Comparative Enhancement of Motor Function and BDNF Expression Following Different Brain Stimulation Approaches in an Animal Model of Ischemic Stroke

Abstract

Background: Combinatory intervention such as high-frequency (50-100 Hz) excitatory cortical stimulation (ECS) given concurrently with motor rehabilitative training (RT) improves forelimb function, except in severely impaired animals after stroke. Clinical studies suggest that low-frequency (≤1 Hz) inhibitory cortical stimulation (ICS) may provide an alternative approach to enhance recovery. Currently, the molecular mediators of CS-induced behavioral effects are unknown. Brain-derived neurotrophic factor (BDNF) has been associated with improved recovery and neural remodeling after stroke and thus may be involved in CS-induced behavioral recovery.

Objective: To investigate whether inhibitory stimulation during RT improves functional recovery of severely impaired rats, following focal cortical ischemia and if this recovery alters BDNF expression (study 1) and depends on BDNF binding to TrkB receptors (study 2).

Methods: Rats underwent ECS + RT, ICS + RT, or noCS + RT treatment daily for 3 weeks following a unilateral ischemic lesion to the motor cortex. Electrode placement for stimulation was either placed ipsilateral (ECS) or contralateral (ICS) to the lesion. After treatment, BDNF expression was measured in cortical tissue samples (study 1). In study 2, the TrkB inhibitor, ANA-12, was injected prior to treatment daily for 21 days.

Results: ICS + RT treatment significantly improved impaired forelimb recovery compared with ECS + RT and noCS + RT treatment.

Conclusion: ICS given concurrently with rehabilitation improves motor recovery in severely impaired animals, and alters cortical BDNF expression; nevertheless, ICS-mediated improvements are not dependent on BDNF binding to TrkB. Conversely, inhibition of TrkB receptors does disrupt motor recovery in ECS + RT treated animals.

Keywords: BDNF; TrkB inhibition; inhibitory brain stimulation; rehabilitation; stroke.

Figure 1.

Timeline of Study. Animals were trained on the SPR to criterion and then assessed using this task before surgeries. Animals received stroke induction and post-operative performance assessments began 3 days after surgery in which the SPR test was given. Animals received rehabilitation for 21 days.

Figure 2.

Electrode Placement and Cortical Punches. Strokes were induced via topical application of endothelin-1, a vasoconstricting peptide, over the motor cortex opposite the preferred reaching limb. A. Then the craniotomy was enlarged and a bipolar epidural electrode was placed over peri-injury motor cortex(eCS).Or B. Then a craniotomy was made over the forelimb area of the non-infarcted motor cortex and a bipolar epidural electrode was implanted (iCS). 3mm cortical punches medial/lateral to the stroke area were obtained. Cortical punches were obtained on the M1 area of the motor cortex. For ECS and ICS, this is where the electrode is placed.

Figure 3

A. Percent Successful Retrievals and Recovery Scores ICS+RT improved more than ECS+RT at week 1 (p=.021), at week 2 (p=.035) and both ECS+RT (p=0.026) and NOCS+RT (p=.013) at week 3. When all severely impaired animals are combined, ICS in this model of stroke demonstrates an additive treatment for animals that exhibit greater post-stroke functional deficits. B. Ipsilesional and Contralesional BDNF Concentrations Cortical punches (3mm) were taken from the primary motor and penumbra areas from stroke and non-stroke hemispheres. Concentrations of BDNF for severely impaired 4 and 9 month rats combined. One-way anova revealed a significant ipsilesional differences between control and ECS+RT (p=.0001). While not significant, there was a trend for an ipsilesional difference between control BDNF levels and NoCS+RT BDNF levels (p=.061). There was also a significant contralesional difference between control and ICS+RT (p=.022). There was also a significant difference between Ipsilesional ICS+RT levels and contralesional ICS+RT levels (p=.045).

Figure 4.

Percent Successful Retrievals and Recovery Scores: Vehicle and ANA-12 Animals. Rats Received ECS or ICS given concurrently with the single pellet reaching task for 3 weeks following ischemic injury. ECS results in no added benefit in aged animals. A. NOCS. There was not a significant interaction effect of Group X Day (F(2,9)=4.32, p=0.655 and there was not a significant interaction of week (p=0.347). B. ICS. There was not a significant interaction effect of Group X Day (F(2,7)=0.583, p=0.570, but there was a significant interaction of week (p=0.031). C. ECS. There was a mean difference at week 3 between groups:(F(1,8)=5.329, p=0.05). D. ECS Mean Difference. There is a mean difference at Week 3 following ECS+RT between Vehicle and ANA-12. A recovery score was calculated (Week 3-PostOP_for animals receiving ECS. There was a mean difference at Week 3 between groups: (F(1,5)=10.042, p=0.025).

Figure 5.

Percent Successful Retrievals: All ANA-12 Groups. A comparison of the different CS treatment groups within the subgroup that received ANA-12 injections. At week 1, there was a significant difference between ICS+ANA12 and ECS+ANA12 (p=.05). Post hoc comparisons (Tukey) reveal no significant differences between NOCS+ANA12 and ECS+ANA12 (p=0.311) or NOCS+ANA12 and ICS+ANA12 (p=0.512) at week 1.