title: Different presynaptic nicotinic receptor subtypes modulate in vivo and in vitro the release of glycine in the rat hippocampus.
abstract: In the present study, using an in vivo approach (a microdialysis technique associated to HPLC with fluorimetric detection) and in vitro purified hippocampal synaptosomes in superfusion, we investigated the glycinergic transmission in the hippocampus, focusing on the nicotinic control of glycine (GLY) release. The acute administration of nicotine in vivo was able to evoke endogenous GLY release in the rat hippocampus. The specific nicotinic agonists PHA-543613 hydrochloride (PHA543613) selective for the α7 nicotinic receptor subtype administered in vivo also elicited GLY release in a similar extent, while the α4β2 agonist 5-IA85380 dihydrochloride (5IA85380) was less effective. Nicotine elicited GLY overflow also from hippocampal synaptosomes in vitro. This overflow was Ca(2+)-dependent and inhibited by methyllycaconitine (MLA), but was not modified by dihydro-beta-erythroidine (DHβE, 1 μM). Choline(Ch)-evoked GLY overflow was Ca(2+) dependent, unaltered in presence of DHβE and blocked by methyllycaconitine (MLA). Additionally, 5IA85380 elicited a GLY overflow, which in turn was Ca(2+) dependent, was significantly inhibited by DHβE but was unaffected by MLA. The GLY overflow produced by these nicotinic agonists quantitatively resembles that evoked by 9 mM KCl. The effects of a high concentration of 5IA85380 (1mM), in the presence of 2 μM DHβE, on the release of GLY was also studied comparatively to that on glutamate and aspartate release. The nicotinic agonist 5IA85380 tested at high concentration (1mM) was able to produce a stimulatory effect of endogenous release of the three amino acids, even in the presence of 2 μM DHβE, indicating the existence of a DHβE resistant, α4β2 nAChR subtype with a functional role in the modulation of GLY, ASP, and GLU release. Our results show that in the rat hippocampus the release of GLY is, at least in part, of neuronal origin and is modulated by the activation of both α7 and α4β2 (low and high affinity) nAChR subtypes.
authors.affiliation: Section of Pharmacology and Toxicology, Department of Experimental Medicine, University of Genoa, Genoa, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Zappettini
authors.forename: Elisa
authors.initials: E
authors.lastname: Mura
authors.forename: Massimo
authors.initials: M
authors.lastname: Grilli
authors.forename: Stefania
authors.initials: S
authors.lastname: Preda
authors.forename: Alessia
authors.initials: A
authors.lastname: Salamone
authors.forename: Guendalina
authors.initials: G
authors.lastname: Olivero
authors.forename: Stefano
authors.initials: S
authors.lastname: Govoni
authors.forename: Mario
authors.initials: M
authors.lastname: Marchi
mesh_terms: D000596:Amino Acids / Q000032:analysis / Q000378:metabolism; D000818:Animals; D019540:Area Under Curve; D001384:Azetidines / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D005470:Fluorometry; D005998:Glycine / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011812:Quinuclidines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D017661:Receptors, Presynaptic / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: C119803:2-fluoro-3-(2-azetidinylmethoxy)pyridine; D000596:Amino Acids; D001384:Azetidines; D019086:Bridged Bicyclo Compounds, Heterocyclic; C579165:Chrna7 protein, rat; C513163:N-(1-azabicyclo(2.2.2)oct-3-yl)furo(2,3-c)pyridine-5-carboxamide; D018722:Nicotinic Agonists; D011725:Pyridines; D011812:Quinuclidines; D011978:Receptors, Nicotinic; D017661:Receptors, Presynaptic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C403531:nicotinic receptor alpha4beta2; D009538:Nicotine; D005998:Glycine