Mesocorticolimbic Generation of Motivation

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PROJECT SUMMARY Aberrant motivation is an important feature of a variety of human mental disorders. Excessive appetitive motivation is implicated in drug addiction and obesity, leading to sometimes compulsive pursuit and overconsumption of drugs or food (1, 2). The nucleus accumbens (NAc), embedded within mesocorticolimbic circuits, plays an important role in excessive incentive motivation. The medial shell region of the NAc is particularly associated with the generation of appetitively motivated behaviors. Beyond the well known role in incentive motivation, mesocorticolimbic systems may also mediate some fearful states. This proposal focuses on the role of local glutamate disruptions in rostral NAc shell in producing positively-motivated behaviors like intense feeding, and the role of glutamate disruptions in caudal zones of NAc shell in producing negatively- motivated behaviors. Mesolimbic dopamine (DA) systems interact with corticolimbic glutamate disruptions for appetitive and fearful motivational salience (5): Aim 1 will identify whether D1 or D2 receptor subtypes are necessary for generation of either positively-motivated behaviors (feeding) in rostral shell or negatively- motivated behaviors (defensive treading) following AMPA receptor blockade. It is also important to understand the larger corticolimbic circuit in which NAc shell is embedded, and particularly to understand how corticolimbic top-down signals regulate generation of appetitive and defensive motivation by NAc. Aim 2 will identify which region of PFC is primarily responsible for modulation of subcortical unconditioned positive and negative motivation: medial OFC, infralimbic or prelimbic. Finally, it is important to understand how psychological context modulates NAc generation of fear and feeding by recruiting corticolimbic circuits. This phenomenon may be relevant to contextual influences on human pathological motivations, as well as to therapeutic interventions. Aim 3 will identify the particular PFC inputs to NAc that mediate environmental modulation of NAc-generation of motivation.