Distribution of acetyl cholinesterase in the hippocampal region of the guinea pig

The subiculum appeared almost identical in the two species, while in the hippocampus essential differences were observed in stratum lacunosum-moleculare and oriens, and a possible correlation of the AChE content to fibre systems known from normal material is considered in detail.

Abstract

1. The distribution of acetyl cholinesterase has been examined in the guinea pig in three areas belonging to the hippocampal region, viz., the entorhinal area, the parasubiculum, and the presubiculum. 2. Formaldehyde-fixed serial frozen sections and unfixed cryostat sections were subjected to a modification of the Koelle thiocholine method. Ethopropazine was used to suppress non-specific cholinesterase. One series of sections was processed according to the copper ferricyanide method of Karnovsky and Roots (1964). 3. In each area the obtained staining displayed a specific pattern of stratification, ceasing at the transition to neighbouring areas. The distribution in the guinea pig has been compared with that in the rat, previously described. 4. The deep part of the cortex was similar with regard to AChE in the three areas, comprising a well-stained layer IV, a paler layer V, and a moderately dark layer VI. 5. In the entorhinal area two subfields were discernible. One termed pars medialis has a very distinct stratification of precipitate; in the other, pars lateralis, a different and much less conspicuous stratification is seen. In pars medialis relative absence of enzyme in layer III and abundance in layer IV are the most striking features. The similarity with the rat is considerable.