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

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.

Modeling paternal attentiveness: distressed pups evoke differential neurobiological and behavioral responses in paternal and nonpaternal mice.

With the exception of parturition and lactation, male California deer mice (Peromyscus californicus) exhibit the same parental responses toward offspring as conspecific females. A closely related species, Peromyscus maniculatus, however, rarely exhibits paternal responses. In the current study, a comparative species approach was used to assess paternal responses in both Peromyscus species with varying levels of paternal experience (biological fathers, pup-exposed virgins, and pup-naïve virgins). Of special interest was the persistence of the males to direct their attention toward a distressed pup housed in a small enclosure (i.e., a barrier existed between males and pups). In addition to pup-directed responses, non-pup-directed responses such as grooming, resting and jumping were recorded. Subsequently, all animals' brains were assessed for fos-immunoreactivity (ir) in several areas previously associated with the paternal brain circuit. Overall, P. californicus exhibited more pup-directed responses as well as less fos-ir in brain areas involved in emotional integration and processing such as the insula and anterior cingulate. In addition to increased activation of emotional regulatory areas, P. maniculatus males, observed to direct their behavior away from the pup, exhibited higher fos-ir in the nucleus accumbens (involved in goal acquisition), perhaps due to a heightened motivation to avoid the pups. Interestingly, experience with pups altered the lateral septum and amygdala activation of P. maniculatus to levels similar to P. californicus biological fathers. Finally, fos-ir was increased in the medial preoptic area, involved in the maintenance of maternal behavior, in the biological fathers of both species. Thus, although biological predispositions toward pup-directed behaviors were observed in P. californicus males, evidence of a few shifts toward the paternal neural activation profile was apparent in P. maniculatus males. Specifically, modifications in fear responses and social processing may represent the cornerstones of the gradual shift from social tentativeness to social attentiveness in the presence of pups.