Aims: 

The prey-catching behavior of the frog consists of a sequence of coordinated activity of different muscles. Snapping of prey object stimulates the trigeminal afferent terminals of oral cavity and pharynx which initiates the contraction of muscles innervated by the glossopharyngeal and vagus (IX-X) nerve. The anatomical background of the influence of sensory trigeminal system on the IX and X motoneurons is not yet examined. The aim of our experiments was to study whether the trigeminal afferent fibers establish direct connections with the motoneurons of glossopharyngeal and vagus nerve.

Methods: 

In anaesthetized animals the trigeminal nerve was filled with fluorescein dextran amine whereas the common root of glossopharyngeal (IX), vagus (X) and accessory (XI) nerves were simultaneously labeled with tetramethylrhodamine dextran amine.

Results: 

With a confocal laser scanning microscope we could detect close appositions between the trigeminal afferent fibers and the somata and the dendritic trees of the general and special visceral motoneurons of the IX-X nerves. In order to show the spatial distribution of these connections within the functionally different subdivisions of the ambiguus nucleus, Neurolucida reconstruction of the brainstem was made showing the spatial distribution of the trigeminal afferents on the dendrites and perikarya of the IX-X motoneurons. To detect only the terminals of the mesencephalic trigeminal nucleus, related to the proprioceptive innervations of the oral cavity, the Gasserian ganglion was destroyed before the fluorescent labeling.

Conclusions: 

The possible monosynaptic connections between the trigeminal afferents and IX-X motoneurons presented here may be one of the morphological substrate of a very quick response during the feeding movements of the frog.

Support: 

OTKA K 67641 and MTA-TKI 242