Relationship between neuropeptide S in amygdala and 5-hydroxytryptamine and GABA in spinal dorsal horns of rats with neuropathic pain

Abstract

Objective To evaluate the relationship between neuropeptide S (NPS) in the amygdala and 5-hydroxytryptamine (5-HT) and GABA in spinal dorsal horns of rats with neuropathic pain. Methods Eighty pathogen-free healthy male Sprague-Dawley rats, weighing 200-260 g, aged 2 months, were divided into 4 groups (n=20 each) using a random number table: sham operation group (group Sham), neuropathic pain group (group NP), low dose NPS group (group L-NPS) and high dose NPS group (group H-NPS). The neuropathic pain model was established by left L5, 6 spinal nerve ligation (SNL) in anesthetized rats.NPS was injected into the bilateral amygdala at 3, 6, 9, 12, 15 and 18 days after SNL in L-NPS group (10 pmol per side) and H-NPS group (100 pmol per side). The mechanical paw withdrawal threshold (MWT) and thermal paw withdrawal latency (TWL) were measured at 2 days before SNL and 1, 4, 7, 11, 14, 17 and 21 days after SNL.Five rats were selected at 7, 14 and 21 days after SNL and sacrificed, and the lumbar segment (L5) of the spinal cord was removed for detection of the expression of 5-HT and GABA in spinal dorsal horns by immunofluorescence histochemistry. Results Compared with group Sham, the MWT was significantly decreased, the TWL was shortened, and the expression of 5-HT and GABA in spinal dorsal horns was down-regulated in NP, L-NPS and H-NPS groups (P<0.05). Compared with group NP, the MWT was significantly increased, the TWL was prolonged, and the expression of 5-HT and GABA in spinal dorsal horns was up-regulated in L-NPS and H-NPS groups (P<0.05). Compared with group L-NPS, the MWT was significantly increased, the TWL was prolonged, and the expression of 5-HT and GABA in spinal dorsal horns was up-regulated in group H-NPS (P<0.05). Conclusion The spinal mechanism of endogenous analgesia induced by NPS in the amygdala may be related to up-regulation of the expression of 5-HT and GABA in spinal dorsal horns of rats with neuropathic pain. Key words: Amygdala; Neuralgia; Spinal cord; Serotonin; Gamma-aminobutyric acid; Neuropeptides