Sex-specific restoration of MK-801-induced sensorimotor gating deficit by environmental enrichment

The effects and mechanism of environmental enrichment on MK-801 induced cognitive impairment in rodents with schizophrenia

Schizophrenia is a severe mental disorder characterized by positive, negative, and cognitive symptoms. Cognitive symptoms are a kind of symptoms with high incidence and great impact on patients. There is no effective treatment in clinical practice. N-methyl-d-aspartic acid (NMDA) receptor hypofunction may be an important cause of cognitive symptoms. MK-801 (also named Dizocilpine), a noncompetitive antagonist of NMDA receptor, is often used to construct a model of NMDA receptor dysfunction. In terms of treatment, environmental enrichment (EE) as an environmental intervention can effectively improve the symptoms of cognitive impairment in rodents. In this paper, we first briefly introduce the background of cognitive symptoms and EE in schizophrenia, and then investigate the manifestations of MK-801 induced cognitive impairment, the improvement of EE on these cognitive impairments based on the MK-801 induced schizophrenia rodent models, and the possible mechanism of EE in improving cognitive symptoms. This article reviews the literature in recent years, which provides an important reference for MK-801 to construct a cognitive symptom model of schizophrenia and the mechanism of EE in improving cognitive symptoms of schizophrenia.

Nicotine-conditioned place preference, reversal learning, and social interaction in MK-801-induced schizophrenia model: Effects of post-weaning enriched environment

Based on the clinical observations of severe cognitive deficits in schizophrenia patients and the relationship between environmental parameters and the severity of schizophrenia symptoms, the present study investigated these parameters in an MK-801-induced schizophrenia model in rats. In addition to, it evaluated whether a post-weaning enriched environment (EE) would affect the nicotine-induced conditioned place preference (CPP) and the motor and cognitive deficits caused by MK-801 treatment. Male Wistar rat pups were injected peritoneally with MK-801 (1 mg/kg) on a daily basis between the 6th and the 10th postnatal days (P) and were exposed to either an enriched or a standard cage from P21 until the end of the experiments. The rats were evaluated in open-field and three-chamber social interaction tests. Moreover, spatial and reversal learning was assessed by the Morris water maze (MWM). Also, the animals were conditioned with 0.6 mg/kg nicotine and tested for CPP. Increased self-grooming, exploratory behavior, potentiated nicotine-CPP, and decreased social behaviors, delayed spatial learning and memory, and impaired reversal learning in the water maze were observed in the MK-801 treatment group. Housing in an EE improved cognitive and behavioral deficits associated with postnatal MK-801 treatment. The results suggested that neonatal N-methyl-D-aspartate (NMDA) receptor hypofunction may cause susceptibility to these behaviors and indicated the importance of environmental conditions in the development of schizophrenia and probably other neuropsychiatric disorders.

Alteration in Cngb1 Expression upon Maternal Immune Activation in a Mouse Model and Its Possible Association with Schizophrenia Susceptibility

Objective

The cyclic nucleotide-gated channel (Cng) regulates synaptic efficacy in brain neurons by modulating Ca^2＋ levels in response to changes in cyclic nucleotide concentrations. This study investigated whether the expression of Cng channel, cyclic nucleotide-gated channel subunit beta 1 (Cngb1) exhibited any relationship with the pathophysiology of schizophrenia in an animal model and whether genetic polymorphisms of the human gene were associated with the progression of schizophrenia in a Korean population.

Methods

We investigated whether Cngb1 expression was related to psychiatric disorders in a mouse model of schizophrenia induced by maternal immune activation. A case-control study was conducted of 275 schizophrenia patients and 410 controls with single-nucleotide polymorphisms (SNPs) in the 5′-near region of CNGB1.

Results

Cngb1 expression was decreased in the prefrontal cortex in the mouse model. Furthermore, the genotype frequency of a SNP (rs3756314) of CNGB1 was associated with the risk of schizophrenia.

Conclusion

Our results suggest that CNGB1 might be associated with schizophrenia susceptibility and maternal immune activation. Consequently, it is hypothesized that CNGB1 may be involved in the pathophysiology of schizophrenia.

Neonatal blockade of NR2A-containing but not NR2B-containing NMDA receptor induces spatial working memory deficits in adult rats

The immature brain is highly sensitive to disturbances in the functioning of N-methyl-d-aspartate (NMDA) receptor in rodents, and blockade of the receptor during postnatal brain development period causes schizophrenia-like behavior in adulthood. During the postnatal period, NR2A- and NR2B-containing NMDA receptors are highly expressed, and these two subunits show different expression patterns in the brain. However, the functions of these two NMDA receptors are unknown. In this study, we treated rats with an NR2A-preferring NMDA receptor antagonist (PEAQX, 10 mg/kg), an NR2B-selective NMDA receptor antagonist (ifenprodil, 7.5 mg/kg), or a nonselective blocker of the NMDA receptor (MK-801, 0.4 mg/kg) during the neonatal period. Rats neonatally treated with MK-801 or PEAQX showed spatial working memory deficits in the Y-maze test. PEAQX-treated rats also showed greater reactivity to acoustic stimuli and hypersensitivity to acute MK-801 challenge. However, ifenprodil treatment did not cause any detectable behavioral changes. These results suggest that the NR2A-containing NMDA receptor is indispensable for proper brain development in rats, and functional disturbances in this subunit impair hippocampus-dependent spatial working memory in adulthood.

Environmental enrichment or selective activation of parvalbumin-expressing interneurons ameliorates synaptic and behavioral deficits in animal models with schizophrenia-like behaviors during adolescence

Synaptic deficit-induced excitation and inhibition (E/I) imbalance have been implicated in the pathogenesis of schizophrenia. Using in vivo two-photon microscopy, we examined the dynamic plasticity of dendritic spines of pyramidal neurons (PNs) and "en passant" axonal bouton of parvalbumin-expressing interneurons (PVINs) in the frontal association (FrA) cortex in two adolescent mouse models with schizophrenia-like behaviors. Simultaneous imaging of PN dendritic spines and PV axonal boutons showed that repeated exposure to N-methyl-D-aspartate receptor (NMDAR) antagonist MK801 during adolescence disrupted the normal developmental balance of excitatory and inhibitory synaptic structures. This MK801-induced structural E/I imbalance significantly correlated with animal recognition memory deficits and could be ameliorated by environmental enrichment (EE). In addition, selective chemogenetic activation of PVINs in the FrA mimicked the effects of EE on both synaptic plasticity and animal behavior, while selective inhibition of PVIN abolished EE's beneficial effects. Electrophysiological recordings showed that chronic MK801 treatment significantly suppressed the frequency of mEPSC/mIPSC ratio of layer (L) 2/3 PNs and significantly reduced the resting membrane potential of PVINs, the latter was rescued by selective activation of PVINs. Such manipulations of PVINs also showed similar effects in PV-Cre; ErbB4^fl/fl animal model with schizophrenia-like behaviors. EE or selective activation of PVINs in the FrA restored behavioral deficits and structural E/I imbalance in adolescent PV-Cre; ErbB4^fl/fl mice, while selective inhibition of PVINs abolished EE's beneficial effects. Our findings suggest that the PVIN activity in the FrA plays a crucial role in regulating excitatory and inhibitory synaptic structural dynamics and animal behaviors, which may provide a potential therapeutic target for schizophrenia treatment.

Prepubertal Environmental Enrichment Prevents Dopamine Dysregulation and Hippocampal Hyperactivity in MAM Schizophrenia Model Rats

BACKGROUND

Schizophrenia (SCZ) is a neurodevelopmental disorder with a progressive, prolonged course. Early prevention for SCZ is promising but overall lacks support from preclinical evidence. Previous studies have tested environmental enrichment (EE) in certain models of SCZ and discovered a broadly beneficial effect in preventing behavioral abnormalities relevant, yet not specific, to the disorder. Nonetheless, whether EE can prevent dopamine (DA) dysregulation, a hallmark of psychosis and SCZ, had not been tested.

METHODS

Using the MAM (methylazoxymethanol acetate) rat model of schizophrenia and saline-treated control animals, we investigated the long-term electrophysiological effects of prepubertal (postnatal day 21-40) EE on DA neurons, pyramidal neurons in the ventral hippocampus, and projection neurons in the basolateral amygdala. Anxiety-related behaviors in the elevated plus maze and locomotor responses to amphetamine were also analyzed.

RESULTS

Prepubertal EE prevented the increased population activity of DA neurons and the associated increase in locomotor response to amphetamine. Prepubertal EE also prevented hyperactivity in the ventral hippocampus but did not prevent hyperactivity in the basolateral amygdala. Anxiety-like behaviors in MAM rats were not ameliorated by prepubertal exposure to EE.

CONCLUSIONS

Twenty-day prepubertal EE is sufficient to prevent DA hyperresponsivity in the MAM model, measured by electrophysiological recordings and locomotor response to amphetamine. This effect is potentially mediated by normalizing excessive firing in the ventral hippocampus without affecting anxiety-like behaviors and basolateral amygdala firing. This study identified EE as a useful preventative approach that may protect against the pathophysiological development of SCZ.

Ketogenic diet and olanzapine treatment alone and in combination reduce a pharmacologically-induced prepulse inhibition deficit in female mice

We used the acute NMDA receptor hypoactivity model of schizophrenia in mice to compare the efficacy of a long-term ketogenic diet and a commonly used antipsychotic, olanzapine, and to explore the interaction between these treatments. We found that a ketogenic diet in female mice was as effective as olanzapine to diminish MK-801-induced disruption of prepulse inhibition (PPI). Furthermore, combination of the diet with olanzapine treatment resulted in a similar effect compared to either treatment alone. These results suggest that ketogenic diet can be used effectively together with antipsychotics drugs over an extended period.

Enriched Environment Reverts Somatostatin Interneuron Loss in MK-801 Model of Schizophrenia

Dysregulation of the inhibitory drive has been proposed to be a central mechanism to explain symptoms and pathophysiological hallmarks in schizophrenia. A number of recent neuroanatomical studies suggest that certain types of inhibitory cells are deficient in schizophrenia, including somatostatin-immunoreactive interneurons (SST+). The present study sought to use stereological methods to investigate whether the number of SST+ interneurons decreased after repeated injections of NMDA receptor antagonist MK-801 (0.5 mg/kg) and to determine the effect of limited exposure to an enriched environment (EE) in adult life on this sub-population of inhibitory cells. Considering that somatostatin expression is highly dependent on neurotrophic support, we explored the changes in the relative expression of proteins related to brain-derived neurotrophic factor-tyrosine kinase B (BDNF-TrkB) signaling between the experimental groups. We observed that early-life MK-801 treatment significantly decreased the number of SST+ interneurons in the medial prefrontal cortex (mPFC) and the hippocampus (HPC) of adult Long Evans rats. Contrarily, short-term exposure to EE increased the number of SST+ interneurons in MK-801-injected animals, except in the CA1 region of the hippocampus, whereas this increase was not observed in vehicle-injected rats. We also found upregulated BDNF-TrkB signaling after EE that triggered an increase in the pERK/ERK ratio in mPFC and HPC, and the pAkt/Akt ratio in HPC. Thus, the present results support the notion that SST+ interneurons are markedly affected after early-life NMDAR blockade and that EE promotes SST+ interneuron expression, which is partly mediated through the BDNF-TrkB signaling pathway. These results may have important implications for schizophrenia, as SST+ interneuron loss is also observed in the MK-801 pre-clinical model, and its expression can be rescued by non-pharmacological approaches.

Effects of Panax ginseng C.A. Meyer extract on the offspring of adult mice with maternal immune activation

To understand maternal immune activation (MIA) during prenatal development, the synthetic double-stranded RNA polyriboinosinic-polyribocytidylic acid [poly(I:C)] has been widely used in animal models to induce behavioral deficits similar to those in schizophrenia and other psychotic disorders. Panax ginseng C.A. Meyer (PG) extract is widely used to treat various kinds of nervous system disorders in Asia particularly China and Korea. The present study aimed to examine the effects of PG extract on MIA offspring using behavioral activity tests and protein expression analyses. Pregnant mice were exposed to poly(I:C) (5 mg/kg) or vehicle treatment on gestation day 9, and the resulting MIA offspring were subjected to vehicle or PG (300 mg/kg) treatment. In the acoustic startle response test, MIA-induced sensorimotor gating deficit was ameliorated by PG. The majority of behavioral parameters measured in the social interaction (non-aggressive or/and aggressive pattern), open field (number/duration of behavior) and forced swimming test (immobility behavior) were significantly altered in the MIA offspring. Western blot and immunohistochemical analyses of the medial prefrontal cortex indicated that the expression levels of certain neurodevelopmental proteins, including dihydropyrimidinase-related 2, LIM and SH3 domain 1, neurofilament medium, and discs large homolog 4, were decreased in the untreated MIA offspring, whereas PG treatment improved behavioral impairments and increased neurodevelopmental protein expression in MIA offspring. These results suggested that PG may be useful in neurodevelopmental disorder therapy, including psychiatric disorders such as schizophrenia, owing to its antipsychotic effects.

Sex Differences in Psychiatric Disease: A Focus on the Glutamate System

Alterations in glutamate, the primary excitatory neurotransmitter in the brain, are implicated in several psychiatric diseases. Many of these psychiatric diseases display epidemiological sex differences, with either males or females exhibiting different symptoms or disease prevalence. However, little work has considered the interaction of disrupted glutamatergic transmission and sex on disease states. This review describes the clinical and preclinical evidence for these sex differences with a focus on two conditions that are more prevalent in women: Alzheimer's disease and major depressive disorder, and three conditions that are more prevalent in men: schizophrenia, autism spectrum disorder, and attention deficit hyperactivity disorder. These studies reveal sex differences at multiple levels in the glutamate system including metabolic markers, receptor levels, genetic interactions, and therapeutic responses to glutamatergic drugs. Our survey of the current literature revealed a considerable need for more evaluations of sex differences in future studies examining the role of the glutamate system in psychiatric disease. Gaining a more thorough understanding of how sex differences in the glutamate system contribute to psychiatric disease could provide novel avenues for the development of sex-specific pharmacotherapies.

BBOX1 is down-regulated in maternal immune-activated mice and implicated in genetic susceptibility to human schizophrenia

Prenatal exposure to infectious or inflammatory insults can increase the risk of developing neuropsychiatric disorders such as bipolar disorder, autism, and schizophrenia in later life. Gamma-butyrobetaine hydroxylase (BBOX 1) is an enzyme responsible for the biosynthesis of l-carnitine, a key molecule in fatty acid metabolism. This cytosolic dimeric protein belongs to the dioxygenase family. In this study, we investigated whether BBOX 1 expression was related to psychiatric disorder in an animal model. We also conducted a case-control study using 284 schizophrenia patients and 409 controls with single-nucleotide polymorphisms (SNPs) in the 5'-near region of BBOX 1. BBOX 1 expression was increased in the medial frontal cortex of a mouse model of schizophrenia induced by maternal immune activation. Furthermore, the genotype and allele frequencies of two SNPs (rs7939644 and rs10767592) were significantly associated with schizophrenia susceptibility. Our results suggest that BBOX 1 might be associated with maternal immune activation and schizophrenia susceptibility. Therefore, it might be involved in the pathophysiology of schizophrenia.

Adolescent environmental enrichment prevents the emergence of schizophrenia-like abnormalities in a neurodevelopmental model of schizophrenia

In the present study, we investigated whether exposure to an enriched environment (EE) during adolescence might affect the behavioural dysfunction (sensorimotor gating deficit, memory and social interaction impairments) and neurochemical changes (GAD67 expression, histone methylation) induced by methylazoxymethanol (MAM) in the MAM-E17 rat model of schizophrenia. EE was introduced for 7 days in early adolescence (days 23-29), and behavioural and biochemical studies were performed on adult rats at postnatal day 70. The results showed that exposure to EE prevented the development of adult behavioural deficits induced by prenatal MAM administration. EE also prevented the decrease in GAD67 mRNA and protein levels induced by MAM in the medial prefrontal cortex (mPFC). Moreover, EE inhibited the reductions in the amount of Gad1 bound to H3K4me3 and in the total H3K4me3 protein level induced by prenatal MAM administration in the adult mPFC. However, there was no effect of EE on behaviour or levels of the various neurochemical markers in adult rats prenatally treated with vehicle. Thus, these results indicate that EE exposure during early adolescence may inhibit the development of schizophrenia related symptoms through epigenetic mechanisms that regulate the expression of genes (e.g., Gad1) that are impaired in schizophrenia.

Modifications of inhibitory transmission onto pyramidal neurons by postnatal exposure to MK-801: Effects of enriched environment

Early enriched environment (EE) prevents several deficits associated with postnatal MK-801 [N-Methyl-d-Aspartate (NMDA) receptor antagonist] treatment such as cognitive and locomotor deficits. We sought physiological correlates to such changes by looking at inhibitory synaptic inputs onto pyramidal cells in a prefrontal cortex slice preparation. Pharmacologically isolated γ-amino-butyric acid _A (GABA_A) receptor-mediated currents were measured using whole-cell patch clamp recordings. Wistar rats were raised in standard or EE from birth up to the time of experiments and were injected with saline or MK-801 (1mg/kg) on postnatal days (P) 6-10. We recorded miniature inhibitory post-synaptic currents (mIPSCs) of pyramidal cells in layer II/III of prefrontal cortex and measured their frequency, amplitude and kinetics. In control animals, the amplitude and frequency of mIPSCs increased strikingly during development from P21 to P28. MK-801 accelerated the development of mIPSCs frequency but caused a significant decrease in the amplitude of mIPSCs on P28 suggesting a significant reduction of inhibition onto pyramidal cells. EE per se led to a significant increase in both frequency and amplitude of mIPSCs, but its application to MK-801-treated rats resulted in moderate rescue of GABAergic transmission on P28. We conclude that postnatal MK-801 leads to reduced inhibitory transmission onto pyramidal cells of prefrontal cortex at adolescence which may underlie behavioural and morphological differences detected in vivo in rats. EE presentation from birth rather prevents GABAergic alterations associated with postnatal MK-801 treatment at adolescence.

Peripubertal exposure to environmental enrichment prevents schizophrenia-like behaviors in the SHR strain animal model

Schizophrenia is a highly disabling mental disorder, in which genetics and environmental factors interact culminating in the disease. The treatment of negative symptoms and cognitive deficits with antipsychotics is currently inefficient and is an important field of research. Environmental enrichment (EE) has been suggested to improve some cognitive deficits in animal models of various psychiatric disorders. In this study, we aimed to evaluate a possible beneficial effect of early and long-term exposure to EE on an animal model of schizophrenia, the SHR strain. Young male Wistar rats (control strain) and SHRs (21 post-natal days) were housed for 6weeks in two different conditions: in large cages (10 animals per cage) containing objects of different textures, forms, colors and materials that were changed 3 times/week (EE condition) or in standard cages (5 animals per cage - Control condition). Behavioral evaluations - social interaction (SI), locomotion, prepulse inhibition of startle (PPI) and spontaneous alternation (SA) - were performed 6weeks after the end of EE. SHRs presented deficits in PPI (a sensorimotor impairment), SI (mimicking the negative symptoms) and SA (a working memory deficit), and also hyperlocomotion (modeling the positive symptoms). EE was able to reduce locomotion and increase PPI in both strains, and to prevent the working memory deficit in SHRs. EE also increased the number of neurons in the CA1 and CA3 of the hippocampus. In conclusion, EE can be a potential nonpharmacological strategy to prevent some behavioral deficits associated with schizophrenia.

Different effects of isolation-rearing and neonatal MK-801 treatment on attentional modulations of prepulse inhibition of startle in rats

RATIONAL

Prepulse inhibition (PPI) is suppression of the startle reflex by a weaker sensory stimulus (prepulse) preceding the startling stimulus. In people with schizophrenia, impairment of attentional modulation of PPI, but not impairment of baseline PPI, is correlated with symptom severity. In rats, both fear conditioning of prepulse and perceptually spatial separation between the conditioned prepulse and a noise masker enhance PPI (the paradigms of attentional modulation of PPI).

OBJECTIVES

As a neurodevelopmental model of schizophrenia, isolation rearing impairs both baseline PPI and attentional modulations of PPI in rats. This study examined in Sprague-Dawley male rats whether neonatally blocking N-methyl-D-aspartate (NMDA) receptors specifically affects attentional modulations of PPI during adulthood.

RESULTS

Both socially reared rats with neonatal exposure to the NMDA receptor antagonist MK-801 and isolation-reared rats exhibited augmented startle responses, but only isolation rearing impaired baseline PPI. Fear conditioning of the prepulse enhanced PPI in socially reared rats, but MK-801-treated rats lost the prepulse feature specificity. Perceptually spatial separation between the conditioned prepulse and a noise masker further enhanced PPI only in normally reared rats. Clozapine administration during adulthood generally weakened startle, enhanced baseline PPI in neonatally interrupted rats, and restored the fear conditioning-induced PPI enhancement in isolation-reared rats with a loss of the prepulse feature specificity. Clozapine administration also abolished both the perceptual separation-induced PPI enhancement in normally reared rats and the fear conditioning-induced PPI enhancement in MK-801-treated rats.

CONCLUSIONS

Isolation rearing impairs both baseline PPI and attentional modulations of PPI, but neonatally disrupting NMDA receptor-mediated transmissions specifically impair attentional modulations of PPI. Clozapine has limited alleviating effects.

Effects of enriched environment on alterations in the prefrontal cortex GFAP- and S100B-immunopositive astrocytes and behavioral deficits in MK-801-treated rats

A plethora of studies have indicated that enriched environment (EE) paradigm provokes plastic and morphological changes in astrocytes with accompanying increments of their density and positively affects the behavior of rodents. We also previously documented that EE could be employed to preclude several behavioral abnormalities, mainly cognitive deficits, attributed to postnatal N-methyl-d-aspartate (NMDA) receptor antagonist (MK-801) treatment, as a rodent model of schizophrenia (SCH) aspects. Given this, the current study quantitatively investigated the number of cells, presumed to be astrocytes, expressing two astroglia-associated proteins (S100B and glial fibrillary acidic protein (GFAP)) by immunohistochemistry in the prefrontal cortex (PFC), along with anxiety and passive avoidance (PA) learning behaviors by utilizing elevated plus maze (EPM) and shuttle-box tests, in MK-801-treated male wistar rats submitted to EE and non-EE rats. Following a treatment regime of sub-chronic MK-801 (1.0mg/kg i.p. daily for five consecutive days from postnatal day (P) 6), S-100B-positive cells and anxiety level were markedly increased, while the GFAP-positive cells and PA learning were notably attenuated. The trend of diminished GFAP-immunopositive cells and elevated S100B-immunostained cells in the PFC was reversed in the SCH-like rats by exposure of animals to EE, commencing from birth up to the time of experiments on P28-85. Additionally, EE exhibited an ameliorating effect on the behavioral abnormalities evoked by MK-801. Overall, present findings support that improper astrocyte functioning and behavioral changes, reminiscent of the many facets of SCH, occur consequential to repetitive administration of MK-801 and that raising rat pups in an EE mitigates these alterations.

Cognitive endophenotypes, gene-environment interactions and experience-dependent plasticity in animal models of schizophrenia

Schizophrenia is a devastating brain disorder caused by a complex and heterogeneous combination of genetic and environmental factors. In order to develop effective new strategies to prevent and treat schizophrenia, valid animal models are required which accurately model the disorder, and ideally provide construct, face and predictive validity. The cognitive deficits in schizophrenia represent some of the most debilitating symptoms and are also currently the most poorly treated. Therefore it is crucial that animal models are able to capture the cognitive dysfunction that characterizes schizophrenia, as well as the negative and psychotic symptoms. The genomes of mice have, prior to the recent gene-editing revolution, proven the most easily manipulable of mammalian laboratory species, and hence most genetic targeting has been performed using mouse models. Importantly, when key environmental factors of relevance to schizophrenia are experimentally manipulated, dramatic changes in the phenotypes of these animal models are often observed. We will review recent studies in rodent models which provide insight into gene-environment interactions in schizophrenia. We will focus specifically on environmental factors which modulate levels of experience-dependent plasticity, including environmental enrichment, cognitive stimulation, physical activity and stress. The insights provided by this research will not only help refine the establishment of optimally valid animal models which facilitate development of novel therapeutics, but will also provide insight into the pathogenesis of schizophrenia, thus identifying molecular and cellular targets for future preclinical and clinical investigations.

Enriched environment improves synaptic plasticity and cognitive deficiency in chronic cerebral hypoperfused rats

Recent studies have indicated that environmental enrichment (EE) increases the sensorial and social stimulations and leads to strengthened plastic changes in the brain. In models of chronic cerebral hypoperfusion, the ability of an EE to restore the cognition depends on hippocampal synaptic plasticity. The mechanisms for this effect have not, however, been adequately studied. Thus, the aim of the present study was to evaluate the neuroprotective effects and underlying mechanism of environmental enrichment by assessment of spatial memory tasks as well as parameters of synaptic plasticity in rats subjected to occlusion of the bilateral common carotid arteries (2-VO) model. Male Sprague-Dawley rats were used in this study. The model group was established by occlusion of the bilateral common carotid arteries. The animals were tested for learning, memory performance and synaptic plasticity using Morris water maze (MWM), 8-arm Radial Maze (RM), and field potential recording, respectively. The rats subjected to 2-VO in EE exhibited a significantly lower number of working errors and reference errors in RM. Moreover, the enriched environment recovered the memory performance of hypoperfused rats and decreased the swimming time to reach the platform in MWM. In addition, conditions of the environment did not have any effect on baseline synaptic transmission and presynaptic plasticity, but housing the animals in EE rescued the impairment of LTP induction induced by 2-VO. These results suggest that EE ameliorates the LTP and spatial memory impairment induced by 2-VO. Our data indicated that the LTP recovery by EE in the rat models of 2-VO is probably mediated by post-synaptic mechanisms.