Studies on stress in African green monkeys (Cercopithecus aethiops) : Stress associated cortisol and prolactin levels, lymphocyte modulation and pathological changes in adrenal cortex, stomach and hippocampus in the African green monkey (C. aethiops)
Abstract: African green monkeys (AGMs) are highly susceptible to captivity-induced stress. An investigation of spontaneous deaths of laboratory confined AGMs at the Institute of Primate Research, Nairobi, Kenya over a period of 7.5 years documented mild to severe gastric mucosal erosions and ulcers in 83 of 260 (32%) necropsies. The lesions numbered between one and 100 and were distributed mainly in the body and fundus of the stomach. Singly housed animals were more frequently affected than group housed individuals. Fourteen monkeys suffering from gastric ulcers showed microscopic changes in the brain. The neural degeneration was prominent in the Cornu Ammonis 1 cell field (CA 1) and CA3 regions and was characterised by shrinkage, disarrangement and loss of the pyramidal neurones. The adrenal cortex of the retrospective cases showed a moderate degree of hyperplasia. Prospective studies in wild caught AGMs revealed that acute gastric lesions developed as early as day one after capture and bilateral adrenal gland enlargement was prominent seven days post-capture No histo-pathological brain changes were found in this group of animals. The mean width of adrenal cortices in the captured monkeys (stressed) measured 1048 µm compared to the mean of 813 µm in resting wild AGMs euthanised by a rifle shot. The hyperplasia of the cortex correlated with high plasma cortisol levels in the affected animals. Mean plasma cortisol levels in resting wild monkeys were 391 nmol/L and increased sharply one day after capture to over 1000 nmol/L. The mean concentrations in singly housed monkeys were 838 nmol/L at 45 days and remained over 700 nmol/L at six months. Lymphocyte immunocompetence showed a negative correlation with the plasma cortisol concentrations. The stimulation indices indicated that the lymphocytes were suppressed as the monkeys were confined for a prolonged period. Mean plasma prolactin concentrations were between 133 and 292 mIU/L, in singly housed monkeys on day 1 and 45 respectively. The mean concentrations decreased to 132 mIU/L at six months. The pathological changes in the adrenal glands, the stomach mucosa and the brain were attributed to stress resulting from long term confinement of the monkeys especially in individual housing. This study demonstrates that i) AGMs are very sensitive animal models of stress research ii) lenient capture techniques are necessary and iii) conscientious care and husbandry are essential for ethical and scientific reasons because this species is highly susceptible to environmental stress.
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