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

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.