The influence of complex and threatening environments in early life on brain size and behaviour.

C. DePasquale,V. A. Braithwaite,A. M. Hirrlinger,T. Neuberger

doi:10.1098/rspb.2015.2564

C. DePasquale, V. A. Braithwaite + Show 2 more

Open Access

https://doi.org/10.1098/rspb.2015.2564

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Abstract

The ways in which challenging environments during development shape the brain and behaviour are increasingly being addressed. To date, studies typically consider only single variables, but the real world is more complex. Many factors simultaneously affect the brain and behaviour, and whether these work independently or interact remains untested. To address this, zebrafish (Danio rerio) were reared in a two-by-two design in housing that varied in structural complexity and/or exposure to a stressor. Fish experiencing both complexity (enrichment objects changed over time) and mild stress (daily net chasing) exhibited enhanced learning and were less anxious when tested as juveniles (between 77 and 90 days). Adults tested (aged 1 year) were also less anxious even though fish were kept in standard housing after three months of age (i.e. no chasing or enrichment). Volumetric measures of the brain using magnetic resonance imaging (MRI) showed that complexity alone generated fish with a larger brain, but this increase in size was not seen in fish that experienced both complexity and chasing, or chasing alone. The results highlight the importance of looking at multiple variables simultaneously, and reveal differential effects of complexity and stressful experiences during development of the brain and behaviour.

Highlights

Since Hebb [1] first described the importance of environmental complexity and its effects on animals, there has been interest in how the environment drives differences in the brain and behaviour
The first anxiety assay was performed after 52 days of treatment exposure (n 1⁄4 18 per treatment) when fish were screened in a novel tank diving test [34]
When juvenile fish were tested, fish reared in plain tanks without chasing spent more time in the bottom of the test tank, showing increased signs of anxiety compared with fish that experienced enrichment and chasing

Summary

Introduction

Since Hebb [1] first described the importance of environmental complexity and its effects on animals, there has been interest in how the environment drives differences in the brain and behaviour. The first anxiety assay was performed after 52 days of treatment exposure (n 1⁄4 18 per treatment) when fish were screened in a novel tank diving test [34]. At this stage the zebrafish were immature and could not be sexed. The pre-optic area (POA) was included in all telencephalon volume measurement, and the whole brain was defined as extending from the most rostral area of the olfactory bulb (glomerular layer of the olfactory bulb) to the terminus of the rhombencephalic ventricle caudally These structures had readily distinguishable boundaries that could be defined in all specimens (figure 1).

Results

Discussion

29. Yun J et al 2010 Chronic restraint stress impairs

34. Cachat J et al 2010 Measuring behavioral and