DISTAL DEGENERATIVE SENSORY NEUROPATHY IN A LONG TERM TYPE 2 DIABETES RAT MODEL

Abstract

Objective: Peripheral neuropathy associated with Type 2 diabetes mellitus (DPN) is not widely modelled. We describe unique features of DPN in Type 2 Zucker diabetic fatty (ZDF) rats.

Research Design and Methods: We evaluated the structural, electrophysiological, behavioural and molecular features of DPN in ZDF rats and littermates over 4 months of hyperglycemia. The status of insulin signaling transduction molecules that might be interrupted in Type 2 diabetes, and selected survival, stress and pain related molecules was emphasized in dorsal root ganglia (DRG) sensory neurons.

Results: ZDF rats developed slowing of motor sciatic-tibial and sensory sciatic digital conduction velocity, and selective mechanical allodynia with preserved thermal algesia. Diabetic sural axons, preserved in number, developed atrophy but there was loss of large calibre dermal and small calibre epidermal axons. In diabetic rats, insulin signal transduction pathways in lumbar DRGs were preserved or had trends toward upregulation: mRNA levels of insulin receptor β subunit (IRβ), IRS-1 (insulin receptor substrate -1) and IRS-2. The numbers of neurons expressing IRβ protein were also preserved. There were trends toward early rises of mRNA levels of HSP27 (Heat shock protein 27), the α2δ1 calcium channel subunit and PI3-K (phosphoinositide 3-kinase) in diabetes. Others were unchanged including NFκ-B (p50/p105) and RAGE (receptor for advanced glycosylation endproducts) as was the proportion of neurons expressing HSP 27, NFκ-B and RAGE protein.

Conclusions: ZDF Type 2 diabetic rats develop a distal degenerative sensory neuropathy accompanied by a selective long term pain syndrome. Neuronal insulin signal transduction molecules are preserved.