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Abstract
Social defeat stress is an ethologically salient stressor which activates dopaminergic
areas and, when experienced repeatedly, has long-term effects on dopaminergic function
and related behavior. The mechanism for these long-lasting consequences remains unclear.
A potential candidate for mediating these effects is brain-derived neurotrophic factor
(BDNF), a neurotrophin involved in synaptic plasticity and displaying alterations
in dopaminergic regions in response to various types of stress. In this study, we
sought to determine whether repeated social defeat stress altered BDNF mRNA and protein
expression in dopaminergic brain regions either immediately after the last stress
exposure or 4 weeks later. Male Sprague-Dawley rats were subjected to social defeat
stress consisting of brief confrontation with an aggressive male rat every third day
for 10 days; control rats were handled according to the same schedule. Animals were
euthanized either 2 h or 28 days after the last stress or handling episode. Our results
show that 2 h after stress, BDNF protein and mRNA expression increased in the medial
prefrontal cortex. At this time-point, BDNF mRNA increased in the amygdala and protein
expression increased in the substantia nigra. Twenty-eight days after stress, BDNF
protein and mRNA expression were elevated in the medial amygdala and ventral tegmental
area. Given the role of BDNF in neural plasticity, BDNF alterations that are long-lasting
may be significant for neural adaptations to social stress. The dynamic nature of
BDNF expression in dopaminergic brain regions in response to repeated social stress
may therefore have implications for lasting neurochemical and behavioral changes related
to dopaminergic function.
Copyright 2010 IBRO. Published by Elsevier Ltd. All rights reserved.