Neurobiological Effects Of Neonatal Maternal Separation And Post-Weaning

Behavioural Brain Research 240 (2013) 110–118

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Behavioural Brain Research
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Research report

Neurobiological effects of neonatal maternal separation and post-weaning environmental enrichment
Ana Laura Vivinetto, Marta Magdalena Suárez, María Angélica Rivarola ∗
Cátedra de FisiologíaAnimal-Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de Córdoba, Av. Vélez Sarsfield 299-X5000JJC, Córdoba, Argentina

h i g h l i g h t s
We examined whether environmental enrichment (EE) could compensate the effects of early maternal separation (MS). Maternal separation impaired inhibitory avoidance but had no effect in object recognition. Grooming behavior in the open fieldwas significantly lower in maternally separated animals. EE reversed the effects of MS in the inhibitory avoidance task and in grooming behavior. c-Fos expression as well as glucocorticoid receptor in the hippocampus were increased by enrichment.

a r t i c l e

i n f o

a b s t r a c t
Throughout the lifespan, the brain has a considerable degree of plasticity and can be strongly influenced bysensory input from the outside environment. Given the importance of the environment in the regulation of the brain structure, behavior and physiology, the aim of the present work was to analyze the effects of different environmental qualities during two critical ontogenic periods (early life and peripuberty) on behavior and hippocampal physiology. Male Wistar rats were separated from theirmothers for 4.5 h daily during the first 3 weeks of life. They were weaned on day 21 and housed under either standard or enriched conditions. At 60 d of age, all animals were then housed in same-treatment groups, two per cage, until testing began on day 74. Emotional and cognitive responses were tested using the open field, novel object recognition test and step-down inhibitory avoidance learning. In thedorsal hippocampus, glucocorticoid receptor expression and neuronal activity were examined by immunoreactivity. Grooming behavior in the open field was found to be significantly lower in maternally separated animals, but post-weaning environmental enrichment completely reversed this tendency. Inhibitory avoidance but not object recognition memory was impaired in maternally separated animals,suggesting that early maternal separation alters learning and memory in a task-specific manner. Again, environmental enrichment reversed the effects of maternal separation on the inhibitory avoidance task. Even though maternal separation did not significantly affect Fos and glucocorticoid receptor (GR) expression, environmental enrichment increased both Fos expression in the total hippocampal area and alsothe overall number of GR positive cells per hippocampal area, mainly due to the changes in CA1. These findings suggest that differential rearing is a useful procedure to study behavioral and physiological plasticity in response to early experience and that, although the effects of adverse experience early in life such as maternal separation can persist until adulthood, some of them can becompensated by early favorable environments, possibly through nervous system plasticity. © 2012 Elsevier B.V. All rights reserved.

Article history: Received 7 May 2012 Received in revised form 8 November 2012 Accepted 12 November 2012 Available online xxx Keywords: Maternal separation Environmental enrichment Hippocampus Memory Glucocorticoid receptors

1. Introduction Over the past decade, theimportance of environmental influences in regulating brain activity, behavior and physiology has been widely recognized [1–7]. There is compelling evidence that stressful experiences early in life affect neuroendocrine, cognitive and behavioral development and lead to greater susceptibility to psychopathology in adulthood [3,8]. A normal interaction between

Abbreviations: MS, maternally separated;...