The essential oil of bergamot enhances the levels of amino acid neurotransmitters in the hippocampus of rat: implication of monoterpene hydrocarbons

Pharmacol Res. 2007 Apr;55(4):255-62. doi: 10.1016/j.phrs.2006.11.010. Epub 2006 Dec 5.

Abstract

The effects of bergamot essential oil (BEO) on the release of amino acid neurotransmitters in rat hippocampus have been studied by in vivo microdialysis and by in vitro superfusion of isolated nerve terminals. Intraperitoneal administration of BEO (100microl/kg) significantly elevated the extracellular concentration of aspartate, glycine and taurine in a Ca(2+)-dependent manner. A dose-relation study generated a bell-shaped curve. When perfused into the hippocampus via the dialysis probe (20microl/20min), BEO produced a significant increase of extracellular aspartate, glycine, taurine as well as of GABA and glutamate. The augmentation of all amino acids was Ca(2+)-independent. Focally injected 1:1 diluted BEO preferentially caused extracellular increase of glutamate. Interestingly, this release appeared to be strictly Ca(2+)-dependent. BEO concentration-dependently enhanced the release of [(3)H]D-aspartate from superfused hippocampal synaptosomes. Similar results were obtained by monitoring the BEO-evoked release of endogenous glutamate. At relatively high concentrations, the BEO-induced [(3)H]d-aspartate release was almost entirely prevented by the glutamate transporter blocker dl-threo-beta-benzyloxyaspartic acid (DL-TBOA) and was Ca(2+)-independent. At relatively low concentrations the release of [(3)H]D-aspartate was only in part ( approximately 50%) DL-TBOA-sensitive and Ca(2+)-independent; the remaining portion of release was dependent on extracellular Ca(2+). Interestingly, the monoterpene hydrocarbon-free fraction of the essential oil appeared to be inactive while the bergapten-free fraction superimposed the releasing effect of BEO supporting the deduction that psoralens may not be implicated. To conclude, BEO contains into its volatile fraction still unidentified monoterpene hydrocarbons able to stimulate glutamate release by transporter reversal and/or by exocytosis, depending on the dose administered.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Transport Systems / drug effects
  • Amino Acid Transport Systems / metabolism
  • Amino Acids / metabolism*
  • Animals
  • Aspartic Acid / metabolism
  • Calcium / metabolism
  • Dose-Response Relationship, Drug
  • Exocytosis / drug effects
  • Glutamic Acid / metabolism*
  • Glycine / metabolism
  • Hippocampus / drug effects*
  • Hippocampus / metabolism
  • In Vitro Techniques
  • Male
  • Microdialysis
  • Monoterpenes / isolation & purification
  • Monoterpenes / pharmacology*
  • Neurotransmitter Agents / metabolism*
  • Oils, Volatile / chemistry
  • Oils, Volatile / pharmacology*
  • Plant Oils / chemistry
  • Plant Oils / pharmacology*
  • Rats
  • Rats, Wistar
  • Synaptosomes / drug effects
  • Synaptosomes / metabolism
  • Taurine / metabolism
  • Time Factors
  • gamma-Aminobutyric Acid / metabolism

Substances

  • Amino Acid Transport Systems
  • Amino Acids
  • Monoterpenes
  • Neurotransmitter Agents
  • Oils, Volatile
  • Plant Oils
  • Taurine
  • Aspartic Acid
  • bergamot oil
  • Glutamic Acid
  • gamma-Aminobutyric Acid
  • Calcium
  • Glycine