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Recently, TX14(A), a prosaposin-derived neurotrophic peptide, was shown to prevent both large and small fiber deficits in streptozotocin diabetes. Here, the efficacy of TX14(A) in reversing established nerve conduction disorders in streptozotocin diabetes, a model of insulin deficiency, and preventing them in galactose feeding, an insulin-replete model of polyol pathway flux, was investigated. Following streptozotocin injection (50 mg/kg ip), TX14(A) treatment (1 mg/kg ip thrice weekly) was initiated in half of the animals. After 8 wk, treatment was begun in half of the untreated animals and discontinued in half of the treated animals, and the experiment continued for 6 wk. TX14(A) reversed established motor and sensory nerve conduction deficits in streptozotocin-diabetic rats and the impact of previous treatment was still evident 3 wk after withdrawal. With the onset of 40% galactose feeding, the same dose of TX14(A) was given to half of the control and half of the galactose-fed animals for 16 wk. TX14(A) was without effect in control animals but it attenuated motor and sensory nerve conduction deficits in galactose-fed rats, an effect associated with amelioration of axonal dwindling in the sciatic nerve. These observations extend the therapeutic utility of TX14(A) and highlight its potential in treating established diabetic neuropathy.

Prosaposin exhibits neurotrophic factor properties that are localized to a 12-amino acid sequence located in the amino terminal portion of the saposin C domain. Prosaptides are peptides derived from the neurotrophic portion of prosaposin; these have been previously reported to be bioactive in neuroblastoma cell lines in vitro. We report that prosaptides were also bioactive in explants of adult primary sensory neurons by dose-dependently increasing both the number (3- to 4-fold) and elongation of these neurites by 50%. Local injection of prosaptides into the gluteus muscle of adult mice also induced sprouting at the motor endplate. Our results indicate that prosaptides are potent neuritogenic factors for both sensory and motor neurons of adult peripheral nerve.

Prosaposin is the precursor of the saposins and has both neurotrophic and myelinotrophic activity in vitro and in vivo. Using an antibody specific for the holoprotein, an immunocytochemical survey demonstrated intense staining of adult rat skeletal, cardiac, and smooth muscle cells. Prosaposin immunoreactivity in muscle appears dependent on innervation, as denervated adult rat skeletal muscles showed decreased immunostaining that returned to normal levels after reinnervation. TX14(A), a peptide derived from the neurotrophic sequence of prosaposin, attenuated the decline in muscle mass loss following nerve injury induced by a constricting ligature. In vitro, both L6 myoblasts and primary chick-embryo myoblasts showed similar prosaposin immunopositivity, mainly in myotubes. TX14(A) induced a threefold increase in L6 myoblast fusion during early stages of differentiation without affecting cell proliferation. The fusion process was decreased in vitro in a dose-dependent fashion by addition of a neutralizing anti-prosaposin antibody. These data suggest that, in addition to neurotrophic and myelinotrophic activities, prosaposin has myotrophic properties.

Background Short-term diabetes causes sensory disorders in rats ranging from thermal hypoalgesia to exaggerated behavioral responses to other sensory stimuli. As impaired neurotrophic support may promote sensory nerve disorders during diabetes, the authors investigated whether TX14(A), a neurotrophic peptide derived from prosaposin, was able to ameliorate nerve disorders in diabetic rats. Methods TX14(A) was delivered by intraperitoneal or intrathecal injection to control or streptozotocin-diabetic rats in either single or multiple (three times weekly) dose regimens. Efficacy was measured against diabetes-induced disorders of sensory nerve conduction velocity, paw withdrawal latency to radiant heat, tactile response thresholds to von Frey filaments, and flinching after paw formalin injection. Results Prolonged TX14(A) treatment of diabetic rats prevented the progressive decline in large sensory fiber conduction velocity in the sciatic nerve, development of paw thermal hypoalgesia, and increased flinching after paw formalin injection. The effect on formalin hyperalgesia persisted for 48 h but not 72 h after injection. No effects were noted in control rats. A single injection of TX14(A) 30 min before testing did not alter thermal response latencies in control or diabetic rats but prevented formalin hyperalgesia in diabetic rats. Tactile allodynia and the prolonged paw thermal hyperalgesia to radiant heat after intrathecal delivery of substance P were also dose-dependently ameliorated in diabetic rats by a single injection of TX14(A), whereas no effects were observed on the responses to these tests in control rats. Conclusions TX14(A) exhibits both neuroprotective and acute antihyperalgesic properties in diabetic rats without altering normal nociceptive function.

Motor and sensory nerve conduction velocities (MNCV and SNCV) were reduced in the sciatic nerve of rats after 4 weeks of untreated streptozotocin-induced diabetes, and declined further during the following 4 weeks. Treating diabetic rats with the novel peptide HP228 had no effect on the decline of MNCV after the first 4 weeks of diabetes but attenuated the decline in SNCV. HP228 treatment also prevented any further decline in MNCV or SNCV between weeks 4 and 8 of diabetes. Consequently, at the conclusion of the study, the nerve conduction velocities (NCVs) in treated rats were significantly (both P < .001) higher than in untreated diabetic rats. Reduced nerve homogenate Na+,K+-adenosine triphosphatase (ATPase) activity in diabetic rats was significantly (P < .05) increased by HP228 but remained significantly (P < .05) lower than in untreated controls. HP228 treatment also reduced nerve Na+,K+-ATPase activity of control rats compared with untreated controls (P < .05). There was no effect of HP228 on the hyperglycemia, nerve polyol accumulation, myo-inositol depletion, reduced nerve laser Doppler blood flow, thermal hypoalgesia, or reduced mean axonal caliber in diabetic rats or on any of these parameters in control rats. These data demonstrate that a novel peptide may protect against the slowing of nerve conduction in prolonged diabetes and that the mechanism of action is unrelated to aldose reductase inhibition, prevention of nerve ischemia, or axonal atrophy. HP228 may prove a potential therapeutic agent for the treatment of prolonged diabetic neuropathy.

In this report, we made use of sorbitol dehydrogenase (SDH)-deficient mutant mice (C57BL/LiA) to test whether there is a close correlation between the level of polyol accumulation and the degree of reduction in motor nerve conduction velocity (MNCV) associated with diabetes. The C57BL/LiA mouse has SDH deficiency due to a G-to-A mutation at the +1 position of intron 8, thus producing only aberrant SDH transcripts. These C57BL/LiA mice should have higher levels of polyol accumulation in the peripheral nerve because of the inability to further metabolize sorbitol to fructose. Here, we confirm by Western blot analysis and high-performance liquid chromatography that these mice lack SDH in the sciatic nerve and other various tissues, whereas normal mice possess SDH. These C57BL/LiA mice do not display any obvious phenotype that includes peripheral neuropathy in the normal laboratory environment and breed normally as described previously, although the tissues that normally contain SDH accumulate more sorbitol. This finding suggested that C57BL/LiA mouse strain is a valid model for studying the role in diabetic neuropathy of the polyol pathway, which consists of two enzymes-aldose reductase for converting glucose to sorbitol and SDH for converting sorbitol to fructose. Sorbitol levels in the sciatic nerve of diabetic C57BL/10N, nondiabetic, and diabetic C57BL/LiA mice were increased 4.3-, 16.6-, and 38.1-fold, respectively, above that of nondiabetic C57BL/10N. The fructose level in the sciatic nerve was increased 2.4-fold in diabetic C57BL/10N mice compared with that of nondiabetic and diabetic C57BL/LiA mice. Diabetic SDH-deficient mice showed an MNCV reduction similar in magnitude to that of diabetic C57BL/10N mice, despite greater nerve sorbitol accumulation and the lack of fructose in the former. The present data suggest that the levels of sorbitol and fructose in the sciatic nerve of mice do not correlate with the severity of MNCV deficit associated with diabetes.

Galactose intoxication of rats was used to disrupt metabolism of Schwann cells and skeletal muscle, two sites that contain the polyol-forming enzyme aldose reductase (AR). Galactose-fed rats develop a neuropathy characterized by nerve conduction deficits and axonal atrophy. To investigate the possibility that galactose metabolism by AR influences axonal function and structure by altering production of neurotrophic factors, the impact of galactose intoxication on nerve and muscle BDNF levels and the effects of exogenous BDNF treatment on galactose neuropathy were examined using biochemical, electrophysiologic and morphometric techniques. Galactose feeding increased BDNF protein in peripheral nerve and muscle. Exogenous BDNF treatment attenuated motor nerve conduction velocity deficits in the sciatic nerve of galactose-fed animals and myelin splitting of motor axons in the ventral root. In contrast, sensory nerve conduction velocity (SNCV) deficits in the sciatic nerve and myelin splitting in the central projections of sensory neurons were not prevented by BDNF treatment. BDNF treatment did not attenuate reduced axonal caliber in the sciatic nerve, but did ameliorate the diminution of the caliber of central sensory projections in the dorsal root. These findings point to the potential use of BDNF in the treatment of peripheral neuropathies.

Sorbitol accumulation and transmembrane efflux in JS1 schwannoma cells were examined during osmotic stress in the presence of a sorbitol dehydrogenase (SD) inhibitor and following return to iso-osmotic conditions. SD inhibition promoted sorbitol accumulation under hyperglycemic and/or hyperosmotic conditions, and sorbitol efflux during iso-osmotic incubation was prevented by cooling to 4 degrees C or by quinidine. It appears that sorbitol levels in JS1 cells are dependent on SD activity and that sorbitol is rapidly removed upon restoring iso-osmotic conditions.

The impact of exaggerated polyol pathway flux on ciliary neurotrophic factor (CNTF)-like bioactivity and expression of CNTF in rat sciatic nerve was examined after 2 months of galactose intoxication. Polyol content was elevated (P < 0.001) and motor nerve conduction velocity reduced (P < 0.05) in galactose-fed rats compared with control animals or control and galactose-fed rats treated with the aldose reductase inhibitor (ARI) Ponalrestat. CNTF-like bioactivity in the galactose-fed group was reduced to 30% of that assayed in the control group (P < 0.001). ARI treatment significantly increased CNTF-like bioactivity by 60% compared with the untreated galactose group (P < 0.05) but did not restore it to control levels. Unexpectedly, bioactivity in ARI-treated control animals was increased by nearly 250% compared with untreated controls (P < 0.005). In addition to the deficit in CNTF bioactivity in untreated galactose rats, the expression of protein, but not of mRNA, was reduced (P < 0.05). In ARI-treated control and galactose-fed rats, the expression of CNTF peptide was significantly enhanced above control levels (both P < 0.05). Concomitant with the reduction in CNTF levels, there was a shift in the axonal size-frequency distribution of myelinated fibers toward smaller axons in galactose-fed rats that was prevented by ARI treatment. Since galactose feeding has little impact on levels of CNTF mRNA, these observations suggest that deficits in CNTF-like bioactivity may result from a posttranscriptional modification of neurotrophic protein expression or turnover. Unlike other functional and structural disorders in galactose neuropathy, factors other than polyol accumulation may contribute to the deficit in CNTF-like bioactivity.

The effect of the inositol trisphosphate analog alpha-trinositol on noxious-evoked behavior, amino acid and prostaglandin E2 (PGE2) release was examined in unanesthetized rats using intrathecal microdialysis probes. Subcutaneous injection of 50 microliters 5% formalin solution produced two phases of pain-like behavior and significant elevation of glutamate, aspartate, glycine, taurine and serine during phase 1. PGE2 concentrations were increased during both phases 1 and 2. Intraperitoneal delivery of 300 mg/kg alpha-trinositol significantly suppressed both phases 1 and 2 of formalin-induced behavior and the associated elevation of amino acids and PGE2. These data demonstrate that the antinociceptive effect of alpha-trinositol corresponds to suppression of noxious-evoked release of amino acids and PGE2 from the spinal cord.

Increased voltage-gated sodium channel activity may contribute to the hyperexcitability of sensory neurons in inflammatory and neuropathic pain states. We examined the levels of the transcript encoding the tetrodotoxin-resistant sodium channel SNS in dorsal root ganglion neurons in a range of inflammatory and neuropathic pain models in the rat. Local Freund's adjuvant or systemic nerve growth factor-induced inflammation did not substantially alter the total levels of SNS mRNA. When NGF-treated adult rat DRG neurons in vitro were compared with NGF-depleted control neurons, SNS total mRNA levels and the levels of membrane-associated immunoreactive SNS showed a small increase (17 and 25%, respectively), while CGRP levels increased fourfold. SNS expression is thus little dependent on NGF even though SNS transcript levels dropped by more than 60% 7-14 days after axotomy. In the streptozotocin diabetic rat SNS levels fell 25%, while in several manipulations of the L5/6 tight nerve ligation rat neuropathic pain model, SNS levels fell 40-80% in rat strains that are either susceptible or relatively resistant to the development of allodynia. Increased expression of SNS mRNA is thus unlikely to underlie sensory neuron hyperexcitability associated with inflammation, while lowered SNS transcript levels are associated with peripheral nerve damage.

The aim of the present study was to determine whether diabetes-induced changes in the distribution of enteric neuropeptides, could be prevented in 12-week streptozotocin-diabetic rats, by rigorous control of glycaemia, using daily adminstration of insulin, or an aldose reductase inhibitor (ponalrestat). The pattern of distribution of nerve fibres and cell bodies, containing immunoreactive vasoactive intestinal polypeptide (VIP), galanin (GAL), calcitonin gene-related peptide (CGRP) and substance P was examined in the myenteric plexus of ileum from control, untreated diabetic, insulin-treated diabetic and aldose reductase inhibitor-treated diabetic rats. The increase in VIP- and GAL-like immunoreactivity, seen in the myenteric plexus of untreated diabetic rat ileum, was not present in the myenteric plexus of ileum from insulin- and aldose reductase inhibitor-treated diabetic rats. With CGRP-like immunoreactive fibres, there was a clear decrease in the ileum of untreated diabetic rats. This was prevented by insulin treatment, but aldose reductase inhibitor treatment had no effect. No alterations in substance P-like immunoreactivity were seen in the myenteric plexus of ileum from any of the groups investigated. Generally, the similarity of effect of ponalrestat and insulin on VIP and galanin expression in this study supports a primary effect of insulin via glycaemic control. The dissimilarity of the effect of the two treatments on CGRP expression may imply a neurotrophic effect of insulin, although there are certainly consequences of hyperglycaemia other than exaggerated flux through the polyol pathway.

To test the osmoregulatory rules of Schwann cell aldose reductase (AR) and myo-inositol, JS1 Schwann cells were grown under control and hyperosmotic conditions with and without excess glucose or galactose. JS1 cells cultured in control conditions possessed AR protein and activity that were not altered by the inclusion of 25 mM glucose or galactose. Following culture with 100 mM NaCl, there was a decline in cell number accompanied by an increase in AR activity, both of which were attenuated by the addition of 25 mM glucose or galactose. Sorbitol was not detected in JS1 Schwann cells following culture in control, glucose-supplemented, or hyperosmotic medium, and dulcitol accumulated only following culture with galactose. However, both polyols were dramatically increased in JS1 cells cultured in hyperosmotic medium supplemented with 25 mM glucose or galactose. In contrast, myo-inositol levels were elevated only during hyperosmotic exposure but decreased when glucose or galactose was also present. These data are consistent with the use of polyol formation by JS1 Schwann cells as a means of responding to osmotic stress.

This study examined the effect of two structurally dissimilar aldose reductase inhibitors, N -[[5-(trifluoromethyl)-6-methoxy-1-napthalenyl]thioxomethyl]- N -methlyglycine (tolrestat) and 4-amino-2,6-dimethylphenyl-sulphonyl nitromethane (ICI 222155), on formalin-evoked behavioural responses in control and diabetic rats and on capsaicin-evoked release of prostaglandin E from spinal cord slices in vitro. Both compounds, given orally for 4 weeks, prevented hyperalgesia in diabetic rats 5–20 min after hindpaw formalin injection. ICI 222155 also prevented hyperalgesia in diabetic rats 21–60 min after formalin, whereas tolrestat suppressed activity in diabetic rats below controls and also suppressed activity in controls when given orally or intrathecally. Capsaicin-evoked release of prostaglandin E from spinal cord slices of control rats was significantly reduced by tolrestat, but not ICI 222155. These data suggest that hyperalgesia in diabetic rats is related to glucose metabolism by aldose reductase, whereas tolrestat has specific effects on formalin-evoked nociception associated with an ability to reduce spinal prostaglandin release.

This study examined the effects of hyperglycemia and treatment with the aldose reductase inhibitor, Tolrestat, on the pain behavior evoked by injection of formalin into the dorsum of a single hind paw. In control rats, injection of formalin (50 microliters of a 5% solution) evoked two phases of flinching of the injected paw (phases 1 and 2), separated by a quiescent period. Four weeks of streptozotocin-induced diabetes or galactose intoxication did not alter the frequency of flinching during either of the active phases but significantly (P0.001 and P0.05, respectively) enhanced flinch frequency during the quiescent period. Concurrent treatment with Tolrestat (50 mg/kg/day by gavage) during hyperglycemia prevented the accumulation of the polyol pathway metabolites sorbitol and fructose in the nerve and spinal cord of streptozotocin-diabetic rats and also significantly (P0.05) reduced the enhanced flinching of diabetic rats during the quiescent period. These data demonstrate that hyperglycemia induces a period of Tolrestate-preventable hyperalgesia in a paradigm that is used to model persistent pain and suggest that exaggerated flux through aldose reductase may initiate changes in nociceptive pathways that could contribute to some of the pain states experienced by patients with diabetic neuropathy.

Patients with diabetes may have peripheral neuropathy, which may have clinical implications for the use of regional nerve block. The effects of local anesthetics on nerve conduction and nerve fiber injury were tested in control rats and at 4 weeks after the onset of diabetes in rats injected with streptozotocin (50 mg/kg intraperitoneally). Nerve conduction was assessed by recording evoked electrical activity in hindpaw muscles following ipsilateral electrical stimulation of the sciatic nerve near the hip. Block of motor nerve conduction was quantified by recording the amplitude of the evoked response at 1-min intervals for up to 15 min after the injection of 500 microliters 1% lidocaine HCl or procaine HCl into the midthigh next to the sciatic nerve. In control animals, procaine was much less effective than lidocaine in producing conduction block. The rate and magnitude of lidocaine-induced conduction block were not significantly different between control and diabetic groups. However, conduction block due to procaine was sufficiently enhanced in diabetic rats to become comparable to that of lidocaine-treated control nerves. Long-lasting injury was assessed in sciatic nerve harvested 2 days after the extraneural injection of saline or 2 or 4% lidocaine HCl. Using a light microscope with a superimposed grid, nerve edema was quantified as the proportion of intersection points falling on extracellular space. Lidocaine induced edema in both control and diabetic nerves, but 4% lidocaine induced significantly more edema in diabetic nerves than in controls. Nerve fiber injury, based on light microscopic scoring of axonal degeneration and demyelination, was not observed in saline-treated nerves.(ABSTRACT TRUNCATED AT 250 WORDS)

This study describes the electrophysiological responses of endoneurial preparations derived from rat sciatic nerve to acute hypoxia in vitro. Preparations from control rats exhibited a 40% decline in compound action potential (CAP) amplitude after 40 min exposure to medium gassed with 8% O2. In preparations from 4 week streptozotocin-diabetic rats CAP declined by only 29%, indicating a resistance to hypoxic conduction blockade. Treating diabetic rats with mixed bovine brain gangliosides (10 mg/kg/day i.p.) exaggerated this resistance to hypoxic conduction blockade as CAP amplitude fell to only 18% of initial values. In a separate experiment, treating non-diabetic rats with gangliosides (10 mg/kg/day i.p.) or adding gangliosides (400 micrograms/ml) directly to the medium in which control nerves were maintained during in vitro recording also significantly attenuated the decline in CAP amplitude after 40 min hypoxia, thus effectively inducing a resistance to hypoxic conduction blockade similar to that observed in nerves from diabetic rats. These studies demonstrate that the systemic or acute local administration of gangliosides induces a resistance to hypoxic conduction block in normal nerve and exaggerates the resistance to hypoxic conduction block of diabetic rats.

Nerve polyol content and (Na+,K+)-adenosine triphosphatase (ATPase) activity of nerve homogenates were studied in a colony of rats fed diets containing either 0%, 10%, 20%, or 40% galactose for 4 months. Nerve water and dulcitol content exhibited dose-dependent increases, whereas nerve myo-inositol content declined with increasing dietary galactose. Homogenate (Na+,K+)-ATPase activity increased with increasing galactose consumption of up to 20% dietary intake and thereafter remained consistently elevated at twice the activity of 0% galactose-fed values. Nerves of rats fed 40% galactose were also examined at the light microscope level and showed evidence of both edema and myelin splitting. These data demonstrate that increased nerve water content, dulcitol accumulation, and myo-inositol depletion parallel the previously reported dose-related increase of endoneurial fluid sodium and chloride in nerves of galactose-fed rats and suggest that elevated nerve homogenate (Na+,K+)-ATPase activity may be related to one or more of these consequences of exaggerated polyol pathway flux.

This study examined sciatic motor nerve conduction velocity (MNCV) and the accumulation of 6-phosphofructokinase (PFK) activity proximal and distal to a sciatic nerve ligature in rats fed a diet containing 20% galactose for 4 weeks. MNCV was reduced in the galactose-fed rats to 94% of controls, (P less than 0.05) but PFK activity accumulations were not different from those in controls. Daily administration of the aldose reductase inhibitor ponalrestat throughout the study to another group of galactose-fed rats prevented dulcitol accumulation, myo-inositol depletion and increased water content of the sciatic nerve seen in galactose-fed rats. This effective aldose reductase inhibition also prevented the reduced MNCV and had no effect on accumulations of PFK activity. These data support earlier work suggesting that deficits in the axonal transport of PFK activity in diabetic rats are unrelated to either exaggerated flux through the polyol pathway, polyol accumulation or ischemic hypoxia and indicate the possible need for the elucidation of other pathogenic mechanisms which may contribute to the development of diabetic neuropathy.

This study describes the electrophysiological responses of endoneurial preparations derived from rat sciatic nerve to acute hypoxia in vitro. Preparations from control rats exhibited a marked decline in compound action potential (CAP) amplitude coupled with an increase in latency, during 40 minutes exposure to 8% O2. In contrast, preparations from 4 week streptozotocin-diabetic rats showed a greatly reduced decline in CAP amplitude, with an increase in latency. Twice-daily insulin treatment of diabetic rats resulted in a pattern of CAP amplitude decline that initially resembled that of untreated diabetics but by 40 min was similar to controls, with latency again increasing during hypoxia. Nerves were also maintained in 25 mmol/l glucose, rather than the 5 mmol/l glucose of the above studies. Under such conditions the performance of nerves from diabetic rats were unaltered. Nerves from control rats exhibited an initial resistance to hypoxia but by 40 min CAP had declined to values of control rats maintained in 5 mmol/l glucose. An increase in latency during hypoxia was also noted in preparations from control or diabetic rats maintained in 25 mmol/l glucose. The maintenance of CAP amplitude during hypoxia by diabetic preparations is initially related to increased substrate availability, with an additional component that is not related to external glucose levels in vitro, and is absent after insulin treatment of diabetic rats.

We measured motor nerve conduction velocity (MNCV), Na(+)-K(+)-ATPase activity, polyol-pathway metabolites, and myo-inositol in sciatic nerves from control mice, galactose-fed (20% wt/wt diet) mice, and galactose-fed mice given the aldose reductase inhibitor ponalrestat (300-mg/kg diet). Treatments were maintained for 4 wk. Galactose feeding was associated with a 21.5% reduction in MNCV (P less than 0.001), which was almost completely prevented by ponalrestat. Galactose-fed mice showed an 81% increase in Na(+)-K(+)-ATPase (P less than 0.01), an effect completely prevented by aldose reductase inhibition. Treatment of a separate galactose-fed group with sorbinil (300 mg/kg diet) also attenuated the MNCV deficit and prevented the increased Na(+)-K(+)-ATPase activity associated with galactosemia. Accumulation of galactitol in the nerves of galactose-fed mice was prevented by aldose reductase inhibition, but there were no alterations in myo-inositol levels in the sciatic nerves of any group. These data show that exaggerated flux through the polyol pathway can cause an MNCV deficit that is unrelated to either myo-inositol levels or NA(+)-K(+)-ATPase activity.

This study measured axonal transport of 6-phosphofructokinase (PFK) and aldolase activities in the sciatic nerves of rats with short-term streptozotocin-induced diabetes. The diabetic rats showed deficits in anterograde (69% of controls; p less than 0.001) and retrograde (33% of controls; p less than 0.01) accumulations of PFK activity as well as its content per unit length of unconstricted sciatic nerve (86% of controls; p less than 0.05). There were no accumulation deficits in aldolase activity in the nerves of the diabetic rats, although the activity per unit length of unconstricted nerve was deficient (81% of controls; p less than 0.05). Treatment of diabetic rats with mixed bovine brain gangliosides (10 mg/kg of body weight/day, i.p.) did not affect the deficit in PFK activity in unconstricted nerve (84% of ganglioside-treated controls; p less than 0.01), but all the other defects in enzyme activities were prevented completely. The diabetic rats also showed a reduction of 7% (p less than 0.01) in sciatic nerve dry weight per unit length, which was prevented by ganglioside treatment. In contrast, the reduced motor nerve conduction velocity, accumulation of polyol pathway metabolites, and depletion of myo-inositol, characteristic of untreated short-term diabetes, were unaffected by ganglioside treatment.

This study examined the anterograde axonal transport of activities of the cytoplasmic enzymes choline acetyltransferase and 6-phosphofructokinase in genetically diabetic C57BL/Ks (db/db) mice and their nondiabetic (+/?) littermates. Diabetic mice exhibited marked reductions in the accumulation of both choline acetyltransferase and 6-phosphofructokinase activity against a constriction of the left sciatic nerve (38% and 51% of nondiabetic values, respectively). Enzyme activities per unit length of unconstricted nerve were not different from those of nondiabetic mice. The nerves of diabetic mice did not accumulate measurable amounts of sorbitol or fructose and showed no myo-inositol depletion. Thus this study concludes that, in diabetic mice, the deficits in anterograde axonal transport of these two enzymes do not arise from the accumulation of sorbitol and fructose nor from depletion of nerve free myo-inositol.

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 ouabainsensitive fraction was 54% of control (p

The sciatic nerve of diabetic C57BL/Ks mice did not accumulate either sorbitol or fructose despite elevated nerve glucose levels, nor did they show a depletion of free myo-inositol. Galactose feeding of both nondiabetic and diabetic mice for five days resulted in marked accumulations of dulcitol in nerve indicating polyol forming activity. Levels of myo-inositol showed small elevations in nerves of galactose-fed mice which reached significance when compared to diabetic mice fed the standard diet. Dulcitol accumulation was prevented by concurrent administration of the aldose reductase inhibitor Statil, but this did not prevent the increased levels of myo-inositol.

Brain tissue taken at necropsy from five cases of Down's syndrome and six controls was analysed for changes in neurotransmitter markers. Concentrations of noradrenaline (NA), dopamine (DA) and its major metabolite homovanillic acid (HVA), 5-hydroxytryptamine (5HT) and its metabolite 5-hydroxyindoleacetic acid (5HIAA) were determined by means of HPLC, whilst choline acetyltransferase (ChAT) was measured by a radiochemical technique. Significant reductions in NA, 5HT and ChAT were found in most cortical and subcortical regions of the Down's syndrome tissue investigated. The neuropathological lesions were assessed using a fluorescent stain for neuritic plaques and neurofibrillary tangles. These were present to varying extents in every Down's syndrome case except the youngest but were not found in control tissue of comparable age. The results indicate profound transmitter deficits and neuropathological abnormalities in adult patients with Down's syndrome, which closely resemble those of Alzheimer's disease.

Ouabain-sensitive ATPase activity (expressed as nmol ADP produced/h/mg (wet) nerve +/- SEM) was measured in homogenates of sciatic nerve from control rats and rats with streptozotocin-induced diabetes of 8 wk duration. Nerves from diabetic rats showed activity (21.7 +/- 2.0) which was significantly (p less than 0.05) less than that of controls (34.6 +/- 4.8). These animals also showed a deficit in conduction velocity (m/sec +/- SEM) of sciatic nerve motoneurones (50.7 +/- 0.4 vs. 57.7 +/- 0.7 in controls; p less than 0.001). In parallel, matched control and diabetic groups were treated daily with mixed gangliosides extracted from bovine brain (10 mg/kg i.p.). After such treatment for 8 wk the deficit in ouabain-sensitive ATPase activity did not develop in the diabetic group (treated diabetics, 31.9 +/- 3.7; treated controls, 34.5 +/- 3.8). However, the treatment did not affect the deficit in motor nerve conduction velocity (treated diabetics, 50.9 +/- 1.1 vs. treated controls, 57.9 +/- 0.5; p less than 0.001). Accumulations of the polyol pathway metabolites--sorbitol and fructose--together with depletion of nerve myo-inositol were similar in both diabetic groups. These data indicate an etiology for the conduction velocity deficit which differs from that of the deficit in ouabain-sensitive ATPase.

This study measured the content of substance P-like immunoreactivity (SPLI) in peripheral nervous tissue (lumbar dorsal root ganglia, sciatic nerve), skin (snout, foot), gastrointestinal tract (stomach, terminal ileum) and in the atria of the heart. Animals studied were long-term (11 months) streptozotocin-diabetic rats compared with age-matched control rats. All diabetic rats were given a very long acting insulin preparation twice weekly to reduce morbidity. Half of the diabetic rats were given the aldose reductase inhibitor, sorbinil (mean dose 30 mg/kg/day body weight by dietary admixture) over the entire protocol. Diabetic rats (given insulin only) showed marked accumulation of sorbitol and fructose together with myo-inositol depletion in their sciatic nerves. The sciatic nerves of the sorbinil-treated diabetic rats contained amounts of sorbitol, fructose and myo-inositol which were similar to those of non-diabetic rats, in spite of large amounts of nerve glucose in the sorbinil-treated animals. Thus, the inhibition of aldose reductase was successful. The L4 and L5 dorsal root ganglia of the diabetic rats showed reduced SPLI (63% and 72% respectively of control ganglia; P less than 0.05). There was also numerical reduction in sciatic nerve SPLI (84% of control nerve). There were no effects of sorbinil treatment on the reduced SPLI levels in ganglia or sciatic nerve. In the gastrointestinal tract the levels of SPLI were reduced in diabetic rats even when data were adjusted to take account of tissue hypertrophy (diabetic SPLI/whole stomach was 60% controls, P less than 0.01 and SPLI/cm ileum was 78%, though the latter did not attain statistical significance). In skin SPLI/unit area was raised in the diabetic rats to 145% of controls for foot skin and 151% for snout skin. Changes in SPLI content of gastrointestinal tract were unaffected by sorbinil treatment; in the skin the elevations were enhanced to 188% and 270% of respective control values for foot and snout skin. The SPLI content of the atria was unaffected by diabetes or sorbinil. These data are not consistent with a generalised impairment of delivery of substance P by axonal transport in experimental diabetes; special factors appear to influence the levels in neurones innervating different tissues. Exaggerated flux through the polyol pathway appears to be uninvolved.

This study examined anterograde and retrograde accumulation of axonally transported 6-phosphofructokinase activity, proximal and distal to sciatic nerve constrictions, in rats with streptozotocin-induced diabetes of 4 weeks' duration. There were deficits in accumulation on both sides of the constriction in untreated diabetic rats (proximal accumulation 66% of controls, p less than 0.05; distal accumulation 32% of controls, p less than 0.01). There was also a reduction in the phosphofructokinase activity per unit length unconstricted sciatic nerve in the untreated diabetic rats (87% of controls, p less than 0.05). Treatment of an age-matched group of diabetic rats with twice-daily insulin prevented all the above changes. There were significant increases, over untreated diabetic rats, in phosphofructokinase activity accumulated at constrictions (p less than 0.01 for both proximal and distal) and in unconstricted nerve (p less than 0.05). Indeed the activities measured in insulin-treated diabetic rats were virtually identical to those of controls. Treatment of a third group of diabetic rats with the aldose reductase inhibitor 'Statil' prevented or attenuated accumulations of polyol pathway metabolites and prevented depletion of myo-inositol in the sciatic nerve. In spite of these indications of effective aldose reductase inhibition, the drug was without effect on the deficits in accumulation of activity at ligatures or unconstricted nerve levels of phosphofructokinase activity. We conclude that short-term experimental diabetes in rats induced defects in both anterograde and retrograde axonal transport of 6-phosphofructokinase activity. These defects were prevented by intensive insulin treatment but were resistant to an effective aldose reductase inhibitor, indicating a lack of involvement of polyol pathway flux in their pathogenesis.

This study was performed on male Wistar rats with streptozotocin-induced diabetes mellitus of 11 months duration. There were two diabetic groups; both were given a long-acting insulin twice weekly to reduce morbidity. One group received no additional treatment whilst the other was given the aldose reductase inhibitor, sorbinil, by dietary admixture (approximate dose was 30 mg/day/kg body weight). At the end of the protocol the lenses of the diabetic rats given insulin alone showed markedly reduced dry weight (70% of controls; p less than 0.01) with increased water content (152% of controls; p less than 0.01). Both of these changes were absent from the lenses of the sorbinil-treated diabetic rats. Lenses from both groups of diabetic rats had elevated glucose contents, with greater levels in the group which received insulin alone. Polyol pathway metabolites were also raised in the diabetic lenses, though sorbinil treatment had markedly attenuated sorbitol accumulation without affecting fructose levels. Lens myo-inositol was almost absent from the diabetic rats which received only insulin (6% of control levels relative to lens dry weight; p less than 0.01). This depletion was substantially attenuated, but not prevented in the sorbinil-treated group (58% of control levels). In the iris the noradrenaline and adrenaline contents were unaltered in either diabetic group. In startling contrast, the iris content of substance P-like immunoreactivity was almost trebled in the insulin alone-treated diabetic rats (282% of controls; p less than 0.01), an effect which was prevented completely by sorbinil (127% of controls; not significantly different).(ABSTRACT TRUNCATED AT 250 WORDS)