Line, S. W., Markowitz, H., Morgan, K. N. et al. 1991. Effect of cage size and environmental enrichment on behavioral and physiological responses of rhesus macaques to the stress of daily events. In: Through the Looking Glass. Issues of Psychological Well-Being in Captive Nonhuman Primates. Novak, M. A. , Petto, A. J. (eds), 160-179. American Psychological Association, Washington DC.

Neither heart rate nor activity varied significantly between the two cage sizes [of barren cages]. Adult, single-housed female rhesus macaques responded with a significant rise in heart rate to being removed from their home cage and replaced after the cage had been cleaned. Once the cage change was completed and the technicians left the room, it was several hours before heart rates returned to the expected level. ... The monkeys' heart rates under the influence of ketamine were increased. ... Restraint with the cage-squeeze mechanism and confinement in a transfer box were both associated with significant increases in plasma cortisol. ... Repeated exposure to brief restraint did not lead to habituation of the heart-rate response.