ON THE ANATOMY OF THE GIANT NEURONS 

 OF THE VISCERAL GANGLION OF APLYSIA 



Theodore H. Bullock 



Department of Zoology, University of California, Los Angeles 



The beautiful photomicrographs and electrical records shown by Arvanitaki 

 and Chalazonitis to this meeting and the remarkable evidence of Tauc (1960) 

 of several kinds of inhibition in the giant neurons of the visceral ganglion of 

 Aplysia point to the great value of this preparation. I am sure we will be 

 hearing much more about it. 



One of the reasons for its interest is the indication of localized activity in 

 various fractions of the membrane electrically visible to a micropipette in the 

 soma. Besides large and small synaptic potentials, excitatory and inhibitory, 

 Tauc has reported various sized small spike-like potentials and pacemaker 

 potentials that are sometimes closer, sometimes farther from the recording 

 electrode tip. Both of the French laboratories have also noted a curious 

 synchronization of adjacent cells at times. 



These and other properties attract attention to the anatomy of the ganglion 

 and particularly of the giant cells and fibers. Arvanitaki, Cardot and Tchou 

 (1941, 1942) have given us the little that is available beyond the gross anatomy 

 of earlier authors (see Hoffmann, 1932-1939). 



The following observations are supplementary to these and, although 

 preliminary, may call attention to the opportunities inherent in this material. 

 The electron microscope work was done by Dr. Elizabeth Batham of the 

 University of Otago, while visiting in our department, and the electrical 

 neuronography by a graduate student, Mr. Lawrence Goldman. 



The visceral ganglion is seen in ordinary histological sections (Fig. 1) to be 

 a typical molluscan ganglion in the following respects. A central core of 

 fibrous matter is surrounded by a rind of cell bodies. Continuous with the 

 core are the two great pleurovisceral connectives, right and left and several 

 large peripheral nerves. The core presents two aspects — tracts consisting of 

 fibers of passage and neuropile distinguished by its finer, more tangled 

 texture. The rind consists of unipolar cells of widely varying sizes, numbering 

 several hundreds, all with large nuclei poor in chromatin and with distinct 

 cytoplasm. Few or no granule-type or globuh-type cells — very small, 



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