Interactions between prelimbic cortex and basolateral amygdala contribute to morphine-induced conditioned taste aversion in conditioning and extinction.

The consequences of exciting or destroying the prelimbic cortex (PrL) or the basolateral amygdala (BLA) remain unclear, including the effects on morphine-induced conditioned taste aversion (CTA) in the conditioning and extinction phases, plasma corticosterone (CORT) levels, and c-Fos/p-ERK expressions in the subareas of the medial prefrontal cortex (i.e., PrL, infralimbic cortex [IL], cingulate cortex 1 [Cg1]), basolateral amygdala (BLA), central amygdala (CeA), hippocampus (i.e., CA1, CA2, CA3, and dentate gyrus [DG]), nucleus accumbens (NAc), lateral hypothalamus (LH), and piriform cortex (PC). During conditioning, excitation of the PrL glutamate neurons via NMDA injections disrupted morphine-induced CTA and decreased plasma CORT levels; moreover, c-Fos and p-ERK expression was hyperactive in the PrL and IL but hypoactive in the Cg1 and BLA. In conditioning, excitation of the BLA glutamate neurons via NMDA injections facilitated morphine-induced CTA and increased plasma CORT levels. The expression of c-Fos and p-ERK was hypoactive in the PrL and IL but hyperactive in the BLA. During extinction, lesion of the PrL glutamate neurons via NMDA injections impaired morphine-induced CTA extinction and enhanced plasma CORT levels. The expression of c-Fos and p-ERK was hypoactive in the PrL and IL but hyperactive in the BLA. In extinction, excitation of the PrL glutamatergic neurons via NMDA injections facilitated morphine-induced CTA extinction and did not affect plasma CORT levels; moreover, the expression of c-Fos and p-ERK was hypoactive in the Cg1, PrL, and IL but hyperactive in the BLA. Altogether, the interaction between the PrL and BLA plays a balancing role in morphine-induced CTA conditioning and extinction. During conditioning, the activity of the PrL correlated negatively with plasma CORT secretions, whereas the activity of the BLA correlated positively with the plasma CORT levels. During extinction, the activity of the PrL correlated negatively with plasma CORT secretions; however, the activity of the BLA may be negatively associated with the plasma CORT levels. The data presented here provide some implications for morphine addiction and dependence.