Transneuronal transport of wheat germ agglutinin-conjugated horseradish peroxidase into trigeminal interneurones of the rat.

Intramuscular injections of either horseradish peroxidase (HRP) or wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) were made into the masseter muscle of rats. Both tracers labeled primary sensory neurones in the V mesencephalic nucleus, motoneurones in the V motor nucleus, and some motoneurones in the facial motor nucleus. WGA-HRP labeled additional neurones in the V main sensory nucleus and the rostral pole of the V nucleus oralis. These were classed as interneurones because they lay in areas outside those known to contain either first-order afferent or motoneurone somata. We argue that these were labeled by retrograde transport of tracer because they lay close to the V motor nucleus, and from some of them processes could be followed into the region of the V motor nucleus.