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Introduction
The rodent maternal separation (MS) model has been used to understand the effects of early life adversity for children. Examples are children who reside in foster care, in orphanages, or experience parental abuse and neglect. Rodent exposure to MS increases the likelihood of developing stress related psychopathology, while also inducing difficulties with learning and memory (Joushi, Sara et al. ,2021). This model separates mice from their mothers for 3 hours daily during their first two weeks of life. Past studies in our laboratory have shown that MS results in reduced social odor preference in adolescent mice that can be prevented by environmental enrichment (EE)(Cornwell, Catherine et al. ,2018). While our most recent study examined whether this preference persists when MS mice are socially mixed with normally reared control mice. Ultimately results from our study suggest that social mixing may have worked as a stressor for the MS mice.
General Experimental Design
Rearing Conditions:
MS litters are removed from their mother for 3 hour daily from postnatal days (PND) 1-14. This separation occurs in a room located away from the vivarium housing at a temperature of 27 °C.This period of MS is followed by a week of undisrupted housing of the mother and pups together on PND 15-20.Control (C) litters are continuously housed with their mother from PND 1-20. On PND 21, both C and MS litters are weaned from their mothers. Then mice are sexed and placed in cages.
Environmental Enrichment and Social Mixing:
Cages environments can be physically and socially enriched. A physically enriched environment uses toys that include a running wheel, tunnel, star, ball, and ring.Clean novel toys were introduced every other day for two weeks by lab members. A socially enriched environment combines MS and Control mice litters in their cages for socialization.
Odor Preference Test
The testing apparatus consists of a plexiglass frame with a screen floor. Below this screen floor was a tray with 3 compartments containing, soiled nest shavings, clean shavings, and a center compartment that was empty.Testing was done in a room illuminated with red light and began following a 30 min habituation period in the room. Each mouse was placed individually in the center of the screen floor and allowed to explore for 180 seconds. Testing sessions were videotaped and the films analyzed for time spent over each odor compartment by a student naive to the rearing history of the subjects.
Testing Apparatus:
Most Recent Experiment Findings
Titled: Social Mixing Counters Effects of Environmental Enrichment on Social Odor Preference Development in Maternally Separated Adolescent CD-1 Mice
Odor Preference Testing:
MVI_1455.MP4Cornwell, Catherine Summer 2022
Results from this Study using Odor Preference:
Control but not MS mice placed in environmentally enriched and socially mixed cages showed a preference for nest odors when given a two-choice test against clean shavings in an odor preference apparatus. A previous study revealed that MS adolescent mice showed no preference between odors when housed in standard cages with no toys and MS-only cage mates, but the enrichment restored normal social odor preference (Cornwell, Catherine et al. ,2018)(Melton, Christopher , 2014). In the present study, MS mice housed in enriched cages with mice reared continuously with their mother before weaning showed no nest odor preference. Thus, the introduction of social mixing cancelled out the effects of EE for MS mice. This suggests that social mixing may serve as an added stressor for the mice thereby making stimuli associated with the home cage less attractive than they are for controls. Using this model supports the idea that lack of socialization in early life may contribute to later social difficulties.
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