Retino-thalamo-cortical and callosal connections visualized with manganese-enhanced magnetic resonance imaging and validated with tract tracing techniques
Ocular dominance columns correlate with patchy callosal connections in Long Evans rats (Laing et al., 2015). We explored in vivo manganese-enhanced magnetic resonance imaging (MEMRI) as a possible strategy for longitudinal studies of plastic changes in the retino-thalamo-cortical and callosal pathways. MnCl 2 was injected either intraocularly or intracortically to label these pathways, respectively. The transport of the paramagnetic ion Mn 2+ was evaluated by comparing images acquired both before and 36 or 12 hours after intraocular or cortical injections, respectively. Images were acquired on a 3T magnet (Philips Achieva, Philips Healthcare, Andover, MA), using a custom surface coil and a T1-weighted MPRAGE image sequence (TR/TE = 23/11 ms; Ti=1000 ms; FA= 10 deg acquired matrix 432x432 mm over 118 slices, voxel size 0.11x0.11x0.2 mm 3 ). To validate the transport of Mn 2+ , each animal also received either an intraocular injection of the transneuronal tracer WGA-HRP, or cortical injections of HRP. Following monocular injections of MnCl 2 , MRI images showed significant, bilateral accumulations of Mn 2+ in regions of the SC, LGN and visual cortex that corresponded with regions labeled with HRP. In adult rats monocularly enucleated at birth, we injected MnCl 2 in the hemisphere contralateral to the remaining eye in an attempt to detect anomalies reported previously in the callosal pattern ipsilateral to the remaining eye. After the scans, the hemisphere injected with MnCl 2 was injected with HRP. MRI images revealed Mn 2+ patterns that closely resembled the callosal patterns demonstrated with HRP in the same animal. Our results suggest that both transneuronal retino-thalamo-cortical, as well as cortico-cortical transport of Mn 2+ provide potentially useful strategies for longitudinal studies of plastic changes in these pathways.
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ScienceOpen Posters
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31
October
2020
Affiliations
[1
] Department of Psychology, University of Washington, Seattle, WA 98195, USA
[2
] Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City,
UT, USA.
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Date
received
: 31
October
2020
Data availability: The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.