Our ability to determine the molecular mechanisms underlying these effects should benefit greatly from appropriate mouse models because these would enable use of powerful transgenic methods. Therefore, we have characterized a mouse model of chronic ES, which was provoked in mouse pups by abnormal, fragmented interactions with the dam. Dam-pup interaction was disrupted by limiting the nesting and bedding material in the cages, a manipulation that affected this parameter in a dose-dependent manner.
At the end of their week-long rearing in the limited-nesting cages, mouse pups were stressed, as apparent from elevated basal plasma corticosterone levels.
In addition, steady-state mRNA levels of CRH in the hypothalamic paraventricular nucleus of ES-experiencing pups were reduced, without significant change in mRNA levels of arginine vasopressin.
Rearing mouse pups in this stress-provoking cage environment resulted in enduring effects: basal plasma corticosterone levels were still increased, and CRH mRNA levels in paraventricular nucleus remained reduced in adult ES mice, compared with those of controls.
In addition, hippocampus-dependent learning and memory functions were impaired in 4- to 8-month-old ES mice.
In summary, this novel, robust model of chronic early life stress in the mouse results in acute and enduring neuroendocrine and cognitive abnormalities.
This model should facilitate the examination of the specific genes and molecules involved in the generation of this stress as well as in its consequences.