Effect of the environmental enrichment on the severity of psychological dependence and voluntary methamphetamine consumption in methamphetamine withdrawn rats

A bibliometric analysis of studies on environmental enrichment spanning 1967-2024: patterns and trends over the years

Environmental Enrichment (EE) has received considerable attention for its potential to enhance cognitive and neurobiological outcomes in animal models. This bibliometric analysis offers a comprehensive evaluation of the EE research spanning from 1967 to 2024, utilizing data extracted from Scopus and analyzed through R and VOSviewer. The volume of publications, citation patterns, and collaborations were systematically reviewed, highlighting important contributions and emerging trends within the field of animal research. Core concepts of EE research are mapped, revealing key themes such as neuroplasticity, cognitive function, and behavioral outcomes. A significant increase in EE research is demonstrated, particularly after the year 2000, reflecting growing scientific and public interest in EE paradigms. This analysis provides insights into the global contributions and collaborative networks that have shaped EE studies over time. The role of EE in advancing the understanding of neurobiological, neurodevelopmental, and neurodegenerative processes is underscored. Influential contributors, leading countries, and high-impact journals in the field of EE are identified, offering a valuable resource for researchers seeking to understand or extend the current knowledge base. The strategic selection of keywords and rigorous data curation methods ensure that the findings accurately reflect the most impactful aspects of EE research in animals. This study serves as an essential reference for future explorations and applications of EE across disciplines. By providing a clear and structured overview of the field, this paper aims to serve as a foundation for ongoing and future research initiatives, encouraging more robust investigations and applications of EE to enhance cognitive and neurological health globally.

Environmental enrichment rescues cognitive impairment with suppression of TLR4-p38MAPK signaling pathway in vascular dementia rats

Increasing evidence demonstrated the promising effects of environmental enrichment (EE) on brain recovery and cognitive performance in animal models of various diseases. However, the effect and molecular mechanisms of EE on vascular dementia (VD) remain to be studied. The aim of this study was to explore the effect of EE on cognitive decline and its mechanism. Sprague-Dawley rats underwent 2-vessel occlusion (2-VO) surgery or sham operation. Subsequently, rats were kept in EE for 4 weeks. In Morris water maze (MWM) test, we demonstrated that EE significantly improved cognitive function in rats with VD. HE staining exhibited morphological changes of neurons and quantitative analysis of TUNEL showed increased apoptotic neurons in hippocampal CA1 region following 2-VO. Results from RT-qPCR showed up-regulation of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) after 2-VO. Western blotting analysis revealed enhanced toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MYD88) and phosphorylated p38 mitogen-activated protein kinase (p-p38MAPK) in 2-VO rats. Whereas administration of EE reduced apoptotic neurons, down-regulated inflammatory factors. Moreover, EE suppressed protein expression of TLR4-p38MAPK pathway. Spearman correlation analysis showed that improved cognitive function was associated with decreased expression of TLR4 and p-p38MAPK proteins. Thus, our study proved that EE has a prominent effect on cognitive impairment and neuronal damage following 2-VO by attenuating inflammation and apoptosis, which may be realized via inhibiting the TLR4-P38MAPK signaling pathway.

Effects of nicotine exposure on oral methamphetamine self-administration, extinction, and drug-primed reinstatement in adolescent male and female rats

BACKGROUND

Adolescent nicotine exposure increases methamphetamine (MA) intake in adult male rats; however, little is known about how nicotine affects MA self-administration during the adolescent period. Therefore, we assessed whether exposing rats to nicotine during early or late adolescence affects oral MA self-administration.

METHODS

146 male and female rats were treated with saline or nicotine (0.16 or 0.64 mg/kg) from postnatal day (PD) 25-PD 34 (the early exposure phase) and/or PD 35-PD 55 (the late exposure phase). Rats began an oral MA self-administration procedure on PD 35.

RESULTS

Only the sex variable, but not nicotine, affected sucrose and MA acquisition, as female rats had more nose pokes than males during training. On the test sessions, female rats exposed to nicotine (0.64 mg/kg) in the early exposure phase had more active nose pokes than saline-treated female rats or nicotine-treated male rats. Rats exposed to nicotine (0.16 mg/kg) in the late exposure phase had fewer active nose pokes during testing than rats exposed to saline. Nose poke responding during extinction was not altered by nicotine exposure, but administering nicotine (0.16 or 0.64 mg/kg) to male rats in the early exposure phase did decrease nose pokes during the drug-primed reinstatement session.

CONCLUSIONS

Our results show that adolescent female rats are more sensitive to the reinforcing effects of oral sucrose and MA than adolescent males, and that preadolescent nicotine exposure enhances oral MA self-administration in female rats. These findings suggest that preteen nicotine use may increase vulnerability to later MA abuse in teenage girls.

Effects of Physical Exercise on the Stereotyped Behavior of Children with Autism Spectrum Disorders

Background and Objectives: Recent studies have shown the existence of a positive relationship between physical exercise, symptomatic improvement, and reduction of damage caused by comorbidities associated with autistic spectrum disorder (ASD) in children, adolescents, and adults. The aim of this systematic review with meta-analysis (SRM) was to estimate the effects of physical exercise (PE) on the stereotyped behaviors of children with a diagnosis of ASD in intervention studies. Materials and Methods: The design followed the PRISMA guidelines and the TREND statement to assess the quality of information in each study. Nine non-randomized intervention trial studies with low, moderate, and vigorous physical exercise, with a duration varying from 8 to 48 weeks and a frequency of 3 times a week, were included in the SRM. The dependent variable episodes of stereotypical behaviors was analyzed in all studies and assessed as the number of episodes demonstrated by the child in pre- versus post-exercise intervention conditions. Results: The eight studies included a total 129 children (115 males and 14 females) with an average age of 8.93 ± 1.69 years. Children with ASD showed a reduction of 1.1 in the number of occurrences of stereotypical behaviors after intervention with physical exercise. Conclusion: Evidence was found to support physical exercise as an effective tool in reducing the number of episodes of stereotypical behaviors in children diagnosed with ASD.

REM sleep deprivation impairs retrieval, but not reconsolidation, of methamphetamine reward memory in male rats

Susceptibility to interference can be a result of memory retrieval and reconsolidation. Given the fact that addiction develops through the neural mechanisms of learning and memory, it would not be surprising that a consolidated drug reward memory may also be susceptible to interference following retrieval/reconsolidation. Due to the critical role of sleep in memory consolidation, sleep deprivation (SD) has been shown to impair memory. Therefore, the major objective of this study was to investigate the effect of rapid eye movement (REM) sleep deprivation (RSD) on the retrieval and reconsolidation of methamphetamine (METH) reward memory in male rats. The animals were trained to acquire METH-induced CPP (2 mg/kg, i.p.). METH reward memory was then reactivated/retrieved in the drug-paired chamber during a drug-free (memory reactivation) session. A period of 48-h RSD paradigm using the multiple platform technique resulted in persistent deficits in the retrieval of METH reward memory. Nevertheless, the same protocol of RSD, which was conducted immediately after the memory reactivation, did not affect the reconsolidation of METH reward memory. Additionally, the RSD episode induced a temporary potentiation of METH-induced hyperlocomotion. Our findings would seem to suggest that sleep is involved in the retrieval, but not reconsolidation, of METH reward memory. The results may also demonstrate that RSD mimics the effects of METH on locomotor activity. The results of this study, therefore, support the idea that sleep is involved in the processing of METH reward memory which can be considered for further investigations to manage the relapse associated with drug-related memory.

Methamphetamine binge administration dose-dependently enhanced negative affect and voluntary drug consumption in rats following prolonged withdrawal: role of hippocampal FADD

While prior studies have established various interacting mechanisms and neural consequences (i.e. monoaminergic nerve terminal damage) that might contribute to the adverse effects caused by methamphetamine administration, the precise mechanisms that mediate relapse during withdrawal remain unknown. This study evaluated the long-term consequences of binge methamphetamine administration (three pulses/day, every 3 hours, 4 days, i.p.; dose-response: 2.5, 5 and 7.5 mg/kg) in adult Sprague-Dawley rats at two behavioral levels following 25 days of withdrawal: (1) negative affect (behavioral despair-forced-swim test, and anhedonia-1% sucrose consumption, two-bottle choice test) and (2) voluntary methamphetamine consumption (20 mg/l, two-bottle choice test). Striatal and hippocampal brain samples were dissected to quantify monoamines content by high-performance liquid chromatography and to evaluate neurotoxicity (dopaminergic and serotonergic markers) and neuroplasticity markers [i.e. cell fate regulator (Fas-associated protein with death domain) FADD] by Western blot. The results showed that methamphetamine administration induced dose-dependent negative effects during prolonged withdrawal in adult rats. In particular, rats treated repeatedly with methamphetamine (7.5 mg/kg) showed (1) enhanced negative affect-increased anhedonia associated with behavioral despair, (2) increased voluntary methamphetamine consumption, (3) enhanced neurotoxicity-decreased dopamine and metabolites in striatum and decreased serotonin in hippocampus, (4) altered neuroplasticity markers-decreased FADD protein and increased p-FADD/FADD balance selectively in hippocampus and (5) higher consumption rates of methamphetamine that were associated with lower FADD content in hippocampus. These results confirm that methamphetamine withdrawal dose-dependently induced negative affect and decreased monoamines content, while also increased voluntary methamphetamine consumption and suggested a role for hippocampal FADD neuroplasticity in these drug-withdrawal adaptations.

Environmental Enrichment During Adulthood Reduces Sucrose Binge-Like Intake in a High Drinking in the Dark Phenotype (HD) in C57BL/6J Mice

Repetitive binge episodes favor transition to binge-eating disorders. Experimental evidence points to positive influence of environmental enrichment (EE) on drug/food addiction, although far less is known regarding EE effects over binge-like consumption. Here, we evaluate the following: (1) whether switching from nonenriched standard environment (SE) to EE housing conditions during adulthood alters a stable pattern of voluntary sucrose (10% w/v) binge-like intake in high (HD) vs. low (LD) drinking phenotypes under a drinking in the dark (DID) schedule; and (2) sucrose binge-like intake in a DID task in response to a pharmacological challenge with an OXr1 antagonist in HD/LD subpopulations after long-term exposure to SE or EE conditions. Adolescent (postnatal day 21; PND21) mice were housed in SE conditions. At PND65, all animals were long-term exposed to sucrose DID. On the first episode of DID (PND65), animals were divided into HD vs. LD subpopulations according to their sucrose intake. On PND85, an OXr1 antagonist test was conducted on HD and LD mice with SB-334867 (SB) administration. On PND95, HD and LD subpopulations were again randomly allocated into two subgroups, resulting in the following experimental conditions: HD-SE, HD-EE, LD-SE and LD-EE. Sucrose binge-like intake continued until PND116, when a second SB test was conducted. The main findings are: (1) a single 2 h episode of sucrose binge drinking in a DID procedure consistently segregates two behavioral subpopulations, HD and LD; (2) when adult mice in standard conditions and long-term exposed to sucrose DID were switched to EE conditions, an immediate reduction in sucrose binge-like intake was observed in HD mice, pointing to a therapeutic role of EE exposure; and (3) administration of the OXr1 antagonist caused an acute reduction in sucrose binge-like intake in HD and LD mice exposed to SE conditions. Importantly, exposure to EE conditions blunted the inhibitory effect of SB on sucrose binge consumption in both behavioral phenotypes, indirectly suggesting a potential EE/OXr1 signaling interaction. We propose the hypothesis that EE might regulate OX-dependent anxiety/compulsivity brain systems, which might secondarily modulate sucrose binge-like intake.

Environmental Enrichment Modulates Drug Addiction and Binge-Like Consumption of Highly Rewarding Substances: A Role for Anxiety and Compulsivity Brain Systems?

Drug addiction is a chronic disorder comprising components of both impulsivity and compulsivity in the so called “addiction cycle” which develops over time from early non-dependent, repetitive, binge-consumption to later post-dependent compulsive consumption. Thus, frequent binge-like intake is a typical pattern of excessive drug intake characteristic of the pre-dependent phase of the addiction cycle, which represent an important risk factor to develop addiction in vulnerable individuals. In this framework, it is of paramount interest to further understand the earliest stage of the addiction cycle so novel approaches would emerge aimed to control repetitive episodes of binge-consumption in non-dependent subjects, protecting vulnerable individuals from transition to dependence. Environmental enrichment (EE) is a preclinical animal model in which animals are housed under novel, social enriched conditions, which allows exercising and provides sensory and cognitive stimulation. EE promotes important improvements for a variety of cognitive processes and clear therapeutic and protective effects preventing ethanol (EtOH) and drug addiction as well. Interestingly, recent observations suggest that EE might additionally modulate binge-like intake of highly palatable caloric substances, including EtOH, which suggests the ability of EE to regulate consumption during the initial stage of the addiction cycle. We have proposed that EE protective and therapeutic effects on binge-consumption of palatable substances might primarily be mediated by the modulatory control that EE exerts on anxiety and impulsivity/compulsivity traits, which are all risk factors favoring transition to drug addiction.

Environmental Enrichment During Adolescence Acts as a Protective and Therapeutic Tool for Ethanol Binge-Drinking, Anxiety-Like, Novelty Seeking and Compulsive-Like Behaviors in C57BL/6J Mice During Adulthood

Repetitive drug/ethanol (EtOH) binge-like consumption during pre-addictive stages favors a transition to addiction in vulnerable organisms. Experimental evidence points to the therapeutic and preventive effects of environmental enrichment (EE) on drug and EtOH addiction; however, little is known regarding EE modulation of binge-like consumption in non-dependent organisms. Here, we explore the impact of early EE on binge-like EtOH consumption: (1) we test whether early EE exposure prevents binge-like EtOH intake (20% v/v) in adult mice under an intermittent drinking in the dark (iDID) schedule; (2) we evaluate the therapeutic effects of EE housing conditions on binge-like EtOH consumption in adult animals; and (3) we compare novelty-seeking and compulsive-like behaviors, and anxiety-like behavior, as measured by the Hole Board (HB) and Elevated Plus Maze (EPM) tests, respectively, in adult EE/standard environment (SE) animals. Adolescent (postnatal day 28; PND28) mice were randomly allocated to two housing conditions (4 animals/cage): EE or SE. At PND67 all the animals were exposed to a schedule of EtOH binge-like iDID. On PND92 half of the animals in each environmental condition (EE and SE) were randomly allocated to two subgroups in a crossover design, where environmental conditions were kept similar to those previously experienced or switched, finally leading to four experimental conditions: EE-EE, EE-SE, SE-SE, and SE-EE. EtOH binge-like consumption continued until PND140, when EPM and HB tests were finally conducted. The main observations were: (1) EE-reared mice showed lower EtOH binge-like intake than SE-reared mice during adulthood, which supports a protective role for EE. (2) when adult EtOH drinking SE-reared mice were switched to EE conditions, a reduction in EtOH binge-like consumption was observed, suggesting a therapeutic role for EE; however, losing EE during adulthood triggered a progressive increase in EtOH binge-like intake. Moreover, (3) EE-housed adult animals with long-term exposure to EtOH binge-drinking showed lower anxiety-like, compulsive-like, and novelty-seeking behaviors than SE-housed mice, irrespective of the specific housing conditions during adolescence. We discuss the primary impact of EE on anxiety-like neurobehavioral brain systems through which it secondarily modulates EtOH binge-like drinking.

Environmental Enrichment Attenuates Morphine-Induced Conditioned Place Preference and Locomotor Sensitization in Maternally Separated Rat Pups

Introduction

This study investigated the effect of the environmental enrichment during adolescence on morphine-induced Conditioned Place Preference (CPP) and locomotor sensitization in maternally separated male and female rat pups.

Methods

Male Wistar rats were allowed to mate with female virgin Wistar rats. Pups were separated from them 3 hours per day during 2-14 days postnatal. All pups were weaned at 21 Postnatal Day (PND) and reared in standard environment or enriched environment from 21 to 50 PND with litter-mates of the same sex. The CPP and behavioral sensitization to morphine were assessed by an unbiased place conditioning paradigm and open filed method.

Results

The results showed that the maternal separation enhanced morphine-induced CPP in both sexes, locomotor sensitization in male pups and tolerance to morphine-induced motor activity in female pups during adolescence. While, male and female pups reared in an EE exhibited a decrease in morphine-induced CPP, locomotor sensitization and tolerance induced by maternal separation compared to their control pups.

Conclusion

Access to enriched environment during adolescence may have a protective effect against morphine-induced reward, locomotor sensitization and tolerance in adolescent male and female rats following maternal separation.

The effects of enriched environment on the behavioral and corticosterone response to methamphetamine in adolescent and adult mice

Methamphetamine alters behavior and the stress response system. Relatively little research has examined the effects of methamphetamine in adolescents and compared these effects to those in adults. Housing in enriched environments has been explored as one way to protect against the effects of methamphetamine, but the findings are conflicting and no study has examined how enriched environment may alter the behavioral and corticosterone responses to methamphetamine in adolescent and adult rodents. We examined the long-term effects of methamphetamine exposure on anxiety, social behavior, behavioral despair, and corticosterone levels in adolescent and adult mice housed in enriched or isolated environments. Enriched environment did not alter the behavioral or corticosterone response to methamphetamine. Methamphetamine exposure decreased anxiety and increased behavioral despair in adult mice, but methamphetamine did not alter behavior in adolescent mice. There was no effect of methamphetamine on social behavior or corticosterone levels. Our findings demonstrate that the specific environmental enrichment paradigm used in this study was not sufficient to mitigate the behavioral effects of methamphetamine and that adolescent mice are relatively resistant to the effects of methamphetamine compared to adult mice.

Methamphetamine binge administration during late adolescence induced enduring hippocampal cell damage following prolonged withdrawal in rats

A recent study from our laboratory demonstrated that binge methamphetamine induced hippocampal cell damage (i.e., impaired cell genesis) in rats when administered specifically during late adolescence (postnatal day, PND 54-57) and evaluated 24 h later (PND 58). The results also suggested a possible role for brain-derived neurotrophic factor (BDNF) regulating cell genesis and survival. This subsequent study evaluated whether these effects persisted in time as measured following prolonged withdrawal. Male Sprague-Dawley rats were treated (i.p.) with BrdU (2 × 50 mg/kg, 3 days, PND 48-50) followed by a binge paradigm (3 pulses/day, every 3 h, 4 days, PND 54-57) of methamphetamine (5 mg/kg, n = 14, M) or saline (0.9% NaCl, 1 ml/kg, n = 12, C). Following 34 days of forced withdrawal (PND 91), rats were killed 45 min after a challenge dose of saline (Sal: C-Sal, n = 6; M-Sal, n = 7) or methamphetamine (Meth: C-Meth, n = 6; M-Meth, n = 7). Neurogenesis markers (Ki-67: cell proliferation; NeuroD: early neuronal survival; BrdU: prolonged cell survival, 41-43 days old cells) were evaluated by immunohistochemistry while neuroplasticity markers (BDNF and Fos forms) were evaluated by Western blot. The main results showed that a history of methamphetamine administration (PND 54-57) induced enduring hippocampal cell damage (i.e., observed on PND 91) by decreasing cell survival (BrdU + cells) and mature-BDNF (m-BDNF) protein content, associated with neuronal survival, growth and differentiation. Interestingly, m-BDNF regulation paralleled hippocampal c-Fos protein content, indicating decreased neuronal activity, and thus reinforcing the persisting negative effects induced by methamphetamine in rat hippocampus following prolonged withdrawal.

Environmental Enrichment as a Positive Behavioral Intervention Across the Lifespan

BACKGROUND

In recent decades, the interest in behavioral interventions has been growing due to the higher prevalence of age-related cognitive impairments. Hence, behavioral interventions, such as cognitive stimulation and physical activity, and along with these, our lifestyle (education level, work position, frequency of cognitive and social activities) have shown important benefits during the cognitive impairment, dementia and even recovery after brain injury. This is due to the fact that this type of intervention and activities promote the formation of a cognitive and brain reserve that allows tolerating brain damage during a long period of time without the appearance of cognitive symptoms. With regard to this, animal models have proved very useful in providing information about the brain mechanisms involved in the development of these cognitive and brain reserves and how they interact with each other.

METHODS

We summarize several studies showing the positive effects of Environmental Enrichment (EE), understood as a housing condition in which animals benefit from the sensory, physical, cognitive and social stimulation provided, on brain and cognitive functions usually impaired during aging.

RESULTS

Most of studies have shown that EE is a successful protocol to improve cognitive functions and reduce anxiety-related behaviors across the lifespan, as well as in animal models of neurodegenerative diseases.

CONCLUSION

Therefore, EE is a laboratory condition in which some aspects of an active lifestyle are reproduced.

Effect of three different regimens of repeated methamphetamine on rats' cognitive performance

Neurocognitive impairment in response to methamphetamine (MA) has been proven in a variety of experimental and clinical studies. Elucidation of the underlying mechanisms of MA-induced cognitive deficits and finding preventive/therapeutic approaches need best-suited animal models. In modeling repeated MA exposure, while some believes that escalating doses simulate drug abuse conditions, others believe this regimen confers a preconditioning protection. The present study aimed to compare the effects of three different regimens of repeated MA administration on memory and cognitive function of adult rats. Rats in two different experimental groups were treated with escalating paradigms consisted of twice-daily i.p. injections; 1-4 mg/kg over 7 days or 1-10 mg/kg over 10 days. The third group received twice-daily doses of 15 mg/kg every other day over 14 days. Spatial working memory, novel object recognition task and anxiety-like behavior were measured sequentially in all MA-treated rats and vehicle-treated controls started from day 8 after last injection. All MA regimens decreased rates of spontaneous alternation in Y-maze and increased anxiety-like response. Short-term recognition memory was unchanged across all MA-treated animals, while long-term memory was impaired in the second and third MA regimen. Though MA deleterious effect especially in recognition memory is somehow dose dependent, preconditioning effect of increasing doses may be ruled out at least in the case of parameters measured here.

Effect of environmental enrichment on physical and psychological dependence signs and voluntary morphine consumption in morphine-dependent and morphine-withdrawn rats

This study was designed to examine the effect of environmental enrichment during morphine dependency and withdrawal on the severity of naloxone-precipitated withdrawal signs, anxiety, and depressive-like behaviors and voluntary morphine consumption in morphine-dependent rats. The rats were injected with bi-daily doses (10 mg/kg, 12 h intervals) of morphine for 14 days following rearing in a standard environment (SE) or enriched environment (EE) during the development of morphine dependence and withdrawal. Then, rats were tested for withdrawal signs after naloxone injection, anxiety (the elevated plus maze) and depression-related behavior (sucrose preference test), and voluntary consumption of morphine using a two-bottle choice paradigm, in morphine-dependent and morphine-withdrawn rats. The results showed that EE decreased naloxone-precipitated withdrawal signs, but not anxiety or sucrose preference during dependence on morphine. The EE-withdrawn rats showed an increase in the elevated plus maze open arm time and entries and higher levels of sucrose preference than SE rats. Voluntary consumption of morphine was lower in the EE-withdrawn rats than in the SE groups in the second period of drug intake. Thus, exposure to EE reduced the severity of morphine dependence and voluntary consumption of morphine, alongside reductions in anxiety and depression-related behavior in morphine-withdrawn rats.

Identification of Treatment Targets in a Genetic Mouse Model of Voluntary Methamphetamine Drinking

Methamphetamine has powerful stimulant and euphoric effects that are experienced as rewarding and encourage use. Methamphetamine addiction is associated with debilitating illnesses, destroyed relationships, child neglect, violence, and crime; but after many years of research, broadly effective medications have not been identified. Individual differences that may impact not only risk for developing a methamphetamine use disorder but also affect treatment response have not been fully considered. Human studies have identified candidate genes that may be relevant, but lack of control over drug history, the common use or coabuse of multiple addictive drugs, and restrictions on the types of data that can be collected in humans are barriers to progress. To overcome some of these issues, a genetic animal model comprised of lines of mice selectively bred for high and low voluntary methamphetamine intake was developed to identify risk and protective alleles for methamphetamine consumption, and identify therapeutic targets. The mu opioid receptor gene was supported as a target for genes within a top-ranked transcription factor network associated with level of methamphetamine intake. In addition, mice that consume high levels of methamphetamine were found to possess a nonfunctional form of the trace amine-associated receptor 1 (TAAR1). The Taar1 gene is within a mouse chromosome 10 quantitative trait locus for methamphetamine consumption, and TAAR1 function determines sensitivity to aversive effects of methamphetamine that may curb intake. The genes, gene interaction partners, and protein products identified in this genetic mouse model represent treatment target candidates for methamphetamine addiction.

Effects of environmental enrichment during induction of methamphetamine dependence on the behavioral withdrawal symptoms in rats

This study was designed to examine the effect of environmental enrichment during METH administration on the behavioral withdrawal symptoms after drug abstinence in rats. Rats reared in standard (SE) or enriched environment (EE) during induction of METH dependence with bi-daily injections of METH (2mg/kg, at 12-h. intervals) for 14 days. Then, rats were evaluated for behavioral withdrawal symptoms, and also for anxiety (elevated plus maze-EPM) and depression (Forced swim test-FST) over a ten day period of abstinence. The results showed that stereotypic behaviors score and the number of rearing were significantly lower in METH/EE rats compared to the SE group during 1-4 days. Also, The METH/EE group exhibited more weight gain during 6-10 days of abstinence. The METH/EE rats exhibited lower levels of immobility after METH abstinence than control group in the FST. EE had no effect on anxiety-like behavior. This study showed that exposure to EE diminished the severity of withdrawal symptoms and depressive-like behavior during spontaneous withdrawal from METH.