Mapping of the Spinal Circuitry Associated with Paw Withdrawal Learning in Spinal Mice

The overall goal of this project was to identify the neural circuitry involved in paw withdrawal learning (PaWL) in complete spinal cord transected (ST) mice. Pseudorabies virus (PRV)-Bartha 152 was injected into the tibialis anterior (TA), the primary muscle involved in this learning. The use of PRV, a transsynaptic retrograde marker, allowed labeling of the TA motoneurons and its associated interneurons in the spinal cord. By combining PRV-Bartha 152 with c-fos (an activity-dependent marker) and CaMKII (a learning-associated marker), the activated motoneurons and interneurons that were associated with spinal learning were identified. Of all PRV+ labeled neurons, 21% were motoneurons and found only on the ipsilateral side of the spinal cord (same side where learning occurred). Sixty-five percent of the labeled interneurons were found on the ipsilateral side of the spinal cord and 14% were found on the contralateral side. A majority (~60%) of the interneurons and motoneurons on the ipsilateral side were activated during PaWL. Moreover, activated PRV+ interneurons that were also positive for CaMKII were mostly located in laminae VI-VII suggesting that the neural circuitry involved in PaWL occurred in these regions. Introduction The spinal cord has the ability to learn complex motor tasks in the absence of supraspinal input (Edgerton et al., 2004, 2008). The neuronal circuitry associated with such learning in the spinal cord, however, remains largely unidentified. By creating anatomical maps of functionally connected neurons it may be possible to gain an understanding of the pathways involved in spinal learning. Identification of these pathways can be utilized for new rehabilitative strategies, such as epidural stimulation and pharmacological treatments that could help patients regain motor function after a spinal cord injury.