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Opioid and orexin hedonic hotspots in rat orbitofrontal cortex and insula

Significance Orbitofrontal cortex, insula, and related cortical regions are implicated in pleasure and motivation. However, determining whether cortical sites help cause hedonic reactions or instead merely encode signals generated elsewhere to facilitate other functions such as cognition remains unresolved. By mapping hedonic effects of individual drug microinjections, we generate detailed anatomical maps for potential gain-of-function affective sites in rat limbic cortex. Here, we show that opioid or orexin stimulations in orbitofrontal cortex and insula causally enhance hedonic “liking” reactions to sweetness and find a third cortical site where the same neurochemical stimulations reduce positive hedonic impact. For comparison, we also map overlapping but separable regions where stimulations increase the motivation to eat. Hedonic hotspots are brain sites where particular neurochemical stimulations causally amplify the hedonic impact of sensory rewards, such as “liking” for sweetness. Here, we report the mapping of two hedonic hotspots in cortex, where mu opioid or orexin stimulations enhance the hedonic impact of sucrose taste. One hedonic hotspot was found in anterior orbitofrontal cortex (OFC), and another was found in posterior insula. A suppressive hedonic coldspot was also found in the form of an intervening strip stretching from the posterior OFC through the anterior and middle insula, bracketed by the two cortical hotspots. Opioid/orexin stimulations in either cortical hotspot activated Fos throughout a distributed “hedonic circuit” involving cortical and subcortical structures. Conversely, cortical coldspot stimulation activated circuitry for “hedonic suppression.” Finally, food intake was increased by stimulations at several prefrontal cortical sites, indicating that the anatomical substrates in cortex for enhancing the motivation to eat are discriminable from those for hedonic impact.