Long-term changes of functional MRI-based brain function, behavioral status, and histopathology after transient focal cerebral ischemia in rats

Abstract

Background and purpose: The relation between recovery of brain function and neurological status after clinical and experimental cerebral ischemia is incompletely characterized. We assessed the evolution of ischemic injury, behavioral status, and brain activity at acute to chronic periods after transient middle cerebral artery occlusion (tMCAO) in rats.

Methods: Male Sprague-Dawley rats were subjected to 20-minute tMCAO (n=10) or sham operation (n=10). Sensorimotor behavioral testing and multimodal (diffusion, perfusion, T2, and functional) MRI, as well as postmortem hematoxylin-eosin staining, were performed before and up to 21 days after tMCAO. MRI and histological parameters were evaluated in 5 regions of interest within the sensorimotor network. Diffusion, perfusion, and T2 lesion volumes were calculated according to previously established viability thresholds.

Results: Diffusion and perfusion lesions were present during occlusion but disappeared completely and permanently within 30 minutes after reperfusion, with no T2 lesions seen. Functional MRI and behavioral deficits did not normalize until 1 and 21 days after tMCAO, respectively. Histology demonstrated selective neuronal cell death at 7 and 21 days after reperfusion.

Conclusions: Twenty-minute tMCAO produced distinct changes on multimodal MRI, histology, and behavioral parameters acutely and chronically. Normal findings on MRI after transient ischemia may not indicate normal tissue status, as behavioral and histological anomalies remain. Behavioral dysfunction persisting long after the recovery of MRI parameters may relate to the subtle neuronal damage seen on histology. Together, these results may help explain unremitting neurological deficits in stroke or transient ischemic attack patients with normal MRI findings.

Figure 1

Regional CBF during tMCAO (mean±SD). ROIs are ipsilesional (black bars). CBF values did not differ significantly between contralesional ROIs and were averaged (Contra; gray bars). *P≤0.05 vs Contra.

Figure 2

Regional ADC during tMCAO (mean±SD). ROIs are ipsilesional (black bars). ADC values did not differ significantly between contralesional ROIs and were averaged (Contra; gray bars). *P≤0.05 vs Contra.

Figure 3

Evolution of regional hypercapnia-evoked (A) ΔCBF_CO2 and (B) ΔBOLD_CO2 in tMCAO rats (mean±SD). ROIs are ipsilesional, and 15-minute to 21-day time points are after reperfusion. Within each contralesional ROI, ΔCBF_CO2 and ΔBOLD_CO2 values did not differ significantly between time points and were averaged (Contra). Statistical comparisons were made between data within each ROI at each postischemic time point with the equivalent baseline value. *P≤0.05 vs Contra.

Figure 4

Evolution of regional forepaw stimulation–evoked (A) ΔCBF_FS and (B) ΔBOLD_FS within ipsilesional (gray bars) and contralesional (Contra; black bar) Sf1 in tMCAO rats (mean±SD). Fifteen-minute to 21-day time points are after reperfusion. ΔCBF_FS and ΔBOLD_FS values did not differ significantly between time points in contralesional Sf1 and were averaged. Statistical comparisons were made between data at each postischemic time point with the equivalent baseline value. *P≤0.05 vs Contra.

Figure 5

Latency to (A) contact and (B) remove and order to (C) contact and (D) remove adhesive labels, as well as (E) forepaw placement results in tMCAO rats (mean±SEM). Five-hour to 21-day time points are after reperfusion. *P≤0.05 vs baseline.