Brain growth of the domestic pig (Sus scrofa) from 2 to 24 weeks of age: a longitudinal MRI study

Abstract

An animal model with brain growth similar to humans, that can be used in MRI studies to investigate brain development, would be valuable. Our laboratory has developed and validated MRI methods for regional brain volume quantification in the neonatal piglet. The aim of this study was to utilize the MRI-based volume quantification technique in a longitudinal study to determine brain growth in domestic pigs from 2 to 24 weeks of age. MRI data were acquired from pigs 2-24 weeks of age using a 3-dimensional magnetization-prepared gradient echo sequence on a Magnetom Trio 3-tesla imager. Manual segmentation was performed for volume estimates of total brain, cortical, diencephalon, brainstem, cerebellar and hippocampal regions. Logistic modeling procedures were used to characterize brain growth. Total brain volume increased 130% (±12%) and 121% (±7%) from 2 to 24 weeks in males and females, respectively. The maximum increase in total brain volume occurred about the age of 4 weeks and 95% of whole brain growth occurred by the age of 21-23 weeks. Logistical modeling suggests there are sexually dimorphic effects on brain growth. For example, in females, the cortex was smaller (p = 0.04). Furthermore, the maximum growth of the hippocampus occurred about 5 weeks earlier in females than males, and the window for hippocampal growth was significantly shorter in females than males (p = 0.02, p = 0.002 respectively). These sexual dimorphisms are similar to what is seen in humans. In addition to providing important data on brain growth for pigs, this study shows pigs can be used to obtain longitudinal MRI data. The large increase in brain volume in the postnatal period is similar to that of human neonates and suggests pigs can be used to investigate brain development.

Fig. 1. Body weight of pigs from 2 to 24 wks of age

Body weight of male pigs higher than female pigs starting at 20 wks of age. The error bars indicate SEM. * = p < 0.01 ** = p < 0.001

Fig. 2. Representative MRI images displaying brain growth from 2 to 24 wks of age

The top images are T1-weighted axial sections (skull stripped) from a female pig at each age (A). The bottom images show the coronal, axial, and sagittal views left to right of a 12 wk old female pig (B). Segmentation is shown for cortex (white), diencephalon (green), hippocampi (blue), cerebellum (red), and brainstem (yellow).

Fig. 3. Brain region growth curves and logistic models

The graphs show total brain and brain region volumes for male and female pigs from 2 to 24 wks of age, as well as logistic growth models for male and female pigs. Error bars indicated SEM.