The Journal of Neurophysiology Vol. 81 No. 1 January 1999, pp. 111-120
Copyright ©1999 The American Physiological Society

Developmental Changes in the Nicotinic Responses of Ciliary Ganglion Neurons

Edward M. Blumenthal, Richard D. Shoop, and Darwin K. Berg

Department of Biology, 0357, University of California, San Diego, La Jolla, California 92093

Blumenthal, Edward M., Richard D. Shoop, and Darwin K. Berg. Developmental changes in the nicotinic responses of ciliary ganglion neurons. J. Neurophysiol. 81: 111-120, 1999. The accumulation of functional neurotransmitter receptors by neurons during development is an essential part of synapse formation. Chick ciliary ganglion neurons express two kinds of nicotinic receptors. One is abundant, contains the 7 gene product, rapidly desensitizes, and binds -bungarotoxin. The other is less abundant, contains multiple gene products (3, 4, 5, and 2 subunits), slowly desensitizes, and binds the monoclonal antibody mAb 35. Rapid application of agonist to freshly dissociated neurons elicits responses from both classes of receptors. Between embryonic days 8 and 15, the whole cell response of 3-containing receptors increases fivefold in peak amplitude and, normalized for cell growth, 1.7-fold in current density. In addition, the response decays more slowly in older neurons, suggesting a developmental decrease in the rate of desensitization. The whole cell response of 7-containing receptors increases 10-fold in peak amplitude over the same period and 3-fold in current density. No change in the rate of desensitization was apparent for 7-containing receptors with developmental age, but analysis was limited by overlap in responses from the two kinds of receptors. Indirect immunofluorescence measurements on dissociated neurons showed that the relative levels of 7-containing receptors on the soma increased during development to the same extent as the whole cell response attributed to them. In contrast, the relative levels of 3-containing receptors increased more during the same time period than did the whole cell response they generated. The immunofluorescence analysis also showed that both classes of receptors become distributed in prominent clusters on the cell surface as a function of developmental age. The results indicate that during this period of synaptic consolidation on the neurons, the two major classes of functional nicotinic receptors undergo substantial upregulation; 3-containing receptors as a class may undergo changes in receptor properties as well.

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