Neurotensin Attenuates Nociception by Facilitating Inhibitory Synaptic Transmission in the Mouse Spinal Cord

Neurotensin (NT) is an endogenous tridecapeptide in the central nervous system. NT-containing neurons and NT receptors are widely distributed in the spinal dorsal horn (SDH), indicating their possible modulatory roles in nociception processing. However, the exact distribution and function of NT, as well as NT receptors (NTRs) expression in the SDH, have not been well documented. Among the four NTR subtypes, NTR2 is predominantly involved in central analgesia according to previous reports. However, the expression and function of NTR2 in the SDH has not yet been directly elucidated. Specifically, it remains unclear how NT-NTR2 interactions contribute to NT-mediated analgesia. In the present study, by using immunofluorescent histochemical staining and immunohistochemical staining with in situ hybridization histochemical staining, we found that dense NT- immunoreactivity (NT-ir) and moderate NTR2-ir neuronal cell bodies and fibers were localized throughout the superficial laminae (laminae I-II) of the SDH at the light microscopic level. In addition, γ-aminobutyric acid (GABA) and NTR2 mRNA were colocalized in some neuronal cell bodies, predominantly in lamina II. Using confocal and electron microscopy, we also observed that NT-ir terminals made both close contacts and asymmetrical synapses with the local GABA-ir neurons. Second, electrophysiological recordings showed that NT facilitated inhibitory synaptic transmission but not glutamatergic excitatory synaptic transmission. Inactivation of NTR2 abolished the NT actions on both GABAergic and glycinergic synaptic release. Moreover, a behavioral study revealed that intrathecal injection of NT attenuated thermal pain, mechanical pain, and formalin induced acute inflammatory pain primarily by activating NTR2. Taken together, the present results provide direct evidence that NT-containing terminals and fibers, as well as NTR2-expressing neurons are widely distributed in the spinal dorsal horn, GABA-containing neurons express NTR2 mainly in lamina II, GABA coexists with NTR2 mainly in lamina II, and NT may directly increase the activity of local inhibitory neurons through NTR2 and induce analgesic effects.

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Upregulation of Spinal ASIC1 and NKCC1 Expression Contributes to Chronic Visceral Pain in Rats

Frontiers in Molecular Neuroscience ◽

10.3389/fnmol.2020.611179 ◽

2021 ◽

Vol 13 ◽

Author(s):

Yong-Chang Li ◽

Yuan-Qing Tian ◽

Yan-Yan Wu ◽

Yu-Cheng Xu ◽

Ping-An Zhang ◽

...

Keyword(s):

Synaptic Transmission ◽

Signaling Pathway ◽

Dorsal Horn ◽

Spinal Dorsal Horn ◽

Visceral Pain ◽

Intrathecal Injection ◽

Adult Rats ◽

Sodium Potassium ◽

Spinal Dorsal ◽

Whole Cell Patch Clamp

Aims: To determine whether acid-sensing ion channel 1 (ASIC1)–sodium-potassium-chloride cotransporter 1 (NKCC1) signaling pathway participates in chronic visceral pain of adult rats with neonatal maternal deprivation (NMD).Methods: Chronic visceral pain was detected by colorectal distension (CRD). Western blotting and Immunofluorescence were performed to detect the expression and location of ASIC1 and NKCC1. Whole-cell patch-clamp recordings were performed to record spinal synaptic transmission.Results: The excitatory synaptic transmission was enhanced and the inhibitory synaptic transmission was weakened in the spinal dorsal horn of NMD rats. ASIC1 and NKCC1 protein expression in the spinal dorsal horn was significantly up-regulated in NMD rats. Incubation of Amiloride reduced the amplitude of mEPSCs. Incubation of Bumetanide (BMT) increased the amplitude of mIPSCs. Intrathecal injection of ASIC1 or NKCC1 inhibitors reversed the threshold of CRD in NMD rats. Also, Amiloride treatment significantly reversed the expression of NKCC1 in the spinal dorsal horn of NMD rats.Conclusion: Our data suggest that the ASIC1-NKCC1 signaling pathway is involved in chronic visceral pain in NMD rats.

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Systemic α2 agonist administration facilitates inhibitory synaptic transmission in the rat spinal dorsal horn mediated through α1 adorenoceptors

PAIN RESEARCH ◽

10.11154/pain.28.145 ◽

2013 ◽

Vol 28 (3) ◽

pp. 145-153

Author(s):

Yusuke Funai ◽

Kiyonobu Nishikawa ◽

Takashi Mori ◽

Akira Asada ◽

Keiji Imoto ◽

...

Keyword(s):

Synaptic Transmission ◽

Dorsal Horn ◽

Spinal Dorsal Horn ◽

Inhibitory Synaptic Transmission ◽

Spinal Dorsal

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Facilitatory Actions of Serotonin Type 3 Receptors on GABAergic Inhibitory Synaptic Transmission in the Spinal Superficial Dorsal Horn

Journal of Neurophysiology ◽

10.1152/jn.91160.2008 ◽

2009 ◽

Vol 102 (3) ◽

pp. 1459-1471 ◽

Cited By ~ 43

Author(s):

Teruyuki Fukushima ◽

Toshiki Ohtsubo ◽

Masayuki Tsuda ◽

Yuchio Yanagawa ◽

Yuuichi Hori

Keyword(s):

Synaptic Transmission ◽

Dorsal Horn ◽

Spinal Dorsal Horn ◽

Gabaergic Neurons ◽

Pcr Analysis ◽

Superficial Dorsal Horn ◽

Inhibitory Synaptic Transmission ◽

Spinal Dorsal ◽

Presynaptic Mechanisms ◽

Type 3

Analgesic effects of serotonin (5-hydroxytryptamine [5-HT]) type 3 (5-HT3) receptors may involve the release of γ-aminobutyric acid (GABA) in the spinal dorsal horn. However, the precise synaptic mechanisms for 5-HT3 receptor-mediated spinal analgesia are not clear. In this study, we investigated whether GABAergic neurons in the superficial dorsal horn (SDH) express functional 5-HT3 receptors and how these 5-HT3 receptors affect GABAergic inhibitory synaptic transmission in the SDH, by using slice preparations from adult glutamate decarboxylase 67–green fluorescent protein (GAD67-GFP) knock-in mice. Tight-seal whole cell recordings from GFP-positive and -negative neurons showed that 5-HT3 receptor-specific agonist 2-methyl-serotonin (2-Me-5-HT) induced inward currents in a substantial population of both GFP-positive and -negative neurons. Additionally, we confirmed expression of 5-HT3 receptors in both types of neurons by single-cell reverse transcription–polymerase chain reaction (RT-PCR) analysis. Further, GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs)—both those evoked by electrical stimulation and those occurring spontaneously in tetrodotoxin (i.e., miniature IPSCs [mIPSCs])—were recorded from GFP-negative neurons. 2-Me-5-HT increased the amplitude of the evoked IPSCs and the frequency of mIPSCs. The amplitude of mIPSCs was not affected by 2-Me-5-HT, suggesting that 5-HT augments GABAergic synaptic transmission via presynaptic mechanisms. The present observations indicate that 5-HT3 receptors are expressed on both somadendritic regions and presynaptic terminals of GABAergic neurons and regulate GABAA receptor-mediated inhibitory synaptic transmission in the SDH. Taken together, these results provide clues for the underlying mechanisms of the antinociceptive actions of 5-HT3 receptors in the spinal dorsal horn.

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