Kazutaka Mogi

Neurokinin B and Dynorphin A in Kisspeptin Neurons of the Arcuate Nucleus Participate in Generation of Periodic Oscillation of Neural Activity Driving Pulsatile Gonadotropin-Releasing Hormone Secretion in the Goat

Gonadotropin-releasing hormone (GnRH) neurons in the basal forebrain are the final common pathway through which the brain regulates reproduction. GnRH secretion occurs in a pulsatile manner, and indirect evidence suggests the kisspeptin neurons in the arcuate nucleus (ARC) serve as the central pacemaker that drives pulsatile GnRH secretion. The purpose of this study was to investigate the possible coexpression of kisspeptin, neurokinin B (NKB), and dynorphin A (Dyn) in neurons of the ARC of the goat and evaluate their potential roles in generating GnRH pulses. Using double and triple labeling, we confirmed that all three neuropeptides are coexpressed in the same population of neurons. Using electrophysiological techniques to record multiple-unit activity (MUA) in the medial basal hypothalamus, we found that bursts of MUA occurred at regular intervals in ovariectomized animals and that these repetitive bursts (volleys) were invariably associated with discrete pulses of luteinizing hormone (LH) (and by inference GnRH). Moreover, the frequency of MUA volleys was reduced by gonadal steroids, suggesting that the volleys reflect the rhythmic discharge of steroid-sensitive neurons that regulate GnRH secretion. Finally, we observed that central administration of Dyn-inhibit MUA volleys and pulsatile LH secretion, whereas NKB induced MUA volleys. These observations are consistent with the hypothesis that kisspeptin neurons in the ARC drive pulsatile GnRH and LH secretion, and suggest that NKB and Dyn expressed in those neurons are involved in the process of generating the rhythmic discharge of kisspeptin.

Ghrelin in domestic animals: distribution in stomach and its possible role

Ghrelin, a novel growth-hormone-releasing acylated peptide, was recently isolated from rat and human stomachs. In rat, peripheral or central administration of ghrelin stimulates the secretion of growth hormone (GH) from the pituitary gland. Recent work suggests that ghrelin plays an important role in energy homeostasis, body weight, and food intake. We examined the distribution of cells immunoreactive to ghrelin in the stomachs of domestic animals and rats, using a polyclonal antibody for the N-terminal fragment of rat ghrelin [1-11]. We measured the plasma levels of ghrelin before and after feeding in cows, and GH levels after central administration of ghrelin in Shiba goats, to elucidate the possible role of ghrelin. Immunostained cells were widely distributed from the neck to the base of the oxyntic gland in all animals. The plasma ghrelin concentration in cows decreased significantly 1 h after feeding, and then recovered to pre-feeding levels. Administration of ghrelin into the third ventricle in Shiba goats dramatically increased the plasma GH concentration dose-dependently. These results suggest that ghrelin plays an important role in GH secretion and feeding regulation in domestic animals.

Oxytocin-gaze positive loop and the coevolution of human-dog bonds

Gaze into my eyes Humans bond emotionally as we gaze into each others eyes—a process mediated by the hormone oxytocin. Nagasawa et al. show that such gaze-mediated bonding also exists between us and our closest animal companions, dogs (see the Perspective by MacLean and Hare). They found that mutual gazing increased oxytocin levels, and sniffing oxytocin increased gazing in dogs, an effect that transferred to their owners. Wolves, who rarely engage in eye contact with their human handlers, seem resistant to this effect. Science, this issue p. 333; see also p. 280 The human-dog bond is facilitated by the interaction of oxytocin feedback loops that emerged over the course of domestication. [Also see Perspective by MacLean and Hare] Human-like modes of communication, including mutual gaze, in dogs may have been acquired during domestication with humans. We show that gazing behavior from dogs, but not wolves, increased urinary oxytocin concentrations in owners, which consequently facilitated owners’ affiliation and increased oxytocin concentration in dogs. Further, nasally administered oxytocin increased gazing behavior in dogs, which in turn increased urinary oxytocin concentrations in owners. These findings support the existence of an interspecies oxytocin-mediated positive loop facilitated and modulated by gazing, which may have supported the coevolution of human-dog bonding by engaging common modes of communicating social attachment.

Gonadotrophin‐Releasing Hormone Pulse Generator Activity in the Hypothalamus of the Goat

Pulsatile release of gonadotrophin‐releasing hormone (GnRH) is indispensable to maintain normal gonadotrophin secretion. The pulsatile secretion of GnRH is associated with synchronised electrical activity in the mediobasal hypothalamus (i.e. multiple unit activity; MUA), which is considered to reflect the rhythmic oscillations in the activity of the neuronal network that drives pulsatile GnRH secretion. However, the cellular source of this ultradian rhythm in GnRH activity is unknown. Direct input from kisspeptin neurones in the arcuate nucleus (ARC) to GnRH cell bodies in the medial preoptic area or their terminals in the median eminence could be the intrinsic source for driving the GnRH pulse generator. To determine whether kisspeptin signalling could be responsible for producing pulsatile GnRH secretion, we studied goats, measured plasma levels of luteinising hormone (LH) and recorded MUA in the posterior ARC, where the majority of kisspeptin neuronal cell bodies are located. Rhythmic volleys of MUA were found to be accompanied by LH pulses with regular intervals in the ARC, where kisspeptin neuronal cell bodies were found. Exogenous administration of kisspeptin stimulated a sustained increase in LH secretion, without influencing MUA, suggesting that the GnRH pulse generator, as reflected by MUA, originated from outside of the network of GnRH neurones, and could plausibly reflect the pacemaker activity of kisspeptin neurones, whose projections reach the median eminence where GnRH fibres project. These observations suggest that the kisspeptin neurones in the ARC may be the intrinsic source of the GnRH pulse generator.

Dogs can discriminate human smiling faces from blank expressions

Dogs have a unique ability to understand visual cues from humans. We investigated whether dogs can discriminate between human facial expressions. Photographs of human faces were used to test nine pet dogs in two-choice discrimination tasks. The training phases involved each dog learning to discriminate between a set of photographs of their owner’s smiling and blank face. Of the nine dogs, five fulfilled these criteria and were selected for test sessions. In the test phase, 10 sets of photographs of the owner’s smiling and blank face, which had previously not been seen by the dog, were presented. The dogs selected the owner’s smiling face significantly more often than expected by chance. In subsequent tests, 10 sets of smiling and blank face photographs of 20 persons unfamiliar to the dogs were presented (10 males and 10 females). There was no statistical difference between the accuracy in the case of the owners and that in the case of unfamiliar persons with the same gender as the owner. However, the accuracy was significantly lower in the case of unfamiliar persons of the opposite gender to that of the owner, than with the owners themselves. These results suggest that dogs can learn to discriminate human smiling faces from blank faces by looking at photographs. Although it remains unclear whether dogs have human-like systems for visual processing of human facial expressions, the ability to learn to discriminate human facial expressions may have helped dogs adapt to human society.

Oxytocin promotes social bonding in dogs

Significance Although the positive impact of social bonds on individual’s fitness has recently been demonstrated, the mechanisms underlying the motivation to form long-term associations remain largely unknown. Current evidence shows that oxytocin modulates social behavior but evidence of its effects in bond maintenance remains scant, especially in nonreproductive contexts. We provide evidence that in the domestic dog oxytocin enhances social motivation to approach and affiliate with conspecifics and human partners, which constitutes the basis for the formation of any stable social bond. Furthermore, endogenous oxytocin levels increased after dogs engaged in affiliation with their dog partners, indicating a stimulation of the oxytocin system during social interactions. Our findings highlight the important role that oxytocin has in the expression of sociality in mammals. Recent evidence suggests that enduring social bonds have fitness benefits. However, very little is known about the neural circuitry and neurochemistry underlying the formation and maintenance of stable social bonds outside reproductive contexts. Oxytocin (OT), a neuropeptide synthetized by the hypothalamus in mammals, regulates many complex forms of social behavior and cognition in both human and nonhuman animals. Animal research, however, has concentrated on monogamous mammals, and it remains unknown whether OT also modulates social bonds in nonreproductive contexts. In this study we provide behavioral evidence that exogenous OT promotes positive social behaviors in the domestic dog toward not only conspecifics but also human partners. Specifically, when sprayed with OT, dogs showed higher social orientation and affiliation toward their owners and higher affiliation and approach behaviors toward dog partners than when sprayed with placebo. Additionally, the exchange of socio-positive behaviors with dog partners triggered the release of endogenous OT, highlighting the involvement of OT in the development of social relationships in the domestic dog. These data provide new insight into the mechanisms that facilitate the maintenance of close social bonds beyond immediate reproductive interest or genetic ties and complement a growing body of evidence that identifies OT as one of the neurochemical foundations of sociality in mammalian species.

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.

Urinary oxytocin as a noninvasive biomarker of positive emotion in dogs

A reliable assay based on physiological parameters that does not require subjective input from the owners is required to assess positive emotions in dogs. In addition, when viewed from an animal welfare perspective, physiological parameters should be collected in a noninvasive manner. Oxytocin (OT) is a biomarker that may be associated with a calm, relaxed state, and positive emotion. We measured the time-lapse in the concentration of plasma OT relative to urinary OT using a radioimmunoassay with sufficient sensitivity and low variability, and examined the relationship between OT and cortisol. Six dogs were injected with exogenous OT intravenously to increase the blood OT concentration. As a result, the highest concentration of urinary OT occurred 1h after the injection, although there was little change in urinary cortisol. Moreover, to evaluate the influence of stimuli on urinary OT and cortisol, we provided three stimuli of eating food, exercising and stroking, all of which were assumed to inspire a positive emotion in dogs, and significantly increased urinary OT concentrations. Our findings indicate that urinary OT might be useful as a noninvasive and objective biomarker of positive emotion in dogs.

Developmental consequences and biological significance of mother–infant bonding

Mother-infant bonding is universal to all mammalian species. Here, we review how mutual communication between the mother and infant leads to mother-infant bonding in non-primate species. In rodents, mother-infant bond formation is reinforced by various pup stimuli, such as tactile stimuli and ultrasonic vocalizations. Evidence suggests that the oxytocin neural system plays a pivotal role in each aspect of the mother-infant bonding, although the mechanisms underlying bond formation in the brain of infants has not yet been clarified. Impairment of mother-infant bonding strongly influences offspring sociality. We describe the negative effects of mother-infant bonding deprivation on the neurobehavioral development in rodent offspring, even if weaning occurs in the later lactating period. We also discuss similar effects observed in pigs and dogs, which are usually weaned earlier than under natural conditions. The comparative understanding of the developmental consequences of mother-infant bonding and the underlying mechanisms provide insight into the biological significance of this bonding in mammals, and may help us to understand psychiatric disorders related to child abuse or childhood neglect.

Morphological Evidence for Direct Interaction between Kisspeptin and Gonadotropin-Releasing Hormone Neurons at the Median Eminence of the Male Goat: An Immunoelectron Microscopic Study

Kisspeptin has been thought to play pivotal roles in the control of both pulse and surge modes of gonadotropin-releasing hormone (GnRH) secretion. To clarify loci of kisspeptin action on GnRH neurons, the present study examined the morphology of the kisspeptin system and the associations between kisspeptin and GnRH systems in gonadally intact and castrated male goats. Kisspeptin-immunoreactive (ir) and Kiss1-positive neurons were found in the medial preoptic area of intact but not castrated goats. Kisspeptin-ir cell bodies and fibers in the arcuate nucleus (ARC) and median eminence (ME) were fewer in intact male goats compared with castrated animals. Apposition of kisspeptin-ir fibers on GnRH-ir cell bodies was very rare in both intact and castrated goats, whereas the intimate association of kisspeptin-ir fibers with GnRH-ir nerve terminals was observed in the ME of castrated animals. Neurokinin B immunoreactivity colocalized not only in kisspeptin-ir cell bodies in the ARC but also in kisspeptin-ir fibers in the ME, suggesting that a majority of kisspeptin-ir fibers projecting to the ME originates from the ARC. A dual immunoelectron microscopic examination revealed that nerve terminals containing kisspeptin-ir vesicles made direct contact with GnRH-ir nerve terminals at the ME of castrated goats. There was no evidence for the existence of the typical synaptic structure between kisspeptin- and GnRH-ir fibers. The present results suggest that the ARC kisspeptin neurons act on GnRH neurons at the ME to control (possibly the pulse mode of) GnRH secretion in males.