Behavioral and biochemical effects of an ICV injection of streptozotocin in old Lewis rats

Exploring the potential of a novel phenoxyethyl piperidine derivative with cholinesterase inhibitory properties as a treatment for dementia: Insights from STZ animal model of dementia

Alzheimer's disease (AD) is a neurodegenerative disease, often characterized by progressive deficits in memory and cognitive functions. Cholinesterase inhibitors have been introduced as promising agents to enhance cognition and memory in both human patients and animal models of AD. In the current study, we assessed the effects of a synthetic phenoxyethyl piperidine derivative, compound 7c, as a novel dual inhibitor of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), on learning and memory, as well as serum and hippocampal AChE levels in an animal model of AD. The model of dementia was induced by intracerebroventricular injection of streptozotocin (STZ, 2 mg/kg) to male Wistar rats. STZ-treated rats received compound 7c (3, 30, and 300 µg/kg) for five consecutive days. ​Passive avoidance (PA) learning and memory, as well as spatial learning and memory using Morris water maze, were evaluated. The level of AChE was measured in the serum and the left and right hippocampus. Findings demonstrated that compound 7c (300 µg/kg) was able to reverse STZ-induced impairments in PA memory, while also reduced the increased AChE level in the left hippocampus. Taken together, compound 7c appeared to act as a central AChE inhibitor, and its role in alleviating cognitive deficits in the AD animal model suggests that it may have therapeutic potential in AD dementia. Further research is required to assess the effectiveness of compound 7c in more reliable models of AD in light of these preliminary findings.

Animal model of Alzheimer's disease induced by streptozotocin: New insights about cholinergic pathway

Alzheimer's disease (AD) is of multifactorial origin, and still presents several gaps regarding its development and progression. Disorders of the cholinergic system are well known to be involved in the pathogenesis of AD, characterized by increased acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) and decreased acetyltransferase (ChAT) enzymatic activities. Late onset AD (LOAD) animal model induced by intracerebroventricular injection of streptozotocin (icv-STZ) showed promising results in this context, due to the similarity with the pathophysiology of human LOAD. Thus, this study aimed to assess the long-term effects of icv-STZ on the cholinergic system, through the measuring of AChE and BChE enzymatic activities in hippocampus, prefrontal cortex and liver of animals euthanized 30 and 120-days after the icv-STZ. Regarding the cholinergic response to icv-STZ, the 30-days and 120-days STZ-induced rats exhibit decreased AChE and BChE activities only in the hippocampus. The cognitive deficit was more consistent in the 30-days post icv-STZ animals, as was the weight loss. This is the first study to investigate the long-term effects (more than 60 days) of the icv-STZ on AChE and BChE activities, and our results, as well as those of a recent study, suggest that the cholinergic system may not be compromised by icv-STZ, at least in the long term, which means that this model may not be the best model for studying the cholinergic system in AD or that it is informative only for a short period.

The Molecular Mechanism of Glucagon-Like Peptide-1 Therapy in Alzheimer's Disease, Based on a Mechanistic Target of Rapamycin Pathway

The mechanistic target of rapamycin (mTOR) is an important molecule that connects aging, lifespan, energy balance, glucose and lipid metabolism, and neurodegeneration. Rapamycin exerts effects in numerous biological activities via its target protein, playing a key role in energy balance, regulation of autophagy, extension of lifespan, immunosuppression, and protection against neurodegeneration. There are many similar pathophysiological processes and molecular pathways between Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM), and pharmacologic agents used to treat T2DM, including glucagon-like peptide-1 (GLP-1) analogs, seem to be beneficial for AD. mTOR mediates the effects of GLP-1 analogs in the treatment of T2DM; hence, I hypothesize that mTOR is a key molecule for mediating the protective effects of GLP-1 for AD.

Protective effect of valproic acid in streptozotocin-induced sporadic Alzheimer's disease mouse model: possible involvement of the cholinergic system

Sporadic Alzheimer's disease (SAD) is a slowly progressive neurological disorder that is the most common form of dementia. Cholinergic system dysfunction and amyloid beta formation are the two main underlying pathological mechanisms for the disease development. In recent studies, insulin receptor desensitization and disturbances in the downstream effects of insulin receptor signaling were observed in the brains of Alzheimer's patients. Currently, intracereberoventricular (ICV) injection of streptozotocin (STZ) is found to induce behavioral, neurochemical, and structural alterations in animals resembling those found in SAD patients. Valproic acid (VPA), a histone deacetylase inhibitor (HDACi), was recently shown to regulate the transcription of several genes in both in vivo and in vitro models of Alzheimer's disease. The aim of the current study is to investigate the potential effect of different doses of valproic acid, in an ICV-STZ-induced animal model of SAD. Streptozotocin-injected mice showed cognitive and spatial memory dysfunction in the Y-maze, object recognition test, and Morris water maze (MWM) neurobehavioral tests. The mice also exhibited a decrease in acetylcholine (ACh) and neprilysin (NEP) levels accompanied by an increase in acetylcholinesterase (AChE) activity. For the first time to our knowledge, our findings have shown that VPA is capable of restoring ACh levels in ICV-STZ-injected mice, as well as normalizing both NEP levels and AChE activity. Via this mechanism, an enhancement of cognitive functions is observed. Thus, VPA is suggested to be a promising therapeutic approach against SAD.

Cognitive effects of vanillic acid against streptozotocin-induced neurodegeneration in mice

CONTEXT

Vanillic acid (VA), a flavoring agent used in food and drug products, obtained naturally from the plant Angelica sinensis (Oliv.) Diels (Apiaceae), used in the traditional Chinese medicine. It is reported to possess strong antioxidant, anti-inflammatory, and neuroprotective effects. However, the pharmacological effects on oxidative stress-induced neurodegeneration are not well investigated.

OBJECTIVE

This study investigates the neuroprotective effect of VA on streptozotocin (STZ)-induced neurodegeneration in mice through behavioral and biochemical parameters.

MATERIALS AND METHODS

The behavioral effects were determined using the Y-maze and open-field habituation memory. In biochemical parameters, acetylcholinesterase (AChE), corticosterone, tumor necrosis factor (TNF)-α, and antioxidants (superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase) were measured. Five groups of animals used were of control, negative control, and three separate groups treated with 25, 50, and 100 mg/kg of VA, respectively, for 28 d. Intracerebroventricular (ICV) injections of STZ were performed for all groups except control on 14th and 16th of 28 d of VA treatment.

RESULTS

VA improved spatial learning and memory retention by preventing oxidative stress compared with control animals. VA at 50 and 100 mg/kg dose significantly (p < 0.001) improved the habituation memory, decreased the AChE, corticosterone, TNF-α, and increased the antioxidants (p < 0.001). VA (100 mg/kg) exhibited dose-dependent effect in all parameters with p < 0.001 except antioxidants in which VA showed the significance of p < 0.01.

DISCUSSION AND CONCLUSION

VA exhibited reduction in AChE, TNF-α, and corticosterone with improved antioxidants to contribute neuroprotection and could be an effective therapeutic agent for treating neurodegenerative disorders.

Bacopa monniera ameliorates cognitive impairment and neurodegeneration induced by intracerebroventricular-streptozotocin in rat: behavioral, biochemical, immunohistochemical and histopathological evidences

The standardized extract of Bacopa monniera (BM) is a complex mixture of ingredients with a uniquely wide spectrum of neuropharmacological influences upon the central nervous system including enhanced learning and memory with known antioxidant potential and protection of the brain from oxidative damage. The present study demonstrates the therapeutic efficacy of BM on cognitive impairment and oxidative damage, induced by intracerebroventricular injection of streptozotocin (ICV-STZ) in rat models. Male Wistar rats were pre-treated with BM at a selected dose (30 mg/Kg) given orally for 2 weeks and then were injected bilaterally with ICV-STZ (3 mg/Kg), while sham operated rats were received the same volume of vehicle. Behavioral parameters were subsequently monitored 2 weeks after the surgery using the Morris water maze (MWM) navigation task then were sacrificed for biochemical, immunohistochemical (Cu/Zn-SOD) and histopathological assays. ICV-STZ-infused rats showed significant loss in learning and memory ability, which were significantly improved by BM supplementation. A significant increase in thiobarbituric acid reactive species and a significant decrease in reduced glutathione, antioxidant enzymes in the hippocampus were observed in ICV-STZ rats. Moreover, decrease in Cu/Zn-SOD expression positive cells were observed in the hippocampus of ICV-STZ rats. BM supplementation significantly ameliorated all alterations induced by ICV-STZ in rats. The data suggest that ICV-STZ might cause its neurotoxic effects via the production of free radicals. Our study demonstrates that BM is a powerful antioxidant which prevents cognitive impairment, oxidative damage, and morphological changes in the ICV-STZ-infused rats. Thus, BM may have therapeutic value for the treatment of cognitive impairment.

New animal models of Alzheimer's disease that display insulin desensitization in the brain

Alzheimer's disease (AD) is a complex neurodegenerative disorder, which involves many underlying pathological processes. Recently, it has been demonstrated that AD also includes impairments of insulin signaling in the brain. Type 2 diabetes is a risk factor for AD, and AD and diabetes share a number of pathologies. The classical hallmarks of AD are senile plaques and neurofibrillary tangles, which consist of amyloid-β and hyperphosphorylated tau. Based on the two hallmarks, transgenic animal models of AD have been developed, which express mutant human genes of amyloid precursor protein, presenilin-1/2, and tau. It is likely that these mouse models are too limited in their pathology. In this work, we describe mouse models that model diabetes and show insulin signaling impairment as well as neurodegenerative pathologies that are similar to those seen in the brains of AD patients. The combination of traditional AD mouse models with induced insulin impairments in the brain may be a more complete model of AD. Interestingly, AD mouse models treated with drugs that have been developed to cure type 2 diabetes have shown impressive outcomes. Based on these findings, several ongoing clinical trials are testing long lasting insulin analogues or GLP-1 mimetics in patients with AD.

Clitoria ternatea ameliorated the intracerebroventricularly injected streptozotocin induced cognitive impairment in rats: behavioral and biochemical evidence

RATIONALE

Clitoria ternatea, commonly known as Aparajita, is used as Medhya rasayana in Ayurveda. The role of C. ternatea in experimental models of cognitive impairment is yet to be explored.

OBJECTIVES

The present study was designed to study the effect of aqueous and hydroalcoholic extracts of C. ternatea on biochemical and behavioral parameters related to cognitive impairment in in vitro and in vivo studies.

METHODS

In vitro free radical scavenging and enzyme-inhibitory (cholinesterase, glycogen synthase kinase-3-β, rho kinase, prolyl endopeptidase, catechol-O-methyl transferase, and lipoxygenase) activities of aqueous and hydroalcoholic extracts of C. ternatea plant were evaluated. Based on in vitro results, hydroalcoholic extract of C. ternatea (100, 300, and 500 mg/kg, p.o.) was selected for evaluation in intracerebroventricularly injected streptozotocin (STZ)-induced cognitive impairment in male Wistar rats. Behavioral assessment was performed at baseline and on the 14th, 21st, and 28th days after STZ injection using elevated plus maze, passive avoidance, Morris water maze, and photoactometer. Oxidative stress parameters (malondialdehyde, reduced glutathione, nitric oxide levels, and superoxide dismutase activity), cholinesterase activity, and rho kinase (ROCK II) expression were studied in cerebral cortex and hippocampus of rats' brain at the end of the study.

RESULTS

The hydroalcoholic extract possessed significantly more in vitro antioxidant and enzyme-inhibitory activities as compared to aqueous extract. The hydroalcoholic extract of C. ternatea prevented STZ-induced cognitive impairment dose dependently by reducing oxidative stress, cholinesterase activity, and ROCK II expression.

CONCLUSION

In vitro and in vivo results suggest the potential of hydroalcoholic extract of C. ternatea for treatment of cognitive deficit in neurological disorders.

Attenuation of oxidative damage-associated cognitive decline by Withania somnifera in rat model of streptozotocin-induced cognitive impairment

Oxidative stress is a critical contributing factor to age-related neurodegenerative disorders. Therefore, the inhibition of oxidative damage, responsible for chronic detrimental neurodegeneration, is an important strategy for neuroprotective therapy. Withania somnifera (WS) extract has been reported to have potent antioxidant and free radical quenching properties in various disease conditions. The present study evaluated the hypothesis that WS extract would reduce oxidative stress-associated neurodegeneration after intracerebroventricular injection of streptozotocin (ICV-STZ) in rats. To test this hypothesis, male Wistar rats were pretreated with WS extract at doses of 100, 200, and 300 mg/kg body weight once daily for 3 weeks. On day 22nd, the rats were infused bilaterally with ICV-STZ injection (3 mg/kg body weight) in normal saline while sham group received only saline. Two weeks after the lesioning, STZ-infused rats showed cognitive impairment in the Morris water maze test. The rats were sacrificed after 3 weeks of the lesioning for the estimation of the contents of lipid peroxidation, reduced glutathione, and activities of glutathione reductase, glutathione peroxidase, and catalase. Pretreatment with WS extract attenuated behavioral, biochemical, and histological alterations significantly in dose-dependent manner in the hippocampus and cerebral cortex of ICV-STZ-infused rats. These results suggest that WS affords a beneficial effect on cognitive deficit by ameliorating oxidative damage induced by streptozotocin in a model of cognitive impairment.

Amelioration of intracerebroventricular streptozotocin induced cognitive impairment by Evolvulus alsinoides in rats: in vitro and in vivo evidence

Evolvulus alsinoides, also known as Shankpushapi, is a commonly used traditional medicine for enhancing memory. We evaluated the in vitro free radical scavenging and enzymes [acetylcholinesterase, butyrylcholinestrase, glycogen synthase kinase-3-β (GSK-3-β), rho kinase (ROCK II), prolyl endopeptidase (PEP), catechol-O-methyl transferase (COMT) and lipoxygenase (LOX)] inhibitory activities of aqueous and hydro-alcoholic extracts of E. alsinoides. Hydro-alcoholic extract of E. alsinoides demonstrated more free radical scavenging activity as compared to aqueous extract. Hydro-alcoholic extract also showed higher cholinesterase, GSK-3-β, ROCK II, PEP, COMT and LOX enzyme inhibitory activities as compared to aqueous extract. Phytochemical analysis revealed more flavanoids in hydro-alcoholic extract as compared to aqueous extract but no significant difference in phenolic content of the two extracts was observed. Based on in vitro data, hydro-alcoholic extract (100, 300 and 500mg/kg, p.o.) was selected for in vivo study in intracerebroventricularly injected streptozotocin (STZ) induced cognitive impairment in male Wistar rats. Elevated plus maze, passive avoidance and Morris water maze were used for assessment of cognitive function on 14th, 21st and 28th day after STZ injection. Oxidative stress parameters (malondialdehyde, reduced glutathione, nitric oxide levels and superoxide dismutase activity), cholinergic dysfunction and rho kinase (ROCK II) expression were studied in cerebral cortex and hippocampus of rat brain at the end of the study. Hydro-alcoholic extract of E. alsinoides dose dependently prevented STZ induced cognitive impairment by reducing the oxidative stress, improving cholinergic function and preventing the increase in rho kinase expression. The results suggest an anti-Alzheimer potential of hydro-alcoholic extract of E. alsinoides.

Cerebral amyloid angiopathy in streptozotocin rat model of sporadic Alzheimer's disease: a long-term follow up study

Cerebral amyloid angiopathy is manifested as accumulation of amyloid β (Aβ) peptide in the wall of meningeal and cerebral arteries, arterioles and capillaries and is frequently found postmortem in sporadic Alzheimer's disease (sAD) patients. It is difficult to assess when and how cerebral amyloid angiopathy develops and progresses in humans in vivo, which is why animal AD models are used. Streptozotocin-intracerebroventricularly (STZ-icv) treated rats have been recently proposed as the model of sAD which develops insulin resistant brain state preceding Aβ pathology development. Vascular Aβ deposits in the brain of STZ-icv-treated rats (3 months old at the time of icv treatment) were visualized by Thioflavine-S staining, Congo red staining and Aβ immunohistochemistry. Thioflavine-S and Congo red staining revealed diffuse congophilic deposits in the wall of meningeal and cortical blood vessels both 6 and 9 months after the STZ-icv treatment. Preliminary Aβ1-42 and Aβ1-16 immunohistochemistry experiments showed positive staining in blood vessels 3 and 9 months after the STZ-icv treatment, respectively. Results suggest that cerebral amyloid angiopathy observed 6 and 9 months after the STZ-icv treatment seems to be a continuation and progression of the amyloid pathology observed already 3 months following the STZ-icv treatment in this non-transgenic sAD animal model.

Insulin-resistant brain state: the culprit in sporadic Alzheimer's disease?

Severe abnormalities in brain glucose/energy metabolism and insulin signaling have been documented to take a pivotal role in early sporadic Alzheimer's disease (sAD) pathology. Indeed, the "insulin-resistant brain state" has been hypothesized to form the core of the neurodegenerative events that occur in sAD. In this vein, intracerebroventricular administration of subdiabetogenic doses of streptozotocin (STZ) in rats can induce an insulin-resistant brain state, which is proposed as a suitable experimental model of sAD. This review highlights the involvement of disturbed brain insulin metabolism in sAD etiopathogenesis. Furthermore, current knowledge demonstrates that central STZ administration produces brain pathology and behavioral changes that resemble changes found in sAD patients. The STZ-intracerebroventricularly treated rat represents a promising experimental tool in this field by providing new insights concerning early brain alterations in sAD, which can be translated in novel etiopathogenic and therapeutic approaches in this disease.

Protective effect of quercetin against intracerebral streptozotocin induced reduction in cerebral blood flow and impairment of memory in mice

The aim of the present study is to investigate the effect of quercetin, a naturally occurring flavonoid, on cerebral blood flow (CBF), brain energy metabolism, memory impairment, oxidative stress and cholinergic dysfunction in brain following intracerebral (i.c.) streptozotocin (STZ) administration in mice. STZ (0.5mg/kg, i.c.) was administered twice at an interval of 48h. We found a significant reduction in CBF as measured by Laser Doppler Flowmetry (LDF). The brain energy metabolism was also altered as evidenced by significant reduction in brain ATP content. Daily treatment with quercetin (2.5, 5 and 10mg/kg, p.o.) starting from the first dose of STZ showed a dose-dependent restoration of CBF and ATP content. Further, quercetin prevented STZ induced memory impairment as assessed by Morris water maze and passive avoidance tests. Biochemical analysis revealed that STZ significantly increased malondialdehyde (MDA), nitrite and depleted glutathione (GSH) levels in the mice brain. Quercetin decreased oxidative and nitrosative stress as evidenced by a significant decrease in MDA, nitrite and increase in GSH levels. Quercetin also attenuated elevated acetylcholinesterase activity in the STZ-treated mice. Neither STZ (i.c.) nor quercetin showed any change in locomotor activity and blood glucose level. The present study demonstrates the beneficial effects of quercetin in improving CBF along with preventing memory impairment, oxidative stress, altered brain energy metabolism and cholinergic dysfunction caused by STZ in mice. Therefore, consumption of dietary stuff rich in quercetin should be encouraged to ward off dementia associated with vascular and neurodegenerative disorders.

Effect of chronic treatment of carvedilol on oxidative stress in an intracerebroventricular streptozotocin induced model of dementia in rats

Objectives

Oxidative stress is emerging as an important issue in the pathogenesis of dementia. This study was conducted to investigate the possible neuroprotective effects of carvedilol against streptozotocin induced behavioural alterations and oxidative damage in rats.

Methods

An intracerbroventricular cannula was implanted in the lateral ventricles of male Wistar rats. Various behavioural (locomotor activity, Morris water maze task) and biochemical parameters (lipid peroxidation, nitrate concentration, catalase, acetylcholinesterase, reduced glutathione and protein) were assessed.

Key findings

Intracerebroventricular administration of streptozotocin caused a significant memory deficit as evaluated in the Morris water maze task paradigms, and caused marked oxidative damage as indicated by significant increases in malondialdehyde and nitrite levels, and depletion of superoxide dismutase, catalase and reduced glutathione levels. It also caused a significant increase in acetylcholinesterase activity. Chronic administration of carvedilol (1 and 2 mg/kg, i.p.) for a period of 25 days starting 4 days before streptozotocin administration resulted in an improvement in memory retention, and attenuation of oxidative damage and acetylcholinesterase activity.

Conclusions

This study demonstrates the effectiveness of carvedilol in preventing cognitive deficits as well as the oxidative stress caused by intracerbroventicular administration of streptozotocin in rats. Carvedilol may have potential in the treatment of neurodegenerative diseases.

Candesartan improves memory decline in mice: involvement of AT1 receptors in memory deficit induced by intracerebral streptozotocin

The Renin-angiotensin system, besides blood pressure regulation, affects learning and memory as evidenced by improvement of cognition in hypertensive patients being treated with AT1 receptor blockers like candesartan. The present study examined the influence of candesartan on memory impairment induced by intracerebral streptozotocin (IC STZ 0.5 mg/kg) in mice. Candesartan (0.05 mg/kg and 0.1 mg/kg, i.p.) was given for 14 days following IC STZ administration. The dose of 0.1 mg/kg significantly improved latency period in passive avoidance test. Further, treatment with 0.1 mg/kg candesartan for 14 days significantly improved spatial memory in mice in water maze test also. In another group, after memory impairment in mice following IC STZ administration, memory improving effect of a 7 days treatment with 0.1 mg/kg candesartan lasted only for 3 subsequent days in water maze task. IC STZ increased oxidative stress but pretreatment with 0.1 mg/kg candesartan decreased oxidative stress as indicated by a decrease in MDA and increase in GSH. Further, candesartan decreased free radicals as evidenced by flow cytometry. IC STZ affected cholinergic system also by increasing acetylcholine esterase activity that was restored by pretreatment with 0.1 mg/kg candesartan. Locomotor activity and serum glucose level remained unaffected by candesartan treatment. These results suggest that AT1 receptors play a facilitatory role in STZ induced memory deficit and corroborate number of human studies that AT1 receptor blockers can be used therapeutically against cognitive decline in hypertensive patients.

The synthetic cannabinoid HU-210 attenuates neural damage in diabetic mice and hyperglycemic pheochromocytoma PC12 cells

Diabetic neuropathy (DN) is a common complication of diabetes mellitus resulting in cognitive dysfunction and synaptic plasticity impairment. Hyperglycemia plays a critical role in the development and progression of DN, through a number of mechanisms including increased oxidative stress. Cannabinoids are a diverse family of compounds which can act as antioxidative agents and exhibit neuroprotective properties. We investigated the effect of the synthetic cannabinoid HU-210 on brain function of streptozotocin (STZ)-induced diabetic mice. These animals exhibit hyperglycemia, increased cerebral oxidative stress and impaired brain function. HU-210, through a receptor independent pathway, alleviates the oxidative damage and cognitive impairment without affecting glycemic control. To study the neuroprotective mechanism(s) involved, we cultured PC12 cells under hyperglycemic conditions. Hyperglycemia enhanced oxidative stress and cellular injuries were all counteracted by HU-210-in a dose dependent manner. These results suggest cannabinoids might have a therapeutic role in the management of the neurological complications of diabetes.

Central insulin resistance as a trigger for sporadic Alzheimer-like pathology: an experimental approach

A growing body of evidence implicates impairments in brain insulin signaling in early sporadic Alzheimer disease (sAD) pathology. However, the most widely accepted hypothesis for AD aetiology stipulates that pathological aggregations of the amyloid beta (Abeta) peptide are the cause of all forms of Alzheimer's disease. Streptozotocin-intracerebroventricularly (STZ-icv) treated rats are proposed as a probable experimental model of sAD. The current work reviews evidence obtained from this model indicating that central STZ administration induces brain pathology and behavioural alterations resembling those in sAD patients. Recently, alterations of the brain insulin system resembling those in sAD have been found in the STZ-icv rat model and are associated with tau protein hyperphosphorylation and Abeta-like aggregations in meningeal vessels. In line with these findings the hypothesis has been proposed that insulin resistance in the brain might be the primary event which precedes the Abeta pathology in sAD.

Chronic administration of pioglitazone attenuates intracerebroventricular streptozotocin induced-memory impairment in rats

Memory impairment induced by intracerebroventricular (ICV) injection of streptozotocin (STZ) in rats is associated with impaired brain glucose and energy metabolism, oxidative stress and impaired cholinergic neurotransmission. Treatment with antioxidants and cholinergic agonists has been reported to produce beneficial effect in this model. However, no reports are available on drugs that improve glucose utilization and metabolism. In the present study, we evaluated the effects of pioglitazone on cognitive performance, oxidative stress and glucose utilization in ICV STZ injected rats (3 mg/kg, on day 1 and 3). Pioglitazone (10 and 30 mg/kg) was administered per oral (p.o.) for 14 days, starting 5 days prior to STZ injection. Cognitive performance was assessed using step-through passive avoidance and Morris water maze task. Malondialdehyde (MDA) and glutathione levels in brain were estimated as parameters of oxidative stress. Glucose utilization by brain was assessed as the amount of glucose consumed from the media by the brain. ICV STZ injected rats showed a severe deficit in learning and memory associated with increased MDA levels (+67.5%), decreased glutathione levels (-29.2%) and impaired cerebral glucose utilization (-44.4%). In contrast pioglitazone treatment improved cognitive performance, lowered oxidative stress and improved cerebral glucose utilization in ICV STZ rats. The present study demonstrates the beneficial effects of pioglitazone in the ICV STZ induced cognitive deficits, which can be exploited for the dementia associated with diabetes and age-related neurodegenerative disorder, where oxidative stress and impaired glucose and energy metabolism are involved.

The impact of diabetes on cognition: What can be learned from rodent models?

Diabetes mellitus is associated with modest impairments in cognition, particularly in the elderly. In addition, the risk of dementia is increased. We review herein studies in rodent models that may help to identify the mechanisms that underlie these adverse effects of diabetes on the brain. Abnormalities in learning and memory, synaptic plasticity, and glutamatergic neurotransmission have now been identified in a number of these models. In general, observations in models characterized by chronic hyperglycaemia and hypoinsulinaemia (referred to as models of type 1 diabetes) are quite consistent, and these models are being increasingly used to study the pathogenesis and to develop new treatments. However, results from models characterized by insulin resistance, hyperinsulinaemia, and modest hyperglycaemia (referred to as models of type 2 diabetes) are much more variable. Moreover, the possible interaction between diabetes and aging has not been examined in sufficient detail. Because clinically relevant cognitive deficits mainly occur in elderly patients with type 2 diabetes, the challenge for researchers in this field will be to further develop adequate models.

Gene expression of alpha-endosulfine in the rat brain: correlative changes with aging, learning and stress

Endosulfine (EDSF) belongs to a highly conserved cAMP-regulated phosphoprotein (ARPP) family and was first isolated from ovine brain as a possible endogenous ligand for sulfonylurea receptors. To explore its involvement in brain functions, we investigated regional distribution of alpha-EDSF gene expression in the rat brain, and its regulation under physiological and pathological conditions. The majority of alpha-EDSF gene was expressed in the pyramidal neurons, which represent the principal excitatory neurons in various brain regions. Down-regulation of alpha-EDSF mRNA was detected in the rat hippocampus during long-term memory consolidation following a spatial learning experience, whereas swimming-related stress caused persistent up-regulation of alpha-EDSF gene expression in several brain regions. These changes, however, were absent from brains of diabetic rats that were subjected to the same behavioral treatments. Intracerebroventricular injection of streptozocin with a toxic dose induced severe learning deficits and brain structure alteration accompanied by a massive increase of alpha-EDSF mRNA in the somatosensory cortex. These results suggest that alpha-EDSF gene expression is differentially regulated by distinct brain processes involving excitatory neuronal activities.

Effect of Centella asiatica on cognition and oxidative stress in an intracerebroventricular streptozotocin model of Alzheimer's disease in rats

1. Centella asiatica, an Indian medicinal plant, has been described as possessing central nervous system activity, such as improving intelligence. In addition, we have demonstrated that C. asiatica has cognitive-enhancing and anti-oxidant properties in normal rats. Oxidative stress or an impaired endogenous anti-oxidant mechanism is an important factor that has been implicated in Alzheimer's disease (AD) and cognitive deficits seen in the elderly. 2. Intracerebroventricular (i.c.v.) streptozotocin (STZ) in rats has been likened to sporadic AD in humans and the cognitive impairment is associated with free radical generation in this model. Therefore, in the present study, the effect of an aqueous extract of C. asiatica (100, 200 and 300 mg/kg for 21 days) was evaluated in i.c.v. STZ-induced cognitive impairment and oxidative stress in rats. 3. Male Wistar rats were injected with STZ (3 mg/kg, i.c.v.) bilaterally on the days 1 and 3. Cognitive behaviour was assessed using passive avoidance and elevated plus-maze paradigms on the days 13, 14 and 21. Rats were killed on the day 21 for estimation of oxidative stress parameters (malondialdehyde (MDA), glutathione, superoxide dismutase and catalase) in the whole brain upon completion of the behavioural task. 4. Rats treated with C. asiatica showed a dose-dependent increase in cognitive behaviour in both paradigms. A significant decrease in MDA and an increase in glutathione and catalase levels were observed only in rats treated with 200 and 300 mg/kg C. asiatica. 5. The present findings indicate that an aqueous extract of C. asiatica is effective in preventing the cognitive deficits, as well as the oxidative stress, caused by i.c.v. STZ in rats.

Neuroprotective effects of novel cholinesterase inhibitors derived from rasagiline as potential anti-Alzheimer drugs

TV3326, (N-propargyl-(3R)-aminoindan-5-yl-ethyl,methyl carbamate) was prepared in order to combine the neuroprotective effects of rasagiline, a selective inhibitor of monoamine oxidase (MAO)-B with the cholinesterase (ChE) inhibitory activity of rivastigmine as a potential treatment for Alzheimer's disease. The study reported here examined the neuroprotective effects of TV3326 against various insults in vitro and in vivo. TV3326 caused a dose related (10-500 microM) reduction in death induced in NGF differentiated rat pheochromocytoma (PC12) cells by 3-4 hour exposure to oxygen-glucose deprivation. A single s.c. injection of TV3326 given five minutes after closed head injury in mice significantly reduced the cerebral edema, and accelerated the recovery of motor function and spatial memory several days later. Unilateral icv injection of streptozotocin (STZ) 1.5 mg in rats, caused specific damage to myelinated neurones in the fornix and corpus callosum accompanied by microgliosis. Three bilateral injections of STZ, 0.25 mg each, caused more widespread damage, and a marked impairment in spatial memory. Chronic oral treatment with TV3326 (75 mumols/kg) reduced the neuronal damage and microgliosis and almost completely prevented the memory impairment. The neuroprotective effect in PC12 cells may be due to a combination of ChE inhibition and antiapoptotic activity. The latter does not result from ChE inhibition. It is associated with the presence of the propargyl group, since it occurs with other propargylamines that do not inhibit MAO, but not with drugs that inhibit only ChE.

Cognitive performance and biochemical markers in septum, hippocampus and striatum of rats after an i.c.v. injection of streptozotocin: a correlation analysis

In the present study we evaluated the effects of an intracerebroventricular injection of streptozotocin on cognitive behavior and biochemical markers in the brain of middle-aged Wistar rats. Intracerebroventricular injected streptozotocin has previously been reported to decrease the central metabolism of glucose. We found that streptozotocin-treated rats showed an impaired cognitive performance in the delayed non-matching to position task and the Morris water escape task. Glial fibrillary acidic protein, an indicator of reactive astroglial changes, was measured in three different (soluble, Triton X-100 soluble and crude cytoskeletal) protein fractions and its content in the fractions of the septum, hippocampus and striatum of streptozotocin-treated rats was increased. Furthermore, the glial fibrillary acidic protein response of each protein fraction to streptozotocin treatment appeared to be differently regulated. In streptozotocin-treated rats the choline acetyltransferase activity was decreased in the hippocampus only, which was correlated with the hippocampal glial fibrillary acidic protein contents of all three hippocampal protein fractions, thus suggesting that the cholinergic deficit is a consequence of direct damage to the hippocampus. The cognitive deficits in both tasks were related to the increased glial fibrillary acidic protein contents, especially of the soluble and cytoskeletal fraction, and the decreased choline acetyltransferase activity in the hippocampus. Taken together, these findings indicate that it is important to take into account which protein fraction has been used for measuring the glial fibrillary acidic protein response to a stressor. Furthermore, intracerebroventricular injected streptozotocin may provide a relevant model for studying neurodegenerative changes due to a metabolic insufficiency and testing neuroprotective effects of substances.

Facilitation of a distributed shuttle-box conditioning with posttraining intracranial self-stimulation in old rats

Old Wistar rats (16-17 months) were trained in a two-way active avoidance task for 5 consecutive days (10 trials/day). Immediately after each training session a lateral hypothalamic intracranial self-stimulation session (ICSS group) or a sham-treatment session (Control group) was given to the animals. Long-term retention was tested 7 days after the last acquisition session. ICSS treatment led to a significant improvement in acquisition. In the long-term retention session the level of avoidance in both groups was similar to that achieved in the last acquisition session, although differences among groups failed to reach statistical significance. These results are compared with those obtained in previous experiments with young adult rats. While ICSS facilitated the process of acquisition in both young and old rats (however, it was much more powerful in young animals), further experiments are needed to elucidate whether this effect is long-lasting in old rats, as occurs in young adult subjects.

Potential role of environmental genotoxic agents in diabetes mellitus and neurodegenerative diseases

Epidemiological data suggest that environmental genotoxins are risk factors for some forms of diabetes mellitus and neurodegenerative diseases. The present commentary focuses on mechanisms involved in genotoxin-induced pancreatic beta-cell and neuronal damage. These two cell types seem to share a similar vulnerability to different forms of DNA damage, and the long-term consequences of repeated genotoxic insults to post-mitotic neurons or slowly proliferating beta-cells remain to be clarified. One intriguing possibility is that genotoxins could act as "slow" toxins in these cells, triggering a cascade of cellular events, which culminates in progressive cell dysfunction and loss. Indeed, exposure to mutagenic nitroso agents such as streptozotocin and cycasin induces long-lasting damage to both beta -cells and neurons. These data on cycasin, a toxin obtained from the cycad plant (Cycas spp.), are of special interest, since this agent may be implicated in both amyotrophic lateral sclerosis/Parkinson dementia complex and diabetes mellitus in the western Pacific area. Future studies are required to sort out the interactions between different genotoxic agents, viral infections, and cellular repair mechanisms on cellular survival and function. Moreover, further epidemiological studies are needed to clarify the role of N-nitrosoureas in diabetes mellitus and neurodegenerative diseases in populations with different genetic backgrounds. Answers to these questions may provide useful information on the pathogenesis of these devastating diseases, and open the possibility for their primary prevention.

Brain enzyme activities after intracerebroventricular injection of streptozotocin in rats receiving acetyl-L-carnitine

Intracerebroventricular (i.c.v.) injection of streptozotocin has been introduced as a means to inhibit glucose utilization in the rat brain, and to induce changes in neurotransmitter systems and behavior which resemble those seen in Alzheimer's disease. In this study, enzyme activities previously investigated in Alzheimer's disease (peptidases, dehydrogenases and acetyltransferases) were measured in the septum and hippocampus of control and streptozotocin-treated rats. Streptozotocin-treated rats receiving acetyl-L-carnitine were also included in the experiments, to assess possible neuroprotective effects of this substance. All enzyme activities in the septum were affected by streptozotocin, with the exception of choline acetyltransferase activity. By contrast, choline acetyltransferase activity was the only enzyme activity affected in the hippocampus. The weight of the septum was reduced in streptozotocin-treated animals. These findings indicate that i.c.v. injection of streptozotocin causes septal damage and enzymatic changes that do not closely resemble those seen in Alzheimer's disease, which are more specific. Acetyl-L-carnitine partly prevented this damage, as reflected by an attenuation of the streptozotocin-induced decrease in hippocampal choline acetyltransferase activity. This finding indicates that streptozotocin-treated rats may be valuable to test possible neuroprotective effects of drugs.

Spatial discrimination learning and choline acetyltransferase activity in streptozotocin-treated rats: effects of chronic treatment with acetyl-L-carnitine

Treatment of rats with i.c.v. injected streptozotocin (STREP) may provide a relevant model of neurodegeneration that is induced by a decrease in the central metabolism of glucose. Acetyl-L-carnitine (ALCAR) enhances the utilization of alternative energy sources and by such a mechanism of action ALCAR could antagonize the effects of STREP treatment. In this study the effects of chronic treatment with ALCAR were evaluated on spatial discrimination learning in the Morris task and choline acetyltransferase (ChAT) activity of middle-aged STREP-treated rats. Chronic treatment with ALCAR attenuated both the STREP-induced impairment in spatial bias and the decrease in hippocampal ChAT activity. These findings indicate that ALCAR treatment has a neuroprotective effect, although further studies are needed to characterize the mechanism of action of ALCAR in this model.