Size Of Myelinated Fibers Research Articles

Morphological and morphometric analysis of the distal branches of the rat brachial plexus

The rat brachial plexus has gained interest recently in neuro-regenerative research due to the advancement of neurosurgical equipment and techniques, but moreover in that it provides a model that can closely resemble the common peripheral nerve injuries seen in humans. The aim of this study was to provide a systematic baseline quantification for fibre type and morphology of the major terminal nerve branches of the rat brachial plexus (radial, ulnar and median) at four surgically accessible sites, through the forelimb. We applied a microstructural and immunohistological analysis of 12 rat brachial plexuses using three forms of micro-visualisation: electron microscopy; whole mount; and immunohistology. The three distal nerves studied showed a similar patterning in terms of the number and size of myelinated fibres, with all proportionally decreasing when moving distally. The fibre types of both the median and ulnar nerve appeared to be homogenously mixed throughout their trajectory, while the radial nerve had a more distinct patterning, especially distal to the elbow, with the entire nerve’s main branch appearing to consist of sensory fibres only. Our microstructural analysis of the rat brachial plexus provides important normative reference data for future peripheral nerve research using the forelimb of the rat.

Effects of Acute Insulin Treatment in the Recurrent Laryngeal Nerve Myelinated Fiber Morphometry in Experimental Diabetes

Reports on vocal cord palsy in diabetic patients are increasing in the literature but few reports deal with the morphology of the RLN in experimental models of diabetes. Also, effects of acute insulin treatment in experimental diabetes are also rarely reported. In the present study, male Wistar rats received a single intravenous streptozotocin (STZ) injection in order to induce diabetes (N=7) while control rats received vehicle (N=9). STZ + insulin animals (N=8) received a daily subcutaneous insulin injection three days after STZ injection. On the 15th day after STZ or vehicle injections, rats were anesthetized for arterial pressure (AP) and heart rate (HR) recordings, prior to RLN removal. Proximal and distal segments of the right and left RLN were prepared for light microscopy morphometry, carried out with the aid of a computer software. Myelinated fiber morphometry showed a tendency (P = 0.07) towards a significant difference in the fiber and axon diameter between control and STZ+insulin, tending to be larger in the control group. The opposite tendency (p=0.07) was observed for the G ratio values, being larger on STZ+insulin group compared to control. Our results show that acute treatment with insulin affects negatively the size of myelinated fibers and axons in the recurrent laryngeal nerve.Support: FAPESP, CNPq, CAPES and FAEPA

Early applied electric field stimulation attenuates secondary apoptotic responses and exerts neuroprotective effects in acute spinal cord injury of rats

Injury potential, which refers to a direct current voltage between intact and injured nerve ends, is mainly caused by injury-induced Ca2+ influx. Our previous studies revealed that injury potential increased with the onset and severity of spinal cord injury (SCI), and an application of applied electric field stimulation (EFS) with the cathode distal to the lesion could delay and attenuate injury potential formation. As Ca2+ influx is also considered as a major trigger for secondary injury after SCI, we hypothesize that EFS would protect an injured spinal cord from secondary injury and consequently improve functional and pathological outcomes. In this study, rats were divided into three groups: (1) sham group, laminectomy only; (2) control group, subjected to SCI only; and (3) EFS group, received EFS immediately post-injury with the injury potential modulated to 0±0.5mV by EFS. Functional recovery of the hind limbs was assessed using the Basso, Beattie, and Bresnahan (BBB) locomotor scale. Results revealed that EFS-treated rats exhibited significantly better locomotor function recovery. Luxol fast blue staining was performed to assess the spared myelin area. Immunofluorescence was used to observe the number of myelinated nerve fibers. Ultrastructural analysis was performed to evaluate the size of myelinated nerve fibers. Findings showed that the EFS group rats exhibited significantly less myelin loss and had larger and more myelinated nerve fibers than the control group rats in dorsal corticospinal tract (dCST) 8weeks after SCI. Furthermore, we found that EFS inhibited the activation of calpain and caspase-3, as well as the expression of Bax, as detected by Western blot analysis. Moreover, EFS decreased cellular apoptosis, as measured by TUNEL, within 4weeks post-injury. Results suggest that early EFS could significantly reduce spinal cord degeneration and improve functional and historical recovery. Furthermore, these neuroprotective effects may be related to the inhibition of secondary apoptotic responses after SCI. These findings support further investigation of the future clinical application of EFS after SCI.

Efficacy of the end-to-side neurorrhaphies with epineural window and partial donor neurectomy in peripheral nerve repair: an experimental study in rats.

End-to-side (ETS) neurorrhaphy was a useful tool in peripheral nerve repair and "baby-sitter" procedure. The study was designed to evaluate the long-term efficacy of ETS with epineurial window and 40% partial donor neurectomy in rats. A total of 60 Lewis rats were divided into three groups (n = 20, each group): following peroneal nerve transection, rats in Group A underwent end-to-end neurorrhaphy; rats in Group B underwent ETS neurorrhaphy of the distal peroneal nerve stump to an epineurial window on the tibial nerve; and rats in Group C underwent ETS neurorrhaphy of the distal peroneal nerve stump to the tibial nerve with 40% partial neurectomy. At 6, 12, 18, and 24 weeks after surgery, electrophysiology, muscle tension, myelinated fiber regeneration, cross-sectional area of muscular fiber, and muscle weight were analyzed. Histology exhibited apparently increased number and size of myelinated fibers in peroneal nerves in Group C, compared with those in Group B. More superior recovery was demonstrated in the electrophysiology and axon regeneration of the peroneal nerves, as well as the maintenance of muscle force, wet weight, and fiber size of the anterior tibial muscles in Group C than those in Group B. ETS neurorrhaphy with partial donor neurectomy can achieve higher efficacy in functional and structural recovery of the recipient system. This study provides the evidence of long-term follow-up for the further investigation of ETS neurorrhaphies with different modalities in peripheral nerve repair and in "baby-sitter" procedure.

Experimental diabetes in neonatal mice induces early peripheral sensorimotor neuropathy

Animal models of diabetes do not reach the severity of human diabetic neuropathy but relatively mild neurophysiological deficits and minor morphometric changes. The lack of degenerative neuropathy in diabetic rodent models seems to be a consequence of the shorter length of the axons or the shorter animal life span. Diabetes-induced demyelination needs many weeks or even months before it can be evident by morphometrical analysis. In mice myelination of the peripheral nervous system starts at the prenatal period and it is complete several days after birth. Here we induced experimental diabetes to neonatal mice and we evaluated its effect on the peripheral nerve 4 and 8weeks after diabetes induction. Neurophysiological values showed a decline in sensory nerve conduction velocity at both time-points. Morphometrical analysis of the tibial nerve demonstrated a decrease in the number of myelinated fibers, fiber size and myelin thickness at both time-points studied. Moreover, aldose reductase and poly(ADP-ribose) polymerase activities were increased even if the amount of the enzyme was not affected. Thus, type 1 diabetes in newborn mice induces early peripheral neuropathy and may be a good model to assay pharmacological or gene therapy strategies to treat diabetic neuropathy.

Structural, morphologic and morphometric study of the phrenic nerve: association between experimental diabetes and arterial hypertension (728.24)

Although the association between hypertension and diabetes is common in clinical practice, it is not well known the contribution of each of these diseases in the development of diabetic neuropathy in patients with hypertension. We investigated the presence of peripheral neuropathy, through morphology and morphometry analysis of the phrenic nerve in normotensive rats (Wistar) and spontaneously hypertensive rats (SHR) with experimentally induced chronic diabetes. Diabetic animals received a single injection of streptozotocin (STZ) intravenously while controls received vehicle on the same date. Twelve weeks after injection, arterial pressure and heart rate were recorded and the right and left phrenic nerves were removed and prepared for embedding in epoxy resin and computer morphometry. The phrenic nerves of SHR and diabetic SHR (SHR + STZ) showed reduced number and density of myelinated fibers and Schwann cell nuclei, compared to Wistar. The SHR and SHR+STZ rats showed myelinated fiber size distributions skewed to the right, with an important reduction of the small myelinated fibers. This finding was more pronounced on diabetic SHR when compared to normotensive diabetic animals. We suggest that hypertension causes a reduction of small myelinated fibers and the association of the hypertension and diabetes did not interfere with the small fiber neuropathy present in the hypertensive animals.Grant Funding Source: CAPES, FAPESP, CNPq and FAEPA

Myelinated fiber distribution in the aortic depressor nerve of male and female spontaneously hypertensive rats (728.22)

Aortic depressor nerve (ADN) is an afferent nerve that contains myelinated (fast conducting) and unmyelinated (slow conduction) fibers that send information from aortic mechanoreceptors to central nervous system [1]. Previous studies form our laboratory [2,3] in spontaneously hypertensive rats (SHR) have demonstrated morphological alterations on the ADN in SHR, using male and female animals indistinctively. In this study we investigated the ADN fiber distribution comparing male and female adult (20 weeks old) SHR. After the (AP) and heart rate (HR) recordings, together with the ADN spontaneous activity, the left ADN were prepared for light microscopy and morphometry. Myelinated fiber distributions were compared between proximal and distal segments in the same gender and between genders. Myelinated axon and G ratio distributions were also investigated. Myelinated fiber diameter range from 1 to 5 µm, with peak (~40% of fibers) at 2 µm while myelinated axon size range from 0.5 to 4 µm, with peak (~50% of axons) at 1.5 µm. No differences were observed between segments or genders. This indicates that gender does not influence on the ADN myelinated fiber size, allowing the use of male and females for morphological studies.[1] Krieger and Marseillan, Am J Physiol, 1963:205; [2] Fazan et. al, J Auton Nerv Syst 77, 1999:133; [3] Fazan et. al, Am J Physiol Heart Circ Physiol 280,2001:H1560.Grant Funding Source: FAPESP, CAPES, CNPq and FAEPA

Laser‐activated adhesive films for sutureless median nerve anastomosis

A novel chitosan adhesive film that incorporates the dye 'Rose Bengal' (RB) was used in conjunction with a green laser to repair transected rat median nerves in vivo. Histology and electrophysiological recording assessed the impact of the laser-adhesive technique on nerves. One week post-operatively, the sham-control group (laser-adhesive technique applied on un-transected nerves) conserved the average number and size of myelinated fibres in comparison to its contralateral side and electrophysiological recordings demonstrated no significant difference with un-operated nerves. Twelve weeks after the laser-adhesive anastomoses, nerves were in continuity with regenerated axons that crossed the anastomotic site.

ErbB2 Receptor Over-Expression Improves Post-Traumatic Peripheral Nerve Regeneration in Adult Mice

In a transgenic mice (BALB-neuT) over-expressing ErbB2 receptor, we investigated the adult mouse median nerve in physiological and pathological conditions. Results showed that, in physiological conditions, the grip function controlled by the median nerve in BALB-neuT mice was similar to wild-type (BALB/c). Stereological assessment of ErbB2-overexpressing intact nerves revealed no difference in number and size of myelinated fibers compared to wild-type mice. By contrast, after a nerve crush injury, the motor recovery was significantly faster in BALB-neuT compared to BALB/c mice. Moreover, stereological assessment revealed a significant higher number of regenerated myelinated fibers with a thinner axon and fiber diameter and myelin thickness in BALB-neuT mice. At day-2 post-injury, the level of the mRNAs coding for all the ErbB receptors and for the transmembrane (type III) Neuregulin 1 (NRG1) isoforms significantly decreased in both BALB/c and BALB-neuT mice, as shown by quantitative real time PCR. On the other hand, the level of the mRNAs coding for soluble NRG1 isoforms (type I/II, alpha and beta) increased at the same post-traumatic time point though, intriguingly, this response was significantly higher in BALB-neuT mice with respect to BALB/c mice. Altogether, these results suggest that constitutive ErbB2 receptor over-expression does not influence the physiological development of peripheral nerves, while it improves nerve regeneration following traumatic injury, possibly through the up-regulation of soluble NRG1 isoforms.

Reproducibility in Nerve Morphometry: Comparison between Methods and among Observers

We investigated the reproducibility of a semiautomated method (computerized with manual intervention) for nerve morphometry (counting and measuring myelinated fibers) between three observers with different levels of expertise and experience with the method. Comparisons between automatic (fully computerized) and semiautomated morphometric methods performed by the same computer software using the same nerve images were also performed. Sural nerves of normal adult rats were used. Automatic and semiautomated morphometry of the myelinated fibers were made through the computer software KS-400. Semiautomated morphometry was conducted by three independent observers on the same images, using the semiautomated method. Automatic morphometry overestimated the myelin sheath area, thus overestimating the myelinated fiber size and underestimating the axon size. Fiber distributions overestimation was of 0.5 μm. For the semiautomated morphometry, no differences were found between observers for myelinated fiber and axon size distributions. Overestimation of the myelin sheath size of normal fibers by the fully automatic method might have an impact when morphometry is used for diagnostic purposes. We suggest that not only semiautomated morphometry results can be compared between different centers in clinical trials but it can also be performed by more than one investigator in one single experiment, being a reliable and reproducible method.

Comparison between morphological and morphometric parameters of recurrent laryngeal nerve in developing spontaneously hypertensive rats

Despite some reports on the peripheral nerve morphology in spontaneously hypertensive rats (SHR), no investigations on the recurrent laryngeal nerve (RLN), known to contain baroreceptor fibers is available in this rat strain. We aimed to describe the normal morphological and morphometric parameters of the recurrent laryngeal nerves in developing SHR. Animals were divided into three groups: Female SHR 5, 8 and 20 week‐old (n=4 in each group). The animals were anesthetized for direct measurement of blood pressure, perfused with a fixative solution and had their right and left RLN, dissected and prepared for light microscopy and morphometry. Body weight increased significantly with aging. Mean arterial pressure was significantly higher in 20‐week old animals compared to 5 week‐old, but not different between 5 and 8‐week old animals or 8 and 20‐week old ones. In general, proximal segments are larger than distal segments with a significant reduction on the myelinated fiber number from proximal to distal. Myelinated fiber size is larger on the older animals, following the increase in body weight. No significant alterations of the nerve morphology were observed in 20‐week old animals, despite the elevated arterial pressure.Grant Funding Source: FAPESP, CNPq, CAPES and FAEPA

Neuroprotective effect of the glucagon-like peptide-1 receptor agonist, synthetic exendin-4, in streptozotocin-induced diabetic rats

Glucagon-like peptide-1 (GLP-1) receptors are widely expressed in neural tissues and diminish neuronal degeneration or induce neuronal differentiation. The aim of this study was to investigate the effect of the GLP-1 pathway on peripheral nerves in streptozotocin-induced diabetic rats. Diabetic and nondiabetic rats were treated with the GLP-1 receptor agonist, synthetic exendin-4 (i.p., 1 nmol·kg(-1)·day(-1)) or placebo for 24 weeks, and current perception threshold values, cAMP levels and nerve fibre size in the sciatic nerve were measured. We also investigated GLP-1 receptor expression, quantitative changes in PGP9.5-positive intraepidermal nerve fibres and cleaved caspase 3-stained Schwann cells by immunohistochemistry. GLP-1 receptor expression was detected in the sciatic nerve and skin. After exendin-4 treatment, the increase seen in current perception threshold values at 2000 and 250 Hz in diabetic rats was reduced. Also, the decrease in myelinated fibre size or axon/fibre area ratio in the sciatic nerve and the loss of intraepidermal nerve fibre in the skin of diabetic rats were ameliorated. These responses were closely associated with the attenuation of Schwann cell apoptosis and improvement in the cAMP level in exendin-4-treated diabetic rats, compared with placebo-treated animals. Synthetic exendin-4 may prevent peripheral nerve degeneration induced by diabetes in an animal model, supporting the hypothesis that GLP-1 may be useful in peripheral neuropathy. The neuroprotection is probably attributable to GLP-1 receptor activation, antiapoptotic effects and restoration of cAMP content.

Brain-derived neurotrophic factor promotes cochlear spiral ganglion cell survival and function in deafened, developing cats.

Postnatal development and survival of spiral ganglion (SG) neurons depend on both neural activity and neurotrophic support. Our previous studies showed that electrical stimulation from a cochlear implant only partially prevents SG degeneration after early deafness. Thus, neurotrophic agents that might be combined with an implant to improve neural survival are of interest. Recent studies reporting that brain-derived neurotrophic factor (BDNF) promotes SG survival after deafness have been conducted in rodents and limited to relatively short durations. Our study examined longer duration BDNF treatment in deafened cats that may better model the slow progression of SG degeneration in human cochleae, and this is the first study of BDNF in the developing auditory system. Kittens were deafened neonatally, implanted at 4-5 weeks with intracochlear electrodes containing a drug-delivery cannula, and BDNF or artificial perilymph was infused for 10 weeks from a miniosmotic pump. In BDNF-treated cochleae, SG cells grew to normal size and were significantly larger than cells on the contralateral side. However, their morphology was not completely normal, and many neurons lacked or had thinned perikaryl myelin. Unbiased stereology was employed to estimate SG cell density, independent of cell size. BDNF was effective in promoting significantly improved survival of SG neurons in these developing animals. BDNF treatment also resulted in higher density and larger size of myelinated radial nerve fibers, sprouting of fibers into the scala tympani, and improvement of electrically evoked auditory brainstem response thresholds. BDNF may have potential therapeutic value in the developing auditory system, but many serious obstacles currently preclude clinical application.

Stereological estimation of the total number of myelinated callosal fibers in human subjects

Using the fractionator principle, the total number, density and diameter size of myelinated callosal fibers were estimated in the corpus callosum (CC) of 10 Danish males between 39 and 60years of age. All sampled brains had been used in previous quantitative studies, for example, studies of neocortical neuron number, and were selected to determine whether the variability in the neocortical neuron number correlated with the total number of myelinated callosal fibers. Middle-aged males had an average of 138×10(6) (coefficient of variance; CV=0.19) myelinated fibers, but did not show any correlation with the neocortical neuron number (r=0.25; P=0.49). The mean area of the CC was estimated to be 7.2cm(2) (CV=0.17), and showed a significant correlation with the number of callosal fibers (r=0.69, P=0.041). Additionally, an overall density decline from the anterior to the posterior region of the CC was observed, with an inverse relationship between the distribution of large and small fibers along the callosal axis. This study suggests that many mechanisms are involved in the development and determination of axonal projections across the CC that cannot simply be explained by the neocortical neuron number. Further, a positive correlation between callosal fibers and the CC area verifies that callosal fibers are the factor responsible for CC size. Finally, the number of callosal fibers and their diameters are distributed along the CC in a specific pattern that reflects interactions with different brain regions.

Recovery process of sciatic nerve defect with novel bioabsorbable collagen tubes packed with collagen filaments in dogs

Autologous nerve graft is the most commonly applied treatment for the patients with peripheral nerve defect, while application is limited because of tissue availability and unfavorable donor site morbidity. To overcome this problem, peripheral nerve regeneration using a nerve conduit has been studied. Especially, nerve conduit using biodegradable materials has been considered promising. In this study, a potential of collagen nerve conduit has been studied with special reference to the regenerating process of a peripheral nerve. Twelve adult female Beagle dogs weighting 10-12 kg were used. The peroneal nerve was cut to make a 30-mm defect. The nerve defect was bridged by the collagen artificial nerve conduit. Comprehensive functional, electrophysiological, morphometrical, and histological analyses were performed until one year after operation. The wet weight of tibialis anterior muscles was only 32.4% of the healthy side at 24 weeks, which was recovered to 77.4% at 52 weeks after denervation. Electrophysiological evaluation of tibialis anterior muscle belly showed polyphasic wave at 52 weeks after implantation, which was almost half amplitude as compared with that of control. The diameters of myelinated nerve fibers thickened day by day, and the average diameter was 5.16 microm at PFN, 3.91 microm at CG, and 3.75 microm at DFN, and average thickness of myelin sheath was 0.94 microm at PFN, 0.46 microm at CG, and 0.55 microm at DFN after 52 weeks. The distribution of myelinated nerve fiber size in the 52 weeks group was distinctly bimodal with the major peak at approximately 2-4 microm and the minor peak at 10-12 microm. These findings were consistent with the distribution of the normal nerve fiber. This study proves the feasibility of the collagen artificial nerve conduit for promoting nerve regeneration, raises new possibilities of seeking alternatives to autograft for nerve repair. The results from this study showed detailed process of morphological, electrophysiological, and functional recovery of the regenerated nerve, which would provide scientific background for this novel therapy.

A stereological method for estimating the total length and size of myelinated fibers in rat cerebral cortex

An efficient and unbiased stereological technique to estimate the total length and total volume of the myelinated fibers in rat cortex is described. Unbiased sampling and measuring principles enable to obtain an unbiased estimation of the true value. In the present design, six tissue blocks were obtained from the entire rat brain cortex in a uniform random fashion. Isotropic, uniform random (IUR) sections were ensured by the use of the isector technique. One section with the thickness of 60 nm was cut from the center of each epon block using an ultramicrotome. Five fields of vision were photographed using electron microscopy. The length density of the myelinated fibers in the cortex was estimated using an unbiased counting frame. The volume density of the myelinated fibers in the cortex was estimated with point counting. The total length and total volume of the myelinated fibers in the cortex were estimated by multiplying the volume of the cortex, obtained using the Cavalieri principle and the length density and volume density of the fibers in the cortex. The sampling variance introduced by the stereological estimation procedure was a small fraction of the observed total variance indicating an efficient sampling protocol.

Faster nerve regeneration after sciatic nerve injury in mice over‐expressing basic fibroblast growth factor

Basic fibroblast growth factor (FGF-2) is expressed in the peripheral nervous system and is up-regulated after nerve lesion. It has been demonstrated that administration of FGF-2 protects neurons from injury-induced cell death and promotes axonal regrowth. Using transgenic mice over-expressing FGF-2 (TgFGF-2), we addressed the importance of endogenously generated FGF-2 on sensory neuron loss and sciatic nerve regeneration. After sciatic nerve transection, wild-type and transgenic mice showed the same degree of cell death in L5 spinal ganglia. Also, the number of chromatolytic, eccentric, and pyknotic sensory neurons was not changed under elevated levels of FGF-2. Morphometric evaluation of intact nerves from TgFGF-2 mice revealed no difference in number and size of myelinated fibers compared to wild-type mice. One week after crush injury, the number of regenerated axons was doubled and the myelin thickness was significantly smaller in transgenic mice. After 2 and 4 weeks, morphometric analysis and functional tests revealed no differences in recovery of sensory and motor nerve fibers. To study the role of FGF-2 over-expression on Schwann cell proliferation during the early regeneration process, we used BrdU-labeling to mark dividing cells. In transgenic mice, the number of proliferating cells was significantly increased distal to the crush site compared to wild-types. We propose that endogenously synthesized FGF-2 influences early peripheral nerve regeneration by regulating Schwann cell proliferation, axonal regrowth, and remyelination.

Morphometric Difference in the Human Maxillary Nerve Fibers between Dentulous and Edentulous Jaw Subjects

This study was conducted to quantify the change in the number and size of myelinated nerve fibers of the maxillary nerve with tooth loss in humans. We carried out a morphometric analysis to compare the number and size of myelinated nerve fibers in the human maxillary nerve between four dentulous and four edentulous jaw cases. Our results indicated that the number of axons decreased by approximately 13,000 with tooth loss. The average size of axons remained unchanged, but there was a change in the fiber size distribution, namely the loss of a large number of small-sized axons was accompanied by the total disappearance of small number of large-sized axons.

Bridging peripheral nerve defects with muscle–vein combined guides

Various tubulization techniques can be used to bridge peripheral nerve lesions with substance loss. Among the different materials that have been used so far in alternative to traditional fresh nerve autografts, fresh muscle-vein combined conduits (made by a vein segment filled with fresh skeletal muscle) proved to be particularly effective. In this study, nerve repair of 10-mm long nerve defects by means of muscle-vein combined tubes was compared with repair by means of traditional nerve autografts in the rat sciatic nerve experimental model. Results did not reveal any significant difference between the two groups of regenerated nerves with respect to the total number, mean density and mean size of myelinated nerve fibers. In addition, we also report the results of an experimental study in the rabbit sciatic nerve model, which showed that fresh skeletal muscle enrichment of the vein segment made it possible to bridge 55-mm long nerve gaps. These results provide further evidence of the effectiveness of fresh muscle-vein combined grafts and support the view that this type of conduit can be used also for repairing long nerve gaps.

Peripheral Nerve Regeneration in Galactosaemic Rats

The use of galactosaemia as a model for some aspects of diabetic polyneuropathy allows the influence of glycation to be studied independently of other effects. There are well‐studied abnormalities of the peripheral nerves in galactosaemic rats, one of which is that the efficiency of regeneration is initially reduced. One possible cause could be that glycated myelin debris in macrophages is less degradable and interferes with macrophage function. Macrophage recognition and ingestion of myelin glycosylated in vitro increases with the duration of incubation in a sugar‐rich medium. This study was performed to investigate a possible correlation between galactosaemia and regeneration, together with the role of macrophages. Galactosaemia was induced by adding galactose to the rats’ diet for 2 months before injury. Following a crush lesion to the sciatic nerve, regeneration was found to be delayed, demonstrated by a reduction in mean myelinated fibre size and density 1 month after crush, although, 2 and 3 months later, the differences did not reach statistical significance. There were also more macrophages in the galactosaemic rats than in the control animals at all time points. The initial delay in regeneration in galactosaemic rats was therefore only temporary and there was little evidence of long‐term deleterious effects. In addition to the morphometric results, immunohistochemistry showed that there were more macrophages in the galactosaemic rats than in the control animals at all time points. Correlating macrophage and myelinated fibre counts suggests that the persistence of debris‐containing macrophages does not appear to have a significant inhibitory effect on nerve regeneration. No evidence was found for persistent basal laminal tubes around the regenerating clusters.