Impaired visual evoked potential and primary axonopathy of the optic nerve in the diabetic BB/W-rat

Prospects of Electrocorticography in Neuropharmacological Studies in Small Laboratory Animals

Electrophysiological methods of research are widely used in neurobiology. To assess the bioelectrical activity of the brain in small laboratory animals, electrocorticography (ECoG) is most often used, which allows the recording of signals directly from the cerebral cortex. To date, a number of methodological approaches to the manufacture and implantation of ECoG electrodes have been proposed, the complexity of which is determined by experimental tasks and logistical capabilities. Existing methods for analyzing bioelectrical signals are used to assess the functional state of the nervous system in test animals, as well as to identify correlates of pathological changes or pharmacological effects. The review presents current areas of applications of ECoG in neuropharmacological studies in small laboratory animals. Traditionally, this method is actively used to study the antiepileptic activity of new molecules. However, the possibility of using ECoG to assess the neuroprotective activity of drugs in models of traumatic, vascular, metabolic, or neurodegenerative CNS damage remains clearly underestimated. Despite the fact that ECoG has a number of disadvantages and methodological difficulties, the recorded data can be a useful addition to traditional molecular and behavioral research methods. An analysis of the works in recent years indicates a growing interest in the method as a tool for assessing the pharmacological activity of psychoactive drugs, especially in combination with classification and prediction algorithms.

Modelling neurodegeneration and inflammation in early diabetic retinopathy using 3D human retinal organoids

Purpose

Diabetic retinopathy (DR) is a complication of diabetes and a primary cause of visual impairment amongst working-age individuals. DR is a degenerative condition in which hyperglycaemia results in morphological and functional changes in certain retinal cells. Existing treatments mainly address the advanced stages of the disease, which involve vascular defects or neovascularization. However, it is now known that retinal neurodegeneration and inflammation precede these vascular changes as early events of DR. Therefore, there is a pressing need to develop a reliable human in vitro model that mimics the early stage of DR to identify new therapeutic approaches to prevent and delay its progression.

Methods

Here, we used human-induced pluripotent stem cells (hiPSCs) differentiated into three-dimensional (3D) retinal organoids, which resemble the complexity of the retinal tissue. Retinal organoids were subjected to high-glucose conditions to generate a model of early DR.

Results

Our model showed well-established molecular and cellular features of early DR, such as (i) loss of retinal ganglion and amacrine cells; (ii) glial reactivity and inflammation, with increased expression of the vascular endothelial-derived growth factor (VEGF) and interleukin-1β (IL-1β), and monocyte chemoattractant protein-1 (MCP-1) secretion; and (iii) increased levels of reactive oxygen species accompanied by activation of key enzymes involved in antioxidative stress response.

Conclusion

The data provided highlight the utility of retinal organoid technology in modelling early-stage DR. This offers new avenues for the development of targeted therapeutic interventions on neurodegeneration and inflammation in the initial phase of DR, potentially slowing the disease's progression.

Supplementary Information

The online version contains supplementary material available at 10.1007/s44164-024-00068-1.

Retinal Cell Damage in Diabetic Retinopathy

Diabetic retinopathy (DR), the most common microvascular complication that occurs in diabetes mellitus (DM), is the leading cause of vision loss in working-age adults. The prevalence of diabetic retinopathy is approximately 30% of the diabetic population and untreated DR can eventually cause blindness. For decades, diabetic retinopathy was considered a microvascular complication and clinically staged by its vascular manifestations. In recent years, emerging evidence has shown that diabetic retinopathy causes early neuronal dysfunction and neurodegeneration that may precede vascular pathology and affect retinal neurons as well as glial cells. This knowledge leads to new therapeutic strategies aiming to prevent dysfunction of retinal neurons at the early stage of DR. Early detection and timely treatment to protect retinal neurons are critical to preventing visual loss in DR. This review provides an overview of DR and the structural and functional changes associated with DR, and discusses neuronal degeneration during diabetic retinopathy, the mechanisms underlying retinal neurodegeneration and microvascular complications, and perspectives on current and future clinic therapies.

Retrobulbarly injecting nerve growth factor attenuates visual impairment in streptozotocin-induced diabetes rats

PURPOSE

To explore whether retrobulbar administration of nerve growth factor (NGF) can restore visual function of streptozotocin-induced diabetes rats.

METHODS

A high-sucrose/high-fat diet and single injection of streptozotocin (STZ) were used in modeling diabetes. During week 13-15 after STZ injection, diabetic rats were received retrobulbar βNGF injection. On week 17 after STZ injection, the rats were tested with flash visual evoked potential (FVEP) to reflect visual function and with both optical coherence tomography (OCT) and hematoxylin and eosin (H&E) staining to show retinal morphological changes. Furthermore, periodic acid-Schiff (PAS) staining for retinal vascular digest preparations was performed to investigate retinal microvascular alterations, and immunofluorescences for slides of the optic nerve or retina were checked to assess astrocyte activation, autophagy level, and the unfolded protein response (UPR).

RESULTS

Retrobulbar βNGF injection significantly improved FVEP of diabetic rats. It also significantly alleviated retinal ganglion cell (RGC) loss and scarcely elicited other retinal/microvascular morphological changes, in OCT, H&E staining, and microvascular preparation. Moreover when diabetes rats treated with NGF, immunostaining of the optic nerve showed downregulation of complement 3d (C3d) and upregulations of glial fibrillary acidic protein (GFAP), S100-A10, microtubule-associated proteins 1A/1B light chain 3b (LC3b), and activating transcription factor 4 (ATF-4), while immunostaining of the retina showed upregulation of LC3b and no expression of ATF-4.

CONCLUSION

Our findings demonstrate that retrobulbar administration of βNGF reduces visual impairment with RGC-loss attenuation and without retinal-microvascular morphological alteration in diabetic rats. Furthermore, enhancements of A2 astrocyte activation, autophagy-protein expression, and ATF-4-mediated UPR may play crucial roles in the protective mechanism of NGF in diabetic visual-pathway neurodegeneration.

Microstructure abnormity in the optic nerve of type 1 diabetic rats revealed by diffusion tensor imaging study

Diabetic retinopathy (DR) is one of a major complication of type 1 diabetes mellitus (T1DM) and a leading cause of blindness. Evidence of animal study has shown that it is not only a microvasucular lesion of the eye, but also a neurodegeneration disease of the visual system. However, the in vivo imaging evidence of axonal degeneration in the diabetic optic nerve is scarce. Diffusion tensor imaging (DTI) technique has been proved to be an effective tool to track the integrity of the nerve fibers in the central nervous system. In this study, type 1 diabetes was induced by intraperitoneally injecting a single dose of streptozotocin (STZ) into Sprague-Dawley rats. DTI combined with histological assessments was carried out on the optic nerve to clarify the microstructural alterations underlying DTI indices changes at 4 weeks (4 w), 8 weeks (8 w) and 12 weeks (12 w) after STZ induction. The retinal changes were analyzed by pathological evaluations at 4 weeks (4 w) and 12 weeks (12 w) after STZ induction. DTI results showed significantly decreased mean diffusivity (MD) and axial diffusivity (Da) in diabetic optic nerve compared to controls at 12 w. Atrophy in diabetic nerves was monitored by high resolution T₂-weighted images. Axonal degeneration without myelin loss of the optic nerve was confirmed by histological examination. Moreover, there are positive correlations between decreased diffusivities (MD and Da) in the optic nerve and reduced total axolemmal area. The diabetic rats showed intense glial activity since 4 w and thinning of the thickness in inner plexiform layer and nerve fiber layer at 12 w in the retina. In conclusion, DTI could in vivo monitor the progression of optic nerve degeneration in diabetes and the findings in our study would help supply axonal protection for DR in preclinical practice.

Methylglyoxal Disrupts Paranodal Axoglial Junctions via Calpain Activation

Nodes of Ranvier and associated paranodal and juxtaparanodal domains along myelinated axons are essential for normal function of the peripheral and central nervous systems. Disruption of these domains as well as increases in the reactive carbonyl species methylglyoxal are implicated as a pathophysiology common to a wide variety of neurological diseases. Here, using an ex vivo nerve exposure model, we show that increasing methylglyoxal produces paranodal disruption, evidenced by disorganized immunostaining of axoglial cell-adhesion proteins, in both sciatic and optic nerves from wild-type mice. Consistent with previous studies showing that increase of methylglyoxal can alter intracellular calcium homeostasis, we found upregulated activity of the calcium-activated protease calpain in sciatic nerves after methylglyoxal exposure. Methylglyoxal exposure altered clusters of proteins that are known as calpain substrates: ezrin in Schwann cell microvilli at the perinodal area and zonula occludens 1 in Schwann cell autotypic junctions at paranodes. Finally, treatment with the calpain inhibitor calpeptin ameliorated methylglyoxal-evoked ezrin loss and paranodal disruption in both sciatic and optic nerves. Our findings strongly suggest that elevated methylglyoxal levels and subsequent calpain activation contribute to the disruption of specialized axoglial domains along myelinated nerve fibers in neurological diseases.

Study of retinal neurodegeneration and maculopathy in diabetic Meriones shawi: A particular animal model with human-like macula

The purpose of this work was to evaluate a potentially useful animal model, Meriones shawi (M.sh)-developing metabolic X syndrome, diabetes and possessing a visual streak similar to human macula-in the study of diabetic retinopathy and diabetic macular edema (DME). Type 2 diabetes (T2D) was induced by high fat diet administration in M.sh. Body weights, blood glucose levels were monitored throughout the study. Diabetic retinal histopathology was evaluated 3 and 7 months after diabetes induction. Retinal thickness was measured, retinal cell types were labeled by immunohistochemistry and the number of stained elements were quantified. Apoptosis was determined with TUNEL assay. T2D induced progressive changes in retinal histology. A significant decrease of retinal thickness and glial reactivity was observed without an increase in apoptosis rate. Photoreceptor outer segment degeneration was evident, with a significant decrease in the number of all cones and M-cone subtype, but-surprisingly-an increase in S-cones. Damage of the pigment epithelium was also confirmed. A decrease in the number and labeling intensity of parvalbumin- and calretinin-positive amacrine cells and a loss of ganglion cells was detected. Other cell types showed no evident alterations. No DME-like condition was noticed even after 7 months. M.sh could be a useful model to study the evolution of diabetic retinal pathology and to identify the role of hypertension and dyslipidemia in the development of the reported alterations. Longer follow up would be needed to evaluate the potential use of the visual streak in modeling human macular diseases.

The Preferential Impairment of Pupil Constriction Stimulated by Blue Light in Patients with Type 2 Diabetes without Autonomic Neuropathy

The main aim of the present paper is to examine whether the pupillary light reflex (PLR) mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs) is impaired in type 2 diabetic patients. One hundred and three diabetic patients without diabetic autonomic neuropathy (DAN) and 42 age-matched controls underwent a series of detailed neurological examinations. The patients were stratified into three groups: stage I, no neuropathy; stage II, asymptomatic neuropathy; stage III, symptomatic but without DAN. The PLR to 470 and 635 nm light at 20 cd/m² was recorded. Small fiber neuropathy was assessed by corneal confocal microscopy and quantifying corneal nerve fiber (CNF) morphology. The 470 nm light induced a stronger and faster PLR than did 635 nm light in all subjects. The PLR to both lights was impaired equally across all of the diabetic subgroups. The postillumination pupil response (PIPR) after 470 nm light offset at ≥1.7 sec was attenuated in diabetic patients without differences between subgroups. Receiver operating characteristic analysis revealed that the PIPR mediated by ipRGCs in patients with stage II and stage III neuropathy was different from that of the control subjects. Clinical factors, nerve conduction velocity, and CNF measures were significantly correlated with PLR parameters with 470 nm light. PLR kinetics were more impaired by stimulation with blue light than with red light in diabetic patients without DAN.

Metabolic Alterations Associated to Brain Dysfunction in Diabetes

From epidemiological studies it is known that diabetes patients display increased risk of developing dementia. Moreover, cognitive impairment and Alzheimer's disease (AD) are also accompanied by impaired glucose homeostasis and insulin signalling. Although there is plenty of evidence for a connection between insulin-resistant diabetes and AD, definitive linking mechanisms remain elusive. Cerebrovascular complications of diabetes, alterations in glucose homeostasis and insulin signalling, as well as recurrent hypoglycaemia are the factors that most likely affect brain function and structure. While difficult to study in patients, the mechanisms by which diabetes leads to brain dysfunction have been investigated in experimental models that display phenotypes of the disease. The present article reviews the impact of diabetes and AD on brain structure and function, and discusses recent findings from translational studies in animal models that link insulin resistance to metabolic alterations that underlie brain dysfunction. Such modifications of brain metabolism are likely to occur at early stages of neurodegeneration and impact regional neurochemical profiles and constitute non-invasive biomarkers detectable by magnetic resonance spectroscopy (MRS).

Nicotine accelerates diabetes-induced retinal changes

PURPOSE

To investigate the effects of nicotine on retinal alterations in early-stage diabetes in an established rodent model.

MATERIALS AND METHODS

Sprague-Dawley rats were examined using a combination of confocal scanning laser ophthalmoscopy and spectral domain optical coherence tomography to determine changes in retinal structure in response to nicotine exposure, diabetes and the combined effects of nicotine and diabetes. Diabetes was induced by a single injection of 65 mg/kg streptozotocin and nicotine injections were administered subcutaneously daily. Retinal thickness in the superior, inferior, nasal and temporal quadrants were determined based on the spectral domain optical coherence tomography (SD-OCT) volume scans (20° × 20°) centered on the optic disc. Segmentation of discrete retinal layers was performed on a subset of SD-OCT cross-sections to further examine changes in each treatment group. Survival of neurons within the ganglion cell layer (GCL) was assessed by confocal morphometric imaging.

RESULTS

The control group did not experience any significant change throughout the study. The nicotine treatment group experienced an average decrease in total retinal thickness (TRT) of 9.4 µm with the majority of the loss localized within the outer nuclear layer (ONL) as determined by segmentation analysis (p < 0.05). The diabetic group exhibited a trend toward decreased TRT while segmentation analysis of the diabetic retinopathy (DR) group revealed significant thinning within the ONL (p < 0.05). The combination of nicotine and diabetes revealed a significant increase of 8.9 µm in the TRT (p < 0.05) accompanied by a decrease in the number of GCL neurons.

CONCLUSIONS

We demonstrated significant temporal changes in retinal morphology in response to nicotine exposure, diabetes and with the combined effects of nicotine and diabetes. These findings may have implications in determining treatment strategies for diabetic patients using products containing nicotine, such as cigarettes, smokeless tobacco, electronic cigarettes or smoking cessation products.

Edaravone protect against retinal damage in streptozotocin-induced diabetic mice

Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one), a free radical scavenger, is used for the clinical treatment of retinal injury. In this study, we investigated the protective effects of edaravone against diabetic retinal damage in the mouse. Diabetic retinopathy in the mouse was induced by injection of streptozotocin. Edaravone was given once-daily and was intraperitoneally (i.p.) treated at a dose of 3 mg/kg from streptozotocin injection to 4 weeks after onset of diabetes. Retinal ganglion cells (RGCs) damage was evaluated by recording the pattern electroretinogram (ERG). RGCs damage was also detected by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, and the levels of reactive oxygen species (ROS) were determined fluorometrically. The expressions of phosporylated-ERK1/2, BDNF, and caspase-3 were determined by Western blot analysis. Retinal levels of ROS, phosphorylated ERK1/2, and cleaved caspase-3 were significantly increased, whereas the expression of BDNF was significantly decreased in the retinas of diabetic mice, compared to nondiabetic mice. Administration of edaravone significantly attenuated diabetes induced RGCs death, upregulation of ROS, ERK1/2 phosphorylation, and cleaved caspase-3 and downregulation of BDNF. These findings suggest that oxidative stress plays a pivotal role in diabetic retinal damage and that systemic administration of edaravone may slow the progression of retinal neuropathy induced by diabetes.

Interferon-gamma (IFN-γ)-mediated retinal ganglion cell death in human tyrosinase T cell receptor transgenic mouse

We have recently demonstrated the characterization of human tyrosinase TCR bearing h3T-A2 transgenic mouse model, which exhibits spontaneous autoimmune vitiligo and retinal dysfunction. The purpose of current study was to determine the role of T cells and IFN-γ in retina dysfunction and retinal ganglion cell (RGC) death using this model. RGC function was measured by pattern electroretinograms (ERGs) in response to contrast reversal of patterned visual stimuli. RGCs were visualized by fluorogold retrograde-labeling. Expression of CD3, IFN-γ, GFAP, and caspases was measured by immunohistochemistry and Western blotting. All functional and structural changes were measured in 12-month-old h3T-A2 mice and compared with age-matched HLA-A2 wild-type mice. Both pattern-ERGs (42%, p = 0.03) and RGC numbers (37%, p = 0.0001) were reduced in h3T-A2 mice when compared with wild-type mice. The level of CD3 expression was increased in h3T-A2 mice (h3T-A2: 174 ± 27% vs. HLA-A2: 100%; p = 0.04). The levels of effector cytokine IFN-γ were also increased significantly in h3T-A2 mice (h3T-A2: 189 ± 11% vs. HLA-A2: 100%; p = 0.023). Both CD3 and IFN-γ immunostaining were increased in nerve fiber (NF) and RGC layers of h3T-A2 mice. In addition, we have seen a robust increase in GFAP staining in h3T-A2 mice (mainly localized to NF layer), which was substantially reduced in IFN-γ ((-/-)) knockout h3T-A2 mice. We also have seen an up-regulation of caspase-3 and -9 in h3T-A2 mice. Based on our data we conclude that h3T-A2 transgenic mice exhibit visual defects that are mostly associated with the inner retinal layers and RGC function. This novel h3T-A2 transgenic mouse model provides opportunity to understand RGC pathology and test neuroprotective strategies to rescue RGCs.

Myopia and diabetes mellitus as modificatory factors of glaucomatous optic neuropathy

Myopic deformation of the eye and metabolic alterations of the nerve tissue of patients with diabetes may modify glaucomatous optic neuropathy (GON). Blockage of axonal transport of neurotrophic factors (NTFs) is the event crucial to understanding the factors that affect GON. The primary, but not sole, blockage site is at the lamina cribrosa (LC). Other than this primary site of damage at the LC, 7 other factors may explain atypical nerve fiber layer (NFL) defects and the vulnerability of the nerve fibers in eyes with high myopia and glaucoma: a second point of blockage at the edge of the posterior scleral foramen; ectatic strain on the NFL; ectasia and distortion of the LC; association of a hypoplastic optic disc; thin and weak collagen fibers; peripapillary chorioretinal atrophy; and myopic neuropathy. Among diabetic patients, diabetic neuropathy in the retinal NFL is present initially, and increased resistance to aqueous outflow leads to ocular hypertension. Superimposition of GON on diabetic neuropathy and ocular hypertension in patients with diabetes may enhance their susceptibility to nerve damage. Results of a meta-analysis study suggested a positive association between diabetes mellitus and glaucoma whereas other reports suggested that leakage of vascular endothelial growth factor, a survival mechanism of ischemic neural tissue, and enhanced stiffness of the LC as a result of diabetic glycation may protect neurons from apoptosis. Thus, modification of GON as a result of diabetes remains controversial.

Sweet memories: 20 years of progress in research on cognitive functioning in diabetes

This paper appears in a special issue of the European Journal of Pharmacology that commemorates the retirement of Professor Willem Hendrik Gispen as distinguished professor of Utrecht University and as editor of the European Journal of Pharmacology. The paper provides an overview of a research line on the impact of diabetes on cognition that we started together 20 years ago, and that continues to this day. I will report how we more or less stumbled upon this topic, that was understudied, but proved to be of definite clinical relevance. I will discuss how we tried to establish animal models, how developments from clinical and experimental studies from around the world led us to reconsider our concepts, and how findings from research on diabetic neuropathy, insulin signaling in the brain, Alzheimer's disease and dementia, and vascular disease and stroke converged and helped to create new ideas and refute others. This voyage has not ended yet, because the ultimate goal is to offer patients with diabetes treatment that can protect them against accelerated cognitive decline. Although this could take another 20 years, the research from Willem Hendrik and his group brought us an important step in the right direction.

Neuroprotective effects of cilostazol on retinal ganglion cell damage in diabetic rats

Neurodegeneration is an important component of diabetic retinopathy, with increasing evidence that retinal ganglion cell (RGC) death occurs early in diabetes. We investigated the effects of cilostazol, which has been widely used to manage diabetic complications, on retinal ganglion cell death in the diabetic retina. Four-week-old Otsuka Long-Evans Tokushima fatty (OLETF) rats and Long-Evans Tokushima Otsuka (LETO) rats as matched nondiabetic controls were treated with daily oral cilostazol at 30 mg/kg or 0.9% saline solution. In OLETF rats at the age of 40 weeks, glial fibrillary acidic protein (GFAP) immunofluorescence staining was upregulated in vertical sections, and showed a more ramified pattern in whole-mount retinas compared with that in LETO rats. Vascular endothelial growth factor (VEGF) expression was limited to the ganglion cell layer in LETO rats, but extended into the outer plexiform layer in OLETF rats. Immunofluorescence staining and Western blotting demonstrated that cilostazol treatment reduced GFAP and VEGF expression in the retinas of OLETF rats. Terminal deoxynucleotidyl transferase-mediated terminal deoxynucleotidyl transferase-mediated digoxigenin-deoxyuridine nick-end labeling (TUNEL) staining revealed an increase in the RGC layer in OLETF compared with LETO rats (P < 0.05), and cilostazol treatment reduced the number of TUNEL-positive cells in OLETF rats (P < 0.05). Relieving retinal ischemia by systemic cilostazol treatment had a noticeable protective effect on RGCs in diabetic rats. Cilostazol treatment may be useful for the management of diabetic retinal vascular dysfunction and neuronal degeneration.

Clinical and experimental links between diabetes and glaucoma

Glaucoma is a leading cause of blindness. It is a multifactorial condition, the risk factors for which are increasingly well defined from large-scale epidemiological studies. One risk factor that remains controversial is the presence of diabetes. It has been proposed that diabetic eyes are at greater risk of injury from external stressors, such as elevated intraocular pressure. Alternatively, diabetes may cause ganglion cell loss, which becomes additive to a glaucomatous ganglion cell injury. Several clinical trials have considered whether a link exists between diabetes and glaucoma. In this review, we outline these studies and consider the causes for their lack of concordant findings. We also review the biochemical and cellular similarities between the two conditions. Moreover, we review the available literature that attempts to answer the question of whether the presence of diabetes increases the risk of developing glaucoma. At present, laboratory studies provide robust evidence for an association between diabetes and glaucoma.

Overexpression of Bcl-2 in vascular endothelium inhibits the microvascular lesions of diabetic retinopathy

Recent studies on the pathogenesis of diabetic retinopathy have focused on correcting adverse biochemical alterations, but there have been fewer efforts to enhance prosurvival pathways. Bcl-2 is the archetypal member of a group of antiapoptotic proteins. In this study, we investigated the ability of overexpressing Bcl-2 in vascular endothelium to protect against early stages of diabetic retinopathy. Transgenic mice overexpressing Bcl-2 regulated by the pre-proendothelin promoter were generated, resulting in increased endothelial Bcl-2. Diabetes was induced with streptozotocin, and mice were sacrificed at 2 months of study to measure superoxide generation, leukostasis, and immunohistochemistry, and at 7 months to assess retinal histopathology. Diabetes of 2 months duration caused a significant decrease in expression of Bcl-2 in retina, upregulation of Bax in whole retina and isolated retinal microvessels, and increased generation of retinal superoxide and leukostasis. Seven months of diabetes caused a significant increase in the number of degenerate (acellular) capillaries in diabetic animals. Furthermore, overexpression of Bcl-2 in the vascular endothelium inhibited the diabetes-induced degeneration of retinal capillaries and aberrant superoxide generation, but had no effect on Bax expression or leukostasis. Therefore, overexpression of Bcl-2 in endothelial cells inhibits the capillary degeneration that is characteristic of the early stages of diabetic retinopathy, and this effect seems likely to involve inhibition of oxidative stress.

Diabetes and cardiovascular autonomic dysfunction: application of animal models

When diabetes is associated with cardiovascular autonomic dysfunction, there is a poor prognosis and increased morbidity and mortality. Information on the mechanisms of diabetes-associated autonomic dysfunction has been provided by advanced studies using physiological, pharmacological, anatomical and molecular methods in experimental animal models of insulin deficiency and resistance. This has been augmented by new approaches which combine diabetes induction with genetically modified animal models. The aim of this review is to outline and discuss the animal models used for the study of insulin deficiency and insulin resistance with a focus on autonomic neural interactions. The goal is to better understand the clinical relevance of cardiovascular autonomic dysfunction associated with diabetes.

Retinal ganglion cells in diabetes

Diabetic retinopathy has long been recognized as a vascular disease that develops in most patients, and it was believed that the visual dysfunction that develops in some diabetics was due to the vascular lesions used to characterize the disease. It is becoming increasingly clear that neuronal cells of the retina also are affected by diabetes, resulting in dysfunction and even degeneration of some neuronal cells. Retinal ganglion cells (RGCs) are the best studied of the retinal neurons with respect to the effect of diabetes. Although investigations are providing new information about RGCs in diabetes, including therapies to inhibit the neurodegeneration, critical information about the function, anatomy and response properties of these cells is yet needed to understand the relationship between RGC changes and visual dysfunction in diabetes.

Contributions of inflammatory processes to the development of the early stages of diabetic retinopathy

Diabetes causes metabolic and physiologic abnormalities in the retina, and these changes suggest a role for inflammation in the development of diabetic retinopathy. These changes include upregulation of iNOS, COX-2, ICAM-1, caspase 1, VEGF, and NF-κB, increased production of nitric oxide, prostaglandin E2, IL-1β, and cytokines, as well as increased permeability and leukostasis. Using selective pharmacologic inhibitors or genetically modified animals, an increasing number of therapeutic approaches have been identified that significantly inhibit development of at least the early stages of diabetic retinopathy, especially occlusion and degeneration of retinal capillaries. A common feature of a number of these therapies is that they inhibit production of inflammatory mediators. The concept that localized inflammatory processes play a role in the development of diabetic retinopathy is relatively new, but evidence that supports the hypothesis is accumulating rapidly. This new hypothesis offers new insight into the pathogenesis of diabetic retinopathy, and offers novel targets to inhibit the ocular disease.

Synaptic transmission changes in the pyramidal cells of the hippocampus in streptozotocin-induced diabetes mellitus in rats

The central nervous system complications of diabetes mellitus (DM) include defects in hippocampal synaptic plasticity induction and difficulties in learning and memory. DM was induced by streptozotocin (STZ) injection in rats. After 12 weeks of DM duration, the rats were decapitated, and hippocampal slices were prepared for in vitro study. Field excitatory postsynaptic potentials (fEPSP) were recorded after repeated stimulations with 50 impulses given either in 10 or 20 Hz. The responses were significantly smaller in the diabetic animals than in the age-matched control rats. The summation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) responses was tested in both groups by stimulating the synapses with five consecutive stimuli given in 50-Hz frequency. Intracellular recording from the pyramidal hippocampal cells of the AMPA summation responses from diabetic and aged-matched control animals revealed a significant lower summation in the diabetic animals compared to the control. It is concluded that responses evoked by high-frequency stimulation (HFS) were significantly higher in the control animals. The defects in diabetic slices could be related to pre- as well as postsynaptic changes, and these defects play an important role in the synaptic plasticity changes seen in STZ-induced diabetic animals.

The effect of short duration streptozotocin-induced diabetes mellitus on the late phase and threshold of long-term potentiation induction in the rat

Long-term potentiation (LTP) was examined in streptozotocin (STZ)-induced diabetic rats of 8 (DM8) and 20 (DM20) weeks duration of diabetes mellitus (DM). DM8 animals showed significant LTP induction, although the potentiation of the synapses was significantly lower than in the control animals. No significant potentiation of the synapses could be demonstrated in DM20 animals. The different aspects of LTP induction in the DM8 animals were studied. The threshold of LTP induction was measured by stimulating the slices with 100 Hz frequency trains of stimuli containing different number of impulses. The results showed increased threshold for LTP induction in the DM8 animals compared to the controls. The late LTP (L-LTP) phase induction was studied by applying 3 repeated HFSs to the afferent fibers. Diabetic animals (DM8) slices failed to maintain the synaptic potentiation induced by the high frequency stimulations (HFSs) for more than 1 h.

Insulin, C-peptide, hyperglycemia, and central nervous system complications in diabetes

Diabetes is an increasingly common disorder which causes and contributes to a variety of central nervous system (CNS) complications which are often associated with cognitive deficits. There appear to be two types of diabetic encephalopathy. Primary diabetic encephalopathy is caused by hyperglycemia and impaired insulin action, which evolves in a diabetes duration-related fashion and is associated with apoptotic neuronal loss and cognitive decline. This appears to be particularly associated with insulin-deficient diabetes. Secondary diabetic encephalopathy appears to arise from hypoxic-ischemic insults due to underlying microvascular disease or as a consequence of hypoglycemia. This type of cerebral diabetic complication is more common in the type 2 diabetic population. Here, we will review the clinical and experimental data supporting this conceptual division of diabetic CNS complications and discuss the underlying metabolic, molecular, and functional aberrations.

Nerve conduction velocity and evoked potential latencies in streptozotocin-diabetic rats: effects of treatment with an angiotensin converting enzyme inhibitor

BACKGROUND

Diabetes mellitus is associated with deficits in cerebral function. Vascular disorders may play a role in the pathogenesis and provide a potential target for treatment. The present study examined if prevention and intervention treatment with the angiotensin converting enzyme inhibitor enalapril could improve peripheral and central neurophysiological deficits in streptozotocin-diabetic rats.

METHODS

Sciatic nerve conduction velocities were measured prior to diabetes induction and again every three weeks. In the prevention study, the final nerve conduction measurements were performed at 15 weeks and in the intervention study at 24 weeks. Brain stem auditory and visual evoked potential latencies were measured every 3 weeks from 10 weeks after diabetes induction. In the prevention study, the final evoked potential measurements were performed at 16 weeks and in the intervention study at 25 weeks. Treatment with the angiotensin converting enzyme inhibitor enalapril was started directly after diabetes induction (prevention treatment) and after 15 weeks of diabetes (intervention treatment).

RESULTS

Nerve conduction velocity, brain stem auditory and visual evoked potential latencies were impaired in diabetic rats. Enalapril prevented deficits in nerve conduction velocity (p < 0.001), brain stem auditory evoked potential latencies (p < 0.01) and visual evoked potential latencies (p < 0.005). Enalapril intervention treatment had no effect on nerve conduction velocity and on visual evoked potential latencies, but improved brain stem auditory evoked potential latencies (p < 0.05) after 10 weeks of treatment.

CONCLUSION

Enalapril partially prevents the development of neurophysiological alterations in the peripheral and central nervous system and partially reverses deficits in brain stem auditory evoked potential latencies in STZ-diabetic rats.

Changes in somatosensory evoked potentials, lipid peroxidation, and antioxidant enzymes in experimental diabetes: effect of sulfur dioxide

The effect of sulfur dioxide (SO2) on brain antioxidant status, lipid peroxidation, and somatosensory evoked potentials (SEPs) was investigated in diabetic rats. A total of 40 rats were divided into 4 equal groups: control (C), SO2 + C (SO2), diabetic (D), and SO2 + D (DSO2). Experimental diabetes mellitus was induced by i.v. injection of alloxan at a dose of 50 mg/kg body weight. Ten ppm SO2 was administered to the rats in the sulfur dioxide groups (SO2 and DSO2) in an exposure chamber. Exposure occurred 1 hr/day, 7 days/wk, for 6 wk; control rats were exposed to filtered air during the same time periods. Although SO2 exposure markedly increased copper, zinc Superoxide dismutase activity, it significantly decreased glutathione peroxidase activity in both the diabetic and nondiabetic groups, compared with the C group. Brain catalase activity was unaltered; however, brain thiobarbituric acid reactive substances (TBARS) were elevated in all experimental groups with respect to the C group. SEP components P1, N1, P2, and N2 were significantly increased in all experimental groups, compared with the C group, and these components were also prolonged in the DSO2 group with respect to the other groups. The authors' findings suggest that exposure to SO2, because it increases lipid peroxidation, can change antioxidant enzyme activities and affect SEP components in diabetic rats.

Diabetic Retinopathy and the NMDA Receptor

Diabetic retinopathy is a major sight-threatening disease and is a leading cause of blindness. There is an emerging body of evidence that suggests that neuronal changes are an early phenomenon in the diabetic retina and that several cell types are affected, including the ganglion cells. The degeneration of these cells is thought to occur via overstimulation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. Characteristic features of the normal mammalian retina and of the diabetic retina, and the involvement of NMDA receptors in diabetic retinopathy, are discussed. (c) 2002 Prous Science. All rights reserved.

Multilateral in vivo and in vitro protective effects of the novel heat shock protein coinducer, bimoclomol: results of preclinical studies

Bimoclomol, the recently developed non-toxic heat shock protein (HSP) coinducer, was shown to display multilateral protective activities against various forms of stress or injuries at the level of the cell, tissue or organism. The compound enhanced the transcription, translation and expression of the 70 kD heat shock protein (HSP-70) in myogenic and HeLa cell lines exposed to heat stress, and increased cell survival on exposure to otherwise lethal thermal injury. Bimoclomol increased contractility of the working mammalian heart, this effect was associated with the increased intracellular calcium transients due to increased probability of opening of ryanodine receptors in the sarcoplasmic reticulum (SR). In healthy tissues these cardiac effects were evident only at relatively high concentrations of the drug, while in the ischemic myocardium bimoclomol exerted significant cardioprotective and antiarrhythmic effects at submicromolar concentrations. It decreased ischemia-induced reduction of contractility and of cardiac output, and dramatically decreased the elevation of the ST-segment during ischemia as well as the occurrence of ventricular fibrillation upon reperfusion. Bimoclomol was also active in various pathological animal models subjected to acute or chronic stress. In the spontaneously hypertensive rats chronic pretreatment with bimoclomol restored sensitivity of aortic rings to acetylcholine; this effect was accompanied by accumulation of HSP-70 in the tissues. Bimoclomol pretreatment significantly diminished the consequences of vascular disorders associated with diabetes mellitus. Diabetic neuropathy, retinopathy, and nephropathy were prevented or diminished, while wound healing was enhanced by bimoclomol. Enhancement of wound healing by bimoclomol was observed after thermal injury as well as following ultraviolet (UV) irradiation. In addition to the beneficial effects on peripheral angiopathies, bimoclomol antagonized the increase in permeability of blood-brain barrier induced by subarachnoid hemorrhager or arachidonic acid. A general and very important feature of the above effects of bimoclomol was that the drug failed to cause alterations under physiological conditions (except the enhanced calcium release from cardiac sarcoplasmic reticulum). Bimoclomol was effective only under conditions of stress. Consistent with its HSP-coinducer property, bimoclomol alone had very little effect on HSP production. Its protective activity became apparent only in the presence of cell damage. Currently, bimoclomol reached the end of the Phase II clinical trial in a group of 410 patients with diabetic complications. Results of this trial will answer the question, whether a compound with promising in vitro and in vivo preclinical findings will produce the anticipated beneficial effects in humans. In the event of a positive outcome of this trial, the indications for bimoclomol will be substantially extended.

Tissue-level thresholds for axonal damage in an experimental model of central nervous system white matter injury

In vivo, tissue-level, mechanical thresholds for axonal injury were determined by comparing morphological injury and electrophysiological impairment to estimated tissue strain in an in vivo model of axonal injury. Axonal injury was produced by dynamically stretching the right optic nerve of an adult male guinea pig to one of seven levels of ocular displacement (Nlevel = 10; Ntotal = 70). Morphological injury was detected with neurofilament immunohistochemical staining (NF68, SM132). Simultaneously, functional injury was determined by the magnitude of the latency shift of the N35 peak of the visual evoked potentials (VEPs) recorded before and after stretch. A companion set of in situ experiments (Nlevel = 5) was used to determine the empirical relationship between the applied ocular displacement and the magnitude of optic nerve stretch. Logistic regression analysis, combined with sensitivity and specificity measures and receiver operating characteristic (ROC) curves were used to predict strain thresholds for axonal injury. From this analysis, we determined three Lagrangian strain-based thresholds for morphological damage to white matter. The liberal threshold, intended to minimize the detection of false positives, was a strain of 0.34, and the conservative threshold strain that minimized the false negative rate was 0.14. The optimal threshold strain criterion that balanced the specificity and sensitivity measures was 0.21. Similar comparisons for electrophysiological impairment produced liberal, conservative, and optimal strain thresholds of 0.28, 0.13, and 0.18, respectively. With these threshold data, it is now possible to predict more accurately the conditions that cause axonal injury in human white matter.

Diabetic neuropathy--a continuing enigma

In this article we will review the clinical signs and symptoms of diabetic somatic polyneuropathy (DPN), its prevalence and clinical management. Staging and classification of DPN will be exemplified by various staging paradigms of varied sophistication. The results of therapeutic clinical trials will be summarized. The pathogenesis of diabetic neuropathy reviews an extremely complex issue that is still not fully understood. Various recent advances in the understanding of the disease will be discussed, particularly with respect to the differences between neuropathy in the two major types of diabetes. The neuropathology and natural history of diabetic neuropathy will be discussed pointing out the heterogeneities of the disease. Finally, the various prospective therapeutic avenues will be dealt with and discussed.

Role of vasoactive factors in the pathogenesis of early changes in diabetic retinopathy

Several interactive and mutually perpetuating abnormal biochemical pathways, such as protein kinase C (PKC) activation, augmented polyol pathway, and non-enzymatic glycation, may be activated as a result of sustained hyperglycemia in diabetes. These abnormal pathways may in turn influence several vasoactive factors, which are probably instrumental in the production of functional and morphological changes in the retina in diabetes. The vasoactive factors such as endothelins, nitric oxide, vascular endothelial growth factors, etc., are of importance in mediating functional and structural alterations in early diabetic retinopathy. Intricate and interactive regulatory mechanism(s) among these factors may control ultimate availability of these molecules to produce biologically significant effects. A better understanding of these factors and their interactions would aid the development of adjuvant therapies for the treatment of diabetic retinopathy.

Retinal neurodegeneration: early pathology in diabetes

Normal vision depends on the normal function of retinal neurons, so vision loss in diabetes must ultimately be explained in terms of altered neuronal function. However to date relatively little attention has been paid to the impact of diabetes on the neural retina. Instead, the focus of most research has been primarily on retinal vascular changes, with the assumption that they cause altered neuronal function and consequently vision loss. An increasing body of evidence suggests that alterations in neuronal function and viability may contribute to the pathogenic mechanisms of diabetic retinopathy beginning shortly after the onset of diabetes. This view arises from neurophysiological, psychometric, histopathological and biochemical observations in humans and experimental animals. The collective evidence from past and recent studies supports the hypothesis that neurodegeneration, together with functional changes in the vasculature, is an important component of diabetic retinopathy. The authors invite other investigators to include the neural retina as a component of their studies so that the pathogenesis of diabetic retinopathy can be understood more clearly.

Effect of islet transplantation on neuroelectrophysiological abnormalities in diabetic inbred Lewis rats: comparison of primary versus secondary prevention

BACKGROUND

Neuroelectrophysiological abnormalities in diabetes indicate nervous function failure. Restoration of euglycemia by islet transplantation may prevent or reverse these abnormalities.

METHODS

Pancreatic islets were transplanted in inbred Lewis rats after 15 days (Ta12, primary prevention) or 8 months (Tb12, secondary prevention) from streptozotocin-induced diabetes. Transplanted and control (normal and diabetic) rats were followed for a total period of 12 months. Metabolic parameters, somato-sensory, brain-stem auditory, and visual evoked potentials were determined at the beginning and at the end of the study and before transplantation for secondary prevention.

RESULTS

The metabolic parameters in transplanted animals were similar to those of normal animals. Ta12 and normal group somato-sensory conduction velocities did not vary and were always significantly higher than those of diabetic animals. By contrast, Tb12 group conduction velocities showed only a partial improvement, values lying between those of diabetic and normal rats. Brain-stem auditory (waves I, II, and III) latencies in Ta12 group were similar to those of normal rats and significantly lower than those of diabetic animals (wave I: P<0.01; waves II and III: P<0.05). Tb12 group wave I and II latency values remained altered (P<0.005 and P<0.01 versus normal values respectively). Visual evoked potentials-P1 wave latencies in transplanted rats were always higher than those of normal and diabetic animals.

CONCLUSIONS

After primary prevention, central and peripheral neurological alterations were abolished. After secondary prevention, transplantation beneficial effects were partial, occurring mainly at peripheral level. These results highlight the importance of early transplantation to prevent hyperglycemia-dependent neuroelectrophysiological alterations.

Neurophysiological changes in the central and peripheral nervous system of streptozotocin-diabetic rats. Course of development and effects of insulin treatment

Diabetes mellitus can affect both the peripheral and the central nervous system. However, central deficits are documented less well than peripheral deficits. We therefore compared the course of development of neurophysiological changes in the central and peripheral nervous systems in streptozotocin-diabetic rats. Sciatic nerve conduction velocities and auditory and visual evoked potentials were measured prior to diabetes induction, and then monthly after diabetes induction for 6 months. In addition, the effect of insulin treatment was examined. Treatment was initiated after a diabetes duration of 6 months and was continued for 3 months. During treatment, evoked potentials and nerve conduction were measured monthly. In a third experiment, conduction velocities in ascending and descending pathways of the spinal cord were examined after 3 and 6 months of diabetes. Impairments of sciatic nerve conduction velocities developed fully during the first 2-3 months of diabetes. In contrast, increased latencies of auditory and visual evoked potentials developed only after 3-4 months of diabetes, and progressed gradually thereafter. Insulin treatment, initiated 6 months after induction of diabetes, improved both nerve conduction velocities and evoked potential latencies. Conduction velocities in the spinal cord tended to be reduced after 3 months of diabetes and were significantly reduced after 6 months of diabetes. The present study demonstrates that in streptozotocin-diabetic rats the course of development of peripheral and central neurophysiological changes differs. Peripheral impairments develop within weeks after diabetes induction, whereas central impairments take months to develop. Insulin can reverse both peripheral and central neurophysiological alterations.

Nodal Na(+)-channel displacement is associated with nerve-conduction slowing in the chronically diabetic BB/W rat: prevention by aldose reductase inhibition

Chronic nerve conduction showing in experimental diabetic neuropathy has been associated with decreased nodal Na+ permeability and an ultrastructurally identifiable loss of axo-glial junctions, which comprise the paranodal voltage channel barrier separating nodal Na+ channels from paranodal K+ channels. In human and experimental diabetic neuropathy these structural changes of the paranodal apparatus correlate closely with the nerve conduction defect. The present immunocytochemical study of the alpha-subunit of the Na+ channel examined whether the breach of the voltage channel barrier may account for a shift in the distribution of Na+ channels explaining decreased nodal Na+ permeability. Biobreeding Wistar (BB/W) rats diabetic for 4-8 months showed a progressive redistribution of nodal Na+ channels across the paranodal barrier into the paranodal and internodal domains which was associated with chronic nerve conduction slowing. The present data suggest that structural damage to the paranodal barrier system in diabetic nerve facilitates the lateral displacement of Na+ channels from the nodal axolemma thereby diminishing their nodal density and the nodal Na+ permeability associated with the chronic nerve conduction defect in experimental diabetes. These abnormalities were prevented by the treatment with an aldose reductase inhibitor, belonging to a class of drugs that, in neuropathic patients, improves nerve-conduction velocity and repairs axo-glial dysjunction of the paranodal apparatus.

Peripheral, but not central, nervous system abnormalities are reversed by pancreatic islet transplantation in diabetic Lewis rats

Neuroelectrophysiological recordings represent a non-invasive and reproducible method of detecting central and peripheral nervous system alterations in diabetes mellitus. In order to evaluate whether the normalization of metabolic control obtained by pancreatic islet transplantation could reverse diabetic neuroelectrophysiological alterations, or prevent further deterioration, we used an experimental model in which pancreatic islets (n = 1200) were injected into the portal vein of inbred Lewis rats (used as islet donors as well as recipients). Islets were injected 4 months after diabetes induction, since previous work had shown functional but not morphological damage at the nervous tissue level at this stage of the disease. Visual (V), brainstem auditory (BA) and somatosensory (S) evoked potentials (EPs) were measured in streptozotocin-induced, islet-recipient diabetic rats (n = 7), streptozotocin-induced diabetic rats (n = 16) and non-diabetic control rats (n = 12). Metabolic parameters and electrophysiological recordings were evaluated before diabetes induction, before transplantation and 4 months later. After transplantation, glycaemic levels returned to normal values within 1 week and remained so until the end of the study, as confirmed by a normal oral glucose tolerance test and by an increase in body weight. Electrophysiological recordings were altered in diabetic animals before transplantation. Four months after transplantation EP recordings improved, with a detectable gradient from the peripheral to the central structures. SEPs were significantly improved in the peripheral tarsus-L6 tract and the L6-cortex tract (P < 0.005 and P < 0.01 versus diabetic rats) and were ameliorated without achieving statistical significance in the central L6-cortex tract. BAEP latency values tended to improve in transplanted rats, but the differences versus non-transplanted diabetic animals failed to reach significance. VEP values remained clearly pathological and even deteriorated after transplantation. These results show that normalization of metabolic control by pancreatic islet transplantation can reverse some of the already established neuroelectrophysiological alterations at the peripheral nervous system level, but does not affect other alterations at the central nervous system level.

Presence and further development of retinal dysfunction after 3-year follow up in IDDM patients without angiographically documented vasculopathy

Abnormalities in neuroretinal function may play a role in the development of diabetic retinopathy. The natural course of diabetic retinal dysfunction in a group of subjects with insulin-dependent diabetes mellitus and with no apparent microvascular alterations in the retina was followed-up with fluorescein angiography and a sensitive electrophysiological technique, i.e., steady-state focal electroretinogram at the macula, for 3 years. Before the beginning and throughout our study, strict glycaemic control was maintained by three or four daily insulin injections under careful monitoring. Analysis of macular electroretinogram provided information from different neural layers. At the first examination, functional activities of postreceptoral neurons were significantly decreased with respect to those of age-matched control subjects. Diabetic patients showed a functional loss of both ganglion cell (0.53 +/- 0.09 vs 0.42 +/- 0.11 microV; t = 5; p = 0.0001) and preganglion cell (0.51 +/- 0.13 vs 0.42 +/- 0.14 microV; t = 2.8; p = 0.007) layers. Diabetes did not alter photoreceptor activity. After 3 years, dysfunction was significantly greater in the preganglion cell layer (0.28 +/- 0.11 microV; t = 6.3; p = 0.0001). Although in some patients further impairment of ganglion cell function was shown, no significant difference was found in 3 years. Photoreceptor function remained unaltered. No vascular abnormalities in the retina were noted after 3 years in this group of patients. Metabolic control was not correlated to functional changes. Our findings suggest that the middle retinal layer is the most sensitive physiological locus of progressive diabetes-induced dysfunction in the absence of angiographically documented abnormalities.

Cerebral function in diabetes mellitus

Diabetes mellitus is a common metabolic disorder associated with chronic complications such as nephropathy, angiopathy, retinopathy and peripheral neuropathy. Diabetes is not often considered to have deleterious effects on the brain. However, long-term diabetes results in a variety of subtle cerebral disorders, which occur more frequently than is commonly believed. Diabetic cerebral disorders have been demonstrated at a neurochemical, electrophysiological, structural and cognitive level; however, the pathogenesis is still not clear. Probably alterations in cerebral blood supply and metabolic derangements play a role, as they do in the pathogenesis of diabetic neuropathy. Furthermore, the brain is also affected by recurrent episodes of hypoglycaemia and poor metabolic control. We describe herein the cerebral manifestations of diabetes and discuss the putative pathogenetic mechanisms.

Early selective neuroretinal disorder in prepubertal type 1 (insulin-dependent) diabetic children without microvascular abnormalities

The duration of diabetes before puberty is not considered relevant to the future development of complications. To evaluate the effects of diabetes on the neural retina, we analysed macular function by steady-state focal electroretinography in 20 prepubescent diabetic children without vascular retinopathy and in 39 sex- and age-matched normal children. The mean (+/- SD) response related to retinal cellular elements between the photoreceptors and ganglion cells was significantly lower in diabetic children than in the control group (0.38 +/- 0.12 vs. 0.51 +/- 0.13 microV; unpaired t-test = 3; P = 0.005). Similarly, ganglion cell function showed a significant impairment in diabetic children with respect to the control group (0.4 +/- 0.13 vs. 0.53 +/- 0.09 microV; unpaired t-test = 5.4; P = 0.0001), whereas the photoreceptors appeared unaffected. Metabolic control and disease duration were not correlated with functional deficits. Our results suggest that before puberty, early diabetes may have a selective effect on the neural retina prior to the appearance of microvascular changes. A focal electroretinogram could identify diabetic children with neurosensory disorders who may have a higher risk of developing microvascular retinopathy.

The preventive effect of aldose reductase inhibition on diabetic optic neuropathy in the BB/W-rat

A polyol-pathway-related mechanism has been invoked in the pathogenesis of murine and human diabetic peripheral neuropathy in which progressive axonal atrophy and axo-glial dysjunction constitute the cardinal structural abnormalities. We have previously reported similar neuroanatomical changes in the optic nerve of 6-month diabetic BB/W-rats. In the present study we demonstrate progression of axonal atrophy and axo-glial dysjunction in the optic nerve in 12-month diabetic BB/W-rats. These structural lesions showed highly significant correlations with the associated prolongation of the latencies of the visual evoked potentials, suggesting that axo-glial dysjunction and axonal atrophy are major determinants for impaired optic nerve function. As in peripheral nerve, the polyol-pathway is present in the optic nerve and is activated by hyperglycaemia and galactosaemia. In this study we further examined the treatment effect of the aldose reductase inhibitor ponalrestat, given from 3 weeks of diabetes and continued throughout the study protocol. This regimen resulted in complete prevention of axo-glial dysjunction, and had a significant ameliorating effect on visual evoked potential latencies, but had no effect on optic nerve axonal atrophy. This latter finding differs from the effect of aldose reductase inhibition on diabetic peripheral nerve and suggests that axonal atrophy of central nerve tracts in diabetes may be the consequence of other metabolic abnormalities or alternatively the present regimen was insufficient to protect central axons from the effects of an increased activity of the polyol pathway.