Horseradish peroxidase localization of cardiac vagal preganglionic somata.

Cardiac vagal preganglionic somata were labeled in cats by the horseradish peroxidase (HRP) technique. The anatomical characteristics of cell bodies with axons in the left and right cervical vagi compared. HRP was injected subepicardially in three groups of pentobarbital anesthetized animals. In two test groups, injections were made after a left and right cervical vagotomy, respectively. In a control group, peripheral cardiac parasympathectomies were performed prior to HRP injection. The controls served to determine the number of somata labeled by HRP uptake via vagal fibers innervating viscera closely approximating the myocardium. After a 48 h survival period the cats were reanesthetized, perfused and fixed. Brain stems were removed, cut in the transverse or sagittal plane and developed with 3,3'-diaminobenzidine. Control cats had 6.8% the number of labeled cell bodies identified in animals with an intact vagus. Thus, few labeled somata in test cats were associated with noncardia tissue. The number, distribution and sizes of labeled cell bodies in test cats were similar. Somata were located ipsilateral to the intact vagus in three regions: the nucleus ambiguus (NA), the dorsal motor nucleus of the vagus (DMN) and an intermediate zone (IZ) between the NA and DMN. The NA contained the maximum number of cell bodies while successively fewer somata were located in the DMN and IZ. Somata of the NA were heterogeneously distributed along the longitudinal neuraxis. The region of maximal cell body concentration was between 1.0 and 1.8 mm rostral to the obex. Somata of the DMN and IZ were homogeneously and sparsely distributed along the neuraxis. The long and short axes of NA somata were larger than corresponding dimensions of cell bodies in the DMN or IZ. However, the dimensions of somata in the DMN and IZ were similar. The identification of labeled cell bodies in three medullary regions and the size differences of the somata in these regions may reflect a central physiological organization of cardia vagal somata.