EFFECTS OF NITRIC OXIDE ON PASSIVE AVOIDANCE LEARNING IN RATS

The effects of a continuous 1-h a day 900-MHz electromagnetic field applied throughout early and mid-adolescence on hippocampus morphology and learning behavior in late adolescent male rats

The purpose of this study was to investigate hippocampus morphology and changes in learning behavior in male rats in late adolescence exposed to the effect of a continuous 1-h a day 900-megahertz (MHz) electromagnetic field (EMF). Twenty-four male Sprague Dawley rats aged 3-weeks were divided equally into control, sham and EMF groups. EMF group rats were exposed to a 900-MHz EMF inside an EMF cage, while the sham group rats were placed in the same cage but were not exposed to such an effect. No procedure was performed on the control group. Following 25-day application of EMF, passive avoidance, 8-arm radial maze and Y-maze tests were applied to determine rats' learning and memory performances. Open field and rotarod tests were applied to assess locomotor activity. At the end of the tests, the animals' brains were removed. Sections were taken and stained with toluidine blue. The regions of the hippocampus were subjected to histopathological evaluation. At histopathological examination, impairments of pyramidal and granular cell structures were observed in the EMF group hippocampus. No significant change was observed in learning, memory or locomotor behavior in any group. In conclusion, 900-MHz EMF applied in early and mid-adolescence causes no changes in learning, memory or locomotor behavior.

Contribution of Brain Tissue Oxidative Damage in Hypothyroidism-associated Learning and Memory Impairments

The brain is a critical target organ for thyroid hormones, and modifications in memory and cognition happen with thyroid dysfunction. The exact mechanisms underlying learning and memory impairments due to hypothyroidism have not been understood yet. Therefore, this review was aimed to compress the results of previous studies which have examined the contribution of brain tissues oxidative damage in hypothyroidism-associated learning and memory impairments.

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

Nitric oxide (NO) is an important intercellular messenger in the control of physiologic functions. It is synthesized by 3 different nitric oxide synthase enzymes (NOS). Uses of non-selective NOS inhibitor (L-NAME) have shown that NO is involved in neuronal plasticity and memory. This study aimed to determine the differential role of NO in spatial memory formation steps. In addition, regarding the roles of ERK and CaMKII in hippocampal plasticity, the hippocampal ERK and CaMKII activities were assessed to identify the effect of L-NAME on those proteins during each phase of memory. Adult male Sprague-Dawely rats weighing 220-280 g were trained in a single session consisting of 8 trials. To evaluate the effect of L-NAME on acquisition, L-NAME (3 or 10 mg/kg/i.p.) was administered 30 min before training. To assess its effect on the consolidation phase, L-NAME (3 or 10 mg/kg/i.p.) was injected immediately after training and a probe test was carried out 24 h later to analyse memory retention. To determine its effect on memory retrieval L-NAME (3 or 10 mg/kg/i.p.) was injected 30 min before probe trial which was conducted 24 h after training. The hippocampi were isolated after behavioural studies and western blotting analysis on hippocampal lysates was performed to illustrate the levels of phosphorylated ERK and CaMKII. The results showed that pre-training administration of L-NAME in 10 mg/kg but not 3mg/kg deteriorates acquisition. Post-training and pre-probe administration of L-NAME in 10 mg/kg but not 3 mg/kg impaired animal's performance in probe test. Additionally L-NAME treatment decreased the amount of phosphorylated (activated) ERK and CaMKII in the hippocampus. This study showed that endogenous nitric oxide is involved not only in all stages of memory, but also in ERK and CaMKII activation in the hippocampus during all 3 stages of memory.

Developmental exposure to chlorpyrifos and diazinon differentially affect passive avoidance performance and nitric oxide synthase-containing neurons in the basolateral complex of the amygdala

Chronic exposure to low doses of organophosphates during brain development can induce persistent neurochemical and behavioral effects. This study sought to determine the long-lasting effects of developmental exposure to chlorpyrifos (CPF) and diazinon (DZN) on passive avoidance (PA) performance and neuronal nitric oxide synthase (nNOS)-containing neurons in the subnuclei within basolateral complex of amygdala (BLC). Developing rats were exposed to daily dose (1mg/kg) of CPF or DZN during gestational days 15-18 and postnatal days (PND) 1-4. PA performance was assessed in young adulthood (PND 60). Brain sections were also processed by NADPH-diaphorase (NADPH-d) and nNOS immunohistochemistry. Gestational exposure to CPF increased NADPH-d(+)/nNOS-immunoreactive (IR) neurons within the basolateral nucleus (BL) and medial paracapsular intercalated cluster, which was along with PA retention impairment in both male and female rats. Prenatal exposure to DZN did not significantly change the number of NADPH-d(+)/nNOS-IR neurons in the BLC while impaired PA retention in females. Postnatal exposure to CPF decreased NADPH-d(+)/NOS-IR neurons in the BL without affecting PA performance. Exposure to DZN during early postnatal period impaired PA retention in both sexes, albeit to a lesser extent in females, and was along with a considerable sex independent reduction of NADPH-d(+)/NOS-IR neurons in all BLC subnuclei. Our data suggest that developmental exposure to apparently subtoxic dose of CPF and DZN elicit long-lasting impairment in PA retention that are associated, but not necessarily correlated with effects on NADPH-d(+)/NOS-IR neurons in BLC of the amygdala.

Involvement of nitric oxide in granisetron improving effect on scopolamine-induced memory impairment in mice

Granisetron, a serotonin 5-HT(3) receptor antagonist, widely used as an antiemetic drug following chemotherapy, has been found to improve learning and memory. In this study, effects of granisetron on spatial recognition memory and fear memory and the involvement of nitric oxide (NO) have been determined in a Y-maze and passive avoidance test. Granisetron (3, 10mg/kg, intraperitoneally) was administered to scopolamine-induced memory-impaired mice prior to acquisition, consolidation and retrieval phases, either in the presence or in the absence of a non-specific NO synthase inhibitor, l-NAME (3, 10mg/kg, intraperitoneally); a specific inducible NO synthase (iNOS) inhibitor, aminoguanidine (100mg/kg); and a NO precursor, l-arginine (750 mg/kg). It is demonstrated that granisetron improved memory acquisition in a dose-dependent manner, but it was ineffective on consolidation and retrieval phases of memory. The beneficial effect of granisetron (10mg/kg) on memory acquisition was significantly reversed by l-NAME (10mg/kg) and aminoguanidine (100mg/kg); however, l-arginine (750 mg/kg) did not potentiate the effect of sub-effective dose of granisetron (3mg/kg) in memory acquisition phase. It is concluded that nitric oxide is probably involved in improvement of memory acquisition by granisetron in both spatial recognition memory and fear memory. This article is part of a Special Issue entitled The Cognitive Neuroscience.

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

INTRODUCTION

The role of ovarian hormones and nitric oxide in learning and memory has been widely investigated.

OBJECTIVE

The present study was carried out to evaluate the effect of the nitric oxide synthase (NOS) inhibitor, N (G)-nitro-L-arginine methyl ester (L-NAME), on the ability of estradiol to improve learning in OVX rats using the Morris water maze.

METHODS

Forty rats were divided into five groups: (1) ovariectomized (OVX), (2) ovariectomized-estradiol (OVX-Est), (3) ovariectomized-L-NAME 10 (OVX-LN 10), (4) ovariectomized-L-NAME 50 (OVX-LN 50) and (5) ovariectomized-estradiol-L-NAME 50 (OVX-Est-LN 50). The animals in the OVX-Est group were treated with a weekly injection of estradiol valerate (2 mg/kg; i.m.). The OVX-LN 10 and OVX-LN 50 groups were treated with daily injections of 10 and 50 mg/kg L-NAME (i.p.), respectively. The animals in the OVX-Est-LN 50 group received a weekly injection of estradiol valerate and a daily injection of 50 mg/kg L-NAME. After 8 weeks, all animals were tested in the Morris water maze.

RESULTS

The animals in the OVX-Est group had a significantly lower latency in the maze than the OVX group (p<0.001). There was no significant difference in latency between the OVX-LN 10 and OVX-LN 50 groups in comparison with the OVX group. The latency in the OVX-Est-LN 50 group was significantly higher than that in the OVX-Est group (p<0.001).

CONCLUSION

These results show that L-NAME treatment attenuated estradiol-mediated enhancement of spatial learning and memory in OVX rats, but it had no significant effect in OVX rats without estrogen, suggesting an interaction of nitric oxide and estradiol in these specific brain functions.

The effect of chronic administration of L-arginine on the learning and memory of estradiol-treated ovariectomized rats tested in the morris water maze

OBJECTIVE

The present study was carried out to evaluate the effect of L-arginine on the learning and memory of estradiol-treated ovariectomized (OVX) rats.

METHODS

Forty-eight rats were divided into six groups: (1) sham, (2) OVX, (3) sham-Est, (4) OVX-Est, (5) sham-Est-LA, and (6) OVX-Est-LA. The animals of the sham-Est and OVX-Est groups were treated by weekly injection of estradiol valerate (2mg/kg). The sham-Est-LA and OVX-Est-LA groups were treated in the same manner but with an additional daily injection of L-arginine (200mg/kg). After eight weeks, animals of all groups were tested in the Morris water maze. The escape latency and path traveled to reach the platform were compared between groups.

RESULTS

Time latency and path length in the OVX group were significantly higher than in the sham group (P<0.05). The OVX-Est group had a significantly shorter traveled path length and time latency compared to the OVX group (P<0.001). Time latency and path length in the sham-Est group was significantly higher than in the sham group (P<0.001). Time latency and path length in the OVX-Est-LA group were significantly higher than in the OVX-Est group.

CONCLUSIONS

These results allow us to propose that chronic treatment with estradiol enhances the spatial learning and memory of OVX rats, and that long term L-arginine treatment attenuates the effects of improvement produced by estradiol in OVX rats.

Nitric oxide contributes to learning and memory deficits observed in hypothyroid rats during neonatal and juvenile growth

INTRODUCTION

Severe cognitive impairment follows thyroid hormone deficiency during the neonatal period. The role of nitric oxide (NO) in learning and memory has been widely investigated.

METHODS

This study aimed to investigate the effect of hypothyroidism during neonatal and juvenile periods on NO metabolites in the hippocampi of rats and on learning and memory. Animals were divided into two groups and treated for 60 days from the first day of lactation. The control group received regular water, whereas animals in a separate group were given water supplemented with 0.03% methimazole to induce hypothyroidism. Male offspring were selected and tested in the Morris water maze. Samples of blood were collected to measure the metabolites of NO, NO2, NO3 and thyroxine. The animals were then sacrificed, and their hippocampi were removed to measure the tissue concentrations of NO2 and NO3.

DISCUSSION

Compared to the control group's offspring, serum thyroxine levels in the methimazole group's offspring were significantly lower (P<0.01). In addition, the swim distance and time latency were significantly higher in the methimazole group (P<0.001), and the time spent by this group in the target quadrant (Q1) during the probe trial was significantly lower (P<0.001). There was no significant difference in the plasma levels of NO metabolites between the two groups; however, significantly higher NO metabolite levels in the hippocampi of the methimazole group were observed compared to controls (P<0.05).

CONCLUSION

These results suggest that the increased NO level in the hippocampus may play a role in the learning and memory deficits observed in childhood hypothyroidism; however, the precise underlying mechanism(s) remains to be elucidated.