Long ascending propriospinal neurons are heterogenous and subject to spinal cord injury induced anatomic plasticity

• Published in: Experimental neurology Vol. 373; p. 114631
• Main Authors: Brown, Brandon L., Anil, Neha, States, Gregory, Whittemore, Scott R., Magnuson, David S.K.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.03.2024
• Subjects: Anatomy; Animals; Hindlimb; Injury; Interneurons - physiology; Labeling; Neuroanatomy; Neuronal Plasticity; Neurons; Plasticity; Propriospinal; Spinal Cord; Spinal Cord Injuries; Tissue clearing; Virus; Virus; Spinal cord; Injury; Neuroanatomy; Plasticity; Propriospinal; Tissue clearing; Labeling; Anatomy
• ISSN: 0014-4886; 1090-2430; 1090-2430
• DOI: 10.1016/j.expneurol.2023.114631

Long ascending propriospinal neurons (LAPNs) are a subset of spinal interneurons that provide direct connectivity between distant spinal segments. Here, we focus specifically on an anatomically defined population of “inter-enlargement” LAPNs with cell bodies at L2/3 and terminals at C5/6. Previous studies showed that silencing LAPNs in awake and freely moving animals disrupted interlimb coordination of the hindlimbs, forelimbs, and heterolateral limb pairs. Surprisingly, despite a proportion of LAPNs being anatomically intact post- spinal cord injury (SCI), silencing them improved locomotor function but only influenced coordination of the hindlimb pair. Given the functional significance of LAPNs pre- and post-SCI, we characterized their anatomy and SCI-induced anatomical plasticity. This detailed anatomical characterization revealed three morphologically distinct subsets of LAPNs that differ in soma size, neurite complexity and/or neurite orientation. Following a mild thoracic contusive SCI there was a marked shift in neurite orientation in two of the LAPN subsets to a more dorsoventral orientation, and collateral densities decreased in the cervical enlargement but increased just caudal to the injury epicenter. These post-SCI anatomical changes potentially reflect maladaptive plasticity and an effort to establish new functional inputs from sensory afferents that sprout post-SCI to achieve circuitry homeostasis. •Dual-viral labeling allows for large volume single neuron reconstructions•Long ascending propriospinal neurons have three distinct morphologies•Spinal cord injury results in shifts in neurite orientation•Long ascending propriospinal neurons' axon targets change post-spinal cord injury