Muscle-specific beta-enolase concentrations after cross- and random innervation of soleus and extensor digitorum longus in rats

The concentration of beta-enolase, a highly specific marker of the skeletal muscle of rats, was determined in a slow-twitch muscle, the soleus (SOL) and a fast-twitch muscle, the extensor digitorum longus (EDL) after cross-innervation, random reinnervation, or denervation. The beta-enolase concentration is normally high in EDL and low in SOL. When the nerves entering into these muscles were cross-sutured, the beta-enolase concentration in EDL decreased and that in SOL increased to reach an almost equal value in 20 weeks and by the 35th week the SOL ultimately had a higher beta-enolase concentration than the EDL. When the sciatic nerve trunk was completely transected and sutured immediately, the beta-enolase concentration in EDL decreased and that of SOL increased; in 20 weeks SOL had a beta-enolase concentration similar to that of the EDL. When these muscles were denervated by cutting the sciatic nerve trunk, their beta-enolase concentrations were markedly lowered, but EDL still retained on the 12th week a beta-enolase value comparable to the normal SOL. Possible mechanisms behind the observed changes in beta-enolase concentration are discussed.     

Acetylcholinesterase histochemistry in the non-endplate region of skeletal muscles and effect of denervation

We measured acetylcholinesterase (AChE) in the non-endplate region of rat muscle, documenting its intrinsic activity within muscle fibers, as well as the extrinsic level in the capillaries and endomysium. When each muscle was considered as a whole, intrinsic AChE activity detected within the fibers was stronger in the fast-twitch extensor digitorum longus than in the slow-twitch soleus. Analysis of individual muscle fibers also showed the same tendency with a higher value in the fast-twitch type II fibers than in the slow-twitch type I fibers. On the average, 73% of the fibers showed intermediate or strong enzymatic activity in the fast-twitch muscle, whereas 56% of the slow-twitch muscle had only low activity. Sectioning or ligation of the sciatic nerve resulted in nearly complete abolition of the enzyme in the non-endplate region of the denervated muscles within 7 days, suggesting that nerve transmission regulates AChE activity not only in the endplate, as is well known, but also outside this region. Human skeletal muscles showed the same pattern of AChE activity in the non-endplate region as seen in rat muscles.     

A distinct difference between slow and fast muscle in acetylcholinesterase recovery after reinnervation in the rat

The changes in acetylcholinesterase (AChE) and choline acetyltransferase (CAT) activity in nerve proximal and distal to the crush site as well as in fast extensor digitorum longus (EDL) and slow soleus (SOL) muscle were studied during denervation and reinnervation in rat. Within 24 h after nerve crush, conduction in the distal nerve and neuromuscular transmission was lost. In the distal nerve segment, AChE and CAT activity showed no initial increase and was reduced to 25% 14 days after crush. During the reinnervation period, AChE and CAT activity recovered to 50% (AChE) and 80% (CAT) of control values and CAT activity in the EDL and SOL muscles followed closely the changes in distal nerve. In muscle, AChE activity was reduced to 15% by 2 weeks postoperatively. Enzyme activity in EDL recovered to 50% of control activity in 5 weeks after crush. In the SOL, end-plate and non-end-plate regions' AChE activity recovered at a faster rate, resulting in a temporary increase in AChE activity to more than control values during the third and fourth week. By the end of the fifth week, AChE activity had returned to control activity. Turnover values for AChE based on the reinnervation data showed a half-life value for AChE in proximal nerve of 32 days, in distal nerve 42 days, in EDL 23 days, and for SOL 5.1 days. The half-life for AChE in both muscles was significantly shorter than that of the nerve, indicating that the nerve did not supply AChE to the muscles. Half-lives for CAT calculated on the basis of the reinnervation data were 11.6 days for proximal nerve, 18.4 days for distal nerve, and 30 days for SOL and EDL muscles. It is concluded that the ability to synthesize AChE in end-plate and non-end-plate regions of muscle is an endogenously programmed event in the development of both fast and slow muscles. The nerve initiates and maintains the synthesis and can modify the rate of synthesis in individual muscle fibers. The mechanism by which the nerve stimulates and maintains AChE synthesis in muscle may be related to the release of trophic factors muscle activity or to a combination of these and other factors still to be investigated.     

Oxidative Enzyme Activity and Soma Size in Motoneurons Innervating the Rat Slow-Twitch and Fast-Twitch Muscles After Chronic Activity

The effects of chronic activity induced by running training on the activity of the mitochondrial enzyme succinate dehydrogenase (SDH) and soma size in motoneurons innervating the slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles were studied in rats using the retrograde neuronal tracer Nuclear Yellow. Rats were assigned to control and trained groups that were subjected to treadmill running for 10 weeks (2 h/day, 30 m/min, 5 days/week). After training, both SOL and EDL muscles showed clear adaptations (citrate synthase activity in the SOL muscle, and the fast-twitch oxidative-glycolytic fiber area of the EDL muscle increased significantly after training). The SDH activity of the motoneurons innervating both SOL and EDL muscles was unchanged by training. However, SOL motoneurons of trained rats had a significantly larger soma size and a significantly higher total SDH activity (SDH activity × soma size) than those of control. Total SDH activity was calculated to examine the absolute SDH protein content of the motoneurons. On the other hand, there was no difference in both soma size and total SDH activity of EDL motoneurons between the two groups. These data demonstrate that chronic activity has a considerably stronger impact on soma size and total oxidative enzyme activity of motoneurons innervating slow-twitch rather than fast-twitch muscles.     

Satellite cells in slow and fast rat muscles differ in respect to acetylcholinesterase regulation mechanisms they convey to their descendant myofibers during regeneration

The hypothesis of satellite cell diversity in slow and fast mammalian muscles was tested by examining acetylcholinesterase (AChE) regulation in muscles regenerating (1) under conditions of muscle disuse (tenotomy, leg immobilization) in which the pattern of neural stimulation is changed, and (2) after cross-transplantation when the regenerating muscle develops under a foreign neural stimulation pattern. Soleus (SOL) and extensor digitorum longus (EDL) muscles of the rat were allowed to regenerate after ischemic-toxic injury either in their own sites or had been cross-transplanted to the site of the other muscle. Molecular forms of AChE in regenerating muscles were analyzed by velocity sedimentation in linear sucrose gradients. Neither tenotomy nor limb immobilization significantly affected the characteristic pattern of AChE molecular forms in regenerating SOL muscles, suggesting that the neural stimulation pattern is probably not decisive for its induction. During an early phase of regeneration, the general pattern of AChE molecular forms in the cross-transplanted regenerating muscle was predominantly determined by the type of its muscle of origin, and much less by the innervating nerve which exerted only a modest modifying effect. However, alkali-resistant myofibrillar ATPase activity on which the separation of muscle fibers into type I and type II is based, was determined predominantly by the motor nerve innervating the regenerating muscle. Mature regenerated EDL muscles (13 weeks after injury) which had been innervated by the SOL nerve became virtually indistinguishable from the SOL muscles in regard to their pattern of AChE molecular forms. However, AChE patterns of mature regenerated SOL muscles that had been innervated by the EDL nerve still displayed some features of the SOL pattern. In regard to AChE regulation, muscle satellite cells from slow or fast rat muscles convey to their descendant myotubes the information shifting their initial development in the direction of either slow or fast muscle, respectively. The satellite cells in fast or slow muscles are, therefore, intrinsically different. Intrinsic information is expressed mostly during an early phase of regeneration whereas later on the regulatory influence of the motor nerve more or less predominates. © 1994 Wiley-Liss, Inc.     

Neural regulation of muscle acetylcholinsterase: effects of batrachotoxin and 6-aminonicotinamide.

Batrachotoxin (BTX), which causes increased Na+ permeability and blocks axoplasmic transport, or 6-aminonicotinamide (6-AN), which causes neuronal damage, was injected into the subarachnoid space of rat lumbar spinal cord. The activity of acetylcholinesterase (AChE) was measured in homogenates of the fast-twitch extensor digitorum longus (EDL) muscle and the slow-twitch soleus (SOL) muscle 10 days after injection. Both drug treatments significantly decreased AChE in EDL and SOL. Correlative electrophysiological measurements were made in intact EDL and SOL after injection of BTX or 6-AN. The results support the hypothesis that AChE in muscle is neurotrophically controlled.     

Electrophysiologic differences between mouse extensor digitorum longus and soleus

Miniature end-plate potentials (MEPPs) and indirectly elicited action potentials were recorded in vivo at 37°C from surface fibers of the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus (SOL) muscles of 3- to 4-month-old Bar Harbor 129 mice. The EDL MEPPs exhibited a significantly higher frequency, smaller amplitude, and shorter duration than the MEPPs of the SOL. Action potentials of EDL fibers exhibited a significantly greater amplitude and shorter duration than SOL fibers. A single stimulus elicited several action potentials from an EDL fiber but only one action potential from a SOL fiber. Fast- and slow-twitch muscle fibers can thus be identified and distinguished on the basis of these electrophysiologic parameters. There was no significant difference in resting membrane potentials between EDL and SOL fibers.     

Changes in isometric contractile properties of fast-twitch and slow-twitch skeletal muscle of C57BL/6J dy2J/dy2J dystrophic mice during postnatal development

Our primary aim was to determine if there exists a preferential involvement of the fast-twitch or slow-twitch skeletal muscle fibers in the dy2J/dy2J strain of murine dystrophy. The changes in the contractile properties of the slow-twitch soleus (SOL) and the fast-twitch extensor digitorum longus (EDL) muscles of normal and dystrophic mice were studied at 4, 8, 12, and 32 weeks of age. Isometric twitch and tetanus tension were decreased in the 4- and 8-week-old dystrophic EDL compared with controls, this situation being reversed in the older animals. At 12 weeks, the dystrophic EDL generated 15% more tetanic tension than normal EDL and by 32 weeks no significant difference was seen between normal and dystrophic EDL twitch or tetanus tension. By 8 weeks, dystrophic EDL exhibited a prolonged time-to-peak twitch tension (TTP) and half-relaxation time (1/2RT) of the isometric twitch which continued to 32 weeks. For the dystrophic SOL, decreased twitch and tetanus tension was observed from 4 to 32 weeks. At 8 and 12 weeks, TTP and 1/2RT of dystrophic SOL were prolonged. However, by 32 weeks there was no longer a significant difference seen in TTP or 1/2RT between normal and dystrophic SOL. Our results appear to indicate that a loss of the primary control which is determining the fiber composition of the individual muscles is occurring as the dystrophic process advances.     

Continuous low amplitude direct current stimulation of the crushed peripheral nerve accelerates the early recovery of choline acetyltransferase but not of acetylcholinesterase activity in fast and slow muscles

We investigated if continuous 1 μA direct current stimulation of the injured nerve, with the cathode electrode at the distal end of the nerve crush injury (cathode stimulation), accelerated the recovery of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity in transiently denervated extensor digitorum longus (EDL) and soleus (SOL) rat muscles. ChAT is a specific marker of cholinergic nerve terminals and may reflect axon ingrowth, and AChE reflects the re-establishment of neuromuscular junctions and recovery of muscle activity. Compared to sham operated animals, the cathode (CA) stimulated rats had a statistically significant larger ChAT activity in the EDL and SOL muscles on days 12 and 14 after nerve crush (P < 0.01, n = 6). The difference in ChAT activity between the groups decreased thereafter. Regarding recovery of muscle AChE, CA stimulation of the crushed sciatic nerve did not detectably accelerate the normalization of activity and pattern of AChE molecular forms in the EDL and SOL muscles. This means that the early rise in ChAT muscle activity in CA stimulated rats was not followed by an accelerated normalization of the neuromuscular transmission in the same group. It is more likely that the higher ChAT activity observed after cathode stimulation indicates a higher ChAT content in regenerating motor nerve endings, rather than a greater number of motor axons entering the muscles. It seems possible that cathode stimulation increased ChAT axonal transport, causing the early increase of ChAT content in the nerve endings. This raises the possibility that the axon transport and subsequent secretion of a trophic factor(s) from the nerve to the reinnervated muscle are enhanced as well, thus shortening the overall time of muscle force recovery in the absence of an appreciable acceleration of recovery of the neuromuscular transmission.     

Acetylcholinesterase activity in motor nerve fibres in correlation to muscle fibre types in rat

Rat muscle nerves were examined histochemically for their activity of acetylcholinesterase (AChE). The corresponding muscles were stained for myofibrillar ATPase and for NADH diaphorase. The nerves to the extensor digitorum longus (EDL) muscle and to the medial head of the gastrocnemius (MG) muscle consist of a motor axons of high AChE activity. Both muscles are characterized by the prevalence of type II muscle fibres. On the other hand, the soleus muscle and the quandratus femoris muscle, both mainly composed of type I muscle fibres, are innervated by a motor axons of low AChE activity. Since it is well established that EDL and MG are typical fast-twitch muscles and that the soleus, and probably also the auadratus femoris, is a typical slow-twitch muscle, it is suggested that, in rat, fast muscles are innervated by motor nerve fibres of high AChE activity and slow muscles are innervated by motor axons of low AChE activity.     

Influence of innervation on molecular forms of acetylcholinesterase in regenerating fast and slow skeletal muscles

Nerve-intact muscle regenerates were prepared by ischemic-toxic injury of slow soleus (SOL) and fast extensor digitorum longus (EDL) muscles of the rat. Rapid innervation of regenerating myotubes modified intrinsic patterns of AChE molecular forms, revealed by velocity sedimentation in linear sucrose gradients. Regarding their onset, the effects of innervation can be classified as early and late. The earliest changes in the SOL regenerates appeared a few days after innervation by their motoneurons: the activity of the 13 S AChE form (A 8) increased significantly in comparison to non-innervated regenerates. The pattern of AChE molecular forms became similar to that in the normal SOL muscle during the 2nd week after injury. In contrast, no major differences were observed between 8 day-old innervated and non-innervated EDL regenerates. Their patterns of AChE molecular forms resembled that in the normal EDL. However, the predominance of the 10 S AChE form (G 4) characteristic for the 2-week old non-innervated regenerates was prevented by innervation. Early effect of innervation observed in the SOL regenerates but not in the EDL may be due to intrinsically different response of the regenerating SOL myotubes to innervation. Rather high extrajunctional activity of the asymmetric 16 S (A 12) molecular form of AChE in early regenerates was reduced to adult level in about 3 weeks in the SOL, and nearly completely suppressed in 5 weeks after innervation in the EDL regenerates. This reduction is assumed to be a late effect of innervation, as well as a decrease of the activity of the 4 S AChE form (G 1) in the SOL regenerates. A suppressive mechanism is activated in the extra-junctional regions of the innervated muscle regenerates during their maturation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Contractile properties, fiber types, and myosin isoforms in fast and slow muscles of hyperactive Japanese waltzing mice

This study focuses on the effects of neuromuscular hyperactivity on the contractile properties, fiber type composition, and myosin heavy chain (MHC) isoform expression of fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles in Japanese waltzing mice (JWM) of the C57BL/6J-v2J strain. The same properties were studied in the homologous muscle of control CBA/J mice (CM). In comparison to CM, the JWM exhibited (i) longer activity periods, prolonged bouts of running and a higher food intake, (ii) slower twitch and tetanic contractions of both EDL and SOL muscles, decreased cold and post-tetanic potentiation of the EDL, as well as increased cold and post-tetanic depressions of the SOL. Electrophoretic analyses of MHC isoform revealed a shift toward slower isoforms in both EDL and SOL muscles of JWM as compared to the homologous muscles of CM, namely, a shift from the fastest MHCIIb to the MHCIId/x isoform in the EDL muscle and a shift from MHCIIa to MHCI in the SOL muscle. The latter also contained a higher percentage of type I fibers and displayed a higher capillary density than the SOL muscle of CM. These findings show that the inherently enhanced motor activity of the JWM leads to fiber type transitions in the direction of slower phenotypes. JWM thus represent a suitable model for studying fast-to-slow fiber transitions under the influence of spontaneous motor hyperactivity.     

Slowing of fast-twitch muscle in the dystrophic mouse

Isometric twitch tension was measured in fast-twitch and slow-twitch muscles of normal and dystrophic ( ) mice in vivo. In dystrophic mice more than 6 months old the fast-twitch extensor digitorum longus (EDL) showed a prolongation of the time to peak tension as well as the time to relax to one-half peak tension ( ) compared with age-matched controls. In younger dystrophic mice (4 to 6 weeks) the time to peak tension was prolonged but not significantly so. This apparent “slowing” of dystrophic fast-twitch muscle was accompanied by a reduction in both cooling potentiation and post-tetanic potentiation toward values typical of slow-twitch muscle. Slow-twitch soleus muscle (SOL) of old mice was almost unaffected by the dystrophic process with regared to its contractile characteristics. However, there appeared to be a slight, but significant “speeding” of young dystrophic SOL compared with age-matched control muscles. This was apparent in reduced times to peak tension and half-relaxation as well as an enhanced cooling potentiation. We suggest that the altered contractile characteristics result from a change in some intrinsic property of the muscle fibers rather than from extrinsic factors such as the additional perimysial connective tissue seen in these muscles.     

Regulation by exercise of the pool of G4 acetylcholinesterase characterizing fast muscles: opposite effect of running training in antagonist muscles

Fast muscles of rodents characteristically differ from their slow-twitch counterparts by exhibiting high levels of G4, i.e., the tetrameric acetylcholinesterase (AChE) molecular form. Converging evidence suggests that this additional G4 pool is specifically regulated by the type of activity actually performed by the muscle. This hypothesis was tested by studying the effect of a chronic increase in neuromuscular activity on the AChE content and distribution of molecular forms of functionally antagonist rat hindlimb muscles. They included the fast ankle extensors gastrocnemius (GAST) and plantaris (PL), the fast ankle flexors tibialis anterior (TA) and extensor digitorum longus (EDL), as well as the slow-twitch soleus (SOL). Neuromuscular activity was enhanced by subjecting the rats to a 12-week training program consisting of repeated sessions of prolonged endurance running on a rodent treadmill. This exercise regimen preferentially affected the G4 pool characterizing fast muscles which exhibited marked and opposite changes according to the functional role of the muscles. The amount of G4 was increased by more than 50% in the ankle extensors GAST and PL, which play a dynamic role, and reduced by about 40% in the ankle flexors TA and EDL, which exhibit a predominant tonic activity during running. The asymmetric forms A12 and A8 were slightly elevated in the fast muscles. In the case of the slow-twitch SOL, running training resulted in a small, nonspecific decrease in AChE content which affected most of the molecular forms. These data indicate that the size of the G4 pool characteristic of fast muscles depends on the type, dynamic or tonic, of activity actually performed. The present results support the conclusion that this G4 pool fulfills a specific and essential function, distinct from that of A12.     

Core myofibers and related alterations induced in rats' soleus muscle by immobilization in shortened position

Experimental induction of core myofibers by tenotomy or local tetanus suggests that mechanical factors such as muscle tension loss, shortening or immobilization may play a role in core fiber formation. To test this hypothesis, we investigated the morphologic alterations induced in soleus (SOL) and extensor digitorum longus (EDL) muscles following immobilization of rats' hindlimb in various positions. The SOL and EDL muscles were immobilized in either shortened or lengthened state by applying wire-meshed plaster cast for 1, 2 and 3 weeks. The muscles were dissected out, measured, weighed and examined by histochemistry and electron microscopy. Gross atrophy was noted in all muscles but was greatest in shortened SOL. The SOL atrophy was diffuse and associated with relative increase in type 2 fibers. In EDL, the atrophy selectively involved fibers with low oxidative enzyme activity. Core myofibers were seen mainly in shortened SOL and consisted of myofibrillar derangement, loss of myofilaments and streaming of Z bands. The preferential involvement of shortened SOL (tonic, fatigue-resistant, slow-twitch muscle) suggests that the functional length, loss of tension subsequent to shortening and intrinsic biochemical properties of the muscle are important in core fiber formation.     

Effects of denervation and immobilisation during development upon [3H]ouabain binding by slow- and fast-twitch muscle of the rat

The effect of innervation and of muscle inactivity upon the normal production of Na+-K+-ATPase sites, assayed by [3H]ouabain binding, in muscle surface membranes has been determined for the rat. In both slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles a large increase was found to occur in [3H]ouabain binding per unit weight of muscle over the first 3 weeks of life. Interruptions of development, brought about by fixation of muscles at different lengths at 5 days of age, had no significant effect upon [3H]ouabain binding by EDL. In contrast, fixation led to a decrease in binding in SOL. When fixed in a shortened position profound morphological changes occurred, although these were not apparent when SOL was fixed in a stretched position. Denervation of SOL at 5 days of age significantly reduced the age related increase in the density of [3H]ouabain binding, whilst denervation of EDL had little effect. It was concluded that normal development of SOL is dependent upon innervation and possibly the resulting muscle activity, whereas development of EDL was relatively independent of innervation.     

Abnormal distribution of proteins in the soleus and extensor digitorum longus of dystrophic mice

Proteins of the whole muscle homogenates of the slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) of normal and dystrophic C57BL/6J mice at 4, 8, 12, and 32 weeks of age were resolved on polyacrylamide isoelectric focusing gels. Gels of the normal SOL proteins at all ages contained two bands specific to SOL and not represented in EDL. Gels of normal EDL contained three bands highly amplified in EDL but barely detectable in SOL. The distribution of proteins in dystrophic SOL was abnormal at all age groups studied due, in part, to a decrease in the proportion of SOL-specific proteins relative to other proteins in the muscle. The distribution of proteins in dystrophic EDL appeared abnormal first at 12 weeks due to a decrease in the relative proportion of EDL-amplified proteins. Due to these and other changes, at 32 weeks the dystrophic SOL and EDL were almost indistinguishable on the basis of their proteins' distributions.     

EFFECTS OF DEXAMETHASONE ON FIBRE SUBTYPES IN RAT MUSCLE

Livingstone I., Johnson M.A. & Mastaglia F.L. (1981) Neuropathology and Applied Neurobiology 7, 381–398 Effects of dexamethasone on fibre subtypes in rat muscle The extent to which dexamethasone treatment produced atrophy of fast-twitch (EDL) and slow-twitch (SOL) muscles in the rat was investigated. The mean weight of steroid-treated EDL muscles was decreased as compared to normal, whereas SOL muscles from normal and dexamethasone-treated animals showed no significant difference. Muscle fibre diameters also showed comparatively minor changes in SOL, which consists of Type 1 (slow oxidative) and Type 2A (fast oxidative/glycolytic) fibres. Rat EDL contains, in addition to Type 1 and Type 2A fibres, two sub-populations of fast glycolytic fibres (Types 2B and 2B'). These fibre types showed the most severe degree of atrophy both after dexamethasone treatment and after denervation. The mean ratio of the weights of denervated to innervated EDL muscles was lower in steroid-treated rats than in normal animals suggesting that the atrophy produced by steroid treatment in conjunction with denervation was more than simply additive. Analysis of the proportions of histochemical fibre types in SOL and EDL showed that dexamethasone treatment produced no major alterations in the fibre type constitution of these muscles. However, further histochemical studies showed that there was relatively severe impairment of myophosphorylase activity in Type 2B' (fast glycolytic) fibres as compared to other fibre types; conversely Type 1 fibres frequently contained increased myophosphorylase. Levels of β-hydroxybutyrate dehydrogenase were low in both normal and steroid-treated EDL but high in SOL which also showed higher general oxidative activity. It is suggested that the particular susceptibility of fast glycolytic fibres to atrophy as a result of steroid treatment may be linked to: 1 the relatively severe reduction of myophosphorylase activity in these fibres and 2 their comparative inability to utilize alternative energy sources, especially substrates derived from free fatty acids.     

Histochemical changes in fast and slow muscles of nutritionally dystrophic rabbits.

Rabbits were rendered dystrophic by feeding them a diet deficient in vitamin E and their fast-twitch EDL and slow-twitch SOL muscles were examined histochemically. The soleus muscle of control rabbits consisted largely of type I fibres with occasional areas of scattered type II fibres. In the nutritionally dystrophic rabbits type II fibres were consistently found homogeneously distributed throughout the entire muscle and in increased proportion. A very similar pattern was observed in the solei of rabbits following sciatic nerve section. The normal EDL contained three fibre types (I, IIoxidative and IIglycolytic). Vitamin E deficiency appeared to be associated with a shift towards an increase in the proportion of IIglycolytic fibres at the expense of IIoxidative. In denervation as well as vitamin E deficiency the type I fibres of the EDL appeared to be spared. A small number of the E-deficient rabbits exhibited degenerative changes in their sciatic and sural nerves. When animals were both denervated and E-deprived the resulting muscle changes were very much more severe than in the case of either challenge in isolation. We suggest that although some of the signs of vitamin E deficiency resemble those of a neural defect there is, in addition, a direct myopathic effect.