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.

Dopamine is a neuromodulator the functions of which in the regulation of complex behaviors such as mood, motivation, and attention are well known. Dopamine appears in the brain early in the embryonic period when none of those behaviors is robust, raising the possibility that dopamine may influence brain development. The effects of dopamine on specific developmental processes such as neurogenesis are not fully characterized. The neostriatum is a dopamine-rich region of the developing and mature brain. If dopamine influenced neurogenesis, the effects would likely be pronounced in the neostriatum. Therefore, we examined whether dopamine influenced neostriatal neurogenesis by influencing the cell cycle of progenitor cells in the lateral ganglionic eminence (LGE), the neuroepithelial precursor of the neostriatum. We show that dopamine arrives in the LGE via the nigrostriatal pathway early in the embryonic period and that neostriatal neurogenesis progresses in a dopamine-rich milieu. Dopamine D1-like receptor activation reduces entry of progenitor cells from the G(1)- to S-phase of the cell cycle, whereas D2-like receptor activation produces the opposite effects by promoting G(1)- to S-phase entry. D1-like effects are prominent in the ventricular zone, and D2-like effects are prominent in the subventricular zone. The overall effects of dopamine on the cell cycle are D1-like effects, most likely because of the preponderance of D1-like binding sites in the embryonic neostriatum. These data reveal a novel developmental role for dopamine and underscore the relevance of dopaminergic signaling in brain development.

Mutual gaze is the most fundamental manifestation of social bonding in humans between mothers and infants and between sexual partners in monogamous species. Dog-to-owner gaze probably evolved as a form of social communication during domestication with humans, leading to the establishment of a human-dog bond that is similar to a mother-infant relationship. Urinary oxytocin increases in mothers following mutual gaze in both mothers and infants. A rise in urinary oxytocin occurs in dogs following mutual gaze, but it is unclear whether the increase also occurs in dog owners.This study investigated the effect of mutual gaze in both dogs and their owners on levels of urinary oxytocin. A primary aim was to determine whether there is a causal relationship between mutual gaze and the release of oxytocin. The authors tested the hypothesis that an oxytocin-mediated positive loop (as has been postulated between mother and infants) exists between humans and dogs that is mediated by gaze. To show that the hormone was a cause not just an effect of the interaction, oxytocin was administered intranasally to dogs, and the gazing interaction between dogs and their owners as well as unfamiliar humans was assessed.Gazing behavior increased urinary oxytocin in dogs as well as their owners. Owners and dogs sharing a long mutual gaze had higher levels of oxytocin in their urine than did owners and dogs with shorter eye contact. Although a prolonged gaze increased oxytocin in dogs, it did not increase levels of oxytoxin in hand-raised pet wolves, suggesting that mutual gaze is not used in wolves as a form of social communication with humans. Female dogs receiving intranasal oxytocin gazed longer at their owners than did those given saline. Moreover, oxytocin levels were increased by intranasal oxytocin in dog owners (who had not been given this hormone). These mutual effects were not seen between dogs and unfamiliar humans or between male dogs and their owners.These findings indicate that oxytocin is the cause, not the effect, of the interaction and support of the existence of an interspecies self-perpetuating oxytocin-mediated positive loop facilitated and modulated by mutual gazing. Gazing behavior may have supported the coevolution of human-dog bonding as a common mode of communicating social attachment.

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Neurochemical changes in the ventromedial hypothalamus (VMH) after a single intravenous injection of streptozotocin were examined, using in vivo brain microdialysis under free-moving conditions. Although streptozotocin-induced diabetes produced significant decreases in extracellular concentrations of noradrenaline (NA), serotonin (5-HT), and their metabolites in the VMH, the ratios of 3-methoxy-4-hydroxyphenylglycol/NA and 5-hydroxyindoleacetic acid (5-HIAA)/5-HT were increased. Experimental diabetes led to a pronounced increase in extracellular GABA, which correlated strongly with the decrease in dialysate levels of NA, and to a smaller extent with that of 5-HT. A modification of dopamine (DA) metabolism was induced in the VMH of diabetic rats, whereas there was no change in dialysate DA levels. Daily injections of insulin were able to restore their levels to normal in the areas tested in the microdialysis study. The equal increases in dialysate 5-HT and 5-HIAA and the better restoration of the 5-HIAA/5-HT ratio after insulin therapy indicate that serotonergic activity may depend on the levels of circulating insulin more than on noradrenergic activity. Circulating NA was reduced in streptozotocin-diabetic rats, suggesting that the diabetes-induced reduction in sympathetic activity is accompanied by decreases in NA, or 5-HT, or both, in the VMH.