Re‐establishment of direct synaptic connections between sensory axons and motoneurons after lesions of neonatal opossum CNS (Monodelphis domestica) in culture

Abstract

For functional recovery after spinal cord injury, regenerating fibres need to grow and to reform appropriate connections with their targets. The isolated central nervous system of neonatal opossums aged 1-9 days has been used to analyse the precision with which neurons become reconnected during regeneration. In culture these preparations maintain their electrical activity and show rapid outgrowth through spinal cord crushes or cuts. By recording electrically and by staining with horseradish peroxidase, we first demonstrated that direct reflex connections were already present at birth between sensory fibres in one segment and motoneurons in the same segment and in adjacent segments. As in previous experiments, 5 days after the spinal cord had been crushed, labelled sensory fibres grew across the lesion to reach the next segment (Woodward et al. (1993) J. Exp. Biol., 176, 77-88; Varga et al. (1995a) Eur. J. Neurosci., 7, 2119-2129, Varga et al. (1995b) Proc. Natl. Acad. Sci. USA, 92, 10959-10963). Beyond the lesion the labelled axons abruptly changed direction, traversed the spinal cord and terminated on labelled motoneurons in the ventral horn. In preparations that had regenerated dorsal root stimulation once again initiated ventral root reflexes. Electron micrographs revealed synapses made by labelled sensory axons on motoneurons. Double staining of growing sensory axons and radial glial fibres showed close association, suggesting guidance. These results indicate that the original pathway is re-established during repair and that appropriate connections are reformed after injury.

Development of motoneurons and primary sensory afferents in the thoracic and lumbar spinal cord of the South American opossumMonodelphis domestica

“…After placing DiI crystals on the entry zone of the dorsal roots, Konstantinidou et al (1995) were unable to label any fibres in layers I and II of the human spinal cord. In the present study GSA was used to verify the DiI labelling, as was shown recently by Fernandez and Nicholls (1998), using the electron microscope, that even on the day of birth, in Monodelphis, groups of small and large diameter axons are present in the central stump of the dorsal root in the cervical region. The GSA staining indicated the presence of C-fibre afferents within the presumptive layers I and II at P14.…”

“…The arrival and arborisation in the lumbar region of ventral horn afferents at P7 provides the basic circuit for the development of a simple stretch reflex. In the cervical region in Monodelphis this pathway has been shown to be present during the first postnatal week, by using electrophysiological analysis (Lepre et al, 1998). Whether the lumbar region would have the same degree of connectivity at this age remains unclear.…”

Ab initio structure prediction of two α‐helical oligomers with a multiple‐chain united‐residue force field and global search

“…Double‐tracing experiments have been carried out also in the opossum spinal cord, and as in the chick, it has been shown that, during the permissive stages, regeneration is indeed due to newly grown fibers rather than to the progression of development (Varga et al, 1996; Lepre et al, 1998; Saunders et al, 1998; Wang et al, 1998a; Martin et al, 2000). These authors have shown that, in addition to anatomical recovery, there is a remarkable functional recovery.…”