Amygdaloid pathway to the trigeminal motor nucleus via the pontine reticular formation in the rat.

The connections of the amygdala with the trigeminal motor nucleus were studied by light and electron microscopy. Horseradish peroxidase (HRP) experiments showed that the pontine reticular formation, ventromedial to the spinal trigeminal nucleus at the level rostral to the genu of the facial nerve, receives fibers from the central nucleus of the amygdala ipsilaterally and sends fibers to the trigeminal motor nucleus contralaterally. Electron microscopic observations were carried out on the pontine reticular formation after electrolytic lesions in the central nucleus of the amygdala and HRP injections into the contralateral trigeminal motor nucleus were made on the same animal. These experiments using the combined degeneration and HRP technique clearly demonstrated that degenerating amygdaloid fibers made synaptic contacts with retrogradely labeled neurons.