ANATOMIC FEATURES

The anatomy of the Syrian hamster has been reviewed by Bivin et al. (1987), Magalhaes (1968), and Murray (2012). Syrian hamsters have a characteristic compact body, short legs, and very short glabrous tails.

Pathology of Laboratory Rodents and Rabbits, Fourth Edition. Stephen W. Barthold, Stephen M. Griffey, and Dean H. Percy. © 2016 John Wiley & Sons, Inc. Published 2016 by John Wiley & Sons, Inc.

The gastrointestinal tract has a number of significant features. As in mice and rats, the incisors (but not the molars) grow continuously (elodont). Many, although not all, genera of hamsters possess buccal pouches, which extend dorsolaterally from the oral cavity on either side of the shoulder region. These structures have been utilized as immunologically privileged sites, which allow xenograft transplants to survive. The utility of hamster cheek pouches as an experimental tool has been largely supplanted by immunodeficient mice. The esophagus enters the stomach at the junction of the nonglandular and glandular stomachs, which are divided by a muscular sphincter (Fig.

FIG. 3.1. Stomach from a hamster, depicting the nonglandular and glandular regions. Note the esophageal entry at the junction of each.

FIG. 3.2. Trophoblast cells within mesometrial vessel in a pregnant hamster.

The respiratory tract is similar to that of other labo­ratory rodents, with no respiratory bronchioles. Lungs have a single left lobe and 5 lobes on the right side (cranial, middle, caudal, intermediate, and accessory). As desert animals, Syrian hamsters have water-conserving kidneys with elongated single papillae that extend into the ureters. The female reproductive tract consists of a duplex uterus with 2 cervical canals that merge into a single external cervical os. There are 7 pairs of mammary glands. The male testes and accessory glands, as with most rodents, are comparatively large and prominent. Adult males develop large adrenal glands, due to enlarge­ment of the zona reticularis to 3 times the size of females. This enlargement is related to season and sexual matu­rity. The hamster placenta differs somewhat from the hemochorial placentation of other laboratory rodents and is termed “labyrinthine hemochorial.” Trophoblas­tic giant cells of the fetal placenta are in direct contact with the maternal bloodstream and tend to migrate within the maternal vasculature. They have a tropism for arterial blood and can be found inside uterine vessels in the mesometrium (Fig. 3.2). They can persist for up to 3 weeks postpartum. On occasion, trophoblasts may be found in the pulmonary vessels of pregnant females.

Erythrocytic polychromasia is relatively common in hamsters, with moderate anisocytosis. Erythrocyte life spans vary from 50 to 78 days. Life spans are increased during hibernation. Leukocyte counts are 5,000-10,000/ml. Approximately 60-75% of the circulating leukocytes are lymphocytes. Neutrophils have densely staining eosinophilic granules and thus may be referred to as heterophils.