Behavioural and electrophyasiological responses in neuropathic pain model of spared nerve injury in the male adult rats

Damage to neural pathways is one of the most significant factors of neuropathic pains, which is characterized by spontaneous burning pain accompanied by allodynia and hyperalgesia. The present study was carried out to explore behavioral and electrophysiological characteristics of neuropathic pain model of Spared Nerve Injury (SNI). In this experimental study, male Sprague-Dawley rats (wt: 230-280 Gms.) were used. Anesthesia was initially induced with sodium pentobarbital (ip) at a dose of 50 mg/kg. Then, SNI surgery operation was performed on them. The animals were tested for their behavioral responses shown as heat and mechano-allodynia and heat and mechano-hyperalgesia prior to the surgery ("0" day), and on the 3rd, 7th, 14th, 21st and 28th day post- operation. Electrophysiological responses by the sciatic nerve were recorded two weeks after the operation. Stimulation of the sural nerve branch and proximal area of auxotomized nerve were recorded proximally. Repeated ANOVA and one-way ANOVA statistical softwares were applied to the results of behavioural testing and electrophysiological responses, respectively. P≤0.05 was considered as the significant level. Compared to the control group, the rats in the SNI group revealed an obvious difference in their behavioral responses towards heat and mechano-stimulation manifested by allodynia and hyperalgesia, respectively (P<0.05, P<0.01). Conduction velocity (CV) significantly reduced in SNI rats compared to the control group (P<0.05). Amplitude also slightly decreased in the SNI group. Compound action potential (CAP) rising time was similar in both SNI and the control animals. SNI models showed acute behavioural responses to both thermal and mechanical allodynia and hyperalgesia stimuli. Besides, electrophysiological recordings of the nerve confirmed nerve damage and injury due to this model, which caused a decrease in nerve conduction.