Environmental enrichment enhanced neurogenesis and behavioral recovery after stroke in aged rats

Abstract

Background and purpose: Age is identified as a significant prognostic factor for poorer outcome after stroke. However, environmental enrichment (EE) has been reported to promote functional recovery after ischemic stroke. The purpose of this study was to investigate whether environmental enrichment was beneficial to ischemic stroke in aged rats.

Methods: Aged rats were randomly assigned as control rats, rats subjected to cerebral ischemia, and rats with cerebral ischemia treated with EE for 30 days. Focal cortical ischemia was induced by intracranial injection of endothelin-1 (ET-1). EE housing began one day after focal ischemia and was maintained for the whole experimental period. We used immunofluorescence staining to analyze the neurogenesis in the subventricular zone (SVZ) and TdT-mediated dUTP-biotin nick-end labeling (TUNEL) assay to evaluate apoptosis. The expression of neuronal nuclei, glial fibrillary acidic protein (GFAP) and Iba-1 around the infarcted area were also measured by double immunohistochemistry.

Results: EE enhanced the proliferation of newborn neurons in the SVZ, as well as increased the long-term survival of newborn neurons. EE also exerted effects on inflammation after stroke. Furthermore, EE suppressed apoptosis and improved the motor functions after stroke in the aged rats.

Conclusions: EE improved post-stroke recovery on the basis of enhancing neurogenesis in aged rats.

Keywords: ET-1; aging; behavioral recovery; environmental enrichment; neurogenesis; stroke.

Figure 1

Study design. The arrows indicate the timing of pre-training, induction of stroke, BrdU labeling, environmental enrichment treatment, behavioral testing and sacrifice.

Figure 2

Proliferation of newborn neurons in the SVZ. (A) Representative confocal images for BrdU⁺/DCX⁺ cells in the SVZ. Scale bar = 100 μm. (B) Quantification of BrdU⁺/DCX⁺ cells in the SVZ (n = 6). Statistical significance: ^*P < 0.01 vs. SHAM, ^**P < 0.01 vs. ISC.

Figure 3

The survival of neuroblasts in the peri-infarct cortex. (A) Representative confocal images for BrdU⁺/NeuN⁺ cells in the peri-infarct cortex. Scale bar = 40 μm. (B) Quantification of BrdU⁺/NeuN⁺ cells in the peri-infarct cortex (n = 6). Statistical significance: ^*P < 0.01 vs. SHAM, ^**P < 0.01 vs. ISC.

Figure 4

Differentiation of neuroblasts in the peri-infarct cortex. (A) Representative confocal images for BrdU⁺/GFAP⁺ cells in the peri-infarct cortex. Scale bar = 100 μm. (B) Quantification of BrdU⁺/GFAP⁺ cells in the peri-infarct cortex (n = 6). Statistical significance: ^*P < 0.01 vs. SHAM, ^**P < 0.01 vs. ISC. (C) Representative confocal images for BrdU⁺/Iba-1⁺ cells in the peri-infarct cortex. Scale bar = 100 μm. (D) Quantification of BrdU⁺/Iba-1⁺ cells in the peri-infarct cortex (n = 6). Statistical significance: ^*P < 0.01 vs. SHAM, ^**P < 0.01 vs. ISC.

Figure 5

Apoptosis in the peri-infarct cortex. A Representative images for TUNEL-positive cells in the peri-infarct cortex. (A) Representative images for TUNEL-positive cells in the peri-infarct cortex. Scale bar = 50 μm. (B) Quantification of TUNEL-positive cells in the peri-infarct cortex (n = 6). Statistical significance: ^*P < 0.01 vs. SHAM, ^**P < 0.01 vs. ISC.

Figure 6

Performance in behavioral tests. Forelimb slip ratio in the beam-walking (n = 6). Statistical significance: ^*P < 0.01 vs. SHAM, ^**P < 0.05 vs. ISC.