Primary neurons of the lateral line nerves and their central projections in hagfishes.

ABSTRACT

The hagfish lateral line system was studied by horseradish peroxidase transganglionic transport. The anterior lateral line nerve innervates the group of lateral line canals situated anteriorly to the eye, and the posterior lateral line nerve innervates the group of canals situated posteriorly to the eye. Although both nerves pass through the muscle fascia at the same point, each runs a different course to the brain. The anterior lateral line nerve runs near the trigeminal nerve and its ganglion is closely attached to the trigeminal ganglion, but both systems are completely independent. The posterior lateral line nerve runs independently of any other cranial nerve and makes a peculiar U-turn at the point of entry to the brain capsule. The anterior lateral line ganglion contains both cutaneous sensory cells (small to large cells) and lateral line sensory cells (small cells); from this ganglion projections run to both the trigeminal sensory nucleus (fine and thick fibers) and medial nucleus of the area acousticolateralis (fine fibers). The posterior lateral line ganglion contains only small lateral line cells that project fine fibers to the medial nucleus of the area acousticolateralis. There are no efferent components in this lateral line system, and its only afferent terminal field is the medial nucleus of the area acousticolateralis.