Fear and feeding in the nucleus accumbens shell: Rostrocaudal segregation of GABA-elicited defensive behavior versus eating behavior

This study examined localization of positive versus negative motivational f unctions mediated by GABA circuits within the accumbens shell. Microinjecti ons of a GABA(A) agonist (0, 25, 75, and 225 ng/0.5 mul muscimol) in rostra l shell sites elicited appetitive increases in eating behavior. In contrast , microinjections in caudal shell sites elicited defensive burying or paw-t reading behavior. Rats whose microinjections landed bilaterally outside of the accumbens shell did not display either behavior. Defensive treading eli cited by caudal shell muscimol microinjection appeared to be a negative mot ivated response to threat (similar in parameters and orientation to normal defensive burying of a threatening electrified shock prod). The nucleus acc umbens shell thus appears functionally heterogeneous in coding motivational valence. The demonstration that muscimol elicits positive eating behavior from rostral shell versus negative defensive behavior from caudal shell sug gests in particular that GABAergic substrates of positive and negative type s of motivated behavior in the nucleus accumbens shell are segregated along a rostrocaudal gradient.