Loss of the Compound Action Potential: an Electrophysiological, Biochemical and Morphological Study of Early Events in Axonal Degeneration in the C57BL/Ola Mouse

Abstract

In the C57BL/Ola (Ola) mouse strain there is a marked slowing of axonal disintegration during Wallerian degeneration. The locus of the mutation controlling this phenomenon (slow Wallerian degeneration--Wlds) has been mapped to chromosome 4, and its protective effect decreases with advancing age. Using biochemical, electrophysiological and histological techniques, the present study was undertaken to determine whether neurofilament phosphorylation and stability are altered or whether calcium-activated proteases are absent in the sciatic nerves of Ola mice. A compound action potential was detectable only when neurofilaments were present and normal axonal architecture was seen. In 1-month-old Ola mice, compound action potentials and neurofilaments were still detectable at 21 days post-transection, whereas both were undetectable by 2 days in BALB/c and C57BL/6J (6J) mice of the same age. Neurofilament levels declined faster with advancing Ola age, confirming previous results, whereas degeneration slowed in ageing BALB/c and 6J mice. In vitro and in vivo degeneration rates were comparable in BALB/c and 6J nerves. Ola nerves, however, showed more rapid decline in vitro than in vivo. Ola and BALB/c nerves frozen and then thawed and incubated in the presence of calcium ions and the ionophore A23187 were not resistant to degradation by intrinsic proteases. Even when a compound action potential could no longer be elicited, however, a majority of nerves still had > 50% of myelinated and unmyelinated axons whose electron microscopic profiles appeared normal. Thus, it appears that the first event in Wallerian degeneration in the Ola mouse is a change at the plasma membrane--a transected nerve becomes unable to conduct a compound action potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Temperature Modulation Reveals Three Distinct Stages of Wallerian Degeneration

“…We confirmed that axonal degeneration in vivo and in vitro in 6N nerves was comparable, with ϳ2.5% of the CAP (relative to control) remaining at 2 d, as previously reported (Tsao et al, 1994). The act of axotomy and removing the nerves for culturing was found to reduce the CAP A wave by ϳ30% within 3 hr, after which the nerve was stable for the next 21 hr ( Fig.…”

“…In Wld mice the first electrophysiologically detectable event in Wallerian degeneration is axonal inability to continue conducting CAPs although the morphology remains relatively preserved (Tsao et al, 1994). Via monitoring the disappearance of CAPs and axonal morphology, this study also demonstrated that axonal degeneration had similar rates in vivo and in vitro.…”

“…Using previously described methods (Perry et al, 1990b(Perry et al, , 1992, we analyzed the maximal peak height and peak area of both A and C waves with the Sigavg Program (C ambridge Electronic Design, C ambridge, UK) after digitization (CED 1401) at 80 kHz and found them to be equivalent (Tsao et al, 1994). Selected nerves were fixed in 2% paraformaldehyde, osmicated for 2 hr, infiltrated with glycerol, and then teased apart and examined by light microscopy.…”

“…For a CAP to be conducted, the plasma membrane and the transmembrane voltage-gated ion channels must remain intact, and the normal intracellular ion levels must be preserved. The existence of the C57BL / Wld (formerly known as the C57BL /Ola) mouse strain, carrying an autosomal dominant mutation (Wld s ) slowing the rate of Wallerian degeneration (CAPs can be conducted up to 3 weeks posttransection), demonstrated for the first time that rapid degeneration in mammals is not a necessary consequence of axotomy (Lunn et al, 1989;Perry et al, 1990a;Tsao et al, 1994). It is also clear that Wallerian degeneration is an active process, with an initiating mechanism that sets into motion a cascade of events leading to the final destruction of axons.…”

“…Via monitoring the disappearance of CAPs and axonal morphology, this study also demonstrated that axonal degeneration had similar rates in vivo and in vitro. Using an in vitro system (described in Tsao et al, 1994), we have investigated the effect of temperature and media [Ca 2ϩ ] on the time course of axonal degeneration (duration of prolonged CAP and, in some experiments, the rate of decline). We asked whether axonal loss in mouse nerves could be delayed by cooling the external media temperature to 25°C and, if so, when, after injury, cooling had to be initiated to prolong axonal survival.…”