No abstract

High glucose levels in the peripheral nervous system (PNS) have been implicated in the pathogenesis of diabetic neuropathy (DN). However, our understanding of the molecular mechanisms that cause the marked distal pathology is incomplete. We performed a comprehensive, system-wide analysis of the PNS of a rodent model of DN. We integrated proteomics and metabolomics from the sciatic nerve (SN), the lumbar 4/5 dorsal root ganglia (DRG), and the trigeminal ganglia (TG) of streptozotocin-diabetic and healthy control rats. Even though all tissues showed a dramatic increase in glucose and polyol pathway intermediates in diabetes, a striking upregulation of mitochondrial oxidative phosphorylation and perturbation of lipid metabolism was found in the distal SN that was not present in the corresponding cell bodies of the DRG or the cranial TG. This finding suggests that the most severe molecular consequences of diabetes in the nervous system present in the SN, the region most affected by neuropathy. Such spatial metabolic dysfunction suggests a failure of energy homeostasis and/or oxidative stress, specifically in the distal axon/Schwann cell-rich SN. These data provide a detailed molecular description of the distinct compartmental effects of diabetes on the PNS that could underlie the distal-proximal distribution of pathology.Diabetic neuropathy (DN) will develop in ;30-50% of patients with diabetes. DN typically presents with sensory symptoms in a distal glove-and-stocking distribution (1,2). It is a poorly understood complication of diabetes, and currently, few treatments are available (3). Raised glucose has long been believed to instigate pathology in DN either through direct neurotoxicity or from the activation of secondary pathways (4,5). However, exactly how these pathways cause nerve conduction velocity deficits, neuropathic pain, distal axonopathy, and numbness in the extremities continues to elude us, and many clinical trials aimed at specific targets have failed due to lack of efficacy (3).Crossover exists between proposed pathogenic pathways in DN, but how these interact is unclear. This question can be approached by implementing extensive -omic technologies to measure many transcripts, proteins, or metabolites in parallel. Gene microarrays were among the first of these technologies to be used, and transcriptomic analyses have been performed on tissues such as the dorsal root ganglia (DRG) from streptozotocin (STZ)-diabetic rats compared with healthy controls (6), the sciatic nerve (SN) of db/db mice compared with those from db/+ mice (7), and sural nerve biopsy specimens from human patients whose neuropathy progressed over 1 year compared with those whose neuropathy did not (based on myelinated fiber density loss) (8). Common changes across these gene array studies highlight altered carbohydrate and lipid metabolism.Because gene transcript levels do not always correlate with protein expression due to varying transcriptional/translational

In any sensory system, the primary afferents constitute the first level of sensory representation and fundamentally constrain all subsequent information processing. Here, we show that the spike timing, reliability, and stimulus selectivity of primary afferents in the whisker system can be accurately described by a simple model consisting of linear stimulus filtering combined with spike feedback. We fitted the parameters of the model by recording the responses of primary afferents to filtered, white noise whisker motion in anesthetized rats. The model accurately predicted not only the response of primary afferents to white noise whisker motion (median correlation coefficient 0.92) but also to naturalistic, texture-induced whisker motion. The model accounted both for submillisecond spike-timing precision and for non-Poisson spike train structure.Wefoundsubstantialdiversityintheresponsesoftheafferentpopulation,butthisdiversitywasaccuratelycapturedbythemodel:a2Dfilter subspace, corresponding to different mixtures of position and velocity sensitivity, captured 94% of the variance in the stimulus selectivity. Our results suggest that the first stage of the whisker system can be well approximated as a bank of linear filters, forming an overcomplete representation of a low-dimensional feature space.