Abstract: Objective To investigate the effect of μ-opioid receptors (μ-ORs) in the central nucleus of the amygdala (CeA) on
feeding and drinking behaviors in rats and evaluate the role of glutamate signaling in opioid-mediated ingestive behaviors.
Methods Stainless steel cannulas were implanted in the unilateral CeA for microinjection of different doses of the selective
μ-OR agonist DAMGO in satiated or water-deprived male SD rats. The subsequent food intake or water intake of the rats was
measured at 60, 120, and 240 min after the injection. The rats receiving microinjections of naloxone (NTX, a nonselective opioid
antagonist) or D-AP-5 (a selective N-methyl-D-aspartic acid-type glutamate receptor antagonist) prior to DAMGO
microinjection were tested for food intake at 60, 120, and 240 min after the injections. Results Injections of DAMGO (1-4 nmol
in 0.5 μl) into the CeA significantly increased food intake in satiated rats, but did not affect water intake in rats with water
deprivation. NTX (26.5 nmol in 0.5μl) injected into the CeA antagonized DAMGO-induced feeding but D-AP-5 (6.3-25.4 nmol
in 0.5 μl) injections did not produce such an effect. Conclusion μ-ORs in the CeA regulate food intake rather than water intake
in rats, and the orexigenic role of μ-ORs is not dependent on the activation of the NMDAreceptors in the CeA.