Ammonia mediates methamphetamine-induced increases in glutamate and excitotoxicity

Laura E. Halpin, Nicole A. Northrop, Bryan K. Yamamoto

Research output: Contribution to journalArticle

27 Scopus citations

Abstract

Ammonia has been identified to have a significant role in the long-term damage to dopamine and serotonin terminals produced by methamphetamine (METH), but how ammonia contributes to this damage is unknown. Experiments were conducted to identify whether increases in brain ammonia affect METH-induced increases in glutamate and subsequent excitotoxicity. Increases in striatal glutamate were measured using in vivo microdialysis. To examine the role of ammonia in mediating changes in extracellular glutamate after METH exposure, lactulose was used to decrease plasma and brain ammonia. Lactulose is a non-absorbable disaccharide, which alters the intestinal lumen through multiple mechanisms that lead to the increased peripheral excretion of ammonia. METH caused a significant increase in extracellular glutamate that was prevented by lactulose. Lactulose had no effect on METH-induced hyperthermia. To determine if ammonia contributed to excitotoxicity, the effect of METH and lactulose treatment on calpain-mediated spectrin proteolysis was measured. METH significantly increased calpain-specific spectrin breakdown products, and this increase was prevented with lactulose treatment. To examine if ammonia-induced increases in extracellular glutamate were mediated by excitatory amino-acid transporters, the reverse dialysis of ammonia, the glutamate transporter inhibitor, DL-threo-β-benzyloxyaspartic acid (TBOA), or the combination of the two directly into the striatum of awake, freely moving rats was conducted. TBOA blocked the increases in extracellular glutamate produced by the reverse dialysis of ammonia. These findings demonstrate that ammonia mediates METH-induced increases in extracellular glutamate through an excitatory amino-acid transporter to cause excitotoxicity.

Original languageEnglish (US)
Pages (from-to)1031-1038
Number of pages8
JournalNeuropsychopharmacology
Volume39
Issue number4
DOIs
StatePublished - Mar 1 2014
Externally publishedYes

Keywords

  • ammonia
  • excitotoxicity
  • glutamate
  • glutamate transporter
  • methamphetamine

ASJC Scopus subject areas

  • Pharmacology
  • Psychiatry and Mental health

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