THE HISTOCHEMICAL DIFFERENTIATION OF TYPES OF CHOLINESTERASES AND THEIR LOCALIZATIONS IN TISSUES OF THE CAT

¹ Wilmer Ophthalmological Institute, Johns Hopkins University and Hospital, Baltimore, Md.

1. The rates of hydrolysis of several choline esters and their thio-analogues have been studied, using purified enzymes and homogenates of cat tissue. The effects of DFP, Nu 683 and Nu 1250 on specific and non-specific ChE's of the cat have been compared.

2. Based on the findings, a histochemical procedure for localizing ChE activity has been modified to permit the individual localizations of the two types of enzyme in cat tissues. The pH of the original incubation solution has been buffered to 6.4 to obtain sharper localization than was obtained previously.

3. Sites of specific ChE activity were stained by incubating tissues in 10^-6 M DFP, followed by incubation in a medium containing AThCh. BuThCh was used as the substrate for localizing non-specific ChE.

4. Sites of activity of the two types of enzymes in several tissues are described and illustrated. In general, regions of the central nervous system examined, skeletal muscle and smooth muscle in some regions were found to contain specific ChE almost exclusively, whereas the reverse was true in sensory ganglia, the adrenal pericapsular ganglia, the hepatic cells, the carotid body and smooth muscle from other sites. Both types of enzyme were revealed in most autonomic ganglia and effector cells.

5. Present results indicate that non-specific ChE plays a role in synaptic transmission similar to that of specific ChE at certain sites in the cat. Previous work which suggests this conclusion is reviewed.

6. Findings are discussed in relation to the older literature and to recent histological and physiological studies.

7. A statement is made concerning the possible pharmacological application of the present technique.

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