Examples of Fos plumes surrounding microinjections. A Fos plume surrounding a DNQX microinjection site in nucleus accumbens (left) is shown compared with vehicle control microinjection. Colored plume map shows average elevations of Fos caused by DNQX microinjection, relative to vehicle. The 2.5-mm rostrocaudal extent of the medial shell can contain up to eight adjacent plume centers or two to three halos without overlapping, perhaps accounting for keyboard effects.

Fos plume maps of appetitive versus fearful behaviors generated by DNQX microinjections. Sagittal maps of ingestive behaviors (eating and drinking, left) and fearful behaviors (defensive treading, right) elicited at each microinjection site are shown. Bars show behaviors at anatomical levels (keyboard effects are visible as incremental step-wise changes across successive bars). (a) Appetitive-ingestive behavior was primarily elicited from the rostral medial shell. The dark and quiet home environment that the rats preferred expanded the positive appetitive-generation zone in a caudal direction. The stressful environment containing loud Iggy Pop music and bright lights (which rats avoided when able) expanded the fearful generation zone in a rostral direction and promoted valence mixtures. (b) Defensive-treading behavior was produced by DNQX microinjections in the caudal half of medial shell. The preferred home environment shrunk the defensive-treading zone to the caudal tip. Conversely, the stressful environment expanded the defensive treading zone in the rostral direction. These procedures were approved by the Committee on Use and Care of Animals at the University of Michigan.

Summary map of glutamatergic valence generation in the medial shell. Purely appetitive sites are shown in green (where DNQX elicited only eating or drinking behaviors). Purely fearful sites are shown in red (where DNQX elicited only defensive-treading behavior). Ambivalent or mixed valence sites are shown in yellow (where DNQX microinjection elicited both appetitive-eating behavior and defensive-treading behavior from the same rat). The home environment expanded the purely appetitive zone compared with the standard environment, whereas the stressful environment expanded the fearful and ambivalent zones.