• The Korean Journal of Pain
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• v.33 no.4
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• pp.318-325
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• 2020

Background: Chemotherapy-induced peripheral neuropathy (CIPN) is a major side effect of anti-cancer drugs. Neurotensin receptors (NTSRs) are widely distributed within the pain circuits in the central nervous system. The purpose of this study was to determine the role of NTSR1 by examining the effects of an NTSR1 agonist in rats with CIPN and investigate the contribution of spinal serotonin receptors to the antinociceptive effect. Methods: Sprague-Dawley rats (weight 150-180 g) were used in this study. CIPN was induced by injecting cisplatin (2 mg/kg) once a day for 4 days. Intrathecal catheters were placed into the subarachnoid space of the CIPN rats. The antiallodynic effects of intrathecally or intraperitoneally administered PD 149163, an NTSR1 agonist, were evaluated. Furthermore, the levels of serotonin in the spinal cord were measured by high-performance liquid chromatography. Results: Intrathecal or intraperitoneal PD 149163 increased the paw withdrawal threshold in CIPN rats. Intrathecal administration of the NTSR1 antagonist SR 48692 suppressed the antinociceptive effect of PD 149163 given via the intrathecal route, but not the antinociceptive effect of intraperitoneally administered PD 149163. Intrathecal administration of dihydroergocristine, a serotonin receptor antagonist, suppressed the antinociceptive effect of intrathecally administered, but not intraperitoneally administered, PD 149163. Injecting cisplatin diminished the serotonin level in the spinal cord, but intrathecal or intraperitoneal administration of PD 149163 did not affect this reduction. Conclusions: NTSR1 played a critical role in modulating CIPN-related pain. Therefore, NTSR1 agonists may be useful therapeutic agents to treat CIPN. In addition, spinal serotonin receptors may be indirectly involved in the effect of NTSR1 agonist.

• The Korean Journal of Pain
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• v.34 no.1
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• pp.58-65
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• 2021

Background: Supraspinal delivery of neurotensin (NTS), which may contribute to the effect of a systemically administered agonist, has been reported to be either pronociceptive or antinociceptive. Here, we evaluated the effects of systemically administered NTSR1 agonist in a rat model of neuropathic pain and elucidated the underlying supraspinal mechanism. Methods: Neuropathic pain was induced by L5 and L6 spinal nerve ligation in male Sprague-Dawley rats. The effects of intraperitoneally administered NTSR1 agonist PD 149163 was assessed using von Frey filaments. To examine the role of 5-HT neurotransmission, a serotonin (5-HT) receptor antagonist dihydroergocristine was pretreated intrathecally, and spinal microdialysis studies were performed to measure the change in extracellular level of 5-HT in response to PD 149163 administration. To investigate the supraspinal mechanism, NTSR1 antagonist 48692 was microinjected into the rostral ventromedial medulla (RVM) prior to systemic PD 149163. Additionally, the effect of intrathecal DHE on intra-RVM PD 149163 was assessed. Results: Intraperitoneally administered PD 149163 exhibited a dose-dependent attenuation of mechanical allodynia. This effect was partially reversed by intrathecal pretreatment with dihydroergocristine and was accompanied by an increased extracellular level of 5-HT in the spinal cord. The PD 149163-produced antinociception was also blocked by intra-RVM SB 48692. Direct injection of PD 149163 into the RVM mimicked the maximum effect of the same drug delivered intraperitoneally, which was reversed by intrathecal dihydroergocristine. Conclusions: These observations indicate that systemically administered NTSR1 agonist produces antinociception through the NTSR1 in the RVM, activating descending serotonergic projection to release 5-HT into the spinal dorsal horn.