Permanence of postsynaptic specializations in the frog sympathetic ganglion cells after denervation

Summary The junctional complex of the axosomatic synapses in the frog sympathetic ganglion is formed by active zones and attachment plates. 16% of the active zones present a dense band or subsynaptic formation on the postsynaptic side. Seven days after the preganglionic fibers have been cut, most of the axon terminals in the ganglion undergo degeneration. The junctional complex is broken by glial cytoplasm, which separates the axon terminals from the neuronal perikaryon. Two distinct morphological types of axonal degeneration are found at this stage: 1. dark and shrunken boutons with a honeycomb appearance, and 2. clear and swollen boutons. These two morphological varieties are interpreted as different aspects of the same degenerative process of the spiral apparatus. Ten days after transection of the preganglionic fibers, most of the degenerating axon terminals have disappeared, and only dark bodies, remnants of such endings, are seen in the glial cytoplasm. Twelve days after the experimental lesion, almost all the axon terminals have disappeared. In all three stages of survival the subsynaptic structures, postsynaptic differentiation and subsynaptic formation, remain unchanged. It is suggested that these structures are not intimately related to the functional integrity of the axon terminals.To the memory of Prof. Fernando de Castro