Interpretation of Freeze-Fracture Replicas of Insect Nervous Tissue

Abstract

Freeze-fracture (FF) replication is an important method for visualizing, at high resolution and in three dimensions, ultrastructural topography of membranes and organelles in hydrated cells without the intervention of embedding media and with little or no chemical fixation. The tissue replicas provide extensive vistas of cleaved membranes. This remarkable technique, which splits unit membranes, also permits resolution of macromolecular architecture of biological membranes particularly with reference to the location of membrane proteins. When correlated with thin section EM, FF confirms and greatly extends our knowledge of specialized intercellular contacts. Observations of the latter provide essential data for cell biology: intercellular adhesion, low resistance metabolic and electronic coupling, chemical transmission and paracellular occluding barriers. The FF technique has also proved invaluable for understanding the nature and location of electrical and chemical junctions.