Retrograde tracer technique for assessment of selective and total subdiaphragmatic vagotomies.

A new protocol that provides a sensitive, reliable, and practical test for completeness of selective as well as total subdiaphragmatic vagotomies is described. This protocol employs a microscopic inventory of retrogradely labeled neurons in topographically distinct regions of the dorsal motor nucleus to determine which vagal branches have been surgically destroyed. Physiological experiments for validation and observations on the use of the method with 243 rats indicate that the protocol described can assess total as well as at least 11 different types of selective subdiaphragmatic vagotomies, including surgeries for which no assays have existed. Furthermore, the technique can identify cases where a branch is only partially destroyed. Other strengths include the facts that the protocol provides a simultaneous inventory of the different branches in a single test, is not influenced by the general health of the animal, and does not interfere with concurrent behavioral or physiological tests. Limitations include the facts that the tracer inventory requires a minimal survival period, can only be done postmortem, and has low resolution for cuts of the vagal hepatic branch. Aspects of the protocol critical to its implementation, including specifics for using the fluorescent tracer true blue, are discussed. Other tracers with similar diffusion characteristics, such as fluoro-gold and fast blue, can be used with equal effectiveness with this protocol.