Glial bundle formation in spinal roots following experimental neuronopathy

Abstract

Spinal motor neurons and dorsal root ganglion cells were caused to degenerate by axoplasmic transport of toxic lectins via the sciatic nerve. Within a few months, loss of axons and glial bundle formation were seen in the proximal portions of the L4-6 ventral and dorsal roots. The glial bundles observed were structurally the same as those described in humans, but they were occasionally also invested with Schwann cell cytoplasmic processes, the cell membrane of which was directly apposed to that of astrocytes. Basal lamina surrounding the outer surface of the bundles was shared by these two as a continuous sheet. This unique complex of astroglial and Schwann cell processes, completely covered by basal lamina, may be a newly formed interface between the central and peripheral nervous systems and thus may severe as a guide and potential pathway for regenerating neurites.

An autopsy case of spinal muscular atrophy type III (Kugelberg‐Welander disease)

“…13,14 Currently, it is proposed that glial bundles may not induce retrograde degeneration of the anterior horn cells, may be formed after nerve degeneration, and serve as a guide for regenerating neurites. 15 Neuropathologic changes other than those in motor neurons were found in the posterior column and dentate nucleus. The posterior column change has been described in other SMA III patients.…”

“…Glial bundles were characteristic, but not specific to SMA, as they were also found, although to a lesser extent, in various diseases including poliomyelitis and ALS 13,14 . Currently, it is proposed that glial bundles may not induce retrograde degeneration of the anterior horn cells, may be formed after nerve degeneration, and serve as a guide for regenerating neurites 15 …”

Is spinal muscular atrophy a disease of the motor neurons only: pathogenesis and therapeutic implications?

“…These glial bundles are most abundant in the lumbar regions and are observed only in the anterior spinal roots and not in the posterior roots. Glial bundles are characteristic, but not specific, to SMA and it is hypothesized that they are secondary to neuronal degeneration, rather than causing the degeneration of anterior horn cells [78]. Another interesting finding raised in this study is that the loss of GABAergic and glutamatergic synapses on MNs could result from the induction of neuronal nitric oxide synthase (nNOS), which is upregulated in SMNΔ7 MNs [67].…”

“…These findings don’t exclude the relevance of this cell type to the elimination of cellular fragments during synapse degeneration [67]. Examination of SMA post mortem spinal cord reveals a severe loss of myelinated fibers with numerous glial bundles in the anterior horns [78]. These glial bundles are most abundant in the lumbar regions and are observed only in the anterior spinal roots and not in the posterior roots.…”

Cell Transplantation to Restore Lost Auditory Nerve Function is a Realistic Clinical Opportunity

“…Normally, astrocytes in the CNS and SCs in the PNS are apart and mutually exclusive but their mutual repulsion decreases following motor and sensory neuron death in the brainstem/spinal cord 135 . As a result, the distal tip of the AO extensively apposes with SCs or is directly wrapped by SC cytoplasm within a common basal lamina 133 , 135 . Distally, SCs form structures called SC columns or bands of Bungner that can guide regenerating axons back to their targets 136 .…”