Characterization of dendritic morphology and neurotransmitter phenotype of thoracic descending propriospinal neurons after complete spinal cord transection and GDNF treatment

Abstract

After spinal cord injury (SCI), poor regeneration of damaged axons of the central nervous system (CNS) causes limited functional recovery. This limited spontaneous functional recovery has been attributed, to a large extent, to the plasticity of propriospinal neurons, especially the descending propriospinal neurons (dPSNs). Compared with the supraspinal counterparts, dPSNs have displayed significantly greater regenerative capacity, which can be further enhanced by glial cell line-derived neurotrophic factor (GDNF). In the present study, we applied a G-mutated rabies virus (G-Rabies) co-expressing green fluorescence protein (GFP) to reveal Golgi-like dendritic morphology of dPSNs. We also investigated the neurotransmitters expressed by dPSNs after labeling with a retrograde tracer Fluoro-Gold (FG). dPSNs were examined in animals with sham injuries or complete spinal transections with or without GDNF treatment. Bilateral injections of G-Rabies and FG were made into the 2nd lumbar (L2) spinal cord at 3 days prior to a spinal cord transection performed at the 11th thoracic level (T11). The lesion gap was filled with Gelfoam containing either saline or GDNF in the injury groups. Four days post-injury, the rats were sacrificed for analysis. For those animals receiving G-rabies injection, the GFP signal in the T7–9 spinal cord was visualized via 2-photon microscopy. Dendritic morphology from stack images was traced and analyzed using a Neurolucida software. We found that dPSNs in sham injured animals had a predominantly dorsal-ventral distribution of dendrites. Transection injury resulted in alterations in the dendritic distribution with dorsal-ventral retraction and lateral-medial extension. Treatment with GDNF significantly increased the terminal dendritic length of dPSNs. The density of spine-like structures was increased after injury, and treatment with GDNF enhanced this effect. For the group receiving FG injections, immunohistochemistry for glutamate, choline acetyltransferase (ChAT), glycine, and GABA was performed in the T7–9 spinal cord. We show that the majority of FG retrogradely-labeled dPSNs were located in the Rexed Lamina VII. Over 90 percent of FG-labeled neurons were glutamatergic, with the other three neurotransmitters contributing less than 10 percent of the total. To our knowledge this is the first report describing the morphologic characteristics of dPSNs and their neurotransmitter expressions, as well as the dendritic response of dPSNs after transection injury and GDNF treatment.

Protective Effects of Estradiol and Dihydrotestosterone following Spinal Cord Injury

“…92 The number of propriospinal neurons proximal to an SCI is severely depleted after a thoracic SCI, but short axon propriospinal neurons within the lumbosacral enlargement show no qualitative loss at 2 weeks. 118 We have demonstrated dendritic changes in propriospinal neurons after SCI, 119 and such changes could result in alterations in the activity of these neurons, leading to the atrophy we observed in lumbar motoneurons. Should such potential reductions in propriospinal neurons be prevented by hormonal treatment, the rescue of the major afferent source to motoneurons could underlie the beneficial effects of hormone treatment on motoneuron dendrities we have observed.…”

Electroacupuncture at Governor Vessel improves neurobehavioral function via silencing complexin I

“…Numerous evidences show that the dendritic spines can change shape, size, and number following various injuries (44,45). GV treatment also promotes synaptic plasticity via regulating CPLX1.…”

“…After SCI, there is an acute reduction in dendritic number in these survived neurons with rapid dendritic atrophy. Meanwhile, spontaneous dendritic plasticity could reflect a compensatory response of the spinal cord to the functional deficits caused by the injury (45,46) As yet, one of the important strategies for treating SCC is to promote axon regeneration in the epicenter (49). Data demonstrated that decreased CPLX1 expression promoted axon regrowth even when neurons were incubated in an inhibitory environment through highly up-regulation of GAP43 involving in axonal growth and regeneration (25,50).…”

Electroacupuncture at Governor Vessel improves neurobehavioral function via reduction of complexin1

“…GV also promotes synaptic plasticity via regulating CPLX1. Numerous evidences show that the dendritic spines can change shape, size, and number following various injuries (Tan&Waxman, 2012;Deng et al, 2016). After SCI, there is an acute reduction in dendritic number in these survived neurons with rapid dendritic atrophy.…”

“…After SCI, there is an acute reduction in dendritic number in these survived neurons with rapid dendritic atrophy. Meanwhile, spontaneous dendritic plasticity could reflect a compensatory response of the spinal cord to the functional deficits caused by the injury (Horch et al, 2011;Deng et al, 2016). Increased dendritic spine density observed in neurons have entered into a more plastic state, which indicate availability to form new synapses (Alvarez&Sabatini, 2007).…”