Benign testicular hyperplasia in Mongolian gerbils (Meriones unguiculatus)

At necropy, 20 out of 35 Mongolian gerbils (Meriones unguiculatus) with prolonged infertility at 12-30 weeks of age were found to have spontaneous hyperplasia in both seminiferous and epididymal tubules. This high incidence of hyperplasia in young gerbils is indication of possible congenital lesions and suggests the possibility of using these animals as a useful model for the further study of male infertility.     

Phonotactic responses to vocalization in adult Mongolian gerbils (Meriones unguiculatus)

Mongolian gerbils have a rich repertoire of vocalization, with at least 13 distinct types of calls observed in a single colony. The purpose of this study was to compare the communicative value of these different call types in a standardized setting. Phonotactic behavior toward vocalizations delivered from loudspeakers was quantified by means of an eight-arm radial maze. Animals were observed to stay near the sound source for longer period of time when short bent-upward frequency-modulated (bUFM) calls, which are observed during seemingly friendly contact, were presented, while animals stayed significantly longer away from the speaker when arched FM (AFM) calls, which are produced by animals under severe physical stress, were presented. Our data show that an 8-arm radial maze can be used to study the function of Mongolian gerbil vocalization and suggest that both bUFM and AFM calls have communicative purposes, increasing the probability that recipient conspecifics approach or escape from the sound source, respectively.     

Indicators for post-surgery recovery in Mongolian gerbils (Meriones unguiculatus)

Telemetric investigations of various parameters are widely used to estimate an animal's state. However, the implantation of the transmitters includes anaesthesia and surgery and has short and longer lasting impacts on the studied object. The aim of the present paper was to evaluate these effects in Mongolian gerbils, namely the hypothermia caused by the anaesthetic and the enduring disturbance of daily rhythmicity until complete recovery. The surgery associated with the implantation of the transmitters differed both in severity and type of anaesthesia. Whereas normal values of body temperature were restored within hours, restoration of daily rhythm required several days, depending on the severity of the surgical procedure. Also, the sensitivity of the body temperature to activity changes was different until the rhythms were re-established. A method based on the rhythm magnitude and shape was proposed to estimate the time until complete recovery of the animals.     

Determination of halothane ED-50 in Mongolian gerbils (Meriones unguiculatus)

The effective dose-50 (ED-50) for halothane anesthesia was studied in 45 male Mongolian gerbils at age 12 weeks. Close control of circadian variation and animal temperature was maintained. Regression analysis for the percent of animals moving in response to a standard stimulus revealed an ED-50 of 1.32 volumes %, a concentration that approximates the ED-50 of the rat.     

Harderian letdown in male mongolian gerbils (Meriones unguiculatus) contributes to proceptive behavior

Adult female gerbils in estrus, like other female rodents, tend to engage in proceptive displays toward conspecific males. The displays, which may be interspersed with the more usual female agonistic activity, if the males are strangers, are preceded by female olfactory investigation of those head areas in the male gerbil where Harderian letdown accumulates most densely. This study explored the possibility that the male Harderian glands are a source of olfactory signals which promote proceptive behavior but suppress female agonistic behavior. Female gerbils in estrus were found to display significantly less than normal rates of proceptive behavior toward Harderianectomized males. The proceptive activity which was observed appeared to be slowed, but the typical pattern was retained. Female aggression, however, was not affected by their estrous condition or by the Harderian state of the males. Possibly Harderian letdown in male gerbils may inform females as to the reproductive competence of the males.     

Differential susceptibility of two stocks of Mongolian gerbils (Meriones unguiculatus) to Leptospira

Mongolian gerbils (Meriones unguiculatus) of Tumble Blook (TUM) and Japan Medical Science (JMS) stocks were compared with regard to susceptibility to Leptospira interrogans serovar copenhageni. The TUM gerbil died 6 to 9 d after intraperitoneal inoculation with 10 organisms, showing jaundice and systemic hemorrhage. However, 25% of the JMS gerbils survived infection with 10(3) or 10(4) organisms and there was no fatal case after infection with 10(2) organisms.     

Intraperitoneal versus subcutaneous telemetry devices in young Mongolian gerbils (Meriones unguiculatus)

Radiotelemetry has become a very popular biotelemetric tool for measuring physiological parameters such as heart rate, blood pressure, body temperature and muscle activity, as well as general behavioural activity in undisturbed, freely moving animals. In most studies using this technique, adult subjects are used. However, sometimes an ontogenetic approach is required to clarify whether changes in one parameter are preceeded or followed by changes in another parameter. Tracking physiological changes in young, developing individuals could explain given states of these animals as adults. Implanting telemetry devices can be done subcutaneously and intraperitoneally, the former method posing less of a challenge on the animal and its recovery from surgery. Because telemetry will be used in weanling gerbils during subsequent studies, we needed to investigate whether subcutaneous implantation of telemetric devices is preferable to intraperitoneal surgery with respect to animal welfare. This is a technical paper describing anaesthetic and surgical techniques in detail during a pre-trial involving subcutaneous (n=10, aged 21-29 days) and intraperitoneal (n=10, aged 19-34 days) implantation of dummy telemetry transmitters (1.9 cm3, 3.6 g after shortening of leads) in weanling gerbils, Meriones unguiculatus. Body weight was measured and analysed over four-day intervals. Optimizing anaesthetic dosages was a first step in this pilot trial. This occurred during the first few subcutaneous implantations. Three animals died while anaesthetized during the subcutaneous procedure but none post-surgery. All animals survived anaesthesia during the intraperitoneal implantation, but two died in the first three days post-surgery. In the former method, the tension on the dermal sutures caused by the presence of the transmitters was too great, resulting in the animals opening the sutures by chewing them. The animals died during the latter procedure probably due to strangulation of the intestine by the excess lead that was coiled in the abdomen. Furthermore, placement of the exposed negative lead of the transmitter on the underlying muscle had to be done on the m. pectoralis transversus in order for it to stay in place as the animal developed. This paper showed that the implantation of a telemetric device in weanling gerbils is feasible and is best executed through the intraperitoneal technique.     

Improving the productivity of breeding colonies of Mongolian gerbils (Meriones unguiculatus)

The productivity of breeding colonies of Mongolian gerbils can be substantially enhanced by using as breeding stock only the 40% of females that exhibit vaginal opening before reaching 25 days of age. Early-maturing females are more likely to breed successfully on first pairing. The lifetime fecundity of early-maturing females is more than twice that of their late-maturing sisters. In those cases in which early-maturing females fail to breed with the first male with which they are paired, they (but not late-maturing females) can be mated with a second male with a high probability of success. Two-thirds of the early-maturing females that failed to reproduce following a first pairing became pregnant following a second. Only 11% of late-maturing females did so.     

Seasonal changes in thermogenesis and body mass in wild Mongolian gerbils (Meriones unguiculatus)

Seasonal adjustments in body mass (BM), nonshivering thermogenesis (NST) and several physiological, hormonal, and biochemical markers were measured in wild-trapped Mongolian gerbils (Meriones unguiculatus) from Inner Mongolia, China. Sexual differences were detected in BM, NST, brown adipose tissue (BAT) mass, and mitochondrial protein content. BM and NST in males were higher in winter (January) and spring (May) than in summer (August), and BM of females was also the highest in winter, but NST remained relatively constant throughout the year. Cytochrome c oxidase activity and mitochondrial uncoupling protein 1 (UCP1) content in BAT were enhanced in winter in males or females, respectively. Serum leptin concentration was the lowest in winter and positively correlated with BM and body fat mass but was negatively correlated with BAT UCP1 content. These data suggest that wild Mongolian gerbils do not depend on a decrease in BM, but instead increase their thermogenic capacity to cope with cold stress. Leptin may be involved in the seasonal regulation in energy balance and thermogenesis in field Mongolian gerbils.     

Enterohepatitis in Mongolian gerbils (Meriones unguiculatus) inoculated perorally with Tyzzer's organism (Bacillus piliformis)

Enterohepatitis was produced in Mongolian gerbils by intragastric inoculation with Tyzzer's organism from natural infection of a gerbil. Death occurred in 50 to 60% animals 5 to 7 days postinoculation (p.i.). On day 3 p.i., when a few necrotic foci appeared in the liver, a large amount of bacterial antigen was present within ileocecal enterocytes and reticuloendothelial cells of the Peyer's patches. Neutrophil and monocyte infiltration was found in the lamina propria. On day 5 or 6 p.i. there was severe necrotizing and hemorrhagic ileotyphlocolitis. Bacterial antigen was abundant within not only enterocytes, but also smooth muscle cells of the ileum and jejunum as well as reticular cells of the mesenteric lymph nodes. On day 7 p.i. the intestinal lesions subsided in the presence of fewer bacteria, while necrotizing hepatitis became well developed. The results indicated that Mongolian gerbils were highly susceptible to the oral route of infection with the Tyzzer's organism.     

Differential susceptibility to Brugia pahangi infection in Mongolian gerbils (Meriones unguiculatus) of different coat colour

The influence of intraspecific host variables on the response to parasitic infections is an important aspect of host-parasite relationships, yet little is known about this aspect of filariasis for lack of a model. This study presents coat colour mutants of the Mongolian gerbil (Meriones unguiculatus) as potential new models for research into the effects of host genetic variation on response to filarial infection. Peak level of microfilaraemia, eosinophil response, body weight and degree of splenomegaly in gerbils infected with Brugia pahangi varied with agouti, albino, and black coat colour. These results suggested that coat colour-related genes might influence host immune response to developmental stages of the parasite and eosinophil-mediated reaction might cause host damage.     

Hormonal regulation of agonistic and affiliative behavior in female mongolian gerbils (Meriones unguiculatus)

Ovarian steroids and oxytocin (OT) have been implicated in the regulation of social behaviors. The purpose of the present study was to examine hormonal substrates of aggression and affiliation in the female Mongolian gerbil (Meriones unguiculatus), a highly social, monogamous rodent. Sexually naive adult females were paired with sexually experienced males for 48 h and their interactions videotaped. Females were gonadally intact and tested during vaginal estrus (INT) or ovariectomized and observed after the following treatments, administered by means of sc injections: EBEB (7 days of estradiol-benzoate); EBP (2 days of EB followed by progesterone), SALEB (saline, days 1-5 then 2 days of EB), OTEB (OT for days 1-5 then 2 days of EB); OTOIL (OT for days 1-5 then 2 days of OIL); or SALOIL (saline days 1-5 then 2 days of OIL). During the first hour of pairing INT females displayed higher levels of affiliation and lower levels of sniffing and agonistic behavior than SALOIL females. All hormonal treatments reduced agonistic behaviors when compared to SALOIL, although none of the hormonal treatments restored affiliation to INT levels. During the 48-h test overt aggression varied by treatment with INT, EBEB, EBP, and OTEB females displaying lower levels than SALOIL, while all groups displayed similar levels of affiliation. The results indicate that OT and E play a significant role in regulating male-directed aggressive behavior in females and that the presence of ovarian hormones as well as OT can increase affiliation during initial contact. Over a sustained period of cohabitation social cues appear to be more important in regulating affiliation than gonadal hormones.     

Photoperiodic refractoriness in energy balance: a specific pattern in Mongolian gerbils (Meriones unguiculatus)

正Dear Editor,Small mammals inhabiting temperate and arctic zone have evolved seasonal life-history traits, such as seasonal body mass cycle and seasonal reproduction. Photoperiod delivers an unambiguous cue to this seasonal acclimatization in most small mammals. Some species lose body mass, and some others increase body mass in short day (SD) compared to those in long-day (LD) acclimation. The variation in body mass is due to the balance of energy intake and expenditure. Basal     

Histological observation on the female prostate in Mongolian gerbils (Meriones unguiculatus).

In Mongolian gerbils, prostatic buds were found in female fetuses at the 23rd day of gestation. In the mothers the well-developed prostate gland consisting of a paired lobes was situated on either side of the neck of the bladder.     

Entamoeba histolytica: lymphoreticular changes in gerbils (Meriones unguiculatus) with experimentally induced cecal amebiasis

Antibody responses and changes in the lymphoreticular tissues of gerbils with experimental cecal amebiasis were studied from 5 to 60 days PI. Changes in the cecum consisted of lymphoid follicle hyperplasia and depletion of lymphocytes, followed by follicle atrophy and histiocytosis. Mesenteric lymphadenopathy, and histologic alterations in the lymph nodes paralleled the progressive development of amebic cecal lesions. Early in the infection (5 to 10 days PI) mesenteric lymph nodes showed cortical follicle hyperplasia, blastogenesis in the paracortical areas (PCA) and intense lymphoblast and plasma cell activity in the medullary cords. At 20 to 30 days PI, the cortical follicles, the PCA and the medulla were depleted of lymphocytes and there was histiocytosis throughout the organ. At 60 days PI, lymphocyte repopulation took place in the PCA, and cortical follicles had active germinal centers. Spleen follicles did not increase in number as the infection progressed, but became hyperplastic. Antibody titers to ameba were low throughout the cecal infection but rose whenever amebic metastasis to the liver occurred. The results of this study indicate that lymphocytes from the submucosal lymphoid follicles and the draining lymph nodes may control the pathogenesis of the infection. Lymphoreticular tissue alterations could result from antigenic stimulation and migration of cells to the sites of infection.     

Developmental changes in several parameters of ultrasonic calling by young Mongolian gerbils (Meriones unguiculatus)

Mongolian gerbils were isolated for one minute on each of the first 14 days of life. The ultrasounds which they produced were displayed on a recorder which allowed measurement of the sound level, duration, shape and temporal patterning of the calls. These components of the pup's response changed with age in various ways. Most of the ultrasounds produced occurred in bouts of regularly spaced calls. The bout length was longest on day 4, and then decreased, but the rate of calling within bouts increased with age. The mean sound level of the calls reached a peak on day 6 and then declined, but one or more pups at each age could produce loud calls. The total rate of production of single calls changed little with age, but production of multiple calls reached a peak on days 4 and 5, and then declined. It seems that the ability of pups to call rapidly and to produce a series of loud, complex calls increases with age. As calling declined, scrabbling movements with the legs increased. Temperature regulation and motor ability are improving during this time. These changes in calling are related to changes in maternal behaviour, especially nest building, which peaked on day 6 in another study. Observations on control litters suggested that daily handling and testing increased the rate of calling on day 5.     

Disruption of pair bonding induces pregnancy failure in newly mated mongolian gerbils (Meriones unguiculatus)

The efficacy of several exteroceptive factors including exposure to a 'strange' male, were tested to induce pregnancy failure in newly mated Mongolian gerbils. Only physical separation of monogamous pairs consistently induced pregnancy failure. This phenomenon was restricted to the immediate period after mating and is believed to be due to disruption of pair bonding, with associated luteal and implantation failure. Concurrent lactation annulled this effect.     

Effect of different photoperiods on gonadal maintenance and development in Mongolian gerbils (Meriones unguiculatus)

The role of photoperiod in adult testicular maintenance and body weight and juvenile development was assessed in male Mongolian gerbils (Meriones unguiculatus). Gerbils were raised on a 14L (14 hr of light) photoperiod. In the first study, adult gerbils with functional testes were transferred to thirteen different photoperiods (0L, 2L, 4L, 6L, 8L, 10L, 12L, 14L, 16L, 18L, 20L, 22L, or 24L) and body weights and testicular size were measured every week for 10 weeks. Body weights were similar in all groups. Testicular regression had occurred in animals housed on 0L, 2L, 4L, 6L, 8L, and 24L by week 10. In the second study, 14L-born prepubertal gerbils were transferred to thirteen different photoperiods as in the first study. Body weights and testicular development were examined for 10 weeks. At the end of 10 weeks the body weights of animals in all groups except 24L were similar to those of adults. Animals in 24L had a lower body weight gain. Exposure to 0L, 2L, and 24L inhibited testicular development and testes weights were significantly different from those of the other groups. These results demonstrate that maintenance of body weight in adult gerbils appears to be independent of photoperiodic signal. Exposure to very long (24L) and short photoperiods (< 10 hr) causes testicular regression in adult gerbils. Moreover, different photoperiods experienced in early life can influence prepubertal testis growth and body weight gain.