Electron microscopic studies of serially sectioned cat spinal α-motoneurons. II. A method for the description of architecture and synaptology of the cell body and proximal dendritic segments



The paper presents a method for ultrastructural analysis and description of neuronal architecture and synaptology of cat spinal α-motoneurons from complete series of consecutive ultrathin sections through the cell body and proximal parts of the dendrites. The method implies that sections are selected for analysis only at certain constant intervals in the series. The occurrence of boutons of different morphological types on the neuronal surface was expressed by their percentage covering of the neuronal membrane. The neuronal surface was divided into a number of compartments and the synaptic covering was calculated separately for each compartment. An interval of 6 μm between the sections was used for these calculations, and the obtained values for synaptic covering were found not to differ significantly from those obtained in controls at 3 μm intervals. The number and location of individual large boutons (C- and M-types) were studied at 3 μm section intervals, and the escape of boutons connected to this procedure was estimated from control observations at 1 μm intervals. It is concluded that detailed information on neuronal synaptology can be obtained with this method, which will be used in three subsequent studies on functionally identified and intracellularly stained cat α-motoneurons.