[Interaction between primary segmental afferents and motor neurons in the spinal cord of the lamprey]

Direct connections between dorsal cell axons and dendrites of motoneurons and giant interneurons in the isolated spinal cord of the lamprey, are described. Single dorsal cells were stimulated through a separate intracellular microelectrode, and unitary synaptic potentials in the motoneuron were recorded. Intracellular injection of HRP into the synaptically connected cells was performed via microelectrodes with 10% HRP solution. The synaptic contacts formed by injected cells were identified under the light microscope. Only dorsal cells and motoneurons in the spinal cord were stained with HRP retrograde transportation from segmental muscles. Similarity of primary afferents and motoneurons intrasegmental connections in the spinal cord of lamprey and some lower vertebrates, is discussed.