Amount but not pattern of protective sensory stimulation alters recovery after permanent middle cerebral artery occlusion

Abstract

Background and purpose: Using a rodent model of ischemia (permanent middle cerebral artery occlusion), our laboratory previously demonstrated that 4.27 minutes of patterned single-whisker stimulation delivered over 120 minutes can fully protect from impending damage when initiated within 2 hours of permanent middle cerebral artery occlusion ("early"). When initiated 3 hours postpermanent middle cerebral artery occlusion ("late"), stimulation resulted in irreversible damage. Here we investigate the effect of altering pattern, distribution, or amount of stimulation in this model.

Methods: We assessed the cortex using functional imaging and histological analysis with altered stimulation treatment protocols. In 2 groups of animals we administered the same number of whisker deflections but in a random rather than patterned fashion distributed either over 120 minutes or condensed into 10 minutes postpermanent middle cerebral artery occlusion. We also tested increased (full-whisker array versus single-whisker) stimulation.

Results: Early random whisker stimulation (condensed or dispersed) resulted in protection equivalent to early patterned stimulation. Early full-whisker array patterned stimulation also resulted in complete protection but promoted faster recovery. Late full-whisker array patterned stimulation, however, resulted in loss of evoked function and infarct volumes larger than those sustained by single-whisker counterparts.

Conclusions: When induced early on after ischemic insult, stimulus-evoked cortical activity, irrespective of the parameters of peripheral stimulation that induced it, seems to be the important variable for neuroprotection.

Figure 1. Experimental group stimulation and assessment

Representative (A) dispersed and (B) condensed +0h single whisker subjects', and (C) full whisker array +0h and (D) +3h subjects' initial dip and overshoot before and 24 hours post-pMCAO. Linear grayscale bar indicates intrinsic signal strength ×10⁻⁴ FC. Streaks correspond to large surface vessels. Illustration depicts timing, location and number of whiskers stimulated during treatment (temporal axis not to scale). Group baseline and +24 hour data are plotted in each graph. Means and standard errors are provided for the area (left) and amplitude (right) of the initial dip (first row) and overshoot (second row). A value of zero indicates no response. Asterisks indicate significant differences between baseline and 24 hour values. Right, representative TTC stained coronal sections. Arrow indicates approximate region vulnerable to pMCAO infarct. Scale bars indicate 5mm.

Figure 2. +0h and +3h full whisker array stimulation data

A. Initial dip images from representative +0h and +3h full whisker array animals. Illustration depicts whiskers stimulated during treatment. All +0h animals regained baseline level cortical function by 90 minutes of stimulation and sustained no infarct, while all +3h animals permanently lost cortical activity and sustained infarct. Linear scale bar indicates intrinsic signal strength ×10⁻⁴ FC. Streaks correspond to large surface vessels. Scale bar indicates 5mm. (B–C) Graphs of group baseline and post-occlusion data. Means and standard errors are provided for the area (left) and amplitude (right) of the initial dip (B) and overshoot (C). A value of zero indicates no response. For +0h animals, asterisks indicate values significantly below and daggers indicate values significantly above baseline. For +3h animals, all post-pMCAO values are unmarked and were zero.

Figure 3. +0h full whisker array versus +0h single whisker data

A. Initial dip images from representative +0h full whisker array and +0h single whisker groups. Illustration depicts whiskers stimulated during treatment. Linear scale bar indicates intrinsic signal strength ×10⁻⁴ FC. Streaks correspond to large surface vessels. Scale bar indicates 5mm. (B–C) Graphs of group baseline and post-occlusion data. Means and standard errors are provided for the area (left) and amplitude (right) of the initial dip (B) and overshoot (C). A value of zero indicates no response. Asterisks indicate values significantly below and daggers indicate values significantly above baseline.

Figure 4. +3h full whisker array versus +3h single whisker infarct volumes

The total infarct volume sustained by +3h single whisker and +3h full whisker array animals according to TTC. Asterisk indicates significant difference in infarct volume between groups.