Neonatal hind-paw injury disrupts acquisition of an instrumental response in adult spinal rats.

The present study was designed to evaluate the impact of neonatal injury on adult spinal plasticity in rats. Subjects were randomly assigned to 1 of 4 experimental conditions: (a) hind-paw injury at Postnatal Day (PD) 2, (b) hind-paw injury at PD 5, (c) anesthesia exposure only on PD 2, or (d) anesthesia exposure only on PD 5. Subjects receiving a unilateral neonatal hind-paw injury showed decreased mechanical threshold (hyperalgesia) on the previously injured hind paw throughout development. This decrease in threshold survived spinal transection (at T2) at 12 weeks of age. Injured subjects also showed significant impairment in a spinal instrumental learning task performed by the previously injured hind paw. This disruption of learning indicates a disruption of spinal plasticity that may be due to induction of long-term changes in nociceptive processing within the spinal cord.