Korean J Physiol Pharmacol.  2011 Dec;15(6):389-395. 10.4196/kjpp.2011.15.6.389.

Blockade of ERK Phosphorylation in the Nucleus Accumbens Inhibits the Expression of Cocaine-induced Behavioral Sensitization in Rats

• Kim S
• Shin JK
• Yoon HS
• Kim JH

• KMID: 2285426
• DOI: http://doi.org/10.4196/kjpp.2011.15.6.389

Abstract

Repeated administration of psychostimulants such as cocaine leads to the development of behavioral sensitization. Extracellular signal-Regulated Kinase (ERK), an enzyme important for long-term neuronal plasticity, has been implicated in such effects of these drugs. Although the nucleus accumbens (NAcc) is the site mediating the expression of behavioral sensitization by drugs of abuse, the precise role of ERK activation in this site has not been determined. In this study we demonstrate that blockade of ERK phosphorylation in the NAcc by a single bilateral microinjections of PD98059 (0.5 or 2.0micro g/side), or U0126 (0.1 or 1.0microg/side), into this site dose-dependently inhibited the expression of cocaine-induced behavioral sensitization when measured at day 7 following 6 consecutive daily cocaine injections (15 mg/kg, i.p.). Acute microinjection of either vehicle or PD98059 alone produced no different locomotor activity compared to saline control. Further, microinjection of PD98059 (2.0micro g/side) in the NAcc specifically lowered cocaine-induced increase of ERK phosphorylation levels in this site, while unaffecting p-38 protein levels. These results indicate that ERK activation in the NAcc is necessary for the expression of cocaine-induced behavioral sensitization, and further suggest that repeated cocaine evokes neuronal plasticity involving ERK pathway in this site leading to long-lasting behavioral changes.

Keyword

Cocaine; Behavioral sensitization; PD98059; U0126; Nucleus accumbens

MeSH Terms

Animals
Butadienes
Cocaine
Flavonoids
MAP Kinase Signaling System
Microinjections
Motor Activity
Negotiating
Neuronal Plasticity
Nitriles
Nucleus Accumbens
Phosphorylation
Phosphotransferases
Rats
Street Drugs
Butadienes
Cocaine
Flavonoids
Nitriles
Phosphotransferases
Street Drugs

Figure

• 

  Fig. 1 Blockade of ERK phosphorylation by a single microinjection of PD98059 in the NAcc inhibits the expression of cocaine-induced locomotor sensitization. (A) Animals were either saline or cocaine pre-exposed for 6 days. At day 7, their locomotor activity was observed after cocaine (15 mg/kg, IP) challenge injections preceded 30 min earlier by an acute single bilateral microinjection of either vehicle or PD98059 (0.5, 2.0µg/side) into the NAcc. Enhanced increase of locomotor activity in cocaine compared to saline pre-exposed animals was dose-dependently inhibited by PD98059 microinjection into the NAcc. Data are shown as group mean (+S.E.M.) total locomotor activity counts observed during the first 1 hour. Numbers of rats in each group are 6~7. Symbols indicate significant differences as revealed by post-hoc Scheffé comparisons following two-way between (microinjections) - within (pre-exposures) ANOVA. ***p<0.001, **p<0.01; significantly more counts in cocaine relative to saline pre-exposed animals. ††p<0.01; significant differences in cocaine pre-exposed animals when PD98059 (2.0µg/side) compared to vehicle was microinjected. (B) Time-course data are shown as group mean (+S.E.M.) locomotion activity counts for every 20 min time-bins obtained during the 2-hr test immediately after cocaine challenge injection. (C) Location of the microinjection cannula tips in the NAcc of rats included in the data analyses. Only rats with injection cannula tips located bilaterally in this site were included. No neuronal damage was observed other than that produced by the insertion of the cannulae. The line drawings are from Paxinos and Watson [15]. Numbers to the right indicate millimeters from bregma.

• 

  Fig. 2 Acute microinjection of vehicle or PD98059 alone into the NAcc produces no different levels of locomotor activity compared to saline control. Locomotor activity is observed after saline (IP) injections following bilateral microinjections of either saline or vehicle (70% DMSO), PD98059 (0.5, 2.0µg/side) into the NAcc. Data are shown as group mean (+S.E.M.) total locomotor activity counts observed for 1 hour (n=5/group).

• 

  Fig. 3 PD98059 in the NAcc lowers cocaine-induced increase of ERK phosphorylation levels in this site. Animals were either saline or cocaine (15 mg/kg) IP challenged following 30 min earlier microinjection of either vehicle or a single dose of PD98059 (2.0 µg/side). After 10 min, brains were removed and the NAcc tissues were punched out. Representative Western blots labeled with antibodies against phosphorylated and total ERK1/2 (A), and p-38 (B), were shown. Blots were scanned and the band intensities were quantified using densitometer. Values are normalized to β-actin and expressed as mean (+S.E.M.) (n=7 to 8/group) transformed to relative amounts of control (vehicle microinjection - saline IP) values. Symbols indicate significant differences as revealed by post-hoc Scheffé comparisons following two-way between (IP challenges) - within (microinjections) ANOVA. **p<0.01; significantly higher levels of p-ERK1/2 in cocaine relative to saline challenged animals. ††p<0.01; significant differences in cocaine challenged animals when PD98059 (2.0µg/side) compared to vehicle was microinjected. Other proteins examined showed no differences between groups.

• 

  Fig. 4 Blockade of ERK phosphorylation by a single microinjection of U0126 in the NAcc inhibits the expression of cocaine-induced locomotor sensitization. Animals were either saline or cocaine pre-exposed for 6 days. At day 7, their locomotor activity was observed after cocaine (15 mg/kg, IP) challenge injections preceded 30 min earlier by acute bilateral microinjections of either vehicle or U0126 (0.1, 1.0µg/side) into the NAcc. Enhanced increase of locomotor activity in cocaine compared to saline pre-exposed animals was dose-dependently inhibited by a single U0126 microinjection into the NAcc. Data are shown as group mean (+S.E.M.) total locomotor activity counts observed during the 1 hour. Numbers of rats in each group are 4~6. Symbols indicate significant differences as revealed by post-hoc Scheffé comparisons following two-way between (microinjections) - within (pre-exposures) ANOVA. **p<0.01; significantly more counts in cocaine relative to saline pre-exposed animals. †p<0.05; significant differences in cocaine pre-exposed animals when U0126 (1.0µg/side) compared to vehicle was microinjected.

Reference

1. Kalivas PW, Stewart J. Dopamine transmission in the initiation and expression of drug- and stress-induced sensitization of motor activity. Brain Res Brain Res Rev. 1991; 16:223–244. PMID: 1665095.

2. Robinson TE, Berridge KC. The neural basis of drug craving: an incentive-sensitization theory of addiction. Brain Res Brain Res Rev. 1993; 18:247–291. PMID: 8401595.

3. Robinson TE, Berridge KC. The psychology and neurobiology of addiction: an incentive-sensitization view. Addiction. 2000; 95(Suppl 2):S91–117. PMID: 11002906.

4. Atkins CM, Selcher JC, Petraitis JJ, Trzaskos JM, Sweatt JD. The MAPK cascade is required for mammalian associative learning. Nat Neurosci. 1998; 1:602–609. PMID: 10196568.

5. Sweatt JD. Mitogen-activated protein kinases in synaptic plasticity and memory. Curr Opin Neurobiol. 2004; 14:311–317. PMID: 15194111.

6. Berhow MT, Hiroi N, Nestler EJ. Regulation of ERK (extracellular signal regulated kinase), part of the neurotrophin signal transduction cascade, in the rat mesolimbic dopamine system by chronic exposure to morphine or cocaine. J Neurosci. 1996; 16:4707–4715. PMID: 8764658.

7. Valjent E, Corvol JC, Pages C, Besson MJ, Maldonado R, Caboche J. Involvement of the extracellular signal-regulated kinase cascade for cocaine-rewarding properties. J Neurosci. 2000; 20:8701–8709. PMID: 11102476.

8. Mattson BJ, Bossert JM, Simmons DE, Nozaki N, Nagarkar D, Kreuter JD, Hope BT. Cocaine-induced CREB phosphorylation in nucleus accumbens of cocaine-sensitized rats is enabled by enhanced activation of extracellular signal-related kinase, but not protein kinase A. J Neurochem. 2005; 95:1481–1494. PMID: 16219028.

9. Valjent E, Corvol JC, Trzaskos JM, Girault JA, Hervé D. Role of the ERK pathway in psychostimulant-induced locomotor sensitization. BMC Neurosci. 2006; 7:20. PMID: 16512905.

10. Perugini M, Vezina P. Amphetamine administered to the ventral tegmental area sensitizes rats to the locomotor effects of nucleus accumbens amphetamine. J Pharmacol Exp Ther. 1994; 270:690–696. PMID: 8071860.

11. Cador M, Bjijou Y, Stinus L. Evidence of a complete independence of the neurobiological substrates for the induction and expression of behavioral sensitization to amphetamine. Neuroscience. 1995; 65:385–395. PMID: 7777156.

12. Ferguson SM, Fasano S, Yang P, Brambilla R, Robinson TE. Knockout of ERK1 enhances cocaine-evoked immediate early gene expression and behavioral plasticity. Neuropsychopharmacology. 2006; 31:2660–2668. PMID: 16407894.

13. Pierce RC, Pierce-Bancroft AF, Prasad BM. Neurotrophin-3 contributes to the initiation of behavioral sensitization to cocaine by activating the Ras/Mitogen-activated protein kinase signal transduction cascade. J Neurosci. 1999; 19:8685–8695. PMID: 10493769.

14. Pellegrino LJ, Pellegrino AS, Cushman AJ. A Stereotaxic Atlas of the Rat Brain. 1979. 2nd ed. New York: Plenum.

15. Paxinos G, Watson C. The Rat Brain in Stereotaxic Coordinates. 1997. 3rd ed. New York: Academic Press.

16. Gerdjikov TV, Ross GM, Beninger RJ. Place preference induced by nucleus accumbens amphetamine is impaired by antagonists of ERK or p38 MAP kinases in rats. Behav Neurosci. 2004; 118:740–750. PMID: 15301601.

17. Miller CA, Marshall JF. Molecular substrates for retrieval and reconsolidation of cocaine-associated contextual memory. Neuron. 2005; 47:873–884. PMID: 16157281.

18. Valjent E, Pascoli V, Svenningsson P, Paul S, Enslen H, Corvol JC, Stipanovich A, Caboche J, Lombroso PJ, Nairn AC, Greengard P, Hervé D, Girault JA. Regulation of a protein phosphatase cascade allows convergent dopamine and glutamate signals to activate ERK in the striatum. Proc Natl Acad Sci U S A. 2005; 102:491–496. PMID: 15608059.

19. Wolf ME. The role of excitatory amino acids in behavioral sensitization to psychomotor stimulants. Prog Neurobiol. 1998; 54:679–720. PMID: 9560846.

20. Vezina P, Kim JH. Metabotropic glutamate receptors and the generation of locomotor activity: interactions with midbrain dopamine. Neurosci Biobehav Rev. 1999; 23:577–589. PMID: 10073895.

21. Kim JH, Perugini M, Austin JD, Vezina P. Previous exposure to amphetamine enhances the subsequent locomotor response to a D1 dopamine receptor agonist when glutamate reuptake is inhibited. J Neurosci. 2001; 21:RC133. PMID: 11222671.

22. Pierce RC, Bell K, Duffy P, Kalivas PW. Repeated cocaine augments excitatory amino acid transmission in the nucleus accumbens only in rats having developed behavioral sensitization. J Neurosci. 1996; 16:1550–1560. PMID: 8778304.

23. Vanderschuren LJ, Kalivas PW. Alterations in dopaminergic and glutamatergic transmission in the induction and expression of behavioral sensitization: a critical review of preclinical studies. Psychopharmacology (Berl). 2000; 151:99–120. PMID: 10972458.

24. Zhang L, Lou D, Jiao H, Zhang D, Wang X, Xia Y, Zhang J, Xu M. Cocaine-induced intracellular signaling and gene expression are oppositely regulated by the dopamine D1 and D3 receptors. J Neurosci. 2004; 24:3344–3354. PMID: 15056714.

25. Zahm DS. An integrative neuroanatomical perspective on some subcortical substrates of adaptive responding with emphasis on the nucleus accumbens. Neurosci Biobehav Rev. 2000; 24:85–105. PMID: 10654664.

26. Di Chiara G. Nucleus accumbens shell and core dopamine: differential role in behavior and addiction. Behav Brain Res. 2002; 137:75–114. PMID: 12445717.