Gioia M, Tredici G, Bianchi R
Exp Brain Res. 1985;58(2):318-32. doi: 10.1007/BF00235313.
In Golgi material, the neurons of the periaqueductal gray matter (PAG) of the cat have been classified into five types, according to the following criteria: number of dendrites per cell, characteristics of secondary arborization, frequency of spines and axon caliber. Type 1 cells, which are multipolar and rich in spines are the most frequent, and are probably intranuclear neurons. Type 4 cells have a short axon which ends in the PAG, but they differ from Type 1 in that their dendritic ramification is of a different type and there are few spines. Type 2 and 3 neurons have a thick axon which runs outside the PAG, and dendrites rich in spines. Type 2 cells have more primary dendrites, while Type 3 neurons have dendrites which may spread outside the PAG. Type 5 cells have dendrites with few spines and no secondary ramification. Their thick and long axon projects outside the PAG. Type 2, 3 and 5 cells have been considered projective neurons. The various neuron types are present in every area of the PAG, although in the ventral region there is a predominance of Type 2 and 5 neurons, in the dorsal regions of Type 2 and 3 cells, and in lateral regions of Type 3 and 5 cells. Local intrinsic circuits have been observed in which both the interneurons and the projective, with early axonic collaterals, are involved. The prevalence of neurons to which an afferent role has been attributed (Type 2 and 3 cells) compared with efferent cells (Type 5), is in agreement with hodological studies which indicate that the PAG receives multiple and numerous afferents in comparison with the relatively scarce efferent fibers. These projections can be intensely and deeply elaborated and modulated by means of local intrinsic circuits.
在高尔基染色材料中，根据以下标准，猫中脑导水管周围灰质（PAG）的神经元已被分为五种类型：每个细胞的树突数量、二级分支的特征、棘突的频率和轴突直径。1型细胞多极且富含棘突，最为常见，可能是核内神经元。4型细胞有一条短轴突，终止于PAG内，但它们与1型细胞的不同之处在于其树突分支类型不同且棘突较少。2型和3型神经元有一条粗大的轴突，延伸至PAG之外，且树突富含棘突。2型细胞有更多的初级树突，而3型神经元的树突可能延伸至PAG之外。5型细胞的树突棘突较少且无二级分支。它们粗大且长的轴突投射至PAG之外。2型、3型和5型细胞被认为是投射神经元。尽管在腹侧区域2型和5型神经元占优势，背侧区域2型和3型细胞占优势，外侧区域3型和5型细胞占优势，但各种神经元类型存在于PAG的每个区域。已观察到局部内在回路，其中中间神经元和具有早期轴突侧支的投射神经元均参与其中。与传出细胞（5型）相比，具有传入作用的神经元（2型和3型细胞）的优势，与束路学研究一致，该研究表明与相对稀少的传出纤维相比，PAG接受多种且大量的传入纤维。这些投射可以通过局部内在回路进行强烈而深入的精细加工和调节。
