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Corpus callosum: interactive effects of infantile handling and testosterone in the rat
V H Denenberg1, R H Fitch, L M Schrott
1Department of Psychology University of Connecticut Storrs, 06269-4154.
Insights
Infant handling and testosterone propionate (TP) influence corpus callosum size in rats. This study reveals a developmental interaction between adrenal and gonadal hormones affecting brain development.
Area of Science:
- Neuroscience
- Developmental Biology
- Endocrinology
Background:
- The corpus callosum, a brain structure, exhibits sexual dimorphism in rats, with males typically having larger callosa.
- Infant handling in rats amplifies this sex difference.
- Previous studies indicated that administering testosterone propionate (TP) to handled female rat pups in infancy results in callosal size comparable to males.
Purpose of the Study:
- To investigate the combined effects of infant handling and hormonal treatments on corpus callosum development in rats.
- To determine if testosterone propionate (TP) administration to nonhandled female rats impacts corpus callosum size.
- To explore the potential interaction between adrenal and gonadal hormones in cortical development.
Main Methods:
- Two experiments were conducted involving male and female rat pups.
- Male pups underwent castration or sham surgery on Day 1 of life.
- Female pups received TP or oil injections on Day 4 of life, with litters either handled or nonhandled during infancy.
Main Results:
- The previously observed effect of handling and TP administration in females leading to larger callosa was confirmed.
- However, TP administration to nonhandled female rats did not result in a significant increase in callosal size.
- Handling was associated with corticosterone release, suggesting a role for adrenal hormones.
Conclusions:
- The findings support a developmental interaction between adrenal hormones (influenced by handling and corticosterone release) and gonadal hormones (like TP) at the cortical level.
- Early-life experiences and hormonal milieu are critical factors in shaping brain structure, specifically the corpus callosum.
- This research provides insights into the complex interplay of hormones and environmental factors during early brain development.
Abstract:
Previous research found that the corpus callosum of male rats is larger than that of females; handling rats in infancy enhances this sex difference; and female rat pups, when handled in infancy and given 1 injection of testosterone propionate (TP) on Day 4 of life, will have callosa as large as those of males. In 2 experiments, male pups were castrated on Day 1 or received sham surgery; female pups were injected with TP on Day 4 or received an oil injection. Litters were handled or nonhandled. The previous finding that females, when handled and given TP in infancy, have a larger callosum was confirmed; however, a TP effect when administered to nonhandled females was not found. Because handling is known to cause a corticosterone release, these findings were interpreted as evidence of a developmental interaction between adrenal and gonadal hormones at the cortical level.