人脳におけるAcetyl CholinesteraseとNAD-diaphoraseの組織化学的分布の比較

A Histochemical Study of the Distribution of Acetyl Cholinesterase and NAD-diaphorase Activities in the Human Brain

I．まえがき

　中枢神経の酵素化学的構築を研究するには，種々の接近法がある：ある部分のできるだけ多数の酵素活性を測り，可能な物質代謝経路を明らかにしようとする方法。もう一つの接近法は解剖学的構造に重点をおきながら，脳のなかのある酵素の局所分布を画く方法である。後者の方法は種々の神経核や伝導路の比較的酵素活性の"格づけ"を行なうことになる。

　われわれは組織化学的方法を用い，人脳における二つの酵素の分布を比較研究した。そのさいとくに脳幹部の解剖学的構造との関連に重点をおいた。その酵素の一つ，NAD-diaphoraseの分布はすでに報告がある^1）が，Acety Cholinesterase（AChe）の人脳の記載はなおふじゅぶんである。ゆえにACheに関する記載に重点をおいた。

　egional distribution of Acetyl Cholinesterase (AChe) and NAD-diaphorase (NAD-d) of the human brain, especially that of diencephalon and brain stem was described and compared with each other using histochemical slides.

　It is hoped that documentation of these enzyme patterns will help in understanding the functional organization of the human brain. As a working hypothesis one may assume that the distribution of NAD-d activity is an approximate parameter of regional differences among brain centers of tissue oxidation or at least of certain phase of tissue oxidation. and that centers containing marked AChe activity do indeed have more active acetylcholine metabolism than do centers with little activity.

　The striking dissimilarities in the regionaldistribution of NAD-d and AChe represent an interesting aspect of functional differentiations of centers and fiber tracts in the human brain.

　One shortcoming of a histochemical mapping, such as cne reported here, is the lack of quantitation of regional enzyme patterns. This shortcoming has been overcome for a few histochemical methods, e. g. for NAD-d (Friede et al, 1963) which can be quantitated by extraction and spectrophotometric determination of the amount of formazan formed in the tissue by the histochemical reaction, using small discs punched from the tissue sections. No such method is available for the histochemical quantitation of AChe activity. Yet, an accurate record of the topographic distribution of activity among and within centers can be as important as quantitation. For example, a detailed account of the distribution of enzyme activity in the crisscrossing fiber bundles of the pons and its regional and cellular variation in the islands of pontine gray matter will give more insight into the functional organization of the pons than an assay of the whole pons, or selected constituents, could give. The validity of histochemical estimates of AChe activity was tested by constant reference to and comparison with biochemical data in human or animal material. The ideal approach for studying regional chemical patterns in the brain is to combine assays and histochemical methods whereby the latter may guide the sampling for the former.

　The significance of marked differences of AChe activity in fiber tracts can be explained best by the theory that axons containing marked AChe activity originate from cell bodies with marked AChe and vice versa, and that axonal AChe contributes substantially to the activity in the neuropil of the nuclei in which the AChe-containg fibers terminate.

　This concept has been supported by transection experiments and many observations in the human brain.