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The effects of early postnatal handling on hippocampal glucocorticoid receptor concentrations: temporal parameters
Insights
Early life handling permanently increases hippocampal glucocorticoid receptor (Gr) concentrations in rats. This effect is most pronounced when handling occurs during the first week of life, indicating a critical developmental window.
Area of Science:
- Neuroscience
- Developmental Biology
- Endocrinology
Background:
- Glucocorticoid receptor (Gr) concentrations in the rat brain increase postnatally.
- Early life environmental stimulation, such as handling, can permanently alter Gr concentrations in the hippocampus.
- The developmental trajectory of neural receptor systems is sensitive to early life experiences.
Purpose of the Study:
- To determine the developmental timing of the handling-induced increase in hippocampal Gr concentrations.
- To investigate the duration of the critical window for early life handling to affect Gr levels.
- To explore the relationship between Gr development and the sensitivity to environmental manipulation.
Main Methods:
- Rats were subjected to daily handling for specific periods during the first three weeks of life.
- Hippocampal Gr concentrations were measured at different time points.
- The effectiveness of handling during distinct developmental phases (Days 1-7, 8-14, 15-21) was compared.
Main Results:
- Handling during the first week of life (Days 1-7) was as effective as handling for the entire first three weeks in increasing hippocampal Gr concentrations.
- Handling during the second week (Days 8-14) showed a reduced effect.
- Handling during the third week (Days 15-21) had no significant effect on Gr concentrations.
- The sensitivity of the hippocampal Gr system to handling diminishes as Gr levels approach adult concentrations.
Conclusions:
- The critical window for early life handling to permanently increase hippocampal Gr concentrations is within the first week of postnatal life.
- The waning sensitivity of the Gr system to handling correlates with the maturation of Gr concentrations.
- Handling may directly influence the number of glucocorticoid receptor sites per cell during a sensitive developmental period.
Abstract:
Glucocorticoid receptor (Gr) concentrations in the rat brain are low at the time of birth and increase towards adult levels during the first two weeks of life. Brief, daily handling of pups for the first 21 days postnatally has been found to permanently increase Gr concentrations within the hippocampus. Thus, the development of this neural receptor system is modifiable by environmental stimulation. The work described in this paper indicates that the handling effect on hippocampal Gr concentrations is apparent as early as Day 7 of life. Moreover, handling on Days 1-7 is as effective in altering Gr concentrations as handling for the first 3 weeks of life; handling on Days 8-14 is somewhat less effective and handling on Days 15-21 is without effect. Thus, the sensitivity of the hippocampal Gr system to this early manipulation wanes through the first 3 weeks of life as Gr concentrations reach adult levels, suggesting that handling may directly alter the number of receptor sites per cell.