Effects of Complete Spinal Cord Transection in Neonatal and Juvenile Rats on Parvalbumin-Positive Inputs and Perineuronal Net Formation on Chx10-Positive V2a Interneurons.

INTRODUCTION: Neonatal rats, but not juvenile rats, show spontaneous hindlimb locomotor recovery after complete thoracic spinal cord transection (SCT). Significant increases in parvalbumin-positive proprioceptive nerve terminals are observed on motoneurons in both neonatal and juvenile rats with SCT compared with intact rats.

METHODS: In the present study, we focused on Chx10-positive V2a interneurons, which partially comprise the central pattern generator, and examined parvalbumin-positive nerve terminals on Chx10 neurons and the perineuronal net formation around these neurons using Wisteria floribunda agglutinin (WFA) as a marker 2 weeks after SCT on postnatal day 5 (neonatal) or day 20 (juvenile).

RESULTS: Rats with CST during the neonatal period had a significantly greater number of parvalbumin-positive terminals on Chx10 neurons compared to age-matched intact rats, whereas no significant difference was detected between rats with SCT during the juvenile period and age-matched intact rats. Chx10 neurons for which ≥50% of the circumference was surrounded by WFA were identified as WFA-positive. The proportion of WFA-positive neurons among Chx10-positive neurons did not differ significantly between neonatal SCT and age-matched intact rats, but was significantly higher in juvenile SCT and age-matched intact rats.

CONCLUSION: These findings suggest that SCT promotes the formation of proprioceptive afferent terminals on Chx10-positive neurons. The significant increase in terminals following SCT in neonatal rats might facilitate spontaneous motor recovery, whereas enhanced perineuronal net formation around Chx10 neurons following juvenile SCT might restrict synaptic formation and impair motor recovery.