Wed, April 28
Speaker: Heather Hayes, PhD (Postdoctoral Candidate)
Title: Sensory processing in a walking spinal cord
Abstract: The spinal cord alone contains sufficient circuitry for producing the basic rhythmic patterns that underlie locomotion. Many of the known properties of this spinal locomotor circuitry have been elucidated using the isolated rodent spinal cord maintained in vitro, in which the locomotor circuitry can be recruited through neurochemicals or electrical stimulation. The circuitry can then be dissected anatomically, physiologically, and pharmacologically. The absence of the blood-brain barrier also allows for exquisite control of the neurochemical environment. While clearly a powerful model, the isolated cord lacks sensory feedback from limb movement, which is known to play a vital role in refining circuit function and output. Further, without intact limbs, we can neither relate neural activity to movement nor study spinal sensory processing. Thus, we developed a novel spinal cord-hindlimb preparation (SCHP) that combines intact sensory feedback and behavioral observability with the advantages of the isolated cord. Essentially, a walking spinal cord. In this talk, I will present the development of the SCHP, as well as our studies on sensory reinforcement and refinement of in vitro locomotion. I will also examine how in vitro SCHP locomotion relates to intact rat locomotion.
Because sensory feedback wields such a strong influence on motor behavior, it must be tightly regulated. Presynaptic inhibition (PSI) is one of the most powerful mechanisms for regulating sensory access to central circuits and is actually "more powerful than postsynaptic inhibition in depressing the central excitatory actions of almost all primary afferent fibers (Eccles 1964)." Before the SCHP, it was "almost technically impossible to record primary afferent depolarizations [the monitor of PSI] during real walking (Menard et al. 1999)" because the DC recordings required are movement sensitive. However, the SCHP allows us to mechanically isolate the spinal cord from the hindlimbs and stabilize the cord, while retaining sensory feedback and intact limb movement. Thus, the SCHP is an ideal model for studying sensory regulation during locomotion via presynaptic inhibition. In this talk, I will discuss the biomechanical variables that influence PSI and the role PSI may be playing in stability and stance-to-swing transitions.
Host: George Hornby