Limits...
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.

Show MeSH

Related in: MedlinePlus

a: NAAG immunoreactivity in neurons and processes of the lateral periaqueductal gray (PAG). Regions denoted with letters in panel A show the areas of enlargement found in panels B – D. NAAG staining was relatively light in the region immediately surrounding the cerebral aqueduct (AQ), which contained small NAAG stained neurons and fine immunoreactive fibers (arrows in B). More neurons and processes were strongly immunoreactive for NAAG at the periphery of the PAG (C and D). The finely punctate staining represents high concentrations of NAAG as would be found in synaptic endings. Bar = 15 μm B – D. b: NAAG immunoreactivity in the raphe magnus (RM) of the brainstem (A). NAAG staining in the RM was similar to adjacent reticular areas with numerous moderately to strongly immunoreactive neurons. Many neuronal processes were immunoreactive for NAAG in the RM (B). Bar = 30 μm in B. c: NAAG-immunoreactivity in apparent synaptic contacts on neurons in the lateral PAG. Areas within boxes in A and C are enlarged in B and D. Panel A is from a region immediately adjacent to the cerebral aqueduct and Panel C is slightly further from the aqueduct. Apparent NAAG-containing synaptic contacts were observed on the surface of perikarya, major dendrites, and in the neuropil. Images acquired with extended depth of field. Bar = 5 μm B and D.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3539905&req=5

Figure 1: a: NAAG immunoreactivity in neurons and processes of the lateral periaqueductal gray (PAG). Regions denoted with letters in panel A show the areas of enlargement found in panels B – D. NAAG staining was relatively light in the region immediately surrounding the cerebral aqueduct (AQ), which contained small NAAG stained neurons and fine immunoreactive fibers (arrows in B). More neurons and processes were strongly immunoreactive for NAAG at the periphery of the PAG (C and D). The finely punctate staining represents high concentrations of NAAG as would be found in synaptic endings. Bar = 15 μm B – D. b: NAAG immunoreactivity in the raphe magnus (RM) of the brainstem (A). NAAG staining in the RM was similar to adjacent reticular areas with numerous moderately to strongly immunoreactive neurons. Many neuronal processes were immunoreactive for NAAG in the RM (B). Bar = 30 μm in B. c: NAAG-immunoreactivity in apparent synaptic contacts on neurons in the lateral PAG. Areas within boxes in A and C are enlarged in B and D. Panel A is from a region immediately adjacent to the cerebral aqueduct and Panel C is slightly further from the aqueduct. Apparent NAAG-containing synaptic contacts were observed on the surface of perikarya, major dendrites, and in the neuropil. Images acquired with extended depth of field. Bar = 5 μm B and D.

Mentions: Using highly specific, multi-stage affinity purified antibodies (see Methods), NAAG immunoreactivity was observed in neurons and axons in the rat PAG and RVM (Figure 1a,b). Consistent with the potential of this transmitter to regulate neurotransmission via activation of presynaptic receptors in these brain regions, putative NAAGergic synapses were observed on the cell bodies and dendrites of PAG neurons, as well as in the neuropil (Figure 1c). While these data alone are insufficient to confirm the synaptic localization of this immunoreactivity, studies with this antibody at the ultrastructural level previously localized NAAG immunoreactivity to synaptic vesicles [30] and optic nerve transection studies demonstrated that NAAG immunoreactivity is associated with NAAG-containing synaptic terminals in various regions of the CNS [31,32]. Additionally, depolarization-induced calcium-dependent NAAG release has been demonstrated repeatedly [10,33]. These data on the presence of NAAG in the PAG and RVM provided a rationale for microinjection of the NAAG peptidase inhibitor ZJ43 into these regions of the pain transmission pathway.


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)

a: NAAG immunoreactivity in neurons and processes of the lateral periaqueductal gray (PAG). Regions denoted with letters in panel A show the areas of enlargement found in panels B – D. NAAG staining was relatively light in the region immediately surrounding the cerebral aqueduct (AQ), which contained small NAAG stained neurons and fine immunoreactive fibers (arrows in B). More neurons and processes were strongly immunoreactive for NAAG at the periphery of the PAG (C and D). The finely punctate staining represents high concentrations of NAAG as would be found in synaptic endings. Bar = 15 μm B – D. b: NAAG immunoreactivity in the raphe magnus (RM) of the brainstem (A). NAAG staining in the RM was similar to adjacent reticular areas with numerous moderately to strongly immunoreactive neurons. Many neuronal processes were immunoreactive for NAAG in the RM (B). Bar = 30 μm in B. c: NAAG-immunoreactivity in apparent synaptic contacts on neurons in the lateral PAG. Areas within boxes in A and C are enlarged in B and D. Panel A is from a region immediately adjacent to the cerebral aqueduct and Panel C is slightly further from the aqueduct. Apparent NAAG-containing synaptic contacts were observed on the surface of perikarya, major dendrites, and in the neuropil. Images acquired with extended depth of field. Bar = 5 μm B and D.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3539905&req=5

Figure 1: a: NAAG immunoreactivity in neurons and processes of the lateral periaqueductal gray (PAG). Regions denoted with letters in panel A show the areas of enlargement found in panels B – D. NAAG staining was relatively light in the region immediately surrounding the cerebral aqueduct (AQ), which contained small NAAG stained neurons and fine immunoreactive fibers (arrows in B). More neurons and processes were strongly immunoreactive for NAAG at the periphery of the PAG (C and D). The finely punctate staining represents high concentrations of NAAG as would be found in synaptic endings. Bar = 15 μm B – D. b: NAAG immunoreactivity in the raphe magnus (RM) of the brainstem (A). NAAG staining in the RM was similar to adjacent reticular areas with numerous moderately to strongly immunoreactive neurons. Many neuronal processes were immunoreactive for NAAG in the RM (B). Bar = 30 μm in B. c: NAAG-immunoreactivity in apparent synaptic contacts on neurons in the lateral PAG. Areas within boxes in A and C are enlarged in B and D. Panel A is from a region immediately adjacent to the cerebral aqueduct and Panel C is slightly further from the aqueduct. Apparent NAAG-containing synaptic contacts were observed on the surface of perikarya, major dendrites, and in the neuropil. Images acquired with extended depth of field. Bar = 5 μm B and D.
Mentions: Using highly specific, multi-stage affinity purified antibodies (see Methods), NAAG immunoreactivity was observed in neurons and axons in the rat PAG and RVM (Figure 1a,b). Consistent with the potential of this transmitter to regulate neurotransmission via activation of presynaptic receptors in these brain regions, putative NAAGergic synapses were observed on the cell bodies and dendrites of PAG neurons, as well as in the neuropil (Figure 1c). While these data alone are insufficient to confirm the synaptic localization of this immunoreactivity, studies with this antibody at the ultrastructural level previously localized NAAG immunoreactivity to synaptic vesicles [30] and optic nerve transection studies demonstrated that NAAG immunoreactivity is associated with NAAG-containing synaptic terminals in various regions of the CNS [31,32]. Additionally, depolarization-induced calcium-dependent NAAG release has been demonstrated repeatedly [10,33]. These data on the presence of NAAG in the PAG and RVM provided a rationale for microinjection of the NAAG peptidase inhibitor ZJ43 into these regions of the pain transmission pathway.

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