A multiple Golgi analysis of the periaqueductal gray in the rabbit

Four variants of the Golgi method have been used, in the rabbit, to reveal the morphological attributes of neurons within the periaqueductal gray. Of these methods, the Golgi-Cox version provided the most satisfactory results in terms of both quality and quantity of cell impregnation. In order to make comparison with other descriptions of Golgi characteristics of the periaqueductal gray, statistical analysis was carried out on the distinguishing features of individual neurons, following two different rationales. One method, primarily based on soma characteristics (shape, area, length, and width) and basic features of the primary dendrites (number, length, and number of end-points) resulted in nine different categories of neurons being recognized: round, ovoid, spindle, pyriform, triangular, pyramidal, rhomboidal, polygonal, and stellate shaped cells. The alternative method principally characterized neurons by an assessment of the degree of dendritic spine development and prominent features of the dendritic tree (number of primary dendrites, length, number of branches, end-points, and degree of spine development). This approach resulted in nine subgroups within three major classes being identified: three spiny, four moderately spiny, and two aspiny classes (subdivision of each of the groups being resultant on neuronal size and/or the degree of dendritic branching). There was no similarity between the nine groups found by the two methods. Some, though little, correlation of neuron type was evidenced with respect to four zonal subdivisions of the periaqueductal gray complex. It remains to be seen how any of these readily recognizable morphological features, or the subgroups (derived on a statistical basis) into which they fall, might be shown to relate to function.