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Título

PRELIMINARY FINDINGS ON CAPTIVE CAPUCHINS’ (SAPAJUS LIBIDINOSUS) HYPOTHALAMIC-PITUITARY-ADRENAL AXIS’ CIRCADIAN RHYTHM.

Resumo

Although the hypothalamic-pituitary-adrenal (HPA) axis is best known for it’s activity during stress response, it also activates during situations not related to stress, following a circadian cycle in which mammals express higher glucocorticoid levels a few hours before awakening. However, allostatic overload has a cumulative “wear and tear” effect on the HPA axis, weakening their activation. We investigated fecal glucocorticoid levels in captive capuchin monkeys (Sapajus libidinosus) to verify if they present HPA axis activation according to their species’ circadian rhythm. We collected 833 fecal samples from 20 females and 25 males, all adults, in different captive enclosures on CETAS (PB and RN) and zoo (PB). Fecal glucocorticoid values (ng/g feces) were quantified following competitive ELISA method. Values were standardized as z scores (log10(x+1), while fecal collection time was categorized into five 2h blocks, with “1” representing samples collected at 7h-8h59min and “5” representing samples collected at 15h-16h59min. Linear regression model with bootstrap, using fecal glucocorticoid as response variable, sex, visitor exposure and collection time as predictors and individual as covariable, found a significant difference in collection time (F=11.883; p<0.001), with influence from sex (F=2.410; p=0.048) and visitor exposure (F=2.454; p=0.045). Regression curve estimation analyses favors cubic model (F=10.574; p<0.001), with a glucocorticoid peak during block 1 probably related to their circadian cycle, followed by a decrease during blocks 3 and 4 probably matching their feeding time, showing they express a healthy circadian cycle. However, the sex effect is detected by a flattening of males’ glucocorticoid peak, while the visitor exposure effect is detected by higher peaks in glucocorticoid values in zoo animals, suggesting male capuchins and zoo capuchins are particularly vulnerable to a “wear and tear” effect on their HPA axis.

Palavras-chave

cortisol; circadian cycle; allostasis.