Environmental enrichment improves novel object recognition and enhances agonistic behavior in male mice.

Environmental enrichment (EE) is an experimental paradigm in which rodents are housed in complex environments containing objects that provide stimulation, the effects of which are expected to improve the welfare of these subjects. EE has been shown to considerably improve learning and memory in rodents. However, knowledge about the effects of EE on social interaction is generally limited and rather controversial. Thus, our aim was to evaluate both novel object recognition and agonistic behavior in NMRI mice receiving EE, hypothesizing enhanced cognition and slightly enhanced agonistic interaction upon EE rearing. During a 4-week period half the mice (n = 16) were exposed to EE and the other half (n = 16) remained in a standard environment (SE). On PND 56-57, animals performed the object recognition test, in which recognition memory was measured using a discrimination index. The social interaction test consisted of an encounter between an experimental animal and a standard opponent. Results indicated that EE mice explored the new object for longer periods than SE animals (P < .05). During social encounters, EE mice devoted more time to sociability and agonistic behavior (P < .05) than their non-EE counterparts. In conclusion, EE has been shown to improve object recognition and increase agonistic behavior in adolescent/early adulthood mice. In the future we intend to extend this study on a longitudinal basis in order to assess in more depth the effect of EE and the consistency of the above-mentioned observations in NMRI mice.

Behavioral effects of combined environmental enrichment and chronic nicotine administration in male NMRI mice.

Environmental enrichment (EE) is an experimental paradigm which provides sensory, social, physical and cognitive stimulation for rodents. Experimental evidence indicates that this type of housing induces different neurobiological and behavioral changes. However, few studies have evaluated the consequences of combined exposure to an enriched environment and nicotine administration during a critical period of development such as adolescence. Taking into account previous studies, it can be hypothesized that a chronic treatment with nicotine would modulate the effects of rearing animals in enriched environments. In the current study, our main aim was to evaluate the effects of EE and chronic nicotine administration on physiological parameters (weight, fluid intake and cotinine levels), motor activity, exploratory behavior, anxiety and learning in male NMRI mice. Half of the mice (n=32) were exposed to an enriched environment (EE) and the other half (n=32) were housed in standard environments (SE) with or without oral nicotine administration (100 µg/ml). After 3 weeks, mice were evaluated in a behavioral battery that included an elevated plus-maze, a hole board, an actimeter and an inhibitory avoidance task. Blood cotinine levels were measured in an additional group of 32 mice in order to confirm nicotine intake. Results indicated that mice reared in an enriched environment gained less body weight and displayed higher fluid intake than those maintained in a standard environment. EE reduced motor activity, exploratory behavior and anxiety, whereas it enhanced inhibitory avoidance learning. In relation to the effects of chronic nicotine treatment, the data reflected a lower increase in body weight and a reduced fluid intake in nicotine-treated mice. In the elevated plus-maze, nicotine induced a reduction of total arm entries and rearings. Cotinine levels were higher in mice that received oral nicotine than in the control group. We conclude that the EE paradigm applied in this study induces physiological and behavioral changes in NMRI mice. Chronic nicotine treatment diminished motor activity displayed by mice in the elevated plus-maze but did not have significant effects on inhibitory avoidance learning. Future studies should explore in greater depth the interaction between environmental factors and nicotine administration using longer periods of EE, a wider range of doses and/or other cholinergic agonists, acute drug administration, and sequential exposure to nicotine and EE.

[Nicotine and animal models: what does the environmental enrichment paradigm tell us?]. / Nicotina y modelos animales: ¿qué nos aporta el paradigma de enriquecimiento ambiental?

The Environmental Enrichment (EE) paradigm is a housing condition which aims is to provide physical, cognitive and sensorial stimulation to rodents. Animals are housed in larger cages containing inanimate objects such as tunnels, toys and running wheels. The main aim of the current work is to tackle the arguments which suggest that EE may diminish vulnerability to developing addiction to nicotine and other drugs of abuse and to review recent experimental studies performed in relation to this subject. We discuss the major changes induced by EE at physical, neurobiological and behavioral levels and review the results of recent studies which indicate that EE promotes both neurochemical (potentiation of the increase in dopamine release induced by nicotine in the brain cortex) and behavioral changes (increased ability to discriminate the presence of reward and decreased impulsivity), thus supporting the hypothesis put forward. In light of these results, EE can be proposed as a model for the study of vulnerability to addiction to different drugs of abuse, including cocaine and nicotine, though further studies are needed in order to establish the neurobiological implications of the effects of exposure to enriched environments and their possible relationship with changes in brain reward systems.

Nicotina y modelos animales: ¿qué nos aporta el paradigma de enriquecimiento ambiental? / Nicotine and animal models: what does the environmental enrichment paradigm tell us?

El Enriquecimiento Ambiental (Environmental Enrichment o EE) es un modelo de alojamiento basada en la estimulación a nivel físico, cognitivo y sensorial de roedores. Esta condición se caracteriza por el alojamiento de un grupo de animales en cajas grandes que contienen distintos objetos como túneles, juguetes y ruedas de correr. El principal objetivo del presente trabajo es plantear los principales argumentos que sugieren que el alojamiento en condiciones de EE puede disminuir la vulnerabilidad a desarrollar adicción a la nicotina y a otras drogas de abuso, así como revisar estudios experimentales recientes relacionados con este área. Con este fin, se presenta una revisión de los principales cambios inducidos por el EE a nivel físico, neurobiológico y conductual y se exponen los resultados obtenidos en diversos estudios recientes que indican que el alojamiento en EE induce cambios neuroquímicos (potenciación del aumento de liberación de dopamina inducida por la nicotina en el córtex cerebral) y conductuales (mayor capacidad para discriminar la presencia de recompensa y disminución de la impulsividad) que apoyarían la hipótesis planteada. En base a estos resultados, cabría proponer el EE como un modelo adecuado para el estudio de la vulnerabilidad a la adicción a diferentes drogas de abuso como la cocaína o la nicotina aunque es necesario realizar más estudios que permitan establecerlas bases neurobiológicas de los efectos inducidos por la exposición a ambientes enriquecidos y su posible relación con modificaciones en los sistemas cerebrales de refuerzo(AU)

The Environmental Enrichment (EE) paradigm is a housing condition which aims is to provide physical, cognitive and sensorial stimulation to rodents. Animals are housed in larger cages containing in animate objects such as tunnels, toys and running wheels. The main aim of the current work is to tackle the arguments which suggest that EE may diminish vulnerability to developing addiction to nicotine and other drugs of abuse and to review recent experimental studies performed in relation to this subject. We discuss the major changes induced by EE at physical, neurobiological and behavioral levels and review the results of recent studies which indicate that EE promotes both neurochemical (potentiation of the increase in dopamine release induced by nicotine in the brain cortex) and behavioral changes (increased ability to discriminate the presence of reward and decreased impulsivity), thus supporting the hypothesis put forward. In light of these results, EE can be proposed as a model for the study of vulnerability to addiction to different drugs of abuse, including cocaine and nicotine, though further studies are needed in order to establish the neurobiological implications of the effects of exposure to enriched environments and their possible relationship with changes in brain reward systems(AU)

Individual differences in novelty-seeking and behavioral responses to nicotine: a review of animal studies.

Individual differences in the behavioral responses to a novel environment have been proposed as a research tool to predict responsiveness to other behavioral tasks, response to certain events and individual vulnerability to nicotine addiction. In rats and mice, novelty seeking (defined as enhanced specific exploration of novel situations) is a complex behavior confirmed by a large body of neurochemical, endocrinological and behavioral data. We review the main standardized procedures employed to measure the novelty seeking trait in rodents and the ontogeny of this behavior throughout the life-span taking into account that novelty seeking can be permanently modified as a consequence of particular early experiences, maternal care, and environmental enrichment. Studies in animal models suggest that individual differences in the sensitivity to nicotine depend on different variables such as basal locomotor activity of the experimental subjects, their response to novel environments (open-field, hole-board) and level of impulsivity. It is concluded that these basic findings contribute to a better understanding of smoking behavior and to the establishment of improved pharmacological treatments if individual differences are borne in mind.