Rationale Extracellular signal-regulated protein kinase (ERK1/2) is a member of the mitogen-activated protein kinase (MAPK) signaling pathway and a key molecular target for ethanol (EtOH) and other drugs of abuse. Objective The aim of the study was to assess the role of two MAPK pathways, ERK1/2 and c-Jun N-terminal kinase (JNK), on the modulation of EtOH and sucrose self-administration. Materials and methods C57BL/6J mice were trained to lever press on a fixed-ratio 4 schedule with 9% EtOH/2% sucrose, or 2% sucrose, as the reinforcer. In experiments 1 and 2, mice were injected with the MEK1/2 inhibitor SL 327 (0–100 mg/kg) and the JNK inhibitor AS 6012452 (0–56 mg/kg) prior to self-administration. In experiment 3, SL 327 (0–100 mg/kg) was administered prior to performance on a progressive ratio (PR) schedule of EtOH reinforcement. In experiment 4, SL 327 and AS 601245 were injected 2 h before a locomotor test. Results SL 327 (30 mg/kg) significantly increased EtOH self-administration without affecting locomotion. Higher doses of SL 327 and AS 601245 reduced EtOH-reinforced responding and locomotor activity. Reductions of both ligands on sucrose self-administration were due to decreases in motor activity. SL 327 pretreatment had no effect on PR responding. Conclusions ERK1/2 activity is more directly involved in modulating the reinforcing properties of EtOH than JNK activity due to its selective potentiation of EtOH-reinforced responding. The specificity of this effect to EtOH self-administration, rather than sucrose self-administration, suggests that the mechanism by which ERK1/2 increases EtOH-reinforced responding does not generalize to all reinforcing solutions and is not due to increased motivation to consume EtOH.

No abstract