Morphine tolerance and reward but not expression of morphine dependence are inhibited by the selectiveglutamate carboxypeptidase II (GCP II, NAALADase) inhibitor, 2-PMPA

Piotr Popik, Ewa Kozela, Malgorzata Wróbel, Krystyna M. Wozniak, Barbara S. Slusher

Research output: Contribution to journalArticle


Inhibition of glutamate carboxypeptidase II (GCP II; NAALADase) produces a variety of effects on glutamatergic neurotransmission. The aim of this study was to investigate effects of GCP II inhibition with the selective inhibitor, 2-PMPA, on: (a) development of tolerance to the antinociceptive effects, (b) withdrawal, and (c) conditioned reward produced by morphine in C57/Blmice. The degree of tolerance was assessed using the tail-flick test before and after 6 days of twice daily (b.i.d.) administration of 2-PMPA and 10 mg/kg of morphine. Opioid withdrawalwas measured 3 days after twice daily morphine (30 or 10 mg/kg) administration, followed by naloxone challenge. Conditioned morphine reward was investigated using conditioned place preference with a single morphine dose (10 mg/kg). High doses of 2-PMPA inhibited the development of morphine tolerance (resembling the effect of 7.5 mg/kg of the NMDA receptor antagonist, memantine) while not affecting the severity of withdrawal. A high dose of 2-PMPA (100 mg/kg) also significantly potentiated morphine withdrawal, but inhibited both acquisition and expression of morphine-induced conditioned place preference. Memantine inhibited the intensity of morphine withdrawalaswellas acquisition and expression of morphine-induced conditioned place preference. In addition, 2-PMPA did not affect learning or memory retrievalin a simple two-trialtest, nor did it produce withdrawalsymptoms in morphine-dependent, placebo-challenged mice. Results suggest involvement of GCP II (NAALADase) in phenomena related to opioid addiction.

Original languageEnglish (US)
Pages (from-to)457-467
Number of pages11
Issue number3
StatePublished - Mar 2003



  • Antinociception
  • Drug reward
  • Glutamate carboxypeptidase II
  • Memory
  • NMDA receptor antagonist
  • Opioid withdrawaland dependence
  • Tolerance

ASJC Scopus subject areas

  • Pharmacology
  • Psychiatry and Mental health

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