On the vegetative network of guinea pig thoracic spinal cord.

A dense AChE-positive network was visualized by light microscopy in the thoracic spinal cord of grown-up guinea pigs of both sexes (bodyweight 250-300 g). This network connects in a horizontal and vertical direction the preganglionic sympathetic nuclei (n. intermediolateralis pars principalis (ILp), n. intermediolateralis pars funicularis (ILf), n intercalatus spinals (IC), n. intercalatus pars paraependymalis (ICpe), (Petras and Cummings, 1972) all along the thoracic spinal cord. In addition to AChE activity, the bundles of fibers of this network also show a strong formaldehyde-induced NA fluorescence. Electron microscopy demonstrated granular vesicles in the cytoplasm of ILp cells. The surface of the ILp and IC neurons is almost entirely covered with synaptic bottons which have clear and granulated synaptic vesicles. The bundles of fibers consists of parallel myelin-free axones and dendrites. On their cource the axones form varicosities. In the varicosities and in the synaptic enlargements there are also clear and granulated (40-100 nm) vesicles. The probable origin of the vegetative network fibers of guinea pig thoracic spinal cord is discussed.