Abstract
The present study was performed to explore the role of galanin and galanin receptor 1 (GalR 1) in nociceptive modulation in the central nucleus of amygdala (CeA) in normal rats and rats with neuropathy, and the involvement of GalR 1 and PKC was also investigated. The hindpaw withdrawal latencies (HWLs) to thermal and mechanical stimulations were increased in a dose-dependent manner after intra-CeA injection of galanin in both normal rats and rats with neuropathy. The increased HWLs were significantly attenuated by intra-CeA injection of galanin receptor antagonist M40, indicating an involvement of galanin receptor in nociceptive modulation in CeA. Furthermore, intra-CeA administration of the GalR 1 agonist M 617 induced increases in HWLs in normal rats, suggesting that GalR 1 may be involved in galanin-induce antinociception in CeA. Additionally, intra-CeA injection of the PKC inhibitor inhibited galanin-induced antinociception, showing an involvement of PKC in galanin-induced antinociception in CeA of normal rats. Moreover, there was a significant increase in GalR1 content in CeA in rats with neuropathy than that in normal rats. These results illustrated that galanin induced antinociception in CeA in normal rats and rats with neuropathy, and there is an up-regulation of GalR1 expression in rats with neuropathy.
Highlights
Galanin, consists of 29 or 30 amino acid in human, is a neuropeptide[1]
Previous studies have demonstrated that galanin and galanin receptors play important roles in the transmission and/or modulation of nociception at spinal levels[6,12], as well as in the brain, such as hypothalamic arcuate nucleus, nucleus accumbens, periaqueductal grey, anterior cingulate cortex and the central nucleus of amygdale[11,13,14,15,16,17,18,19,20,21,22,23,24]
The results demonstrated that intra-central nucleus of amygdala (CeA) injection of galanin induced significant antinociceptive effects in normal rats
Summary
Consists of 29 or 30 amino acid in human, is a neuropeptide[1]. It is known that there are three kinds of galanin receptor subtypes, including galanin receptor 1 (GalR 1), galanin receptor 2 (GalR 2) and galanin receptor 3 (GalR 3), and all of these belong to G protein coupled receptors[2,3,4,5]. Previous studies have demonstrated that galanin and galanin receptors play important roles in the transmission and/or modulation of nociception at spinal levels[6,12], as well as in the brain, such as hypothalamic arcuate nucleus, nucleus accumbens, periaqueductal grey, anterior cingulate cortex and the central nucleus of amygdale[11,13,14,15,16,17,18,19,20,21,22,23,24]. Recent research work demonstrated that CeA represents a convergence of pathway for pain, stress and emotion[30]. These studies are full proved that the CeA plays an important role in nociceptive modulation. The present study was performed to determine whether GalR1 is involved in galanin-induced antinociception in CeA in normal rats, and further to demonstrate the antinociceptive effects induced by intra-CeA injection of galanin in rats with neuropathy, as well as the galanin and GalR1 expression in CeA in normal rats and rats with neuropathy
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