Three-dimensional reconstruction of specialized endoplasmic reticulum in neurons of the rat substantia gelatinosa

Specializations of the agranular endoplasmic reticulum have been observed in neurons of the rat substantia gelatinosa. Three-dimensional models of immature and mature forms were reconstructed from stereomicrographs obtained with the high voltage electron microscope. The immature specializations consisted of two or more parallel, interconnected agranular cisternae with an electron dense material between adjacent cisternal walls. Mature specializations appeared whorl-like in cross-section. Throughout differentiation and maturity, the specialized agranular cisternae are connected to subsurface cisternae by the granular endoplasmic reticulum. These structures may play a role in chemical storage or synthesis.