Effects of a novel arginine-vasopressin derivative, NC-1900, on the spatial memory impairment of rats with transient forebrain ischemia

The IC87201 (a PSD95/nNOS Inhibitor) Attenuates Post- Stroke Injuries

N-methyl-D-aspartate receptor-dependent excitotoxicity is one of the most important mechanisms underlying stroke injury and the resulting neuronal death. In the present study, in order to reduce post-stroke brain injury and improve behavioral performance, a new molecule named IC87201, which acts as an inhibitor of PSD95/nNOS interaction in the intracellular signaling pathway of NMDA receptors, was administered. Using the middle cerebral artery occlusion (MCAO) technique, 24 adult male rats were subjected to one hour of cerebral ischemia. Animals were randomly divided into sham, MCAO, MCAO + DXM, and MCAO + IC87201 groups, and in the last two groups, intraperitoneal injection of dextromethorphan hydrobromide monohydrate (DXM), as an NMDA antagonist, and IC87201 was performed after ischemia. Neurobehavioral scores were evaluated for seven days, and on the last two days, the rats' memory performance was appraised using the passive avoidance test. On seventh day, the brain tissue was properly prepared for stereological analysis. Stereological studies of the hippocampus CA1 and CA3 regions revealed that changes in the total and infarcted volumes, total number of neurons, non-neurons, and dead neurons are the consequences of cerebral ischemia. Also, following cerebral ischemia, neurobehavioral and memory function impairments which were assessed by modified neurological severity scores (mNSS) and passive avoidance test, were observed. The aforementioned impairments were recovered after administration of IC87201 significantly and more potently than DXM. Based on our findings, IC87201 successfully attenuated post-ischemia damages. Therefore, this molecule can be considered as a new therapeutic approach in future research.

Memory deficits and hippocampal inflammation in cerebral hypoperfusion and reperfusion in male rats: Neuroprotective role of vanillic acid

Ischemic stroke is one of the leading causes of neurological deterioration and mortality worldwide. Neuroprotective strategies are being investigated to minimize cognitive deficits after ischemic events. Here we investigated the neuroprotective potential of vanillic acid (VA) in an animal model of transient bilateral common carotid artery occlusion and reperfusion (BCCAO/R). Adult male Wistar rats (250-300 g) were randomly divided in 4 groups and submitted to either cerebral hypoperfusion-reperfusion or a sham surgery after two-weeks of pretreatment with VA and/or normal saline. To induce the animal model of hypoperfusion, bilateral common carotid arteries were occluded (2VO model) for 30 min, followed by 72 h of reperfusion. Subsequently, their cognitive performance was evaluated in a Morris water maze (MWM) test, and also hippocampi were removed for ELISA assays and TUNEL staining test. The results showed that 2VO significantly reduced the spatial memory performance in MWM. As well as, BCCAO/R increased the level of IL-6, TNF-α and TUNEL positive cells, and also decreased the contents of IL-10 in the hippocampus of vehicle- pretreated groups as compared to the sham-operated groups. Furthermore, 14 consecutive days pretreatment with VA significantly restored the spatial memory, decreased the levels of IL-6, TNF-α and TUNEL positive cells and also increased the IL-10 levels in the hippocampi of the BCCAO/R rats. VA alone did not show any change neither in the status of various cytokines nor behavioral and TUNEL staining tests over sham values. Our data confirm that VA could potentially serve as a novel, promising, and accessible neuroprotective agent against cerebrovascular insufficiency states and vascular dementia.

Vanillic acid attenuates cerebral hyperemia, blood-brain barrier disruption and anxiety-like behaviors in rats following transient bilateral common carotid occlusion and reperfusion

Transient bilateral common carotid artery occlusion (tBCCAO), followed by reperfusion, is a model of transient global hypoperfusion. In the present study we aimed to investigate the probable effects of Vanillic acid (VA) on some physiological parameters including cerebral hyperemia, blood-brain barrier (BBB) disruption, anxiety behaviors and neurological deficits induced by bilateral occlusion of the common carotid arteries and reperfusion (BCCAO/R) in rats. Rats were randomly divided into four groups; Sham, BCCAO/R, VA and VA+ BCCAO/R. Chronic cerebral hypoperfusion was induced after 2 weeks of pretreatment by VA. Subsequently, sensorimotor scores, elevated plus maze tests, cerebral hyperemia, and BBB disruption were evaluated 72 h after 30 min of BCCAO. Pretreatment of rats by VA improved sensory motor signs, anxiolytic behavior in BCCAO/R rats compared with untreated rats (p < 0.05). Further, VA attenuated reactive hyperemia and BBB disruption in BCCAO/R rats compared with untreated rats (p < 0.01). To our knowledge, this study is the first to reveal VA could attenuate reactive hyperemia and improve BBB disruption following BCCAO/R, and could improve neurological scores and anxiety like behaviors in this model of cerebral hypoperfusion. These results suggest that VA could be a promising pretreatment agent in cerebral hypoperfusion.

Hippocampal place cell responses to distal and proximal cue manipulations in dopamine D2 receptor-knockout mice

The human hippocampus is critical for learning and memory. In rodents, hippocampal pyramidal neurons fire in a location-specific manner and form relational representations of environmental cues. The important roles of dopaminergic D1 receptors in learning and in hippocampal neural synaptic plasticity in novel environments have been previously shown. However, the roles of D2 receptors in hippocampal neural plasticity in response to novel and familiar spatial stimuli remain unclear. In order to clarify this issue, we recorded from hippocampal neurons in dopamine D2 receptor-knockout (D2R-KO) mice and their wild-type (WT) littermates during manipulations of distinct spatial cues in familiar and novel environments. Here, we report that D2R-KO mice showed substantial deficits in place-cell properties (number of place cells, intra-field firing rates, spatial tuning, and spatial coherence). Furthermore, although place cells in D2R-KO mice responded to manipulations of distal and proximal cues in both familiar and novel environments in a manner that was similar to place cells in WT mice, place fields were less stable in the D . The axes represent the differences between the peak and the valley of each waveform of EL2 and EL3.2R-KO mice in the familiar environment, but not in the novel environment. The present results suggested that D2 receptors in the hippocampus are important for place response stability. The place-cell properties of D2R-KO mice were similar to aged animals, suggesting that the alterations of place-cell properties in aged animals might be ascribed partly to alterations in the D2R in the HF of aged animals.

T-817MA, a neurotrophic agent, ameliorates the deficits in adult neurogenesis and spatial memory in rats infused i.c.v. with amyloid-beta peptide

BACKGROUND AND PURPOSE

Adult neurogenesis occurs throughout life in the subgranular zone and the dentate gyrus of the hippocampus. Deficient neurogenesis may be responsible for deficient hippocampal functions in neurodegenerative disorders such as Alzheimer's disease (AD). T-817MA [1-{3-[2-(1-Benzothiophen-5-yl)ethoxy] propyl}-3-azetidinol maleate] is a newly synthesized agent for AD treatment with neuroprotective effects against toxicity from amyloid-beta peptide (Abeta) and actions promoting neurite outgrowth in vitro. Furthermore, systemic administration of T-817MA ameliorated cognitive dysfunctions caused by neurodegeneration in a rat model of AD, induced by intracerebroventricular (i.c.v.) infusion of Abeta. The present study investigated quantitative relationships between spatial memory performance in Abeta-infused rats and hippocampal neurogenesis, and the effects of T-817MA on neuronal proliferation in vivo.

EXPERIMENTAL APPROACH

Seven weeks after infusion of Abeta (peptide 1-40; 300 pmol.day(-1); i.c.v.), rats were tested in a place learning task in which they were required to alternately visit two reward places in an open field to obtain intracranial self-stimulation as rewards.

KEY RESULTS

Rats given Abeta infusions for 10 weeks displayed spatial memory impairments and a decrease in neurogenesis compared with those infused with vehicle. Treatment of the Abeta-infused rats with T-817MA (8.4 mg.kg(-1).day(-1), p.o.) significantly increased hippocampal neurogenesis and ameliorated spatial learning impairments. Furthermore, spatial learning in the task was significantly correlated with neurogenesis.

CONCLUSIONS AND IMPLICATIONS

These results suggest that defective hippocampal neurogenesis is a new target for AD treatment. The neurotrophic compound T-817MA increased hippocampal neurogenesis in an AD model and might be useful for treatment of AD patients.

Effect of vasopressin on survival of Purkinje neurons in rat cerebellar slices after an in vitro simulated ischemia

BACKGROUND

Arginine vasopressin (AVP) is frequently used in patients under the risk of brain injury. It has been shown to induce brain injury after ischemia and reperfusion in in vivo animal models. We determined the effect of vasopressin on the brain injury after ischemia-reperfusion using in vitro model.

METHODS

Cerebellar brain slices were prepared from adult Sprague-Dawley rats. They were then subjected to simulated ischemia (oxygen-glucose deprivation) for 20 min in the absence (control) or presence of vasopressin (5, 10, 50, 100, 500 pg/ml). After being recovered in oxygenated artificial cerebrospinal fluid for 5 h, they were fixed for morphologic examination to determine the percentage of live Purkinje cells.

RESULTS

There were no differences in the survival rate of Purkinje cells among the control and vasopressin groups.

CONCLUSIONS

Vasopressin at concentrations studied has no direct effect on brain ischemia-reperfusion injury.

Ameliorative effects of a neuroprotective agent, T-817MA, on place learning deficits induced by continuous infusion of amyloid-beta peptide (1-40) in rats

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive decline due to neuronal loss and neural network dysfunction. It has been postulated that progressive neuronal loss in AD is consequence of the neurotoxic properties of the amyloid-beta peptide (Abeta). In the present study, we investigated the effect of T-817MA (1-{3-[2-(1-benzothiophen-5-yl)ethoxy] propyl}-3-azetidinol maleate), a newly synthesized neurotrophic compound, on place learning deficits in rats with hippocampal damages. To induce granule cell loss in the dentate gyrus (DG) of the hippocampus, Abeta (1-40) was continuously infused (300 pmol/day) into the cerebral ventricle using a mini-osmotic pump for 5 weeks. Three weeks after the Abeta infusion, the rats were tested in a place learning task, which required them to alternatively visit two diametrically opposed areas in an open field to obtain intracranial self-stimulation reward. The results indicated that the Abeta-infused rats without treatment of T-817MA displayed learning impairment in the task; their performance level was significantly inferior to that of the vehicle rats. Treatment of T-817MA (8.4 mg/kg/day, p.o.) significantly improved the task performance of the Abeta-infused rats. Furthermore, T-817MA prevented granule cell loss due to Abeta-infusion, which was correlated to task performance of the rats. However, other cognitive enhancer, an acetylcholinesterase inhibitor, had no such effects. The results demonstrated that T-817MA ameliorated learning deficits induced by Abeta infusion, which might be attributed to neuroprotection in the hippocampus.

Effect of NC-1900, an active fragment analog of arginine vasopressin, and inhibitors of arachidonic acid metabolism on performance of a passive avoidance task in mice

In this study, we investigated the effect of administration of inhibitors of each of the arachidonic acid metabolism pathways and the effect of co-administration of these inhibitors with NC-1900, a fragment analog of arginine vasopressin, on step-through passive avoidance task performance. All drugs were administered just after the acquisition trial in the passive avoidance task. Intracerebroventricular (i.c.v.) administration of nordihydroguaiaretic acid (NDGA, 1 and 10 microg), a phospholipase A2 (PLA2) and lipoxygenase (LOX) inhibitor, and of arachidonyl trifluoromethyl ketone (ATK, 1 and 10 microg), a specific PLA2 inhibitor caused reductions in latency on the retention trial. The i.c.v. administration of either of baicalein (0.1-10 microg), a 12-LOX inhibitor, or AA-861 (0.1-10 microg), a 5-LOX inhibitor, did not influence the latency. Intraperitoneal administration of indomethacin (20 mg/kg), a non-specific COX inhibitor, or NS-398 (10 mg/kg), a specific COX-2 inhibitor, impaired performance on the retention trial in the task, while piroxicam (20 mg/kg), a specific COX-1 inhibitor, did not. Subcutaneous administration of NC-1900 (0.1 ng/kg) ameliorated the reduction of latency caused by NDGA, ATK, indomethacin, or NS-398. These results suggested that the COX-2 pathway of arachidonic acid metabolism may be important for learning and/or memory in the passive avoidance task in mice, and that the ameliorating effect of NC-1900, in part, is due to mimicking of the effects of metabolites of the COX-2 pathway.

NC-1900, an arginine–vasopressin analogue, ameliorates social behavior deficits and hyperlocomotion in MK-801-treated rats: Therapeutic implications for schizophrenia

We previously reported that chronic administration of N-methyl-D-aspartate (NMDA) antagonists reduced the density of vasopressin V1a receptors in several brain regions in rats that demonstrated social interaction deficits and increased locomotor activity. These observations indicate the ability of arginine-vasopressin (AVP), or its analogues, to modulate behavioral abnormalities associated with blockade of NMDA receptors. The present study was performed to investigate the effect of NC-1900, an AVP analogue, on social behavior and locomotor activity in rats treated with MK-801, a non-competitive NMDA receptor antagonist. Male Wistar rats were administered MK-801 (0.13 mg/kg/day ip) or saline for 14 days. Social behavior and locomotor activity were measured 45 min after the injection of NC-1900 (10 ng/kg sc) or saline together with the last MK-801 or vehicle administration. Social interaction was quantified by an automated video-tracking system, and stereotyped behavior and ataxia were manually measured. Acute administration of NC-1900 partially reversed MK-801-induced hyperlocomotion and deficits in social interaction, while NC-1900 itself did not affect these behavioral measures in animals chronically treated with vehicle saline. These results suggest that the central AVP system may interact with glutamatergic and dopaminergic transmissions, and indicate potential therapeutic effects of AVP analogues on positive and negative symptoms of schizophrenia.

Effect of pretraining administration of NC-1900, a vasopressin fragment analog, on memory performance in non- or CO2-amnesic mice

In the present study, we investigated the facilitative effect of NC-1900, a new arginine vasopressin (AVP(1-9)) fragment analog, on memory performance in eight-arm radial maze or passive avoidance (PA) tasks in nonamnesic and amnesic (PA tasks only) mice. In the radial maze, all injections (subcutaneous) were given daily 60 min before each trail. NC-1900 (1 ng/kg)-treated animals showed enhancement of performance, and AVP(4-9) (1 microg/kg), an AVP(1-9) fragment, had similar effects, although the effective dose was 1000-fold higher. In the PA task, all drugs were administrated subcutaneously 60 min before the acquisition trial (Acq.), and the amnesic mice were exposed to CO(2) just after the Acq. NC-1900 (1 ng/kg) enhanced the memory performance of nonamnesic mice and ameliorated CO(2)-induced amnesia. AVP(4-9) (1 microg/kg) had a similar effect, although only at higher doses, while AVP(1-9) (0.1-1 microg/kg) had no effect. The facilitating effect of NC-1900 on nonamnesic mice was inhibited by coinjection [Pmp(1)-Tyr(Me)(2)]-AVP (Pmp,Tyr-AVP; 1 microg/kg), a V(1A) antagonist, but not by OPC-31260, a vasopressin(2) (V(2)) antagonist. The effect of NC-1900 on CO(2)-induced amnesia was also decreased by coinjection of Pmp,Tyr-AVP or [deamino-Pen(1), Me-Tyr(2)]-AVP (10 microg/kg), both of which are V(1) antagonists. These results suggested that NC-1900 has a more potent effect on facilitation of memory via the V(1A) receptor than AVP(4-9) in non- and CO(2)-amnesic conditions.

Facilitative effect of a novel AVP fragment analog, NC-1900, on memory retention and recall in mice

In order to determine the mechanism of action of a new AVP(4-9) analog, NC-1900, on memory processes, memory retention and retrieval tests were conducted in a step-through passive avoidance (PA) task in mice. The administration of NC-1900 facilitated memory retention and retrieval in the PA task through vasopressin1A (V1A) receptors but not V2 receptors. The effect of NC-1900 on memory retention test performance appeared to be due to activation of the protein kinase C (PKC) signaling pathway via V1A receptors; however, the modulation of PKC was not essential for the facilitative effect of the new peptide in the retrieval test. The facilitation of memory retrieval by NC-1900 may also be mediated by other non-PKC-dependent signaling pathways, such as the phospholipase C-inositol trisphosphate pathway.

Effect of I.C.V. injection of AT4 receptor ligands, NLE1-angiotensin IV and LVV-hemorphin 7, on spatial learning in rats

Central administration of angiotensin IV (Ang IV) or its analogues enhance performance of rats in passive avoidance and spatial memory paradigms. The purpose of this study was to examine the effect of a single bolus injection of two distinct AT4 ligands, Nle1-Ang IV or LVV-haemorphin-7, on spatial learning in the Barnes circular maze. Mean number of days for rats treated with either Nle1-Ang IV or LVV-haemorphin-7 to achieve learner criterion is significantly reduced compared with controls (P < 0.001 and P < 0.05 respectively). This is due to enhanced ability of the peptide-treated rats to adopt a spatial strategy for finding the escape hatch. In all three measures of learning performance, (1) the number of errors made, (2) the distance travelled and (3) the latency in finding the escape hatch, rats treated with either 100 pmol or 1 nmol of Nle1-Ang IV or 100 pmol LVV-haemorphin-7 performed significantly better than the control groups. As early as the first day of testing, the rats treated with the lower dose of Nle1-Ang IV or LVV-haemorphin-7 made fewer errors (P < 0.01 and P < 0.05 respectively) and travelled shorter distances (P < 0.05 for both groups) than the control animals. The enhanced spatial learning induced by Nle1-Ang IV (100 pmol) was attenuated by the co-administration of the AT4 receptor antagonist, divalinal-Ang IV (10 nmol). Thus, administration of AT4 ligands results in an immediate potentiation of learning, which may be associated with facilitation of synaptic transmission and/or enhancement of acetylcholine release.

Contribution of hippocampal place cell activity to learning and formation of goal-directed navigation in rats

Although extensive behavioral studies have demonstrated that hippocampal lesions impair navigation toward specific places, the role of hippocampal neuronal activity in the development of efficient navigation during place learning remains unknown. The aim of the present study was to investigate how hippocampal neuronal activity changes as rats learn to navigate efficiently to acquire rewards in an open field. Rats were pre-trained in a random reward task where intracranial self-stimulation rewards were provided at random locations. Then, the rats were trained in a novel place task where they were rewarded at two specific locations as they repeatedly shuttled between them. Hippocampal neuronal activity was recorded during the course of learning of the place task. The rats learned reward sites within several sessions, and gradually developed efficient navigation strategies throughout the learning sessions. Some hippocampal neurons gradually changed spatial firing as the learning proceeded, and discharged robustly near the reward sites when efficient navigation was established. Over the learning sessions, the neuronal activity was highly correlated to formation of efficient shuttling trajectories between the reward sites. At the end of the experiment, spatial firing patterns of the hippocampal neurons were re-examined in the random reward task. The specific spatial firing patterns of the neurons were preserved if the rats navigated, as if they expected to find rewards at the previously valid locations. However, those specific spatial firing patterns were not observed in rats pursuing random trajectories. These results suggest that hippocampal neurons have a crucial role in formation of an efficient navigation.