In vivo retinotopic mapping of superior colliculus using manganese-enhanced magnetic resonance imaging Kevin C. Chan a,b , Jiang Li c , Phillis Kau c , Iris Y. Zhou a,b , Matthew M. Cheung a,b , Condon Lau a,b , Jian Yang a,b , Kwok-fai So c , Ed X. Wu a,b,c, ⁎ a Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong, China b Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong, China c Department of Anatomy, The University of Hong Kong, Pokfulam, Hong Kong, China abstract article info Article history: Received 2 March 2010 Revised 27 May 2010 Accepted 6 July 2010 Available online 13 July 2010 Keywords: Manganese-enhanced MRI Retinotopic mapping Superior colliculus Intraorbital optic nerve Partial transection Anterograde axonal transport The superior colliculus (SC) is a dome-shaped subcortical laminar structure in the mammalian midbrain, whose superficial layers receive visual information from the retina in a topological order. Despite the increasing number of studies investigating retinotopic projection in visual brain development and disorders, in vivo, high-resolution 3D mapping of topographic organization in the subcortical visual nuclei has not yet been available. This study explores the capability of 3D manganese-enhanced MRI (MEMRI) at 200 μm isotropic resolution for in vivo retinotopic mapping of the rat SC upon partial transection of the intraorbital optic nerve. One day after intravitreal Mn 2+ injection into both eyes, animals with partial transection at the right superior intraorbital optic nerve in Group 1 (n = 8) exhibited a significantly lower T1-weighted signal intensity in the lateral region of the left SC compared to the left medial SC and right control SC. Partial transection toward the temporal or nasal region of the right intraorbital optic nerve in Group 2 (n = 7) led to T1-weighted hypointensity in the rostral or caudal region of the left SC, whereas a clear border was observed separating 2 halves of the left SC in all groups. Previous histological and electrophysiological studies showed that the retinal ganglion cell axons emanating from superior, inferior, nasal and temporal retina projected respectively to the contralateral lateral, medial, caudal and rostral SC in rodents. While this topological pattern is preserved in the intraorbital optic nerve, it was shown that partial transection of the superior intraorbital optic nerve led to primary injury predominantly in the superior but not inferior retina and optic nerve. The results of this study demonstrated the sensitivity of submillimeter-resolution MEMRI for in vivo, 3D mapping of the precise retinotopic projections in SC upon reduced anterograde axonal transport of Mn 2+ ions from localized regions of the anterior visual pathways to the subcortical midbrain nuclei. Future MEMRI studies are envisioned that measure the topographic changes in brain development, diseases, plasticity and regeneration therapies in a global and longitudinal setting. © 2010 Elsevier Inc. All rights reserved. Introduction The functions of the central nervous system depend upon precisely organized neuronal connections (Herrero et al., 2002; Humphries et al., 2010; Petersen, 2007; Romanelli et al., 2005; Scicolone et al., 2009; Silver and Kastner, 2009; Upadhyay et al., 2007). Among the complex neural networks, the superior colliculus (SC) is a dome-shaped subcortical laminar structure in the mammalian midbrain, which is important in coordinating visual, somatosensory and auditory stimuli to guide animal behavior (Baba et al., 2007; Dori et al., 1998; Tiao and Blakemore, 1976). In particular, the superficial layers of the SC receive visual information from the retina in a topological order (McLaughlin et al., 2003; Plas et al., 2005; Siminoff et al., 1966; Simon and O'Leary, 1991), whereby the retinal ganglion cell axons emanating from superior, inferior, nasal and temporal retina projected to the contralateral lateral, medial, caudal and rostral SC respectively in rodents (McLaughlin et al., 2003; Plas et al., 2005; Siminoff et al., 1966; Simon and O'Leary, 1991). Despite the increasing number of studies investigating the retinotopic projection in visual brain development and disorders (Chandrasekaran et al., 2005; Dunlop et al., 2007; Finlay et al., 1979; Haustead et al., 2008; Jeffery and Thompson, 1986; McLaughlin et al., 2003; O'Leary and McLaughlin, 2005; Scicolone et al., 2009; Simon and O'Leary, 1992; So, 1979), the majority of in vivo techniques on brain organization, such as electrophysiology and optical imaging, focus on the cortex (Issa et al., 2008; Kalatsky et al., 2005; Kim et al., 2006; Peterson et al., 1998). The precise topological projection in the subcortical structures NeuroImage 54 (2011) 389–395 ⁎ Corresponding author. Laboratory of Biomedical Imaging and Signal Processing, Departments of Electrical and Electronic Engineering, Anatomy and Medicine, The University of Hong Kong, Hong Kong, China. Fax: +852 2819 9711. E-mail address: ewu@eee.hku.hk (E.X. Wu). 1053-8119/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.neuroimage.2010.07.015 Contents lists available at ScienceDirect NeuroImage journal homepage: www.elsevier.com/locate/ynimg