Social motivation and its hypothalamic neural basis in mice

Abstract

This thesis investigates the hypothalamic neural circuits controlling social motivation in mice using social operant tasks. Mice, like other animals, show various social behaviors. Controlling motivation for different types of social behaviors are critical for individual survival and reproductive success. However, studying motivations for social behaviors and related neural circuits was often hampered by the difficulty of temporally separating the different phases of a behavior, one with motivation growing and the other with action happening. One solution for this issue is the use of a social operant task, and in the two studies presented here, I fully leverage the social operant task to study the social motivation and its hypothalamic neural basis. In the first study, I investigate the hypothalamic circuits controlling male mice’s aggressive behaviors against subordinate males. In mice, ventromedial hypothalamus ventrolateral part (VMHvl) is known to be a critical hub for aggression, and our team first recorded the neural activity from that region while the recorded male mice engaged in aggressive behaviors, both in a naturalistic setting and in a social operant task, and we confirmed the similarity of neuronal activity pattern during aggression between the two settings. Then we recorded and also optogenetically stimulated the populational activity from its upstream inhibitory hypothalamic regions, and found that the recorded two upstream regions had distinct effects on aggressive motivation and action, as long as the individual neuron’s activity in the downstream VMHvl. Thus, I show how the hypothalamic neural circuits control the aggressive motivation and action in male mice. In the second study, I investigated how the social motivation to different social targets is expressed. Our team built another social operant task in which an animal can choose between male and female animals as the social reward, and manipulated the amount of one of the two social rewards. Our data suggests that male mice have separable, independent social motivations for male and female rewards which female mice do not seem to have. Together these studies increase our understanding of how social motivation is represented andcontrolled in the brain.