Environmental enrichment may protect against neural and behavioural damage caused by withdrawal from chronic alcohol intake

Neurobehavioral effects of environmental enrichment and drug abuse vulnerability: An updated review

Environmental enrichment consisting of social peers and novel objects is known to alter neurobiological functioning and have an influence on the behavioral effects of drugs of abuse in preclinical rodent models. An earlier review from our laboratory (Stairs and Bardo, 2009) provided an overview of enrichment-specific changes in addiction-like behaviors and neurobiology. The current review updates the literature in this extensive field. Key findings from this updated review indicate that enrichment produces positive outcomes in drug abuse vulnerability beyond just psychostimulants. Additionally, recent studies indicate that enrichment activates key genes involved in cell proliferation and protein synthesis in nucleus accumbens and enhances growth factors in hippocampus and neurotransmitter signaling pathways in prefrontal cortex, amygdala, and hypothalamus. Remaining gaps in the literature and future directions for environmental enrichment and drug abuse research are identified.

Environmental Enrichment Components Required to Reduce Methamphetamine-Induced Behavioral Sensitization in Mice: Examination of Behaviors and Neural Substrates

Environmental enrichment (EE) involves the presentation of various sensory, physical, social, and cognitive stimuli in order to alter neural activity in specific brain areas, which can ameliorate methamphetamine (MAMPH)-induced behavioral sensitization and comorbid anxiety symptoms. No previous studies have comprehensively examined which EE components are critical for effectively reducing MAMPH-induced behavioral sensitization and anxiety. This study examined different housing conditions, including standard housing (SH, No EE), standard EE (STEE), physical EE (PEE), cognitive EE (CEE), and social EE (SEE). In the beginning, mice were randomly assigned to the different combinations of housing conditions and injections, consisting of No EE/Saline, No EE/MAMPH, STEE/MAMPH, PEE/MAMPH, CEE/MAMPH, and SEE/MAMPH groups. Then, the mice received intraperitoneal injections of 1 mg/kg MAMPH or normal saline daily for 7 days, followed by a final injection of 0.5 mg/kg MAMPH or normal saline. After behavioral tests, all mice were examined for c-Fos immunohistochemical staining. The results showed that MAMPH induced behavioral sensitization as measured by distance traveled. MAMPH appeared to induce lowered anxiety responses and severe hyperactivity. All EE conditions did not affect MAMPH-induced lowered anxiety behaviors. STEE was likely more effective for reducing MAMPH-induced behavioral sensitization than PEE, CEE, and SEE. The c-Fos expression analysis showed that the medial prefrontal cortex (i.e., cingulate cortex 1 (Cg1), prelimbic cortex (PrL), and infralimbic cortex (IL)), nucleus accumbens (NAc), basolateral amygdala (BLA), ventral tegmental area (VTA), caudate-putamen (CPu), and hippocampus (i.e., CA1, CA3, and dentate gyrus (DG)) contributed to MAMPH-induced behavioral sensitization. The Cg1, IL, NAc, BLA, VTA, CPu, CA3, and DG also mediated STEE reductions in MAMPH-induced behavioral sensitization. This study indicates that all components of EE are crucial for ameliorating MAMPH-induced behavioral sensitization, as no individual EE component was able to effectively reduce MAMPH-induced behavioral sensitization. The present findings provide insight into the development of non-pharmacological interventions for reducing MAMPH-induced behavioral sensitization.

Environmental Enrichment Rescues Endocannabinoid-Dependent Synaptic Plasticity Lost in Young Adult Male Mice after Ethanol Exposure during Adolescence

Binge drinking (BD) is a serious health concern in adolescents as high ethanol (EtOH) consumption can have cognitive sequelae later in life. Remarkably, an enriched environment (EE) in adulthood significantly recovers memory in mice after adolescent BD, and the endocannabinoid, 2-arachydonoyl-glycerol (2-AG), rescues synaptic plasticity and memory impaired in adult rodents upon adolescent EtOH intake. However, the mechanisms by which EE improves memory are unknown. We investigated this in adolescent male C57BL/6J mice exposed to a drinking in the dark (DID) procedure four days per week for a duration of 4 weeks. After DID, the mice were nurtured under an EE for 2 weeks and were subjected to the Barnes Maze Test performed the last 5 days of withdrawal. The EE rescued memory and restored the EtOH-disrupted endocannabinoid (eCB)-dependent excitatory long-term depression at the dentate medial perforant path synapses (MPP-LTD). This recovery was dependent on both the cannabinoid CB1 receptor and group I metabotropic glutamate receptors (mGluRs) and required 2-AG. Also, the EE had a positive effect on mice exposed to water through the transient receptor potential vanilloid 1 (TRPV1) and anandamide (AEA)-dependent MPP long-term potentiation (MPP-LTP). Taken together, EE positively impacts different forms of excitatory synaptic plasticity in water- and EtOH-exposed brains.

Chronic Ethanol Differentially Modulates Glutamate Release from Dorsal and Ventral Prefrontal Cortical Inputs onto Rat Basolateral Amygdala Principal Neurons

The medial prefrontal cortex (mPFC) and the basolateral amygdala (BLA) have strong reciprocal connectivity. Projections from the BLA to the mPFC can drive innate, anxiety-related behaviors, but it is unclear whether reciprocal projections from the mPFC to BLA have similar roles. Here, we use optogenetics and chemogenetics to characterize the neurophysiological and behavioral alterations produced by chronic ethanol exposure and withdrawal on dorsal mPFC (dmPFC) and ventral mPFC (vmPFC) medial prefrontal cortical terminals in the BLA. We exposed adult male Sprague Dawley rats to chronic intermittent ethanol (CIE) using vapor chambers, measured anxiety-like behavior on the elevated zero maze, and used electrophysiology to record glutamatergic and GABAergic responses in BLA principal neurons. We found that withdrawal from a 7 d CIE exposure produced opposing effects at dmPFC (increased glutamate release) and vmPFC (decreased glutamate release) terminals in the BLA. Chemogenetic inhibition of dmPFC terminals in the BLA attenuated the increased anxiety-like behavior we observed during withdrawal. These data demonstrate that chronic ethanol exposure and withdrawal strengthen the synaptic connections between the dmPFC and BLA but weakens the vmPFC–BLA pathway. Moreover, facilitation of the dmPFC–BLA pathway during withdrawal contributes to anxiety-like behavior. Given the opposing roles of dmPFC–BLA and vmPFC–BLA pathways in fear conditioning, our results suggest that chronic ethanol exposure simultaneously facilitates circuits involved in the acquisition of and diminishes circuits involved with the extinction of withdrawal-related aversive behaviors.

Effects of environmental enrichment on reinstatement of methamphetamine-induced conditioned place preference

OBJECTIVE

The influence of environmental enrichment (EE) on reinstatement to methamphetamine (METH) seeking in rat model was investigated.

METHODS

Wistar rats were divided to receive saline (1 ml/kg) or METH (1 mg/kg, i.p.) for 8 days during the conditioning training in the conditioned place preference (CPP) paradigm, which is one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. Rats were then kept in either isolated (IE) or enriched environment (EE) for 30 days during the extinction training. Animals were finally examined for reinstatement provoked by i.p. injections of METH.

RESULTS

Saline injections during the conditioning phase did not change CPP during reinstatement in animals of IE or EE control groups. METH injections reinstated place preference in the IE animal group. Interestingly, EE significantly blocked this reinstatement effects of METH.

CONCLUSION

These results show the important role of social interactions and positive environment conditions in preventing reinstatement to drug use.

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.