The role of nitric oxide in spatial memory stages, hippocampal ERK and CaMKII phosphorylation

Nanocurcumin prevents memory impairment, hippocampal apoptosis, Akt and CaMKII-α signaling disruption in the central STZ model of Alzheimer's disease in rat

The central route of streptozotocin (STZ) administration has been introduced as a rat model of sporadic Alzheimer's disease (AD). Curcumin was suggested to possess possible neuroprotective effects, which may be profitable in AD. However, the low bioavailability of curcumin hinders its beneficial effects in clinical studies. Earlier studies suggested that a bovine serum albumin-based nanocurcumin, produces superior neuroprotective effects compared to natural curcumin. In the present study, the protective effect of nanocurcumin in rat model of central STZ induced memory impairment was assessed. In addition, due to the importance of the hippocampus in memory, the amounts of hippocampal active caspase-3, Akt, and CaMKII-α were evaluated. Adult male Wistar rats weighing 250-300 g were used. STZ (icv) was injected during days 1 and 3 (3 mg/kg in divided), and nanocurcumin or curcumin 50 mg/kg/oral gavage was administered daily during days 4-14. Morris water maze training was performed on days 15-17, and the retention memory test was achieved on the 18th day. Following memory assessment, the rats were sacrificed and the hippocampi were used to assess caspase-3 cleavage, Akt, and CaMKII-α signaling. The findings revealed that nanocurcumin ingestion (but not natural curcumin) in the dose of 50 mg/kg was capable to prevent the impairment of water maze learning and memory induced by central STZ. Molecular assessments indicated that STZ treatment increased the caspase-3 cleavage in the hippocampus while deactivating Akt and CaMKII-α. Nanocurcumin reduced caspase-3 cleavage to a non-significant level compared to control group and restored Akt and CaMKII-α within the hippocampus while natural curcumin exerted no significant effect. These findings might suggest that nanocurcumin can restore memory deficit, hippocampal apoptosis as well as Akt and CaMKII-α signaling disruption associated with brain insulin resistance.

Cholinergic deficit induced memory retrieval impairment and hippocampal CaMKII-alpha deregulation is counteracted by sub-chronic agmatine treatment in mice

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative disease characterized by brain cholinergic dysfunction. Evidence suggests the impairment of memory retrieval phase in AD. It has been shown that CaMKII-α expressing neurons are selectively reduced in the hippocampus in AD brains. The present study aimed to investigate the effect of scopolamine on the memory retrieval phase and the hippocampal CaMKII-α signaling. In addition, the effect of sub-chronic administration of agmatine against scopolamine induced memory and possible hippocampal CaMKII-α deregulation was investigated in mice. Adult male NMRI mice were administered with agmatine at the doses of 5, 10, 20, 30 and 40 mg/kg/i.p. or saline for 11 days. Acquisition and retrieval tests of passive avoidance task were performed on days 10 and 11, respectively (30 Min following agmatine treatment). Scopolamine (1 mg/kg/i.p.) was administered once, 30 Min before retrieval test. Upon completion of the behavioral tasks, the hippocampi were isolated for western blot analysis to detect the phosphorylated and total levels of CaMKII-α and beta actin proteins. The results showed that scopolamine induced memory retrieval deficit and decreased the phosphorylated level of hippocampal CaMKII-α. Sub-chronic agmatine treatment at the dose of 40 mg/kg prevented scopolamine induced memory retrieval deficit and restored the level of hippocampal phosphorylated CaMKII-α. This study suggests that hippocampal CaMKII-α might play a role in scopolamine induced amnesia and sub-chronic agmatine prevents the impairing effect of scopolamine on the retrieval phase of memory and the phosphorylation of hippocampal CaMKII-α protein.

Neuronal Nitric Oxide Synthase and Post-Translational Modifications in the Development of Central Nervous System Diseases: Implications and Regulation

In the Central Nervous System (CNS), Nitric Oxide (NO) is mainly biosynthesized by neuronal Nitric Oxide Synthase (nNOS). The dysregulated activation of nNOS in neurons is critical in the development of different conditions affecting the CNS. The excessive production of NO by nNOS is responsible for a number of proteins' post-translational modifications (PTMs), which can lead to aberrant biochemical pathways, impairing CNS functions. In this review, we briefly revise the main implications of dysregulated nNOS in the progression of the most prevalent CNS neurodegenerative disorders, i.e., Alzheimer's disease (AD) and Parkinson's disease, as well as in the development of neuronal disorders. Moreover, a specific focus on compounds able to modulate nNOS activity as promising therapeutics to tackle different neuronal diseases is presented.

Agmatine prevents the memory impairment and the dysfunction of hippocampal GSK-3β and ERK signaling induced by aluminum nanoparticle in mice

The growing usage of aluminum nanoparticles (Al-NP) and their exposure may influence body function. Considering the proposed relationship between Al and the pathogenesis of Alzheimer's disease and the concern about the effect of this nanoparticle on brain health and cognitive function, the use of neuroprotective agents might be helpful. According to the reported neuroprotective effects of agmatine, in the present study, the possible protective effect of agmatine was assessed in mice model of Al-NP-induced memory impairment. In addition, due to the roles of hippocampal Glycogen synthase kinase-3 beta (GSK-3β) and ERK signaling in memory and its disorders, these pathways were also investigated. Al-NP (10 mg/kg/p.o.) with/without agmatine (5 or 10 mg/kg/i.p.) was administered to adult male NMRI mice for 5 days. Novel object recognition (NOR) test session was used to assess cognitive function. Following the behavioral assessments, the hippocampi were used to determine the phosphorylated and total levels of GSK-3β and ERK as well as GAPDH using western blot analysis. The results showed that Al-NP impaired NOR memory in mice while agmatine 10 mg/kg prevented the memory deficit induced by Al-NP. Furthermore, Al-NP activated GSK-3β as well as ERK signals within the hippocampus while agmatine prevented the effects of Al-NP on GSK-3β and ERK signals within the hippocampus. Besides supporting the neuroprotective effects of agmatine, these findings suggest the possibility of the connection of hippocampal GSK-3β and ERK signaling in the neuroprotective effect of this polyamine against Al-NP.

Behind the scenes: Are latent memories supported by calcium independent plasticity?

N-methyl-D-aspartate receptors (NMDARs) can be considered to be the de facto "plasticity" receptors in the brain due to their central role in the activity-dependent modification of neuronal morphology and synaptic transmission. Since the 1980s, research on NMDARs has focused on the second messenger properties of calcium and the downstream signaling pathways that mediate alterations in neural form and function. Recently, NMDARs were shown to drive activity-dependent synaptic plasticity without calcium influx. How this "nonionotropic" plasticity occurs in vitro is becoming clearer, but research on its involvement in behavior and cognition is in its infancy. There is a partial overlap in the downstream signaling molecules that are involved in ionotropic and nonionotropic NMDAR-dependent plasticity. Given this, and prior studies of the cognitive impacts of ionotropic NMDAR plasticity, a preliminary model explaining how NMDAR nonionotropic plasticity affects learning and memory can be established. We hypothesize that nonionotropic NMDAR plasticity takes part in latent memory encoding in immature rodents through nonassociative depression of synaptic efficacy, and possibly shrinking of dendritic spines. Further, the late postnatal alteration in NMDAR composition in the hippocampus appears to reduce nonionotropic signaling and remove a restriction on memory retrieval. This framework substantially alters the canonical model of NMDAR involvement in spatial cognition and hippocampal maturation and provides novel and exciting inroads for future studies.

The effects of subchronic agmatine on passive avoidance memory, anxiety-like behavior and hippocampal Akt/GSK-3β in mice

Agmatine, a polyamine derived from l-arginine, has been suggested to modulate memory. However, the available evidence regarding the effect of agmatine on the memory of intact animals is contradictory. This study aimed to assess the dose-response effect of subchronic agmatine on passive avoidance memory and anxiety-like parameters of elevated plus maze in adult intact mice. Furthermore, considering the roles of Akt/GSK-3β signaling pathway in memory and Alzheimer's disease, the hippocampal contents of phosphorylated and total forms of Akt and GSK-3β proteins were determined using the western blot technique. Agmatine was administered intraperitoneally at the doses of 10, 20, 30, 40 and 80 mg/kg/daily to adult male NMRI mice for 10 days after which the behavioral assessments were performed. Upon completion of the passive avoidance test, the hippocampi were removed for western blot analysis to detect the phosphorylated and total levels of Akt and GSK-3β proteins. Results showed the biphasic effect of agmatine on passive avoidance memory; in lower doses (10, 20 and 30 mg/kg), agmatine impaired memory whereas in higher ones (40 and 80 mg/kg) improved it. Though, agmatine in none of the doses affected animals' anxiety-like parameters in an elevated plus maze. Moreover, the memory-improving doses of agmatine augmented Akt/GSK-3β pathway. This study showed the biphasic effect of agmatine on passive avoidance memory and an augmentation of hippocampal Akt/GSK-3β signaling pathway following the memory-improving doses of this polyamine.

Impaired spatial memory in adult vitamin D deficient BALB/c mice is associated with reductions in spine density, nitric oxide, and neural nitric oxide synthase in the hippocampus

Vitamin D deficiency is prevalent in adults and is associated with cognitive impairment. However, the mechanism by which adult vitamin D (AVD) deficiency affects cognitive function remains unclear. We examined spatial memory impairment in AVD-deficient BALB/c mice and its underlying mechanism by measuring spine density, long term potentiation (LTP), nitric oxide (NO), neuronal nitric oxide synthase (nNOS), and endothelial NOS (eNOS) in the hippocampus. Adult male BALB/c mice were fed a control or vitamin D deficient diet for 20 weeks. Spatial memory performance was measured using an active place avoidance (APA) task, where AVD-deficient mice had reduced latency entering the shock zone compared to controls. We characterised hippocampal spine morphology in the CA1 and dentate gyrus (DG) and made electrophysiological recordings in the hippocampus of behaviourally naïve mice to measure LTP. We next measured NO, as well as glutathione, lipid peroxidation and oxidation of protein products and quantified hippocampal immunoreactivity for nNOS and eNOS. Spine morphology analysis revealed a significant reduction in the number of mushroom spines in the CA1 dendrites but not in the DG. There was no effect of diet on LTP. However, hippocampal NO levels were depleted whereas other oxidation markers were unaltered by AVD deficiency. We also showed a reduced nNOS, but not eNOS, immunoreactivity. Finally, vitamin D supplementation for 10 weeks to AVD-deficient mice restored nNOS immunoreactivity to that seen in in control mice. Our results suggest that lower levels of NO and reduced nNOS immunostaining contribute to hippocampal-dependent spatial learning deficits in AVD-deficient mice.

Comprehensive Analysis of Mouse Hippocampal Lysine Acetylome Mediated by Sea Cucumber Peptides Preventing Memory Impairment

Memory impairment is becoming a potential health issue with the delicacy of diet and social stress. Sea cucumber peptides (SCP) prevent memory impairment, as previously reported. In this study, further research was performed using hippocampal lysine-acetylome to explore molecular regulation mechanisms. C57BL/6 mice were treated with scopolamine via intraperitoneal injection to simulate memory impairment. To determine the influence of SCP on the total acetylated-protein level of the hippocampus, acetylated-proteomics was performed. SCP increased the acetylation level of histone (H3 and H4). Meanwhile, for non-histones, the differentially acetylated proteins were involved in multiple memory-related pathways, as shown by KEGG enrichment analysis. Additionally, long-term potentiation was confirmed by western blotting. Finally, a combined analysis of proteome and lysine acetylome revealed that SCP contributed to synaptic vesicle cycle regulation and dopamine metabolism. Consequently, our findings revealed that SCP was potentially neuroprotective by regulating post-transcriptional hippocampal protein acetylation.

Nanomicellar curcuminoids attenuates renal ischemia/reperfusion injury in rat through prevention of apoptosis and downregulation of MAPKs pathways

Renal ischemia/reperfusion (I/R) injury is considered as a main problem in clinical practice. Curcuminoids, the active constituents of turmeric, seem to have potential renoprotective effects. However, the poor bioavailability of curcuminoids restricts their therapeutic effects. In the present study, the effect of nanomicellar curcuminoids (NC) treatment on renal function, histology, total antioxidant capacity (TAC), total oxidative stress (TOS), caspase-3 level as well as mitogen activated protein kinases (MAPKs: JNK, p38 and ERK) phosphorylation were evaluated following renal I/R. Adult male Sprague-Dawley rats were administered NC at the dose of 25 mg/kg 1 h before renal ischemia induction. The animals were subjected to bilateral renal ischemia for 60 min and reperfusion for 24 h. Subsequently, blood urea nitrogen (BUN), creatinine (Cr), renal histopathology, TAC, TOS, and oxidative stress index, cleaved caspase-3 level, Bax and MAPKs signaling were evaluated. The results indicated that NC pretreatment at the dose of 25 mg/kg significantly improved renal function as well as histolopatholgical damages. Moreover, NC reduced the level of renal oxidative stress, cleaved caspase-3 and Bax (as the proapoptotic proteins) and suppressed the activated Jun N-terminal Kinase (JNK), p38 and extracellular receptor kinase (ERK) signaling induced by renal I/R. The findings of the current study indicate that NC might prevent the injury induced by renal I/R through suppression of oxidative stress, apoptosis and MAPKs pathways.

Effects of sub-chronic caffeine ingestion on memory and the hippocampal Akt, GSK-3β and ERK signaling in mice

Caffeine, one of the most widely consumed psychoactive substance in the world, has been shown to affect mood, memory, alertness, and cognitive performance. This study aimed to assess the effect of sub-chronic oral gavage of caffeine on memory and the phosphorylation levels of hippocampal Akt (protein kinase B), GSK-3β (Glycogen Synthase Kinase-3beta) and ERK (extracellular signal-regulated kinase) in mice. Adult male NMRI mice were administered with caffeine at the doses of 0.25, 0.5, 0.75 and 1.5 mg/kg/oral gavage for 10 days before behavioral assessments. Upon completion of the behavioral tasks, the hippocampi were isolated for western blot analysis to detect the phosphorylated and total levels of Akt, GSK-3β and ERK proteins. The results showed that sub-chronic caffeine ingestion at the dose of 0.5 mg/kg improves memory in mice both in passive avoidance and novel object recognition tasks. Furthermore, this memory enhancing dose of caffeine elevated the ratios of phosphorylated to total contents of hippocampal Akt, GSK-3β and ERK. This study suggests that sub-chronic low dose of caffeine improves memory and increases the phosphorylation of hippocampal Akt, GSK-3β and ERK proteins.

Exercise-induced Nitric Oxide Contributes to Spatial Memory and Hippocampal Capillaries in Rats

Exercise has been argued to improve cognitive function in both humans and rodents. Angiogenesis significantly contributes to brain health, including cognition. The hippocampus is a crucial brain region for cognitive function. However, studies quantifying the capillary changes in the hippocampus after running exercise are lacking. Moreover, the molecular details underlying the effects of running exercise remain poorly understood. We show that endogenous nitric oxide contributes to the beneficial effects of running exercise on cognition and hippocampal capillaries. Four weeks of running exercise significantly improved spatial memory ability and increased the number of capillaries in the cornu ammonis 1 subfield and dentate gyrus of Sprague-Dawley rats. Running exercise also significantly increased nitric oxide synthase activity and nitric oxide content in the rat hippocampus. After blocking the synthesis of endogenous nitric oxide by lateral ventricular injection of NG-nitro-L-arginine methyl ester, a nonspecific nitric oxide synthase inhibitor, the protective effect of running exercise on spatial memory was eliminated. The protective effect of running exercise on angiogenesis in the cornu ammonis 1 subfield and dentate gyrus of rats was also absent after nitric oxide synthase inhibition. Therefore, during running excise, endogenous nitric oxide may contribute to regulating spatial memory ability and angiogenesis in cornu ammonis 1 subfield and dentate gyrus of the hippocampus.

Effect of carbamylated erythropoietin Fc fusion protein (CEPO-Fc) on learning and memory impairment and hippocampal apoptosis induced by intracerebroventricular administration of streptozotocin in rats

Intracerebroventricular (icv) administration of streptozotocin (STZ) has been used as a metabolic model of sporadic Alzheimer's disease (AD). Erythropoietin (EPO) possesses neuroprotective and memory-improving effects, which might be advantageous in treating different characteristics of AD. Nevertheless, the hematopoietic effect of EPO has hindered its application as a neuroprotective agent. Previous studies have shown that a new Epo derivative called carbamylated Erythropoietin-Fc (CEPO-Fc), yield noticeable neuroprotective effects without affecting hematopoiesis. In this study, the neuroprotective effects of CEPO-Fc on icv-STZ induced memory impairment and hippocampal apoptosis were examined. Adult male Wistar rats weighing 250-300 g were used. STZ was administered on days 1 and 3 (3 mg/kg in divided doses/icv), and CEPO-Fc was administered at the dose of 5000 IU/ip/daily during days 4-14. The animals were trained in Morris water maze during days 15-17, and the memory retention test was performed on the 18th day. Following behavioral studies, the animals were sacrificed and their hippocampi isolated to determine the amounts of cleaved caspase-3 (the landmark of apoptosis). The results showed that CEPO-Fc treatment at the dose of 5000 IU/kg/ip was able to prevent the learning and memory deficit induced by icv-STZ. Western blot analysis revealed that STZ prompted the cleavage of caspase-3 in the hippocampus while pretreatment with CEPO-Fc significantly reduced the cleavage of this protein. Collectively, our findings suggest that CEPO-Fc could restore STZ-induced learning and memory impairment as well as apoptosis in the hippocampal region in a rat model of sporadic AD induced by icv-STZ.

Modulation of AMPA Receptors by Nitric Oxide in Nerve Cells

Nitric oxide (NO) is a gaseous molecule with a large number of functions in living tissue. In the brain, NO participates in numerous intracellular mechanisms, including synaptic plasticity and cell homeostasis. NO elicits synaptic changes both through various multi-chain cascades and through direct nitrosylation of targeted proteins. Along with the N-methyl-d-aspartate (NMDA) glutamate receptors, one of the key components in synaptic functioning are α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors—the main target for long-term modifications of synaptic effectivity. AMPA receptors have been shown to participate in most of the functions important for neuronal activity, including memory formation. Interactions of NO and AMPA receptors were observed in important phenomena, such as glutamatergic excitotoxicity in retinal cells, synaptic plasticity, and neuropathologies. This review focuses on existing findings that concern pathways by which NO interacts with AMPA receptors, influences properties of different subunits of AMPA receptors, and regulates the receptors’ surface expression.

Sub-chronic oral cinnamaldehyde treatment prevents scopolamine-induced memory retrieval deficit and hippocampal Akt and MAPK dysregulation in male mice

Objectives: Cholinergic system dysfunction was found to play a key role in Alzheimer's disease (AD) pathogenesis. Therefore, the animal model of scopolamine-induced amnesia has been widely used in AD researches. Cinnamon, as a spice commonly used in cuisine, has been shown to exert some therapeutic effects. The most abundant compound in cinnamon is cinnamaldehyde which recently was shown to exert several neuroprotective effects in animal models. Therefore, this study aimed to assess whether cinnamaldehyde has the potency to prevent memory retrieval impairment and hippocampal protein kinase B (Akt) and MAPK (extracellular signal-regulated kinase (ERK)) alterations induced by scopolamine in mice.Methods: Adult male mice were pretreated with cinnamaldehyde (12.5, 25, 40 and 100 mg/kg/oral gavage) 10 days before training. The training of passive avoidance task was performed on the 10^th day and a memory retention test was done 24 h later. Scopolamine (1 mg/kg) was injected intraperitoneally, 30 min before the retention test to induce memory retrieval deficit. At the complement of the behavioral experiments, the hippocampi were isolated for western blot analysis to assess the phosphorylated and total levels of hippocampal MAPK and Akt proteins.Results: The results showed that cinnamaldehyde pretreatment at the dose of 100 mg/kg significantly prevented the amnesic effect of scopolamine. Furthermore, cinnamaldehyde prevented scopolamine induced dysregulations of hippocampal MAPK and Akt.Discussion: The results of the present study revealed that oral sub-chronic cinnamaldehyde administration has the capability to prevent memory retrieval deficit induced by cholinergic blockade and restores hippocampal MAPK and Akt dysregulations.

Ellagic acid prevents dementia through modulation of PI3-kinase-endothelial nitric oxide synthase signalling in streptozotocin-treated rats

Ellagic acid (EGA)-enriched dietary supplements are widely acclaimed, owing to its versatile bioactivities. Previously, we reported that chronic administration of EGA prevented the impairment of cognitive abilities in rats using the intracerebroventricular-administered streptozotocin (STZ-ICV) model of Alzheimer's disease. Impairment of phosphoinositide 3 (PI3)-kinase-regulated endothelial nitric oxide synthase (eNOS) activity by central administration of STZ in rodents instigates dementia. The aim of the present study was to delineate the role of PI3-kinase-eNOS activity in the prevention of STZ-ICV-induced memory dysfunctions by EGA. The Morris water maze and elevated plus maze tests were conducted, and brain oxidative stress markers (TBARS, GSH, SOD, CAT), nitrite, acetylcholinesterase (AChE), LDH, TNF-α and eNOS were quantified. Administration of EGA (35 mg/k, p.o.) for 4 weeks daily attenuated the STZ-ICV (3 mg/kg)-triggered increase of brain oxidative stress, nitrite and TNF-α levels; AChE and LDH activity; and decline of brain eNOS activity. The memory restoration by EGA in STZ-ICV-treated rats was conspicuously impaired by N(G)-nitro-L-arginine methyl ester (L-NAME) (20 mg/kg, 28 days) and wortmannin (5 μg/rat; ICV) treatments. Wortmannin (PI3-kinase inhibitor) and L-NAME groups manifested elevated brain oxidative stress, TNF-α content and AChE and LDH activity and diminished nitrite content. L-NAME (arginine-based competitive eNOS inhibitor) enhanced the eNOS expression (not activity) whereas wortmannin reduced the brain eNOS levels in EGA- and STZ-ICV-treated rats. However, the L-NAME group exhibited superior cognitive abilities in comparison to the wortmannin group. It can be concluded that EGA averted the memory deficits by precluding the STZ-ICV-induced loss of PI3-kinase-eNOS signalling in the brain of rats.

Selective cephalic upregulation of p-ERK, CamKII and p-CREB in response to glyceryl trinitrate infusion

Background A common characteristic of migraine-inducing substances is that they cause headache and no pain in other areas of the body. Few studies have compared pain mechanisms in the trigeminal and spinal systems and, so far, no major differences have been noted. We compared signalling molecules in the trigeminal and spinothalamic system after infusion of the migraine-provoking substance glyceryltrinitrate. Method A catheter was placed in the femoral vein of rats and one week later glyceryltrinitrate 4 µg/kg/min was infused for 20 min. Protein expression in the dura mater, trigeminal ganglion, nucleus caudalis, dorsal root ganglion and the dorsal horn of the thoracic spinal cord was analysed at different time points using western blotting and immunohistochemistry. Results Glyceryltrinitrate caused a threefold increase in expression of phosphorylated extracellular signal-regulated kinases at 30 min in the dura mater and nucleus caudalis ( P < 0.05) and at 2 h in the trigeminal ganglion with very few expressions in the dorsal root ganglion. In the nucleus caudalis, expression of phosphorylated extracellular signal-regulated kinases and Cam KII increased 2.6-fold and 3.2-fold, respectively, at 2 h after glycerytrinitrate infusion ( P < 0.01). p-CREB/ATF-1 upregulation was observed only at 30 min ( P < 0.05) in the nucleus caudalis. None of these markers showed increased expression in the regions of thoracic spinal cord dorsal horn. Conclusion The dura, trigeminal ganglion and nucleus caudalis are activated shortly after glycerytrinitrate infusion with long-lasting expression of phosphorylated extracellular signal-regulated kinases observed in the nucleus caudalis. These activations were not observed at the spinal level.

Caffeic acid phenethyl ester rescued streptozotocin-induced memory loss through PI3-kinase dependent pathway

The present study was undertaken to elucidate the role of PI3-kinase signaling in memory enhancing potential of caffeic acid phenethyl ester (CAPE) against cognitive defects in rats after centrally administered streptozotocin as a model of Alzheimer's disease. The Morris water maze and elevated plus maze paradigms showed profound loss of memory in adult Wistar rats (180-200 g) injected with streptozotocin (3 mg/kg) bilaterally (STZ-ICV) on day 1 and 3. Intraperitoneal administration of CAPE (6 mg/kg, i.p., 28 days) attenuated STZ-ICV triggered memory loss in rats. Treatment with PI3-kinase inhibitor (wortmannin, 5 μg/rat, ICV) or NOS blocker (L-NAME, 20 mg/kg, i.p., 28 days) interfered with memory restorative function of CAPE in STZ treated rats. In biochemical analysis markers of oxidative stress (TBARS, GSH, SOD, CAT), nitrite, AChE, TNF-α, eNOS and NFκB were measured in brain of rats on day 28. Interestingly, L-Arginine (100 mg/kg, i.p., 28 days) group exhibited moderate (p > 0.05) decline in memory functions. The brain oxidative stress, TNF-α, AChE activity and NFκB levels were elevated, and eNOS level was lowered by STZ-ICV treatment. Administration of CAPE lowered oxidative stress, AChE, nitrite and TNF-α levels in brain of rats. The eNOS level was enhanced and NFκB level was decreased by CAPE in STZ treated rats. Wortmannin injection elevated the brain oxidative stress, AChE activity and TNF-α levels, and decreased the nitrite, eNOS and NFκB level. Rise of brain oxidative stress parameters, AChE activity, TNF-α, eNOS and NFκB levels, and decline in brain nitrite content was observed in L-NAME treated group. L-Arginine administration showed modest effects (p > 0.05) on oxidative stress parameters. Brain nitrite content was enhanced although eNOS, NFκB levels, and AChE activity was decimated by L-Arginine treatment. It can be concluded that PI3-kinase mediated nitric oxide facilitation is an essential feature of CAPE action in STZ-ICV treated rats.

Uncovering the Signaling Pathway behind Extracellular Guanine-Induced Activation of NO System: New Perspectives in Memory-Related Disorders

Mounting evidence suggests that the guanine-based purines stand out as key player in cell metabolism and in several models of neurodegenerative disorders, such as Parkinson's and Alzheimer's diseases. Guanosine (GUO) and guanine (GUA) are extracellular signaling molecules derived from the breakdown of the correspondent nucleotide, GTP, and their intracellular and extracellular levels are regulated by the fine-tuned activity of two major enzymes, purine nucleoside phosphorylase (PNP) and guanine deaminase (GDA). Noteworthy, GUO and GUA, seem to play opposite roles in the modulation of cognitive functions, such as learning and memory. Indeed GUO, despite exerting neuroprotective, anti-apoptotic and neurotrophic effects, causes a decay of cognitive activities, whereas GUA administration in rats results in working memory improvement (prevented by L-NAME pre-treatment). This study was designed to investigate, in a model of SH-SY5Y neuroblastoma cell line, the signal transduction pathway activated by extracellular GUA. Altogether, our results showed that: (i) in addition to an enhanced phosphorylation of ASK1, p38 and JNK, likely linked to a non-massive and transient ROS production, the PKB/NO/sGC/cGMP/PKG/ERK cascade seems to be the main signaling pathway elicited by extracellular GUA; (ii) the activation of this pathway occurs in a pertussis-toxin sensitive manner, thus suggesting the involvement of a putative G protein coupled receptor; (iii) the GUA-induced NO production, strongly reduced by cell pre-treatment with L-NAME, is negatively modulated by the EPAC-cAMP-CaMKII pathway, which causes the over-expression of GDA that, in turn, reduces the levels of GUA. These molecular mechanisms activated by GUA may be useful to support our previous observation showing that GUA improves learning and memory functions through the stimulation of NO signaling pathway, and underscore the therapeutic potential of oral administration of guanine for treating memory-related disorders.

Alterations in neurobehaviors and inflammation in hippocampus of rats induced by oral administration of microcystin-LR

Microcystin-LR (MC-LR) is a widely studied toxic peptide secreted by certain water blooms of cyanobacteria that exhibit hepatotoxicity and neural toxicity. This study aimed to observe the neurotoxic effects of low-dose MC-LR exposure by oral administration. Male Sprague-Dawley (SD) rats were administered orally every 2 days for 8 weeks with pure water and 0.2, 1.0, and 5.0 μg/kg MC-LR. The Morris water maze test was used to assess the spatial learning and memory capability of rats. The activation of astrocytes and nitric oxide synthase (NOS) was evaluated by immunohistochemistry, and concentrations of nitric oxide (NO) in rat hippocampus were analyzed. Slight liver dysfunction was observed in the 5.0 μg/kg MC-LR-treated rats. Impairment of spatial learning and memory was also observed in the 5.0 μg/kg MC-LR-treated rats. Astrocytes in the hippocampus of the 5.0 μg/kg MC-LR-treated rats showed enhanced activation and cell density; the inflammatory indicators, NOS and NO, increased in accordance with astrocyte activation. This study showed that oral exposure of MC-LR had adverse affects on neurobehaviors, and induced inflammation in memory-related brain regions.