Distribution and synaptic localization of nicotinic acetylcholine receptors containing a novel alpha7 subunit isoform in embryonic rat cortical neurons.

摘要

Neuronal nicotinic acetylcholine receptors (nAChRs) containing the alpha7 subunit isoform, alpha7-2 (alpha7-2-nAChRs), have previously been found to form functional homopentameric channels that desensitize slowly and bind alpha-bungarotoxin (alphaBgt) in a rapidly reversible manner. This isoform incorporates a novel cassette exon in the extracellular, ligand binding domain of the native receptor. Although this alpha7 subunit isoform has been detected in peripheral ganglia as well as in the central nervous system, little is known about the cellular function of alpha7-2-nAChRs. Co-localization immunocytochemical studies were conducted in an embryonic rat cultured cortical neuron model using a polyclonal antibody (Ab 87) raised against the amino acid sequence of the cassette exon, in combination with (1) an antibody that recognizes all known alpha7-nAChRs, (2) alphaBgt, and (3) antibodies directed against multiple cellular markers. The pattern of alpha7-2-nAChR expression was consistent with alpha7 staining in general, based on co-distribution of mAb319 and alphaBgt signals. However, alpha7-2-nAChRs clearly represent a distinct subset of alpha7 receptors. The alpha7-2-nAChR subtype was found throughout the cell-soma surface and was localized to a subpopulation of dendrites. Punctate staining characteristic of synaptic alpha7-2 targeting was observed at post-synaptic densities and intermittently at pre-synaptic locations. The alpha7-2 subunit was expressed on both GABAergic and non-GABAergic neurons. These studies reveal that receptors containing the alpha7-2 subunit constitute a subpopulation of alpha7-nAChRs and likely participate in cell-to-cell signaling in developing synapses of central neurons.