title: Spinal cord neuron inputs to the cuneate nucleus that partially survive dorsal column lesions: A pathway that could contribute to recovery after spinal cord injury.
abstract: Dorsal column lesions at a high cervical level deprive the cuneate nucleus and much of the somatosensory system of its major cutaneous inputs. Over weeks of recovery, much of the hand representations in the contralateral cortex are reactivated. One possibility for such cortical reactivation by hand afferents is that preserved second-order spinal cord neurons reach the cuneate nucleus through pathways that circumvent the dorsal column lesions, contributing to cortical reactivation in an increasingly effective manner over time. To evaluate this possibility, we first injected anatomical tracers into the cuneate nucleus and plotted the distributions of labeled spinal cord neurons and fibers in control monkeys. Large numbers of neurons in the dorsal horn of the cervical spinal cord were labeled, especially ipsilaterally in lamina IV. Labeled fibers were distributed in the cuneate fasciculus and lateral funiculus. In three other squirrel monkeys, unilateral dorsal column lesions were placed at the cervical segment 4 level and tracers were injected into the ipsilateral cuneate nucleus. Two weeks later, a largely unresponsive hand representation in contralateral somatosensory cortex confirmed the effectiveness of the dorsal column lesion. However, tracer injections in the cuneate nucleus labeled only about 5% of the normal number of dorsal horn neurons, mainly in lamina IV, below the level of lesions. Our results revealed a small second-order pathway to the cuneate nucleus that survives high cervical dorsal column lesions by traveling in the lateral funiculus. This could be important for cortical reactivation by hand afferents, and recovery of hand use.
authors.affiliation: Department of Psychology, Vanderbilt University, Nashville, Tennessee, 37240, USA.
authors.forename: Chia-Chi
authors.initials: CC
authors.lastname: Liao
authors.affiliation: Department of Psychology, Vanderbilt University, Nashville, Tennessee, 37240, USA.
authors.forename: Gabriella E
authors.initials: GE
authors.lastname: DiCarlo
authors.affiliation: Department of Psychology, Vanderbilt University, Nashville, Tennessee, 37240, USA.
authors.forename: Omar A
authors.initials: OA
authors.lastname: Gharbawie
authors.affiliation: Department of Psychology, Vanderbilt University, Nashville, Tennessee, 37240, USA.
authors.forename: Hui-Xin
authors.initials: HX
authors.lastname: Qi
authors.affiliation: Department of Psychology, Vanderbilt University, Nashville, Tennessee, 37240, USA.
authors.forename: Jon H
authors.initials: JH
authors.lastname: Kaas
mesh_terms: D000818:Animals; D016645:Aotidae; D001710:Biotin / Q000031:analogs & derivatives; D001931:Brain Mapping; D002574:Cervical Vertebrae; D002772:Cholera Toxin; D003911:Dextrans; D006225:Hand / Q000503:physiopathology; D008526:Medulla Oblongata / Q000473:pathology / Q000503:physiopathology*; D008839:Microelectrodes; D009434:Neural Pathways / Q000473:pathology / Q000503:physiopathology; D056347:Neuroanatomical Tract-Tracing Techniques; D056325:Neuronal Tract-Tracers; D009474:Neurons / Q000473:pathology / Q000502:physiology*; D012453:Saimiri; D013003:Somatosensory Cortex / Q000473:pathology / Q000503:physiopathology; D013116:Spinal Cord / Q000473:pathology / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000473:pathology / Q000503:physiopathology*
chemical_list: D003911:Dextrans; D056325:Neuronal Tract-Tracers; C076397:biotinylated dextran amine; D001710:Biotin; D002772:Cholera Toxin
keywords: cortical reactivation; cuneate nucleus; dorsal column lesion; lateral funiculus; second-order spinal cord pathway
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