Research into the neural circuits that underlie the amplification of motivation has been focused on the traditional ;;reward pathway.” Recent work, however, has implicated another striatal level structure, the central nucleus of the amygdala, in the amplification of motivation. Here, I extend these findings and demonstrate mu opioid receptor activation of the central nucleus of the amygdala enhances the motivational power of cues associated with reward. Recent findings in from human imaging studies have hinted that another striatal level structure, the neostriatum, may also participate in the amplification of motivation. Here, I demonstrate that mu opioid receptor activation in neostriatum enhances motivation for learned cues and primary rewards. Mu opioid receptor activation in dorsolateral neostriatum potently enhanced the attractiveness of cues in a manner similar to amygdala activation and did so in a manner not consistent with a habit hypothesis. However, consumption of primary rewards was not enhanced.Here, I demonstrated for the first time that enkephalin in dorsomedial neostriatum surges when rats consume a sweet, fatty food. Further, this consumption can be stimulated by microinjection of a mu opioid receptor activating drug. Although, dorsomedial neostriatal activation participated in motivation for primary rewards, activation did not have an effect on motivation for learned cues. Finally, in ventrolateral neostriatum, mu opioid receptor activation enhanced the attractiveness of a contiguous cue and motivation to consume primary rewards. These findings extend the neural substrates of motivation beyond traditional reward structures and have implications for the description and treatment of disorders of intense motivation such as drug addiction and binge eating.
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