Perineurial sodium-potassium-ATPase activity in streptozotocin-diabetic rats

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.

The blood-nerve barrier: enzymes, transporters and receptors--a comparison with the blood-brain barrier

The blood-brain barrier (BBB) has been much more extensively investigated than the blood-nerve barrier (BNB). Nevertheless it is clear that there are both similarities and differences in the molecular and morphophysiological characteristics of the two barrier systems. A number of enzymes, transporters and receptors have been investigated at both the BNB and BBB, as well as in the perineurium of peripheral nerves, which is also a metabolically active diffusion barrier. While there have been few systematic comparisons of the distribution of these molecules in both the BNB and BBB, it is apparent from the data available, reviewed in this article, that their distribution also supports the concept of the BNB and BBB having some features in common but also showing distinct identities. These similarities and differences cannot simply be accounted for by the presence of the inductive influences of astrocytes at the BBB and absence at the BNB. Whether the Schwann cell also has the capacity to induce some BNB properties remains to be determined.

Induction of p75NGFR in human diabetic neuropathy

In this immunohistochemical study we investigated the expression of low-affinity NGF receptor (p75NGFR) in peripheral nerves from 16 patients with type I or type II diabetes mellitus. Fourteen nerves from age- and sex-matched normal individuals and nine nerves from non-diabetic patients with ischemic neuropathy served as controls. All nerve samples were preliminarily examined by standard histology, fiber teasing and electron microscopy. Increased p75NGFR immunoreactivity was detectable within the endoneurium of cross-sections from ischemic and particularly from diabetic nerves. Immuno-teasing demonstrated that p75NGFR immunostaining was distributed along the entire length of isolated nerve fibers undergoing axonal degeneration. Quantitative assessment of p75NGFR immunoreactivity, performed by histospectrophotometry and expressed as percentage of adsorbance, was 21.20 +/- 3.50 in nerves from diabetic patients, 13.35 +/- 3.62 in nerves from non-diabetic patients with ischemic neuropathy and 9.02 +/- 2.75 in normal controls. The increased expression of p75NGFR in diabetic nerves is consistent with an axonopathic defect and further suggests involvement of NGF and other neurotrophins in the pathogenesis of human diabetic neuropathy.

Decrease of nerve Na+,K(+)-ATPase activity in the pathogenesis of human diabetic neuropathy

A decrease in Na+,K(+)-ATPase activity is claimed to play a central role in the pathogenesis of electrophysiological and morphological abnormalities that characterize the neuropathic complications in different animal models of diabetes mellitus. The peripheral nerves from 17 patients with either type I or type II diabetes mellitus were studied to assess the importance of changes in Na+,K(+)-ATPase activity in chronic human diabetic neuropathy. Sixteen nerves from age- and sex-matched normal individuals, and 12 nerves from non-diabetic neuropathic subjects undergoing vascular or orthopedic surgery served as negative and positive controls, respectively. All specimens were processed blind. Ouabain-sensitive ATPase activity was measured by a modified spectrophotometric coupled-enzyme assay. Standard histology, fiber teasing and electron microscopy were used to establish the normal or neuropathological patterns of surgical material. Morphometric analysis permitted calculation of fiber density in each nerve specimen and correlation of this figure with the relevant enzymatic activity. Na+,K(+)-ATPase activity was approximately 59% lower in nerves from diabetic patients than in normal controls (P < 0.01) and approximately 38% lower in nerves from non-diabetic patients with neuropathy (P < 0.01). Although nerves from both neuropathic conditions had significantly fewer fibers than those from normal individuals (diabetic -33%, and non-diabetic -22%), the decreases in Na+,K(+)-ATPase activity and fiber density were not correlated only in specimens from diabetic patients (r2 = 0.096; P = 0.22). Taken together with data from experimental animal models, these results suggest that the reduction in Na+,K(+)-ATPase activity in diabetic nerves is not an epiphenomenon secondary to fiber loss; rather, it may be an important factor in the pathogenesis and self-maintenance of human diabetic neuropathy.

Ganglioside treatment modifies abnormal elemental composition in peripheral nerve myelinated axons of experimentally diabetic rats

Effects of ganglioside administration on elemental composition of peripheral nerve myelinated axons and Schwann cells were determined in streptozotocin-induced diabetic rats and nondiabetic controls. Diabetic rats (50 days after administration of streptozocin) exhibited a loss of axoplasmic K and Cl concentrations in sciatic nerve relative to control, whereas intraaxonal levels of these elements increased in tibial nerve. These regional changes in diabetic rat constitute a reversal of the decreasing proximodistal gradients for K and Cl concentrations that characterize normal peripheral nerve. Treatment of diabetic rats with a ganglioside mixture for 30 days (initiated 20 days after the administration of streptozocin) returned proximal sciatic nerve axoplasmic K and Cl concentrations to control levels, whereas in tibial axons, concentrations of these elements increased further relative to diabetic levels. Also in the ganglioside/diabetic group, mean axoplasmic Na concentrations were reduced and Ca levels were elevated. Mixed ganglioside treatment of nondiabetic rats significantly increased axoplasmic dry weight concentrations of K and Cl in proximal sciatic and tibial axons. Schwann cells did not exhibit consistent alterations in elemental content regardless of treatment group. Changes in elemental composition evoked by ganglioside treatment of diabetic rats might reflect the ability of these substances to stimulate Na+,K(+)-ATPase activity and might be related to the mechanism by which gangliosides improve functional deficits in experimental diabetic neuropathy.

A freeze-fracture study of the perineurium in galactose neuropathy: morphological changes associated with endoneurial oedema

Feeding rats with galactose as 40% of their diet results in peripheral nerve oedema related to the intrafascicular accumulation of galactitol and sodium. In this study, associated changes in the perineurium were examined by the freeze-fracture replication technique. Perineurial cells are linked by tight junctions (zonulae occludentes). In normal animals these are made up of anastomosing strands organized in a belt-like arrangement along the margins of continuous cells. The majority of the tight junctions in the galactose-fed animals displayed structural abnormalities. These ranged from slight separation of the strands to fragmentation and dispersal, with looping of isolated strands. Some of the tight junctions contained large dilated compartments within the junctional network. Short lengths of intramembranous particles, probably representing assembly or disassembly of tight junctional strands, were also observed. The membranes of perineurial cells normally possess numerous openings of caveolae. A quantitative assessment showed that the mean density of these caveolae openings was increased in the galactose-fed rats as compared with controls. The alterations in the tight junctions resemble those that have been produced experimentally in epithelia by subjecting them to abnormal osmotic gradients. They also resemble those seen in human diabetic neuropathy in which osmotic disturbances involving the perineurium have been considered to occur. If the alterations involve the inner layers of the perineurium, they are likely to impair its barrier function. The increased number of caveolae openings in galactose neuropathy may represent a reaction to the endoneurial oedema and indicate that the pinocytotic-like vesicles have a transport function.

Rubidium (86Rb+) influx into dorsal root ganglia and sciatic nerve endoneurium of control and streptozotocin-diabetic rats: comparison with enzymatic Na,K-ATPase activity

Streptozotocin (STZ)-induced diabetes in the rat causes a significant reduction in ouabain-sensitive Na,K-ATPase pumping activity measured by 86Rb+ influx, in sciatic endoneurium (by 54%) and dorsal root ganglia (by 22%). For endoneurium, the change is similar to that of ouabain-sensitive enzymatic Na,K-ATPase activity (42%), but in dorsal root ganglia, the decrease in enzymatic Na,K-ATPase activity was much greater. 86Rb+ efflux from dorsal root ganglia showed no difference between diabetic and control animals, confirming that the abnormal 86Rb+ influx reflects Na,K-ATPase function and not abnormal membrane permeability. The significance of these findings to pathogenetic mechanisms in diabetic neuropathy is discussed.

Adenosine triphosphatase in nerves and ganglia of rats with streptozotocin-induced diabetes or galactosaemia; effects of aldose reductase inhibition

This study measured the ouabain-sensitive and ouabain-resistant adenosine triphosphatase activity in homogenates of the sciatic nerves and of pooled fourth and fifth lumbar dorsal root ganglia from rats fed 20% galactose or made diabetic with streptozotocin for either 4 or 8 weeks. Diabetes caused reductions in both fractions of sciatic nerve adenosine triphosphatase activity. After 8 weeks the ouabain-sensitive fraction was 54% of control (p less than 0.05) and the ouabain-resistant fraction was 57% of control (p less than 0.05). Galactose feeding more than doubled the ouabain-sensitive adenosine triphosphatase activity in the sciatic nerve (225% of control after 4 weeks, 215% of control after 8 weeks of galactose feeding, both p less than 0.01) and produced a progressive increase in the ouabain-resistant fraction (119% of control at 4 weeks (p less than 0.05) and 176% of control at 8 weeks (p less than 0.01)). In a group of rats fed galactose for 5 days, sciatic nerve ouabain-sensitive adenosine triphosphatase activity was 165% of control. Treatment with the aldose-reductase inhibitors tolrestat, ponalrestat or sorbinil prevented accumulation of polyol and depletion of myo-inositol in the sciatic nerves, indicating effective inhibition of aldose reductase. These drugs prevented completely the effect of galactose on the sciatic nerve adenosine triphosphatase activity, but had no significant effect on the reduction in adenosine triphosphatase activity in the sciatic nerves of diabetic rats. In the dorsal root ganglia galactose feeding had no measurable effect on the adenosine triphosphatase activity. Diabetes caused a modest numerical reduction in the ouabain-sensitive activity only.(ABSTRACT TRUNCATED AT 250 WORDS)

Perineurial calcification

A study of the occurrence of extracellular deposits of calcium in the perineurium of the human sural nerve demonstrated that there is a higher incidence in abnormal nerves than in normal material and that, of the conditions examined, nerves from cases of diabetic neuropathy showed the greatest incidence of calcification. It seems likely that the process of calcification is similar to that operating in other tissues, with deposition on matrix vesicles or lipid droplets, probably derived from the perineurial cells. The increased incidence in diabetic neuropathy is presumably related to metabolic abnormality consequent upon the diabetic state.

Water content, vasoactive intestinal polypeptide and substance P in intact and crushed sciatic nerves of normal and streptozotocin-diabetic rats

Observations on streptozotocin-diabetic rats have confirmed overhydration of peripheral nerve. As in previous studies, the sorbitol and fructose content, when expressed in terms of wet weight of nerve was found to be increased and myo-inositol decreased. The reduction in myo-inositol content was less, although still significant, when expressed in terms of protein content. Nerve water content increased during Wallerian degeneration following a crush injury in both normal and diabetic animals, but was relatively less in the latter. Vasoactive intestinal polypeptide (VIP) concentrations were significantly increased in diabetic nerve, those for substance P being normal. Both became severely reduced during Wallerian degeneration following nerve crush and ligature. The significance of these findings is discussed. The accumulation of water in the endoneurial compartment may be related to impaired extraction by the perineurium, to which the increased VIP content may contribute. These changes are unlikely to be responsible for nerve fibre damage.