Isolation calls and retrieving behavior in laboratory and wild-derived golden hamsters—No sign for inbreeding depression

Isolated juvenile golden hamsters produce ultrasonic and audible vocalizations, so-called isolation calls, as a reaction to being separated from their mother and nest and their cooling down. Their aim is to stimulate mothers to search and retrieve the pups. In this work, the vocalization of juvenile laboratory (Zoh:GOHA; Institute of Zoology, Martin-Luther-University Halle-Wittenberg) and juvenile wild-derived golden hamsters (captured in northern Syria and southern Turkey) from birth up to the age of 18 days were digitally recorded, analyzed and compared using an ultrasonic microphone and the software Avisoft. Furthermore, the retrieving behavior of the mothers was observed and compared. The results showed that the number of isolation calls was age-specific and the structure of the calls was influenced by body temperature, body mass and sex of the pups. The age of the pups determined retrieval by the maternal golden hamsters; however these did not discriminate between their own pups or foreign pups. In spite of enormous genetic differences between wild-derived and laboratory golden hamsters, only minor differences between the strains were found.     

Discomfort-related changes in pup ultrasonic calls of fat-tailed gerbils Pachyuromys duprasi

Rodent pups vocalize when placed in social isolation. We apply a method of “joint calls” for examining discomfort in rodent pup ultrasonic (>20 kHz) calls. Previously, this method has been developed for audible calls of fur farm mammals. Using a repeated measures design to exclude effects of individual identity and age on the analysed variables, we compared the ultrasonic call variables produced by 8–40-day pups of fat-tailed gerbils Pachyuromys duprasi during two subsequent experimental stages, the Isolation Stage and the Handling Stage. We considered that discomfort-related negative emotional arousal increased towards the Handling Stage compared to the Isolation Stage because of cumulative effects of handling and time of pup isolation from the nest. At the Isolation Stage, the call rate (calls/s) was higher from 10 to 18 days of age, whereas both the maximum amplitude frequency and power quartiles of joint calls were lower than at the Handling Stage from 20 to 32 days of age. At the same time, in audible (<20 kHz) vocalizations of a wide range of mammalian species, both the higher call rate and the upward shift of the maximum amplitude frequency and power quartiles indicate the discomfort-related increase of negative emotional arousal. We discuss the advantages of the method of joint calls for express-analyses of power variables for large sequences of ultrasonic vocalizations of complex acoustic structure during experimental trials.     

Pronounced juvenile circadian core temperature rhythms exist in several strains of rats but not in rabbits

Torpor-like circadian variations of core temperature are well documented for suckling-age Zucker rat pups. To determine (1) whether this juvenile circadian rhythm is as strongly expressed in other rat strains, and (2) whether a similar rhythm is expressed in rabbit pups, we recorded core temperature and metabolic rate of artificially reared pups. Wistar, Brown Norway, and Long Evans pups were studied for 30 h under moderate cold loads (ambient temperature=28°C) when 9–11 days old, i.e. at the age and ambient temperature for which the rhythm has been most thoroughly characterized in Zucker rats. Chinchilla bastard rabbit pups were studied under similar conditions when they were 3–8 days old, the youngest age at which the rhythm can be easily detected in rats. Rat pups of each strain showed clear circadian rhythms with sharp decreases of core temperature and metabolic rate in subjective morning. Core temperature amplitudes were in the order Wistar < Brown Norway < Zucker < Long Evans strain. In contrast, the rabbit pups maintained stable high levels of core temperature and metabolic rate throughout the day. A torpor-like decrease of core temperature in the morning is thus not a pecularity of the Zucker rat strain but also occurs in other pigmented rat strains, whereas rabbit pups at a similar developmental stage do not show a circadian core temperature rhythm.     

A behavioral comparison of the common laboratory rat strains Lister Hooded,Lewis, Fischer 344 and Wistar in an automated homecage system

Behavioral characterization is an important part of establishing novel animal models, but classical behavioral tests struggle to reveal conclusive results due to problems with both reproducibility and validity. On the contrary, automated homecage observations are believed to produce robust outcomes that relate more to natural animal behavior. However, information on the behavior of background strains from such observations, which could provide important reference material, is rare. For this reason, we compared the behavior of the commonly used Lister Hooded, Lewis, Fischer 344 and Wistar rats during 70 h of exposure to an automated homecage system at 2, 4 and 6 months of age. We found considerable strain differences in metabolic parameters, novelty‐induced and baseline activity‐related behavior as well as differences in the development of these parameters with age. The results are discussed in terms of advantages and disadvantages of the system compared to classical behavioral tests, as well as the system's ability to recreate common findings in literature .     

Strain differences in parturition behavior and survival probability in rats (Rattus Norvegicus).

Three strains of laboratory rats (Wu:Cpb, CPB-B and WKY/Cpb) differing widely in reproductive success were compared concerning the role played by maternal behavior in the survival probability of pups. Parturition behavior of the dams was selected for study as pups are most dependent on the mother's behavior at, and immediately after birth. Great strain differences in survival rate of life born pups were found. However, differences between strains in parturition behavior were found to be restricted to only one pup oriented behavior and some non social behaviors. Besides no pups died at the day of birth nor did it seem probable that the strain differences we found in parturition behavior can be held responsible for the eventual death of pups during parturition. The suggestion is presented that strain differences in maternal behavior which affect survival chances of pups are to be looked for in the lactation period.     

人为疼痛刺激下金色中仓鼠幼鼠叫声的发育过程

金色中仓鼠幼鼠可以利用可听声和超声信号与母鼠进行交流,这些声音可以反映个体的寒冷、饥饿、疼痛等不同生理状态和需求。因疼痛诱发的叫声对于维持幼鼠的存活也有着重要意义。本实验通过录制人为疼痛刺激下,不同日龄金色中仓鼠的叫声,分析并比较了5 - 30 日龄金色中仓鼠不同发声信号特征(可听声出现频次、可听声持续时程、可听声主频率、超声出现频次、超声持续时程、超声主频率)的性别差异;同时记录了幼鼠的两种发声随日龄的变化趋势。结果发现:幼鼠两种叫声的各种参数均未表现性二型现象。幼鼠超声发生频次随日龄增加而逐渐减少。而可听声却正相反,随日龄增加而逐渐上升,并在20 日龄时达到最高峰,之后逐渐下降。可听声持续时程也随日龄而增加。综上,在人为疼痛刺激下,随着日龄增加,幼鼠更倾向于使用可听 声而非超声与母兽进行交流。     

Ultrasonic isolation calls in genetically high- and low-emotional rat pups.

The present study was undertaken to investigate the relationship between the emotionality and the modulation of ultrasonic vocalizations in Tsukuba High Emotional (THE) and Tsukuba Low Emotional (TLE) strain rat pups 3-18 days old. The THE pups, while isolated from their dam and littermates and placed in a cold environment, emitted ultrasonic isolation calls at a high rate until day 15. In contrast, ultrasound production was at a consistently low level throughout the test period in the TLE pups. The ultrasonic isolation calls of THE pups were attenuated to the same level as those of the TLE pups after administration of diazepam (1 mg/kg, s.c.), a benzodiazepine receptor agonist, at 6 and 12 days of age. These findings suggest that the high emotionality of the rat pups was reflected largely by the emission of ultrasounds in response to isolation distress rather than the number of the benzodiazepine receptors in the brain that might play a role in physiologic mediation of the rat pup isolation call.     

Unusual repertoire of vocalizations in the BTBR T+tf/J mouse model of autism

BTBR T+ tf/J (BTBR) is an inbred mouse strain that displays social abnormalities and repetitive behaviors analogous to the first and third diagnostic symptoms of autism. Here we investigate ultrasonic vocalizations in BTBR, to address the second diagnostic symptom of autism, communication deficits. As compared to the commonly used C57BL/6J (B6) strain, BTBR pups called more loudly and more frequently when separated from their mothers and siblings. Detailed analysis of ten categories of calls revealed an unusual pattern in BTBR as compared to B6. BTBR emitted high levels of harmonics, two-syllable, and composite calls, but minimal numbers of chevron-shaped syllables, upward, downward, and short calls. Because body weights were higher in BTBR than B6 pups, one possible explanation was that larger thoracic size was responsible for the louder calls and different distribution of syllable categories. To test this possibility, we recorded separation calls from FVB/NJ, a strain with body weights similar to BTBR, and 129X1/SvJ, a strain with body weights similar to B6. BTBR remained the outlier on number of calls, displaying low numbers of complex, upward, chevron, short, and frequency steps calls, along with high harmonics and composites. Further, developmental milestones and growth rates were accelerated in BTBR, indicating an unusual neurodevelopmental trajectory. Overall, our findings demonstrate strain-specific patterns of ultrasonic calls that may represent different lexicons, or innate variations in complex vocal repertoires, in genetically distinct strains of mice. Particularly intriguing is the unusual pattern of vocalizations and the more frequent, loud harmonics evident in the BTBR mouse model of autism that may resemble the atypical vocalizations seen in some autistic infants.     

Ultrasonic Vocalizations in Rat Sexual Behavior

Ultrasonic vocalizations are very conspicuous during rat matingactivity. Two types of calls are produced by both sexes. Thefirst, brief complex calls with the main frequency centeredabout 50 kHz, occur primarily in conjunction with solicitationand mounting activity. The second type of call is the long,22 kHz whistle which is emitted mainly by the male during thepostejaculatory refractory period, but also by both male andfemale at other times during the copulatory sequence. The occurrenceof ultrasonic vocalizations is correlated with sexual motivationof rats. Males emit more 50 kHz calls before successful matingtests than before tests in which they fail to ejaculate. Furthermore,more vocalizations are emitted by the pair prior to intromissionsthan prior to mounts without intromission. Just before ejaculationthere is a large increase in the rate of calling and, at times,transition by the male to calling at 22 kHz. This latter eventmay represent physiological dearousal by the male. Followingejaculation, the male characteristically emits 22 kHz vocalizationsand exhibits a sleep-like EEG pattern. The function of the postejaculatoryvocalization may be to enforce separation between the matingpair, while at the same lime maintaining contact between thepartners. Fifty kHz calls, on the other hand, prime and facilitatesexual responsiveness of the female. Tape recorded vocalizationsof mating rats facilitate solicitation behavior of estrous femalesin the presence of castrated males, and such females also showa preference for these sounds in a "Y" maze. Deafening of femalesdoes not affect their normal pacing of copulatory contacts,but it drastically reduces their solicitation behavior. Thestudies summarized in this paper lead us to conclude that ultrasonicvocalizations play a major role in the integration of reproductiveactivity in the Norway rat, Rattus norvegicus.     

Anxiety and behavior in WAG/Rij strain rats with genetically induced absence attacks

Behavior of nonlinear rats and animals from Wistar and WAG/Rij (with inborn generalized absence epilepsy) strains was examined in the elevated plus-maze and the hole board. WAG/Rij rats demonstrated low exploratory behavior in both tests. In the elevated plus-maze, WAG/Rij rats were more balanced and more anxious than Wistar and nonlinear rats. Administration of ethosuximide completely eliminated spike-wave discharges but did not change behavioral interstrain differences. Since the spike-wave patterns develop in WAG/Rij at the age of 3 months, the behavior of young (2-moth-old) pups from different strains was compared and significant differences were revealed. Correlation between the genetically defined features (spike-wave discharges) and behavioral peculiarities in WAG/Rij rats is supposed.     

The effects of repeated early deprivation on ultrasonic vocalizations and ontogenetic development in mandarin vole pups

Early deprivation is popularly used in rodent models as an early life social stress to investigate and determine the factors that affect the development of the brain and behavior. Ultrasonic calls made by pups play an important role in parental–pup interactions during the neonatal period. However, whether repeated early deprivation affects the properties of ultrasonic vocalizations (USVs) produced by mandarin vole (Microtus mandarinus) pups, and whether ontogenetic development is subsequently affected, remains unclear. Here we measured USVs and developmental parameters in mandarin vole pups deprived of their parents and littermates for 3 h per day (ED, which is significantly different from 5 min isolation used to induce USVs) and another pup group developed under normal nest conditions (PC). Repeated measures analysis indicated that the number of USVs from ED pups was significantly lower than those from PC pups during the postnatal period (p < 0.05). The pulse durations of ED pups were longer than those of PC pups at two (p < 0.001) and five days of age (p < 0.05), but shorter at 14 days of age (p < 0.001). Compared with PC pups, the frequency range of the ED pups was wider at 18–45 kHZ, variable during the first week, smaller and narrower at 18–30 kHZ at eight and 11 days of age, and became stable similar to PC pups at 25 kHZ after 14 days of age. ED also reduced pup body weight significantly and resulted in earlier eye opening compared with PC pups (p < 0.001). A positive relationship was also found between USV emissions and levels of parental care received by pups. It appears that pup USVs are an important age-dependent behavioral phenotype and an effective communicative method between parents and offspring. Prolonged parental and littermate deprivation (ED) may alter USVs emitted by pups and then ontogenetic development and parental care. Mandarin voles show USV properties similar to socially monogamous rodents and this add further support to the hypothesis that species with different social systems produce different patterns of ultrasonic vocalizations. USVs, ontogenetic development and parental care are closely associated.     

The effect of ambient temperature on body temperature and on ultrasonic behaviour in litters of albino laboratory mice deprived of their mothers

Litters of mouse pups of various ages when deprived of their mother and kept for one hour at ambient temperatures of 3°C, 12°C and 22°C lose heat less rapidly than pups isolated individually at similar temperatures. The litters are able to maintain constant body temperatures of 35–37°C by day 8 at 22°C, by day 19 at 12°C and by day 21 at 3°C. Very little ultrasound is detected from litters of any age up to 21 days at 22°C while at 12°C ultrasound is mainly detected from pups of 4 and 6 days; very few calls are produced by older pups at this temperature. Considerably more calls are emitted at 3°C than at either of the two higher temperatures. At 3°C the total number of calls emitted during the hour-long exposure period varied markedly with age. There were two peaks of calling, one on day 6 and the other on day 16. The temporal pattern of calling throughout the hour-long exposure period at 3°C was similar in pups of 4 and 6 days and in pups of 8, 10, 12, 14 and 16 days, but differed between these two groups. In the younger group of pups the rate of calling rose to a peak and then decreased to zero as the pups became comatose; in the older pups the rate of calling was low initially then either rose throughout the rest of the hour or rose to a high level that was maintained. It is suggested that the various patterns of ultrasonic calling can be associated with the physiological development of mouse litters.     

Comparative study on isolation calls emitted from hamster pups.

Waveforms of isolation calls emitted from hamster pups, which were Syrian hamsters, Djungarian hamsters, and Chinese hamsters, were compared in a basic study on improving reproduction by decrease of cannibalism, because it was reported that maternal behavior was induced by isolation calls in rodents. Isolation calls of hamster pups, isolated from their mother and receiving cold stress, were collected by Real-Time Spectrogram (RTS), and calculated to spectrograms and power spectra by SIGNAL. Isolation calls consisted of ultrasonic vocalizations (USVs) and audible vocalizations (ADVs) in each species. Waveforms of isolation calls emitted by the hamster pups, were shown to have several characteristic features. In this study, the species specificity of isolation calls was shown in hamster pups. It would seem that the species specificity originates in the differences of sensitivity to cold stress via the autonomic nerve in hamsters.     

Echolocation in the large molossid bats Eumops glaucinus and Nyctinomops macrotis

Eumops glaucinus and Nyctinomops macrotis, the largest molossid bats in Cuba, were investigated. Both species of bats share the same guild in the island and are similar in size, which allow the prediction of overlapping echolocation inventories following both the "vocal plasticity hypothesis" and the "scaling hypothesis." In addition, large body size predicts the emission of low frequency calls in the human audible range. Calls recorded during hunting show that the bats' echolocation repertoires are very similar and of low frequency, with most differences in search calls. Matches were found in the calls' design, duration, slope, bandwidth, and spectral parameters. Statistical differences between search calls are consistent with the predictions from the "scaling hypothesis," considering that E. glaucinus is only slightly larger than N. macrotis. The echolocation calls emitted by both species are in the frequency range below 20-25 kHz, which identifies both species as the only ones with echolocation in the human audible range in Cuba.     

Low dose of disulfiram and l-dopa evoked synergistic modification in behavior of Wistar and WAG/Rij rats

Comparative analysis of behaviors of two rat strains, Wistar and WAG/Rij, was performed. No behavioral differences between Wistar and WAG/Rij were found in the emotional resonance test. Disulfiram injection produced similar effects in both rat strains. Animals of the first group (with slow acquisition of emotional resonance reaction) transformed into the animals of the second group (with fast acquisition). Passive avoidance conditioning was successfully reproduced in Wistar and was significantly impaired in WAG/Rij. A low dose of disulfiram injected before or immediately after conditioning substantially improved the reproduction to a greater extent in WAG/Rij than Wistar strains thus eliminating in interstrain differences. Active avoidance conditioning was more successful in WAG/Rij than in Wistar rats However, on the next day conditioning in WAG/Rij was substantially impaired. Administration of the low dose of disulfiram or L-DOPA prior to conditioning impaired the acquisition but improved the reproduction on the following day in both strains, but disulfiram injection after conditioning improved conditioning in WAG/Rij to a greater extent than in Wistar. Thus, the pharmacologic enhancement of the reward system substantially changed animal behavior and improved memory consolidation.     

A comparative study of isolation-induced ultrasonic vocalization in rodent pups.

The purpose of this study was to determine whether species differences in neonatal vocalizations of rodent pups could be observed. Ultrasonic vocalizations of pups of 5 rodent species, mouse (ICR), vole (Microtus arvalis), Syrian hamster, rat (Wistar-Imamichi), and Mongolian gerbil were recorded from 3 to 15 or 21 days of age. Recordings were made under conditions of separation from mothers and litter mates in a cooled chamber (approximately 10 degrees C). The major species differences observed were age specific and species specific frequencies. The Mongolian gerbil displayed a different frequency change with age. Namely, the day on which ultrasonic vocalizations ceased was delayed in Mongolian gerbil compared with the other rodents. The modal peak frequencies of ultrasound emitted from pups at 3 days of age were low (around 35 kHz) in the vole and the Syrian hamster, medium (around 45 kHz) in the rat and the Mongolian gerbil, and high (around 55 kHz) in the mouse.     

Stress and pain responses in rats lacking CCK1 receptors

CCK involvement in stress- and pain-responsiveness was examined by studying the behavior of infant (11-12-days-old) and adult OLETF rats that do not express CCK1 receptors. Infant odor- and texture-preferences were also assessed. We hypothesized that OLETF rats will show behavioral patterns similar to those previously observed after CCK1 antagonist administration. Rate of separation-induced ultrasonic vocalization was significantly greater in OLETF compared to controls, in two separate studies. Infant pups of the two strains did not differ in odor- and texture-preference tests. OLETF rats showed consistently longer hot-plate paw-lift (as infants, in two separate studies) and paw-lick (as adults) latencies. SUMMARY: OLETF pups vocalized in isolation more than controls and showed relative hypoalgesic responses, evident also in adulthood, in concordance with the pharmacological literature.     

Independent ingestion and microstructure of feeding patterns in infant rats lacking CCK-1 receptors

Otsuka Long-Evans Tokushima fatty (OLETF) rats are a strain of Long-Evans Tokushima Otsuka (LETO) rats that do not express CCK-1 receptors, developing in adulthood, hyperphagia, obesity, and non-insulin-dependent diabetes mellitus (NIDDM). We examined weight gain and meal patterns during a 30-min independent ingestion test on postnatal days 2-4 and again on days 9-11 in OLETF and LETO rat pups. OLETF pups were significantly heavier compared with their LETO controls at both ages, and they consumed significantly more of the sweet milk diet. The difference in intake can be attributed to a significant increase in meal size and duration. Number of clusters and bursts of licking within a meal were greater in OLETF rat pups, with no difference between strains in burst and cluster size. Interlick interval (ILI) was not significantly different between OLETF and LETO pups. This measure decreased on days 9-11 compared with days 2-4 in both strains. Latency to start feeding was significantly shorter on days 2-4 in OLETF vs. LETO pups, but this difference disappeared at the second test at the older age. Two- to four-day-old OLETF pups consumed a larger volume of milk during the first minute of feeding, and their initial lick rate and decay of lick rate were significantly larger compared with their LETO controls. Lack of CCK-1 receptors, or other OLETF-related abnormalities, therefore, resulted in a satiation deficit, leading to increased meal size, hyperphagia, and increased weight gain as early as 2-4 postnatal days.     

Impact of intra- and interstrain cross-fostering on mouse maternal care

The importance of maternal care in shaping an individual's phenotype in health and disease is becoming more and more apparent in both human and animal studies. However, in mouse studies using inbred strains or knockout mice to analyze the genetic influences on the development of normal and aberrant behavioral phenotypes, maternal behavior is very poorly characterized and often ignored. This study provides an extensive analysis of spontaneous maternal behavior of inbred mice in three conditions: (1) comparing two commonly used strains, (2) analyzing the impact of adopting pups from the same strain (intrastrain cross-fostering) and (3) analyzing the impact of adopting pups from a different strain (interstrain cross-fostering). For each condition, maternal behavior was analyzed continuously over 23-h periods on postnatal days 2, 4, 6 and 9. We report that (1) the maternal behavior of C57BL/6J and DBA/2J dams toward their biological offspring is highly similar, (2) intrastrain cross-fostering has minimal impact on maternal behavior of C57BL/6J and DBA/2J dams, (3) interstrain cross-fostering does not modify the strain differences in maternal care observed between AKR and C3H/He mothers and (4) the pup strain does influence the amount of maternal behavior shown by both mothers in interstrain cross-fostering. These latter findings demonstrate that both mother strain and pup strain are key determinants of maternal behavior.     

Comparison of the instrumental reinforcer devaluation effect in two strains of rats (Wistar and Lister)

In this experiment, the effect of the reinforcer devaluation upon instrumental performance was analysed in two strains of rats (Wistar and Lister): Food deprived rats were trained to press a lever for sucrose pellets in a single session. Immediately after the fulfilment of this session, half of the Wistar and Lister rats received an injection of lithium chloride (LiCl), while the remaining animals were injected with a sodium chloride (NaCl) solution. A subsequent extinction test showed that the subjects who had received immediate LiCl did not press the lever as often as those injected with NaCl. No differences in response suppression were found between the two strains of rats. These results also show that a single devaluation experience is sufficient for an impact on instrumental performance.