Research reportDifferential effects of naloxone on rewarding electrical stimulation of the central nucleus of the amygdala and parabrachial complex in a place preference study

- Electrical stimulation (ES) was used to study the brain mechanisms of reward.
- ES of central amygdala (CeA) and external lateral parabrachial nuclei induced place preferences.
- Naloxone (Nx), an opioid antagonist, blocked the rewarding effect of parabrachial ES.
- However, this antagonist failed to interrupt the rewarding ES of the amygdala.
- Distinct Nx effects support reward systems differ anatomically and neurochemically.

The central nucleus of the amygdala (CeA) is considered to be involved in different affective, sensory, regulatory, and acquisition processes. This study analyzed whether electrical stimulation of the PB-CeA system induces preferences in a concurrent place preference (cPP) task, as observed after stimulation of the parabrachial-insular cortex (PB-IC) axis. It also examined whether the rewarding effects are naloxone-dependent. The results show that electrical stimulation of the CeA and external lateral parabrachial subnucleus (LPBe) induces consistent preference behaviors in a cPP task. However, subcutaneous administration of an opiate antagonist (naloxone; 4 mg/ml/kg) blocked the rewarding effect of the parabrachial stimulation but not that of the amygdala stimulation. These results are interpreted in the context of multiple brain reward systems that appear to differ both anatomically and neurochemically, notably with respect to the opiate system.