A COMPARISON OF CHOLINESTERASE DISTRIBUTION IN THE CEREBELLUM OF SEVERAL SPECIES *

PREVIOUS efforts in this laboratory have been directed toward systematic mappings of oxidative enzyme activity in the brain. A comparison of the distribution patterns of enzymes involved in glycolysis, citric acid cycle, and hexose-monophosphate shunt revealed almost monotonous similarity both among enzymes and among species; differences were subtle and observed only upon careful scrutiny (FRIEDE, FLEMING and KNOLLER, 1963). In contrast, the present article reports on an almost bewildering species variability in the distribution of acetylcholinesterase (AChE)? and non-specific cholinesterase (ChE)? in the cerebellum. The discussion of these observations lead to somc basic conclusions regarding central synaptic organization. Also, these findings demonstrate the fundamental importance of complete systematic mappings for a just study of the complex chemical architecture of the brain. MATERIAL AND METHODS The following species were used in this study: human, squirrel monkey, cat, cow, rabbit, rat, squirrel, hamster, mouse, pigeon, canary, and parakeet. At least four brains of each species were studied with the exception of monkey and canary, which two brains were available for each. The human material was from normal brains obtained between 5 and 10 hr after death. The animals were either anaesthesized with sodium pentobarbital, or decapitated, and the brains immediately removed. The procedure was as follows: 1) Blocks 2-3 mm thick were fixed in 10% neutral formalin at 4" for 3-4 hr. 2) 30p frozen sections were placed back into formalin for 30 min. 3) Sections were thoroughly washed in two changes of 0.4 M-tris-HC1 buffer, pH 7.0, at 4" for 6&90 min. Thorough rinsing was important for removing formalin which interferes with the reaction (HOLMSTEDT, 1957). 4) The inhibitor control sections were treated at room temperature for 30 min in M inhibitor solution in 0.4 M-tris-HCI buffer, pH 7-0. M solutions were prepared from lo-' M stock solutions. Eserine and BW stock solutions were aqueous and stored at 4"; DFP stock solution was in anhydrous propylene glycol, stored in a desiccator at room temperature. Inhibitor studies were done only for AChE, and the sections were transferred directly from the inhibitor solution to acetylthiocholine iodide incubation medium containing M of the inhibitor. 5) The composition of the incubation media based on the GEREBTZOFF (1959) method was: 0.2 M-tris-maleate buffer, pH 6.6, 44.0 ml; 3.75% glycine, 1.0 ml; 0.1 M-cupric acetate, 1.0 ml; acetyl or butyryl thiocholine iodide, 4.0 ml. All solutions were made up in glass distilled water; the