Focal conduction block in the dorsal root ganglion in experimental allergic neuritis

Abstract

Acute experimental allergic neuritis was induced in Lewis rats by inoculation with bovine intradural root myelin and adjuvants. In terminal experiments, sensory conduction was assessed in rats with hindlimb ataxia and weakness by stimulating the exposed sciatic nerve and recording directly from the exposed L-4 spinal nerve, dorsal root ganglion, dorsal root, and dorsal root entry zone. Focal conduction block was present in a high proportion of large-diameter fibers in the dorsal root ganglion. In contrast, nerve conduction in the peripheral nerve and spinal nerve was essentially normal apart from probable conduction block in some fibers in the proximal spinal nerve in a minority of rats. The afferent volley arriving at the dorsal root entry zone of the spinal cord was greatly reduced, as a consequence of the conduction block in the dorsal root ganglion and probable conduction block in the dorsal root. The M wave recorded from the fourth dorsal interosseus muscle of the hindfoot was normal in amplitude but slightly prolonged in latency and the H reflex was absent. These electrophysiological findings correlated well with the histological findings of inflammation and prominent demyelination in the dorsal root ganglia and dorsal roots with minimal involvement of the proximal spinal nerve and no involvement of the sciatic nerve. It is concluded that the hindlimb ataxia in rats with this form of acute experimental allergic neuritis is due to demyelination-induced nerve conduction block in the dorsal root ganglia and probably in the dorsal roots.Experimental allergic neuritis (EAN) is an autoimmune demyelinating disease of the peripheral nervous system (PNS) induced by inoculation with PNS tissue [1] or P2 protein [2] and adjuvants. In its acute form, it is widely studied as an animal model of the human disorder, the Guillain-Barré syndrome. The distribution of lesions in the PNS differs among different models of acute EAN. In rabbits and mice with acute EAN induced by inoculation with whole PNS tissue, the dorsal root ganglion is the most consistently affected region of the PNS [1,3]. The dorsal root ganglion is also a major site of involvement in rats with PNS myelin-induced or P2-induced acute EAN [4,5]. Electrophysiological studies in animals with acute EAN have demonstrated conduction abnormalities in the PNS [6-14], but have not assessed whether focal conduction block occurs in the dorsal root ganglion. We have previously demonstrated focal conduction block in the dorsal root ganglia of rabbits and, to a lesser extent, in rats with acute experimental allergic encephalomyelitis, an autoimmune demyelinating disease that affects the central nervous system and also results in PNS lesions similar to those of EAN [ 1 5 -1 8 ] . The present study was undertaken to determine whether similar focal conduction block occurs in the dorsal root ganglion in rats with EAN. Materials and Methods Induction of EANFemale Lewis rats (JC strain) bred by the Central Animal Breeding House of the University of Queensland (Brisban...

Neurophysiological changes in demyelinating and axonal forms of acute experimental autoimmune neuritis in the Lewis rat

“…The absence of significant changes in F‐wave persistence or latency in rats that had hindlimb paraparesis only (receiving day 8 PI LNC) and the marked changes in the SEPs at this time suggest that most of the symptoms of disease in these rats could be due to demyelination in and around the DRG. Several studies have emphasized the focal involvement of the DRG in Lewis rats with the same severity of EAN 22, 23, 30…”