Terminations of primary afferents on lumbar motoneurons in the turtle Pseudemys scripta elegans.

The existence of monosynaptic contacts between primary afferents and motoneurons in the lumbar spinal cord of the turtle Pseudemys scripta elegans was demonstrated by intracellular injections of horseradish peroxidase. Three afferent-motoneuron combinations were satisfactorily labeled and revealed 1, 4 and 6 contacts respectively. All contacts were made on the dorsal dendritic tree of the motoneurons. It is suggested that the contacting primary afferents are from muscle spindles.