Oxytocin and mutual communication in mother-infant bonding

Mother-infant bonding is universal to all mammalian species. In this review, we describe the manner in which reciprocal communication between the mother and infant leads to mother-infant bonding in rodents. In rats and mice, mother-infant bond formation is reinforced by various social stimuli, such as tactile stimuli and ultrasonic vocalizations (USVs) from the pups to the mother, and feeding and tactile stimulation from the mother to the pups. Some evidence suggests that mother and infant can develop a cross-modal sensory recognition of their counterpart during this bonding process. Neurochemically, oxytocin in the neural system plays a pivotal role in each side of the mother-infant bonding process, although the mechanisms underlying bond formation in the brains of infants has not yet been clarified. Impairment of mother-infant bonding, that is, deprivation of social stimuli from the mother, strongly influences offspring sociality, including maternal behavior toward their own offspring in their adulthood, implying a “non-genomic transmission of maternal environment,” even in rodents. The comparative understanding of cognitive functions between mother and infants, and the biological mechanisms involved in mother-infant bonding may help us understand psychiatric disorders associated with mother-infant relationships

Comparison of owner-reported behavioral characteristics among genetically clustered breeds of dog (Canis familiaris).

During the domestication process, dogs were selected for their suitability for multiple purposes, resulting in a variety of behavioral characteristics. In particular, the ancient group of breeds that is genetically closer to wolves may show different behavioral characteristics when compared to other breed groups. Here, we used questionnaire evaluations of dog behavior to investigate whether behavioral characteristics of dogs were different among genetically clustered breed groups. A standardized questionnaire, the Canine Behavioral Assessment and Research Questionnaire (C-BARQ), was used, and breed group differences of privately-owned dogs from Japan (n = 2,951) and the United States (n = 10,389) were analyzed. Results indicated that dogs in the ancient and spitz breed group showed low attachment and attention-seeking behavior. This characteristic distinguished the ancient group from any other breed groups with presumed modern European origins, and may therefore, be an ancestral trait

Intranasal administration of oxytocin promotes social play in domestic dogs

In a recent paper, we examined whether oxytocin in the domestic dog modulates the maintenance of close social bonds in non-reproductive contexts. We found that exogenous oxytocin promotes positive social behaviors not only toward conspecifics, but also toward human partners. Here we examined in further detail the effect that oxytocin manipulation has on social play. When sprayed with oxytocin, subjects initiated play sessions more often and played for longer periods of time than when sprayed with saline. Furthermore, after oxytocin nasal intake dogs displayed play signals more often than after saline administration, suggesting that oxytocin enhances dogs' play motivation. To our knowledge, this study provides the first evidence that oxytocin promotes social play in the domestic dog. We use these results to hypothesize on the potential therapeutic use of oxytocin for promoting social behaviors and treating social deficits in the domestic dog

The Frequency Variations of the Oxytocin Receptor Gene Polymorphisms among Dog Breeds

The domestic dog (Canis familiaris) has been diverged from wolves 15,000–100,000 years ago and certain genetic changes may have enabled them to adapt to the human social niche. In this study, we investigated the polymorphisms of the oxytocin receptor gene in dogs and wolves in order to investigate the possibility of the genetic change in the oxytocin system during dog domestication processes. Genotypes of the oxytocin receptor gene polymorphisms were determined in dogs and wolves. The single nucleotide polymorphisms (SNP; rs22927829, rs8679682, rs22896457) were observed in the sampled dogs. On the other hand, for the SNPs rs22927823 and rs22927826, only homozygous GG genotypes were observed (n=25). The frequencies of the SNPs (rs8679682 and rs22896457) were significantly different among wolves and dogs, and also among dog breed groups (p<0.05, chi-square test). The frequency profile of these SNPs among dog breed groups supports the hypothesis that there were selections on the oxytocin receptor gene during the dog domestication processes

A Role for Strain Differences in Waveforms of Ultrasonic Vocalizations during Male–Female Interaction

Male mice emit ultrasonic vocalizations (USVs) towards females during male–female interaction. It has been reported that USVs of adult male mice have the capability of attracting females. Although the waveform pattern of USVs is affected by genetic background, differences among strains with respect to USV and the effects of these differences on courtship behavior have not been analyzed fully. We analyzed USV patterns, as well as actual social behavior during USV recording, in 13 inbred mouse strains, which included laboratory and wild-derived strains. Significant effects of strain were observed for the frequency of USV emission, duration, and frequency of the waveform category. Principal component (PC) analysis showed that PC1 was related to frequency and duration, and PC2–4 were related to each waveform. In the comparison of USV patterns and behaviors among strains, wild-derived KJR mice displayed the highest scores for PC2–4, and female mice paired with KJR males did not emit rejection-related click sounds. It is assumed that the waveforms emitted by KJR males have a positive effect in male–female interaction. Therefore, we extracted waveforms in PC2–4 from the USV recordings of KJR mice to produce a sound file, "HIGH2-4". As a negative control, another sound file ("LOW2-4") was created by extracting waveforms in PC2-4 from strains with low scores for these components. In the playback experiments using these sound files, female mice were attracted to the speaker that played HIGH2-4 but not the speaker that played LOW2-4. These results highlight the role of strain differences in the waveforms of male USVs during male–female interaction. The results indicated that female mice use male USVs as information when selecting a suitable mate

The naked truth:a comprehensive clarification and classification of current 'myths' in naked mole-rat biology

The naked mole-rat (Heterocephalus glaber) has fascinated zoologists for at least half a century. It has also generated considerable biomedical interest not only because of its extraordinary longevity, but also because of unusual protective features (e.g. its tolerance of variable oxygen availability), which may be pertinent to several human disease states, including ischemia/reperfusion injury and neurodegeneration. A recent article entitled 'Surprisingly long survival of premature conclusions about naked mole-rat biology' described 28 'myths' which, those authors claimed, are a 'perpetuation of beautiful, but falsified, hypotheses' and impede our understanding of this enigmatic mammal. Here, we re-examine each of these 'myths' based on evidence published in the scientific literature. Following Braude et al., we argue that these 'myths' fall into four main categories: (i) 'myths' that would be better described as oversimplifications, some of which persist solely in the popular press; (ii) 'myths' that are based on incomplete understanding, where more evidence is clearly needed; (iii) 'myths' where the accumulation of evidence over the years has led to a revision in interpretation, but where there is no significant disagreement among scientists currently working in the field; (iv) 'myths' where there is a genuine difference in opinion among active researchers, based on alternative interpretations of the available evidence. The term 'myth' is particularly inappropriate when applied to competing, evidence-based hypotheses, which form part of the normal evolution of scientific knowledge. Here, we provide a comprehensive critical review of naked mole-rat biology and attempt to clarify some of these misconceptions