Effects of unilatral- and bilateral inhibition of rostral ventral tegmental area and central nucleus of amygdala on morphine-induced place conditioning in male Wistar rat.

Abstract

The rostral ventral tegmental area (VTAR) and central nucleus of amygdala (CeA) are considered the main regions for induction of psychological dependence on abused drugs, such as morphine. The main aim of this study was to investigate the transient inhibition of each right and left side as well as both sides of the VTAR and the CeA by lidocaine (2%) on morphine reward properties using the conditioned place preference (CPP) method. Male Wistar rats (250±20g) 7days after recovery from surgery and cannulation were conditioned to morphine (7.5mg/kg) in CPP apparatus. Five minutes before morphine injection in conditioning phase, lidocaine was administered either uni- or bilaterally into the VTAR (0.25μL/site) or CeA (0.5μL/site). The results revealed that lidocaine administration into the left side, but not the right side of the VTAR and the CeA reduced morphine CPP significantly. The reduction was potentiated when lidocaine was injected into both sides of the VTAR and the CeA. The number of compartment crossings was reduced when lidocaine was injected into both sides of the VTAR and the CeA as well as the left side. Rearing was reduced when lidocaine was injected into the right, but not the left side of the VTAR. Sniffing and rearing increased when animals received lidocaine in the right side and reduced in the group that received lidocaine in the left side of the CeA. It was concluded that the right and the left side of VTAR and the CeA play different roles in morphine-induced activity and reward.