Neurobehavioral Effects of Restricted and Unpredictable Environmental Enrichment in Rats

Abstract

To study how motivational factors modulate experience-dependent neurobehavioral plasticity, we modify a protocol of environmental enrichment (EE) in rats. We assumed that the benefits derived from EE might vary according to the level of incentive salience attributed to it. To enhance the rewarding properties of EE, access to the EE cage varied randomly from 2 to 48 h for 30 days (REE). The REE group was enriched only 50% of the time and was compared to standard housing and continuous EE (CEE) groups. As behavioral readout, we analyzed the spontaneous activity and the ultrasonic vocalizations (USVs) within the EE cage weekly, and in the open field test at the end of the experiment. In the cage, REE increased the utilization of materials, physical activity, and the rate of appetitive USVs. In the OF, the CEE-induced enhancements in novelty habituation and social signaling were equaled by the REE. At the neural level, we measured the expression of genes related to neural plasticity and epigenetic regulations in different brain regions. In the dorsal striatum and hippocampus, REE upregulated the expression of the brainderived neurotrophic factor, its tropomyosin kinase B receptor, and the DNA methyltransferase 3A. Altogether, our results suggest that the higher activity within the cage and the augmented incentive motivation provoked by the REE boosted its neurobehavioral effects equaling or surpassing those observed in the CEE condition. As constant exposures to treatments or stimulating environments are virtually impossible for humans, restricted EE protocols would have greater translational value than traditional ones.

The cage test as an easy way to screen and evaluate spontaneous activity in preclinical neuroscience studies

“…The information could be used for allocating subjects to the groups, as covariates during statistical analyses, and for classifying subjects based on particular traits in studies of individual differences. Based on our previous experience with this test [7 , 28 , 31] , we offer a comprehensive protocol for its implementation, a suggested strategy for its analysis, and a procedure for allocating and balancing the subjects to the experimental groups. All experimental procedures reported in this protocol were done in accordance with the guidelines of the Costa Rican Ministry of Science and Technology for the Care and Use of Laboratory Animals and were approved by the Institutional Committee for Animal Care and Use of the University of Costa Rica (CICUA-047-17).…”

“…Locomotion is a general indicator of psychomotor reactivity and an index of anxiety (the motivation to escape from unknown and unpredictable stimuli). [8 , 12 , 19 , 28 , 30 , 31 , 36] . Rearing Rearing consists of a bipedal posture (>45° from the floor), in which the animal extends its head upwards, executing a series of lateral movements using its vibrissae (whiskers) to sense the surroundings (by smelling and touching out).…”

“…Because uncertainty and ambiguity about possible threats naturally evoke rearing, it has been interpreted as an anxiety-like behavior. [4 , 5 , 28 , 31] . Grooming Grooming consists of a set of complex, self-directed movements aimed at the care of the body surface.…”

“…However, grooming interpretation in the context of behavioral sciences is still a vividly open discussion. [1 , 8 , 12 , [16] , [17] , [18] , 21 , 22 , 25 , 28 , [30] , [31] , [32] , 37 , 38] . USVs Most rodent species, including laboratory rats and mice, emit USVs (i.e., >20 kHz) produced by a whistle mechanism through their larynx's constriction.…”

Developing Proprioceptive Countermeasures to Mitigate Postural and Locomotor Control Deficits After Long-Duration Spaceflight

“…In animal studies, sensory environmental enrichment has been shown to provide a CNS protective effect against radiation ( Fan et al, 2007 ) and promote social and behavioral adaptability in response to changing environmental conditions ( Gelfo, 2019 ; Gubert and Hannan, 2019 ). Even short but highly rewarding interactions with a stimulating context can induce positive effects on brain and behavior comparable to those produced by extended exposures ( Rojas-Carvajal et al, 2020 ). Thus, VR could augment proprioceptive training by providing an interesting virtual environment that will keep crewmembers cognitively engaged and challenged during long-duration exploration class missions ( Wu et al, 2016 ).…”