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Social stress induces hypothalamo‐pituitary‐adrenal axis responses in lactating rats bred for high trait anxiety

Hypothalamo‐pituitary‐adrenal axis responses to various stressors are typically attenuated during lactation, including in rats selectively bred for high or low anxiety. As high‐anxiety dams are more aggressive towards intruders than low‐anxiety dams during maternal defence, we investigated their hypothalamo‐pituitary‐adrenal axis responses to this social stress. Maternal defence induced elevated stress responses in high‐anxiety dams only; nerve‐growth‐factor‐induced gene B mRNA expression in the parvocellular paraventricular nucleus and adrenocorticotropin hormone secretory responses were substantially enhanced after maternal defence. In contrast, secretory responses to a non‐social stress (elevated platform) were not different between high‐ and low‐anxiety dams. Thus, responsiveness of the stress axis in lactation is dependent upon the innate level of anxiety of the dam and, as a consequence, her reactiveness to social threat.