1. ¹Neuroscience Program, University of Michigan, Ann Arbor, MI, USA
2. ²San Raffaele Research Institute and University, Milano, Italy
3. ³Istituto di Psicologia, Facoltà di Medicina, Università degli Studi di Milano, Milano, Italy
4. ⁴Department of Psychology, University of Michigan, Ann Arbor, MI, USA

Correspondence: Dr TE Robinson, Department of Psychology (Biopsychology), University of Michigan, East Hall, 525 East University Avenue, Ann Arbor, MI 48109-1109, USA. Tel: 734 763 1304; Fax: 734 763 7480; E-mail: ter@umich.edu

Received 26 May 2005; Revised 18 November 2005; Accepted 21 November 2005; Published online 11 January 2006.

Abstract

The ability of cocaine to produce lasting neural adaptations in mesocorticolimbic brain regions is thought to promote drug seeking and facilitate addiction in humans. The Ras-controlled Raf-MEK-ERK protein kinase signaling cascade has been implicated in the behavioral and neurobiological actions of cocaine in animals. However, these pharmacological studies have not been able to determine the specific role of the two predominant isoforms of ERK (ERK1 and ERK2) in these processes. We report here that deletion of the ERK1 isoform, which leads to increased ERK2 stimulus-dependent signaling, facilitates the development of cocaine-induced psychomotor sensitization and the acquisition of a cocaine conditioned place preference. Conversely, pharmacological blockade of ERK signaling attenuates the development of psychomotor sensitization to cocaine. Finally, cocaine-evoked gene expression in mesocorticolimbic brain regions is potentiated in ERK1-deficient mice. Thus, alterations in ERK signaling influence both the neurobiological impact of cocaine and its ability to produce enduring forms of drug experience-dependent behavioral plasticity. Our results suggest that enhanced ERK2 signaling following repeated drug exposure may facilitate the development of forms of cocaine-induced plasticity that contribute to addiction.