Three-axis Modification of Coordinates Enables Accurate Stereotactic Targeting in Non-human Primate Brains of Different Sizes
Hyung-Sun Kim1, Goo-Hwa Kang1, Hanlim Song2, Ra Gyung Kim2, Ji-Young Park2, Jeong Ho Hwang1, and Hyoung-Ihl Kim2,3*
1Animal model research group, Korea Institute of Toxicology, Jeongup 53212, Korea.
2Neuromodulation Lab, Department of Biomedical Science and Engineering, Gwangju Institute of Science and technology, Gwangju 61005, Korea.
3Department of Neurosurgery, Presbyterian Medical Center, Jeonju 54987, Korea.
Correspondence to: *To whom correspondence should be addressed.
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Received: January 15, 2019; Revised: May 8, 2019; Accepted: May 13, 2019
The brain grows with age in non-human primates (NHPs). Therefore, atlas-based stereotactic coordinates cannot be used directly to target subcortical structures if the size of the animal's brain differs from that used in the stereotactic atlas. Furthermore, growth is non-uniform across different cortical regions, making it difficult to simply apply a single brain-expansion ratio. We determined the skull reference lines that best reflect changes in brain size along the X, Y, and Z axes and plotted the changes in reference-line length against the changes in body weight. The skull reference lines had a linear relationship with body weight. However, comparison of skull reference lines with body weight confirmed the non-uniform skull growth during postnatal development, with skull growth more prominent in the X and Y axes than the Z axis. Comparing the differences between the atlas-based lengths and those calculated empirically from plot-based linear fits, we created craniometric indices that can be used to modify stereotactic coordinates along all axes. We verified the accuracy of the corrected stereotactic targeting by infusing dye into internal capsule in euthanized and preserved NHP brains. Our axis-specific, craniometric-index-adjusted stereotactic targeting enabled us to correct for targeting errors arising from differences in brain size. Histological verification showed that the method was accurate to within 1 mm. Craniometric index-adjusted targeting is a simple and relatively accurate method that can be used for NHP stereotactic surgery in the general laboratory, without the need for high-resolution imaging.
Keywords: Stereotaxy, Nonhuman primate, Skull, Body weight