On the diurnal rhythm of activity of Meriones unguiculatus (Milne-Edwards, 1867).

The diurnal rhythm of activity of Meriones unguiculatus (Milne-Edwards, 1867) is examined under natural and artificial light. The activity of 2 animals in captivity was registered actographically. Meriones unguiculatus seems to be more active during the night than during the day and showsed activity in the forenoon was registered.     

Demonstration of dopamine-immunoreactive cells in the gastrointestinal tract of gerbils (Meriones unguiculatus).

We investigated dopamine immunoreactivity in the small intestine of gerbils (Meriones unguiculatus), using a sensitive and selective antibody against glutaraldehyde-conjugated dopamine. Dopamine-immunoreactive cells were found within the mucosal epithelium along the entire extent of the small intestine. Labeled cells were regularly distributed in the upper half of the intestinal villi, basally attached to the basement membrane and always reaching as far as the epithelial surface. Dopamine-containing cells revealed a spindle-like shape, and both light and electron microscopic characteristics relate them to typical open-type gut endocrine cells. Thus, this current study directly identified dopamine as a probable secretory product in basal granulated cells of the small intestine. The functional significance of these cells is discussed in relation to the current view of dopaminergic actions in peripheral tissues.     

Development of the squamosomandibular articulation in the Mongolian gerbil (Meriones unguiculatus). II. Succinate dehydrogenase activity

Synopsis Succinate dehydrogenase activity has been studied, according to the method of Nachlaset al. (1957), in the developing tissues forming the squamosomandibular articulation in the Mongolian gerbil from its inception through the sixth postnatal day. Increased activity was observed in the chondroblasts, osteoblasts and mesenchymal tissues of the developing articulation. The chondroclasts of the developing mandibular condyle displayed intense reaction as did the osteoclasts of the developing bony articulation. Succinate dehydrogenase activity appeared to be related to the functional maturity of the cellular elements of the developing joint.     

Determination of Giardia lamblia cyst infective dose for the Mongolian gerbil (Meriones unguiculatus).

The purpose of this study was to determine the 50% infective dose for Giardia lamblia (CDC:0284:1) cysts in Mongolian gerbils (Meriones unguiculatus). The log10 50% infective dose results calculated by probit analysis and the Spearman-Karber method were 2.45 and 2.50, respectively.     

Determination of Giardia lamblia cyst infective dose for the Mongolian gerbil (Meriones unguiculatus).

The purpose of this study was to determine the 50% infective dose for Giardia lamblia (CDC:0284:1) cysts in Mongolian gerbils (Meriones unguiculatus). The log10 50% infective dose results calculated by probit analysis and the Spearman-Karber method were 2.45 and 2.50, respectively.     

Production of antibodies to sheep red blood cells and Brucella abortus in Mongolian gerbils (Meriones unguiculatus).

The levels of total and 2-mercaptoethanol (2-ME)-resistant antibodies in male Mongolian gerbils (Meriones unguiculatus) to sheep red blood cells (SRBC) were higher than those in male C57BL/6 mice after the first and second immunizations. On the other hand, the total antibody level to Brucella abortus (BA) in gerbils was comparable to that in mice, whereas 2-ME-resistant antibody titers were lower after the first and second immunizations than in mice. After injection of 8 x 10(4) SRBC, male gerbils did not produce either total or 2-ME-resistant antibodies after the first immunization, but they produced total and 2-ME-resistant antibodies after the first to the fourth immunizations with different dilutions of BA, and both types of antibody titers significantly increased with the repeated immunizations. There were no sex differences in total and 2-ME-resistant antibody production to SRBC.     

Induction of pseudopregnancy in the mongolian gerbil (Meriones unguiculatus) by vaginal stimulation.

In rats, pseudopregnancy has been induced by mating with vasectomized males, by mechanical stimulation of the uterine cervix with a glass rod or vibrator, and by stimulation of the vagina with a tampon. On the other hand, no practical data are available in reports on the induction of pseudopregnancy in Mongolian gerbils. Pseudopregnancy of gerbils has been induced by mating with vasectomized males. But this method was uncertain because the incidence of pseudopregnancy was lower than that obtained in rats by other means. In the present study, two experiments were undertaken as follows. 1) Copulatory behavior of gerbils was observed for one hour to determine the most effective stimulation interval. 2) From the results of Experiment 1, female gerbils in estrus were mechanically stimulated to test the effectiveness of inducing pseudopregnancy by vaginal stimulation at various time intervals. The results of these experiments indicated that, although the frequency of copulatory behavior varied among individuals, on average the most effective method for inducing pseudopregnancy was stimulation of 5 min duration and at 20 or 30 min intervals. Because the incidence of pseudopregnancy induced by such mechanical stimulation (83.3%) was higher than that induced by mating with vasectomized males (30.0%), this method might be useful in inducing pseudopregnancy in Mongolian gerbils.     

The effect of barn owls (Tyto alba) on the activity and microhabitat selection of Gerbillus allenbyi and G. pyramidum

Predation plays an important role in ecological communities by affecting prey behavior such as foraging and by physical removal of individual prey. In regard to foraging, animals such as desert rodents often balance conflicting demands for food and safety. This has been studied in the field by indirectly manipulating predatory risk through the alteration of cues associated with increased risk such as cover or illumination. It has also been studied by directly manipulating the presence of predators in aviaries. Here, we report on experiments in which we directly manipulated actual predatory risk to desert rodents in the field. We conducted a series of experiments in the field using a trained barn owl (Tyto alba) to investigate how two species of coexisting gerbils (Gerbillus allenbyi and G. pyramidum) respond to various cues of predatory risk in their natural environment. The gerbils responded to risk of predation, in the form of owl flights and owl hunger calls, by reducing their activity in the risky plot relative to the control plot. The strongest response was to owl flights and the weakest to recorded hunger calls of owls. Furthermore, when risk of predation was relatively high, as in the case with barn owl flights, both gerbil species mostly limited their activity to the safer bush microhabitat. The response of the gerbils to risk of predation disappeared very quickly following removal of the treatment, and the gerbils returned to normal levels of activity within the same night. The gerbils did not respond to experimental cues (alarm clock), the presence of the investigators, the presence of a quiet owl, and recorded white noise. Using trained barn owls, we were able to effectively manipulate actual risk of predation to gerbils in natural habitats and to quantify how gerbils alter their behavior in order to balance conflicting demands of food and safety. The method allows assessment of aspects of behavior, population interactions, and community characteristics involving predation in natural habitats.     

Comparative study of the gastrocnemius and soleus muscles of the Egyptian desert rodent Gerbillus pyramidum and the albino rat.

The hind limb muscles of the Egyptian desert rodent Gerbillus pyramidum and the albino rat were studied macroscopically and microscopically, using ordinary and histochemical techniques. The results revealed a relatively long hind limb and a relatively long tendon of the gastrocnemius group in G. pyramidum as compared with the albino rat. The dark fibres (red) were dominant in the muscles of the former animal and its spindles similarly contained more dense intrafusal fibres than the spindles of the albino rat. The correlation between these findings and the frequency and power of movement of the hind limbs in G. pyramidum was discussed.     

Immune response of the Mongolian gerbil (Meriones unguiculatus) to sheep red blood cells.

The immune responses of Mongolian gerbils, Meriones unguiculatus, to sheep red blood cells (SRBC) were studied as compared to those of mice. After a single injection of SRBC, hemagglutinin titers in gerbils were significantly lower and hemolytic plaque-forming cells (PFC) in the spleen were less in number as compared to the response of mice. In gerbils the PFC response to a higher dose of bacterial lipopolysaccharide (LPS) was rather higher than in mice. The delayed-type hypersensitivity (DTH) assay on the foot-pad revealed that the responsiveness was considerably lower in gerbils than in mice.     

Migration behaviour and pathogenesis of five ascarid nematode species in the Mongolian gerbil Meriones unguiculatus

To understand the characteristic features of the Mongolian gerbil, Meriones unguiculatus, as an animal model of ascarid infections, the migration behaviour and pathogenesis of larvae were investigated in experimentally infected gerbils. Embryonated eggs from each of Toxocara canis, Baylisascaris procyonis, B. transfuga, Ascaris suum, and A. lumbricoides were orally inoculated into gerbils and larvae were recovered from various organs at designated periods. In T. canis-infected gerbils, larvae were present in the liver 3 days after infection and in the skeletal muscle and brain via the heart and lungs at a similar rate. In B. procyonis- and B. transfuga-infected gerbils, larvae were present in the lungs within 24 h after infection, with some having reached the brain by that time. After 24 h, larvae of B. procyonis tended to accumulate in the brain, while those of B. transfuga accumulated in skeletal muscles. In A. suum- and A. lumbricoides-infected gerbils, larvae remained in the liver on day 5 post-infection and elicited pulmonary haemorrhagic lesions, which disappeared 7 days after initial infection. Thereafter, no larvae of any type were recovered. Ocular manifestations were frequently observed in T. canis- and B. procyonis infected gerbils, but were rare in B. transfuga-infected gerbils. In the cases of A. suum and A. lumbricoides, migration to the central nervous system and eyes was extremely rare, and larvae had disappeared by 2 weeks post-infection. Fatal neurological disturbances were observed in B. procyonis-infected gerbils, whereas irreversible non-fatal neurological symptoms were observed in the case of B. transfuga.     

The pathology of the Mongolian Gerbil (Meriones unguiculatus): a review.

Both naturally occurring disease processes and experimental models of human disease in the Mongolian gerbil were reviewed. The gerbil was highly susceptible to cerebral infarction following unilateral ligation of one common carotid artery and was useful in studies of the pathogenesis of stroke. Spontaneous epileptiform seizures mimicked those of human idiopathic epilepsy, and both seizure-sensitive and resistant strains have been bred. Perhaps because of its more efficient nephron, the gerbil accumulated four to six times as much renal lead as the rat, and the gerbil has been proposed as an experimental model of lead nephropathy. On standard diets, about 10% of the animals became obese, and some showed decreased glucose tolerance, elevated serum immunoreactive insulin and diabetic changes in the pancreas and other organs. Some breeders exhibited hyperactivity of the adrenal cortex associated with hyperglycemia, hyperlipidemia and degenerative vascular disease. Although dietary supplements of cholesterol were toxic and did not induce atherosclerosis, the gerbil was useful in other studies of cholesterol absorption and metabolism. Spontaneous, insidious periodontal disease became evident after about 6 months on standard diets, and dental caries were induced by cariogenic diets or by pathodontic streptococci. Spontaneous neoplasia occurred in 8.4--24% of gerbils, usually after 2 years of life. Adrenal cortical, ovarian and cutaneous tumors were the most consistently reported neoplasms.