Abstract
Retrograde tracing is a key facet of neuroanatomical studies involving long distance projection neurons. Previous groups have utilized a variety of tools ranging from classical chemical tracers to newer methods employing viruses for gene delivery. Here, we highlight the usage of a lentivirus that permits highly efficient retrograde transport (HiRet) from synaptic terminals within the cervical and lumbar enlargements of the spinal cord. By injecting HiRet, we can clearly identify supraspinal and propriospinal circuits innervating motor neuron pools relating to forelimb and hindlimb function. We observed robust labeling of propriospinal neurons, including high fidelity details of dendritic arbors and axon terminals seldom seen with chemical tracers. In addition, we examine changes in interneuronal circuits occurring after a thoracic contusion, highlighting populations that potentially contribute to spontaneous behavioral recovery in this lesion model. Our study demonstrates that the HiRet lentivirus is a unique tool for examining neuronal circuitry within the brain and spinal cord.
Highlights
Mapping studies of neuroanatomical pathways of the central and peripheral nervous system utilized tracing of neurons and axons with chemical tracers
We show that discrete unilateral injections of highly efficient retrograde transport (HiRet) lentivirus into either the cervical or lumbar spinal cord label well-defined locations within the spinal cord and brainstem when compared to previous studies using retrograde chemical tracers
This viral vector supports better definition of pathways that innervate specific regions of the brain or spinal cord and provides an advantage compared to AAVs that are used for retrograde mapping where uptake by axons en passage needs to be taken into account (Tervo et al, 2016)
Summary
Mapping studies of neuroanatomical pathways of the central and peripheral nervous system utilized tracing of neurons and axons with chemical tracers Markers such as biotinylated dextran amines (BDAs) (Veenman et al, 1992), cholera toxin beta subunit (Trojanowski et al, 1982; Luppi et al, 1990), fluorogold (Schmued and Fallon, 1986), microbeads (Katz et al, 1984; Katz and Iarovici, 1990) and Phaseolus vulgaris-leucoagglutinin (Gerfen and Sawchenko, 1984) provide a clear and distinct labeling of neuronal morphology including somas, dendrites, and axons. Use of these tracers does not provide information regarding synaptic connectivity of a set population of neurons
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