Plasticity of fin command system function following spinal transection in larval sea lamprey

The descending control of dorsal fin posture by a reidentifiable reticulospinal command neuron (I1), was examined in the sea lamprey, Petromyzon marinus. Intracellular stimulation of I1 controls the posture of both dorsal fins. Spinal transection between the fins results not only in loss of control of posterior dorsal fin posture, but after 2 h, the control of the anterior dorsal fin as well. Anterior dorsal fin responses remained absent at 4, 5 and 6 days after transection. Stimulation of I1 could control anterior dorsal fin posture in specimens which had recovered the ability to right during swimming (77 and 100 days after transection), although higher than normal stimulus frequencies were required. I1 control of posterior dorsal fin posture did not recover.