FURTHER OBSERVATIONS OF ULTRASTRUCTURE OF SYNAPTOSOMES SEPARATED FROM SPINAL-CORD AND MEDULLA, WITH ESPECIAL EMPHASIS ON POSTSYNAPTIC MEMBRANE

Synaptosomes from the rat medulla and spinal cord were examined [by electron microscopy] in an attempt to formulate morphological criteria for distinguishing between those found in 2 subfractions of P1 (nuclear fraction). The mean diameter of those in the lighter of the subfractions (P1C) was 0.6 .mu.m, with a preponderance in the range 0.4-0.6 .mu.m and a minor peak at 0.7-0.8 .mu.m. Subjunctional bodies were associated with 60.2% of the junctional regions in this subfraction. Those in the heavy subfraction (P1D) had a larger overall diameter (0.7 .mu.m) and a greater percentage of them had visible junctional regions (68.1% opposed to 51.6%), but of the junctional regions a lower percentage had associated subjunctional bodies (36.2%). The subjunctional bodies consisted of a central core with 5 spokes radiating from it. The tips of the spokes were connected by fine strands which connected individual bodies to neighboring ones and to the postsynaptic thickening. The persistence of subjunctional bodies in synaptosomes highlighted the strength of the attachment between them and the postsynaptic thickening, and suggested that these bodies may be integral components of the postsynaptic thickening complex. They may also help in the formulation of criteria by which different populations of these synaptosomes may be separated from each other.