The location of cardiac vagal preganglionic neurones in the brain stem of the dogfish Scyliorhinus canicula.

The locations, within the brain stem, of vagal efferent preganglionic neurones with axons in the two pairs of cardiac vagal rami of the dogfish have been defined by the retrograde intra-axonal transport of horseradish peroxidase (HRP). HRP was applied to the cardiac rami in one of two ways: either as crystals placed on the cut central end of the nerve or as a dried concentrated solution administered into the nerve on the tip of a fine pin. No difference was observed in the number of labelled cell bodies identified using either method. Labelled branchial cardiac vagal motoneurones were found ipsilaterally in the medial division of the vagal motor column, in the lateral division of the vagal motor column, and scattered between these two locations. In contrast, visceral cardiac vagal motoneurones were confined to the ipsilateral medial division of the vagal motor column. We suggest that the dual location of cell bodies supplying axons to the branchial cardiac branch of the vagus may represent a separation of function with respect to the two types of activity conducted by this nerve. Cardiac efferent fibres are confined in their exit from the brain to a middle group of vagal rootlets. This corresponds to the topographical representation of cardiac efferent somata within the extent of the vagal motor column.