title: Repeated monitoring of corneal nerves by confocal microscopy as an index of peripheral neuropathy in type-1 diabetic rodents and the effects of topical insulin.
abstract: We developed a reliable imaging and quantitative analysis method for in vivo corneal confocal microscopy (CCM) in rodents and used it to determine whether models of type 1 diabetes replicate the depletion of corneal nerves reported in diabetic patients. Quantification was reproducible between observers and stable across repeated time points in two rat strains. Longitudinal studies were performed in normal and streptozotocin (STZ)-diabetic rats, with innervation of plantar paw skin quantified using standard histological methods after 40 weeks of diabetes. Diabetic rats showed an initial increase, then a gradual reduction in occupancy of nerves in the sub-basal plexus so that values were significantly lower at week 40 (68 ± 6%) than age-matched controls (80 ± 2%). No significant loss of stromal or intra-epidermal nerves was detected. In a separate study, insulin was applied daily to the eye of control and STZ-diabetic mice and this treatment prevented depletion of nerves of the sub-basal plexus. Longitudinal studies are viable in rodents using CCM and depletion of distal corneal nerves precedes detectable loss of epidermal nerves in the foot, suggesting that diabetic neuropathy is not length dependent. Loss of insulin-derived neurotrophic support may contribute to the pathogenesis of corneal nerve depletion in type 1 diabetes.
authors.affiliation: Department of Pathology, School of Medicine, University of California, San Diego, La Jolla, CA, USA.
authors.forename: Debbie K
authors.initials: DK
authors.lastname: Chen
authors.forename: Katie E
authors.initials: KE
authors.lastname: Frizzi
authors.forename: Lucie S
authors.initials: LS
authors.lastname: Guernsey
authors.forename: Kelsey
authors.initials: K
authors.lastname: Ladt
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Mizisin
authors.forename: Nigel A
authors.initials: NA
authors.lastname: Calcutt
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D003315:Cornea / Q000294:innervation*; D003922:Diabetes Mellitus, Type 1 / Q000097:blood / Q000150:complications / Q000209:etiology; D004195:Disease Models, Animal; D006442:Glycated Hemoglobin / Q000378:metabolism; D007328:Insulin / Q000097:blood / Q000494:pharmacology / Q000627:therapeutic use; D051379:Mice; D018613:Microscopy, Confocal / Q000295:instrumentation / Q000379:methods*; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods*; D009412:Nerve Fibers / Q000473:pathology*; D010523:Peripheral Nervous System Diseases / Q000097:blood / Q000209:etiology / Q000473:pathology*; D051381:Rats; D012867:Skin / Q000294:innervation; D013311:Streptozocin / Q000633:toxicity
chemical_list: D001786:Blood Glucose; D006442:Glycated Hemoglobin; D007328:Insulin; D013311:Streptozocin
keywords: diabetic neuropathy; distal neuropathy; in vivo corneal confocal microscopy; insulin therapy; streptozotocin; type 1 diabetes