Interaction of interaural cues and their contribution to the lateralisation of Mongolian gerbils (Meriones unguiculatus).

The main sound localisation cues in the horizontal plane are interaural time and level differences (ITDs and ILDs, respectively). ITDs are thought to be the dominant cue in the low-frequency range, ILDs the dominant cue in the high-frequency range. ITDs and ILDs co-occur. Their interaction and contribution to the lateralisation of pure tones by Mongolian gerbils was investigated behaviourally using cross-talk cancellation techniques for presenting ITDs and ILDs independently. First, ITDs were applied to pure tones with frequencies ≤ 2 kHz to the ongoing waveform, at the onsets and offsets, or in both the ongoing waveform and at the onsets and offsets. Gerbils could lateralise tones only if ongoing ITDs were present indicating that ongoing ITDs are decisive for the lateralisation of low-frequency tones. Second, an ITD was added to 2-to-6-kHz tones with varying ILD. Gerbils' lateralisation was unaffected by the ITD indicating that a large ILD provides a strong lateralisation cue at those frequencies. Finally, small ILDs were applied to 2-kHz tones with an ongoing ITD, pointing either to the same or opposing sides as the ITD. Gerbils' lateralisation was driven by the ITD but strongly affected by the ILD indicating that both interaural cues contribute to the lateralisation.

The different baseline characteristics of cognitive behavior test between Mongolian gerbils and rats.

The Mongolian gerbil is a popular laboratory animal useful across many research fields. In the area of cognitive behavioral research the gerbil have been shown exhibit an anxiety-like profile on the elevated plus-maze, and they could be useful as an animal model for testing anxiolytics and antidepressants. However, there are few reports that thoroughly describe the behavioral characteristics of the gerbils in common cognitive behavior tests. In the present study, we used 7 behavior tests to detect the baseline characteristics of the gerbils and compare them to the Sprague Dawley rats. Collectively, the gerbils showed significantly different behavior characteristics in the open field test, elevated plus maze, grip strength, social interaction and fear conditioning compared to the rats. However, no difference was found between gerbils and rats in sucrose preference or Barnes maze test. The data showed that the Mongolian gerbil exhibited higher social interaction and exploratory activity, but lower conditioning fear and grip strength compared with the rats. These results indicate that the gerbil may be a sensitive animal model in behavioral brain research particularly in the areas of anxiety and fear.

Gerbils exhibit stable open-arms exploration across repeated testing on the elevated plus-maze.

Repeated testing on the elevated plus-maze (EPM) leads rats and mice to avoid the open-arms of the apparatus. The effect of multiple exposures to the EPM on the behavioral profile of gerbils is unknown. In this study, young and middle-aged gerbils were exposed to the EPM and four retests were carried out 24, 48, 72 and 96h after the first trial in order to determine whether animals exhibited open-arms avoidance. In addition, groups of young and middle-aged gerbils were exposed to the EPM for 20-min followed by a 5-min retest trial 24h apart to analyze the effect of a prolonged exposure to the EPM on open-arms exploration during first trial and retest. Gerbils exhibited high exploration of open-arms during the first trial and progressive locomotor decrease across repeated testing. Unlike previous reports for rats and mice, young gerbils showed a stable open-arms exploration both across multiple exposures and during a prolonged exposure to EPM. Middle-aged gerbils also exhibited a stable open-arms exploration during retest prior to the 20-min test. Results suggest a reliable repeated test paradigm for the EPM using our proposed methodology for gerbils.

Everybody loses: intraspecific competition induces tragedy of the commons in Allenby's gerbils.

Interference competition may lead to a tragedy of the commons in which individuals driven by self-interest reduce the fitness of the entire group. We investigated this hypothesis in Allenby's gerbils, Gerbillus andersoni allenbyi, by comparing foraging behaviors of single vs. pairs of gerbils. We recorded strong interference competition within the foraging pairs. Competition reduced the amount of time the gerbils spent foraging, as well as foraging efficiency since part of the foragers' attention was directed toward detecting competitors (apparent predation risk). Single gerbils harvested significantly more food than the combined efforts of two gerbils foraging together. Competition reduced the success of both individuals within a pair by more than 50%, making this a case of the tragedy of the commons where each individual's investment in competition reduces the success of all individuals within the group, including its own. Despite their great costs, competitive behaviors will be selected for as long as one individual achieves higher fitness than the other. In nature, interspecific interactions, such as predation risk, may act to reduce and regulate the deleterious effects of intraspecific competition.

The effect of different working definitions on behavioral research involving stereotypies in Mongolian gerbils (Meriones unguiculatus).

Many sources of variation in animal experiments are related to characteristics of the animal or its husbandry conditions. In ethologic studies, observational methods can also affect interexperimental variation. Different descriptions for a behavior can lead to divergent findings that may be incorrectly attributed to other factors if not recognized as stemming from a classification dissonance. Here we discuss 2 observational studies in Mongolian gerbils (Meriones unguiculatus). The first study describes how data vary when 2 different working definitions are used for stereotypic digging: WD(mor), a definition based on a morphologic description of the behavior, and WD(12), a definition that relies mainly on a duration criterion of digging bouts (greater than 12 s). The total duration and number of stereotypic bouts were 22.0% and 63.1% lower, respectively, when WD(12) was applied compared with WD(mor). However, strong correlations existed between data generated by WD(mor) and WD(12), indicating that the 2 definitions yielded qualitatively similar results. The second study provides the first report that laboratory gerbils develop stereotypic behavior that is characterized by alternating bouts of digging and bar-gnawing. Of the 1685 stereotypy bouts investigated, 9.1% comprised both stereotypies, 87.6% consisted of digging only, and 3.3% consisted of bar gnawing only. Working definitions that neglect combined stereotypies can result in considerable underestimation of stereotypic behavior in Mongolian gerbils.

Perception and neural representation of size-variant human vowels in the Mongolian gerbil (Meriones unguiculatus).

Humans reliably recognize spoken vowels despite the variability of the sounds caused by the across-subject variability of the speakers' vocal tract. The vocal tract serves as a resonator which imprints a spectral envelope onto the sounds generated by the vocal folds. This spectral envelope contains not only information about the type of vocalization but also about the size of the speaker: the larger the speaker, the lower the formant frequencies of the spoken vowels. In a combined psychophysical and electrophysiological study in the Mongolian gerbil (Meriones unguiculatus), we investigated the perception and neural representation of human vowels spoken by speakers of different sizes. Gerbils trained to discriminate two standard vowels, correctly assigned vowels spoken from different-sized human speakers. Complementary electrophysiological recordings from neurons in the auditory brainstem, midbrain, and primary auditory cortex show that the auditory brainstem retains a truthful representation of the frequency content of the presented vowel sounds. A small percentage of neurons in the midbrain and auditory cortex, however, showed selectivity for a certain vowel type or vocal tract length which is not related to the pure-tone, frequency response area, indicative of a preprocessing stage for auditory segregation of size and structure information.

Adopted cognitive tests for gerbils: validation by studying ageing and ischemia.

Transient occlusion of common carotid arteries in gerbils is a simple and widely used model for assessing histological and functional consequences of transient forebrain ischemia and neuroprotective action of pharmaceuticals. In the present study we aimed to introduce additional behavioural tests as novel object recognition and food-motivated hole-board learning in order to measure attention and learning capacity in gerbils. For validating these cognitive tests the effects of ageing (4, 9 and 18 months) and those of transient forebrain ischemia induced by bilateral carotid occlusion at 9 months of age were investigated. Neuronal cell death was estimated in the hippocampus using TUNEL and caspase-3 double fluorescence labelling and confocal microscopy. Ageing within the selected range although influenced ambulatory activity, did not considerably change attention and memory functions of gerbils. As a result of transient ischemia a selective neuronal damage in CA1 and CA2 regions of the hippocampus has been observed and tested 4 days after the insult. Ischemic gerbils became hyperactive, but showed decreased attention and impaired spatial memory functions as compared to sham-operated controls. According to our results the novel object recognition paradigm and the hole-board spatial learning test could reliably be added to the battery of conventional behavioural tests applied previously in this species. The novel tests can be performed within a wide interval of adult age and provide useful additional methods for assessing ischemia-induced cognitive impairment in gerbils.

Effects of isolation-rearing on the development of social behaviors in male Mongolian gerbils (Meriones unguiculatus).

Social isolation has been shown to modify behavioral patterns and neuroendocrine function in many species. In this study, we examined the influence of post-weaning social isolation on the behavioral development and fecal testosterone and corticosterone levels of male Mongolian gerbils. In Experiment 1, isolation-reared (IR) males spent more time engaged in social-sniffing. IR males also showed more aggressive and anxiety-related behaviors than group-reared males (GR; three animals per cage). In Experiment 2, a screen-divided-reared condition (SDR) was examined in addition to GR (two males per cage) and IR males. In the SDR group, two subjects were separated by a wire mesh screen allowing for sensory communication and limited physical contact but not direct social interactions. SDR males showed similar patterns in sniffing and anxiety-related behaviors to IR males; however, an increase in aggression was not observed. No differences in fecal testosterone and corticosterone levels were found among males in different rearing conditions. These results suggest that post-weaning social isolation affects behavioral development without affecting testosterone and corticosterone levels. The behavioral changes observed may therefore be regulated by different mechanisms; increases in social-sniffing and anxiety-related behaviors may be caused by the deprivation of direct social interactions, whereas the enhancement of aggressive behaviors may be caused by the lack of sensory stimulation and limited physical contact with other individuals.

On the border: perimeter patrolling as a transitional exploratory phase in a diurnal rodent, the fat sand rat (Psammomys obesus).

Exploration is an initial phase of constructing spatial representation. In an illuminated environment, exploration by nocturnal rodents takes the form of home-base behavior, with the rodents organizing their activity in relation to the base, repeatedly orienting and returning to it. In the dark, home base behavior in gerbils is preceded by looping exploration, in which travel paths tangle into loops that close at various locations so that the gerbils pilot from one loop to the next. In the present study we tested a diurnal gerbil, the fat sand rat, Psammomys obesus, in both a lit and a dark open field in order to compare its exploratory behavior with that of nocturnal rodents. We found that under lit conditions, fat sand rats used perimeter patrolling, traveling mainly along the walls of the open field. In perimeter patrolling the animal probably monitors its location in relation to the perimeter (arena walls), and not to a specific location as in home base. In the dark, fat sand rats first used looping, and gradually shifted to perimeter patrolling exploration. We suggest that perimeter patrolling is a transient phase in which the animal evaluates possible locations for a home base. Thus, perimeter patrolling is an intermediate phase between looping, which is based on piloting from one landmark to the next, and home base exploration, in which the animal continuously orients to a specific location. This spatial behavior of perimeter patrolling may shed light on phases of information processing and spatial representation during exploration and navigation.

Forward masking in gerbils: the effect of age.

We investigated forward masking in 21 gerbils as a function of age (5-47 months) using 400ms maskers at 40dB SPL and a 20ms, 2.85kHz probe presented 2.5ms after the masker. Elevated thresholds for the unmasked probe were only observed in animals older than 3 years. Unmasked thresholds showed no significant age-dependent hearing loss in animals below 3 years of age. In these animals without peripheral hearing loss, we found a significant age-dependent increase of masker-induced threshold shift. A regression analysis revealed that threshold shift increased from 23dB in 1 year old gerbils to 37dB in 3 year old animals. Increased forward masking in these animals with no sign of peripheral hearing loss points to a central processing deficit.

Housing and husbandry conditions affect stereotypic behaviour in laboratory gerbils.

An artificial burrow was developed which fits into standard laboratory cages and significantly reduces stereotypic digging in gerbils. Also, the causes of bar-chewing were assessed experimentally. Neither the lack of gnawing material, nor the spatial proximity of cage-lid bars and food in the hopper nor the routine husbandry procedure of transferring juvenile gerbils to a fresh cage, but premature separation of juvenile gerbils from their parents before the birth of younger siblings significantly increased bar-chewing.

Male expulsion in cooperative Mongolian gerbils (Meriones unguiculatus).

Mongolian gerbils are territorial rodents of steppes and semideserts of Mongolia and Northern China. At least under laboratory conditions, the family life is characterized by long-term harmonious and short-term aggressive periods in which some members are expelled. The purpose of this study was to clarify which features of male offspring promote their expulsion. Therefore body mass, absolute and relative weight of testes and epididymis, histology of testes and testosterone concentrations were analyzed in males derived from five families living in semi-natural enclosures with food and water ad libitum. Males expelled (EFM, n=40) had significantly higher relative testes and relative epididymis weight and higher testosterone concentrations in harmonious periods than it did non-attacked ones (IFM, n=13). A stepwise discriminant analysis has established the relative testes weight as decisive for the affiliation to EFM or IFM. Based on this parameter, 71.7% of the offspring could be classified correctly. Moreover, histological results showed that 50.0% of integrated and 29.4% of the expelled family members had incomplete spermiogenesis, indicating a reduced fertility. It is concluded, that males do compete for reproduction within the families which triggers the expulsion of the males with the highest reproductive capacity.

Burrowing in rodents: a sensitive method for detecting behavioral dysfunction.

Virtually all rodents display burrowing behavior, yet measurement of this behavior has not yet been standardized or formalized. Previously, parameters such as the latency to burrow and the complexity of the burrow systems in substrate-filled boxes in the laboratory or naturalistic outdoor environments have been assessed. We describe here a simple protocol that can quantitatively measure burrowing in laboratory rodents, using a simple apparatus that can be placed in the home cage. The test is very cheap to run and requires minimal experimenter training, yet seems sensitive to a variety of treatments, such as the early stages of prion disease in mice, mouse strain differences, lesions of the hippocampus and prefrontal cortex in mice, also effects of lipopolysaccharide and IL-1beta in rats. Other species such as hamsters, gerbils and Egyptian spiny mice also burrow in this apparatus, and with suitable size modification probably almost any burrowing animal could be tested in it. The simplicity, sensitivity and robustness of burrowing make it ideal for assessing genetically modified animals, which in most cases would be mice. The test is run from late afternoon until the next morning, but only two measurements need to be taken.

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.

Age-related changes on marking, marking-like behavior and the scent gland in adult Mongolian gerbils (Meriones unguiculatus).

Marking behavior, marking-like behavior [3], and changes of the scent glands were observed in aged Mongolian gerbils. In Experiment 1, changes in the marking and marking-like behavior with aging were evaluated in adult male and female Mongolian gerbils of an inbred strain aged 6 to 36 months. The frequency of marking behavior in males was significantly higher than females throughout the observation period except at 36 months of age. On the other hand, frequency of marking-like behavior in males, but not in females decreased with aging, significantly. In Experiment 2, changes of the scent gland in adult males and females aged 6 to 36 months were morphologically evaluated. Macroscopic examination revealed an increase in the size length and width of the glands of males aged 12 months and females aged 6 months. Histologically the glands of all the males and females aged 6 months developed moderately or well. Some of the 12-month-old males and females showed acinar atrophy of the glands, and all the females aged 18 months or more had highly atrophied scent glands. From these results, we concluded that there is no relationship between the changes of marking behavior and those of the scent glands in aged male Mongolian gerbils, and assume that marking behavior in aged animals does not have an important meaning as marking. In Experiment 3, marking and marking-like behavior in castrated adult Mongolian gerbils aged 16 weeks were observed. The result showed that marking behavior, not marking-like behavior was inhibited after castration. From these findings, we consider that generally marking behavior in Mongolian gerbils consists of androgen-dependent marking behavior and androgen-independent marking behavior (marking-like behavior).

Marking behavior is innate and not learned in the Mongolian gerbil.

We studied whether marking behavior in Mongolian gerbils would be innate or learned behavior. The marking behavior was defined as "animals rubbing their abdominal scent glands on small protruding objects". Between 21 and 90 days of age, Mongolian gerbils, which were kept under such conditions that they would be unable to learn this behavior, were observed at intervals of 5-15 days to find out if there were signs of the behavior or not. Six male and four female Mongolian gerbils were used for observing. Neonate Mongolian gerbils during the age of 3 to 28 days were fostered by ICR mother mice. Weaning Mongolian gerbils were then individually kept away from the others. Marking behavior was observed in 2 out of 6 males at 50 days of age and 2 of 4 females at 60 days and the mean frequency of the marking behavior for 10 min was 3.5 in the males and 5.0 in the females. These results suggest that marking behavior was innate and not learned behavior in Mongolian gerbils.

Effects of experience on the parental responses of male Mongolian gerbils.

We examined responses of adult male Mongolian gerbils to nest site and young during the hours preceding and days following birth of a litter. We found that (a) male attendance at the nest site was markedly reduced for several hours following the birth of pups; (b) this lack of contact by males with nest and pups did not result from active exclusion of males from the nest by their mates; (c) males lacking previous experience of pups, but not those familiar with pups, avoided contact with pups on the day of their birth; and (4) 3-day-old gerbil pups were attractive even to males encountering young for the first time.

Effects of food deprivation and metabolic fuel utilization on food hoarding by jirds (Meriones shawi).

Food hoarding plays an important role in the energetic repertoire of a variety of mammalian species. Both food hoarding and food intake have been examined in rodents using several energetic challenges including food deprivation, treatment with metabolic fuel blockers, and enhancement of fuel storage. In the present experiment, we examined food hoarding by female jirds (Meriones shawi), a desert rodent species occupying the arid steppes and desert regions of Egypt. Jirds are prodigious hoarders in the field; however, virtually nothing is known about their hoarding within controlled laboratory settings. In the present study, the effects of food deprivation as well as alterations in metabolic fuel utilization (i.e., 2-deoxy-D-glucose and isophane insulin) on food hoarding and food intake were tested in female jirds using a simulated burrow system. Jirds decreased body mass and increased food consumption following either 32 or 56-h food deprivation. Food hoarding, however, was virtually abolished after food deprivation and treatment with 2-DG. In contrast, isophane insulin treatment had no effect on food consumption or hoarding in this species. Taken together, the present results suggest that total body mass (fat), rather than short-term metabolic fuel utilization, regulates both food consumption and hoarding in female jirds. In addition, these results provide a novel set of appetitive responses to these energetic challenges in small mammals.

Pair-bond disruption in Mongolian gerbils: effects on subsequent social behaviour.

Gerbils are social rodents which form stable male-female pairs. These pair bonds appear to be based on prolonged association rather than an exclusive mating relationship. However, both sexes contribute to territorial defense and pup rearing. Therefore, pair-bond disruption may be expected to have consequences for subsequent behaviour. This hypothesis was examined in a series of laboratory studies. Behavioural consequences of pair-bond disruption were seen in both sexes and the optimum housing parameters were found to be to pair males and females for 5 weeks and to examine their behaviour 1 week after pair-bond disruption. Two further studies using these parameters were conducted to examine the combined influence of pair-bond disruption and the sex of the animal being interacted with. Results across all studies revealed a consistent pattern. Females showed increased immobility in contact, that is, freezing upon another animal's approach, and altered cage-orientated behaviour, regardless of the sex of the animal they were interacting with. In contrast, males showed decreased social investigation and offense and initiated fewer social interactions. However, these effects were only seen in interactions with other males. No changes in social behaviour were evident in interactions between pair-bond-disrupted males and females. The behavioural strategies of pair-bond-disrupted males and females in a social situation therefore differ. From these studies, it may be concluded that pair-bond disruption has consistent and reproducible effects on subsequent social behaviour in gerbils and that there are important sex differences in the behavioural expression of this.