EXCITATORY TRANSMITTER SUBSTANCES

Publisher Summary This chapter discusses excitatory transmitter substances. The acetylcholine metabolism of sympathetic ganglia has been studied ever since the cholinergic nature of transmission was recognized. When the preganglionic nerve to the superior cervical ganglion is severed, the choline-acetylase in the distal segment virtually disappears in a few days, while there is even a transitory increase in the segment proximal to the section. Hence, it seems that the Ach manufacturing system is produced in the nerve cell and travels thence along the axon to the site of manufacture of ACh in the nerve terminals. The rate of synthesis is maintained at a high level even though the total Depot-acetylcholine (ACh) is not appreciably depleted. The ACh metabolism at neuromuscular synapses is much more difficult to investigate because they form a minute part of a nervemuscle preparation. ACh has been shown to be an excitatory transmitter at very few invertebrate synapses—for example, at neuromuscular synapses in the longitudinal muscle of the leech and in the retractor muscles of the holothurians.