Abstract
Histochemical localization has confirmed that both the heart muscle and the cardiac ganglion along with its branches have cholinesterase activity. Acetylcholinesterase (AChE) is localized in the nerve fibers of the cardiac ganglion and its side (segmental branch) nerves and in the lateral nerves, but AChE could not be demonstrated in the cytoplasm of the ganglionic cell bodies. The dorsal cardioregulatory nerves (segmental cardiac nerves), arising in the central nervous system, also stain intensely for AChE. Butyrylcholinesterase is localized in the cardiac muscle tissue. The presence of intensely staining AChE in the cardiac ganglion and its branches, the lateral nerves and the cardioregulatory nerves sustains the notion that a cholinergic system is involved in the regulation of the Limulus heart.