Differences in stress reactivity of laboratory macaques measured by heart period and respiratory sinus arrhythmia

Some laboratory primates are more likely than others to react to anxiety-provoking stressors. Individuals that overreact to stressors may experience diminished psychological well-being and would be inappropriate for some experiments. The differences between reactive and nonreactive individuals may be reflected in heart period and respiratory sinus arrhythmia (RSA). Using surface electrodes and radio telemetry, we measured these two cardiac variables in seven male and ten female singly caged longtailed macaques (Macaca fascicularis) when they were exposed to two stressors, a sudden noise (whistle test) and an unfamiliar technician wearing capture gloves (glove test). Behavior was videotaped during both tests. For the whistle test, cardiac data were recorded before, during, and after two 1 minute whistle blasts separated by 90 min. For the glove test, data were recorded in 1 minute blocks every 8 minutes over 96 minutes before, during, and after 1 minute exposure to the gloved technician. Heart period was decreased and RSA was suppressed during both the whistle and glove exposures. After the whistle test, the cardiac activity of most subjects returned to baseline levels within 10 minutes. The glove test produced more extended suppression, with greater individual differences, than the whistle test. There were greater individual differences in RSA than in heart period. These enhanced individual differences were used to define stress reactors that differed from nonreactors in their cardiac data profiles. Of 16 subjects that completed the glove test, five were identified as reactors.