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NAAG peptidase inhibition in the periaqueductal gray and rostral ventromedial medulla reduces flinching in the formalin model of inflammation.

Yamada T, Zuo D, Yamamoto T, Olszewski RT, Bzdega T, Moffett JR, Neale JH - Mol Pain (2012)

Bottom Line: The group II mGluR antagonist LY341495 blocked these effects of ZJ43 on the PAG and RVM.NAAG peptidase inhibition in the PAG and RVM did not affect the thermal withdrawal response in the hot plate test.Footpad inflammation also induced a significant increase in glutamate release in the PAG.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, Georgetown University, Washington, DC, USA.

ABSTRACT

Background: Metabotropic glutamate receptors (mGluRs) have been identified as significant analgesic targets. Systemic treatments with inhibitors of the enzymes that inactivate the peptide transmitter N-acetylaspartylglutamate (NAAG), an mGluR3 agonist, have an analgesia-like effect in rat models of inflammatory and neuropathic pain. The goal of this study was to begin defining locations within the central pain pathway at which NAAG activation of its receptor mediates this effect.

Results: NAAG immunoreactivity was found in neurons in two brain regions that mediate nociceptive processing, the periaqueductal gray (PAG) and the rostral ventromedial medulla (RVM). Microinjection of the NAAG peptidase inhibitor ZJ43 into the PAG contralateral, but not ipsilateral, to the formalin injected footpad reduced the rapid and slow phases of the nociceptive response in a dose-dependent manner. ZJ43 injected into the RVM also reduced the rapid and slow phase of the response. The group II mGluR antagonist LY341495 blocked these effects of ZJ43 on the PAG and RVM. NAAG peptidase inhibition in the PAG and RVM did not affect the thermal withdrawal response in the hot plate test. Footpad inflammation also induced a significant increase in glutamate release in the PAG. Systemic injection of ZJ43 increased NAAG levels in the PAG and RVM and blocked the inflammation-induced increase in glutamate release in the PAG.

Conclusion: These data demonstrate a behavioral and neurochemical role for NAAG in the PAG and RVM in regulating the spinal motor response to inflammation and that NAAG peptidase inhibition has potential as an approach to treating inflammatory pain via either the ascending (PAG) and/or the descending pain pathways (PAG and RVM) that warrants further study.

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ZJ43 microinjection into the RVM. Formalin injection into the dorsal surface of the left rat hind-paw induced two phases of hindpaw flinching in the saline injected control rats (n = 7). a. Microinjection of 150 μg of ZJ43 (n = 7) into the contralateral RVM reduced both of phases of the pain response observed after the formalin injection. Pre-treatment with 1 mg/kg (i.p.) of the group II mGluR antagonist LY341495 (n = 10) blocked the effect of ZJ43 in the RVM. b. Sum of flinches following microinjection of saline, ZJ43 or ZJ43 with LY341495 into the RVM. Phase one data are the sum of flinches for the first 10 min. Phase two data are the sums of flinches from 10–60 min. Data are calculated from Figure 6a.
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Figure 6: ZJ43 microinjection into the RVM. Formalin injection into the dorsal surface of the left rat hind-paw induced two phases of hindpaw flinching in the saline injected control rats (n = 7). a. Microinjection of 150 μg of ZJ43 (n = 7) into the contralateral RVM reduced both of phases of the pain response observed after the formalin injection. Pre-treatment with 1 mg/kg (i.p.) of the group II mGluR antagonist LY341495 (n = 10) blocked the effect of ZJ43 in the RVM. b. Sum of flinches following microinjection of saline, ZJ43 or ZJ43 with LY341495 into the RVM. Phase one data are the sum of flinches for the first 10 min. Phase two data are the sums of flinches from 10–60 min. Data are calculated from Figure 6a.

Mentions: NAAG-like immunoreactivity was found in the RVM, including the nucleus raphe magnus (Figure 1b). Microinjection of ZJ43 (150 μg) into the RVM also significantly reduced flinching in the rapid (p < 0.001) and slow (p < 0.01) phases of the inflammatory pain response (Figure 6a, b). The mGluR 2/3 antagonist LY341495 (i.p.) again reduced the effect of the peptidase inhibitor on the first phase of the flinching response (p < 0.05) and blocked the effect in the slow phase (p < 0.01) (Figures 6a, b). ZJ43 was effective in a dose-dependent manner (p <0.05) in both phases of the flinching response (Figure 7).


NAAG peptidase inhibition in the periaqueductal gray and rostral ventromedial medulla reduces flinching in the formalin model of inflammation.

Yamada T, Zuo D, Yamamoto T, Olszewski RT, Bzdega T, Moffett JR, Neale JH - Mol Pain (2012)

ZJ43 microinjection into the RVM. Formalin injection into the dorsal surface of the left rat hind-paw induced two phases of hindpaw flinching in the saline injected control rats (n = 7). a. Microinjection of 150 μg of ZJ43 (n = 7) into the contralateral RVM reduced both of phases of the pain response observed after the formalin injection. Pre-treatment with 1 mg/kg (i.p.) of the group II mGluR antagonist LY341495 (n = 10) blocked the effect of ZJ43 in the RVM. b. Sum of flinches following microinjection of saline, ZJ43 or ZJ43 with LY341495 into the RVM. Phase one data are the sum of flinches for the first 10 min. Phase two data are the sums of flinches from 10–60 min. Data are calculated from Figure 6a.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 6: ZJ43 microinjection into the RVM. Formalin injection into the dorsal surface of the left rat hind-paw induced two phases of hindpaw flinching in the saline injected control rats (n = 7). a. Microinjection of 150 μg of ZJ43 (n = 7) into the contralateral RVM reduced both of phases of the pain response observed after the formalin injection. Pre-treatment with 1 mg/kg (i.p.) of the group II mGluR antagonist LY341495 (n = 10) blocked the effect of ZJ43 in the RVM. b. Sum of flinches following microinjection of saline, ZJ43 or ZJ43 with LY341495 into the RVM. Phase one data are the sum of flinches for the first 10 min. Phase two data are the sums of flinches from 10–60 min. Data are calculated from Figure 6a.
Mentions: NAAG-like immunoreactivity was found in the RVM, including the nucleus raphe magnus (Figure 1b). Microinjection of ZJ43 (150 μg) into the RVM also significantly reduced flinching in the rapid (p < 0.001) and slow (p < 0.01) phases of the inflammatory pain response (Figure 6a, b). The mGluR 2/3 antagonist LY341495 (i.p.) again reduced the effect of the peptidase inhibitor on the first phase of the flinching response (p < 0.05) and blocked the effect in the slow phase (p < 0.01) (Figures 6a, b). ZJ43 was effective in a dose-dependent manner (p <0.05) in both phases of the flinching response (Figure 7).

Bottom Line: The group II mGluR antagonist LY341495 blocked these effects of ZJ43 on the PAG and RVM.NAAG peptidase inhibition in the PAG and RVM did not affect the thermal withdrawal response in the hot plate test.Footpad inflammation also induced a significant increase in glutamate release in the PAG.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, Georgetown University, Washington, DC, USA.

ABSTRACT

Background: Metabotropic glutamate receptors (mGluRs) have been identified as significant analgesic targets. Systemic treatments with inhibitors of the enzymes that inactivate the peptide transmitter N-acetylaspartylglutamate (NAAG), an mGluR3 agonist, have an analgesia-like effect in rat models of inflammatory and neuropathic pain. The goal of this study was to begin defining locations within the central pain pathway at which NAAG activation of its receptor mediates this effect.

Results: NAAG immunoreactivity was found in neurons in two brain regions that mediate nociceptive processing, the periaqueductal gray (PAG) and the rostral ventromedial medulla (RVM). Microinjection of the NAAG peptidase inhibitor ZJ43 into the PAG contralateral, but not ipsilateral, to the formalin injected footpad reduced the rapid and slow phases of the nociceptive response in a dose-dependent manner. ZJ43 injected into the RVM also reduced the rapid and slow phase of the response. The group II mGluR antagonist LY341495 blocked these effects of ZJ43 on the PAG and RVM. NAAG peptidase inhibition in the PAG and RVM did not affect the thermal withdrawal response in the hot plate test. Footpad inflammation also induced a significant increase in glutamate release in the PAG. Systemic injection of ZJ43 increased NAAG levels in the PAG and RVM and blocked the inflammation-induced increase in glutamate release in the PAG.

Conclusion: These data demonstrate a behavioral and neurochemical role for NAAG in the PAG and RVM in regulating the spinal motor response to inflammation and that NAAG peptidase inhibition has potential as an approach to treating inflammatory pain via either the ascending (PAG) and/or the descending pain pathways (PAG and RVM) that warrants further study.

Show MeSH
Related in: MedlinePlus