Quantitative distribution of choline acetyltransferase activity in rat trapezoid body

• Published in: Hearing research 2018-12, Vol.370, p.264-271
• Main Authors: Linker, Lauren A., Carlson, Lissette, Godfrey, Donald A., Parli, Judy A., Ross, C. David
• Format: Article
• Language: English
• Subjects: Acetylcholine; Acetylcholine - metabolism; Acetylcholinesterase; Acetylcholinesterase - metabolism; Animals; Auditory; Auditory Pathways - enzymology; Choline O-Acetyltransferase - metabolism; Cochlea - innervation; Cochlear nucleus; Cochlear Nucleus - metabolism; GPI-Linked Proteins - metabolism; Hearing; Male; Rats, Inbred BN; Rats, Inbred F344; Rats, Long-Evans; Trapezoid Body - enzymology
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/j.heares.2018.08.008

There is evidence for a function of acetylcholine in the cochlear nucleus, primarily in a feedback, modulatory effect on auditory processing. Using a microdissection and quantitative microassay approach, choline acetyltransferase activity was mapped in the trapezoid bodies of rats, in which the activity is relatively higher than in cats or hamsters. Maps of series of sections through the trapezoid body demonstrated generally higher choline acetyltransferase activity rostrally than caudally, particularly in its portion ventral to the medial part of the spinal trigeminal tract. In the lateral part of the trapezoid body, near the cochlear nucleus, activities tended to be higher in more superficial portions than in deeper portions. Calculation of choline acetyltransferase activity in the total trapezoid body cross-section of a rat with a comprehensive trapezoid body map gave a value 3–4 times that estimated for the centrifugal labyrinthine bundle, which is mostly composed of the olivocochlear bundle, in the same rat. Comparisons with other rats suggest that the ratio may not usually be this high, but it is still consistent with our previous results suggesting that the centrifugal cholinergic innervation of the rat cochlear nucleus reaching it via a trapezoid body route is much higher than that reaching it via branches from the olivocochlear bundle. The higher choline acetyltransferase activity rostrally than caudally in the trapezoid body is consistent with evidence that the centrifugal cholinergic innervation of the cochlear nucleus derives predominantly from locations at or rostral to its anterior part, in the superior olivary complex and pontomesencephalic tegmentum. •Choline acetyltransferase (ChAT) catalyzes synthesis of transmitter acetylcholine.•ChAT activity in the trapezoid body serves as a marker of cholinergic nerve fibers.•ChAT activity is higher in rat trapezoid body than in cat or hamster trapezoid body.•ChAT activity is higher rostrally than caudally in rat trapezoid body.•The trapezoid body of rat carries about 3 times the ChAT as its olivocochlear bundle.