Estrus, gestation, and placentation were studied in the Virginia opossum (Didelphis virginiana) and the gray short-tailed oppossum (Monodelphis domestica), representatives of the prototypic, New World marsupial family Didelphidae. Didelphis is a large (3,000 g), pouched opossum that exhibits a 28-day estrous cycle, spontaneous estrus and ovulation, and a high ovulation rate (60 ova per cycle). Monodelphis is a small (100 g), pouchless opossum with male-induced estrus and ovulation and a moderate ovulation rate (12 ova per cycle). Implantation occurs on day 10 of the 13-day gestation period in Didelphis and on day 12 of the 15-day gestation in Monodelphis. Gestation and placentation, including the ultrastructural features of trophoblastic apposition to the uterine mucosa, are very similar in Didelphis and Monodelphis. Differences, such as a larger increase in uterine volume and a more highly folded endometrium following implantation in Monodelphis are minor. They appear to be related to the smaller maternal body size and the relatively larger uterine load of embryos in Monodelphis. Because body size is one of the major variables among New World marsupials, the descriptions of gestation and placentation presented here for Didelphis and Monodelphis, provide a basis for comparison in future studies of didelphid marsupials.

The development of physiological responsiveness to male stimuli in peripubertal female gray short-tailed opossums was examined in this study. Prepubertal females were exposed directly or indirectly to male chemicals (odors) or to no male stimuli. All females exposed directly to deposited male stimuli (22/22) showed estrus at a mean (+/- SEM) age of 127 +/- 2 days. Only 59% (13/22) of females exposed indirectly showed estrus, and at an older mean age of 162 +/- 5 days (p less than 0.01). Vaginal estrus was not observed in any of the females isolated from male stimuli (0/11). Direct exposure of prepubertal females to male odors was associated with higher uterine weights compared to those of indirectly exposed and isolated females. Reproductive success, measured as litter production, of peripubertal females greater than 140 days old was comparable to adult reproductive success. This study has shown that reproductive maturation in pubertal female opossums requires male stimuli, that this stimulus appears to be pheromonal, and that direct exposure to deposited male odors is the most effective stimulus for female reproductive maturation.

Examination of temperature-metabolism relations found no significant differences between thermoregulation of temperature housed laboratory cotton-top tamarins (Saguinus oedipus) and wild tamarins in Colombia, S.A. The results indicate that tamarins do not acclimate to a temperature environment and are metabolically stressed at Ta less than 32 degrees C. This is consistent with an hypothesis of chronic metabolic stress as a factor in the etiology of cotton-top tamarin colitis, which is restricted to captive populations and not found in wild tamarins.

The cotton-top tamarin is a nonhuman primate noted for susceptibility to juvenile onset colitis and subsequent colon cancer. About 80% develop colitis in captive environments outside the tropics. The aim was to determine the prevalence of colitis and colorectal cancer in tamarins living wild in their tropical habitat. Endoscopic biopsy was used to compare severity of colitis, inflammatory/immune cell densities, mucosal dysplasia, and occurrence of cancer in wild tamarins in a tropical habitat with tamarins living captive in a temperate climate. Six colon biopsies from each of 69 captives showed severe colitis in 64.5% of biopsies and moderate colitis in 19.5%. Severe colitis was not found in 88 wild tamarins; 13% had moderate colitis. Densities of polymorphonuclear leukocytes, plasma cells, and mononuclear cells in the lamina propria were related directly to the severity of four grades of colitis (normal, mild, moderate, and severe). Histologic or gross signs of carcinoma were detected in 12 captives and low- or high-grade dysplasia in 15. Neither cancer nor dysplasia was found in any of the wild tamarins. The observations suggest that colitis and cancer in the tamarin model are linked to environmental factors.

Parallel changes in spontaneously occurring inflammation in colonic Thiry-Vella loops and the in-line colon of cotton-top tamarins were studied in a colitis-inducing environment at 8 and 15 months following surgical preparation of the loops. Gross disease severity and numbers of inflammatory/immune cells per unit area of lamina propria in histological sections from endoscopic biopsies were analyzed. Cell counts and severity of colitis declined over time in the Thiry-Villa loops while the disease followed its characteristic course in the remaining large bowel and in the colons of controls. Perfusion of the loops with the animals' feces increased the density of the cellular infiltrate in the lamina propria in parallel with increased severity of inflammation. Electron micrographs of the colonic mucosa showed invasion by microorganisms. The predominant microorganism had characteristics of Helicobacter sp. The results implicate the fecal stream as a factor in the persistence of colitis in the tamarin model. Nevertheless, fecal factors appear not to be the primary trigger, as evidenced by findings that the disease is not expressed in wild-living tamarins and that it enters remission when affected animals are transferred to natural conditions from a colitis-inducing environment. Both an adverse environment and the fecal contents appear to be required for expression of the disease.