Appearance of new alpha-bungarotoxin-acetylcholine receptors in cultured sympathetic ganglia of chick embryos

Expression of nicotinic acetylcholine receptors in the rat superior cervical ganglion on mRNA and protein level

The expression of nicotinic acetylcholine receptors (nAChR) in the rat superior cervical ganglion was investigated by Western blotting, immunohistochemistry and non-radioactive in situ hybridization applying probes for the alpha 4-1 and beta 2 subunit mRNA. Immunoblot analysis of homogenized ganglia using the anti-nAChRs antibody WF6 revealed a labeled protein band of apparent molecular weight of 40 kDa which is typical for the alpha subunit of nAChRs. Applying double-labeling immunofluorescence with antibodies against tyrosine hydroxylase, nAChR-like molecules were identified in most postganglionic neurons and in a subpopulation of small intensely fluorescent (SIF) cells. alpha 4-1 and beta 2 subunit mRNAs were detected in all perikarya of postganglionic sympathetic neurons but not in SIF cells. These results suggest that antibodies raised against purified Torpedo AChR bind to nAChR in sympathetic ganglia and indicate that alpha 4-1 and beta 2 subunits are constituents of nAChRs in sympathetic postganglionic neurons but not of SIF cells.

Distribution of muscarinic receptors on cultured myenteric neurons

The distribution of neurotransmitter receptors over the neuronal cell surface remains an outstanding question in neurobiology. In this study we have used autoradiographic procedures to localize muscarinic receptors on living cultures of enteric neurons, using the specific irreversible muscarinic ligand, [3H]propylbenzilylcholine mustard ([3H]PrBCM). Most of the label was associated with nerve processes surrounding the cell bodies and along the lengths of many of the neurites radiating from the cell bodies; a small proportion of the nerve cell bodies was also seen to be labeled. The distribution of autoradiograph silver grains along both varicose and non-varicose neurites demonstrated that muscarinic receptors were present on both pre-terminal and terminal regions of the nerve fibres.

Extra-synaptic localization of alpha-bungarotoxin receptors in cultured chick ciliary ganglion neurons

Surface [125I]alpha-bungarotoxin receptors were localized on dissociated cultures of embryonic chick ciliary ganglion neurons by electron microscopic autoradiography. Grain density was 4-5-fold higher on cell body membrane versus neuritic process membrane, and there was no apparent concentration of grains at morphologically identifiable inter-neuronal synapses.

Histological localization of binding sites of alpha-bungarotoxin and of antibodies specific to acetylcholine receptor in goldfish optic nerve and tectum

Goldfish optic nerve as well as ganglion cell neurites grown in culture selectively bind rhodamine-labeled alpha-bungarotoxin following tissue fixation. Binding is competed for by unlabeled bungarotoxin, by carbamylcholine and tubocurarine, but not by atropine. In cross-sections, the label is seen confined to axonal bundles. The binding is not detectable without prior fixation and is very faint in brain sections, even after fixation. To further establish the nature of the binding, immunocytochemical studies were performed, taking advantage of a high cross-reactivity found between goldfish brain and antibodies against eel acetylcholine receptor (AChR). Antigenic sites were detected by an indirect unlabeled antibody complexed to horseradish peroxidase. Anti-AChR antibody binding to optic nerve and neurites in culture correlated with that seen with alpha-bungarotoxin. Binding of anti-AChR was observed in the brain, and was reduced in the denervated tectum following unilateral optic nerve crush or enucleation. The results are discussed in relation to functions of receptor proteins in the retinotectal system.

Isolation of rat brain subcellular fraction enriched in putative neurotransmitter receptors and synaptic junctions

A simple reliable method was developed for the rapid isolation of a synaptic plasma membrane-enriched fraction from rat brain. The procedure involves the direct lysis of a crude mitochondrial fraction followed by a combined flotation-sedimentation density gradient centrifugation in a fixed-angle centrifuge rotor. All fractions have been characterized with respect to relative enrichment of (Na+-K+)ATPase activity as well as putative cholinergic neurotransmitter receptors determined by [125I]alpha-bungarotoxin and [3H]quinuclidinyl benzilate binding. The 2- to 4-fold relative enrichment of putative receptor binding sites correlated well with the 4-fold enrichment of morphologically identifiable synaptic junctions in the synaptic plasma membrane enriched fraction.