[Chemical neuroanatomy of cholinergic neurons]

Acetylcholine (ACh), the first neurotransmitter to be discovered from the frog heart, is distributed widely in both the central and peripheral nervous systems. In the brain, for example, ACh plays important roles in several higher functions such as memory and learning. In peripheral organs, ACh has been shown to be a neurotransmitter in spinal motoneurons, all autonomic preganglionic neurons, all parasympathetic postganglionic neurons, and an exceptional sympathetic postganglionic neurons innervating the sweat gland. There has been, however, no good method to visualize ACh in tissues and organs. So far, immunohistochemistry for its synthetic enzyme choline acetyltransferase (ChAT: E. C. 2. 3. 1. 6) has been used as the most reliable marker for morphological studies of cholinergic neurons. Despite the fact that most antibodies against ChAT clearly stain central cholinergic systems, they have poor ability to detect peripheral cholinergic systems. We found that there are two types of ChAT expressed in the rat pterygopalatine ganglion. One is identical to the ChAT in the brain, and another (pChAT) lacks exons 6, 7, 8, and 9. The peripheral cholinergic system is now clearly demonstrated by immunohistochemistry using our antiserum raised against the recombinant pChAT.