Appetite for Aggression: An Investigation of the Satiability of Aggression and the Role of the Shell of the Ventromedial Hypothalamus in Regulating Motivation for Aggression in Mice

Abstract

Satiety is commonly thought to explain fullness after eating. The possibility of satiety of the motivation for social behaviors, particularly aggression, was investigated in this experiment. The shell of the ventromedial hypothalamus (VMH) was proposed as a regulator of satiety of aggression because it had been previously implicated in regulating hunger satiety and aggression. Behavior in a modified nose-poke set-up, called the Flying Operant paradigm in which the resident mouse would poke for the reward of an aggressive encounter of a variable duration, was analyzed based on 3 characteristics: average poke rate, poke latencies, and poke clustering. This analysis revealed that poke rate would increase during short duration encounters and that poke clustering was dependent on which motivational category the experimental mouse was in: highly motivated or not highly-motivated. Neural activity in the shell was also recorded, by using fiber photometry, during the experimentation in the Flying Operant paradigm, when the interaction time was varied and when a 5-minute free interaction with a male or female mouse was performed before experimentation in the paradigm. The fiber photometry signal revealed a sharp dip in VMH shell activity time-locked to nose poke and a quick and sharp increase when the aggressive encounter was initiated that was sustained even after the aggressive encounter concluded. The data was interpreted to suggest that VMH shell activity encodes an internal state of motivation for aggression. Activity in the shell would increase as motivation for aggression was sated.