Vagotomy induced changes in acetyl cholinesterase staining and substance P-like immunoreactivity in the gustatory lobes of goldfish.

Abstract

In teleost fish, the visceral sensory nuclei of the medulla are clearly separated into gustatory lobes and a general visceral sensory nucleus. Those branches of the vagus nerve which innervate the orobranchial cavity terminate in the vagal gustatory lobe, while the general visceral component of the vagus nerve terminates in the separate general visceral nucleus. In goldfish, the vagal lobe is a complex, laminated structure containing both motor and sensory elements. Transection of the vagus nerve results in distinct changes in the pattern of acetylcholinesterase staining and substance-P-like (SPL) immunoreactivity in the vagal lobe of goldfish. Following vagotomy, cholinesterase activity is eliminated from layers 4 and 6, both being layers in which primary gustatory afferent fibers terminate. In addition, SPL immunoreactive fibers disappear from the capsular root of the vagus nerve. These results indicate that the primary afferent input to the gustatory lobe involves at least two cytochemically distinct fiber types, one containing substance-P-immunoreactive material and the other containing or inducing acetylcholinesterase activity. Vagotomy also affects immunostaining and cholinesterase activity of the motoneurons deep in the vagal lobe. Following nerve transection, acetylcholinesterase activity is diminished, and SPL-immunoreactivity increased in the affected motoneurons. Similar changes were observed in axotomized motoneurons of other cranial nerve nuclei.