Alpha-bungarotoxin receptors in the chick ciliary ganglion: behaviour in vivo and in vitro

Cholinergic nicotinic receptors have been investigateci in the ciliary ganglion of adult chick by means of ['•"IJa-bungarotoxin binding to whole and homogenized ganglia. The behaviour of receptors has been compared in vivo (after simultaneous pre- and postganglionic axotomy) and in nitro (ganglia in organ culture). A decrease in receptor number was found both in vivo and in nitro, although the resulta dinered quantitatively in thè two cases. The loss of receptors was more evident in whole than in homogenized ganglia, suggesting that mechanisms of receptor degradation and masking may occur simultaneously. Additional experiments m vitro indicate that the behaviour of thè receptors is influenced by inhibitors of energy metabolism (dinitrophenoi plus iodoacetic acid, sodium cyanide) but not by an mhibitor of protein synthesis (cycloheximide). Thè receptor modifications in vitro are accompanied by a decrease of other cholinergic markers, such as acetylcholinesterase and cholinacetyltransferase activities. Morphological investigations of organ-cultured ganglia indicate that thè biochemical modifications descnbed above are not due to significant degenerative changes of ganglionic neurons. The results indicate that thè a-bunga'rotoxin receptors behave rather similarly in vivo and, under our conditions, in vitro and suggest a dependence of these receptors on peripheral signals. These signais wouid appear to be mediated by energy-dependent processes without thè synthesis of proteins being required.