A LIGHT AND ELECTRON-MICROSCOPE STUDY OF THE CONNECTIONS BETWEEN THE PREGANGLIONIC FIBERS AND THE INTRALINGUAL GANGLION-CELLS IN THE RAT

The topographical distribution of the preganglionic neurons sending pr ojection fibers to the tongue, and the connections between their fiber s and the intralingual ganglion cells, were examined in the rat. When horseradish peroxidase injections were made into the anterior two-thir ds of the tongue, labeled neuronal cell bodies were distributed mainly in the lateral reticular formation at the level between the rostral p art of the facial nucleus and the caudal part of the superior olivary complex. On the other hand, after horseradish peroxidase injections in to the posterior one-third of the tongue, labeled neuronal cell bodies were found mainly in the rostromedial part of the nucleus of the soli tary tract, and additionally in the lateral reticular formation just v entral to the rostral part of the nucleus of the solitary tract. In bo th cases, labeled neuronal cell bodies were always found in the hypogl ossal nucleus. The anterograde tracing study with Phaseolus vulgaris-l eucoagglutinin or Fluoro-ruby confirmed the topographical organization suggested by the retrograde tracing study; when the tracer injections were centered on the lateral reticular formation at the level of the rostral part of the facial nucleus or on the rostral part of the nucle us of the solitary tract, labeled fibers distributed mainly in the ant erior or posterior or part of the tongue, respectively. It was also sh own that the axon terminals of the preganglionic fibers labeled with F luoro-ruby made close contacts with the intralingual ganglion cells im munopositive for neuron specific enolase. The electron microscopy comb ined with the anterograde tracing method with biotinylated dextran ami ne further indicated that the preganglionic fibers made synaptic conta cts with the soma and dendritic processes of the intralingual ganglion cells.