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Abstract
Research on oxytocin (OT) has yielded two seemingly unrelated sets of discoveries:
OT has prosocial effects, and it elicits termination of feeding, especially of food
rich in carbohydrates. Here we investigated whether OT's involvement in food intake
is affected by the social context in mice, with particular focus on the role of dominance.
We used two approaches: injections and gene expression analysis. We housed two males
per cage and determined a dominant one. Then we injected a blood-brain barrier penetrant
OT receptor antagonist L-368,899 in either dominant or subordinate animals and gave
them 10-min access to a sucrose solution in the apparatus in which social exposure
was modified and it ranged from none to unrestricted contact. L-368,899 increased
the amount of consumed sugar in dominant mice regardless of whether these animals
had access to sucrose in the non-social or social contexts (olfactory-derived or partial
social exposure). The antagonist also increased the proportion of time that dominant
mice spent drinking the sweet solution in the paradigm in which both mice had to share
a single source of sucrose. L-368,899-treated subordinate mice consumed more sucrose
solution than saline controls only when the environment in which sugar was presented
was devoid of social cues related to the dominant animal. Finally, we investigated
whether hypothalamic OT gene expression differs between dominant and subordinate mice
consuming sugar and found OT mRNA levels to be higher in dominant mice. We conclude
that social context and dominance affect OT's effect on appetite for sucrose.