Physiological and anatomical studies on large neurons of central nervous system of the sea lamprey (Petromyzon marinus). II. Dorsal cells and giant interneurons.

Abstract

Intracellular recordings were made from dorsal cells and giant interneurons in isolated spinal cords of small adult sea lampreys. Electrical stimulation and dye injection showed that one or more processes of dorsal cells lay in dorsal roots, and that most cells had a long anterior process within the cord. Conventional synaptic potentials were rarely seen in dorsal cells on stimulation of the spinal cord or dorsal roots, but stimulation of dorsal cells produced both excitatory and inhibitory potentials in giant interneurons. Serial section tracings and antidromic stimulation showed that the axons of giant interneurons cross in the ventral commissure and extend towards the brain. Stimulation of posterior giant interneurons led to monosynaptic excitation of more anterior ones. Stimulation of one pair of Muller axons produced monosynaptic composite EPSP''s (excitatory post-synaptic potentials) in homolateral giant interneurons. The first component of the EPSP represented a rectifying electrical coupling between the two elements, while the second component probably arose from chemical transmission.