Time-lag of urinary and salivary cortisol response after a psychological stressor in bonobos (Pan paniscus)

Abstract

Cortisol is often measured as a marker for stress. Therefore, a profound validation of the time-lag between the stressor and the increase and peak in cortisol levels is needed. No study measured both the urinary and salivary cortisol time-lag after a psychological stressor. In this study, we used a frequent sampling study design to (1) describe the urinary and salivary cortisol pattern during a control day; and (2) characterize the induced excretion pattern of urinary and salivary cortisol after a psychological stressor in six zoo-housed bonobos. Liquid chromatography-tandem mass spectrometry was used to analyze 71 urine and 162 saliva samples collected on a control and a test day. We found that the time-lag between the stressor and the maximal cortisol concentration was similar in urine and saliva (160 min after the stressor). However, salivary cortisol after the stressor did show a faster and steeper increase than urinary cortisol. We also show inter-individual variation in the baseline and stress levels of cortisol, which should be considered in future cortisol studies. Our research highlights the importance of validation studies to confirm relevant sampling windows for cortisol sampling in order to obtain biologically meaningful results.

Salivary Cortisol Reaction Norms in Zoo-Housed Great Apes: Diurnal Slopes and Intercepts as Indicators of Stress Response Quality

“…As the intercept of the curve is the constant with which cortisol levels decrease, and the decrease is assumed to be steady, the bias introduced in our data due to difference in the timing of sample collection should be relatively mild. For both, the estimates of SCI and SCS, a major concern would have been if the steep decline in cortisol levels associated with the awakening response [ 23 , 67 ] would have been included in our sample, which is not the case though. However, future studies should ideally keep sampling conditions constant across species to avoid potential difficulties in the interpretation of results.…”

“…This approach means, however, that we did not include samples from the early morning or late afternoon as done in human studies of cortisol slopes [ 10 , 80 ]. Previous studies in chimpanzees [ 67 ], bonobos [ 23 ], and orangutans [ 52 ] have demonstrated that also in these species, there is a peak in salivary cortisol in early morning (depending a bit on when samples were taken 6 a.m. in chimpanzees, 8:30 in bonobos), followed by a steep decline until noon, and then followed by a slower decline between noon and 4 p.m. with nearly half of the level at 4 p.m. compared to noon [ 23 , 67 ]. This means in our study we only measured the slow decline during the afternoon.…”

“…Blood cortisol levels reach a nadir in the first few hours of sleep and remain low during the night [ 15 , 16 , 17 , 18 ]. This diurnal pattern is widespread across different diurnal species, e.g., domestic animals (horses [ 19 ]), cetaceans ( Tursiops aduncus, Orcinus orca [ 20 ]), elephants (( Loxodonta africana and Elephas maximus [ 21 ]), ( Elephas maximus [ 22 ])), and apes ( Pan paniscus ) [ 23 ], and can be detected not only in blood, but also in other body fluids, such as saliva [ 19 , 22 , 23 ] and urine [ 21 ]. This rhythm has been linked to the function of diverse processes, such as sleep–wake-patterns e.g., [ 24 ], metabolism, learning, and memory, e.g., [ 25 ], or immune functions [ 26 ].…”

Dietary Factors, Time of the Week, Physical Fitness and Saliva Cortisol: Their Modulatory Effect on Mental Distress and Mood

“…Interestingly, this significant association died out between MASQ and K10 scores when cortisol after exercise was incorporated into the model. Since cortisol levels were not assessed on Wednesday but Saturday (and during a downtime), this suggests a potential lag-time between negative affect and cortisol levels [ 40 ]. Taken together, it seems that the relationship between K10, MASQ, and cortisol levels before exercise is stronger on a peak day (Wednesday) compared with a weekend (Saturday).…”

Transition to siblinghood causes substantial and long-lasting physiological stress reactions in wild bonobos

“…The five-fold increase in cortisol that we observed in our study is an unusually strong physiological response. For comparison, captive bonobos exposed to an experimental stress test exhibited a two-fold increase in cortisol levels (Verspeek et al, 2021). A similar cortisol response occurs in group members in response to infant birth, but levels returned to normal within one day (Behringer et al, 2009).…”