It is known that the early environment affects the
mental development of rodent and human offspring. However, it is not known specifically whether a
postpartum depressive state influences the
depressive state in offspring. Using learned helplessness (LH) in rats as an animal model of depression, we examined the influence of maternal
postpartum LH on responses to the LH test of offspring. Dam rats were judged as LH or non-helpless (nLH) on
postnatal days (PN) 2-3, and maternal behavior was recorded during PN2-14. On PN 45-46, offspring were subjected to the LH test. Plasma
corticosterone (
CORT) levels,
hippocampal levels of
glucocorticoid receptor (GR) and
brain-derived neurotrophic factor (
BDNF)
mRNA were measured before and after the LH test in offspring. Active nursing in LH dams was significantly lower than that in nLH dams. Susceptibility to LH in the offspring of LH dams was significantly higher than in those of nLH dams, and was negatively
correlated with active nursing by LH dams. The GR
mRNA levels before and after the LH test were lower in the offspring of LH dams than in those of nLH dams, and the reduced basal GR
mRNA and protein might have resulted in the higher
CORT response after the LH test. There was no significant difference in
BDNF mRNA in the offspring of LH and nLH dams. These findings suggest that early
postpartum LH decreased active nursing and increased depression-like behavior in the adolescent offspring via dysfunction of the
hypothalamic-pituitary-adrenal axis.
