The vegetative network in the thoracolumbar spinal cord of the guinea pig: a comparison of the distribution of AChE-enzyme activity and choline acetyltransferase-like immunoreactivity.

Histochemically the acetylcholinesterase (AChE) enzyme activity and immunocytochemically the choline acetyltransferase-like immunoreactivity (ChAT-LI) were located in the components of the vegetative network of the thoracolumbar spinal cord of the guinea pig. Both reaction products showed an identical distribution among the preganglionic sympathetic cells and the processes of the vegetative network, namely: cells of the nucleus intermediolateralis pars principalis (ILp), the nucleus intermediolateralis pars funicularis (ILf), the nucleus intercalatus spinalis (IC) and the nucleus intercalatus paraependymalis (ICpe; terminology according to Petras and Cummings 1972). In longitudinal horizontal sections through the intermediate zone of the thoracolumbar spinal cord both AChE-positive- and ChAT-like immunoreactive nerve fibers were organized into two longitudinal lateral fascicles (FLL), two longitudinal medial fascicles (FLM) as well as oblique and transverse bundles that interconnect repeatedly the autonomic cell groups of this zone along the spinal cord and contribute to the ladder-like shape of the vegetative network. The ChAT-like immunostaining of the vegetative network showed that the dendrites of the ILp cells are oriented mainly in a rostrocaudal, but also in a mediolateral direction. Similar orientation of the dendrites was observed for the ICpe cell groups of the thoracolumbar intermediate zone. Thus it is evident that ILp cell bodies and dendrites are involved in the formation of the FLL, whereas the ICpe cells and their dendrites--of the FLM. The IC cells send their dendrites towards both the ILp and ICpe cells and build up together with dendrites of the ILp and ICpe cells the transverse and oblique interconnecting bundles. The vegetative network is strongly developed within the intermediate zone of T1-T4 (mostly T3) and T7-T8 segments of the spinal cord. In these segments a greater variety of interconnections between the preganglionic sympathetic cell groups which are constituents of the network are also revealed. In the remaining segments the vegetative network is more poor developed. In the first two lumbar segments the distance between the interconnecting bundles in the rostrocaudal direction diminishes to 100 microns in contrast to 300-500 microns within the upper segments. The results obtained reveal that the cholinergic preganglionic sympathetic nuclei of the intermediate zone of the thoracolumbar spinal cord together with their dendrites represent the basis (frame) of the ladder-like vegetative network to which join in addition different peptidergic fibers of supraspinal, peripheral and propriospinal origin.