Husbandry and observation methods of a breeding colony of marmosets (Callithrix jacchus) for behavioural research

[Establishment of retinal disease models using non-human primates and its strategy for drug discovery]

Retinal diseases such as glaucoma, diabetic retinopathy, age-related macular degeneration and retinitis pigmentosa are the major causes of blindness. However, these pathological mechanisms remain to be elucidated, and development of new therapeutic agents has been desired. A large number of experimental animal models using rodents (rats and mice) have been used for the evaluations of the pathogenesis and novel therapeutic candidates in retinal diseases. However, the anatomy of the retina in rodents is different from that in humans, as rodents have no macular. Conversely, non-human primates have macular similar to humans, and therefore rhesus and cynomolgus monkeys are widely used as experimental animal models of retinal diseases. Here, we will introduce non-human primate models of retinal diseases and their pharmacological approaches, with a focus on our research findings.

Fathering style influences health outcome in common marmoset (Callithrix jacchus) offspring

In the cooperative breeding common marmoset monkey, Callithrix jacchus, fathers share the care responsibility and energetic load with their mate from the time their infants are born. However, not all fathers show the same level of participation in direct infant care. Here we present the first results demonstrating that fathering style can improve both survival and growth trajectory of a male's offspring during the first 30 weeks of life and that these infant outcomes are consistent within a father throughout successive births. Twenty-four marmoset fathers were tested for their responsiveness to an infant distress call when their infants were approximately two weeks old. These fathers were categorized as either responsive (RS) or nonresponsive (NRS) based on their response to the calls. Survival past 1 month was then determined and bi-monthly weights of current infants through 30 weeks of age were taken. Infant survival to the first month was significantly higher with RS fathers than with NRS fathers during this critical time period. Infants from RS fathers also had a higher growth trajectory with significant differences in body weight in the 28th and 30th week after birth. Only the RS fathers showed a significant increase in serum testosterone in response to infant cries suggesting a physiological role of testosterone in the motivation to search for the infant. Furthermore, all offspring born to RS fathers from subsequent births also showed a significantly higher survival rate and higher growth trajectory than for offspring of NRS fathers. These results suggest that fathering style is a consistent trait and responsive fathers improve infant survival rate and growth during the first 30 weeks. Such fathering style traits may be passed on to the male offspring due to environmental or genetic factors.

Establishment of the ocular hypertension model using the common marmoset

The purpose of this study was to establish an experimental glaucoma model in the common marmoset (Callithrix jacchus). Chronic intraocular pressure (IOP) elevation was induced by laser trabeculoplasty twice at 2-week intervals in the left eyes of 4 common marmosets. IOP was measured before and at 4, 7, 8, 11, 13 weeks after first laser treatment, and ophthalmoscopic examinations were also performed. At 13 weeks after laser treatment, each eye was enucleated, and retinal cross-sections and optic nerve were prepared for histological examination. Mean IOP values measured at the above 5 time points were over 40 mmHg in laser-treated eyes in 3 marmosets, but IOP in one marmoset was transiently increased to 26.6 mmHg at 7 weeks and then declined to the baseline level. In ophthalmoscopy, deepened and enlarged optic disc cupping, depending on the extent of IOP elevation and duration, were observed in laser-treated eyes of 3 marmosets with persistent IOP elevation, but there was no apparent change in the optic disc in the laser-treated eye of one marmoset with transient IOP elevation. Histological examination showed marked atrophy with deepened and enlarged cupping of optic disc, thinning of retinal nerve fiber layer and retinal ganglion loss in the retina, and axonal atrophy and loss in the optic nerve, depending on the extent of IOP elevation and duration. In conclusion, we succeeded in producing an experimental glaucoma model in the common marmoset, and this model may be useful in elucidating the pathophysiological mechanism for glaucoma.

Behavioral discrimination between circumgenital odor from peri-ovulatory dominant and anovulatory female common marmosets (Callithrix jacchus)

Social peer groups of callitrichid monkeys [marmosets and tamarins] exhibit intrasexual dominance hierarchies in captivity. This laboratory study employed two-choice behavioral discrimination bioassys to test the hypothesis that scent from female common marmosets contains chemical cues that permit discrimination between dominant females in the periovulatory versus luteal phase of the ovarian cycle and females holding dominant versus subordinate status. When scent from only dominant females was presented, marmosets directed significantly greater amounts of investigatory behavior toward peri-ovulatory scent versus scent collected during the luteal phase of the ovarian cycle. Animals of both sexes demonstrated significant discriminatory behavior between scent deposited by dominant versus subordinate females, but only when the dominant female was in the peri-ovulatory phase of the ovarian cycle. Test animals directed equal amounts of investigative behavior toward scent from luteal-phase dominant females and subordinate females. Female test subjects deposited significantly more scent marks over presented scents than did male subjects, particularly when the scent had been donated by a peri-ovulatory female. Chemical odors specific to the periovulatory and luteal phases of the ovarian cycle may play a role in mediating behavioral interactions among marmosets.

The lung of the marmoset (Callithrix jacchus): ultrastructure and morphometric data

Owing to its small size (body weight 300-400 g), its modest demands on animal husbandry, and in particular its relatively long life-span (up to 12 years) the common marmoset (cotton ear marmoset: Callithrix jacchus (Cj)) might be a useful animal model to study the adaptive capacity to different energetic demands, adverse environmental influences such as air pollution, and aging of the lung. In order to describe the gas exchange apparatus of healthy marmosets as a basis for further pulmonary research, the lungs of three young adult animals have been analysed both qualitatively and quantitatively (by morphometry) at the light and electronmicroscopic level. Qualitatively, there is a general similarity in the architecture and structure of lung parenchyma between marmosets and other mammals. Quantitatively, the alveolar surface area was found to be 7662+/-1647 cm(2). Capillary surface area and volume were 6000+/-1549 cm(2), and 1.01+/-0.34 ml, respectively. The harmonic mean thickness of the air-blood barrier was 0.517+/-0.117 microm. These morphometric parameters allowed to estimate the diffusing capacity for oxygen at 0.0299+/-0.0134 ml O(2) (sec mmHg)(-1). In comparison with mammals of similar body size (rats, quinea pigs) it appears that the marmoset has a higher gas exchanging capacity of the lung, which might reflect the 'athletic' activity of this small primate. An incidental finding worth mentioning is the individual variability of septal structures due to variations in capillary blood volume and hematocrit. The distinction between such functional variations and subtle pathologic alterations of lung tissue requires a morphometric analysis at the electron-microscopic level.

Husbandry and breeding of a newly-established colony of cotton-topped tamarins (Saguinus oedipus oedipus)

From November 1976 to February 1979 a total of 8 litters were born to 6 females. Of the 14 infants, 10 were successfully reared by their parents. Housing, nutrition, a balance between environmental stability and stimulation, and female multiparity are seen as factors contributing to the breeding success of this colony. A controlled male and female pairing programme provided information on mating behavior and gestation length. One gestation of at least 166 days was observed, longer than that of the common marmoset.

Density distribution, characterization, and comparative aspects of the major serum lipoproteins in the common marmoset (Callithrix jacchus), a New World primate with potential use in lipoprotein research

Qualitative, quantitative, and comparative aspects of the serum lipoprotein profile in the Common marmoset (Callithrix jacchus), a New World primate, are described. Density gradient ultracentrifugation was used to evaluate lipoprotein distribution and to establish criteria for isolation of discrete molecular fractions. The major lipoprotein classes banded isopycnically on the gradient with the following hydrated densities: VLDL, d less than 1.017 g/mL; LDL, d = 1.027--1.055 g/mL; HDL fraction I, d = 1.070--1.127 g/mL; and HDL fraction II, d = 1.127--1.156 g/mL. Electrophoretic, immunological, and electron microscopic analyses attested to the purity of these fractions: the characteristics of each were assessed by chemical analysis, electron microscopy, immunological techniques, and polyacrylamide gel electrophoresis of their protein moieties. Marmoset VLDL and LDL were closely akin to those of man in size and chemical composition, although the former were richer in triglyceride; electrophoretic and immunological data showed the major protein component of VLDL and LDL to be a counterpart to human apo-B. The two HDL subfractions, i.e., HDL-I and HDL-II, corresponded in size and chemical composition to human HDL2 and HDL3, respectively, although slight differences in neutral lipid content were detected. By immunological and electrophoretic criteria, the major apolipoprotein of marmoset HDL was analogous to human apo-AI. In contrast, marked dissimilarities were evident in the complements of low molecular weight, tetramethylurea-soluble polypeptides of marmoset and human lipoproteins. Quantitatively, the human and marmoset lipoprotein profiles were not dissimilar, although HDL was the major class (approximately 50%); in fasting animals, serum concentrations of VLDL, LDL, and HDL were 50--90, 170--280, and 338--408 mg/dL, respectively. C. jacchus was distinct from man in displaying a greater proportion of its total HDL in the less dense (HDL-II) subfraction (marmoset HDL-I/HDL-II = approximately 4:1; human HDL2/HDL3 = approximately 1:3). These data indicate that, as an experimental animal for lipoprotein research, the Common marmoset combines the advantages of ready availability and maintenance with a serum lipoprotein profile which resembles, in many qualitative and quantitative aspects, that found in man.