Modular organization of turtle spinal interneurons during normal and deletion fictive rostral scratching.
During normal rostral scratching in the spinal turtle, there is rhythmic alternation between hip-flexor and hip-extensor motor activity. During rostral scratching with hip-extensor deletions, there are successive bursts of hip-flexor motor activity and no activity in hip-extensor motor neurons. We characterized the ON- and OFF-phases of 72 descending propriospinal interneurons with distinct activity bursts during normal rostral scratching. We also studied the activity of these interneurons during deletion scratching. Hip-extensor interneurons were active when hip-flexor motor neurons were quiet in normal scratching and had zero overlap with hip-flexor motor activity. This population of hip-extensor interneurons, termed the hip-extensor module or hip-extensor unit-burst generator, was mainly quiet during deletion scratching. Our observation supports the concept that a module is a neuronal population that may be active or quiet in a coordinated manner during a spinal motor rhythm. During normal scratching, hip-flexor interneurons were active during hip-flexor motor activity, and spanning interneurons were active during both hip-flexor motor activity and quiescence. Hip-flexor and spanning interneurons with intermediate overlap with hip-flexor motor activity fired in bursts during deletion scratching. Hip-flexor and spanning interneurons with large overlap with hip-flexor motor activity fired continuously during deletion scratching. Key features of hip-flexor and spanning interneuron firing during normal scratching were preserved during deletion scratching. Thus these features do not require activity in the hip-extensor module in every cycle of a motor rhythm.
Stein
Paul S G
PS
Department of Biology, Washington University, St. Louis, Missouri 63130, USA. stein@biology.wustl.edu
Daniels-McQueen
Susan
S
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D006614:Hindlimb / Q000502:physiology; D007395:Interneurons / Q000502:physiology*; D009043:Motor Activity / Q000502:physiology*; D010507:Periodicity; D010812:Physical Stimulation / Q000379:methods; D012018:Reflex / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013116:Spinal Cord / Q000502:physiology*; D014426:Turtles