Identification of genes associated with human-canine communication in canine evolution.

The dog (Canis familiaris) was the first domesticated animal and hundreds of breeds exist today. During domestication, dogs experienced strong selection for temperament, behaviour, and cognitive ability. However, the genetic basis of these abilities is not well-understood. We focused on ancient dog breeds to investigate breed-related differences in social cognitive abilities. In a problem-solving task, ancient breeds showed a lower tendency to look back at humans than other European breeds. In a two-way object choice task, they showed no differences in correct response rate or ability to read human communicative gestures. We examined gene polymorphisms in oxytocin, oxytocin receptor, melanocortin 2 receptor, and a Williams-Beuren syndrome-related gene (WBSCR17), as candidate genes of dog domestication. The single-nucleotide polymorphisms on melanocortin 2 receptor were related to both tasks, while other polymorphisms were associated with the unsolvable task. This indicates that glucocorticoid functions are involved in the cognitive skills acquired during dog domestication.

Pup exposure facilitates retrieving behavior via the oxytocin neural system in female mice.

Parental behavior in mammals is innate, but it is also facilitated by social experience, specifically social interactions between the parent and infant. Social interactions with infants also induce the alloparental behavior of virgin animals. Oxytocin (OT) plays an important role in mediating alloparental behavior. Although parental behavior is modulated by the medial preoptic area (MPOA) and adjacent regions, it is unclear how OT acts in these regions as a control mechanism of alloparental behavior promoted by adult-pup interaction. The aim of this study was to investigate the role of OT for facilitating effects of adult-pup interactions on alloparental behavior via neural activity of preoptic area (POA), including MPOA and adjacent area. For this purpose, we conducted behavioral tests and examined the neural activity of the OT system in POA. Virgin female mice that were repeatedly exposed to pups showed shorter retrieving latencies and higher number of c-Fos expressing neurons in POA, particular in lateral preoptic area (LPO) compared to control animals that were exposed to pups only one time. In addition, repeated pup exposure increased the proportion of OT neurons and OTR neurons expressing c-Fos in POA. The concentration of OT also significantly increased in the POA. Finally, infusion of an OT antagonist into the POA area blocked the facilitating effects of repeated pup exposure on retrieving behavior. These results demonstrated that the facilitating effects of repeated pup exposure on alloparental behavior occurred via an organizational role of the OT system.

Sex differences in spatiotemporal expression of AR, ERα, and ERß mRNA in the perinatal mouse brain.

It has been shown that every masculinized function might be organized by a particular contribution of androgens vs. estrogens in a critical time window. Here, we aimed to investigate the sex differences in brain testosterone levels and in the spatiotemporal dynamics of steroid receptor mRNA expression in perinatal mice, by using enzyme immunoassay and real-time PCR, respectively. We found that testosterone levels in the forebrain transiently increased around birth in male mice. During the perinatal period, levels of androgen receptor mRNA in the hypothalamus (hypo) and prefrontal cortex (PFC) were higher in male mice than in female mice. Estrogen receptor α (ERα) mRNA levels in the hypo and hippocampus were higher in male mice than in female mice before birth. In contrast, ERß mRNA expression in the PFC was higher in female mice immediately after birth. These spatiotemporal sex differences in steroid receptor expression might contribute to organizing sex differences of not only reproductive function, but also anxiety, stress responses, and cognition in mice.

Testosterone inhibits facilitating effects of parenting experience on parental behavior and the oxytocin neural system in mice.

Parental behavior in mammals is facilitated by sensory experiences from infant, and by endocrine hormones. However, the interactions between these factors in the parental behavior of nonreproductive adults are not understood. We examined the interactive effects of gonadal hormones and the experience of repeated pup exposure on parental behavior in sexually naive mice. We also compared oxytocin (OT) expression levels in the paraventricular nucleus of the hypothalamus to behavioral outcomes. Clear sex differences were observed in retrieving tests; initial retrieving latency was shorter in females than in males, and 5-time pup exposure shortened retrieving latency in females only. Gonadectomy influenced neither initial retrieving latency nor pup sensitization in females. In contrast, gonadectomy shortened initial retrieving latency and caused pup sensitization in males. Estrogen implants given simultaneously with gonadectomy further shortened the initial retrieving latency in males, but pup sensitization was not affected and occurred in both sexes. In contrast, simultaneous testosterone implants impaired pup sensitization in both sexes. Similar to the results for responsiveness to pups, the number of OT neurons was increased by gonadectomy in males only. In comparison to gonadectomy only, OT neurons were decreased by simultaneous testosterone implants, but were not influenced by estrogen in either sex. Considering the parallel inhibitory effects of testosterone on both pup sensitization and number of OT neurons, we postulate that sex differences in parental responsiveness facilitated by repeated pup exposure were caused by an inhibitory effect of testosterone via the OT neural system in mice.

Organizational effects of estrogen on male-type vulnerability to early weaning.

We previously reported that early-weaned (postnatal day 14) male ICR mice, compared to normally weaned animals, exhibited a persistent increase in anxiety-related behavior in the elevated plus maze test. In this study, we examined whether steroid hormone manipulations on postnatal day 0 and at the ages of 2 or 3 weeks affected male-type vulnerability to early weaning. Neither castration nor ovariectomy at the age of 3 weeks affected male-type vulnerability. However, in males, castration at the age of 2 weeks attenuated the increased anxiety levels induced by early weaning, and the implantation of testosterone or estradiol, but not of dihydrotestosterone, restored the effects of early weaning. In contrast, in females, neonatal treatment with testosterone propionate together with testosterone at the age of 2 weeks, which reversed sexual behavior to the male type, did not affect anxiety levels in response to early weaning. When pregnant females were repeatedly treated with testosterone propionate on embryonic days 14, 17, and 19, in addition to testosterone treatment at the age of 2 weeks, the anxiety levels in female were increased by early weaning. Furthermore, the prenatal treatment of estradiol benzoate, but not dihydrotestosterone, induced enhanced anxiety levels by early weaning in females. These results suggest that neural systems are masculinized by estrogen from the embryonic phase to the early postnatal period and are responsible for the high levels of anxiety elicited by early weaning.

Pup odor and ultrasonic vocalizations synergistically stimulate maternal attention in mice.

Pup ultrasonic vocalizations (USVs), which are emitted by hypothermic pups, and pup odor are thought to be triggers of maternal behavior in mice. We investigated whether pup odor stimulated maternal responses to pup USVs in mother C57BL/6 mice. Two-choice tests were conducted by introducing mothers into a test cage in which a tube was attached on each long wall, and the duration spent in each tube was compared. Pup USVs were reproduced by an ultrasonic speaker at the tube end. In some cases, cotton with pup odor was also presented at the end of the tube. Compared to no stimuli, mothers did not specifically approach the sole presentation of either reproduced pup USVs or pup odor. However, compared to the sole presentation of pup odor, the simultaneous presentation of pup USVs and odor induced a specific approach response. These results suggested that pup USVs and odor synergistically stimulated maternal behavior. In addition, it was confirmed that mothers approached hypothermic pups emitting pup USVs for longer than anesthetized silent pups. To investigate the underlying neural mechanisms, we observed neural responses to various stimuli with the immunohistochemistry of c-fos expression. In the bed nucleus of the stria terminalis, the medial preoptic area, the central nucleus of the amygdala, and the basolateral amygdala, the numbers of c-fos-positive cells were significantly increased following the simultaneous presentation of pup USVs and odor compared to the presentation of each alone, suggesting that these nuclei were involved in multimodal processing related to maternal behavior.