LABELING OF NEURONS IN THE RAT SUPERIOR CERVICAL-GANGLION AFTER INJECTION OF WHEAT-GERM-AGGLUTININ HORSERADISH-PEROXIDASE INTO THE CONTRALATERAL GANGLION - EVIDENCE OF TRANSNEURONAL LABELING

Recent studies have shown that injection of the tracer wheat-germ aggl utinin-horseradish peroxidase (WGA-HRP) into the superior cervical gan glion (SCG) of one side results in labelling of neurons in the contral ateral SCG and the stellate ganglion. This study was designed to verif y whether or not bilateral projections from the superior cervical gang lion to the midline structures, particularly to the pineal gland, play a role in the transport of WGA-HRP to the contralateral SCG. One grou p of rats received WGA-HRP injection into the right SCG (group I). Fou r groups of rats underwent the following operations prior to the injec tion of WGA-HRP into the right superior cervical ganglion: transection of the external carotid nerve (group II), transection of the internal carotid nerve (group III), transection of the external carotid nerve combined with pinealectomy (group IV), transection of both the interna l and the external carotid nerves (group V). The mean number of labell ed neurons in the left SCG of each group were found as follows: group I, 1516+/-221 (mean+/-S.D.); group II, 861+/-122; group III, 543+/-99; group IV, 562+/-144; group V, 220+/-52. The results of this study sug gest that the contralateral labelling depends on the transneuronal tra nsport of WGA-HRP through the terminal fields of innervation of the mi dline structures that receive bilateral projections from both SCGs.