Stable behavioral inhibition and glucocorticoid production as predictors of longevity

Abstract

Several personality/temperament traits have been linked to health outcomes in humans and animals but underlying physiological mechanisms for these differential outcomes are minimally understood. In this paper, we compared the strength of a behavioral trait (behavioral inhibition) and an associated physiological trait (glucocorticoid production) in predicting life span. In addition, we examined the relative stability of both the behavioral and physiological traits within individuals over a significant portion of adulthood, and tested the hypothesis that a stable behavioral trait is linked with a stable physiological bias. In a sample of 60 Sprague-Dawley male rats, we found that stable inhibition/neophobia was a stronger predictor of life span than stably elevated glucocorticoid production. In addition, these predictors appeared to have an additive influence on life span in that males with both risk factors (stable inhibition and consistently high glucocorticoid production) had the shortest life spans of all, suggesting both traits are important predictors of life span. Across a 4-month period in young adulthood, inhibition and glucocorticoid reactivity were relatively stable traits, however these two traits were not highly correlated with one another. Interestingly, baseline glucocorticoid production was a better predictor of life span than reactivity levels. The results indicate that glucocorticoid production in young adulthood is an important predictor of life span, although not as strong a predictor as inhibition, and that other physiological processes may further explain the shortened life span in behaviorally-inhibited individuals.

Figure 1

Study timeline.

Figure 2

Comparison of male mean approach latencies on two novel arenas (one non-social and one social) from 2.5−4 to 8 months of age.

Figure 3

Comparison of (a) male corticosterone reactivity (AUCi) at 4 and 8 months of age, and (b) male baseline corticosterone at 4 and 6 months of age.

Figure 4

Life span for males that were stably inhibited (black) was significantly shorter than for stably non-inhibited (white) and mixed (grey).

Figure 5

(a) Males with consistently high overall corticosterone production (black) lived shorter than males with consistently low (white) and mixed levels (grey). (b) Males with consistently high baseline corticosterone production (black) lived shorter than males with consistently low levels (white). (c) Males with consistently high reactivity (AUCi)corticosterone levels (black) did not have a shorter life span than males with consistently low levels (white).

Figure 6

Males that were stably inhibited and had stably elevated corticosterone production (black) lived significantly shorter than males that were either inhibited or had high corticosterone (grey) or males that were neither inhibited nor had high corticosterone (white).