VAGAL AND GASTRIC CONNECTIONS TO THE CENTRAL NERVOUS-SYSTEM DETERMINED BY THE TRANSPORT OF HORSERADISH-PEROXIDASE

Horseradish peroxidase (HRP, Sigma Type VI) crystals were encased in a parafilm envelope and applied to the transected central ends of the left and right cervical vagus nerves and the anterior and posterior esophageal vagus nerves of adult male hooded rats. Injection of 30% HRP were made into the muscle wall of the fundus and antrum regions of the stomach. The brain stem, spinal cord and corresponding dorsal root ganglia, superior cervical sympathetic ganglion and the nodose ganglion were removed and cut into 50 .mu.m sections. Sequential sections were examined under a microscope. In tissue from animals that had HRP applied to the cervical vagus nerves, retrogradely labeled neurons were identified ipsilaterally in the medulla located in the dorsal motor nucleus of the vagus (DMN) and the nucleus ambiguous (NA). Labeled cells extended from the DMN into the spinal cord in ventral-medial and laminae X regions [cervical] C1 and C2 of cervical segments. Many neurons were labeled in the nodose ganglion. Anterogradely labeled terminals were observed throughout and adjacent to the solitary nucleus (NTS) dorsal to the DMN and intermixed among labeled neurons located in the DMN. In tissue from animals that had HRP applied to the esophageal vagus nerves, similar labeling was observed. Fewer neurons were identified in the NA, the nodose ganglion and only in laminae X of the cervical spinal cord segments C1 and C2. Very little terminal labeling was observed in and adjacent to the NTS. Labeled neurons in tissue from animals that had HRP injected into the stomach wall were observed bilaterally in the DMN, nodose ganglion, and only in laminae X at the C1 and C2 levels of the spinal cord. Labeled neurons also were observed in the dorsal root ganglia of the thoracic cord. Cervical cord and Na neurons are important in the supradiaphragmatic motor innervation by the vagus. Many afferents to the NTS originate above the diaphragm. Some afferents from the stomach enter the CNS via the thoracic spinal cord.