Sex-dependent effects of environmental enrichment on spatial memory and brain-derived neurotrophic factor (BDNF) signaling in a developmental "two-hit" mouse model combining BDNF haploinsufficiency and chronic glucocorticoid stimulation

Grech, Adrienne M., Ratnayake, Udani, Hannan, Anthony J., van den Buuse, Maarten, and Hill, Rachel A. (2018) Sex-dependent effects of environmental enrichment on spatial memory and brain-derived neurotrophic factor (BDNF) signaling in a developmental "two-hit" mouse model combining BDNF haploinsufficiency and chronic glucocorticoid stimulation. Frontiers in Behavioral Neuroscience, 12. 227.

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Abstract

Neurodevelopmental disorders are thought to be caused by a combination of adverse genetic and environmental insults. The "two-hit" hypothesis suggests that an early first "hit" primes the developing brain to be vulnerable to a second "hit" during adolescence which triggers behavioral dysfunction. We have previously modeled this scenario in mice and found that the combined effect of a genetic hapolinsuffuciency in the brain-derived neurotrophic factor (BDNF) gene (1st hit) and chronic corticosterone (CORT) treatment during adolescence (2nd hit), caused spatial memory impairments in adulthood. Environmental enrichment (EE) protocols are designed to stimulate experience-dependent plasticity and have shown therapeutic actions. This study investigated whether EE can reverse these spatial memory impairments. Wild-type (WT) and BDNF heterozygous (HET) mice were treated with corticosterone (CORT) in their drinking water (50 mg/L) from weeks 6 to 8 and exposed to EE from 7 to 9 weeks. Enriched housing included open top cages with additional toys, tunnels, housing, and platforms. Y-maze novel preference testing, to assess short-term spatial memory, was performed at 10 weeks of age. At week 16 dorsal hippocampus tissue was obtained for Western blot analysis of expression levels of BDNF, the BDNF receptor TrkB, and NMDA receptor subunits, GluNR1, 2A and 2B. As in our previous studies, spatial memory was impaired in our two-hit (BDNF HET + CORT) mice. Simultaneous EE prevented these impairments. However, EE appeared to worsen spatial memory performance in WT mice, particularly those exposed to CORT. While BDNF levels were lower in BDNF HET mice as expected, there were no further effects of CORT or EE in males but a close to significant female CORT x EE x genotype interaction which qualitatively corresponded with Y-maze performance. However, EE caused both sex- and genotype-specific effects on phosphorylated TrkB residues and GluNR expression within the dorsal hippocampus, with GluNR2B levels in males changing in parallel with spatial memory performance. In conclusion, beneficial effects of EE on spatial memory emerge only following two developmental disruptions. The mechanisms by which EE exerts its effects are likely via regulation of multiple activity-dependent pathways, including TrkB and NMDA receptor signaling.

Item ID: 55942
Item Type: Article (Research - C1)
ISSN: 1662-453X
Keywords: brain-derived neurotrophic factor, spatial memory, environmental enrichment, hippocampus, corticosterone, stress, neuroplasticity
Copyright Information: © 2018 Grech, Ratnayake, Hannan, van den Buuse and Hill. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Funders: National Health and Medical Research Council (NHMRC)
Projects and Grants: NHMRC Project Grant GNT1044777, NHMRC Principal Research Fellowship GNT1117148
Date Deposited: 24 Oct 2018 09:38
FoR Codes: 11 MEDICAL AND HEALTH SCIENCES > 1109 Neurosciences > 110903 Central Nervous System @ 100%
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