Intracellular calcium and desensitization of acetylcholine receptors

Abstract

The effects of constricting post-ganglionic sympathetic nerves have been studied in the cat splenic nerve and guinea-pig hypogastric nerve. The results obtained using a fluorescence method for the histochemical localization of noradrenaline have been compared with electron microscopic findings. A close correlation was found between the accumulation of fluorescent material, attributable to noradrenaline, and of vesicles with an electron dense core (granular vesicles) believed to contain noradrenaline, proximal to the constriction in these nerves. This accumulation of noradrenaline was visible by 1 h after operation and increased rapidly in amount during the succeeding hours. It apparently reached a maximum after approximately 2 days and was found in what appeared to be newly formed axons 3 to 4 days after operation. Reserpine reduces the fluorescence and the number of vesicles with electron dense cores which accumulate proximal to the constriction. It is suggested, (1) that the fluorescent material is due, at least in part, to the presence of the granular vesicles, and (2) that the constriction has blocked the normal proximo-distal movement of noradrenaline which is believed to occur in post-ganglionic sympathetic axons.