Positive and negative motivation in nucleus accumbens shell: bivalent rostrocaudal gradients for GABA-elicited eating, taste "liking"/"disliking" reactions, place preference/avoidance, and fear.

Microinjection of the GABA(A) agonist muscimol in the rostral medial accumbens shell in rats elicits appetitive eating behavior, but in the caudal shell instead elicits fearful defensive treading behavior. To further test the hypothesis that rostral shell muscimol microinjections produce positive motivational states, whereas caudal shell muscimol produces negative states, we measured behavioral place preference/avoidance conditioning and affective hedonic and aversive orofacial expressions of taste-elicited "liking" and "disliking" (gapes, etc.) in addition to fear and feeding behaviors. Farthest rostral muscimol microinjections (75 ng) caused increased eating behavior and also caused positive conditioned place preferences and increased positive hedonic reactions to the taste of sucrose. By contrast, caudal shell microinjections elicited negative defensive treading and caused robust negative conditioned place avoidance and negative aversive reactions to sucrose or quinine tastes. Intermediate rostral microinjections elicited effects of mixed positive/negative valence (positive appetitive eating behavior but negative place avoidance and negative taste reactions at mid-rostral sites, and sometimes positive eating simultaneously with fearful defensive treading more caudally). These results indicate that GABAergic neurotransmission in local microcircuits in nucleus accumbens mediates motivated/affective behavior that is bivalently organized along rostrocaudal gradients.