as a microvascular pathology. However, some data have suggested that the retinal photoreceptors (PRs) might be important in the pathogenesis of this ocular disease. In this study the organization of the PRs in control and diabetic-induced rats was compared using multiphoton microscopy. The PR mosaic was imaged at different locations in non-stained retinas. The density of PRs was directly quantified from cell counting. The spatially resolved density presents a double-slope pattern (from the central retina towards the periphery) in both healthy and pathological samples, although the values for the latter were significantly lower all across the retina. Moreover, Voronoi analysis was performed to explore changes in PR topography. In control specimens a hexagonally packed structure was dominant. However, despite the non-controlled effects of the disease in retinal structures, this PR regularity was fairly maintained in diabetic retinas.

Activation of mineralocorticoid receptors facilitate the acquisition of fear memory extinction and impair the generalization of fear memory in diabetic animals

RATIONALE

Studies point out a higher prevalence of posttraumatic stress disorder (PTSD) in individuals with diabetes mellitus. It is known that glucocorticoid (GR) and mineralocorticoid (MR) receptors are implicated in fear memory processes and PTSD. However, there is no preclinical studies addressing the involvement of these receptors on abnormal fear memories related to diabetic condition.

OBJECTIVES

By inducing a contextual conditioned fear memory, we generate a suitable condition to investigate the extinction and the generalization of the fear memory in streptozotocin-induced diabetic (DBT) rats alongside the expression of the cytosolic and nuclear GR and MR in the hippocampus (HIP) and prefrontal cortex (PFC). Moreover, we investigated the involvement of the MR or GR on the acquisition of fear memory extinction and on the generalization of this fear memory. When appropriate, anxiety-related behavior was evaluated.

METHODS

Male Wistar rats received one injection of steptozotocin (i.p.) to induce diabetes. After 4 weeks, the animals (DBTs and non-DBTs) were subjected to a conditioned contextual fear protocol.

RESULTS

The expression of MR and GR in the HIP and PFC was similar among all the groups. The single injection of MR agonist was able to facilitate the acquisition of the impaired fear memory extinction in DBTs animals together with the impairment of its generalization. However, the GR antagonism impaired only the generalization of this fear memory which was blocked by the previous injection of the MR antagonist. All treatments were able to exert anxiolytic-like effects.

CONCLUSIONS

The results indicate that MR activation in DBT animals disrupts the overconsolidation of aversive memory, without discarding the involvement of emotional behavior in these processes.

An enriched environment prevents diabetes-induced cognitive impairment in rats by enhancing exosomal miR-146a secretion from endogenous bone marrow-derived mesenchymal stem cells

Increasing evidence suggests that an enriched environment (EE) ameliorates cognitive impairment by promoting repair of brain damage. However, the mechanisms by which this occurs have not been determined. To address this issue, we investigated whether an EE enhanced the capability of endogenous bone marrow-derived mesenchymal stem/stromal cells (BM-MSCs) to prevent hippocampal damage due to diabetes by focusing on miRNA carried in BM-MSC-derived exosomes. In diabetic streptozotocin (STZ) rats housed in an EE (STZ/EE), cognitive impairment was significantly reduced, and both neuronal and astroglial damage in the hippocampus was alleviated compared with STZ rats housed in conventional cages (STZ/CC). BM-MSCs isolated from STZ/CC rats had functional and morphological abnormalities that were not detected in STZ/EE BM-MSCs. The miR-146a levels in exosomes in conditioned medium of cultured BM-MSCs and serum from STZ/CC rats were decreased compared with non-diabetic rats, and the level was restored in STZ/EE rats. Thus, the data suggest that increased levels of miR-146a in sera were derived from endogenous BM-MSCs in STZ/EE rats. To examine the possibility that increased miR-146a in serum may exert anti-inflammatory effects on astrocytes in diabetic rats, astrocytes transfected with miR-146a were stimulated with advanced glycation end products (AGEs) to mimic diabetic conditions. The expression of IRAK1, NF-κB, and tumor necrosis factor-α was significantly higher in AGE-stimulated astrocytes, and these factors were decreased in miR-146a-transfected astrocytes. These results suggested that EEs stimulate up-regulation of exosomal miR-146a secretion by endogenous BM-MSCs, which exerts anti-inflammatory effects on damaged astrocytes and prevents diabetes-induced cognitive impairment.

Diabetes induces mitochondrial dysfunction and alters cholesterol homeostasis and neurosteroidogenesis in the rat cerebral cortex

The nervous system synthesizes and metabolizes steroids (i.e., neurosteroidogenesis). Recent observations indicate that neurosteroidogenesis is affected by different nervous pathologies. Among these, long-term type 1 diabetes, together with other functional and biochemical changes, has been shown to alter neuroactive steroid levels in the nervous system. Using an experimental model of type 1 diabetes (i.e., streptozotocin injection) we here show that the levels of these molecules are already decreased in the rat cerebral cortex after one month of the initiation of the pathology. Moreover, decreased levels of free cholesterol, together with alterations in the expression of molecules involved in cholesterol biosynthesis, bioavailability, trafficking and metabolism were detected in the rat cerebral cortex after one month of diabetes. Furthermore, mitochondrial functionality was also affected in the cerebral cortex and consequently may also contribute to the decrease in neuroactive steroid levels. Altogether, these results indicate that neurosteroidogenesis is an early target for the effect of type 1 diabetes in the cerebral cortex.

Cerebrovascular complications of diabetes: focus on cognitive dysfunction

The incidence of diabetes has more than doubled in the United States in the last 30 years and the global disease rate is projected to double by 2030. Cognitive impairment has been associated with diabetes, worsening quality of life in patients. The structural and functional interaction of neurons with the surrounding vasculature is critical for proper function of the central nervous system including domains involved in learning and memory. Thus, in this review we explore cognitive impairment in patients and experimental models, focusing on links to vascular dysfunction and structural changes. Lastly, we propose a role for the innate immunity-mediated inflammation in neurovascular changes in diabetes.

Blockade of store-operated calcium entry alleviates high glucose-induced neurotoxicity via inhibiting apoptosis in rat neurons

Altered store-operated calcium entry (SOCE) has been suggested to be involved in many diabetic complications. However, the association of altered SOCE and diabetic neuronal damage remains unclear. This study aimed to investigate the effects of altered SOCE on primary cultured rat neuron injury induced by high glucose. Our data demonstrated that high glucose increased rat neuron injury and upregulated the expression of store-operated calcium channel (SOC). Inhibition of SOCE by a pharmacological inhibitor and siRNA knockdown of stromal interaction molecule 1 weakened the intracellular calcium overload, restored mitochondrial membrane potential, downregulated cytochrome C release and inhibited cell apoptosis. As well, treatment with the calcium chelator BAPTA-AM prevented cell apoptosis by ameliorating the high glucose-increased intracellular calcium level. These findings suggest that SOCE blockade may alleviate high glucose-induced neuronal damage by inhibiting apoptosis. SOCE might be a promising therapeutic target in diabetic neurotoxicity.

Effects of metformin on inflammation and short-term memory in streptozotocin-induced diabetic mice

The aim of the present study was to analyze the action of metformin on short-term memory, glial cell activation and neuroinflammation caused by experimental diabetic encephalopathy in C57BL/6 mice. Diabetes was induced by the intraperitoneal injection of a dose of 90mg/kg of streptozotocin on two successive days. Mice with blood glucose levels ≥200dl/ml were considered diabetic and were given metformin hydrochloride at doses of 100mg/kg and 200mg/kg (by gavage, twice daily) for 21 days. On the final day of treatment, the mice underwent a T-maze test. On the 22nd day of treatment all the animals were anesthetized and euthanized. Diabetic animals treated with metformin had a higher spatial memory score. The hippocampus of the diabetic animals presented reactive gliosis, neuronal loss, NF-kB signaling activation, and high levels of IL-1 and VEGF. In addition, the T-maze test scores of these animals were low. Treatment with metformin reduced the expression of GFAP, Iba-1 (astrocyte and microglial markers) and the inflammation markers (p-IKB, IL-1 and VEGF), while enhancing p-AMPK and eNOS levels and increasing neuronal survival (Fox-1 and NeuN). Treatment with metformin also improved the spatial memory scores of diabetic animals. In conclusion, the present study showed that metformin can significantly reduce neuroinflammation and can decrease the loss of neurons in the hippocampus of diabetic animals, which can subsequently promote improvements in spatial memory.

Bone marrow-derived mesenchymal stem cells improve diabetes-induced cognitive impairment by exosome transfer into damaged neurons and astrocytes

The incidence of dementia is higher in diabetic patients, but no effective treatment has been developed. This study showed that rat bone marrow mesenchymal stem cells (BM-MSCs) can improve the cognitive impairments of STZ-diabetic mice by repairing damaged neurons and astrocytes. The Morris water maze test demonstrated that cognitive impairments induced by diabetes were significantly improved by intravenous injection of BM-MSCs. In the CA1 region of the hippocampus, degeneration of neurons and astrocytes, as well as synaptic loss, were prominent in diabetes, and BM-MSC treatment successfully normalized them. Since a limited number of donor BM-MSCs was observed in the brain parenchyma, we hypothesized that humoral factors, especially exosomes released from BM-MSCs, act on damaged neurons and astrocytes. To investigate the effectiveness of exosomes for treatment of diabetes-induced cognitive impairment, exosomes were purified from the culture media and injected intracerebroventricularly into diabetic mice. Recovery of cognitive impairment and histological abnormalities similar to that seen with BM-MSC injection was found following exosome treatment. Use of fluorescence-labeled exosomes demonstrated that injected exosomes were internalized into astrocytes and neurons; these subsequently reversed the dysfunction. The present results indicate that exosomes derived from BM-MSCs might be a promising therapeutic tool for diabetes-induced cognitive impairment.

Peripheral Levels of AGEs and Astrocyte Alterations in the Hippocampus of STZ-Diabetic Rats

Diabetic patients and streptozotocin (STZ)-induced diabetes mellitus (DM) models exhibit signals of brain dysfunction, evidenced by neuronal damage and memory impairment. Astrocytes surrounding capillaries and synapses modulate many brain activities that are connected to neuronal function, such as nutrient flux and glutamatergic neurotransmission. As such, cognitive changes observed in diabetic patients and experimental models could be related to astroglial alterations. Herein, we investigate specific astrocyte changes in the rat hippocampus in a model of DM induced by STZ, particularly looking at glial fibrillary acidic protein (GFAP), S100B protein and glutamate uptake, as well as the content of advanced glycated end products (AGEs) in serum and cerebrospinal fluid (CSF), as a consequence of elevated hyperglycemia and the content of receptor for AGEs in the hippocampus. We found clear peripheral alterations, including hyperglycemia, low levels of proinsulin C-peptide, elevated levels of AGEs in serum and CSF, as well as an increase in RAGE in hippocampal tissue. We found specific astroglial abnormalities in this brain region, such as reduced S100B content, reduced glutamate uptake and increased S100B secretion, which were not accompanied by changes in GFAP. We also observed an increase in the glucose transporter, GLUT-1. All these changes may result from RAGE-induced inflammation; these astroglial alterations together with the reduced content of GluN1, a subunit of the NMDA receptor, in the hippocampus may be associated with the impairment of glutamatergic communication in diabetic rats. These findings contribute to understanding the cognitive deficits in diabetic patients and experimental models.

Influence of type 1 diabetes on basal and agonist-induced permeability of the blood-brain barrier

Type 1 diabetes mellitus (T1D) impairs endothelial nitric oxide synthase (eNOS)‐dependent responses of cerebral arterioles. However, the influence of T1D on another critical aspect of endothelial cell function in the cerebral microcirculation, i.e., regulation of permeability of the blood–brain barrier (BBB), remains largely unknown. Our goal was to examine basal and agonist‐induced changes in permeability of the BBB in nondiabetic and type 1 diabetic (streptozotocin; 50 mg/kg IP) rats. On the day of the experiment (2–3 months after streptozotocin), a craniotomy was made over the parietal cortex in nondiabetic and diabetic rats. We measured the permeability of the BBB (FITC‐dextran‐10K) under basal conditions and during application of histamine. We also measured diameter of cerebral arterioles in response to histamine in the absence and presence of NG‐monomethyl‐L‐arginine (L‐NMMA). We found that basal permeability of the BBB was elevated in T1D and application of histamine did not produce a further increase in permeability. In contrast, basal permeability of the BBB was minimal in nondiabetics and histamine produced an increase in permeability. In addition, histamine‐induced arteriolar dilation was less in diabetics than in nondiabetics, and vasodilation to histamine was inhibited by L‐NMMA. Our findings suggest that T1D‐induced endothelial dysfunction leads to an increase in basal permeability of the BBB, but decreases the ability of the endothelium of the BBB to respond to an important inflammatory mediator. Thus, T1D impairs two critical aspects of endothelial cell function in the cerebral microcirculation, i.e., basal and agonist‐induced changes in permeability of the BBB and arteriolar dilation.

Pharmacotherapy with 17β-estradiol and progesterone prevents development of mouse experimental autoimmune encephalomyelitis

BACKGROUND

Pregnant women with multiple sclerosis (MS) show disease remission in the third trimester concomitant with high circulating levels of sex steroids. Rodent experimental autoimmune encephalomyelitis (EAE) is an accepted model for MS. Previous studies have shown that monotherapy with estrogens or progesterone exert beneficial effects on EAE. The aim of the present study was to determine if estrogen and progesterone cotherapy of C57BL/6 female mice provided substantial protection from EAE.

METHODS

A group of mice received single pellets of progesterone (100 mg) and 17 β-estradiol (2.5 mg) subcutaneously 1 week before EAE induction, whereas another group were untreated before EAE induction. On day 16 we compared the two EAE groups and control mice in terms of clinical scores, spinal cord demyelination, expression of myelin basic protein and proteolipid protein, macrophage cell infiltration, neuronal expression of brain-derived neurotrophic factor mRNA and protein, and the number of glial fribrillary acidic protein (GFAP)-immunopositive astrocytes.

RESULTS

Clinical signs of EAE were substantially attenuated by estrogen and progesterone treatment. Steroid cotherapy prevented spinal cord demyelination, infiltration of inflammatory cells and GFAP+ astrogliocytes to a great extent. In motoneurons, expression of BDNF mRNA and protein was highly stimulated, indicating concomitant beneficial effects of the steroid on neuronal and glial cells.

CONCLUSIONS

Cotherapy with estrogen and progesterone inhibits the development of major neurochemical abnormalities and clinical signs of EAE. We suggest that a combination of neuroprotective, promyelinating and immuno-suppressive mechanisms are involved in these beneficial effects.

Experimental diabetes mellitus type 1 increases hippocampal content of kynurenic acid in rats

BACKGROUND

Diabetes mellitus (DM) is frequently associated with peripheral and central complications and has recently emerged as a risk factor for cognitive impairment and dementia. Kynurenic acid (KYNA), a unique tryptophan derivative, displays pleiotropic effects including blockade of ionotropic glutamate and α7 nicotinic receptors. Here, the influence of experimental diabetes on KYNA synthesis was studied in rat brain.

METHODS

DM was induced by i.p. administration of streptozotocin (STZ). Five weeks later, KYNA content and the activity of semi-purified kynurenine aminotransferases (KATs) were measured in frontal cortex, hippocampus and striatum of diabetic and insulin-treated rats, using HPLC-based methods.

RESULTS

Hippocampal but not cortical or striatal KYNA concentration was considerably increased during DM, either untreated or treated with insulin (220% and 170% of CTR, respectively). The activity of kynurenine aminotransferase I (KAT I) was not affected by DM in all of the studied structures. KAT II activity was moderately increased in cortex (145% of CTR) and hippocampus (126% of CTR), but not in striatum of diabetic animals. Insulin treatment normalized cortical but not hippocampal KAT II activity.

CONCLUSIONS

A novel factor potentially implicated in diabetic hippocampal dysfunction has been identified. Observed increase of KYNA level may stem from the activation of endogenous neuroprotection, however, it may also have negative impact on cognition.

Aminoguanidine changes hippocampal expression of apoptosis-related genes, improves passive avoidance learning and memory in streptozotocin-induced diabetic rats

Cognitive dysfunction occurs in patients with diabetes mellitus. The objective of this study was to examine whether bilateral intrahippocampal CA1 (intra-CA1) injection of aminoguanidine (AG) can either affect the Bcl-2 family gene expression or reduce the diabetic imposing abnormalities of passive avoidance learning (PAL) and memory. Rats were divided into five groups: control (C), control treated with normal saline (CS), control treated with AG (S-AG), diabetics (D), and diabetics treated with AG (D-AG). Diabetes mellitus was induced by a single intraperitoneal injection of streptozotocin (STZ) (50 mg/kg). AG (30 μg/rat) or vehicle was administered intra-CA1 bilaterally at the onset of hyperglycemia. PAL was assessed 7 weeks later. Animals were killed, and hippocampus was dissected following the behavioral test. The expressions of Bax, Bcl-2, and Bcl-xl mRNAs were measured using semiquantitative RT-PCR technique. The result of passive avoidance task showed that AG significantly improved the cognitive performance in diabetic rats. Moreover, AG treatment decreased the levels of Bcl-2 and Bcl-xL expressions in diabetic group. The ratio of Bax/Bcl-2 and Bax/Bcl-xL decreased significantly in AG-treated diabetic animals. In conclusion, initial treatment with AG by intra-CA1 micro-injection improves the impaired passive avoidance task in STZ-induced diabetic rats which may be related to the decreased Bax/Bcl-2 and Bax/Bcl-xL ratios.

Glibenclamide treatment modulates the expression and localization of myosin-IIB in diabetic rat brain

BACKGROUND

Myosin-IIB is a non-muscle isoform in the brain with increased expression in the brains of diabetic rats. Chronic hyperglycemia caused by diabetes can impair learning and memory. Oral hypoglycemic agents such as glibenclamide have been used to control hyperglycemia. We report changes in the expression and distribution of myosin-IIB in the frontal cortex and hippocampus of diabetic rats treated with glibenclamide.

METHODS

The brains were removed after 43 days of treatment with glibenclamide (6 mg/kg bw orally), homogenized and analyzed by Western blotting, qRT-PCR and immunohistochemistry.

RESULTS

Myosin-IIB expression increased in the brains of diabetic rats. However, protein expression returned to control levels when treated with glibenclamide. In addition, the expression of MYH10 gene encoding non-muscle myosin heavy chain-B decreased in diabetic rats treated with glibenclamide. Moreover, we found weak myosin-IIB labeling in the hippocampus and frontal cortex of rats treated with glibenclamide. Therefore, the expression of myosin-IIB is affected by diabetes mellitus and may be modulated by glibenclamide treatment in rats. Structural changes in the hippocampus and prefrontal cortex are reversible, and glibenclamide treatment may reduce the patho-physiological changes in the brain.

CONCLUSIONS

Our findings can contribute to the understanding of the regulation of myosins in the brains of diabetic rats.

Ginsenoside Rb1 protects hippocampal neurons from high glucose-induced neurotoxicity by inhibiting GSK3β-mediated CHOP induction

Ginsenoside Rb1 is generally recognized as one of the principal bioactive ingredients in ginseng and shows neuroprotective effects in various neurons. Endoplasmic reticulum (ER) stress is considered to play an important role in numerous neurodegenerative disorders. Recently, glucogen synthase kinase 3β (GSK3β) was reported to regulate ER stress-induced C/EBP homologous protein (CHOP) in neuronal cells. Therefore, in this study, we investigated the effects of ginsenoside Rb1 on GSK3β-mediated ER stress in high glucose-treated hippocampal neurons. Results from the MTT assay showed that treatment with 1 µM Rb1 for 72 h protected neurons from high glucose-induced cell injury. Using western blot analysis, we found that treatment with Rb1 effectively inhibited the phosphorylation of the high glucose-induced protein kinase RNA-like ER kinase (PERK) and of GSK3β, and reduced the level of the CHOP protein. The levels of these proteins were also decreased by treatment with the GSK3β inhibitor Licl. Rb1 also significantly decreased the mRNA expression of the gene CHOP, as shown by quantitative RT-PCR analysis. Taken together, the present results suggested that Rb1 may protect neurons from high glucose-induced cell damage by inhibiting GSK3β‑mediated CHOP induction, providing a potentially new strategy for preventing and treating cognitive impairment caused by diabetes.

Altered expression of histone and synaptic plasticity associated genes in the hippocampus of streptozotocin-induced diabetic mice

Accumulating evidence indicates that hyper-glycaemia is deleterious to brain function, in particular to the hippocampus. It is thought this hippocampal dysfunction may contribute to hyperglycaemia related cognitive impairment, such as that which manifests with diabetes. In the present study, we investigated the effects of diabetes-related hyperglycaemia on hippocampal gene expression, in order to identify potential mechanisms that might be associated with the cognitive dysfunction that develops with diabetes mellitus. Genome-wide gene expression profiling was carried out on the hippocampi from streptozotocin (STZ)-induced diabetic mice, and from vehicle treated control mice. Genes of interest that satisfied expression fold-change and statistical criteria, and that were considered to be potentially associated with cognitive function, were further tested by real time, quantitative polymerase chain reaction (qPCR) analysis. We found that STZ-induced diabetes resulted in decreased hippocampal expression of genes involved in epigenetic regulation and synaptic plasticity, for example, histone deacetylases and glycogen synthase kinase 3 beta (HDACs and GSK3β). We also found increased expression of genes involved in signalling cascades related to cell growth, cell survival and energy metabolism, such as neurotropic tyrosine kinase receptor type 2, apolipoprotein E, and protein tyrosine phosphatase receptor type (Ntrk2, APOE, PTPRT). To our knowledge this is the first study to demonstrate a gene expression profile implicating epigenetic modifications and alterations of synaptic plasticity associated genes in diabetes mellitus. The present study will improve our understanding of the neural mechanisms that might underpin diabetes-related cognitive dysfunction.

Dietary resveratrol supplementation normalizes gene expression in the hippocampus of streptozotocin-induced diabetic C57Bl/6 mice

Diabetes is associated with cognitive impairment and brain aging, with alterations in hippocampal neurogenesis and synaptic plasticity implicated in these changes. As the prevalence of diabetes continues to rise, readily implemented strategies are increasingly needed in order to protect the brain's cognitive functions. One possibility is resveratrol (RES) (3,5,4- trihydroxystilbene), a polyphenol of the phytoalexin family that has been shown to be protective in a number of neuropathology paradigms. In the present study, we sought to determine whether dietary supplementation with RES has potential for the protection of cognitive functions in diabetes. Diabetes was induced using streptozotocin, and once stable, animals received AIN93G rodent diet supplemented with RES for 6 weeks. Genome-wide expression analysis was conducted on the hippocampus and genes of interest were confirmed by quantitative, real-time polymerase chain reaction. Genome-wide gene expression analysis of the hippocampus revealed that RES supplementation of the diabetic group resulted in 481 differentially expressed genes compared to non-supplemented diabetic mice. Intriguingly, gene expression that was previously found significantly altered in the hippocampus of diabetic mice, and that is implicated in neurogenesis and synaptic plasticity (Hdac4, Hat1, Wnt7a, ApoE), was normalized following RES supplementation. In addition, pathway analysis revealed Jak-Stat signaling was the most significantly enriched pathway. The Jak-Stat pathway induces a pro-inflammatory signaling cascade, and we found most genes involved in this cascade (e.g. Il15, Il22, Socs2, Socs5) had significantly lower expression following RES supplementation. These data indicate RES could be neuroprotective and beneficial for the maintenance of cognitive function in diabetes.

Neuroprotective effects of ginsenoside Rb1 on high glucose-induced neurotoxicity in primary cultured rat hippocampal neurons

Ginsenoside Rb1 is one of the main active principles in traditional herb ginseng and has been reported to have a wide variety of neuroprotective effects. Endoplasmic reticulum (ER) stress has been implicated in neurodegenerative diseases, so the present study aimed to observe the effects of ginsenoside Rb1 on ER stress signaling pathways in high glucose-treated hippocampal neurons. The results from MTT, TUNEL labeling and Annexin V-FITC/PI/Hoechst assays showed that incubating neurons with 50 mM high glucose for 72h decreased cell viability and increased the number of apoptotic cells whereas treating neurons with 1 μM Rb1 for 72h protected the neurons against high glucose-induced cell damage. Further molecular mechanism study demonstrated that Rb1 suppressed the activation of ER stress-associated proteins including protein kinase RNA (PKR)-like ER kinase (PERK) and C/EBP homology protein (CHOP) and downregulation of Bcl-2 induced by high glucose. Moreover, Rb1 inhibited both the elevation of intracellular reactive oxygen species (ROS) and the disruption of mitochondrial membrane potential induced by high glucose. In addition, the high glucose-induced cell apoptosis, activation of ER stress, ROS accumulation and mitochondrial dysfunction can also be attenuated by the inhibitor of ER stress 4-phenylbutyric acid (4-PBA) and anti-oxidant N-acetylcysteine(NAC). In conclusion, these results suggest that Rb1 may protect neurons against high glucose-induced cell injury through inhibiting CHOP signaling pathway as well as oxidative stress and mitochondrial dysfunction.

Molecular basis of hippocampal energy metabolism in diabetic rats: the effects of SOD mimic

Hippocampal structural changes associated with diabetes-related cognitive impairments are well described, but their molecular background remained vague. We examined whether/how diabetes alters molecular basis of energy metabolism in hippocampus readily after diabetes onset, with special emphasis on its redox-sensitivity. To induce diabetes, adult Mill Hill hybrid hooded rats received a single alloxan dose (120 mg/kg). Both non-diabetic and diabetic groups were further divided in two subgroups receiving (i) or not (ii) superoxide dismutase (SOD) mimic, [Mn(II)(pyane)Cl2] for 7 days, i.p. Treatment of the diabetic animals started after blood glucose level ≥12 mM. Diabetes decreased protein levels of oxidative phosphorylation components: complex III and ATP synthase. In contrast, protein amounts of glyceraldehyde-3-phosphate dehydrogenase, pyruvate dehydrogenase, and hypoxia-inducible factor-1α - the key regulator of energy metabolism in stress conditions, were higher in diabetic animals. Treatment with SOD mimic restored/increased the levels of oxidative phosphorylation components and returned hypoxia-inducible factor-1α to control level, while diabetes-induced up-regulation of glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase, was additionally stimulated. To conclude, our results provide insight into the earliest molecular changes of energy-producing pathways in diabetes that may account for structural/functional disturbance of hippocampus, seen during disease progression. Also, data suggest [Mn(II)(pyane)Cl2] as potential therapeutic agent in cutting-edge approaches to threat this widespread metabolic disorder.

Functional profile of the binary brain corticosteroid receptor system: mediating, multitasking, coordinating, integrating

This contribution is focused on the action of the naturally occurring corticosteroids, cortisol and corticosterone, which are secreted from the adrenals in hourly pulses and after stress with the goal to maintain resilience and health. To achieve this goal the action of the corticosteroids displays an impressive diversity, because it is cell-specific and context-dependent in coordinating the individual's response to changing environments. These diverse actions of corticosterone are mediated by mineralocorticoid- and glucocorticoid-receptors that operate as a binary system in concert with neurotransmitter and neuropeptide signals to activate and inhibit stress reactions, respectively. Classically MR and GR are gene transcription factors, but recently these receptors appear to mediate also rapid non-genomic actions on excitatory neurotransmission suggesting that they integrate functions over time. Hence the balance of receptor-mediated actions is crucial for homeostasis. This balanced function of mineralo- and glucocorticoid-receptors can be altered epigenetically by a history of traumatic (early) life events and the experience of repeated stressors as well as by predisposing genetic variants in signaling pathways of these receptors. One of these variants, mineralocorticoid receptor haplotype 2, is associated with dispositional optimism in appraisal of environmental challenges. Imbalance in receptor-mediated corticosterone actions was found to leave a genomic signature highlighting the role of master switches such as cAMP response element-binding protein and mammalian target of rapamycin to compromise health, and to promote vulnerability to disease. Diabetic encephalopathy is a pathology of imbalanced corticosterone action, which can be corrected in its pre-stage by a brief treatment with the antiglucocorticoid mifepristone.

Angiotensin-(1-7) via the mas receptor alleviates the diabetes-induced decrease in GFAP and GAP-43 immunoreactivity with concomitant reduction in the COX-2 in hippocampal formation: an immunohistochemical study

We have previously shown that chronic treatment with angiotensin-(1-7) [Ang-(1-7)] can prevent diabetes-induced cardiovascular dysfunction. However, effect of Ang-(1-7) treatment on diabetes-induced alterations in the CNS is unknown. The aim of this study was to test the hypothesis that treatment with Ang-(1-7) can produce protection against diabetes-induced CNS changes. We examined the effect of Ang-(1-7) on the number of cyclooxygenase-2 (COX-2) immunoreactive neurons and the glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes and assessed the changes in the neuronal growth-associated protein-43 (GAP-43) of the hippocampal formation in streptozotocin-induced diabetes in rats. Animals were sacrificed 30 days after induction of diabetes and/or treatment with Ang-(1-7). Ang-(1-7) treatment significantly prevented diabetes-induced decrease in the number of GFAP immunoreactive astrocytes and GAP-43 positive neurons in all hippocampal regions. Co-administration of A779, a selective Ang-(1-7) receptor antagonist, inhibited Ang-(1-7)-mediated protective effects indicating that Ang-(1-7) produces its effects through activation of receptor Mas. Further, Ang-(1-7) treatment through activation of Mas significantly prevented diabetes-induced increase in the number of the COX-2 immunolabeled neurons in all sub-regions of the hippocampus examined. These results show that Ang-(1-7) has a protective role against diabetes-induced changes in the CNS.

Depressive phenotypes evoked by experimental diabetes are reversed by insulin

Clinical studies suggest a bidirectional relationship between diabetes and depression, where diabetes may increase risk for depressive symptoms and depression may increase risk for diabetes. Preclinical models examining the effects of diabetes on brain and behavior can provide insights to the pathophysiology underlying this relationship. The current study comprehensively examined, in C57BL/6 mice, the development of depressive phenotypes evoked by diabetes induced by streptozotocin (STZ) and determined if insulin treatment was able to reverse the diabetes-related changes on brain and affective behavior. Since anxiety is often comorbid with mood disturbances, behavioral tests for both anxiety and depression were administered. Possible physiological correlates of behavioral changes, including hippocampal cell proliferation, brain derived neurotrophic factor, and plasma corticosterone, were also measured. STZ-induced diabetes resulted in increased immobility in the tail suspension test, increased intracranial self-stimulation thresholds, decreased hippocampal cell proliferation, and increased corticosterone levels. Insulin treatment, on the other hand, reduced hyperglycemia, reversed the behavioral effects, and returned hippocampal cell proliferation and corticosterone to levels comparable to the control group. Anxiety-related behaviors were unaffected. This study showed that experimental diabetes in the mouse produced depressive phenotypes that were reversed by insulin therapy. Changes in reward-related behaviors and hippocampal cell proliferation may be useful markers to identify therapeutic interventions for comorbid diabetes and depression.

RU486 (mifepristone) ameliorates cognitive dysfunction and reverses the down-regulation of astrocytic N-myc downstream-regulated gene 2 in streptozotocin-induced type-1 diabetic rats

Diabetic cognitive dysfunction (DCD), usually accompanied with chronically elevated glucocorticoids and hippocampal astrocytic alterations, is one of the most serious complications in patients with type-1 diabetes. However, the role for chronically elevated glucocorticoids and hippocampal astrocytic activations in DCD remains to be elucidated, and it is not clear whether astrocytic N-myc downstream-regulated gene 2 (NDRG2, involved in cell differentiation and development) participated in DCD. In the present study, three months after streptozotocin (STZ)-induced type-1 diabetes onset, rats showed cognitive impairments in Morris water maze test as well as elevated corticosterone level. Diabetic rats also presented down-regulation of glial fibrillary acidic protein (GFAP, a key indicator of astrocytic reactivity) and NDRG2 in hippocampus revealed by immunohistochemistry staining, real-time PCR and Western blot. Moreover, the diabetic cognitive impairments were ameliorated by 9-day glucocorticoids receptor (GR) blockade with RU486, and the down-regulation of hippocampal NDRG2 and GFAP in diabetic animals was also attenuated by 9-day GR blockade. These results suggest that glucocorticoids-GR system is crucial for DCD, and that astrocytic reactivity and NDRG2 are involved in these processes. Thus, inhibiting GR activation in the hippocampus may be a novel therapeutic strategy for treating DCD.

Diabetes as a chronic metabolic stressor: causes, consequences and clinical complications

Diabetes mellitus is an endocrine disorder resulting from inadequate insulin release and/or reduced insulin sensitivity. The complications of diabetes are well characterized in peripheral tissues, but there is a growing appreciation that the complications of diabetes extend to the central nervous system (CNS). One of the potential neurological complications of diabetes is cognitive deficits. Interestingly, the structural, electrophysiological, neurochemical and anatomical underpinnings responsible for cognitive deficits in diabetes are strikingly similar to those observed in animals subjected to chronic stress, as well as in patients with stress-related psychiatric illnesses such as major depressive disorder. Since diabetes is a chronic metabolic stressor, this has led to the suggestion that common mechanistic mediators are responsible for neuroplasticity deficits in both diabetes and depression. Moreover, these common mechanistic mediators may be responsible for the increase in the risk of depressive illness in diabetes patients. In view of these observations, the aims of this review are (1) to describe the neuroplasticity deficits observed in diabetic rodents and patients; (2) to summarize the similarities in the clinical and preclinical studies of depression and diabetes; and (3) to highlight the diabetes-induced neuroplasticity deficits in those brain regions that have been implicated as important pathological centers in depressive illness, namely, the hippocampus, the amygdala and the prefrontal cortex.

Enhanced angiotensin II-mediated central sympathoexcitation in streptozotocin-induced diabetes: role of superoxide anion

Studies have shown that the superoxide mechanism is involved in angiotensin II (ANG II) signaling in the central nervous system. We hypothesized that ANG II activates sympathetic outflow by stimulation of superoxide anion in the paraventricular nucleus (PVN) of streptozotocin (STZ)-induced diabetic rats. In α-chloralose- and urethane-anesthetized rats, microinjection of ANG II into the PVN (50, 100, and 200 pmol) produced dose-dependent increases in renal sympathetic nerve activity (RSNA), arterial pressure (AP), and heart rate (HR) in control and STZ-induced diabetic rats. There was a potentiation of the increase in RSNA (35.0 ± 5.0 vs. 23.0 ± 4.3%, P < 0.05), AP, and HR due to ANG II type I (AT(1)) receptor activation in diabetic rats compared with control rats. Blocking endogenous AT(1) receptors within the PVN with AT(1) receptor antagonist losartan produced significantly greater decreases in RSNA, AP, and HR in diabetic rats compared with control rats. Concomitantly, there were significant increases in mRNA and protein expression of AT(1) receptor with increased superoxide levels and expression of NAD(P)H oxidase subunits p22(phox), p47(phox), and p67(phox) in the PVN of rats with diabetes. Pretreatment with losartan (10 mg·kg(-1)·day(-1) in drinking water for 3 wk) significantly reduced protein expression of NAD(P)H oxidase subunits (p22(phox) and p47(phox)) in the PVN of diabetic rats. Pretreatment with adenoviral vector-mediated overexpression of human cytoplasmic superoxide dismutase (AdCuZnSOD) within the PVN attenuated the increased central responses to ANG II in diabetes (RSNA: 20.4 ± 0.7 vs. 27.7 ± 2.1%, n = 6, P < 0.05). These data support the concept that superoxide anion contributes to an enhanced ANG II-mediated signaling in the PVN involved with the exaggerated sympathoexcitation in diabetes.

Short-term environmental enrichment enhances adult neurogenesis, vascular network and dendritic complexity in the hippocampus of type 1 diabetic mice

Background

Several brain disturbances have been described in association to type 1 diabetes in humans. In animal models, hippocampal pathological changes were reported together with cognitive deficits. The exposure to a variety of environmental stimuli during a certain period of time is able to prevent brain alterations and to improve learning and memory in conditions like stress, aging and neurodegenerative processes.

Methodology/Principal Findings

We explored the modulation of hippocampal alterations in streptozotocin-induced type 1 diabetic mice by environmental enrichment. In diabetic mice housed in standard conditions we found a reduction of adult neurogenesis in the dentate gyrus, decreased dendritic complexity in CA1 neurons and a smaller vascular fractional area in the dentate gyrus, compared with control animals in the same housing condition. A short exposure -10 days- to an enriched environment was able to enhance proliferation, survival and dendritic arborization of newborn neurons, to recover dendritic tree length and spine density of pyramidal CA1 neurons and to increase the vascular network of the dentate gyrus in diabetic animals.

Conclusions/Significance

The environmental complexity seems to constitute a strong stimulator competent to rescue the diabetic brain from neurodegenerative progression.

Enriched environment prevents memory deficits in type 1 diabetic rats

Studies have shown that an enriched environmental (EE) enhances hippocampal neurogenesis and dendritic branching in rodents, improving the performance in learning and memory task. Diabetes, however, is associated with memory deficits and decreasing in cell proliferation in the hippocampal dentate gyrus (DG), possibly related with higher glucocorticoid levels. Thus, our objective was to investigate the influence of EE on the memory deficits and cell proliferation of diabetic rats. For this, we reared rats for 2 months during early stages of life in standard environments (control rats) or EE. At adulthood, control and EE groups were divided and half of them induced to diabetes by a single injection of streptozotocin, 60 mg/kg, via i.p. Memory deficit was evaluated in these groups in the novel object-placement recognition task 11 days after diabetes induction. BrdU label cells were detected by immunohistochemistry after 3 days of administration to correlate cell proliferation in the DG area and performance in the memory task. Our results showed that EE decreased memory deficits in diabetic-induced rats (p < 0.05). Although cell proliferation in the DG was lower in the diabetic rats, enriched environment did not interfere in this parameter. These findings suggest that enriched environment is able to prevent or delay the development of memory deficits caused by diabetes in rats.

Neuronal plasticity and antidepressants in the diabetic brain

The hippocampus, a limbic structure linked to higher brain functions, appears vulnerable in diabetic subjects that have a higher risk of stroke, dementia, and cognitive decline. The dentate gyrus (DG) of the hippocampus is one of the limited neurogenic brain areas during adulthood; neurons born in the DG are involved in some types of learning and memory processes. We found a decrease in the ability for proliferation and neuronal differentiation of newborn cells, measured by bromodeoxyuridine incorporation in the DG, from streptozotocin-induced diabetic mice. The hilar region, formed by mature neurons presenting higher sensitivity to brain damage, showed a reduced neuronal density in diabetic mice with respect to vehicle-treated mice. Interestingly, in a spontaneous model of type 1 diabetes, we corroborated a decrease in the rate of neurogenesis in the nonobese diabetic mice compared to control strains, and this reduction was also found during the prediabetic stage. The antidepressant fluoxetine administered over a period of 10 days to diabetic mice was effective in preventing changes in proliferation and differentiation of new neurons. Confocal microscope studies, including using neuronal and glial markers, suggested that differentiation toward a neuronal phenotype was decreased in diabetic animals and was reversed by the antidepressant treatment. In addition, the loss of hilar neurons was avoided by fluoxetine treatment. Several reports have demonstrated that high susceptibility to stress and elevated corticosterone levels are detrimental to neurogenesis and contribute to neuronal loss. These features are common in some types of depression, diabetes, and aging processes, suggesting they participate in the reported hippocampal abnormalities present in these conditions.

Glucocorticoid receptor blockade normalizes hippocampal alterations and cognitive impairment in streptozotocin-induced type 1 diabetes mice

Type 1 diabetes is a common metabolic disorder accompanied by an increased secretion of glucocorticoids and cognitive deficits. Chronic excess of glucocorticoids per se can evoke similar neuropathological signals linked to its major target in the brain, the hippocampus. This deleterious action exerted by excess adrenal stress hormone is mediated by glucocorticoid receptors (GRs). The aim of the present study was to assess whether excessive stimulation of GR is causal to compromised neuronal viability and cognitive performance associated with the hippocampal function of the diabetic mice. For this purpose, mice had type 1 diabetes induced by streptozotocin (STZ) administration (170 mg/kg, i.p.). After 11 days, these STZ-diabetic mice showed increased glucocorticoid secretion and hippocampal alterations characterized by: (1) increased glial fibrillary acidic protein-positive astrocytes as a marker reacting to neurodegeneration, (2) increased c-Jun expression marking neuronal activation, (3) reduced Ki-67 immunostaining indicating decreased cell proliferation. At the same time, mild cognitive deficits became obvious in the novel object-placement recognition task. After 6 days of diabetes the GR antagonist mifepristone (RU486) was administered twice daily for 4 days (200 mg/kg, p.o.). Blockade of GR during early type 1 diabetes attenuated the morphological signs of hippocampal aberrations and rescued the diabetic mice from the cognitive deficits. We conclude that hippocampal disruption and cognitive impairment at the early stage of diabetes are caused by excessive GR activation due to hypercorticism. These signs of neurodegeneration can be prevented and/or reversed by GR blockade with mifepristone.

Effects of treadmill exercise on cell proliferation and differentiation in the subgranular zone of the dentate gyrus in a rat model of type II diabetes

In the present study, we investigated the effects of a treadmill exercise on serum glucose levels and Ki67 and doublecortin (DCX) immunoreactivity, which is a marker of cell proliferation expressed during cell cycles except G0 and early G1 and a marker of progenitors differentiating into neurons, respectively, in the subgranular zone of the dentate gyrus (SZDG) using a type II diabetic model. At 6 weeks of age, Zucker lean control (ZLC) and Zucker diabetic fatty (ZDF) rats were put on a treadmill with or without running for 1 h/day/5 consecutive days at 22 m/min for 5 weeks. Body weight was significantly increased in the control (without running)-ZDF rats compared to that in the other groups. In the control groups blood glucose levels were increased by 392.7 mg/dl in the control-ZDF rats and by 143.3 mg/dl in the control-ZLC rats. However, in the exercise groups, blood glucose levels were similar between the exercise-ZLC and ZDF rats: The blood glucose levels were 110.0 and 118.2 mg/dl, respectively. Ki67 positive nuclei were detected in the SZDG in control and exercise groups. The number of Ki67 positive nuclei was significantly high in exercise groups compared to that in the control groups. In addition, Ki67 positive cells were abundant in ZLC groups compared to those in ZDF groups. DCX-immunoreactive structures in the control-ZDF rats were lower than that in the control-ZLC rats. In the exercise groups, DCX-immunoreactive structures (somata and processes with tertiary dendrites) and DCX protein levels were markedly increased in both the exercise-ZLC and ZDF rats compared to that in the control groups. These results suggest that a treadmill exercise reduces blood glucose levels in ZDF rats and increases cell proliferation and differentiation in the SZDG in ZLC and ZDF rats compared to those in control groups.

Adrenal hypersensitivity precedes chronic hypercorticism in streptozotocin-induced diabetes mice

Previous studies have demonstrated that type 1 diabetes is characterized by hypercorticism and lack of periodicity in adrenal hormone secretion. In the present study, we tested the hypothesis that hypercorticism is initiated by an enhanced release of ACTH leading subsequently to adrenocortical growth and increased output of adrenocortical hormones. To test this hypothesis, we used the streptozotocin (STZ)-induced diabetes mouse model and measured hypothalamic-pituitary-adrenal axis activity at different time points. The results showed that the expected rise in blood glucose levels induced by STZ treatment preceded the surge in corticosterone secretion, which took place 1 d after diabetes onset. Surprisingly, circulating ACTH levels were not increased and even below control levels until 1 d after diabetes onset and remained low until d 11 during hypercorticism. In response to ACTH (but not vasopressin), cultures of adrenal gland cells from 11-d diabetic mice secreted higher amounts of corticosterone than control cells. Real-time quantitative PCR revealed increased expression of melanocortin 2 and melanocortin 5 receptors in the adrenal glands at 2 and 11 d of STZ-induced diabetes. AVP mRNA expression in the paraventricular nucleus of the hypothalamus was increased, whereas hippocampal MR mRNA was decreased in 11-d diabetic animals. GR and CRH mRNAs remained unchanged in hippocampus and paraventricular nucleus of diabetic mice at all time points studied. These results suggest that sensitization of the adrenal glands to ACTH rather than an increase in circulating ACTH level is the primary event leading to hypercorticism in the STZ-induced diabetes mouse model.