Gillian D. Sales

Ultrasound and aggressive behaviour in rats and other small mammals.

Aggressive behaviour has been observed in rats, Rattus norvegicus, and fourteen other species of small mammals. Ultrasounds were detected during aggressive behaviour in at least seven of these species, and in rats two distinct types of signal were recorded. Short ultrasounds of 3 to 65 ms duration and at frequencies of about 50 kHz were produced in aggressive situations, while long pulses up to 3400 ms duration and at about 25 kHz appeared to be synchronous with the long exhalations of submissive rats. Aggressive behaviour was reduced in encounters where long pulses were emitted. The physical characteristics of the ultrasounds produced by the different species are described and the importance of these signals in the establishment and maintenance of social relationships in small mammals is discussed.

The effect of 22 kHz calls and artificial 38 kHz signals on activity in rats

Ultrasonic calls at 22 kHz are emitted by adult rats Rattus norvegicus when submissive, after and sometimes before copulation and in aversive situations, but the function of these calls, if any, is not known. This study examined the effect of 22 kHz calls on the behaviour of individuals. Rats were exposed singly for 5 min to a tape-recorded test signal; 22 kHz calls or artificial 38 kHz signals or tape noise. All rats were exposed to tape noise before and after the test signal. Both of the ultrasonic signals, and particularly the 22 kHz calls, decreased locomotor activity in rats during replay and for 5 min afterwards. Rats sniffed the loudspeaker less during the replay of 22 kHz calls than during the other test signals. These results complement others showing that constant frequency ultrasound from visual display units and oscilloscopes also depresses activity. In natural aggressive situations 22 kHz calls could allow a subordinate to escape and prevent the dominant wasting time in pursuit. In the laboratory exposure of rats to natural or artificial ultrasound could affect ongoing or subsequent behaviour and so be a confounding experimental variable.

Methylmercury speciation influences brain gene expression and behavior in gestationally-exposed mice pups.

The greatest source of human exposure to methylmercury (MeHg) is the diet, in particular the consumption of seafood. To investigate the importance of dietary MeHg speciation on neurotoxicity, balb/c mice dams were exposed to MeHgCys (the naturally-occurring salt) and MeHgCl (the laboratory salt), at concentrations up to 4.5 mg/kg, for 11 weeks (inclusive of 3 weeks gestational and 2 weeks post-partum exposure). Impacts of developmental exposure were assessed in their offspring by monitoring transcriptomic (brain gene expression via microarray and quantitative PCR), tissue mercury (Hg) accumulation, and neurobehavioral endpoints. There were no differences in tissue Hg accumulation between the two forms of MeHg presented, but differences in pup behavior and gene expression endpoints were noted. For example, MeHgCl, but not MeHgCys, impaired pup activity in an open field assessment. Similar impacts of MeHgCl were noted in adults. A total of 131 genes were differentially-regulated in pup brains following maternal exposure to MeHg, 50 of which were specific to MeHgCys and 35 specific to MeHgCl. Regulated genes were significantly enriched for several annotation categories including metal/zinc-binding and transcription regulation. In contrast few antioxidant genes were differentially regulated. This analysis provided insight into mechanisms by which MeHg may impair cellular processes in addition to behavioral impairments such as those associated with learning and memory. The results show differences between the toxic impacts of MeHg species, and also highlight the potential utility of an integrated approach incorporating gene expression with behavioral endpoints.

Ultrasonic calls of wild and wild-type rodents

Abstract Acoustic design of rodent ultrasonic signals and evolutionary selection pressures involved in this process are considered through a comparative approach to ultrasonic signal structure. Frequency characteristics of calls of wild and wild-type rodents are reviewed, together with factors that may affect call design. These include the mechanism of ultrasound production, phylogeny, ecology and habits of the signaler and recipient, the function of calls and the sensory abilities of recipients. There are no species-specific frequency bands or patterns, but there are some phylogenetic differences. The previously proposed whistle mechanism of ultrasound production can account for some differences in calling in different situations. There is some evidence for matching of call structure to habitat, function and receiver sensory abilities. Areas that deserve further study are highlighted.

ULTRASONIC VOCALIZATIONS OF INFANT SHORT-TAILED FIELD VOLES, MICROTUS AGRESTIS

Abstract Ultrasonic vocalizations of infant rodents are used in developmental studies and for investigating the effects of drugs or environmental pollutants. Few studies, however, have analyzed the frequency characteristics of these ultrasonic vocalizations. This study investigates the physical and vocal development of infants (1–14 days old) of the short-tailed field vole, Microtus agrestis, under 2 conditions of isolation: at 23°C immediately after being isolated from the nest or at 23°C after 10 min of isolation at 27°C. Seventy-three percent of the infants vocalized, and there was great variation among calling infants in the number of vocalizations emitted. More infants, especially males, called during the 2nd period of isolation than during the 1st, and latency to call increased with age in males. The ultrasonic vocalizations were comparable to those recorded from North American voles. Vocalizations were classified into 7 categories on the basis of characteristics of the fundamental frequency. Simple calls were emitted most commonly and became more frequent in older infants, whereas the proportion of calls with a down-sweep in frequency and audible clicks decreased with age. The emission of ultrasonic calls, therefore, appears to reflect changes both in physical development of the infants and in their external environment.

Aggression and vocalization behaviour of three sympatric vole species during conspecific and heterospecific same-sex encounters

The purpose of the present study was to compare the behaviour with vocalization of three sympatric species of voles during encounters within a species and during interactions between particular pairs of species. Bank voles, common voles and field voles were trapped in southeastern Poland and their behaviour and vocalization investigated using 10-min open field tests. Results showed clear differences in behaviour and vocalization between the species of voles. Bank vole interactions were more agonistic than those of common voles and of field voles as seen in the number of attacks, latency to the first attack and duration of attack. Females of the latter two species emitted significantly more ultrasounds than female bank voles. During male encounters common voles produced the highest numbers of ultrasounds. The ultrasonic calls emitted by female and male field voles occurred at a higher frequency (kHz) than those of both bank voles and common voles. The duration of these sounds was similar for all three species of voles. Voles in heterospecific encounters emitted very few ultrasounds. Our results have shown that ultrasounds are a part of bank vole, common vole and field vole behaviour and could play a significant role in vole communication.

Effects of perinatal octylphenol on ultrasound vocalization, behavior and reproductive physiology in rats

A rodent diet containing paraffin wax was designed to administer the environmental estrogen octylphenol (OP) to nonpregnant, pregnant and lactating rats. The estrogenic activity of OP via this diet was first confirmed in ovariectomized adult animals: 20 mg OP/kg/day increased the mitoses in the vaginal epithelium, and 60 mg OP/kg/day stimulated mitoses in the uterine luminal epithelium. The effects on a variety of reproductive and nonreproductive parameters were then investigated in the offspring of dams fed OP (100-250 mg/kg/day during gestation and lactation). A number of modest reproductive and morphological effects observed in the offspring including decreased body weights in adults of both sexes, disrupted vaginal cyclicity and decreases in seminiferous tubule diameter and testis, kidney, spleen and ovary weights. Behavioral effects included increased sexual arousal in males, increased sexual motivation in females towards a female teaser and increased motor activity by females. Ultrasonic vocalizations by pups at Postnatal Day (PND) 7 were reduced in number and duration in both sexes. There were no effects of perinatal OP on ano-genital distance, prepuce separation, aggressive behavior or adult ultrasound vocalization. These observations confirm that the dietary intake of estrogenic amounts of OP during pregnancy and lactation can have a wide variety of effects in the offspring.

Home bedding modifies ultrasonic vocalization of infant bank voles.

Bank vole,Clethrionomys glareolus, pups, similar to many other infant rodents, emit ultrasonic vocalizations when they are removed from the nest and cooled. Infants exposed to bedding from their home cage produced fewer and shorter calls than infants tested without bedding. Sound frequencies were significantly higher in infants exposed to home bedding than in other experimental groups. These results provide evidence that infant bank voles are able to identify the presence of home bedding, probably on the basis of odor. This appears to be the first report of shifts in frequency of pup ultrasonic calls in response to olfactory cues.

Male–female interactions and ultrasonic vocalization in three sympatric species of voles during conspecific and heterospecific encounters

Using ultrasonic vocalization, the present study examined the behaviour of three sympatrically living species of voles: common voles, field voles and bank voles during heterosexual encounters both within and between species. Voles were trapped in south-eastern Poland and their behaviour and vocalization investigated using 10-min open field tests. Conspecific heterosexual pairs of all three species of voles presented high social activity but the kind of behaviour was different. Bank vole male–female interactions were more agonistic than those of common voles and of field voles as seen in the number of aggressive approaches and latency to the first attack. Common voles and field voles emitted significantly more ultrasounds and spent longer time on the production of ultrasonic calls than bank voles. The duration of sounds was similar but the frequency of calls emitted by field voles was higher than those of common voles and bank voles. Voles in heterospecific encounters of male with female showed shorter duration of sniffing and emitted very few ultrasounds. The current work has shown that ultrasounds are part of male–female behaviour in common voles, field voles and bank voles and could play a significant role in vole communication.

Comparison of the oestrogenic effects of infant milk formulae, oestradiol and the phytoestrogen coumestrol delivered continuously in the drinking water to ovariectomised mice

The potential oestrogenic effects of infant milk formulae, coumestrol and oestradiol delivered in the drinking water were investigated in ovariectomised mice. None of the infant formulae tested (three soya, two cows milk) produced any uterotrophic or mitotic responses in the reproductive tract, although the soya milks displayed weak oestrogenic activity in vitro. Studies of the interactions between coumestrol and oestradiol were undertaken to investigate claims that phytoestrogens may act as oestrogen antagonists. The responses to coumestrol (100 g/ml drinking water) and 17-oestradiol (100 ng/ml) given separately were similar. Combined administration begun simultaneously produced only additive effects on uterine weight and cell proliferation in the vagina and uterus. While pretreatment with coumestrol for 24 h reduced the mitotic response of the uterus 48 h after placement of an oestradiol implant, the uterine weight increase was unaffected and the apparent reduction in mitoses reflected the natural fluctuations in the underlying cycle of cell proliferation. These studies indicate that coumestrol acts as a typical oestrogen and shows only additive effects with oestradiol. The results also indicate that infant soya milk formulae do not constitute a large enough source of oestrogenic compounds to invoke oestrogenic effects in the reproductive tract of mature mice.