In vivo diffusion tensor imaging of the neonatal rat brain development

Diffusion tensor imaging (DTI) is a sensitive tool for the assessment of brain development and developmental injury. In this study, in vivo DTI experiments were performed on a Bruker horizontal 11.7 T system on healthy Wistar rats at P2, P4, P6, P8, and P10 (n= 6 for each time point). Later rats were sacrificed for histology. The most striking finding was a profound decrease in fractional anisotropy (FA) in the cortex. Cortical apparent diffusion coefficient (ADC) increased until P6 and decreased subsequently with relatively small subcortical changes. Microtubule-associated protein 2 (MAP2) staining revealed a peak in axonal and dendritic growth at P6 with subsequent decline; glial fibrillary acidic protein showed degeneration of radial glia and proliferation of astrocytes. The declines in cortical FA agree with previous ex vivo magnetic resonance imaging-based studies and reflect neonatal cortical organization. The ADC peak at P6 in the cortex coincided with axonal and dendritic growth (MAP2) and the beginning of myelination (MBP).

Fig. 1: A) Average DTI colormap images of neonatal rat from P2 to P10. B) Time related FA and ACD changes in selected cortical and whie matter structures. Abbreviations: MCX – motor cortex, SCX sensory cortex, VCX – visual cortex, scc – splenium corporis callosi, cp – cerebral peduncle C) Esitmated daily changes in FA, ADC, and local volume (measured by Log-Jacobian) between P2 and P10 in the same section as in A. Unit of the ADC is 10 – 3 mm2/s.