Cholinesterase in Rhodnius is limited to the neuropile, the nerve-roots, and the larger nerves. None is present in the axons; it seems to be confined to the interneuronal cytoplasm, the product of the glial cells. The intensity of the reaction is greatest in the synaptic regions and appears to be proportional to the amount of interneuronal material.

The ganglion cells contain traces of a non-specific esterase; and larger amounts of non-specific esterase occur in the glial layer between the cells. A similar enzyme is plentiful within the perineurium cells.

Non-specific esterases occur in many other tissues: salivary glands and alimentary canal, pericardial cells, haemocytes, oenocytes, dermal glands and epidermal cells, germ-cells and fat-body. Esterase is absent from the muscle endplates. The cytoplasmic localization and the reaction of these enzymes to inhibitors are described.

In the fat-body, each droplet of fat has a single well-defined ‘cap’ of esterase, presumably lipase. It is suggested that this controls the transfer of triglycerides to and from the storage vacuoles. Esterase is not associated with the mitochondria; but there is evidence that the enzyme may be disposed as fine filaments, particularly over the surface of the nucleus. Some of these widely distributed ‘esterases’ may be cathepsins.

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