Streptozotocin diabetic mice display depressive-like behavior and alterations in the structure, neurotransmission and plasticity of medial prefrontal cortex interneurons

Erythropoietin restrains the inhibitory potential of interneurons in the mouse hippocampus

Severe psychiatric illnesses, for instance schizophrenia, and affective diseases or autism spectrum disorders, have been associated with cognitive impairment and perturbed excitatory-inhibitory balance in the brain. Effects in juvenile mice can elucidate how erythropoietin (EPO) might aid in rectifying hippocampal transcriptional networks and synaptic structures of pyramidal lineages, conceivably explaining mitigation of neuropsychiatric diseases. An imminent conundrum is how EPO restores synapses by involving interneurons. By analyzing ~12,000 single-nuclei transcriptomic data, we generated a comprehensive molecular atlas of hippocampal interneurons, resolved into 15 interneuron subtypes. Next, we studied molecular alterations upon recombinant human (rh)EPO and saw that gene expression changes relate to synaptic structure, trans-synaptic signaling and intracellular catabolic pathways. Putative ligand-receptor interactions between pyramidal and inhibitory neurons, regulating synaptogenesis, are altered upon rhEPO. An array of in/ex vivo experiments confirms that specific interneuronal populations exhibit reduced dendritic complexity, synaptic connectivity, and changes in plasticity-related molecules. Metabolism and inhibitory potential of interneuron subgroups are compromised, leading to greater excitability of pyramidal neurons. To conclude, improvement by rhEPO of neuropsychiatric phenotypes may partly owe to restrictive control over interneurons, facilitating re-connectivity and synapse development.

Protective effects of chronic humanin treatment in mice with diabetic encephalopathy: A focus on oxidative stress, inflammation, and apoptosis

Diabetes is known to cause cognitive impairments through various mechanisms, including oxidative stress, inflammation, and apoptosis. Humanin (HN) has been shown to have protective effects on cognitive impairments induced by factors such as Aβ, muscarinic receptor antagonists, and aging in rodents. However, the mechanisms underlying the protective effects of HN in the prefrontal cortex and hippocampus in the context of diabetes are not well understood. In this study, we aimed to investigate the potential protective role of HN on oxidative stress, inflammation, and apoptosis in mice with diabetes. We divided the mice into four groups, including a control group (treated with saline), a humanin group (treated with 4 mg/kg of HN), a streptozotocin (STZ) group (diabetic control), and an STZ+Humanin group. The mice were administered HN daily for 15 days. Our results showed that in the prefrontal cortex and hippocampus of the diabetes group, oxidative stress parameters, pro-inflammatory cytokines, apoptosis and, blood glucose levels were increased, while antioxidant and anti-inflammatory cytokines were diminished compared to the control group. However, HN treatment was able to modulate these markers, including blood glucose and the markers of oxidative stress, inflammation, and apoptosis. In conclusion, our findings suggest that hyperglycemia, oxidative stress, inflammation, and apoptosis may contribute to the development of diabetes-induced cognitive impairments. By regulating these changes with HN treatment, we may be able to positively contribute to the treatment of cognitive impairments induced by diabetes.

Maternal diabetes decreases the expression of GABAAα1, GABAB1, and mGlu2 receptors in the visual cortex of male rat neonates

AIMS

This study examines the impact of maternal diabetes on the expression of GABAB1, GABAAα1, and mGlu2 receptors in the primary visual cortex layers of male rat newborns.

MAIN METHODS

In diabetic group (Dia), diabetes was induced in adult female rats using an intraperitoneal dose of Streptozotocin (STZ) 65 (mg/kg). Diabetes was managed by daily subcutaneous injection of NPH insulin in insulin-treated diabetic group (Ins). Control group (Con) received normal saline intraperitoneally rather than STZ. Male offspring born to each group of female rats were euthanized via CO2 inhalation at P0, P7, and P14 days after delivery and the expression of GABAB1, GABAAα1, and mGlu2 receptors in their primary visual cortex was determined using immunohistochemistry (IHC).

KEY FINDINGS

The expression of GABAB1, GABAAα1, and mGlu2 receptors increased gradually with age in the male offspring born to Con group while the highest expression was detected in layer IV of the primary visual cortex. In Dia group newborns, the expression of these receptors was significantly reduced in all layers of the primary visual cortex at every three days. Insulin treatment in diabetic mothers restored the expression of these receptors to normal levels in their newborns.

SIGNIFICANCE

The study indicates that diabetes reduces the expression of GABAB1, GABAAα1, and mGlu2 receptors in the primary visual cortex of male offspring born to diabetic rats at P0, P7, and P14. However, insulin treatment can counteract these effects.

Microglial NLRP3 inflammasome activation mediates diabetes-induced depression-like behavior via triggering neuroinflammation

BACKGROUND

Abundant evidence suggests that the prevalence and risk of depression in people with diabetes is high. However, the pathogenesis of diabetes-related depression remains unclear. Since neuroinflammation is associated with the pathophysiology of diabetic complications and depression, this study aims to elucidate the neuroimmune mechanism of diabetes-related depression.

METHODS

Male C57BL/6 mice were injected with streptozotocin to establish a diabetes model. After screening, diabetic mice were treated with the NLRP3 inhibitor MCC950. Then, metabolic indicators and depression-like behaviors were evaluated in these mice, as well as their central and peripheral inflammation. To explore the mechanism of high glucose-induced microglial NLRP3 inflammasome activation, we performed in vitro studies focusing on its canonical upstream signal I (TLR4/MyD88/NF-κB) and signal II (ROS/PKR/P₂X₇R/TXNIP).

RESULTS

Diabetic mice exhibited depression-like behaviors and activation of NLRP3 inflammasome in hippocampus. In vitro high-glucose (50 mM) environment primed microglial NLRP3 inflammasome by promoting NF-κB phosphorylation in a TLR4/MyD88-independent manner. Subsequently, high glucose activated the NLRP3 inflammasome via enhancing intracellular ROS accumulation, upregulating P₂X₇R, as well as promoting PKR phosphorylation and TXNIP expression, thereby facilitating the production and secretion of IL-1β. Inhibition of NLRP3 with MCC950 significantly restored hyperglycemia-induced depression-like behavior and reversed the increase in IL-1β levels in the hippocampus and serum.

CONCLUSION

The activation of NLRP3 inflammasome, probably mainly in hippocampal microglia, mediates the development of depression-like behaviors in STZ-induced diabetic mice. Targeting the microglial inflammasome is a feasible strategy for the treatment of diabetes-related depression.

Function of the GABAergic System in Diabetic Encephalopathy

Diabetes is a common metabolic disease characterized by loss of blood sugar control and a high rate of complications. γ-Aminobutyric acid (GABA) functions as the primary inhibitory neurotransmitter in the adult mammalian brain. The normal function of the GABAergic system is affected in diabetes. Herein, we summarize the role of the GABAergic system in diabetic cognitive dysfunction, diabetic blood sugar control disorders, diabetes-induced peripheral neuropathy, diabetic central nervous system damage, maintaining diabetic brain energy homeostasis, helping central control of blood sugar and attenuating neuronal oxidative stress damage. We show the key regulatory role of the GABAergic system in multiple comorbidities in patients with diabetes and hope that further studies elucidating the role of the GABAergic system will yield benefits for the treatment and prevention of comorbidities in patients with diabetes.

Hyperglycemia-associated Alzheimer's-like symptoms and other behavioral effects attenuated by Plumeria obtusa L. Extract in alloxan-induced diabetic rats

Diabetes mellitus is a chronic metabolic complaint with numerous short- and long-term complications that harm a person's physical and psychological health. Plumeria obtusa L. is a traditional medicine used in the treatment of diabetes to reduce complications related to behavior. Plumeria is a genus with antipsychotic activities. The objective of this study was to examine the effects of a methanolic extract of Plumeria obtusa L. in the attenuation of diabetes, on symptoms of Alzheimer disease, and on other associated behavioral aspects. A single dose of alloxan was administered to an experimental group of rats to induce development of diabetes (150 mg/kg, intraperitoneal) and the rats were then administered selected doses of methanolic extract of Plumeria obtusa L. (Po.Cr) or glibenclamide (0.6 mg/kg) for 45 consecutive days. Behavioral effects were evaluated using three validated assays of anxiety-related behavior: the open field test, the light and dark test, and the elevated plus maze. Anti-depressant effects of Plumeria obtusa L. were evaluated using the forced swim test (FST) and memory and learning were assessed using the Morris water maze (MWM) task. Po.Cr was also evaluated for phytochemicals using total phenolic content (TPC), total flavonoid content (TFC), and high-performance liquid chromatography assays, and antioxidant capability was assessed through assays of DPPH radical scavenging, total oxidation capacity, and total reducing capacity. In the alloxan-induced model of diabetes, the administration of Po.Cr and glibenclamide for 45 days produced a marked decrease (p < 0.001) in hyperglycemia compared to control animals. Po.Cr treatment also resulted in improvement in indicators, such as body weight and lipid profile (p < 0.05), as well as restoration of normal levels of alanine transaminase (ALT) (p < 0.001), a biomarker of liver function. Diabetic rats presented more Alzheimer-like symptoms, with greater impairment of memory and learning, and increased anxiety and depression compared to non-diabetic normal rats, whereas treated diabetic rats showed significant improvements in memory and behavioral outcomes. These results demonstrate that Po.Cr reversed alloxan-induced hyperglycemia and ameliorated Alzheimer-related behavioral changes, which supports additional study and assessment of conventional use of the plant to treat diabetes and associated behavioral complications.

Impact of stress on inhibitory neuronal circuits, our tribute to Bruce McEwen

This manuscript is dedicated to the memory of Bruce S. McEwen, to commemorate the impact he had on how we understand stress and neuronal plasticity, and the profound influence he exerted on our scientific careers. The focus of this review is the impact of stressors on inhibitory circuits, particularly those of the limbic system, but we also consider other regions affected by these adverse experiences. We revise the effects of acute and chronic stress during different stages of development and lifespan, taking into account the influence of the sex of the animals. We review first the influence of stress on the physiology of inhibitory neurons and on the expression of molecules related directly to GABAergic neurotransmission, and then focus on specific interneuron subpopulations, particularly on parvalbumin and somatostatin expressing cells. Then we analyze the effects of stress on molecules and structures related to the plasticity of inhibitory neurons: the polysialylated form of the neural cell adhesion molecule and perineuronal nets. Finally, we review the potential of antidepressants or environmental manipulations to revert the effects of stress on inhibitory circuits.

Melatonin reverses depressive and anxiety like-behaviours induced by diabetes: involvement of oxidative stress, age, rage and S100B levels in the hippocampus and prefrontal cortex of rats

Diabetes is associated with depression and anxiety symptoms. The current investigation was designed to explore the effect of melatonin on depressive and anxiety like-behaviours, oxidative stress, levels of AGE, RAGE and S100B in streptozotocin-induced diabetic rats. The animals were divided into four groups: Normoglycemic; Normoglycemic + melatonin; diabetic; diabetic + melatonin (10 mg/kg, for 4 weeks). The malondialdehyde (MDA), reduced glutathione (GSH), AGE, RAGE and S100B were measured and the depressive and anxiety like-behaviours were assessed by forced swimming and elevated plus maze tests, respectively. Melatonin ameliorates depressive and anxiety like-behaviours. Concomitantly, melatonin reversed diabetes induced increase of MDA, AGE and decrease of GSH and S100B levels in the hippocampus and prefrontal cortex. In conclusion, our results showed that melatonin administration may exert antidepressant-like and anxiolytic effects in diabetic rats through normalising of AGE/RAGE, S100B and oxidative stress in the prefrontal cortex and hippocampus.

2-Heptanone reduces inhibitory control of the amygdala over the prelimbic region in rats

Basolateral amygdala (BLA) nuclei and their reciprocal connections with prelimbic (PL) and infralimbic (IL) regions of the medial prefrontal cortex (mPFC) are involved in the regulation of fear. 2-Heptanone is released in urine in stressed rats, and the olfactory detection of this odor produces immediate avoidance and alarm reactions and modifies neuronal activity in limbic connections in non-stressed rats. If 2-heptanone acts as a danger signal, then long-lasting actions would be expected. The aim of the present study was to investigate whether the forced inhalation of 2-heptanone modifies the response capacity of the BLA-mPFC circuit in the long term (48 h). Single-unit extracellular recordings were obtained from the PL and IL during electrical stimulation of the BLA (square-wave pulses; 1 ms, 20 µA, 0.3 Hz, 110 stimuli over a total duration of 360 s) in three groups of Wistar rats: control group (no sensory stimulation), unpredictable auditory stimulation group, and 2-heptanone stimulation group. A brief-latency (1 ms), short-duration (5 ms) paucisynaptic response followed BLA stimulation and was unaffected by any sensorial stimulation. The paucisynaptic response was followed by a mostly inhibitory and long-lasting (>750 ms) afterdischarge in the control and auditory stimulation groups. In the 2-heptanone group, the inhibitory afterdischarge shifted to an excitatory afterdischarge after ∼250 ms in the PL and after ∼500 ms in the IL. Importantly, the rats that were included in this study were born in local housing facilities. Thus, these animals were never in contact with predators and instead in contact with only conspecifics. These results indicate that the forced inhalation of 2-heptanone is able to modify BLA-mPFC responsivity in the long term. 2-Heptanone decreases inhibitory control of the amygdala over mPFC activity. Disinhibition of the mPFC may lead to the adaptive expression of defensive behaviors, even in animals that are not in the presence of predators.

Myrsinoic acid B from Myrsine coriacea reverses depressive-like behavior and brain oxidative stress in streptozotocin-diabetic rats

AIMS

Major depressive disorder (MDD) affects approximately 322 million people worldwide and is a common comorbidity in patients with diabetes mellitus (DM). A possible pathophysiological mechanism correlating both diseases is the increased oxidative stress in brain regions due to hyperglycemia. Myrsine coriacea (Primulaceae) is popularly known as "capororoca" and studies have been shown that this plant exhibits several pharmacological properties attributed to myrsinoic acid A (MAA) and B (MAB). Indeed, previous results have been shown its effects on the central nervous system, leading us to explore possible psychotropic effects.

MAIN METHODS

The effects of treatment with hydroalcoholic extract of the barks from Myrsine coriacea (HEBMC, 150 mg/kg, o.g.), MAA (5 mg/kg, o.g.), and MAB (3 mg/kg, o.g.) were evaluated in streptozotocin (75 mg/kg, i.p.)-induced diabetic female rats. After 28 days of treatments, rats were submitted to the forced swim test (FST) and open field test (OFT). Also, superoxide dismutase (SOD) and catalase (CAT) activities, reduced glutathione (GSH) and lipid hydroperoxides (LOOH) levels were evaluated in the hippocampus (HIP) and prefrontal cortex (PFC) of these rats.

KEY FINDINGS

The treatment with MAA or MAB increased the latency of first immobility in diabetic rats, and the HEBMC administration decreased the immobility time, and increase the climbing in FST. However, only MAB treatment reduces the immobility time, increases the climbing, and swimming in FST, and increases the crossing of diabetic animals in the OFT. Besides, this behavioral improvement promoted by MAB administration was accompanied by reducing in oxidative stress in the HIP and PFC, but not reducing hyperglycemia in diabetic rats.

SIGNIFICANCE

The results suggest that MAB's antioxidant effect in the HIP of diabetic animals may be essential to its antidepressant-like effect.

Structural Alterations in Deep Brain Structures in Type 1 Diabetes

Even though well known in type 2 diabetes, the existence of brain changes in type 1 diabetes (T1D) and both their neuroanatomical and clinical features are less well characterized. To fill the void in the current understanding of this disease, we sought to determine the possible neural correlate in long-duration T1D at several levels, including macrostructural, microstructural cerebral damage, and blood flow alterations. In this cross-sectional study, we compared a cohort of 61 patients with T1D with an average disease duration of 21 years with 54 well-matched control subjects without diabetes in a multimodal MRI protocol providing macrostructural metrics (cortical thickness and structural volumes), microstructural measures (T1-weighted/T2-weighted [T1w/T2w] ratio as a marker of myelin content, inflammation, and edema), and cerebral blood flow. Patients with T1D had higher T1w/T2w ratios in the right parahippocampal gyrus, the executive part of both putamina, both thalami, and the cerebellum. These alterations were reflected in lower putaminal and thalamic volume bilaterally. No cerebral blood flow differences between groups were found in any of these structures, suggesting nonvascular etiologies of these changes. Our findings implicate a marked nonvascular disruption in T1D of several essential neural nodes engaged in both cognitive and motor processing.

Dissecting Sholl Analysis into Its Functional Components

Sholl analysis has been an important technique in dendritic anatomy for more than 60 years. The Sholl intersection profile is obtained by counting the number of dendritic branches at a given distance from the soma and is a key measure of dendritic complexity; it has applications from evaluating the changes in structure induced by pathologies to estimating the expected number of anatomical synaptic contacts. We find that the Sholl intersection profiles of most neurons can be reproduced from three basic, functional measures: the domain spanned by the dendritic arbor, the total length of the dendrite, and the angular distribution of how far dendritic segments deviate from a direct path to the soma (i.e., the root angle distribution). The first two measures are determined by axon location and hence microcircuit structure; the third arises from optimal wiring and represents a branching statistic estimating the need for conduction speed in a neuron.

Keap1/Nrf2/HO-1 signaling pathway contributes to p-chlorodiphenyl diselenide antidepressant-like action in diabetic mice

RATIONALE

The association between depression and diabetes has been recognized for many years, but the nature of this relationship remains uncertain.

OBJECTIVES

This study investigated the antidepressant-like effect of (p-ClPhSe)₂ on mice made diabetic by streptozotocin (STZ) and the contribution of cerebral cortical Keap1/Nrf2/HO-1 signaling pathway for this effect.

METHODS

Male adult Swiss mice received streptozotocin (STZ, 200 mg/kg, i.p.) to induce diabetes (glycemia ≥ 200 mg/dl) or citrate buffer (5 ml/kg, control group). The mice were treated with (p-ClPhSe)₂ at the dose of 5 mg/kg, i.g., for 7 days. Mice performed behavior tests, tail suspension (TST), and forced swimming tests (FST), to evaluate depressive-like phenotype.

RESULTS

Diabetic mice showed an increase in immobility time in the TST and FST when compared to the control group. The protein contents of Keap1/Nrf2/HO-1 pathway were decreased in the cerebral cortex of diabetic mice. Diabetic mice had an increase in the relative adrenal weight and a decrease in the protein content of glucocorticoid receptor. The levels of TBARS and RS and SOD activity were found altered in the cerebral cortex of diabetic mice. The number of FJC-positive cells was increased in the cerebral cortex of diabetic mice. Treatment with (p-ClPhSe)₂ was effective against depressive-like phenotype, oxidative stress, and FJC-positive cells of diabetic mice. (p-ClPhSe)₂ did not reverse the parameters of HPA axis evaluated in this study. (p-ClPhSe)₂ modulated the cerebral cortical Keap1/Nrf2/HO-1 pathway in diabetic mice.

CONCLUSIONS

This study demonstrates the contribution of cerebral cortical Keap1/Nrf2/HO-1 pathway in the (p-ClPhSe)₂ antidepressant-like action in diabetic mice.

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

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

Aging and Central Auditory Disinhibition: Is It a Reflection of Homeostatic Downregulation or Metabolic Vulnerability?

Aging-related changes have been identified at virtually every level of the central auditory system. One of the most common findings across these nuclei is a loss of synaptic inhibition with aging, which has been proposed to be at the heart of several aging-related changes in auditory cognition, including diminished speech perception in complex environments and the presence of tinnitus. Some authors have speculated that downregulation of synaptic inhibition is a consequence of peripheral deafferentation and therefore is a homeostatic mechanism to restore excitatory/inhibitory balance. As such, disinhibition would represent a form of maladaptive plasticity. However, clinical data suggest that deafferentation-related disinhibition tends to occur primarily in the aged brain. Therefore, aging-related disinhibition may, in part, be related to the high metabolic demands of inhibitory neurons relative to their excitatory counterparts. These findings suggest that both deafferentation-related maladaptive plastic changes and aging-related metabolic factors combine to produce changes in central auditory function. Here, we explore the arguments that downregulation of inhibition may be due to homeostatic responses to diminished afferent input vs. metabolic vulnerability of inhibitory neurons in the aged brain. Understanding the relative importance of these mechanisms will be critical for the development of treatments for the underlying causes of aging-related central disinhibition.

Type 2 Diabetes Leads to Axon Initial Segment Shortening in db/db Mice

Cognitive and mood impairments are common central nervous system complications of type 2 diabetes, although the neuronal mechanism(s) remains elusive. Previous studies focused mainly on neuronal inputs such as altered synaptic plasticity. Axon initial segment (AIS) is a specialized functional domain within neurons that regulates neuronal outputs. Structural changes of AIS have been implicated as a key pathophysiological event in various psychiatric and neurological disorders. Here we evaluated the structural integrity of the AIS in brains of db/db mice, an established animal model of type 2 diabetes associated with cognitive and mood impairments. We assessed the AIS before (5 weeks of age) and after (10 weeks) the development of type 2 diabetes, and after daily exercise treatment of diabetic condition. We found that the development of type 2 diabetes is associated with significant AIS shortening in both medial prefrontal cortex and hippocampus, as evident by immunostaining of the AIS structural protein βIV spectrin. AIS shortening occurs in the absence of altered neuronal and AIS protein levels. We found no change in nodes of Ranvier, another neuronal functional domain sharing a molecular organization similar to the AIS. This is the first study to identify AIS alteration in type 2 diabetes condition. Since AIS shortening is known to lower neuronal excitability, our results may provide a new avenue for understanding and treating cognitive and mood impairments in type 2 diabetes.

Glucagon-like Peptide-1 (GLP-1) and neurotransmitters signaling in epilepsy: An insight review

Epilepsy is one of the most prevalent neurological disorder affecting more than 50 million people worldwide. Numerous studies have suggested that an imbalance in glutamatergic (excitatory) and GABAergic (inhibitory) neurotransmitter system is one of the dominating pathophysiological mechanisms underlying the occurrence and progression of seizures. Further, this alteration in GABAergic and glutamatergic system disrupts the delicate balance of other neurotransmitters system in the brain. Emerging strides have documented the protective role of GLP-1 signaling on altered neurotransmitters signaling in Epilepsy and associated co-morbidities. GLP-1 is neuropeptide and synthesized by preproglucagon (PPG) neurons in the brain. GLP-1 receptors are widely distributed throughout the brain including hippocampus (CA3 and CA1 region) and implicated in various neurological disorders like Epilepsy. A complete understanding of alteration in neurotransmitters signaling will provide essential insight into the basic pathogenic mechanisms of epilepsy and may uncover novel targets for future drug therapies. Presently, treatment of epilepsy is palliative in nature, providing only symptomatic relief to patients. The apparent or traditional approach of treating epileptic subjects with anti-epileptic drugs is associated with variety of adverse effects. Therefore, alternative approaches that can restore altered neurotransmitter signaling are being tried and adopted. Present review is an attempt to highlight the emerging protective role of GLP-1 signaling on altered neurotransmitters signaling in epilepsy. Authors have made significant efforts to discuss effect of various GLP-1 analogs on various neurotransmitters system and associated molecular and cellular pathways as a potential drug target for the management of epilepsy and associated co-morbidities. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

NMDA Receptors Regulate the Structural Plasticity of Spines and Axonal Boutons in Hippocampal Interneurons

N-methyl-D-aspartate receptors (NMDARs) are present in both pyramidal neurons and interneurons of the hippocampus. These receptors play an important role in the adult structural plasticity of excitatory neurons, but their impact on the remodeling of interneurons is unknown. Among hippocampal interneurons, somatostatin-expressing cells located in the stratum oriens are of special interest because of their functional importance and structural characteristics: they display dendritic spines, which change density in response to different stimuli. In order to understand the role of NMDARs on the structural plasticity of these interneurons, we have injected acutely MK-801, an NMDAR antagonist, to adult mice which constitutively express enhanced green fluorescent protein (EGFP) in these cells. We have behaviorally tested the animals, confirming effects of the drug on locomotion and anxiety-related behaviors. NMDARs were expressed in the somata and dendritic spines of somatostatin-expressing interneurons. Twenty-four hours after the injection, the density of spines did not vary, but we found a significant increase in the density of their en passant boutons (EPB). We have also used entorhino-hippocampal organotypic cultures to study these interneurons in real-time. There was a rapid decrease in the apparition rate of spines after MK-801 administration, which persisted for 24 h and returned to basal levels afterwards. A similar reversible decrease was detected in spine density. Our results show that both spines and axons of interneurons can undergo remodeling and highlight NMDARs as regulators of this plasticity. These results are specially relevant given the importance of all these players on hippocampal physiology and the etiopathology of certain psychiatric disorders.

Ocular Nerve Growth Factor Administration Modulates Brain-derived Neurotrophic Factor Signaling in Prefrontal Cortex of Healthy and Diabetic Rats

AIMS

Nerve growth factor (NGF) eyedrops (ed-NGF) activate brain neurons, stimulate growth factors, including brain-derived neurotrophic factor (BDNF), and exert neuroprotection in the forebrain of streptozotocin-induced diabetic rats (STZ rats). In this study, the effects of ed-NGF on BDNF signaling in the prefrontal cortex (PFC) were explored in healthy and STZ-diabetic rats, in which cortical neuronal and axonal loss, and altered circulating BDNF associated with depressive phenotype are also described.

METHODS

STZ and healthy (CTR) adult rats received ed-NGF twice a day for 2 weeks. Depressive phenotype was identified by force swimming test (FST). Proteins extracted from PFC were processed for ELISA and Western blot analyses to measure the expression of BDNF, proBDNF, and their receptors and intracellular signals.

RESULTS

ed-NGF treatment modulates BDNF pathway in PFC and normalizes the STZ-induced BDNF alterations by stimulating TRK-mediated survival mechanism. A decreased latency in FST was also found in STZ rats, while no change was observed comparing CTR + NGF and STZ + NGF with CTR.

CONCLUSION

The present data confirm the capacity of ed-NGF treatment to affect brain neurons and lead to brain damage recovery by activating protective and remodeling pathways triggered by BDNF. We suggest that the ed-NGF-induced changes in BDNF signaling might influence the manifestation of depressive phenotype in diabetic rats.

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

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Diabetes negatively affects cortical and striatal GABAergic neurons: an effect that is partially counteracted by exendin-4

Diabetes negatively affects specific subtypes of inhibitory neurons in brain areas that regulate sensory and motor functions. This impairment can be partially reversed by exendin-4 (Ex-4). The findings could contribute to the development of treatments against diabetic neurological complications.

Type 2 diabetic (T2D) patients often develop early cognitive and sensorimotor impairments. The pathophysiological mechanisms behind these problems are largely unknown. Recent studies demonstrate that dysfunctional γ-aminobutyric acid (GABAergic) neurons are involved in age-related cognitive decline. We hypothesized that similar, but earlier dysfunction is taking place under T2D in the neocortex and striatum (two brain areas important for cognition and sensorimotor functions). We also hypothesized that the T2D-induced effects are pharmacologically reversible by anti-diabetic drugs targeting the glucagon-like peptide-1 receptor (GLP-1R). We determined the effect of T2D on cortical and striatal GABAergic neurons positive for glutamic acid decarboxylase-67 (GAD67), calbindin (CB), parvalbumin (PV) and calretinin (CR) by using immunohistochemistry and quantitative microscopy. Young and middle-aged T2D Goto-Kakizaki (GK) (a model of spontaneous T2D) and Wistar rats were used. Furthermore, we determined the therapeutic potential of the GLP1-R agonist exendin-4 (Ex-4) by treating middle-aged GK rats for 6 weeks with 0.1 μg/kg Ex-4 twice daily. We show that T2D reduced the density of GAD67-positive neurons in the striatum and of CB-positive neurons in both striatum and neocortex. T2D also increased the average volume of PV-positive interneurons in the striatum. Ex-4 treatment increased the density of CB-positive neurons in the striatum of GK rats. Our data demonstrate that T2D negatively affects GAD67 and CB-positive GABAergic neurons in the brain during aging, potentially identifying some of the pathophysiological mechanisms to explain the increased prevalence of neurological complications in T2D. We also show a specific, positive effect of Ex-4 on striatal CB-positive neurons, which could be exploited in therapeutic perspective.

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

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