Distributions of active spinal cord neurons during swimming and scratching motor patterns

Abstract

The spinal cord can generate motor patterns underlying several kinds of limb movements. Many spinal interneurons are multifunctional, contributing to multiple limb movements, but others are specialized. It is unclear whether anatomical distributions of activated neurons differ for different limb movements. We examined distributions of activated neurons for locomotion and scratching using an activity-dependent dye. Adult turtles were stimulated to generate repeatedly forward swimming, rostral scratching, pocket scratching, or caudal scratching motor patterns, while sulforhodamine 101 was applied to the spinal cord. Sulforhodamine-labeled neurons were widely distributed rostrocaudally, dorsoventrally, and mediolaterally after each motor pattern, concentrated bilaterally in the deep dorsal horn, the lateral intermediate zone, and the dorsal to middle ventral horn. Labeled neurons were common in all hindlimb enlargement segments and the pre-enlargement segment following swimming and scratching, but a significantly higher percentage were in the rostral segments following swimming than rostral scratching. These findings suggest that largely the same spinal regions are activated during swimming and scratching, but there are some differences that may indicate locations of behaviorally specialized neurons. Finally, the substantial inter-animal variability following a single kind of motor pattern may indicate that essentially the same motor output is generated by anatomically variable networks.

Shared Components of Rhythm Generation for Locomotion and Scratching Exist Prior to Motoneurons

“…Collectively, these studies make it unlikely that the swimming and scratching pathways are completely separate prior to motoneurons. However, earlier studies also suggest that there are some differences between the spinal interneuronal networks for two rhythmic behaviors ( Ritter et al, 2001 ; Berkowitz, 2002 , 2008 ; Li et al, 2007 ; McLean et al, 2007 ; Liao and Fetcho, 2008 ; McLean and Fetcho, 2008 ; Satou et al, 2009 ; Frigon and Gossard, 2010 ; Mui et al, 2012 ; Hao et al, 2014 ). Combining these findings with the current findings, one can conclude that to the extent that there are swim and/or scratch-specialized spinal interneurons that contribute to rhythm and/or pattern generation, they appear to have their effects predominately or exclusively on interneurons, not motoneurons.…”

Lognormal firing rate distribution reveals prominent fluctuation–driven regime in spinal motor networks

“…To avoid the confounding factors of supraspinal input, we spinalized the turtle. The transection was performed at the spinal cord at segments (D3-4) caudal to the cervical segments, where the local circuitry has only little or no involvement in generation of motor patterns (Mortin and Stein, 1989; Hao et al, 2014; Mui et al, 2012). The adult turtle preparation is capable of producing elaborate motor patterns such as scratching.…”

Purines released from astrocytes inhibit excitatory synaptic transmission in the ventral horn of the spinal cord

“…Neuronal networks located in the ventral horns of the spinal cord are essential for motor control (Kjaerulff and Kiehn, 1996; Prut and Perlmutter, 2003; Lanuza et al, 2004; Dai et al, 2005; Brocard et al, 2010; Mui et al, 2012). Their architecture provides the necessary stability for generating stereotyped movements.…”