The distribution of acetylcholine receptors in chick ciliary ganglion neurons following disruption of ganglionic connections

Abstract

Chick ciliary ganglion neurons have nicotinic acetylcholine receptors (AChRs) that mediate primary chemical synaptic transmission through the ganglion. Previous studies have shown that preganglionic denervation reduces the total number of AChRs in the ganglion about 3-fold in 10 d, while postganglionic axotomy reduces AChR levels about 10-fold in 5 d. Since the neurons contain large numbers of intracellular AChRs in addition to the surface AChRs, the present studies were undertaken to determine whether either surface or internal AChR pools are changed selectively by the operations. An anti-AChR monoclonal antibody followed by an HRP-conjugated secondary antibody was used to visualize AChR distributions on neurons in ciliary ganglia 5 d after postganglionic axotomy and 10 d after preganglionic denervation. Ganglia were permeabilized by treatment with saponin to obtain access to intracellular receptors. The results show that the operations do not qualitatively change the subcellular localization of AChRs, but they do alter the levels relative to control ganglia. Axotomy produces substantial declines both in the number of synaptic AChRs and in the number of intracellular AChRs. Denervation produces a significant, though less extensive decline in the number of intracellular receptors while having no detectable effect on the number of synaptic AChRs. Small alterations in receptor distribution would have gone undetected by the present techniques. Regulation of neuronal AChRs differs in several respects from that described for muscle AChRs: presynaptic input appears to be less important for controlling neuronal AChRs, while signals from the postsynaptic target tissue may be essential for maintaining synaptic receptors on the neurons.