Electroencephalography in the diagnosis of hydrocephalus in golden hamsters (Mesocricetus auratus).

The golden hamster (Mesocricetus auratus) is a popular laboratory animal and is used in a multitude of behavioural studies. However, it has been shown that it suffers from different forms of hereditary hydrocephalus, which may result in behavioural changes. This prospective study was designed to look into the usefulness of electroencephalography (EEG) measurements in the diagnosis of hydrocephalus in hamsters. The EEGs of the hydrocephalic hamsters were evaluated double-blind and showed a high-voltage slow wave activity, with a fast activity superimposed onto it. This pattern has already been well described in other hydrocephalic species and differed significantly from the EEGs that were obtained from the normal hamsters. It was concluded from our study that a background activity with an amplitude over 50 muV in combination with a frequency of < or =5 Hz was highly indicative of hydrocephalus in young hamsters. We believe that the EEG could be a very useful diagnostic tool in the screening for hydrocephalus in hamsters.

Photic and non-photic effects on the daily activity pattern of Mongolian gerbils.

The paper analyses the daily activity pattern of Mongolian gerbils with and without access to a running wheel. To evaluate the synchronizing and the masking effects of light, experiments were performed under different photoperiods (L:D=14:10 h and 10:14 h), and light and dark pulses were applied at different phases of the day-night cycle. In order to get a more direct estimate of the central pacemaker of the circadian system, the body temperature rhythm was investigated via implanted transmitters. Without access to a running wheel, the daily activity pattern was bimodal. One peak occurred in the first half of the light time, the other one around the light-dark transition. Also, the gerbils were more active during the light phase as compared to the dark phase. After unlocking the running wheel, the gerbils were active mainly during the dark time. The activity peak in the first half of the light phase remained, the second one shifted by a phase delay into the dark time. These results were found under both LD-regimens. Light during the night nearly completely suppressed running wheel activity, switching off the light during the day time induced wheel running. Whereas wheel running was clearly affected by light and dark pulses, the general activity was not. The body temperature rhythm also shows two peaks, with the second one being bigger and coinciding with the endogenous component of the circadian body temperature rhythm. It was found around light-off. After unlocking the running wheel, the maximum of the body temperature rhythm shifted to the night. This was not primarily a consequence of the changed activity pattern as shown by means of purification analysis. Removing the direct effects of motor activity led to a body temperature curve that could be described by a cosine function, and the delay shift was found also for the purified data, a better estimate of the endogenous circadian component. The wheel-associated increase in nocturnality is not only due to masking effects of wheel-running activity on the body temperature and activity rhythms. It also involves clock-related processes. Changes in the phase preference may serve as an adaptation mechanism to the changes in the animal's natural environment.

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.

Genetic spatial structure of European common hamsters (Cricetus cricetus)--a result of repeated range expansion and demographic bottlenecks.

The spatial genetic structure of common hamsters (Cricetus cricetus) was investigated using three partial mitochondrial (mt) genes and 11 nuclear microsatellite loci. All marker systems revealed significant population differentiation across Europe. Hamsters in central and western Europe belong largely to two allopatric mitochondrial lineages south and northwest of the Carpathian and Sudetes. The southern group, 'Pannonia', comprises populations inside the Carpathian basin (Czech Republic, Hungary) while the second group, 'North', includes hamsters from Belgium, the Netherlands, France, and Germany. Isolation of the lineages is maintained by a combination of geographical and ecological barriers. Both main phylogeographical groups show signs of further subdivision. North is separated into highly polymorphic central German and less polymorphic western populations, which most likely split during late glacial expansion (15,000-10,000 bp). Clock estimates based on haplotype distributions predict a divergence of the two major lineages 85,000-147,000 bp. Expansion times fall during the last glaciation (115,000-10,000 bp) corroborating fossil data, which identify Cricetus cricetus as characteristic of colder climatic phases. Despite the allopatry of mt haplotypes, there is an overlap of nuclear microsatellite alleles between phylogeographical units. Although there are strong evidence that Pannonian hamsters have persisted inside the Carpathian basin over the last 50,000 years, genetic differentiation among European hamsters has mainly been caused by immigration from different eastern refugia. Possible source populations are likely to be found in the Ukrainian and the southern Russian plains--core areas of hamster distribution. From there, hamsters have repeatedly expanded during the Quaternary.

Comparative studies of body mass, body measurements and organ weights of wild-derived and laboratory golden hamsters (Mesocricetus auratus).

All laboratory golden hamsters originate from a sibling pairing back in 1930. To investigate possible differences between domesticated and wild conspecifics, descendants of both strains were maintained under standardized laboratory conditions individually and in unisexual groups. Body mass and food consumption were monitored from birth to 22 weeks of age. The animals were subsequently sacrificed, and body measurements and body composition were analysed. In addition, the absolute and relative masses of different organs were measured. Laboratory hamsters gained more body mass through higher food consumption. However, they did not get fatter, since relative fat values were the same for both strains. Body measurements revealed only minor differences (in body and ear lengths). As deducible from the body mass, the organs (spleen, kidneys, adrenal glands, testes, epididymis and ovaries) were seen to be heavier in laboratory hamsters. Furthermore, with the exception of the kidneys, the same went for the relative values. There were distinct sexual specific differences in both strains only for body fat ( male symbol male symbol upward arrow ) and adrenal glands ( male symbol male symbol upward arrow ). In females, group housing induced an elevated level of aggression. In general, these housing conditions led to social stress symptoms, such as heavier adrenal glands. Additionally, spleen, kidneys, ovaries, body length and mass, body water and body fat were increased in group-housed hamsters. In conclusion, no major differences between laboratory and wild-derived hamsters were observed.

Low microsatellite variation in laboratory gerbrils.

The Mongolian gerbil has become a model organism of increasing importance for the understanding of aging, epilepsy, the process of domestication or sociobiological questions. We report the development and characterization of the first nine polymorphic dinucleotide repeat loci in this species. Average observed heterozygosity and allele number of laboratory animals measured 0.136 (SE = +/-0.065) and 1.78 (SE = +/-0.278) compared to 0.761 (SE = +/-0.025) and 9.2 (SE = +/-0.57) found for a reference group of wild gerbils. The extreme low genetic variation observed in laboratory animals is caused by several severe population size bottlenecks due to the initial founder event and the later establishment of subpopulations. Reduced levels of allelic polymorphism in experimental animals hamper genetic mapping or parental studies. Therefore experiments relying on kinship analyses have to be carried out on wild animals. Estimates of genetic identity and parental exclusion were calculated as Pid = 2.8 x 10(-12) and Pex > 0.999 in wild gerbils. Laboratory gerbil strains show the expected high degree of genetic similarity. However, significant allele frequency differences (P < .001) between American and European gerbils at some microsatellite loci may still allow discrimination between breeding lines.

Activity rhythms of wild and laboratory golden hamsters (Mesocricetus auratus) under entrained and free-running conditions.

The golden hamster (Mesocricetus auratus) is one of the most frequently used laboratory animals, particularly in chronobiological studies. One reason is its very robust and predictable rhythms, although the question arises whether this is an inbreeding effect or rather is typical for the species. We compared the daily (circadian) activity rhythms of wild and laboratory golden hamsters. The laboratory hamsters were derived from our own outbred stock (Zoh:GOHA). The wild hamsters included animals captured in Syria and their descendants (F1). Experiments were performed under entrained (light: dark [LD] 14h:0h) and under free-running (constant darkness, DD) conditions. Locomotor activity was recorded using passive infrared detectors. Under entrained conditions, the animals had access to a running wheel for a certain time to induce additional activity. After 3 weeks in constant darkness, a light pulse (15 min, 100 lux) was applied at circadian time 14 (CT14). Both laboratory and wild hamsters showed well-pronounced and very similar activity rhythms. Under entrained conditions, all hamsters manifested about 80% of their total 24h activity during the dark portion of the LD cycle. The robustness of the daily rhythms was also similar. However, interindividual variability was higher in wild hamsters for both measures. All animals used the running wheels almost exclusively during the dark portion of the LD cycle, although the wild hamsters were three times more active. The period length, measured in constant darkness, was significantly shorter in wild (23.93h +/- 0.10h) than in laboratory hamsters (24.06 +/- 0.07h). The light-induced phase changes were not different (about 1.5h). In summary, these results indicate that the laboratory hamster is not much different from the wild type.

Circadian activity rhythms and sensitivity to noise in the Mongolian gerbil (Meriones unguiculatus).

Since consistent data on endogenous circadian rhythms of Mongolian gerbils are not available, the main aim of our study was to identify suitable conditions to receive stable and reproducible free-running rhythms of activity under different light intensities. Another objective was to determine the role of social cues as an exogenous zeitgeber in the absence of a light-dark (LD) cycle. We performed two long-term sets of experiments with adult male gerbils kept in climatic chambers under various photoperiods of at least 30 days each. In all cases, the time of lights on in the chambers differed from the daily starting hour of work in the animal house. Always, two animals per chamber were kept separately in cages with a running wheel while their activity was monitored continuously. During the first set, only three of eight animals developed intra- and interindividual variable free-running rhythms. The activity patterns seemed to be influenced by human activities outside, indicating high sensitivity to external factors. Subsequently, we damped the chambers and the room and restricted access to the room. In the following noise-reduced set, all gerbils developed comparable free-running rhythms of activity. We determined the mean of the free-running period tau, the activity-rest relationship alpha/theta and the amount of running wheel activity per day: tau = 23.7h +/- 0.08h under low light (5 lux) and 25.5h +/- 0.19h under high light intensities (450 lux); alpha/theta = 0.53 +/- 0.08 under 5 lux and 0.34 +/- 0.04 under 450 lux. The amount of daily activity was 12 times as high under 5 lux as under 450 lux. There was no indication that the two animals in one chamber socially synchronized each other. In conclusion, the pronounced rhythm changes in accordance with Aschoff's theory support the view that gerbils are mainly nocturnal animals.

Effects of social stress on behavior and corpus luteum in female golden hamsters (Mesocricetus auratus).

The consequences of group-keeping as a social stressor on the solitary-living golden hamster were studied. Two females at the same stage of the estrous cycle were kept together for 5 weeks. Behavioral observations showed that the dominance structures within groups were unstable. Intensity of aggression was highest at metestrous, whereas the greatest activity was observed during the estrous stage. After 1 week, the body masses of singly kept and group-kept hamsters were different. Five weeks after the onset of the experiment, the body mass of the singly kept hamsters had increased by 3.6%, and that of the group-kept hamsters by 25%. The plasma progesterone level of group-kept females was 60 to 70% higher than that of singly kept females. The absolute masses of the adrenal glands and the ovaries were higher in group-kept females. Nevertheless, the relative masses did not differ. Whereas a significant positive correlation between the weights of both organs and the body mass was observed in singly kept females, in group-kept females such a correlation was only observed between body and ovary weight. Number and size of corpora lutea were enlarged in group-kept individuals, and this seems to be responsible for elevated plasma progesterone titres. These results indicate social stress in group-kept female hamsters.

Beta-adrenoceptor blockade and open-field behavior in male golden hamsters.

Open-field behavior was compared between untreated, saline-treated, and butoxamine (a beta-2-adrenoceptor antagonist) treated (15 and 5 mg/kg body weight) male golden hamsters (Mesocricetus auratus). Butoxamine-treated males spent significantly more time self-grooming than saline-treated and untreated males. Especially, untreated males and very similar saline control males showed a clear time sequential structure of behavior with two axes: a grooming-grooming sequence and a highly organized flankmark followed by scrape axis. The degree of this organization was markedly decreased in the butoxamine-treated males, showing an increase in organization of the transition between grooming acts. In general, these males displayed a more stereotypic pattern of behavior than the other. To reveal a systematic relation between the flankmark-scrape response and the exposition to butoxamine and to keep the numbers of experimental animals low, mixed samples were created through consecutive summing of the individual transition matrices of six males treated with 5 mg/kg b.wt. butoxamine to the 15 mg/kg b.wt. sample. By analyzing all samples separately, a positive linear relation between the number of low dosed males in the samples and the degree of organization of the flankmark-scrape sequence was found. The results suggest that the analysis of the transitional structure of behavior during short-term challenges can considerably contribute to an estimation of the coping style and seems to be a more sensitive method than comparing frequencies of behavioral indicators of stress.

Housing conditions affect susceptibility to mercury in the golden hamster.

Individually-housed and group-housed golden hamsters (Mesocricetus auratus), aged 8 weeks, were studied with regard to their susceptibility to a single gavage of mercuric chloride (10 mg/kg body weight). Body weight and food consumption were measured for 10 days (day -9 to day 0) in a pre-application period and for 13 days (day 1 to day 13) in a post-application period. Mercuric chloride administration significantly reduced body weight gain in both isolated and grouped hamsters at day 1 compared to vehicle controls. While the individually-housed treated hamsters recovered during the post-application period, the group-housed treated hamsters showed a reduced body weight gain over the whole post-application period. Results are discussed in relation to elevated susceptibility to intoxication in group-housed hamsters triggered by high social stress. This study highlights the need to carefully consider the housing conditions which can influence the results of teratological experiments.

Behavioral alterations in male golden hamsters exposed to chlorodibromomethane.

A number of behavioral parameters in male golden hamsters (Mesocricetus auratus) exposed to chlorodibromomethane (CDBM) were registered over a 10-day (day -9 to day 0) pretest period and a 14-day (day 1 to day 14) test period beginning at 8 weeks of age. Whereas the subchronically treated group (5 mg/kg body weight) only showed significantly increased water bottle contacts on days 4-7 compared with vehicle controls, the acutely treated group (50 mg/kg body weight) exhibited significantly increased locomotor activity on days 3-6 and decreased wheel running at day 6 until day 9. In the open field, the acutely exposed males displayed significantly more flank-mark movements at days 4 and 7 than did the vehicle control animals. After day 9, the acutely treated males showed no differences in any parameter compared with the control males, indicating recovery. During the social confrontation on day 14, the subchronically exposed males bit and approached the intruder significantly less often than did the control males, indicating an impairment of selected social behavior affected by CDBM. Our results of low-level (5 mg/kg) behavioral effects contribute to the general characterization of CDBM and suggest that tests on social capabilities in behavioral toxicology provide significant results in a field of low-level and sublethal chronic application on small samples of experimental animals.

Time of day and stress response to different stressors in experimental animals. Part I: Golden hamster (Mesocricetus auratus Waterhouse, 1839).

The present paper describes the effects of animal house routine stressors on adult golden hamsters during activity time (2 hrs after lights off) and rest time (2 hrs after lights on). In addition, for determination of norm values, the circadian rhythms of the stress indicators heart rate, core body temperature and general activity of unstressed animals were telemetrically registered via implanted transmitters. The three circadian patterns of the nocturnal golden hamster under L:D = 12:12 were unimodal with a main peak after lights off. The physiological norm values (mean over 24 hours +/-SD) were: heart rate 324 +/- 18 bpm, core body temperature 37.5 +/- 0.5 degrees C and activity 114 +/- 123 units/5 min. The mean body temperature of females was significantly higher (0.4 degree C) and its mean activity level was significantly (40%) lower than that of males. The stress responses were dependent on the time of day and on the kind of stressor. The stress responses were significantly stronger during the rest time of the animals (i.e. light period), and it resulted in the subsequent ranking of stressors: handling < vaginal smear < intruder/resident confrontation < cage changing < grouping. There were no sex-dependent stress response differences. The results of this study were compared with identical investigations on the social Mongolian gerbil (J. Exp. Anim. Sci. 1996/97; 38: No. 3).

Measurement of physiological parameters and activity in a Mongolian gerbil during gravidity and lactation with an implanted transmitter.

This communication reports the first use of a transmitter implanted into the abdominal cavity of a small pregnant rodent to simultaneously measure the heart rate, core body temperature and general locomotory activity with no apparent side effects to the animals. Using this method the heart rate of one female Mongolian gerbil (Meriones unguiculatus) decreased from a mean of 303 +/- 6 (SE) (beats per minute) during gravidity to a level of 248 +/- 3 (SE) (beats per minute) during lactation. At the same time, the core body temperature increased from 37.7 +/- 0.05 (SE) degrees C to 38.0 +/- 0.03 (SE) degrees C. During pregnancy the general locomotory activity of this female followed the normal nocturnal pattern for this species (i.e., greater activity during the dark period) but there was an overall reduction in activity to 85% of the nonpregnant state. The level of activity was further reduced during lactation to about 43% of the nonpregnant state. This was largely the result of less activity during the dark period so that activity in the dark period and light period became more or less equivalent.