Between 2011−2013, Zoological Research has released 3 special issues on Primates and Animal Models of Human Diseases. Now, after a year of preparation, we are pleased to release this fourth special issue. In this issue, we compiled 12 review, research articles and letters to the editor, each examining different aspects of scientific and medical research using non-primates as an animal model, with a special emphasis on recent developments in genetic, virological, behavioristic and methodological studies.

One of the key obstacles preventing wider applications of non-human primates (including their closest relative, tree shrew) in biomedical research is a lack of fundamental biological information on these models. To that end, Fan et al carried out a genome-wide study on positive gene selection to interpret the genetic bases of locomotor adaptation in the Chinese tree shrew (Tupaia belangeri chinensis), and Zhang et al measured serum immunoglobulin IgG, IgM, IgA, complement C3, C4 and CRP levels in 3−11 year old captive northern pig-tailed macaques (Macaca leonina) located at the Kunming Primate Research Center of Chinese Academy of Sciences, which currently maintains the largest captive population of Macaca leonina in China.

Another focus of this special issue is certain human diseases that are difficult to study using traditional rodent animal models, such as Mycobacterium tuberculosis (M. tb) and human immunodeficiency virus (HIV) co-infection, which is growing global public health problem. More effective research on such diseases could be done if there was a more effective animal model. In this issue, Guo et al accordingly reviewed recent developments in animal models for M. tb/HIV co-infection, with a focus on the non-human primate models. Similarly, Lei et al showed that Macaca leonina has the potential to be a promising animal model for human HIV/AIDS studies. Mo et al compared the different parameter settings of white matter diffusion tensor imaging (DTI) in rhesus macaques (Macaca mulatta) and screened out the optimal setting.

While finding more effective models is an important step in furthering the use of non-human primates in biomedical research, there is also the issue of the methodologies used to create such models. Tian & Ma pointed out that a common restriction in conventional animal models is that most of the human diseases-like abnormalities are induced via artificial interventions, such as drug administration. However, more elegant and subtle animal models should accurately exhibit the pathological symptoms of human mental diseases and not simply imitate certain syndromes. Consequently, effective animal models are supposed to be developed through psychological methods consistently associated with known theories of mental disorders. In their large-sized study on mental illness and cynomolgus monkeys (Maca fascicularis), Tian & Ma highlighted the need to more deeply consider both genetic factors and environmental factors in animal models, rather than simply relying on drugs that can induce mimicked symptoms. Wang addressed the advantages of using non-human primates and tree shrews in the studies of drug addictions.  

As a corollary to much of the research into non-human primates we highlighted in this issue, animal behaviors are among the most direct indexes needed to demonstrate the effects of medications and the outcomes of diseases, but they also serve as a foundation in wild species conservation. Chu et al reported a huddling-based paradigm that represents the postpartrum depression (PPD) in primates and provides a great translational efficiency and research platform for systematically investigating the etiology, treatment, prevention of PPD. Self-directed behavior (SDB) is characterized as an indicator of anxiety, frustration and stress in nonhuman primates. Zhang et al collected SDB data from one group of free-ranging Tibetan macaques (Macaca thibetana) at Mt. Huangshan, China, and their observations suggest that SDB is not only an index of anxiety in Tibetan macaques, but also can provide a new insight into evaluation of social relationships between individuals. Cui et al likewise clarified the hierarchy and social relationships in a one-male unit of captive Rhinopithecus bieti observed between August 1998 and March 1999, and found that in adult male Tibetan (Macaca thibetana), Barbary (M. sylvanus), and stump-tailed macaques (M. arctoides), bridging is a ritualized infant-handling behavior. Collecting further data from a group of habituated, provisioned Tibetan macaques, Bauer et al supported the agonistic buffering hypothesis of the underlying mechanisms of bridging. Such behaviors observed in these studies can also be profoundly influenced by human social industrialization, which may have implications for human-animal interaction in developing or using non-human primate models for scientific research. To that end, Yuan et al evaluated the influences of tsaoko plantation on the habitats of eastern hoolock gibbon (Hoolock leuconedys) and provided useful suggestions for future species conservation.

Ultimately, we hope that this new collection of papers on “Primates and Animal Models of Human Diseases” will continue to raise the profile of primate research, and provide some valuable insights into the implications for the future use of non-human primate models for biomedical research. We warmly welcome your contributions and thoughts on these issues for inclusion in our next special issue on this topic.

	Editor-in-Chief
	Executive-Editor-in-Chief