High-resolution MEMRI characterizes laminar specific ascending and descending spinal cord pathways in rats

Manganese Enhanced MRI (MEMRI) utilizing different manganese chloride (MnCl2) delivery methods, has yielded valuable architectural, functional and connection information about the brain. MEMRI also has the potential in characterizing neural pathways in the spinal cord. The spinal cord grey matter is anatomically composed of nine distinct cellular laminae, where each of the laminae receives input from a specific type of neuronal population and process or serves as a relay region in a specific sensory or motor pathway. This type of laminar arrangement in the spinal cord is currently only visualized by histological methods. It is of significant interest to determine whether laminar specific enhancement by Mn2+ can be achieved in the spinal cord, as has been reported in the brain and olfactory pathway. Here we focus on using MEMRI to determine the specific laminae of the thoracic region of the spinal cord. We focus on MnCl2 changes in the ascending and descending tracts of the spinal cord. Major factors in applying this technique in the spinal cord are the ability to acquire high-resolution spinal cord images and to determine a noninvasive route of administration which will result in uptake by the central nervous system. We have applied the MEMRI approach by intraperitoneal (i.p). delivery of MnCl2 and imaged lumbar and thoracic spinal cord levels in rats to determine whether T1 weighted MRI can detect spinal cord laminae 48 hours following MnCl2 administration. T1 weighted images of the lower lumbar level were obtained from MnCl2 injected and control rats. Here we demonstrate laminar specific signal enhancement in the spinal cord of rats administered with MnCl2 vs. controls in MRI of the cord with ultra-high, 69 μm in-plane resolution. We also report reduced T1 values over time in MnCl2 groups across laminae I-IX. The regions with the largest T1 enhancements were observed to correspond to laminae that contain either high cell density or large motor neurons, making MEMRI an excellent tool for studying spinal cord architecture, physiology and function in different animal models.