The reticulo-raphe connection. An experimental study using the method of antegrade degeneration and the method of retrograde horseradish peroxidase transport tracing in the rat.

The method of antegrade degeneration (23 rats) and the method of retrograde HRP transport tracing (7) rats were used for a study of the reticulo-raphe connection. Electrolytic lesions were induced using the stereotactic technique (DC 0.1 mA, 5-10 mV, 5-10 secs). A Hamilton syringe was used for the HRP injections (0.1 microml 30% HRP, Sigma VI, for 45 mins). Literary data so far known were corroborated, and new information was added concerning projections to the raphe nuclei and the discovery of a reticulo-raphe projection coming also from the nuclei of the oblongata. The whole reticulo-raphe connection was found to be organized in the descending direction. The medial reticular formation nuclei were seen projecting to all the raphe nuclei at the corresponding level, and to all the more caudalward localized raphe nuclei. A very low intensity projection from the lateral reticular formation nuclei to the raphe system was found. The retrograde method showed mainly medium sized reticular neurones to be involved in the reticulo-raphe connection. Large and giant neurones were never found labeled in the experiments. The medial reticular formation neurones were always labeled less intensively compared with the intensity of the benzidine reaction in the neurones of the raphe system nuclei (mainly the ncl. raphealis dorsalis and ncl. linearis caudalis).