Activation by N-acetyl-L-aspartate of acutely dissociated hippocampal neurons in rats via metabotropic glutamate receptors.

Abstract

PURPOSE:

We previously reported that an increase in the N-acetyl-L-aspartate (NAA) level due to the lack of aspartoacylase gene was found in the brain of the tremor rat (tm/tm), which is a mutant with a causative gene named tm that shows epileptic seizures. Therefore, NAA is suggested to be one of the factors involved in the induction of epileptic seizures. Patch-clamp studies were performed to determine whether NAA produces an excitatory effect on acutely dissociated rat hippocampal neurons.

METHODS:

Acutely dissociated hippocampal neurons were prepared from normal Wistar rats aged 3-4 weeks. NAA-induced currents were investigated by using the whole-cell voltage-clamp recording technique.

RESULTS:

Application of NAA at concentrations of 100 nM to 1 mM through a U-tube for 2 s produced an inward current in a concentration-dependent manner at a holding potential of -60 mV. When the current-voltage relation was examined, the reversal potential of the NAA-induced current was found to be approximately 0 mV. The NAA-induced current was inhibited by bath application of the metabotropic glutamate receptor (mGluR) antagonist (+/-)-alpha-methyl-4-carboxyphenylglycine (MCPG) and by intracellular application of guanosine 5'-O-(2-thiodiphosphate) (GDP-betaS), a nonhydrolyzable GDP analogue. However, the NAA-induced current remained unaffected by glutamic acid diethyl ester, a non-N-methyl-D-aspartate (NMDA)-subtype ionotropic glutamate receptor antagonist, or the voltage-dependent ion channel blockers tetrodotoxin, CdCl2, and tetraethylammonium-chloride. Conversely, the mGluR agonist, trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD) also induced an inward current, with a reversal potential of 0 mV. The ACPD-induced current also was inhibited by MCPG.

CONCLUSIONS:

These results suggest that NAA acts on the G protein-coupled mGluRs to induce an inward current that results in excitation of the neurons, thereby contributing to the occurrence of epileptic seizures.

• Authors: Hai-Dun Yan, Kumatoshi Ishihara, Tadao Serikawa, Masashi Sasa
• Journal: Epilepsia (Epilepsia) Vol. 44 Issue 9 Pg. 1153-9 (Sep 2003) ISSN: 0013-9580 [Print] United States
• PMID: 12919386 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Receptors, Metabotropic Glutamate
• Aspartic Acid
• N-acetylaspartate

Topics

• Action Potentials (drug effects, physiology)
• Animals
• Aspartic Acid (analogs & derivatives, pharmacology, toxicity)
• Dose-Response Relationship, Drug
• Epilepsy (chemically induced, physiopathology)
• Hippocampus (cytology, drug effects, physiology)
• In Vitro Techniques
• Neurons (cytology, drug effects, physiology)
• Rats
• Rats, Wistar
• Receptors, Metabotropic Glutamate (physiology)