Pre-synaptic nicotinic receptors evoke endogenous glutamate and aspartate release from hippocampal synaptosomes by way of distinct coupling mechanisms
Article first published online: 13 JUL 2010
© 2010 The Authors. British Journal of Pharmacology © 2010 The British Pharmacological Society
British Journal of Pharmacology
Volume 161, Issue 5, pages 1161–1171, November 2010
How to Cite
Zappettini, S., Grilli, M., Salamone, A., Fedele, E. and Marchi, M. (2010), Pre-synaptic nicotinic receptors evoke endogenous glutamate and aspartate release from hippocampal synaptosomes by way of distinct coupling mechanisms. British Journal of Pharmacology, 161: 1161–1171. doi: 10.1111/j.1476-5381.2010.00958.x
- Issue published online: 13 JUL 2010
- Article first published online: 13 JUL 2010
- Received12 April 2010Revised8 June 2010Accepted22 June 2010
- nicotinic receptor subtypes;
- endogenous glutamate;
- endogenous aspartate;
- rat hippocampus;
- neurotransmitter release
BACKGROUND AND PURPOSE The present work aimed to investigate whether and through which mechanisms selective α7 and α4β2 nicotinic receptor (nAChR) agonists stimulate endogenous glutamate (GLU) and aspartate (ASP) release in rat hippocampus.
EXPERIMENTAL APPROACH Rat hippocampal synaptosomes were purified on Percoll gradients and superfused in vitro to study endogenous GLU and ASP release. The synaptosomes were superfused with selective α7 and α4β2 nAChR agonists and antagonists. The excitatory amino acid (EAA) content of the samples of superfusate was determined by HPLC after pre-column derivatization and separation on a chromatographic column coupled with fluorimetric detection.
KEY RESULTS Choline (Ch), a selective α7 receptor agonist, elicited a significant release of both GLU and ASP which was blocked by the α7 receptor antagonist methyllycaconitine (MLA), but was unaltered by the α4β2 receptor antagonist dihydro-β-erythroidine (DHβE). The stimulant effect of Ch was strongly reduced in a Ca2+-free medium, was not inhibited by Cd2+ and tetrodotoxin (TTX), but was antagonized by dantrolene, xestospongin C and thapsigargin. 5-Iodo-A-85380 dihydrochloride (5IA85380), a selective α4β2 receptor agonist, elicited EAA release in a DHβE-sensitive, MLA-insensitive fashion. The 5IA85380-evoked release was dependent on extracellular Ca2+, blocked by Cd2+ and TTX, but unaffected by dantrolene.
CONCLUSIONS AND IMPLICATIONS Our study shows for the first time that rat hippocampal synaptosomes possess α7 and α4β2 nAChR subtypes, which can enhance the release of endogenous GLU and ASP via two distinct mechanisms of action. These results extend our knowledge of the nicotinic modulation of excitatory synaptic transmission in the hippocampus.