Functional inactivation of orexin 1 receptors in CA1 region impairs acquisition, consolidation and retrieval in Morris water maze task

Orexin containing neurons in the lateral hypothalamic area (LHA) produce orexin-A (hypocretin-1) and orexin-B (hypocretin-2) and send their axons to the hippocampus, which predominantly expresses orexin 1 receptors (OX1Rs) showing a higher affinity to orexin-A. Recent studies have shown that central administration of orexin-A has an effect on learning and memory but literature concerning the role of orexinergic system in cognition remains controversial. Therefore, we examined the effect of pre-training, post-training and pre-probe trial intrahippocampal CA1 administration of a selective OX1R the orexin 1 receptor antagonist SB-334867-A (1.5, 3, 6 microg/0.5 microl) on acquisition, consolidation and retrieval in a single-day testing version of Morris water maze (MWM) task. Our results show that, SB-334867-A impaired acquisition, consolidation and retrieval of MWM task as compared with the control group. This drug had no effect on escape latency of a non-spatial visual discrimination task. Therefore, it seems that endogenous orexins, especially orexin-A, play an important role in spatial learning and memory in the rat.

Agmatine prevents LPS-induced spatial memory impairment and hippocampal apoptosis

Neuroinflammation is associated with a number of neurodegenerative diseases. It is known that lipopolysaccharide (LPS) treatment induces neuroinflammation and memory deterioration. Agmatine, the metabolite of arginine by arginine decarboxylase, is suggested to be a neuroprotective agent. The aim of this study was to explore if agmatine can prevent LPS-induced spatial memory impairment and hippocampal apoptosis. Adult male Wistar rats (200-250 g) were trained in water maze for 4 days (3 days in hidden platform and the last day in visible platform task). Saline, LPS (250 microg/kg/ip) or (and) agmatine (5 or 10 mg/kg) were administered 4h before every training session. LPS treatment impaired water maze place learning while agmatine co-administration prevented it. Also western blot studies revealed that LPS induces hippocampal caspase-3 activation while agmatine treatment prevented it.

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.

The selective orexin 1 receptor antagonist SB-334867-A impairs acquisition and consolidation but not retrieval of spatial memory in Morris water maze

The novel neuropeptides orexin-A and orexin-B derive from a common 130-amino acid precursor molecule (prepro-orexin), are mainly localized to neurons within and around the lateral hypothalamus, and exhibit high affinity to the closely related G-Protein-coupled receptors orexin 1 and 2 receptor (OX1R, OX2R). Orexinergic neurons send their axons to the hippocampal formation (CA1, CA2 and dentate gyrus), which expresses OX1Rs. Recent studies have shown that central administration of orexin-A and orexin-B have effects on learning and memory but literature concerning the role of orexinergic system in cognition remains controversial. More recently, antagonists have been described. The most potent and selective is SB-334867-A, which has an affinity of 40 nM at OX1R which is at least 50-fold selective over OX2R. It is likely that the intracerebroventricular (i.c.v.) administration may block OX1Rs in many brain regions. Previously we have shown that intra-CA1 injection of SB-334867-A impairs acquisition, consolidation and retrieval of spatial memory in MWM task. In the present study, the effect of pre-training, post-training and pre-probe of trial intra-DG (dentate gyrus) administration of SB-334867-A (1.5, 3, 6 microg/0.5 microl) on acquisition, consolidation and retrieval in a single-day testing version of MWM (Morris water maze) task was examined. Our results show impaired acquisition and consolidation of MWM task for SB-334867-A as compared with the control group. However, SB-334867-A had no effect on retrieval in spatial memory. Also, this antagonist had no effect on escape latency of a non-spatial visual discrimination task. Therefore, it seems that endogenous orexin-A and orexin-B, through DG OX1Rs, play an important role in spatial learning and memory in the rat.

The effect of antagonization of orexin 1 receptors in CA1 and dentate gyrus regions on memory processing in passive avoidance task

The hippocampal formation plays an essential role in associative learning like passive avoidance (PA) learning. It has been shown; orexin-containing terminals and orexin receptors densely are distributed in the hippocampal formation. We have previously demonstrated that antagonization of orexin 1 receptor (OX1R) in CA1 region of hippocampus and dentate gyrus (DG) impaired spatial memory processing. Although, there are few studies concerning function of orexinergic system on memory processing in PA task, but there is no study about physiological function of OX1R on this process. To address this, the OX1R antagonist, SB-334867-A, was injected into DG or CA1 regions of hippocampus and evaluated the influence of OX1R antagonization on acquisition, consolidation and retrieval in PA task. Our results show that, SB-334867-A administration into CA1 region impaired memory retrieval but not PA acquisition and consolidation. However, SB-334867-A administration into DG region impaired acquisition and consolidation but not PA memory retrieval. Therefore, it seems that endogenous orexins play an important role in learning and memory in the rat through OX1Rs.

Moderate treadmill exercise ameliorates amyloid-β-induced learning and memory impairment, possibly via increasing AMPK activity and up-regulation of the PGC-1α/FNDC5/BDNF pathway

Alzheimer's disease (AD) is a neurodegenerative disorder associated with loss of memory and cognitive abilities. Previous evidence suggested that exercise ameliorates learning and memory deficits by increasing brain derived neurotrophic factor (BDNF) and activating downstream pathways in AD animal models. However, upstream pathways related to increase BDNF induced by exercise in AD animal models are not well known. We investigated the effects of moderate treadmill exercise on Aβ-induced learning and memory impairment as well as the upstream pathway responsible for increasing hippocampal BDNF in an animal model of AD. Animals were divided into five groups: Intact, Sham, Aβ_1-42, Sham-exercise (Sham-exe) and Aβ_1-42-exercise (Aβ-exe). Aβ was microinjected into the CA1 area of the hippocampus and then animals in the exercise groups were subjected to moderate treadmill exercise (for 4 weeks with 5 sessions per week) 7 days after microinjection. In the present study the Morris water maze (MWM) test was used to assess spatial learning and memory. Hippocampal mRNA levels of BDNF, peroxisome proliferator-activated receptor gamma co-activator 1 alpha (PGC-1α), fibronectin type III domain-containing 5 (FNDC5) as well as protein levels of AMPK-activated protein kinase (AMPK), PGC-1α, BDNF, phosphorylation of AMPK were measured. Our results showed that intra-hippocampal injection of Aβ_1-42 impaired spatial learning and memory which was accompanied by reduced AMPK activity (p-AMPK/total-AMPK ratio) and suppression of the PGC-1α/FNDC5/BDNF pathway in the hippocampus of rats. In contrast, moderate treadmill exercise ameliorated the Aβ_1-42-induced spatial learning and memory deficit, which was accompanied by restored AMPK activity and PGC-1α/FNDC5/BDNF levels. Our results suggest that the increased AMPK activity and up-regulation of the PGC-1α/FNDC5/BDNF pathway by exercise are likely involved in mediating the beneficial effects of exercise on Aβ-induced learning and memory impairment.

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.

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.

Effect of reversible inactivation of the reuniens nucleus on spatial learning and memory in rats using Morris water maze task

The involvement of thalamic midline nuclei (MLN) in early stage of Alzheimer's disease and in diencephalic amnesia has drawn attention to the connectivity between the nucleus reuniens (RE) and structures of medial temporal lobe. RE is major source of thalamic afferents to the hippocampus and has been shown to exert powerful excitatory action on CA1 of hippocampus, which is supposed to be involved in learning and memory processes. However, the role of the RE on spatial memory is a controversial issue. The present study was designed to evaluate the role of the RE in acquisition, consolidation and retrieval of spatial reference memory (RM) and working memory (WM). We assessed the effect of reversible inactivation of RE with tetracaine (0.5 microl, 2%) on different stages of memory. Rats were trained on RM and WM versions of the Morris water maze (MWM) task. RE was inactivated before or immediately after training or before the probe trial of retrieval tests. The data showed that reversible inactivation of the RE significantly impaired both RM and WM versions of MWM. Therefore, it seems that nucleus reuniens of thalamus plays a role in spatial RM and WM version of the MWM task in rats.

Anastrozole improved testosterone-induced impairment acquisition of spatial learning and memory in the hippocampal CA1 region in adult male rats

Neurohormones like testosterone and estrogen have an important role in learning and memory. Many biological effects of androgens in the brain require the local conversion of these steroids to an estrogen. The current research has conducted to assess the effect of testosterone, estrogen and aromatase inhibitor (anastrozole) on spatial discrimination of rats, using Morris water maze and also the pathway of the effect of testosterone by using anastrozole. Adult male rats were bilaterally cannulated into CA1 region of hippocampus and divided into 15 groups. Different groups received DMSO 0.5 microl and DMSO 0.5 microl + DMSO 0.5 microl as control groups and different doses of testosterone enanthate (TE) (20, 40 and 80 microg/0.5 microl), estradiol valerat (EV) (1, 2.5, 5, 10, and 15 microg/0.5 microl), anastrozole (An) (0.25, 0.5, 1 microg/0.5 microl), TE 80 microg/0.5 microl + anastrozole 0.5 microg/0.5 microl and EV 15 microg/0.5 microl + anastrozole 0.5 microg/0.5 microl all days before training. TE and EV were injected 30-35 min before training and anastrozole was injected 25-30 min before training. Our results have shown both TE 80 microg/0.5 microl and EV 15 microg/0.5 microl groups increase in escape latency and traveled distance to find invisible platform. Also we have shown that anastrozole dose dependently decreases escape latency and traveled distance. We resulted that both TE and EN impaired acquisition of spatial learning and memory but anastrozole improved it. Anastrozole also could be buffered TE-induced impairment effect but not EV.

Antinociceptive effect of intra-hippocampal CA1 and dentate gyrus injection of MK801 and AP5 in the formalin test in adult male rats

Previous research has shown that the hippocampus processes pain related-information, probably through hippocampal neurons that respond exclusively to painful stimulation. In the current experiments we tested whether blocking NMDA receptors in the hippocampal CA1 region and dentate gyrus could reduce nociceptive behaviors in rats. The competitive and noncompetitive NMDA receptor antagonists 2-amino-5-phosphonopentanoic acid (AP5; 3.75 microg/0.75 microl) and MK801 (1.5, 3, 6 microg/0.5 microl) were injected into the dentate gyrus and CA1 area of behaving rats 5 min before subcutaneous injection of formalin irritant. Pain behaviors in both acute and tonic phases of the formalin test were significantly reduced by AP5 (3.75 microg/0.75 microl) and MK801 (3 microg/0.5 microl, but not 1.5 and 6 microg/0.5 microl) injection to the dentate gyrus. In the CA1, injection of AP5 had no effect while injection of the effective dose of MK801 (3 microg/0.5 microl) had a significant antinociceptive effect. This effect was apparent only during the late phase of the formalin test. These results support the hypothesis that NMDA-sensitive mechanisms are involved in acute and persistent pain-related processing in the dentate gyrus and with tonic pain processing in the hippocampal CA1 region.

The study of spatial memory in adult male rats with injection of testosterone enanthate and flutamide into the basolateral nucleus of the amygdala in Morris water maze

Extensive evidence suggests that the amygdala is involved in memory. The presence of androgenic and estrogenic receptors in the amygdala may reflect a possible involvement in certain activities of this part of the brain. Since sex steroids are known to play role in the maintenance and modulation of behavior, particularly spatial cognition throughout the life span, it was interesting to explore the role of these receptors in spatial memory. Therefore, an experiment was designed to investigate the effect of testosterone enanthate as an agonist and flutamide as an antagonist of androgenic receptors on spatial memory and learning. Wistar rats were bilaterally cannulated into basolateral nucleus of amygdala. Animals in different groups including vehicle (dimethyl sulfoxide) were proven to be inert for memory and learning. Testosterone enanthate (20, 40, 80 and 120 microg/0.5 microl), and flutamide (2, 5, 10, 20 and 40 microg/0.5 microl) were injected in both cannulae 30 min before each training day. After 4 days of experiments, results indicate a dose-dependent increase in parameters of escape latencies and travel distances to find the invisible platform in the group that received 120 microg/0.5 microl testosterone enanthate as compared to the control and vehicle groups. Flutamide had no effect on spatial memory. Therefore, it appears that androgens may effect memory and learning in amygdala. This is a feature that requires further investigation.

Post-training intrahippocampal infusion of the COX-2 inhibitor celecoxib impaired spatial memory retention in rats

In this study, we investigated the effects of intrahippocampal infusion of indomethacin as a non-selective cyclooxygenase inhibitor and celecoxib as a selective cyclooxygenase-2 inhibitor on spatial memory in the Morris water maze. Rats were trained for 3 days; each day included two blocks, and each block contained 4 trials. Tests were performed 48 h after surgery. Bilateral intrahippocampal infusion of indomethacin (0.01, 0.1, or 1 M) did not show any significant effect on spatial memory retention at these concentrations in rats. We also examined effects of infusion of celecoxib (0.02, 0.06, or 0.1 M) on memory retention. Bilateral infusion of 0.1 M celecoxib significantly altered escape latency and traveled distance in rats. These results strongly suggest that cyclooxygenase-2 is involved in spatial memory retention.

Effect of reversible inactivation of the supramammillary nucleus on spatial learning and memory in rats

Memory includes processes such as acquisition, consolidation and retrieval. Reference memory (RM) and working memory (WM) are two kinds of memory that can be assessed in rodents using spatial tasks, especially using the Morris water maze. The Morris water maze is particularly sensitive to hippocampal lesions. The supramammillary nucleus (SuM) has strong links with the hippocampus and septum. The role of the SuM on spatial learning is controversial. In the present study, involvement of SuM in the different steps of spatial RM and WM was investigated in the Morris water maze using reversible inactivation of SuM with lidocaine. Lidocaine (0.5 microl, 4%) was injected into the SuM through a guide cannula implanted above the SuM. The rats were trained on RM and WM versions of the Morris water maze. SuM was inactivated before training or immediately after training or before the probe trial of retrieval tests. Reversible inactivation of the SuM impaired consolidation of RM, and of consolidation and retrieval of WM. Therefore, it seems that activity of SuM neurons plays a role in spatial RM and WM learning and memory in the rat.

The effect of intrahippocampal injection of testosterone enanthate (an androgen receptor agonist) and anisomycin (protein synthesis inhibitor) on spatial learning and memory in adult, male rats

In most mammals, the hippocampus has a well-documented role in spatial memory acquisition. High concentration of androgen receptors in fundamental centers of learning and memory in brain such as hippocampus shows that there may be some relationships between androgen receptors and cognitive aspects of brain. Previous studies, which have shown sex-dependent differences in hippocampal morphology and physiology, suggest a modulatory role for sex steroids in hippocampal function. Androgens have been shown to modulate some hippocampal-mediated behaviors including learning and memory. To study the mechanism of action of androgens in processes underlying learning and memory, anisomycin, a protein synthesis inhibitor was used to prevent the genomic effects of testosterone. Therefore, the effects of anisomycin and testosterone together were assessed on rat's performance in MWM. Rats received anisomycin (2.5 microg/0.5 microl), testosterone (80 microg/0.5 microl) or both anisomycin (2.5 microg/0.5 microl) and testosterone (80 microg/0.5 microl) through the connulas in the CA1 region. Anisomycin was injected 20 min and testosterone was injected 35 min before training each day. The results showed that anisomycin (2.5 microg/0.5 microl) and testosterone (80 microg/0.5 microl) increased latencies to find the invisible platform. But the group that received testosterone and anisomycin together was decrease in latency and traveled distance to find the invisible platform.

Posttraining intrahippocampal infusion of a protein kinase AII inhibitor impairs spatial memory retention in rats

The role of protein kinase AII (PKA II) in spatial memory retention in male rats and its regulation of cholinergic gene expression were explored through the effects of intrahippocampal infusion of H-89, a selective PKA II inhibitor. Alterations in escape latency, travel distance, and swimming speed in a Morris water maze were measured. Animals were trained for 3 days; each day included two blocks, and each block contained four trials. Stereotaxic surgery was employed for the infusions after the last trial on the third day of training, and the animals were tested 48 hr after surgery. Bilateral intrahippocampal infusion of H-89 (2.5 or 5 microM) into the CA1 region generated significant alterations in escape latency and traveled distance but not swimming speed. The response was fairly dose dependent, and the maximal effect was obtained with 5 microM H-89. After behavioral testing, several of the infused animals were transcardially perfused and their brains removed. Brain tissue sections from these rats were subjected to immunohistochemical staining analysis with anticholine acetyltransferase (ChAT) antibodies. These analyses indicated that 5 microM H-89 infusions qualitatively reduced the density of ChAT-containing cholinergic nerve terminals in the dorsal hippocampus. The intrahippocampal infusions with 5 microM H-89 also caused an apparent reduction in the number of ChAT-containing neurons in the medial septum. Our results suggest that PKA II is involved in regulation of cholinergic gene expression and plays an important role in spatial memory retention in rats.

Intra CA1 insulin microinjection improves memory consolidation and retrieval

Although the brain was considered as an insulin-insensitive organ, recent studies have shown that insulin receptors exist in the brain and insulin modulates some of the brain tasks. Insulin and its receptor are found in specific areas 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. The improving effect of insulin on spatial memory acquisition has been shown. In the present study, the effect of insulin microinjection into the CA1 region of rat hippocampus on spatial memory consolidation and retrieval has been investigated. Insulin in 12 MU (but not in 0.5 and 6 MU) improved both memory retrieval and consolidation.

Post-training intrahippocampal infusion of nicotine prevents spatial memory retention deficits induced by the cyclo-oxygenase-2-specific inhibitor celecoxib in rats

Recently, we demonstrated that intrahippocampal infusion of the cyclo-oxygenase (COX)-2-specific inhibitor celecoxib impaired spatial memory retention in the Morris water maze. In the present work, we investigated the effects of nicotine, infused in the rat dorsal hippocampus several minutes after infusion of celecoxib, on memory retention in the Morris water maze. Rats were trained for 3 days; each day included two blocks, and each block contained four trials. Test trials were conducted 48 h after surgery. As expected, bilateral intrahippocampal infusion of celecoxib (19 microg/side; 0.1 m) increased escape latency and travel distance in rats, indicating significant impairment of spatial memory retention. We also examined the effects of bilateral infusion of nicotine (0.5, 1.0 and 2.0 microg/side) on memory retention. Infusion of 1 microg nicotine significantly decreased escape latency and travel distance but not swimming speed, compared with controls, suggesting memory retention enhancement by nicotine at this concentration. In separate experiments, bilateral infusion of nicotine, infused 5 min after 0.1 m (19 microg/side) celecoxib infusion, was associated with escape latency, travel distance and swimming speed profiles very similar to those in control animals. Brain tissue sections from several of these animals were subjected to immunohistochemical staining analysis with anti-COX-2 antibodies. Quantification analysis by optical density measurements showed that the celecoxib infusion reduced the immunoreactivity of COX-2-containing neurons in the CA1 area of the hippocampus compared with controls, although this reduction was not significant. However, infusion of a combination of celecoxib and nicotine significantly increased this immunoreactivity compared with levels in control and celecoxib-infused groups. These results suggest that nicotine prevented or reversed the adverse effects of celecoxib on spatial memory retention and protected or restored the immunostaining pattern of COX-2 neurons in the rat dorsal hippocampus.

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.

Genomic and nongenomic effects of intrahippocampal microinjection of testosterone on long-term memory in male adult rats

In addition to their well-known genomic effects via intracellular receptors, androgens rapidly alter neuronal excitability through a nongenomic pathway. The nongenomic effect of testosterone, as the main androgen, apart from its traditional effects, was assessed in one of the fundamental centers of learning and memory, the hippocampus, on long-term memory (LTM) in passive avoidance conditioning. Different doses of testosterone enanthate (T) or testosterone-BSA (T-BSA) bilaterally were injected into the CA1 region of the hippocampus 15 min before shock delivery (1 mA during 5 s) in a two-compartment passive avoidance apparatus. After 24 h, animals were tested for passive avoidance retrieval. Bilateral injection of 20 microg T or 55 microg T-BSA into the CA1 significantly decreases step-through latency. Therefore, it seems that testosterone can impair LTM in passive avoidance conditioning both via intracellular receptors and through nongenomic pathway.

The effects of anisomycin (a protein synthesis inhibitor) on spatial learning and memory in CA1 region of rats hippocampus

Inhibition of protein synthesis has been shown to affect long-term memory in a wide variety of animal species. But little is known regarding the neuroanatomical location of protein synthesis in different memory tasks. In this study, the effect of intrahippocampal injection of anisomycin, an inhibitor of brain protein synthesis on spatial memory was examined in Morris Water Maze. At first, rats were connulated bilaterally into the CA1 region and then different doses of anisomycin (1.25-2.5 micro g/0.5 micro l) on its vehicle (saline) were injected bilaterally into the CA1 region of rats hippocampus 20 min before training each day. The results showed dose-dependent increases in latencies to find the invisible platform and traveled distances in anisomycin received group compared to the control group. Therefore, it appears that protein synthesis inhibition in the CA1 region of hippocampus impair spatial learning in Morris Water Maze.

The effect of severe zinc deficiency and zinc supplement on spatial learning and memory

Zinc deficiency during pregnancy and during lactation has been shown to impair cognitive function and motor activity in offspring rats. In the present study, the effect of zinc deficiency and zinc supplement on spatial learning and memory in Morris Water Maze (MWM) and motor activity in open field were investigated. Pregnant rats after mating were divided to three groups. Control group fed a standard diet and a zinc deficient (ZnD) group fed a diet deficient in zinc (0.5-1.5 ppm) and a zinc supplement (ZnS) group fed a standard diet and enhanced zinc in the drinking water (10 ppm). All the diets were exposed during the last trisemester of pregnancy and during lactation. Rat's offspring in these groups were tested for spatial learning and memory in MWM at post natal day (PND) 56 and were tested for motor activity in open field at PND 66.The Escape Latency (EL) and Traveled Distance (TD) in the ZnD group were increased but Percentage of Time Spent in the target quadrant (PTS) was decreased compared to the control group. In addition, these were no significant differences in EL and TD, but PTS had significant increase in ZnS compared to the control group. In the open field, Total Distance Moved (TDM) and Time of Motor Activity (TMA) for the ZnD were decreased compared to the control group, but there were no significant differences in TDM and TMA between control and ZnS groups. These findings suggest that zinc deficiency during the last trimester of pregnancy and during lactation impaired spatial learning and memory in their offsprings and has also negative effect on motor activity. In addition, ZnS has a significant effect on spatial learning and memory but no effect on motor activity in their offsprings.

Enhanced antinociception by intracerebroventricularly administered orexin A in histamine H1 or H2 receptor gene knockout mice

Orexins are neuropeptides that are mostly expressed in the posterior and lateral hypothalamus, and related to the central control of appetite, arousal, and antinociception. Orexin neurons projected to the tuberomammillary nucleus and orexins may release histamine from the histamine neurons in this nucleus. Histamine is known to cause hypernociception. The roles of histamine H1 and H2 receptors in the orexin A-induced antinociception, however, have not been clarified yet. Here we studied the effects of histamine H1 and H2 receptors on orexin A-produced antinociception using histamine receptor knockout mice in four assays of nociception; the hot-plate, the tail-flick, the tail-pressure and the capsaicin tests. Furthermore we studied effects of histamine H1 and H2 receptor antagonists on orexin A-produced antinociception in C57BL/6 mice. The antinociceptive effects of i.c.v. orexin A were greater in histamine H1 receptor or H2 receptor knockout mice than in the wild-type mice in all four assays of pain. Furthermore, treatment of C57BL/6 mice with a combination of i.c.v. orexin A and d-chlorpheniramine (a histamine H1 receptor antagonist) or cimetidine (a histamine H2 receptor antagonist) showed a greater antinociception than i.c.v. orexin A alone in all four assays. These findings suggest the possibility that orexin A may activate H1 and H2 receptors in the supraspinal levels through the release of histamine from neurons, which might attenuate the antinociceptive effects of orexin A. Thus, the blocking of the histamine H1 or H2 receptor may produce antinociception and enhance the orexin A-induced antinociception.