Research in Progress 
in the Howard Hughes Medical Institute, 1991 
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Visualization of phosphorylation of tyrosine residues in the nicotinic acetylcholine receptor at 
cholinergic synapses in the electric organ (electroplax) of the electric ray Torpedo. The electro- 
plax were immunofluorescently labeled with rhodamine- coupled a-bungarotoxin to localize the 
receptor (red) and with antibodies to phosphotyrosine to localize phosphotyrosine residues 
(green). The two fluorescent signals are superimposable; however, they have been artificially 
separated to allow a side-by-side comparison of the labeling patterns. Tyrosine phosphorylation 
of the nicotinic receptor in the postsynaptic cell is regulated by the innervating neuron and plays 
a role in regulating the sensitivity of the receptor to its neurotransmitter and in clustering the 
receptor beneath the nerve terminal. 
Research of Richard L. Huganir. 
Copyright © 1991 by the Howard Hughes Medical Institute 
All rights reserved. Address correspondence to 
Dr. W. Maxwell Cowan 
Vice President and Chief Scientific Officer 
Howard Hughes Medical Institute 
Printed in the United States of America 
