The lamprey isolated spinal cord as a model for anesthetic effects on vertebrate locomotor systems

The lamprey has been used extensively as a model for vertebrate locomotion. Relatively much is known about the anatomical and functional organization of lamprey sensorimotor circuits. The ability to induce locomotion and selectively perfuse the isolated spinal cord enables the assessment of anesthetic effects on locomotor interneurons. We selectively delivered isoflurane (ISO) to the mid-portion of lamprey isolated spinal cords and measured its effect on fictive locomotion using spectral analyses. Concentrations that depressed or abolished motor output also disrupted locomotor activity and intersegmental coordination in spinal regions outlying ISO application. The results suggest that ISO's immobilizing effect in lampreys is attributed to a direct action on central pattern generator interneurons. The results might be extended to mammals, as our studies in rats also suggest that ISO acts preferentially on spinal locomotor systems. Thus, the lamprey isolated nervous system can serve as a useful tool to investigate the neurophysiological and pharmacological processes that underlie anesthetic immobilizing action.