QUANTITATIVE-ANALYSES OF ANATOMICAL AND ELECTROTONIC STRUCTURES OF CRAYFISH NONSPIKING INTERNEURONS BY 3-DIMENSIONAL MORPHOMETRY

The three-dimensional structure of premotor nonspiking interneurons in the terminal abdominal ganglion of crayfish have been studied quantit atively by using a confocal laser-scanning microscope. Their passive m embrane properties have also been studied electrophysiologically to an alyze their electrotonic structure. In either one of the two major mor phological types, anterolateral (AL) and posterolateral (PL), that are characterized by different locations of cell bodies in the ganglion, the monopolar cell body is connected with a fine primary process to a thick main segment projecting numerous fine secondary processes. These two types of cells share a common dendritic field in the neuropil, sh owing similar anatomical characteristics of dendrites. Electrotonic an alyses based on the present anatomical and physiological measurements have revealed that the steady-state voltage-attenuation factors for th e secondary processes were not statistically different between the AL- and PL-type cells. Comparison between the premotor nonspiking interneu rons and an identified sensory nonspiking interneuron, which was studi ed previously, has revealed that voltage attenuation over secondary pr ocesses in both the centripetal and the centrifugal directions was sig nificantly greater in the sensory than in the premotor interneurons, a lthough the anatomical length of each secondary process from its termi nal to the main segment was not different between them. Differences in the electrotonic structure between sensory and premotor nonspiking in terneurons indicate their different modes of synaptic integration in t he control of postsynaptic nerve cells. (C) 1998 Wiley-Liss, Inc.