Determinations of nerve and glial cell volumes in histological sections

Abstract

Summary A method is described for determination of nerve and glial cell volumes in usual histological sections. The brain or spinal cord are split into two halves along the midline. Following simultaneous histological treatment both halves are embedded in the same paraffin block in such a way as to obtain transverse sections from one half and sagittal sections from the other. In transverse sections major (a) and minor (b) axes of cell body or nucleus are measured, while sagittal sections are used for measuring the third axis (c). From the mean lengths of the axes their ratio is estimated to deduce an expression for calculating the c axis from a and b values. The volume can then be calculated from two-axis measurements using the three-axis ellipsoidal formula. In such a way, rat spinal motoneurones, Deiters' neurones and layer V motor cortex pyramids were investigated. As judged from optical reconstruction, the neuronal volume can be determined from two axes by the following equations: V = 1/6π ab [(a + b)/3] (for motoneurone soma); V = 1/6π ab √ab (for Deiters' neuronal soma); V = 1/6π ab √a2−b2 (for cortical pyramidal soma); V = 1/6π ab2 (for motoneurones and Deiters' neuronal nucleus). The nuclear volumes of perineuronal glia can be calculated according to the formula V = 1/6 π a2b for satellites of spinal motoneurones or Deiters' neurones, and V = 1/6 π ab2 for satellites surrounding cortical pyramids.