Combination of NEP 1-40 treatment and motor training enhances behavioral recovery after a focal cortical infarct in rats

Abstract

Background and purpose: Although myelin-associated neurite outgrowth disinhibitors have shown promise in restoring motor function after stroke, their interactive effects with motor training have rarely been investigated. The present study examined whether a combinatorial treatment (NEP 1-40+motor rehabilitation) is more effective than either treatment alone in promoting motor recovery after focal ischemic injury.

Methods: Adult rats were assigned to one of 3 treatment groups (infarct/NEP 1-40+motor training, infarct/NEP 1-40 only, infarct/motor training only) and 2 control groups (infarct/no treatment, intact/no treatment). A focal ischemic infarct was induced by microinjecting endothelin-1 into the motor cortex. Therapeutic treatments were initiated 1 week postinfarct and included intraventricular infusion of the pharmacological agent NEP 1-40 and motor training (skilled reach task). Behavioral assessments on skilled reach, foot fault, and cylinder tests were conducted before the infarct and for 5 weeks postinfarct.

Results: Rats demonstrated significant forelimb impairment on skilled reach and foot fault tests after the infarct. Although all infarct groups improved over time, motor training alone and NEP 1-40 alone facilitated recovery on the skilled reach task at the end of treatment Weeks 2 and 4, respectively. However, only NEP 1-40 paired with motor training facilitated recovery after 1 week of treatment in addition to treatment at Weeks 2 and 4. Finally, only the NEP 1-40+motor training group maintained a performance level equivalent to that of the intact group over the entire period of posttreatment assessment.

Conclusions: This study suggests that behavioral training interacts with the effects of the axonal growth promoter, NEP 1-40, and may accelerate behavioral recovery after focal cortical ischemia.

Figure 1

Experimental timeline showing the drug treatment (pump implant) and/or motor training started on postinfarct Week 1 and continued for 4 weeks. Behavioral assessments were performed on postinfarct Days 4 and 6 (Week 1 data are the means of Days 4 and 6) and weekly during postinfarct Weeks 2 to 5.

Figure 2

A, Nissl stains showing the infarct (black arrowheads) in the motor cortex in the right hemisphere from one representative rat. Left section is 1.8 mm rostral and right section is 0.6 caudal to bregma. Cannula track (white arrow) shown in the left hemisphere. Scale bar=1 mm. B, There were no differences in lesion volume between groups. NEP+TR, NEP 1–40+motor training; NEP, NEP 1–40; TR, motor training; LC, lesion only, no treatment). Error bar=SEM.

Figure 3

Skilled reach performance. The infarct significantly impaired use of the forelimb to retrieve food pellets (P<0.001). After the infarct (dashed line), but before treatment initiation (ie, postinfarct Days 4 and 6 combined), there were no differences in performance between groups. During the treatment period (gray region), there was a significant time effect (P=0.0001), group effect (P=0.0001) and group×time interaction (P=0.012). Post hoc simple effects analysis of the interaction showed that there was a significant treatment effect among groups for each week. Performance of the NEP+TR group was significantly improved compared with the lesion only control group (LC) throughout the 4-week treatment period. Error bar=SEM.

Figure 4

Foot fault performance. Data represent the difference of foot faults between the preinfarct preferred forelimb (or impaired forelimb) and the nonpreferred forelimb (or intact forelimb) divided by the total number of movements. Negative values represent more foot faults with the intact fore-limb ipsilateral to the infarct. The infarct significantly impaired forelimb coordination and increased foot faults before the treatments (P=0.02). During treatment period, there was no significant group effect or group×time interaction. Error bar=SEM.

Figure 5

Cylinder test performance. There were no significant differences in performance among groups either before or after the infarct. Error bar=SEM.