The nucleus magnocellularis in the red-eared turtle, Chrysemys scripta elegans: Eighth nerve endings and neuronal types

Abstract

Eighth nerve endings and neuronal types in the nucleus magnocellularis were analyzed in the red-eared turtle ( Chrysemys scripta elegans). One group of turtles had horseradish peroxidase (HRP) injected into the surgically exposed inner ear. Following injection the animals survived for 3–5 days and then their 8th nerve fibers and endings were analyzed. A second group of turtles were impregnated by the Golgi-Kopsch technique. This also demonstrated 8th nerve endings and neurons in the nucleus magnocellularis. A third group had brains stained with cresyl violet to demonstrate normal morphology. Two types of neurons were present in the nucleus magnocellularis; bushy and stellate. Bushy neurons had a single primary dendrite with little branching and spines. Stellate neurons had 3–5 primary dendrites with secondary order branching and dendritic spines. Thick 8th nerve axons gave rise to endbulbs of Held and their axons formed bouton-type ending. Endbulbs of Held were presently only on bushy neurons while bouton-type terminals were only on stellate neurons. Endbulbs of Held had two patterns; one group was cup-shaped and surrounded approximately 1 2 of the soma without appendages. A second type had a smaller cup with 3–5 extensions to other parts of the cell. Stellate neurons had terminal boutons adjacent to the cell membrane. They appeared in some situations as a necklace surrounding the neuron.