alpha7-Containing nicotinic receptors are segregated to the somatodendritic membrane of the cholinergic neurons in the avian nucleus semilunaris.
Segregation of ion channels and neurotransmitter receptors is an important mechanism for determining the functionality of the nervous system. In the case of nicotinic acetylcholine receptors, electrophysiological and anatomical studies have demonstrated that these receptors can be located at the somatodendritic and the axon terminal portions of neurons. Functionally, somatodendritic nicotinic receptors mediate fast excitatory transmission and possibly regulate other cell functions, while presynaptic nicotinic receptors enhance the release of neurotransmitters from axon terminals. Neurons in the mesencephalic lateral spiriform nucleus of the chick do not appear to restrict the localization of nicotinic receptors to specific membrane compartments, since receptors containing alpha5 and/or beta2 subunits are found both on the cell bodies and on the axonal projections of these neurons [Torrao A. S. et al. (1996) Brain Res. 743, 154-161]. We report here that, in contrast to lateral spiriform neurons, neurons in the nucleus semilunaris do appear to compartmentalize nicotinic receptors. The cholinergic nucleus semilunaris neurons express a high density of alpha7-containing nicotinic receptors on their somas [Britto L. R. G. et al. (1992) J. comp. Neurol. 317, 325-340]. However, when we examined the projections of these neurons in the lateral spiriform nucleus, we found no evidence for expression of alpha7-containing receptors on the cholinergic fibers from nucleus semilunaris neurons. Furthermore, patch-clamp electrophysiological recording from lateral spiriform neurons indicated an absence of presynaptic alpha7-containing nicotinic receptors capable of modulating the release of acetylcholine. We conclude that neurons are capable of segregating alpha7-containing nicotinic receptors to specific areas of their plasma membrane. Such targeting of nicotinic receptors would play an important role in determining their functional role in neurons.
Department of Pharmacology, The George Washington University Medical Center, 2300 Eye St. NW, Washington, DC 20037, USA. phmems@gwumc.edu
E M
EM
Sorenson
D G
DG
El-Bogdadi
Y
Y
Nong
V A
VA
Chiappinelli
D000157:Aconitine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001923:Brain Chemistry / Q000502:physiology*; D002645:Chickens; D002795:Choline O-Acetyltransferase / Q000032:analysis; D003712:Dendrites / Q000737:chemistry* / Q000201:enzymology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D018733:Nicotinic Antagonists / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000032:analysis* / Q000502:physiology; D013477:Superior Colliculi / Q000737:chemistry / Q000502:physiology; D064569:alpha7 Nicotinic Acetylcholine Receptor
D018691:Excitatory Amino Acid Antagonists; D018733:Nicotinic Antagonists; D011810:Quinoxalines; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C054634:methyllycaconitine; C056723:FG 9041; D002795:Choline O-Acetyltransferase; D000157:Aconitine