Insulin Within the Arcuate Nucleus Has Paradoxical Effects on Nociception in Healthy and Diabetic Rats

Broad nervous circuits originate from the hypothalamic arcuate nucleus project to many parts of the brain which are related to pain perception. Insulin receptors have been found in the arcuate nucleus. Since nociception may be affected in type 1 diabetes, the present study aimed to investigate the intra-arcuate nucleus insulin role in pain perception in STZ-induced diabetic and healthy rats. For this purpose, regular insulin was microinjected within the arcuate nucleus and the pain tolerance was measured using the hot plate and the tail-flick apparatus in the rats. The results showed that the arcuate nucleus suppression with lidocaine could increase thermal nociception in non-diabetic animals. Also, insulin within the arcuate nucleus decreased the acute thermal pain perception in these animals. STZ-induced diabetes produced hypoalgesia which latency of these tests, progressively increased over time after induction of diabetes; also, in the same animal group, intra-arcuate injection of insulin reduced the latency of nociception. Therefore, intra-arcuate insulin has paradoxical and controversial effects in healthy and diabetic rats’ nociception. These effects seem to be due to insulin effect on releasing of pro-opio-melano-cortin and its derivatives.