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Developmental changes in c-fos expression to an age-specific social stressor in infant rats
1Department of Psychiatry, Columbia University College of Physicians and Surgeons, 1051 Riverside Drive, Unit 40, New York, NY 10032, USA. cpw14@columbia.edu
Insights
Young rats exhibit immobility when encountering adult males, a response that changes with age. This study reveals age-specific brain activity patterns, particularly in the amygdala, linked to this developing defensive behavior.
Area of Science:
- Neuroscience
- Developmental Biology
- Animal Behavior
Background:
- Young rats display immobility when exposed to adult males, a behavior that diminishes with age.
- This age-related decline in immobility correlates with reduced perceived infanticidal threat.
Purpose of the Study:
- To investigate the neural mechanisms underlying the developmental changes in male-induced immobility in young rats.
- To map the age-specific brain activation patterns associated with defensive immobility.
Main Methods:
- Assessed immediate-early gene c-fos expression in young rats (postnatal days 7, 14, 21) exposed to adult males.
- Compared c-fos expression in brain regions between male-exposed and control groups.
- Observed behavioral immobility in response to male exposure.
Main Results:
- On postnatal day 14, male-exposed rats showed significantly increased c-fos expression in the hypothalamus, amygdala, periaqueductal gray, and locus ceruleus.
- On postnatal day 21, similar but distinct amygdala nuclei activation was observed in immobile, male-exposed rats.
- No significant differences in c-fos expression were found on day 7; control levels of immobility in 21-day-old rats lacked elevated c-fos.
Conclusions:
- Male exposure induces age-specific c-fos expression in specific brain areas of young rats.
- Differential activation of neuronal populations in areas like the amygdala underlies developmental changes in defensive immobility.
- These findings highlight the neural substrates contributing to the ontogeny of defensive behaviors.
Abstract:
Young rats become immobile when exposed to a potentially infanticidal adult male rat. Male-induced immobility declines during the preweaning period, paralleling the decrease in infanticidal threat. To investigate the neural substrates underlying the developmental change in immobility, male-induced expression of the immediate-early gene c-fos was assessed on postnatal days 7, 14 and 21. A huddle of three young rats was exposed to an adult male behind a screen. As control, three littermates were put in the testing chamber but not exposed to the male. On day 7, male exposed and control pups were immobile most of the time and c-fos expression did not differ between conditions. On day 14, rats in the presence of the male stopped ongoing behaviors and became immobile. They had significantly higher c-fos expression in the paraventricular nucleus of the hypothalamus, the amygdala, the periaqueductal gray, and the locus ceruleus. On day 21, the male-exposed rats that were immobile had elevated c-fos expression in a similar pattern as on day 14, however, different nuclei of the amygdala were activated. In contrast, male-exposed 21-day-old rats that showed control levels of immobility did not have elevated c-fos expression in these areas. These results demonstrate that male exposure induced c-fos expression in brain areas of young rats in an age-specific pattern. Some of the activated brain areas seem to have contributed to immobility. Differential activation of neuronal populations may underlie developmental changes in defensive immobility during early ontogeny.
