Nociceptive and histomorphometric characteristics of median nerves of rats with obesity induced by monosodium glutamate

AIMS: To compare nociception and, histomorphometrically, the transverse section of peripheral nerves (median) of Wistar rats submitted to obesity model induced by monosodium glutamate with control animals. METHODS: Fourteen Wistar rats divided into control and obese groups were used. During the five first days since birth the rats from obese group received a daily subcutaneous injection of monosodium glutamate (4 g/kg body weight/day), while the control group received hypertonic saline (1.25 g/kg body weight/day). Nociception was evaluated by the withdrawal threshold of the limb, using digital analgesymeter type Von Frey, with the stimulus given in the palmar region of the right hind paw. The first assessment was carried out about 20 days before euthanasia, and the second assessment was performed on the day before euthanasia. Subsequently the median nerve was dissected in the elbow region and processed with cross sections for histological analysis. The analyzed variables were: number of axons per field; axons, fibers and myelin sheath diameters, and G coefficient. The results were analyzed using the t test for independent samples and paired t test, with a significance level of 5%. RESULTS: Fourteen rats were assessed, being seven of the obese group and seven of control group. The evaluation of nociception showed that the animals of the obese group had lower withdrawal threshold. For histomorphometric data, the results showed no significant differences between the two groups. CONCLUSIONS: The obese animals showed lower nociceptive threshold, however, there were no morphometric differences of the median nerves between animals subjected to the model of obesity induced by monosodium glutamate and the control group