Paper or Plastic? Exploring the Effects of Natural Enrichment on Behavioural and Neuroendocrine Responses in Long‐Evans Rats

Abstract

Enriched environments are beneficial to neurobiological development; specifically, rodents exposed to complex, rather than standard laboratory, environments exhibit evidence of neuroplasticity and enhanced cognitive performance. In the present study, the nature of elements placed in the complex environment was investigated. Accordingly, rats (n = 8 per group) were housed either in a natural environment characterised by stimuli such as dirt and rocks, an artificial environment characterised by plastic toys and synthetic nesting materials, a natural/artificial environment characterised by a combination of artificial and natural stimuli or a laboratory standard environment characterised by no enrichment stimuli. Following exposure to emotional and cognitive behavioural tasks, including a cricket hunting task, a novel object preference task and a forced swim task, brains were processed for glial fibrillary acidic protein (GFAP)-, neuronal nuclei (NeuN)- and brain-derived neurotrophic factor (BDNF) immunoreactivity. Baseline and stress foecal samples were collected to assess corticosterone (CORT) and dehydroepiandrosterone (DHEA). Natural environment animals exhibited shorter diving latencies and increased diving frequencies in the second forced swimming task, along with higher DHEA/CORT ratios, and higher GFAP immunoreactivity in the hippocampus. The type of environmental enrichment did not influence levels of BDNF immunoreactivity in the CA1, CA3 and dentate gyrus of the hippocampus; however, natural environment animals exhibited higher levels of NeuN immunoreactivity in the retrosplenial cortex, an area involved in spatial memory and other cognitive functions. These results suggest that, in addition to enhancing behavioural and endocrinological variables associated with resilience, exposure to natural stimuli might alter plasticity in brain areas associated with cortical processing and learning.

Duration of Environmental Enrichment Determines Astrocyte Number and Cervical Lymph Node T Lymphocyte Proportions but Not the Microglial Number in Middle-Aged C57BL/6 Mice

“…However, no differences in CD4 + and CD8 + early activation T cell markers were observed after both short-and long-term EE. Our results are in contrast to the known neuroprotective effects of EE (Young et al, 1999;Singhal et al, 2014a;Bardi et al, 2016). Nonetheless, the enhanced cytotoxic immunity could be attributed to the observed decrease in locomotion in a threatening environment (open field) and increases in anxiety-like behavior in middle-aged C57BL/6 mice after long-term EE that we have reported in our recent publication (Singhal et al, 2019).…”

Enriched Environment Exposure Enhances Social Interactions and Oxytocin Responsiveness in Male Long-Evans Rats

“…Further, compared to animals placed in an environment with artificial stimuli, the natural-enriched animals exhibited less anxiety-typical behavior in response to a predator odor (Lambert et al, 2016 ). In a similar study, natural enriched rats exhibited more evidence of emotional regulation in a challenging swim escape task, evidenced by shorter latencies and increased frequencies of diving responses as well as higher DHEA/corticosteroid ratios; however, no differences in hippocampal BDNF levels were observed between the natural- and artificial-enriched groups (Bardi et al, 2016 ). These findings confirmed earlier observations of the UC Berkeley team indicating more neuroanatomical modifications in enriched animals housed in a naturalistic outdoor habitat that provided opportunities for burrowing and exposed the animals to additional natural elements than encountered by the laboratory enriched animals (as described in Rosenzweig et al, 1972 ).…”

“…These findings confirmed earlier observations of the UC Berkeley team indicating more neuroanatomical modifications in enriched animals housed in a naturalistic outdoor habitat that provided opportunities for burrowing and exposed the animals to additional natural elements than encountered by the laboratory enriched animals (as described in Rosenzweig et al, 1972 ). If the natural environments stimulate more species-relevant responses (directed toward both physical and social stimuli), this habitat presents an optimal environment to investigate the influence of social interactions on neurobiological outcomes observed in various enriched environments (Thorpe, 1963 ; Renner and Rosenzweig, 1986 ; Bardi et al, 2016 ; Lambert et al, 2016 ).…”

Experience during early adulthood shapes the learning capacities and the number of synaptic boutons in the mushroom bodies of honey bees (Apis mellifera)

“…This is in contrast with a large part of the literature on the effects of environmental enrichment, where animals were studied outside of their natural context, in laboratory rearing conditions corresponding rather to impoverished environments (Rosenzweig and Bennett 1996). Hence, we would like to stress the importance of considering the impact of ecological conditions on how the brain and behavior of animals mature, in line with recent vertebrate studies highlighting the differences between naturalistic environments and artificially enriched environments in cognitive neuroscience (Landers et al 2011;Schaefers 2013;Bardi et al 2016;Lambert et al 2016). Within this framework, to our knowledge this is the first demonstration that natural conditions are important for the proper maturation of learning performances and their underlying neural networks in an invertebrate model.…”