In the study, the investigators measured the density of cholinergic fibers that link neurons in untreated older monkeys and in aged monkeys who received transplants of genetically-altered brain cells.
Cholinergic fibers supplying C cells of the thyroid have been identified in chickens, but their existence in humans has yet to be described.[8] All these nerves are accompanied by Schwann cells, and it is therefore surprising that granular cell tumors are not encountered more commonly in the thyroid.