Effects of vitamin E on lead-induced impairments in hippocampal synaptic plasticity

Intestinal toxicity of Pb: Structural and functional damages, effects on distal organs and preventive strategies

Lead (Pb) is one of the most common heavy metal pollutants that possesses multi-organ toxicity. For decades, great efforts have been devoted to investigate the damage of Pb to kidney, liver, bone, blood cells and the central nervous system (CNS). For the common, dietary exposure is the main avenue of Pb, but our knowledge of Pb toxicity in gastrointestinal tract (GIT) remains quite insufficient. Importantly, emerging evidence has documented that gastrointestinal disorders affect other distal organs like brain and liver though gut-brain axis or gut-liver axis, respectively. This review focuses on the recent understanding of intestinal toxicity of Pb exposure, including structural and functional damages. We also review the influence and mechanism of intestinal toxicity on other distal organs, mainly concentrated on brain and liver. At last, we summarize the bioactive substances that reported to alleviate Pb toxicity, providing potential dietary intervention strategies to prevent or attenuate Pb toxicity.

Embryonic exposures to cadmium and PAHs cause long-term and interacting neurobehavioral effects in zebrafish

Developmental exposure to either polycyclic aromatic hydrocarbons (PAHs) or heavy metals has been shown to cause persisting and overlapping neurobehavioral effects in animal models. However, interactions between these compounds have not been well characterized, despite their co-occurrence in a variety of environmental media. In two companion studies, we examined the effects of developmental exposure to cadmium (Cd) with or without co-exposure to prototypic PAHs benzo[a]pyrene (BaP, Exp. 1) or fluoranthene (FA, Exp. 2) using a developing zebrafish model. Zebrafish embryos were exposed to Cd (0-0.3 μM), BaP (0-3 μM), FA (0-1.0 μM), or binary Cd-PAH mixtures from 5 to 122 h post fertilization (hpf). In Exp. 1, Cd and BaP produced independent effects on an array of outcomes and interacting effects on specific outcomes. Notably, Cd-induced deficits in dark-induced locomotor stimulation were attenuated by BaP co-exposure in the larval motility test and BaP-induced hyperactivity was attenuated by Cd co-exposure in the adolescent novel tank test. Likewise, in Exp. 2, Cd and FA produced both independent and interacting effects. FA-induced increases on adult post-tap activity in the tap startle test were attenuated by co-exposure with Cd. On the predator avoidance test, FA- and 0.3 μM Cd-induced hyperactivity effects were attenuated by their co-exposure. Taken together, these data indicate that while the effects of Cd and these representative PAHs on zebrafish behavior were largely independent of one another, binary mixtures can produce sub-additive effects for some neurobehavioral outcomes and at certain ages. This research emphasizes the need for detailed risk assessments of mixtures containing contaminants of differing classes, and for clarity on the mechanisms which allow cross-class toxicant interactions to occur.

The effects of carvacrol and p-cymene on Aβ1-42 -induced long-term potentiation deficit in male rats

AIMS

Alzheimer's disease (AD) is the most common type of dementia in which oxidative stress plays an important role. In this disease, learning and memory and the cellular mechanism associated with it, long-term potentiation (LTP), are impaired. Considering the beneficial effects of carvacrol (CAR) and p-cymene against AD, their effect was assessed on in vivo hippocampal LTP in the perforant pathway (PP)-dentate gyrus (DG) pathway in an Aβ1-42 -induced rat model of AD.

METHODS

Male Wistar rats were randomly assigned to five groups: sham: intracerebroventricular (ICV) injection of phosphate-buffered saline, Aβ: ICV Aβ1-42 injections, Aβ + CAR (50 mg/kg), Aβ + p-cymene (50 mg/kg), and Aβ + CAR + p-cymene. Administration of CAR and p-cymene was done by gavage daily 4 weeks before and 4 weeks after the Aβ injection. The population spike (PS) amplitude and field excitatory postsynaptic potentials (fEPSP) slope were determined in DG against the applied stimulation to the PP.

RESULTS

Aβ-treated rats exhibited impaired LTP induction in the PP-DG synapses, resulting in significant reduction in both fEPSP slope and PS amplitude compared to the sham animals. Aβ-treated rats consumed either CAR or p-cymene separately (but not their combination), and showed an enhancement in fEPSP slope and PS amplitude of the DG granular cells.

CONCLUSIONS

These data indicate that CAR or p-cymene can ameliorate Aβ-associated changes in synaptic plasticity. Surprisingly, the combination of CAR and p-cymene did not yield the same effect, suggesting a potential interaction between the two substances.

Vitamin E Ameliorates Impaired Ovarian Development, Oxidative Stress, and Disrupted Lipid Metabolism in Oreochromis niloticus Fed with a Diet Containing Olive Oil Instead of Fish Oil

Aquaculture feed containing olive oil (OO) instead of fish oil (FO) can cause oxidative stress and impair gonad development in fish. We determined the effect of dietary OO-induced oxidative stress on ovarian development, and explored whether vitamin E (VE) could mitigate negative effects. Female Nile tilapia (Oreochromis niloticus) were fed for 10 weeks with four diets: 5% OO + 70 mg/kg VE, 5% OO + 200 mg/kg VE, 5% FO + 70 mg/kg VE, or 5% FO + 200 mg/kg VE. Dietary OO reduced the specific growth rate and gonadosomatic index, inhibited superoxide dismutase and catalase, delayed ovarian development, decreased serum sex hormone levels, and reduced ovarian triglyceride and n-3 highly unsaturated fatty acid contents. The transcript levels of genes encoding sex hormone receptors (erα, fshr, lhr) and components of the lipid metabolism pathway (pparα, pparγ, hsl, accα, elovl6), the nrf2 signaling pathway (nrf2, keap1), and the nf-κb signaling pathway (nf-κb, tnfα, infγ, il1β) differed between the 70VE/OO and 70VE/FO groups. Supplementation with 200 mg/kg VE mitigated the adverse effects of OO by improving antioxidant capacity and alleviating inflammation and abnormal lipid metabolism. This may be because VE is an antioxidant and it can regulate the nrf2-nf-κb signaling pathway.

Extraction, Purification, Structural Characteristics, Biological Activity and Application of Polysaccharides from Portulaca oleracea L. (Purslane): A Review

Portulaca oleracea L. (purslane) is a widely distributed plant with a long history of cultivation and consumption. Notably, polysaccharides obtained from purslane exhibit surprising and satisfactory biological activities, which explain the various benefits of purslane on human health, including anti-inflammatory, antidiabetic, antitumor, antifatigue, antiviral and immunomodulatory effects. This article systematically reviews the extraction and purification methods, chemical structure, chemical modification, biological activity and other aspects of polysaccharides from purslane collected in the Chinese Pharmacopoeia, Flora of China, Web of Science, PubMed, Baidu Scholar, Google Scholar and CNKI databases in the last 14 years, using the keywords "Portulaca oleracea L. polysaccharides" and "purslane polysaccharides". The application of purslane polysaccharides in different fields is also summarized, and its application prospects are also discussed. This paper provides an updated and deeper understanding of purslane polysaccharides, which will provide useful guidance for the further optimization of polysaccharide structures and the development of purslane polysaccharides as a novel functional material, as well as a theoretical basis for its further research and application in human health and manufacturing development.

Effectiveness of coenzyme Q10 on learning and memory and synaptic plasticity impairment in an aged Aβ-induced rat model of Alzheimer's disease: a behavioral, biochemical, and electrophysiological study

RATIONALE

Aging is the major risk factor for Alzheimer's disease (AD), and cognitive and memory impairments are common among the elderly. Interestingly, coenzyme Q10 (Q10) levels decline in the brain of aging animals. Q10 is a substantial antioxidant substance, which has an important role in the mitochondria.

OBJECTIVE

We assessed the possible effects of Q10 on learning and memory and synaptic plasticity in aged β-amyloid (Aβ)-induced AD rats.

METHODS

In this study, 40 Wistar rats (24-36 months old; 360-450 g) were randomly assigned to four groups (n = 10 rats/group)-group I: control, group II: Aβ, group III: Q10; 50 mg/kg, and group IV: Q10+Aβ. Q10 was administered orally by gavage daily for 4 weeks before the Aβ injection. The cognitive function and learning and memory of the rats were measured by the novel object recognition (NOR), Morris water maze (MWM), and passive avoidance learning (PAL) tests. Finally, malondialdehyde (MDA), total antioxidant capacity (TAC), total thiol group (TTG), and total oxidant status (TOS) were measured.

RESULTS

Q10 improved the Aβ-related decrease in the discrimination index in the NOR test, spatial learning and memory in the MWM test, passive avoidance learning and memory in the PAL test, and long-term potentiation (LTP) impairment in the hippocampal PP-DG pathway in aged rats. In addition, Aβ injection significantly increased serum MDA and TOS levels. Q10, however, significantly reversed these parameters and also increased TAC and TTG levels in the Aβ+Q10 group.

CONCLUSIONS

Our experimental findings suggest that Q10 supplementation can suppress the progression of neurodegeneration that otherwise impairs learning and memory and reduces synaptic plasticity in our experimental animals. Therefore, similar supplemental Q10 treatment given to humans with AD could possibly provide them a better quality of life.

Neuroprotective effects of vinpocetine, as a phosphodiesterase 1 inhibitor, on long-term potentiation in a rat model of Alzheimer's disease

BACKGROUND

Vinpocetine (Vin) is known as a phosphodiesterase 1 inhibitor (PDE1-I) drug with multilateral effects, including antioxidant and anti-inflammatory activity. In this research, we investigated the neuroprotective and therapeutic effects of Vin through hippocampal synaptic plasticity on a rat's model of Alzheimer's disease (AD) induced by an intracerebroventricular (ICV) injection of beta-amyloid (Aβ).

METHODS

Sixty adult male Wistar rats were randomly divided into six groups: 1. control, 2. sham, 3. Aβ, 4. pretreatment (Vin + Aβ): Vin (4 mg/kg, gavage) for 30 days and then, inducing an AD model by an ICV injection of Aβ(1-42), 5. treatment (Aβ + Vin): inducing an AD model and then receiving Vin for 30 days by gavage, and 7. pretreatment + treatment (Vin + Aβ + Vin): receiving Vin by gavage for 30 days before and 30 days after the induction of an AD model. After these procedures, via stereotaxic surgery, the stimulating electrodes were placed at the perforant pathway (PP) and the recording electrodes were implanted in the dentate gyrus.

RESULTS

Excitatory postsynaptic potential (EPSP) slope and population spike (PS) amplitude in the Aβ group meaningfully diminished compared to the control group after the induction of long-term potentiation (LTP).

CONCLUSIONS

Vin could significantly prevent the Aβ effects on LTP. It can be concluded that pretreatment and treatment with Vin can be neuroprotective against harmful consequences of Aβ on hippocampal synaptic plasticity.

Effects of sesamin on Aβ1-42-induced oxidative stress and LTP impairment in a rat model of Alzheimer's disease

The present study examined the protective effect of sesamin (Ses) on β-amyloid (Aβ)-induced long-term potentiation (LTP) impairment at the PP-DG synapses in male rats. Wistar rats were randomly assigned to seven groups: control, sham, Aβ; ICV Aβ_1-42 microinjection, Ses, Aβ + Ses; first, ICV Aβ injections and then receiving Ses, Ses + Aβ: four weeks of pretreatment with Ses and then Aβ injection, and Ses + Aβ + Ses: pre (four weeks) and post (four weeks) treatment with Ses. Ses-treated groups received 30 mg/kg of Ses once a day by oral gavage for four weeks. After the treatment period, the animals were positioned in a stereotaxic device for surgery and field potential recording. The population spike (PS) amplitude and slope of excitatory postsynaptic potentials (EPSP) were evaluated in the DG region. Serum oxidative stress biomarkers (total oxidant status (TOS) and total antioxidant capacity (TAC)) were measured. Aβ impaired LTP induction at the PP-DG synapses evidenced by a decrease in EPSP slope and PS amplitude of LTP. In Aβ rats, Ses increased EPSP slope and PS amplitude of LTP in the DG granular cells. Also, an increase in TOS and a reduction in TAC caused by Aβ were significantly corrected by Ses. Ses could prevent Aβ-induced LTP impairment at the PP-DG synapses in male rats, which can be due to its preventive effects on oxidative stress.

Alhagi maurorum Ethanolic Extract Rescues Hepato-Neurotoxicity and Neurobehavioral Alterations Induced by Lead in Rats via Abrogating Oxidative Stress and the Caspase-3-Dependent Apoptotic Pathway

This work investigated the probable protective effect of an Alhagi maurorum ethanolic extract on the hepatotoxicity and neurotoxicity accompanied by neurobehavioral deficits caused by lead in rats. Rats in four groups were orally administered distilled water, ethanolic extract of A. maurorum (300 mg/kg BW daily), lead (100 mg/kg BW daily for 3 months), and lead + A. maurorum extract. The results demonstrated that lead exposure resulted in elevated locomotor activities and sensorimotor deficits associated with a decrease in brain dopamine levels. Moreover, lead exposure significantly increased liver function markers. In addition, the lead-treated rats exhibited extensive liver and brain histological changes and apoptosis. The lead treatment also triggered oxidative stress, as demonstrated by the increase in malondialdehyde (MDA) concentrations with a remarkable reduction in the activities of antioxidant enzymes, reduced glutathione (GSH) levels, and transcriptional mRNA levels of antioxidant genes in the liver and brain. Nevertheless, co-treatment with the A. maurorum extract significantly ameliorated the lead-induced toxic effects. These findings indicate that the A. maurorum extract has the ability to protect hepatic and brain tissues against lead exposure in rats through the attenuation of apoptosis and oxidative stress.

Electrophysiological study of the interactive role of the cannabinoid breakdown inhibitors and L-type calcium channels on granular neurons in the hippocampal dentate gyrus in rats

The interaction between L-type voltage-dependent Ca²⁺ channels and the endocannabinoid system (eCs) in synaptic plasticity is controversial. In the present research, the impact of acute administration of URB597, as an endocannabinoid breakdown inhibitor, was evaluated after chronic injection of verapamil, as a Ca²⁺ channels blocker, on inducing long-term potentiation (LTP) in the rat's hippocampal dentate gyrus (DG). Treatment of male Wistar rats was done using intraperitoneal(i.p) injection of verapamil hydrochloride (n = 8) and saline (n = 10), as the solvent of verapamil once a day within 13 days. Anesthetization was done by i.p injection of urethane and the rats were located in the stereotaxic apparatus for surgery, electrode implantation, and field potential recording. After observing a steady-state baseline response, saline or URB597 were injected (n = 9). Measurement of the population spike (PS) amplitude and slope of field excitatory postsynaptic potentials (fEPSPs) in the DG region was performed as a result of perforant pathway (PP) stimulation. Our treatments could inhibit LTP. Our results indicated that the chronic administration of verapamil produced a significant decrease in the slope of fEPSP and PS amplitude. Also, acute URB597 administration decreased the slope of fEPSP and PS amplitude compared to the saline group. Moreover, URB597 administration in combination with chronic administration of verapamil produced a greater decrease in fEPSP slope and PS amplitude than the saline group. These findings indicated that verapamil and URB597 disrupted LTP induction in the DG. Moreover, an interaction was observed between Ca²⁺ channels and eCs. Therefore, the eCs possibly play a selective role in synaptic plasticity.

Effects of the hydroalcoholic extract of Rosa damascena on hippocampal long-term potentiation in rats fed high-fat diet

High-fat diets (HFDs) and obesity can cause serious health problems, such as neurodegenerative diseases and cognitive impairments. Consumption of HFD is associated with reduction in hippocampal synaptic plasticity. Rosa damascena (R. damascena) is traditionally used as a dietary supplement for many disorders. This study was carried out to determine the beneficial effect of hydroalcoholic extract of R. damascena on in vivo hippocampal synaptic plasticity (long-term potentiation, LTP) in the perforant pathway (PP)-dentate gyrus (DG) pathway in rats fed with an HFD. Male Wistar rats were randomly assigned to four groups: Control, R. damascena extract (1 g/kg bw daily for 30 days), HFD (for 90 days) and HFD + extract. The population spike (PS) amplitude and slope of excitatory post-synaptic potentials (EPSP) were measured in DG area in response to stimulation applied to the PP. Serum oxidative stress biomarkers [total thiol group (TTG) and superoxide dismutase (SOD)] were measured. The results showed the HFD impaired LTP induction in the PP-DG synapses. This conclusion is supported by decreased EPSP slope and PS amplitude of LTP. R. damascena supplementation in HFD animals enhanced EPSP slope and PS amplitude of LTP in the granular cell of DG. Consumption of HFD decreased TTG and SOD. R. damascena extract consumption in the HFD animals enhanced TTG and SOD. These data indicate that R. damascena dietary supplementation can ameliorate HFD-induced alteration of synaptic plasticity, probably through its significant antioxidant effects and activate signalling pathways, which are critical in controlling synaptic plasticity.

Targeting redox-altered plasticity to reactivate synaptic function: A novel therapeutic strategy for cognitive disorder

Redox-altered plasticity refers to redox-dependent reversible changes in synaptic plasticity via altering functions of key proteins, such as N-methyl-d-aspartate receptor (NMDAR). Age-related cognitive disorders includes Alzheimer's disease (AD), vascular dementia (VD), and age-associated memory impairment (AAMI). Based on the critical role of NMDAR-dependent long-term potentiation (LTP) in memory, the increase of reactive oxygen species in cognitive disorders, and the sensitivity of NMDAR to the redox status, converging lines have suggested the redox-altered NMDAR-dependent plasticity might underlie the synaptic dysfunctions associated with cognitive disorders. In this review, we summarize the involvement of redox-altered plasticity in cognitive disorders by presenting the available evidence. According to reports from our laboratory and other groups, this "redox-altered plasticity" is more similar to functional changes rather than organic injuries, and strategies targeting redox-altered plasticity using pharmacological agents might reverse synaptic dysfunctions and memory abnormalities in the early stage of cognitive disorders. Targeting redox modifications for NMDARs may serve as a novel therapeutic strategy for memory deficits.

Neuroprotective and long term potentiation improving effects of vitamin E in juvenile hypothyroid rats

Abstract. Protective effects of vitamin E (Vit E) on long term potentiation (LTP) impairment, neuronal apoptosis and increase of nitric oxide (NO) metabolites in the hippocampus of juvenile rats were examined. The rats were grouped (n=13) as: (1) control; (2) hypothyroid (Hypo) and (3) Hypo-Vit E. Propylthiouracil (PTU) was given in drinking water (0.05%) during 6 weeks. Vit E (20 mg/ kg) was daily injected (IP). To evaluate synaptic plasticity, LTP from the CA1 area of the hippocampus followed by high frequency stimulation to the ipsilateral Schafer collateral pathway was carried out. The cortical and hippocampal tissues were then removed to measure NO metabolites. The brains of 5 animals in each group were removed for apoptosis study. The hypothyroidism status decreased the slope, 10–90% slope and amplitude of field excitatory post synaptic potential (fEPSP) compared to the control group (P<0.01–P<0.001). Injection of Vit E increased the slope, 10–90% slope and amplitude of the fEPSP in the Hypo-Vit E group in comparison to the Hypo group (P<0.05–P<0.01). TUNEL positive neurons and NO metabolites were higher in the hippocampus of the Hypo rats, as compared to those in the hippocampus of the control ones (P<0.001). Treatment of the Hypo rats by Vit E decreased apoptotic neurons (P<0.01–P<0.001) and NO metabolites (P<0.001) in the hippocampus compared to the Hypo rats. The results of the present study showed that Vit E prevented the LTP impairment and neuronal apoptosis in the hippocampus of juvenile hypothyroid rats.

Coenzyme Q10 supplementation reverses diabetes-related impairments in long-term potentiation induction in hippocampal dentate gyrus granular cells: An in vivo study

Diabetes mellitus (DM) is associated with impaired hippocampal synaptic plasticity. Coenzyme Q10 (CoQ10) acts as an antioxidant and exerts neuroprotective effects. Accordingly, this study aimed at evaluating the effects of CoQ10 on hippocampal long-term potentiation (LTP) and paired-pulse facilitation (PPF) in streptozotocin (STZ)-induced diabetic rats. Male Wistar rats were randomly divided into six groups (n = 8 per group) as follows and treated for 90 days: the control, control + low dose of CoQ10 (100 mg/kg), control + high dose of CoQ10 (600 mg/kg), diabetic, diabetic + low dose of CoQ10, and diabetic + high dose of CoQ10 groups. Diabetes was induced by a single intraperitoneal injection of 50 mg/kg STZ. The population spike (PS) amplitude and slope of excitatory post synaptic potentials (EPSPs) were measured in dentate gyrus (DG) area in response to the stimulation applied to the perforant path (PP). The results showed that the STZ-induced diabetes impaired LTP induction in the PP-DG synapses. This finding is supported by the decreased EPSP slope and PS amplitude of LTP (P < 0.05). Both low- and high-dose CoQ10 supplementation in the control and diabetic animals enhanced EPSP slope and PS amplitude of LTP in the granular cells of DG (P < 0.05). PPF was affected by LTP induction in diabetic animals receiving the high dose of CoQ10 (P < 0.05). It is suggested that CoQ10 administration could attenuate deteriorative effect of STZ-induced diabetes on in vivo LTP in the DG. The enhanced transmitter release can be partly one of the possible underlying mechanism(s) responsible for the LTP induction in the diabetic animals treated with CoQ10.

Dietary vitamin E deficiency inhibits fat metabolism, antioxidant capacity, and immune regulation of inflammatory response in genetically improved farmed tilapia (GIFT, Oreochromis niloticus) fingerlings following Streptococcus iniae infection

Vitamin E plays an important role in maintaining normal metabolism and physiological functions in animals. The health of fish fingerlings directly affects the rate of disease incidence in adult fish, and healthy fingerlings ultimately result in better breeding outcomes for cultured fish. To date, no previous studies have focused on the effects vitamin E deficiency on tilapia at the fingerling stage. In this study, we investigated the effects of dietary vitamin E on the growth, fat metabolism, antioxidant capacity, and inflammatory response of genetically improved farmed tilapia (GIFT, Oreochromis niloticus) fingerlings. Vitamin E at different concentrations (0, 20, 40, 80, 160, and 320 mg/kg) was added to the diet and GIFT were fed for 55 days. Then, the GIFT were intraperitoneally injected with Streptococcus iniae and tested for infection. Vitamin E deficiency decreased growth and increased the food conversion ratio of GIFT fingerlings. Vitamin E deficiency also reduced the white blood cell count, increased hematocrit and hemoglobin contents in the blood, increased serum aspartate aminotransferase and alanine aminotransferase activities, and increased liver stress (P < 0.05). Vitamin E deficiency inhibited fat metabolism, down-regulated the expression of genes encoding lipoprotein lipase and heart-type and liver-type fatty acid-binding proteins, and increased serum total protein and fat deposition. Vitamin E deficiency significantly decreased superoxide dismutase, glutathione peroxidase, and catalase activities, increased malondialdehyde content, and caused oxidative damage. Vitamin E deficiency also up-regulated the expression of genes encoding interleukin 1β and tumor necrosis factor α in the head kidney, and stimulated a pro-inflammatory response. Overall, vitamin E deficiency inhibited growth, impaired fat metabolism, and disrupted the inflammatory response of GIFT fingerlings, whereas vitamin E supplementation in the diet reversed these negative effects. The diets with high concentrations of vitamin E (160-320 mg/kg) led to vitamin E accumulation in the fish tissues and rapid activation of the inflammatory response and antioxidant capacity in GIFT fingerlings exposed to S. iniae.

Serotonin type 6 receptor antagonist attenuates the impairment of long-term potentiation and memory induced by Abeta

Alzheimer's disease (AD) is the most common cause of dementia, characterized by memory impairment and synaptic loss. Long-term potentiation (LTP), a type of synaptic plasticity, is impaired during AD. Serotonin type 6 receptor (5-HT6R) inactivation is proposed as a therapeutic target for AD. This study examined the effects of chronic administration of the 5-HT6R antagonist, SB-258585, on cognitive, memory, and hippocampal plasticity in a rat model of AD. Abeta neurotoxicity was induced in rats using Aβ (1.35 pmol intracerebroventricular [ICV] injection). The following groups were formed: control sustained surgery and saline-treated, Aβ+saline (1 μL ICV for 30 days), and Aβ+SB-258585 (0.024 mg/kg, ICV for 30 days). The learning and memory were tested using the novel object recognition and passive avoidance tests. Next, anesthetized rats were placed in a stereotaxic apparatus. The population spike (PS) amplitude and the slope of the excitatory postsynaptic potentials (fEPSPs) of the LTP were measured following high-frequency stimulation in the dentate gyrus. The Aβ injection reduced step-through latency in the passive avoidance test and decreased the discrimination index in the novel object test. Aβ diminished both the amplitude of hippocampal neuron population spikes and the slope of excitatory postsynaptic potentials, compared to the control group. The administration of SB-258585 in rats receiving Aβ attenuated the Aβ-induced deficits in cognition, memory, and LTP in comparison with the Aβ group. It can be concluded that chronic treatment with SB-258585 antagonist can prevent Aβ-related deficiencies in learning and memory performance by improving neuronal plasticity. SB-258585 can prevent the progression of AD.

Influence of Chronic Coenzyme Q10 Supplementation on Cognitive Function, Learning, and Memory in Healthy and Diabetic Middle-Aged Rats

Diabetes mellitus can induce impairment in learning and memory. Cognitive and memory deficits are common in older adults and especially in those with diabetes. This is mainly because of hyperglycemia, oxidative stress, and vascular abnormalities. Coenzyme Q10 (CoQ10) can decrease oxidative stress, hyperglycemia, and inflammatory markers, and improve vascular function. Therefore, the aim of the present study was to investigate the possible effects of CoQ10 on cognitive function, learning, and memory in middle-aged healthy and diabetic rats. Adult middle-aged male Wistar rats (390-460 g, 12-13 months old) were divided into 6 experimental groups. Diabetes was induced by a single i.p. injection of streptozotocin (60 mg/kg). CoQ10 (20 or 120 mg/kg, orally by gavage) was administered for 45 days. The cognitive function and learning memory of rats were evaluated using novel object recognition (NOR) and passive avoidance tests. The discrimination index of the NOR test in the diabetic groups receiving CoQ10 (20 or 120 mg/kg) and the healthy group receiving CoQ10 (120 mg/kg) was significantly higher than that in the control group. In addition, the step through latency was significantly longer and the time spent in the dark compartment was significantly shorter in the diabetic groups receiving CoQ10 than in the control group. CoQ10 supplementation can improve learning and memory deficits induced by diabetes in older subjects. In addition, CoQ10 at higher doses can improve cognitive performance in older healthy subjects.

Different doses of methamphetamine alter long-term potentiation, level of BDNF and neuronal apoptosis in the hippocampus of reinstated rats

Methamphetamine (METH) is a psychostimulant. The precise mechanisms of its effects remain unknown and current relapse treatments have low efficacy. However, brain-derived neurotrophic factor (BDNF) and neuronal plasticity are essential contributors, despite paradoxical reports and a lack of comprehensive studies. Therefore, we investigated the effects of different doses of METH on long-term potentiation (LTP), BDNF expression and neuronal apoptosis in the hippocampus of reinstated rats. Rats were injected intraperitoneally with METH (1, 5, or 10 mg/kg) or saline, and trained in a conditioned place preference paradigm. Following implementation of the reinstatement model, electrophysiology, western blotting and TUNEL assay were performed to assess behavior, LTP components, BDNF expression, and neuronal apoptosis, respectively. The results demonstrated that the preference scores, population spike amplitude and BDNF expression markedly decreased in the METH (10 mg/kg) group compared with the other groups. In contrast, METH (5 mg/kg) significantly increased these factors more than the control group. There was no change in variables between METH (1 mg/kg) and the control group. Also, apoptosis of the hippocampus was increased in the METH (10 mg/kg) group compared with the METH (5 mg/kg) group. These results suggest that alterations in synaptic plasticity, expression of BDNF and neuronal apoptosis in the hippocampus has a vital role in the context-induced reinstatement of METH seeking.

Spirulina platensis attenuates the associated neurobehavioral and inflammatory response impairments in rats exposed to lead acetate

Heavy metals are well known as environmental pollutants with hazardous impacts on human and animal health because of their wide industrial usage. In the present study, the role of Spirulina platensis in reversing the oxidative stress-mediated brain injury elicited by lead acetate exposure was evaluated. In order to accomplish this aim, rats were orally administered with 300 mg/kg bw Spirulina for 15 d, before and simultaneously with an intraperitoneal injection of 50 mg/kg bw lead acetate [6 injections through the two weeks]. As a result, the co-administration of Spirulina with lead acetate reversed the most impaired open field behavioral indices; however, this did not happen for swimming performance, inclined plane, and grip strength tests. In addition, it was observed that Spirulina diminished the lead content that accumulated in both the blood and the brain tissue of the exposed rats, and reduced the elevated levels of oxidative damage indices, and brain proinflammatory markers. Also, because of the Spirulina administration, the levels of the depleted biomarkers of antioxidant status and interleukin-10 in the lead-exposed rats were improved. Moreover, Spirulina protected the brain tissue (cerebrum and cerebellum) against the changes elicited by lead exposure, and also decreased the reactivity of HSP70 and Caspase-3 in both cerebrum and cerebellum tissues. Collectively, our findings demonstrate that Spirulina has a potential use as a food supplement in the regions highly polluted with heavy metals.

Effect of a 5-HT1D receptor agonist on the reinstatement phase of the conditioned place preference test and hippocampal long-term potentiation in methamphetamine-treated rats

Methamphetamine (METH)-seeking relapse is associated with memory and synaptic plasticity changes. Serotonin is a key neuromodulator in this process. While there is a known distribution of 5-HT_1D receptors in reward and memory areas, such as the hippocampus, its physiological function is currently unknown. Here, we evaluated effect of a 5-HT_1D receptor agonist, PNU142633, on the reinstatement of METH-seeking behavior and long-term potentiation. Rats were implanted with a cannula into lateral ventricle, then treated with saline or METH (5 mg/kg) during the acquisition phase of the conditioned place preference (CPP) test. On day 13 of the extinction phase, METH groups were divided into four groups: METH (0: saline, 1, or 2.5 (priming METH) mg/kg; i.p.) + vehicle (5 µl/rat) or a priming dose of METH (2.5 mg/kg; i.p.) + PNU (2 µg/5 µl; i.c.v.) and their preference scores were calculated on reinstatement day (day 14). Immediately following this, electrophysiology was performed to assay the field excitatory postsynaptic potential (fEPSP) slope and population spike (PS) amplitude between groups. The results showed that CPP induction by METH gradually declined to extinction on days 12 and 13. A priming METH treatment significantly increased preference for the METH-paired chamber when compared with other groups, but pre-treatment with PNU significantly attenuated this effect. PS amplitude and fEPSP slopes in vehicle + priming METH rats were greater when compared with other groups. Furthermore, PNU attenuated the priming METH-induced increase in PS amplitude. These findings suggest that PNU can decrease synaptic transmission and prevent METH reinstatement in rats.

The effect of chronic stimulation of serotonin receptor type 7 on recognition, passive avoidance memory, hippocampal long-term potentiation, and neuronal apoptosis in the amyloid β protein treated rat

RATIONALE

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory impairment, neuronal death, and synaptic loss in the hippocampus. Long-term potentiation (LTP), a type of synaptic plasticity, occurs during learning and memory. Serotonin receptor type 7 (5-HTR7) activation is suggested as a possible therapeutic target for AD.

OBJECTIVE

The aim of the present study was to examine the effects of chronic treatment with the 5-HTR7 agonist, AS19, on cognitive function, memory, hippocampal plasticity, amyloid beta (Aβ) plaque accumulation, and apoptosis in an adult rat model of AD.

METHODS

AD was induced in rats using Aβ (single 1 μg/μL intracerebroventricular (icv) injection during surgery). The following experimental groups were included: control, sham-operated, Aβ + saline (1 μL icv for 30 days), and Aβ + AS19 (1 μg/μL icv for 30 days) groups. The animals were tested for cognition and memory performance using the novel object recognition and passive avoidance tests, respectively. Next, anesthetized rats were placed in a stereotaxic apparatus for electrode implantation, and field potentials were recorded in the hippocampal dentate gyrus. Lastly, brains were removed and Aβ plaques and neuronal apoptosis were evaluated using Congo red staining and TUNEL assay, respectively.

RESULTS

Administration of AS19 in the Aβ rats increased the discrimination index of the novel object recognition test. Furthermore, AS19 treatment decreased time spent in the dark compartment during the passive avoidance test. AS19 also enhanced both the population spike (PS) amplitude and the field excitatory postsynaptic potential (fEPSP) slope evoked potentials of the LTP components. Aβ plaques and neuronal apoptosis were decreased in the AS19-treated Aβ rats.

CONCLUSIONS

These results indicate that chronic treatment with a 5-HTR7 agonist can prevent Aβ-related impairments in cognition and memory performance by alleviating Aβ plaque accumulation and neuronal apoptosis, hence improving neuronal plasticity. AS19 may be useful as a therapeutic agent for AD.

Effects of thymol on amyloid-β-induced impairments in hippocampal synaptic plasticity in rats fed a high-fat diet

Obesity and a high-fat diet (HFD) are known to increase the incidence of Alzheimer's disease (AD). Oxidative stress, a major risk factor for AD, is increased with HFD consumption. Thymol (Thy) has antioxidant properties. Therefore, in the present study, we examined the protective and therapeutic effects of Thy on amyloid-β (Aβ)-induced impairments in the hippocampal synaptic plasticity of HFD-fed rats. In this study, 72 adult male Wistar rats were randomly assigned to 9 groups (n = 8 rats/group): Group 1 (control; standard diet); Group 2: Control + phosphate-buffered saline (PBS) + Oil (Thy vehicle); Group 3 (HFD + PBS); Group 4: (HFD + Aβ); Group 5: Control + PBS + Thy; Group 6: (HFD + Aβ + Oil); Group 7: Control + Aβ + Thy; Group 8: HFD + PBS + Thy; Group 9: (HFD + Aβ + Thy). After stereotaxic surgery, the field potentials were recorded after the implantation of the recording and stimulating electrodes in the dentate gyrus (DG) and perforant pathway, respectively. Following high-frequency stimulation, the long-term potentiation (LTP) of the population spike (PS) amplitude and the slope of the excitatory postsynaptic potentials (EPSPs) were measured in the DG. The HFD rats that received Aβ exhibited a significant decrease in their EPSP slope and PS amplitude as compared to the control group. In contrast, Thy administration in the HFD + Aβ rats reduced the decrease in the EPSP slope and PS amplitude. Thy decreased the Aβ-induced LTP impairments in HFD rats. The HFD significantly increased serum malondialdehyde levels and decreased total antioxidant capacity and total glutathione levels; whereas, Thy supplementation significantly reversed these parameters. Therefore, these results suggest that Thy, a natural antioxidant, can be therapeutic against high risk factors for AD, such as HFD.

Resistance training and hawthorn extract ameliorate cognitive deficits in streptozotocin-induced diabetic rats

It has been shown that diabetic rats display cognitive impairment. The aim of this study was to investigate the effects of resistance training and natural antioxidants on learning and memory in type 1 diabetic rats. For this purpose, fifty male Wistar rats were randomly divided into five groups: (i) Control (Con, n=10), (ii) Diabetic (D, n=10), (iii) Diabetic+Resistance training (DRT, n=10), (iv) Diabetic+natural antioxidants (DHE, n=10), and (v) Diabetic+Resistance training+ natural antioxidants (DRH, n=10). Climbing the ladder for a period of 5days/week for 10 consecutive weeks was considered as the resistance training model in our study. Natural antioxidants (100mg/kg per day) were administered to natural antioxidant groups for a period of 10 weeks. Moreover, spatial and passive avoidance learning and memory function were evaluated by Morris Water Maze (MWM) and shuttle box tests. The results showed that, mean of total escape latency decreased 25% (P<0.0001) in the DRH group compared with the D group in MWM. The percentage of time spent in the target quadrant identically decreased (34%) in the D and DHE groups compared with the Con group (p=0.001). In this regard, time spent in the dark Compartment (TDC) respectively rose 86% and 95% in the D and DHE groups compared with the Con group (p<0.05), and decreased 88% in the DRT and DRH groups compared with the D group in the shuttle box test (p<0.05). Furthermore, we noticed that total antioxidant capacity increase and lipid peroxidation decrease in response to the treatments in the diabetic rats as well. Therefore, the current study indicated that exercise training and natural antioxidants synergistically ameliorated learning and memory deficits in type 1 diabetic rats via reducing oxidative stress. Hence, it may propose a potential role of resistance training and natural antioxidants as an adjuvant therapy for the prevention and treatment of diabetic complications.

Effects of Hypericum scabrum extract on learning and memory and oxidant/antioxidant status in rats fed a long-term high-fat diet

A high-fat diet (HFD) causes deficits in learning and memory by increasing oxidative stress. Antioxidants are known to improve learning and memory. Since Hypericum scabrum (H. scabrum) extract is rich in antioxidants, the aim of this study was to investigate the effects of the administration of H. scabrum extract on passive avoidance learning (PAL), novel object recognition (NOR), and locomotor activity in male rats on a HFD. Fifty-four male Wistar rats (weighing 220 ± 10 g) were divided into the following six groups: (1) Control (standard diet), (2) Ext100 (standard diet supplemented with 100 mg/kg extract once/day), (3) Ext300 (standard diet supplemented with 300 mg/kg extract once/day), (4) HFD (high-fat diet), (5) HFD + Ext100, and (6) HFD + Ext300. Rats in these groups were maintained on their respective diets for 3 months. In the PAL test, the step-through latencies in the retention test (STLr) were significantly higher in the HFD + extract group than in the HFD group. The time spent in the dark compartment (TDC) was significantly lesser and the time spent in exploring the novel object was significantly greater in the HFD + extract group than in the HFD group. In the HFD-fed rats, the activity of catalase had significantly decreased, and level of malondialdehyde had significantly increased; H. scabrum extract administration significantly reversed these changes. In conclusion, these results suggested that the administration of H. scabrum extract and its strong antioxidant properties enhanced learning and memory and reversed the memory impairment induced by chronic HFD consumption.

The interactive role of CB1 receptors and L-type calcium channels in hippocampal long-term potentiation in rats

Long-term potentiation (LTP) of synaptic responses is a widely researched model of synaptic plasticity that occurs during learning and memory. The cannabinoid system is an endogenous system that modulate this kind of synaptic plasticity. In addition, voltage dependent calcium channels is essential for induction of LTP at some synapses in the hippocampus. However, there is currently debate over the interaction between L-type calcium channels and cannabinoid system on the synaptic plasticity. In this study, we examined the effects of an acute administration of the cannabinoid antagonist AM251 following a chronic administration of the Ca²⁺ channel blocker verapamil on LTP induction in the hippocampal dentate gyrus(DG) of rats. Male Wistar rats were administered verapamil(10,25,50mg/kg) or saline intraperitoneally(IP) daily for 13days(n=10/group). After this treatment period, animals were anesthetized with an IP injection of urethane; the recording and stimulating electrodes were positioned in the DG and the perforant pathway. After obtaining a steady state baseline response, a single IP injection of saline or AM251(1 or 5mg/kg) was administered. LTP was induced by high-frequency stimulation(HFS). The population spike(PS) amplitude and the slope of excitatory postsynaptic potentials(EPSP) were compared between the experimental groups. The acute administration of the CB1 antagonist AM251 increased LTP induction. The EPSP slopes and PS amplitude in the verapamil and AM251 groups differed after HFS, such that AM251 increased LTP, whereas verapamil decreased LTP induction. These findings suggest that there are functional interactions between the L-type calcium channels and cannabinoid system in this model of synaptic plasticity in the hippocampus.

Effects of Hypericum Scabrum extract on anxiety and oxidative stress biomarkers in rats fed a long-term high-fat diet

The continuous and long-term consumption of a high-fat diet (HFD) leads to weight gain and obesity. A HFD and obesity increase the risks of psychiatric disorders, such as anxiety and depression. In this study, we investigated the effects of a Hypericum Scabrum (H. scabrum) extract, which is an antioxidant, on anxiety in rats fed a long-term HFD. Sixty male Wistar rats were divided into the following six groups: (1) Control (standard diet), (2) Ext100 [standard diet supplemented with extract (100 mg/kg once/day)], (3) Ext300 [standard diet supplemented with extract (300 mg/kg once/day)], (4) HFD, (HFD), (5) HFD + Ext100, and (6) HFD + Ext300. The groups were fed their diet for 3 months. Anxiety was measured with the elevated plus-maze test. At the end of the study, blood samples were taken, and biochemical parameters and oxidative stress biomarker levels were determined in the plasma. Compared to the control group, the HFD group exhibited significant decreases in both the time in the open arms and number of entries into the open arms. H. scabrum extract supplementation significantly increased these parameters in the HFD-fed groups. The HFD significantly increased serum malondialdehyde levels and significantly decreased total glutathione levels, while H. scabrum extract supplementation significantly reversed these parameters. In conclusion, these results showed that a HFD increased anxiety behavior. In contrast, H. scabrum extract supplementation had anxiolytic effects and reversed the effects of the HFD, which suggested that the effects of H. scabrum extract supplementation were due to its strong antioxidant properties.

α-Tocopherol and Hippocampal Neural Plasticity in Physiological and Pathological Conditions

Neuroplasticity is an "umbrella term" referring to the complex, multifaceted physiological processes that mediate the ongoing structural and functional modifications occurring, at various time- and size-scales, in the ever-changing immature and adult brain, and that represent the basis for fundamental neurocognitive behavioral functions; in addition, maladaptive neuroplasticity plays a role in the pathophysiology of neuropsychiatric dysfunctions. Experiential cues and several endogenous and exogenous factors can regulate neuroplasticity; among these, vitamin E, and in particular α-tocopherol (α-T), the isoform with highest bioactivity, exerts potent effects on many plasticity-related events in both the physiological and pathological brain. In this review, the role of vitamin E/α-T in regulating diverse aspects of neuroplasticity is analyzed and discussed, focusing on the hippocampus, a brain structure that remains highly plastic throughout the lifespan and is involved in cognitive functions. Vitamin E-mediated influences on hippocampal synaptic plasticity and related cognitive behavior, on post-natal development and adult hippocampal neurogenesis, as well as on cellular and molecular disruptions in kainate-induced temporal seizures are described. Besides underscoring the relevance of its antioxidant properties, non-antioxidant functions of vitamin E/α-T, mainly involving regulation of cell signaling molecules and their target proteins, have been highlighted to help interpret the possible mechanisms underlying the effects on neuroplasticity.

Neuroprotective effects of metformin against Aβ-mediated inhibition of long-term potentiation in rats fed a high-fat diet

Metformin (Met) is used to treat neurodegenerative disorders such as Alzheimer's disease (AD). Conversely, high-fat diets (HFD) have been shown to increase AD risk. In this study, we investigated the neuroprotective effects of Met on β-amyloid (Aβ)-induced impairments in hippocampal synaptic plasticity in AD model rats that were fed a HFD. In this study, 32 adult male Wistar rats were randomly assigned to four groups: group I (control group, regular diet); group II (HFD+vehicle); group III (HFD+Aβ); or group IV (Met+HFD+Aβ). Rats fed a HFD were injected with Aβ to induce AD, allowed to recover, and treated with Met for 8 weeks. The rats were then anesthetized with intraperitoneal injections of urethane and placed in a stereotaxic apparatus for surgery, electrode implantation, and field potential recording. In vivo electrophysiological recordings were then performed to measure population spike (PS) amplitude and excitatory postsynaptic potential (EPSP) slope in the hippocampal dentate gyrus. Long-term potentiation (LTP) was induced by high-frequency stimulation of the perforant pathway. Blood samples were then collected to measure plasma levels of triglycerides, low-density lipoproteins, very low-density lipoprotein, and cholesterol. After induction of LTP, PS amplitude and EPSP slope were significantly decreased in Aβ-injected rats fed a HFD compared to vehicle-injected animals or untreated animals that were fed a normal diet. Met treatment of Aβ-injected rats significantly attenuated these decreases, suggesting that Met decreased the effects of Aβ on LTP. These findings suggest that Met treatment is neuroprotective against the detrimental effects of Aβ and HFDs on hippocampal synaptic plasticity.