Loss of Ephaptic Contacts in the Murine Thalamus during Osmotic Demyelination Syndrome

Abstract

Background and aim:A murine model mimicking osmotic demyelination syndrome (ODS) revealed with histology in the relay posterolateral (VPL) and ventral posteromedial (VPM) thalamic nuclei adjoined nerve cell bodies in chronic hyponatremia, amongst the damaged 12 h and 48 h after reinstatement of osmolality. This report aims to verify and complement with ultrastructure other neurophysiology, immunohistochemistry, and molecular biochemistry data to assess the connexin-36 protein, as part of those hinted close contacts.This ODS investigation included four groups of mice: Sham (NN; n = 13), hyponatremic (HN; n = 11), those sacri ced 12 h after a fast restoration of normal natremia (ODS12h; n = 6) and mice sacri ced 48 h afterward, or ODS48 h (n = 9). Out of these, thalamic zones samples included NN (n = 2), HN (n = 2), ODS12h (n = 3) and ODS48h (n = 3). Results: Ultrastructure illustrated junctions between nerve cell bodies that were immunolabeled with connexin36 (Cx36) with light microscopy and Western blots. These cell's junctions were reminiscent of low resistance junctions characterized in other regions of the CNS with electrophysiology. Contiguous neurons showed neurolemma contacts in intact and damaged tissues according to their location in the ODS zones, at 12 h and 48 h post correction along with other demyelinating alterations. Neurons and ephaptic contact measurements indicated the highest alterations, including nerve cell necrosis in the ODS epicenter and damages decreased toward the outskirts of the demyelinated zone. Conclusion: Ephapses contained C × 36between intact or ODS injured neurons in the thalamus appeared to be resilient beyond the core degraded tissue injuries. These could maintain intercellular ionic and metabolite exchanges between these lesser injured regions and, thus, would partake to some brain plasticity repairs.

Thalamic Neuron Resilience during Osmotic Demyelination Syndrome (ODS) Is Revealed by Primary Cilium Outgrowth and ADP-ribosylation factor-like protein 13B Labeling in Axon Initial Segment

“…Thus, in a sample of LM random field of view, those labeled ARL13B NN, HN, ODS12h and ODS48h thalamic structures are illustrated, and exemplify the marked contrast shown by the AIS structures that appear in the CNS tissues where nucleoli reveal transcripts in ODS48h > ODS12h > HN appearances. Furthermore, as shown previously in the thalamic nuclei, some nerve cell bodies display a twin association as they join by ephaptic contacts [69]. The specificity of ARL13B immunolabeling is verified using technical and biological controls (Figure A1).…”

“…The LM yellow-ochre hue aspects of the ARL13B immunolabeled thalamic tissues appear as if covered with an overall from which scattered hole-like, oval to round shapes appear as 'holes in the fabric', where the nerve cell bodies, either isolated or as joined pairs or triplets exhibit poor contrast, as shown before with resilient nerve cells [66]; meanwhile, they maintain low resistance contact junctions with each other, as noted in Figure 12A [69]. However, the nuclei, poorly stained, disclose orthochromasy where contrasted nucleoli in pale blue staining according to hemalum reveal accumulated RNA transcripts with a chromatin DNA-stained dark blue hue [155,156].…”

“…These accumulated transcripts would show some similarity, as in the growth cones [243][244][245][246][247]250]. The murine investigation model of ODS that we developed [62,64,65] would suggest that after regional CNS damages, the altered thalamic regions can recover some of the relay thalamus functions following tissue repairs according to their location from the damaged epicenter, that has undergone necrosis where regional demyelination accompanied a classic 'liquefaction necrosis' after progressive rebalanced osmolality [62,[64][65][66][67][68][69]. Accordingly, the investigated time lapses after reinstatement of osmolarity indicated some neural and oligodendrocyte resilience and reorganizations post-ODS.…”

“…Even though thalamic neurons seem not to degenerate inside ODS demyelinating lesions, several reports from our group using TEM analysis pointed out signs of cellular adaptation at the level of their neuronal cell bodies. Among them, neuron cell bodies early emerged from the ODS challenge with deeply indented nuclei owing nucleolus translational activation, huge amounts of polysomes along with secretory-like activities [66,68,69]. Another main fine structure revealed at the axonal hillock was a primary cilium appendage that corresponded with contrasted rod-shaped structures or shaft larger growths in the ODS surrounding regions after chronic hyponatremia, 12 h and 48 h time lapses following rapid reinstatement of sodium balance.…”