Biomedical subjects

N Naghdi

Publications and source records attributed to N Naghdi.

7 recordsLinked to original sources

PubMed2006

Insulin protects against stress-induced impairments in water maze performance.

The presence of insulin receptor in the hippocampus suggests that this organ is a target for insulin. However, unlike the classic peripheral insulin target tissues such as adipocyte, muscle and liver, where the primary function of insulin is to regulate glucose homeostasis, insulin in the central nervous system (CNS) exhibits more diverse actions, most of which have not been clearly understood. A direct role of hippocampal insulin receptor signaling in improving cognitive functions, including learning and memory, and the association of insulin receptor deterioration with brain degenerative dementia (e.g., Alzheimer's disease) have attracted increasing interest. Additionally it has been shown that insulin can be a neuroprotective agent against memory loss induced by ischemia, lesions and some pharmacological agents. In the present study we evaluate the hypothesis that the bilateral intra CA1 insulin injection can protects against stress-induced memory deficit. Chronic restraint stress (2h per day x 7 days) significantly impaired spatial performance in Morris water maze and elevated serum corticosterone level. Intrahippocampal insulin microinjection was done 15-20 min before every stress episode. Insulin in low dose (0.5 MU) had no significant effect on memory deficit induced by stress. But in higher doses (6 and 12 MU) insulin protects animals against the deleterious effect of stress. Insulin alone daily injection had no effect on water maze performance. These results suggest that spatial learning and memory is compromised during chronic stress and insulin may protect against this effect.

Analysis of Variance↗

PubMed2006

The effect of intrahippocampal insulin microinjection on spatial learning and memory.

Insulin is best known for its action on peripheral target tissues such as the adipocyte, muscle and liver to regulate glucose homeostasis. Insulin and its receptor are found in specific area of CNS with a variety of region-specific functions different from its direct glucose regulation in the periphery. The hippocampus and cerebral cortex distributed insulin/insulin receptor has been shown to be involved in brain cognitive functions. Previous studies about the effect of insulin on memory are controversial. In the present study, the effect of insulin microinjection into CA1 region of rat hippocampus on water maze performance has been investigated. Insulin had a discrepant effect dose dependently. The spatial learning and memory were impaired with lower dose of insulin, had not changed with intermediate doses, while they improved with higher doses. These results suggest that insulin may have a dose-dependent effect on spatial learning and memory.

Animals↗

PubMed2005

Microinjection of ritanserin into the dorsal hippocampal CA1 and dentate gyrus decrease nociceptive behavior in adult male rat.

Prenatal 5HT depletion causes a significant decrease in the level of nociceptive sensitivity during the second phase of the formalin test behavioral response. These experiments were designed to test whether blocking 5HT2A/2c receptors in the CA1 region of the hippocampus and dentate gyrus would decrease nociceptive behaviors induced by a peripheral noxious stimulus formalin as an animal model of unremitting human being. The 5HT2A/2c receptor antagonist ritanserin (2, 4 and 8 microg/0.5 microl) was injected into the CA1 area and dentate gyrus of behaving rats 5 min before subcutaneous injection of formalin irritant. Nociceptive behaviors in both phases of the formalin test were significantly decreased by ritanserin (4 and 8 microg/0.5 microl) and ritanserin had no effect at 2 microg/0.5 microl. These results support the hypothesis that the hippocampal formation may modify the processing of incoming nociceptive information and that 5HT2A/2c receptor-sensitive mechanisms in the hippocampus may play a role in nociception and/or the expression of related behaviors.

Animals↗

PubMed2002

Impaired spatial learning in the Morris water maze induced by serotonin reuptake inhibitors in rats.

The effects of selective serotonin reuptake inhibitors citalopram and fluoxetine on spatial learning were assessed in rats. Adult male rats were subjected to 4 days of training in the Morris water maze with the invisible platform. Animals received different doses of citalopram (1-8 mg/kg; i.p.) or fluoxetine (1-16 mg/kg; i.p.) or their vehicles (saline or distilled water respectively) 30 minutes before training each day. The results showed that citalopram at doses of 4 and 8 mg/kg and fluoxetine at doses of 8 and 16 mg/kg significantly increased latencies to find the platform and traveled distances compared to the control group. Therefore, it appears that selective serotonin reuptake inhibitors can cause learning deficits in complex spatial tasks such as Morris water maze.

Animals↗

PubMed2001

The effects of intrahippocampal testosterone and flutamide on spatial localization in the Morris water maze.

The high density of the androgen receptors in fundamental centers of learning and memory, such as hippocampus, shows that there must be some relationships between the androgen receptors and cognitive aspects. To determine the role of hippocampal androgen receptors in spatial learning, the current research has been conducted to assess the effect of testosterone enanthate, as the agonist, and flutamide, as the antagonist, of these receptors on spatial discrimination of rats, using the Morris water maze (MWM). Adult male rats were bilaterally cannulated into the CA1 region of their hippocampus. Different groups received different doses of flutamide (2, 5, 10 and 20 microg/0.5 microl) or testosterone enanthate (20, 40 and 80 microg/0.5 microl) through the cannulas 30 min before training for 3 days. The results showed dose-dependent increases in latencies and traveled distances to find the invisible platform both in flutamide- and testosterone-treated groups as compared to the control group, with peak effects at doses of 5 microg/0.5 microl for flutamide and 80 microg/0.5 microl for testosterone. Therefore, it seems that both androgen receptor blockade and exogenous testosterone can effect spatial localization of adult, male rats.

Androgen Antagonists↗

PubMed2000

Lidocaine reversible inactivation of the median raphe nucleus has no effect on reference memory but enhances working memory versions of the Morris water maze task.

Numerous studies in the past have dealt with the role of serotonergic system lesions in tasks aimed at measurement of cognitive behavior, but the literature concerning the role of serotonin in cognition remains controversial. Rats with electrolytic lesions of the median raphe nucleus (MRN) were found to display a profound impairment in both the acquisition and retention of spatial memory task. In this study, the lidocaine inactivation was employed to evaluate the involvement of the rat's median raphe nucleus in reference and working memory versions of the Morris water maze (MWM) task. Lidocaine (0.5 microl, 2%) was injected through a single cannula aimed at the MRN; control groups were treated in the same way with a 0.5 microl injection of saline. In Experiment 1, rats were trained in a reference memory version of the MWM with two blocks of four trials per day for three consecutive days, with intra-cerebral injection made 5 min before training. No significant difference was found. In Experiment 2, intra-cerebral injection was applied immediately after two blocks of four trials, and in Experiment 3, the drug was injected 5 min before retention test in rats that had received eight trials per day on three consecutive days. Again, no significant difference between control and treatment groups was found. These results indicate that MRN has no role in acquisition, consolidation and retrieval of spatial reference memory. In subsequent experiments, rats were trained in a working memory version of the MWM task to find a new target position in trial 1, and retrieval was tested 75 min later. MRN inactivation 5 min before (Experiment 4) and immediately after the acquisition trial (Experiment 5) enhanced spatial working memory. It is concluded that normal activity of the MRN has no role in formation and retrieval of reference memory, but it has an inhibitory role in working memory. Our results are confirmed with other studies suggesting that the serotonergic system has a different role in long-term and short-term memory. Interaction with other neurotransmitter systems like acetylcholine may be involved in this case.

Anesthetics, Local↗

PubMed1999

Reversible inactivation of the median raphe nucleus enhances consolidation and retrieval but not acquisition of passive avoidance learning in rats.

Involvement of median raphe nucleus (MRN) in acquisition, consolidation and retrieval of passive avoidance (PA) was investigated with functional suppression of this area by lidocaine. Rats carrying a chronically implanted cannula aimed at the MRN were trained on a step-through passive avoidance task and received intra-MRN injection of lidocaine or saline 5 min before training or 5, 90 and 360 min after acquisition trial or 5 min before the retrieval test. Lidocaine MRN inactivation had no effect on PA learning. Lidocaine injected 5 and 90 min after the acquisition trial significantly enhanced avoidance of the dark compartment in comparison with the control group injected with saline. But PA retention was not affected by lidocaine injected 360 min after acquisition or 5 min before training. Retention latency significantly increased, when lidocaine injected 5 min before retrieval test. Step-through latency of naive rats was not affected by MRN blockade. Furthermore, reversible inactivation of MRN did not have a significant effect on locomotor activity. Our results indicate that the MRN contributes to PA consolidation at least until 90 min after acquisition and involves in PA retrieval. It is concluded that functional ablation of the MRN may disrupt the inhibitory actions of MRN projections to sub-cortical circuits participating in PA memorization and retrieval.

Analysis of Variance↗