Brain poster session: neurogenesis

Background and aims: Neurogenesis is upregulated following stroke, and may contribute to brain repair. Neurogenesis is typically studied invasively. Recently, transgenic mice were generated that express either Discoma sp reef coral red fluorescent protein (DsRed) (Couillard-Després et al. Eur J Neurosci 2006;24: 1535–45), or the bioluminescent enzyme luciferase (LUC) (Couillard-Després et al. Mol Imaging 2008; 7:28–34), under the control of the migrating neuroblast promoter doublecortin (DCX). Therefore, the aims of this project were to employ noninvasive multimodal imaging to observe the timecourse and expression patterns of the neurogenic response following focal ischemia, in vivo. Methods: Male CD1 DCX-LUC mice (37 to 44 g) (n = 4) and C57/BL6 DCX-DsRed mice (29 to 35 g) (n = 3) received different durations (30, 20, or 10 mins) of transient middle cerebral artery occlusion (MCAO); one DsRed mouse received a sham procedure. Optical imaging was performed to detect fluorescence, or bioluminescence (using intraperitoneal administration of 150 mg/kg of luciferin), at 23 days prior to and 12 days post MCAO. Anatomical magnetic resonance imaging (MRI) scans (spin echo T2-weighted, and 3D fast low angle shot (FLASH) images) were acquired 4 days prior to and 7 days post-MCAO at 11.7 T. Two DsRed mice (including the sham) were sacrificed at 7 days post-MCAO and the other animals at 12 days. Brain tissue was processed for fluorescent immunohistochemistry for the imaging reporters in combination with DCX and GFAP. Results: Ischemia durations of 30 mins produced extensive lesions and mortality, as observed from T2 maps, whereas smaller subcortical insults were produced using 10 to 20 mins of occlusion. No fluorescent signal was detected from the C57/BL6 DCX-DsRed animals in vivo, but photons produced from the oxidation of luciferin in the CD1 DCX-LUC mice were observed and counted. Emission was highest in the head in a pattern similar to the pathway of the rostral migratory stream in the brain (Figure 1C and D). Following MCAO the bioluminescent signal increased and appeared to shift laterally towards the injured hemisphere (Figure 1E and F). Improved localization will be possible using co-registration of the optical images to the FLASH 3D MRI data set (Figure 1A and B). Conclusions: These preliminary results indicate that monitoring the neurogenic response in vivo follow-