Insulin is essential for the recovery from allodynia induced by complete Freund's adjuvant.
OBJECTIVE
To determine the effect of streptozotocin (STZ)-induced diabetes on the development and recovery of thermal and mechanical hyperalgesia associated with inflammation induced by subcutaneous injection of complete Freund's adjuvant (CFA).


BACKGROUND
The response to nociceptive injury in diabetes differs from that seen in normal individuals in that diabetic patients have increased susceptibility to infections and recover slowly or incompletely from infections and tissue injury due to an abnormal inflammatory response. We have chosen to examine the effect of STZ-induced hypoinsulinemia on the hyperalgesia associated with the enhanced inflammatory state that is induced by the subcutaneous injection of CFA to delineate the potential role of insulin in the development of chronic pain.


METHODS
STZ- and vehicle-treated Sprague-Dawley rats were tested using thermal and mechanical stimulation after subcutaneous injection of CFA. The behavioral response was compared with that similarly determined in non-diabetic controls and insulin-depleted rats that received insulin replacement.


RESULTS
Recovery of the thermal hyperalgesic response to baseline levels occurred over a period of 9-14 days, but the allodynic response to mechanical stimulation persisted for the duration of the study in STZ-treated rats. Insulin replacement prevented the delay in recovery of mechanical allodynia, but had no obvious effect on nociception in uninflamed tissue.


CONCLUSIONS
Normal insulin function is essential for recovery from mechanical allodynia associated with inflammation induced by CFA. Altered insulin metabolism may selectively influence fiber-type specific mechanisms related to mechanical allodynia associated with inflammation and wound healing.
Casey
Gregory P
GP
Department of Cell Biology and Anatomy, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA.
Paul
Dennis
D
Gould
Harry J
HJ
D000818:Animals; D001522:Behavior, Animal; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology; D005620:Freund's Adjuvant / Q000009:adverse effects*; D006358:Hot Temperature; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced* / Q000276:immunology; D007249:Inflammation / Q000139:chemically induced / Q000276:immunology; D007328:Insulin / Q000008:administration & dosage / Q000378:metabolism*; D008297:Male; D010147:Pain Measurement; D051381:Rats; D017207:Rats, Sprague-Dawley; D014110:Touch
D007328:Insulin; D005620:Freund's Adjuvant