Chronic treatment with the nitric oxide synthase inhibitor, L-NAME, attenuates estradiol-mediated improvement of learning and memory in ovariectomized rats

Neuroprotective effects of exercise in rodent models of memory deficit and Alzheimer's

Alzheimer's disease (AD) is a fastest growing neurodegenerative condition with no standard treatment. There are growing evidence about the beneficial effects of exercise in brain health promotion and slowing the cognitive decline. The aim of this study was to review the protective mechanisms of treadmill exercise in different models of rodent memory deficits. Online literature database, including PubMed-Medline, Scopus, Google scholar were searched from 2003 till 2017. Original article with English language were chosen according to following key words in the title: (exercise OR physical activity) AND (memory OR learning). Ninety studies were finally included in the qualitative synthesis. The results of these studies showed the protective effects of exercise on AD induced neurodegerative and neuroinflammatory process. Neuroperotective effects of exercise on the hippocampus seem to be increasing in immediate-early gene c-Fos expression in dentate gyrus; enhancing the Wnt3 expression and inhibiting glycogen synthase kinase-3β expression; increasing the 5-bro-mo-2'-deoxyridine-positive and doublecortin-positive cells (dentate gyrus); increasing the level of astrocytes glial fibrillary acidic protein and decrease in S100B protein, increasing in blood brain barrier integrity; prevention of oxidative stress injury, inducing morphological changes in astrocytes in the stratum radiatum of cornu ammonis 1(CA1) area; increase in cell proliferation and suppress apoptosis in dentate gyrus; increase in brain-derived neurotrophic factor and tropomyosin receptor kinase B expressions; enhancing the glycogen levels and normalizing the monocarboxylate transporter 2 expression.

Oxidative stress evoked damages leading to attenuated memory and inhibition of NMDAR–CaMKII–ERK/CREB signalling on consumption of aspartame in rat model

Many controversial reports are available on the use of aspartame as it releases methanol as one of its metabolite during metabolism. The present study proposes to investigate whether long term (90 days) aspartame (40 mg/kg b.wt) administration could induce oxidative stress and alter the memory in Wistar strain male albino rats. To mimic the human methanol metabolism, methotrexate (MTX)-treated rats were included as a model to study the effects of aspartame. Wistar strain albino rats were administered with aspartame (40 mg/kg b.wt) orally and studied along with controls and MTX-treated controls. Aspartame interfered in the body weight and corticosterone levels in the rats. A marked increase in the mRNA and protein expression of neuronal nitric oxide synthase (nNOS) and induced nitric oxide synthase (iNOS) which resulted in the increased nitric oxide radical’s level indicating that aspartame is a stressor. These reactive nitrogen species could be responsible for the altered cell membrane integrity and even cause death of neurons by necrosis or apoptosis. The animals showed a marked decrease in learning, spatial working and spatial recognition memory deficit in the Morris water maze and Y-maze performance task which could have resulted due to reduced hippocampal acetylcholine esterase (AChE) activity. The animal brain homogenate also revealed the decrease in the phosphorylation of NMDAR1–CaMKII–ERK/CREB signalling pathway, which well documents the inhibition of phosphorylation leads to the excitotoxicity of the neurons and memory decline. This effect may be due to methanol which may also activate the NOS levels, microglia and astrocytes, inducing neurodegeneration in brain. Neuronal shrinkage of hippocampal layer due to degeneration of pyramidal cells revealed the abnormal neuronal morphology of pyramidal cell layers in the aspartame treated animals. These findings demonstrate that aspartame metabolites could be a contributing factor for the development of oxidative stress in the brain.

The effects of tamoxifen on spatial and nonspatial learning and memory impairments induced by scopolamine and the brain tissues oxidative damage in ovariectomized rats

Background:

Modulatory effects of tamoxifen (TAM) on the central nervous system have been reported. The effects of TAM on spatial and nonspatial learning and memory impairments induced by scopolamine and the brain tissues oxidative damage was investigated.

Materials and Methods:

The ovariectomized (OVX) rats were divided and treated: (1) Control (saline), (2) scopolamine (Sco; 2 mg/kg, 30 min before behavioral tests), (3–5) Sco-TAM 1, Sco-TAM 3 and Sco-TAM 10. TAM (1, 3 or 10 mg/kg; i.p.) was daily administered for 6 weeks.

Results:

In Morris water maze (MWM), both the latency and traveled distance in the Sco-group were higher than control (P < 0.001) while, in the Sco-TAM 10 group it was lower than Sco-group (P < 0.05). In passive avoidance test, the latency to enter the dark compartment was higher than control (P < 0.05 – P < 0.01). Pretreatment by all three doses of TAM prolonged the latency to enter the dark compartment compared to Sco-group (P < 0.05 – P < 0.001). The brain tissues malondialdehyde (MDA) concentration was increased while, superoxide dismutase activity (SOD) decreased in the Sco-group compared to control (P < 0.05 – P < 0.01). Pretreatment by TAM lowered the concentration of MDA while, increased SOD compared to Sco-group (P < 0.05 – P < 0.001).

Conclusions:

It is suggested that TAM prevents spatial and nonspatial learning and memory impairments induced by scopolamine in OVX rats. The possible mechanism(s) might at least in part be due to protection against the brain tissues oxidative damage.

The effects of tamoxifen on learning, memory and brain tissues oxidative damage in ovariectomized and naïve female rats

Background:

Regarding the modulatory effects of tamoxifen (TAM) on the actions of estrogen in the present study, the effects of TAM on learning, memory and brain tissues oxidative damage in ovariectomized (OVX) and naοve female rats was investigated.

Materials and Methods:

The animals were divided into: (1) Sham, (2) OVX, (3) Sham-tamoxifen (Sham-TAM) and (4) ovariectomized-tamoxifen (OVX-TAM). The animals of the Sham-TAM and OVX-TAM groups were treated by TAM (1 mg/kg; 4 weeks).

Results:

In Morris water maze, the escape latency in the OVX group was higher than in the Sham group (P < 0.01). The time latency in the animals of OVX-TAM group was lower than that of OVX group (P < 0.01); however, there were no significant differences between the Sham-TAM and Sham groups. In the probe trial, the time spent in target quadrant (Q₁) by the animals of OVX group was lower than that of Sham group (P < 0.01). Interestingly, the animals of OVX-TAM group spent more times in target quadrant (Q₁) compared with OVX group (P < 0.01). In passive avoidance test, the animals of OVX group had lower latencies to enter the dark compartment compared with the Sham group (P < 0.05). The time latency to enter the dark compartment by animals of OVX-TAM group was higher than in OVX group (P < 0.01). In OVX-TAM group, the total thiol concentration was significantly higher (P < 0.05) and malondialdehyde concentration was lower (P < 0.01) than OVX group.

Conclusions:

These results allow us to propose that TAM enhances learning and memory of OVX rats. The possible mechanism may be due to the protective effects against brain tissues oxidative damage.

Brain Tissues Oxidative Damage as A Possible Mechanism of Deleterious Effects of Propylthiouracil- Induced Hypothyroidism on Learning and Memory in Neonatal and Juvenile Growth in Rats

INTRODUCTION

The role of brain tissues oxidative damage in learning and memory impairments has been well documented. It is also well known that thyroid hormones have a critical role for the brain functions. The purpose of this study was to investigate the role of brain tissues oxidative damage as a possible mechanism of deleterious effects of propylthiouracil (PTU) - induced hypothyroidism on learning and memory in neonatal and juvenile growth in rats.

METHODS

Fourteen pregnant female Wistar rats were kept in separate cages. After delivery, they were randomly divided into two groups including control and PTU. Rats in the control group received normal drinking water, whereas the second group received drinking water supplemented with 0.02% PTU from the first day after delivery through the first two months of the life of offspring (the pups of rats). After 60 days, nine male offspring of each group were randomly selected and tested in the Morris water maze (MWM). Then, samples of blood were collected to measure thyroxine. Finally, the brains were removed and total thiol groups and molondialdehyde (MDA) concentrations were determined.

RESULTS

Compared to the control group's offspring, serum thyroxine levels in the PTU group's off spring were significantly low (P<0.001). In MWM, the escape latency and traveled path in the PTU group were significantly higher than that in the control group (P<0.01- P<0.001). In PTU group, the total thiol concentrations in both cortical and hippocampal tissues were significantly lower and MDA concentrations were higher than control group (P<0.001).

DISCUSSION

It seems that deleterious effect of hypothyroidism during neonatal and juvenile growth on learning and memory is at least in part due to brain tissues oxidative damage.

The effects of soy extract on spatial learning and memory damage induced by global ischemia in ovariectomised rats

BACKGROUND

The effects of soy extract on memory as well as the oxidative damage to brain tissue induced by ischemia was investigated in ovariectomised (OVX) rats.

METHODS

THE RATS WERE DIVIDED INTO: 1) Sham; 2) OVX; 3) Sham‑Ischemia; 4) OVX‑Ischemia; 5) OVX-Ischemia-S 20; and 6) OVX-Ischemia-S 60. The common carotid artery was occluded (30 minutes), and it was then re-perfused. The OVX-Ischemia-S 20 and OVX-Ischemia-S 60 groups received 20 or 60 mg/kg of soy extract for eight weeks before the ischemia.

RESULTS

The Sham-Ischemia and OVX-Ischemia groups took a longer time to reach the platform while, spent a shorter time in the target quadrant (Q1) than the Sham and OVX. The escape latencies in the OVX-Ischemia-S 20 and OVX-Ischemia-S 60 groups were lower while, time spent in the Q1 was higher than that of the OVX-Ischemia. In the rotarod test, there were no significant differences between the groups. The hippocampal concentrations of malondialdehyde (MDA) in the Sham-Ischemia and OVX-Ischemia groups were higher than the Sham and OVX. Pre-treatment by 20 and 60 mg/kg of the extract reduced the MDA.

CONCLUSION

It is suggested that soy prevents memory impairment and brain tissue oxidative damage due to ischemia in OVX rats.

Effects of the hydro-alcoholic extract of Nigella sativa on scopolamine-induced spatial memory impairment in rats and its possible mechanism

OBJECTIVE

To evaluate the effect of Nigella sativa (NS) extract on memory performance and its possible mechanisms in scopolamine (Sco)-induced spatial memory impairment model using Morris water maze test.

METHODS

Thirty-two male Wistar rats were randomly divided into four groups. The control group received saline instead of both NS extract and Sco. The Sco group was treated by saline for two weeks, and was injected by Sco (2 mg/kg, intraperitoneally) 30 min before each trail in Morris water maze test. Sco+NS 200 and Sco+NS 400 groups were daily treated by 200 or 400 mg/kg of NS (intraperitoneally) for two weeks, respectively, and were finally injected by Sco 30 min before Morris water maze test. The brains of animals were removed to determine the acetylcholinesterase (AChE) activity and oxidative stress criteria in cortical tissues.

RESULTS

Time latency and path length in the Sco group were significantly higher than in the control group (P<0.01), while the Sco+NS 400 group showed a significantly shorter traveled path length and time latency compared with the Sco group (P<0.01). AChE activity in the cortical tissues of the Sco group was significantly higher than the control group (P<0.01), while AChE activity in the Sco+NS 200 and Sco+NS 400 groups was lower than the Sco group (P<0.01). Following Sco administration, malondialdehyde (MDA) concentrations were increased (P<0.01) in comparison with the control group, while cortical total thiol content decreased (P<0.01). Pretreatment with extracts caused a significant elevation in cortical total thiol content (P<0.01) and reduction in cortical MDA concentration (P<0.01) compared with the Sco group.

CONCLUSIONS

Hydro-alcoholic extract of NS prevents Sco-induced spatial memory deficits and decreases the AChE activity as well as oxidative stress of brain tissues in rats. Our results support the traditional belief about the beneficial effects of NS in nervous system. Moreover, further investigations are needed for better understanding of this protective effect.

Phytoestrogen α-zearalanol ameliorates memory impairment and neuronal DNA oxidation in ovariectomized mice

OBJECTIVE

The aim of this study was to evaluate the effect of a novel phytoestrogen, α-Zearalanol, on Alzheimer's disease-related memory impairment and neuronal oxidation in ovariectomized mice.

METHODS

Female C57/BL6 mice were ovariectomized or received sham operations and treatment with equivalent doses of 17β-estradiol or α-Zearalanol for 8 weeks. Their spatial learning and memory were analyzed using the Morris water maze test. The antioxidant enzyme activities and reactive oxygen species generation, neuronal DNA oxidation, and MutT homolog 1 expression in the hippocampus were measured.

RESULTS

Treatment with 17β-estradiol or α-Zearalanol significantly improved spatial learning and memory performance in ovariectomized mice. In addition, 17β-estradiol and α-Zearalanol attenuated the decrease in antioxidant enzyme activities and increased reactive oxygen species production in ovariectomized mice. The findings indicated a significant elevation in hippocampi neuronal DNA oxidation and reduction in MutT homolog 1 expression in estrogen-deficient mice, but supplementation with 17β-estradiol or α-Zearalanol efficaciously ameliorated this situation.

CONCLUSION

These results demonstrate that α-Zearalanol is potentially beneficial for improving memory impairments and neuronal oxidation damage in a manner similar to that of 17β-estradiol. Therefore, the compound may be a potential therapeutic agent that can ameliorate neurodegenerative disorders related to estrogen deficiency.

Decreased nitric oxide levels in the hippocampus may play a role in learning and memory deficits in ovariectomized rats treated by a high dose of estradiol

The effects of a high estradiol dose on memory and on nitric oxide metabolites in hippocampal tissues were investigated. Sham-Est and OVX-Est Groups were treated with 4 mg/kg of estradiol valerate for 12 weeks. Time latency and path length were significantly higher in the Sham-Est and OVX-Est Groups than in the Sham and OVX Groups, respectively (p<0.001). The animals in the Sham-Est and OVX-Est Groups spent lower time in the target quadrant (Q1) than those of the Sham and OVX Groups during the probe trial test (p<0.05 and <0.001, respectively). Significantly lower nitric oxide metabolite levels in the hippocampi of the Sham-Est and OVX-Est Groups were observed than in the Sham and OVX ones (p<0.001). These results suggest that decreased nitric oxide levels in the hippocampus may play a role in the learning and memory deficits observed after treatment with a high dose of estradiol, although the precise underlying mechanisms remain to be elucidated.

Different effects of scopolamine on learning, memory, and nitric oxide metabolite levels in hippocampal tissues of ovariectomized and Sham-operated rats

Different effects of scopolamine on learning, memory, and nitric oxide (NO) metabolites in hippocampal tissues of ovariectomized (OVX) and sham-operated rats were investigated. The animals in the Sham-Scopolamine (Sham-Sco) and OVX-Scopolamine (OVX-Sco) Groups were treated with 2 mg/kg scopolamine before undergoing the Morris water maze, while the animals in the Sham and OVX Groups received saline. The time latency and path length were significantly higher in both the Sham-Sco and the OVX-Sco Groups, in comparison with the Sham and OVX Groups, respectively (p<0.001). Significantly lower NO metabolite levels in the hippocampi of the Sham-Sco Group were observed, compared with the Sham Group (p<0.001), while there was no significant difference between the OVX-Sco and OVX Groups. The decreased NO level in the hippocampus may play a role in the learning and memory deficits induced by scopolamine. However, it seems that the effect of scopolamine on hippocampal NO differs between situations of presence and absence of ovarian hormones.

Different effects of L-arginine on morphine tolerance in sham and ovariectomized female mice

OBJECTIVE

The roles of gonadal hormones and nitric oxide (NO) on the analgesic effects of morphine, tolerance to morphine, and their interactions have been widely investigated. In the present study, the effect of L-arginine (an NO precursor) on morphine tolerance in sham and ovariectomized (OVX) female mice was investigated.

METHODS

Forty mice were divided into sham and OVX groups. On the first day, a hot plate test ((55±0.2) °C; cut-off 30 s) was carried out as a base record 15 min before injection of morphine (10 mg/kg, subcutaneously (s.c.)) and was repeated every 15 min after injection. The sham group was then divided into two subgroups: sham-tolerance-L-arginine (Sham-Tol-LA) and sham-tolerance-saline (Sham-Tol-Sal) which received either L-arginine 50 mg/kg (intraperitoneally (i.p.)) or saline 10 ml/kg (i.p.), respectively, three times in a day for three consecutive days. Morphine tolerance was induced in animals by injecting 30 mg/kg morphine (s.c.) three times/day for three days. This treatment was also used for OVX subgroups. On the fifth day, the hot plate test was repeated. The analgesic effect of morphine was calculated as the maximal percent effect (MPE). The results were compared using repeated measure analysis of variance (ANOVA).

RESULTS

There was no significant difference in MPE between the OVX and sham groups. The MPEs in both the Sham-Tol-Sal and OVX-Tol-Sal groups were lower than those in both the sham and OVX groups (P<0.01). The MPE in the OVX-Tol-Sal group was greater than that in the Sham-Tol-Sal group (P<0.01). The MPE in the Sham-Tol-LA group was higher than that in the Sham-Tol-Sal group (P<0.01). However, there was no significant difference between the Sham-Tol-LA and sham groups or between the OVX-Tol-LA and OVX-Tol-Sal groups.

CONCLUSIONS

The results of the present study showed that repeated administration of morphine causes tolerance to the analgesic effect of morphine. L-arginine could prevent tolerance to morphine but its effect was different in the presence of ovarian hormones.