Swimming kinematics and performance of spinal transected lampreys with different levels of axon regeneration

Abstract

Axon regeneration is critical for restoring neural function after spinal cord injury. This has prompted a series of studies on the neural and functional recovery of lampreys after spinal cord transection. Despite this, there are still many basic questions remaining about how much functional recovery depends on axon regeneration. Our goal was to examine how swimming performance was related to degree of axon regeneration in lampreys recovering from spinal cord transection by quantifying the relationship between swimming performance and percent axon regeneration of transected lampreys after 11 weeks of recovery. We found that while swimming speeds varied, they did not relate to percent axon regeneration. In fact, swimming speeds were highly variable within individuals meaning that most individuals could swim at both moderate and slow speeds, regardless of percent axon regeneration. However, none of the transected individuals were able to swim as fast as the control lampreys. To swim fast, control lamprey generated high amplitude body waves with long wavelengths. Transected lampreys generated body waves with lower amplitude and shorter wavelengths than controls and to compensate, transected lamprey increased their wave frequencies to swim faster. As a result, transected lampreys had significantly higher frequencies than control lamprey at comparable swimming velocities. These data suggest that the control lampreys swam more efficiently than transected lampreys. In conclusion, there appears to be a minimal recovery threshold in terms of percent axon regeneration required for lampreys to be capable of swimming, however, there also seems to be a limit to how much they can behaviorally recover.

Spontaneous regeneration of cholecystokinergic reticulospinal axons after a complete spinal cord injury in sea lampreys

“…4 ). Recent work has shown that transected larval lampreys increase their wave frequencies to swim faster (i.e., transected lampreys have higher frequencies than control lampreys with similar velocities) and that they have lower amplitudes than control animals [58] . In the same sense, in our data we also observed a positive correlation between frequency and velocity in injured animals but no correlation between amplitude and velocity ( Fig.…”

Full regeneration of descending corticotropin-releasing hormone axons after a complete spinal cord injury in lampreys

“…One of the animal models for the study of successful and spontaneous spinal cord regeneration is the sea lamprey Petromyzon marinus . Mature larval sea lampreys recover a high degree of their swimming [5] and burrowing [6] abilities and behaviors at around 10 weeks after a complete SCI. In lampreys, regenerated axons make new synapses below the site of a complete SCI [7] and functional recovery is associated with the regeneration of descending axons [8] .…”