Quantitative Cortical Mapping of Fractional Anisotropy in Developing Rat Brains

Abstract

Cortical development is associated with a series of events that involve axon and dendrite growth and synaptic formation. Although these developmental processes have been investigated in detail with histology, three-dimensional and quantitative imaging methods for rodent brains may be useful for genetic and pharmacological studies in which cortical developmental abnormalities are suspected. It has been shown that diffusion tensor imaging (DTI) can delineate the columnar organization of the fetal and early neonatal cortex based on a high degree of diffusion anisotropy along the columnar structures. This anisotropy is known to decrease during brain development. In this study, we applied DTI to developing rat brains at five developmental stages, postnatal days 0, 3, 7, 11 and 19, and used diffusion anisotropy as an index to characterize the structural change. Statistical analysis reveals four distinctive cortical areas that demonstrate a characteristic time course of anisotropy loss. This method may provide a means to delineate specific cortical areas and a quantitative method to detect abnormalities in cortical development in rodent pathological models.

Diffusion Tensor Imaging of Cortical Surface Development

“…In a recent publication of The Journal of Neuroscience, Huang et al (2008) reported that FA could be used to quantitatively map spatiotemporal patterns of cortical development in the rat brain. Although well investigated at the cellular level, cortical development during the early postnatal period remains largely unmapped across all cortical regions in the whole brain because of the practical limitations of histological methods.…”

“…To characterize whole-brain structural development, high-resolution DTI images of ex vivo rat brains were acquired at five time points during postnatal development [postnatal day 0 (P0), P3, P7, P11, and P19]. Using FA to index the degree of cortical columnar organization at single measurement points, the authors identified an age-dependent decrease in FA with regional specificity in the cortex [Huang et al (2008), their Fig. 4 (http://www.…”

“…jneurosci.org/cgi/content/full/28/6/1427/ F4)]. In addition to single-point analysis, maps of FA values across the entire brain surface were generated at each developmental time point to visualize cortical maturation dynamics [Huang et al (2008), their Fig. 3 (http://www.jneurosci.…”

“…The authors recognized the importance of using a regionselection method that reduced point misplacement and aligned the data from different developmental time points by selecting FA map slices from the same anatomical locations. This slice selection was accomplished by proportional distance scaling along the anterior-posterior axis [Huang et al (2008), their Fig. 1 (http:// www.jneurosci.org/cgi/content/full/28/6/ 1427/F1)].…”

“…1 (http:// www.jneurosci.org/cgi/content/full/28/6/ 1427/F1)]. Cortical measurement points were then defined for these slices by conserving the angle from midline of an initial point set created using an atlas overlay on the P19 brain [Huang et al (2008), their Fig. 2 (http://www.jneurosci.org/ cgi/content/full/28/6/1427/F2)].…”