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Gi- and Gq-coupled ADP (P2Y) receptors act in opposition to modulate nociceptive signaling and inflammatory pain behavior.

Malin SA, Molliver DC - Mol Pain (2010)

Bottom Line: Agonists for these receptors inhibit nociceptive signaling in isolated neurons and reduce behavioral hyperalgesia in vivo.Anti-nociceptive actions of these receptors appear to be antagonized by the Gq-coupled ADP receptor, P2Y1, which is required for the full expression of inflammatory hyperalgesia.Taken together, our data suggest that Gi-coupled P2Y receptors are broadly expressed in nociceptors, inhibit nociceptive signaling in vivo, and represent potential targets for the development of novel analgesic drugs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dept Medicine; Dept Neurobiology, University of Pittsburgh, Pittsburgh, PA, USA. sachamalin@gmail.com

ABSTRACT

Background: Investigations of nucleotide signaling in nociception to date have focused on actions of adenosine triphosphate (ATP). Both ATP-gated ion channels (P2X receptors) and G protein-coupled (P2Y) receptors contribute to nociceptive signaling in peripheral sensory neurons. In addition, several studies have implicated the Gq-coupled adenosine diphosphate (ADP) receptor P2Y1 in sensory transduction. In this study, we examined the expression and function of P2Y1 and the Gi-coupled receptors P2Y12, P2Y13 and P2Y14 in sensory neurons to determine their contribution to nociception.

Results: We detected mRNA and protein for ADP receptors P2Y12 and P2Y13 in mouse dorsal root ganglia (DRG). P2Y14, a homologous Gi-coupled nucleotide receptor, is also expressed in DRG. Immunohistochemical analysis of receptor distribution indicated that these receptors are widely expressed in nociceptive neurons. Using ratiometric calcium imaging, we found that ADP evokes increases in intracellular calcium in isolated DRG neurons and also produces a pertussis toxin-sensitive inhibition of depolarization-evoked calcium transients. The inhibitory effect of ADP was unaltered in the presence of the selective P2Y1 antagonist MRS2179 and in neurons isolated from P2Y1 knockout mice, whereas ADP-evoked calcium transients were greatly reduced. Analysis of behavioral responses to noxious heat before and after inflammatory injury (injection of complete Freund's adjuvant into the hindpaw) revealed that P2Y1 is required for the full expression of inflammatory hyperalgesia, whereas local injection of agonists for Gi-coupled P2Y receptors reduced hyperalgesia.

Conclusions: We report that Gi-coupled P2Y receptors are widely expressed in peripheral sensory neurons. Agonists for these receptors inhibit nociceptive signaling in isolated neurons and reduce behavioral hyperalgesia in vivo. Anti-nociceptive actions of these receptors appear to be antagonized by the Gq-coupled ADP receptor, P2Y1, which is required for the full expression of inflammatory hyperalgesia. We propose that nociceptor sensitivity is modulated by the integration of nucleotide signaling through Gq- and Gi-coupled P2Y receptors, and this balance is altered in response to inflammatory injury. Taken together, our data suggest that Gi-coupled P2Y receptors are broadly expressed in nociceptors, inhibit nociceptive signaling in vivo, and represent potential targets for the development of novel analgesic drugs.

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ADP has opposing effects on behavioral nociceptive thresholds in the presence and absence of P2Y1. ADP has opposite effects on withdrawal latencies to noxious heat stimuli (Hargreaves test) in the presence and absence of P2Y1. A) P2Y1-/- mice show a deficit in thermal hyperalgesia at day 3 following CFA injection, compared to wildtype mice. B) Injection of ADP into the hindpaw of naïve mice caused thermal hyperalgesia in wildtype mice, but hypoalgesia in P2Y1-/- mice. C) Mice were injected with ADP in the hindpaw three days after CFA injection and thermal response thresholds were measured. ADP injection had no effect on thermal thresholds in inflamed wildtype mice, but reversed thermal hyperalgesia in P2Y1-/- mice. D) Hindpaw injection of MRS2500, a P2Y1 antagonist, in inflamed wildtype mice acutely reversed thermal hyperalgesia compared to saline injection. Injection of either IDP (E) or UDPG (F) into the inflamed hindpaw reversed inflammation-evoked thermal hyperalgesia. n = 10 mice/cohort.
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Figure 5: ADP has opposing effects on behavioral nociceptive thresholds in the presence and absence of P2Y1. ADP has opposite effects on withdrawal latencies to noxious heat stimuli (Hargreaves test) in the presence and absence of P2Y1. A) P2Y1-/- mice show a deficit in thermal hyperalgesia at day 3 following CFA injection, compared to wildtype mice. B) Injection of ADP into the hindpaw of naïve mice caused thermal hyperalgesia in wildtype mice, but hypoalgesia in P2Y1-/- mice. C) Mice were injected with ADP in the hindpaw three days after CFA injection and thermal response thresholds were measured. ADP injection had no effect on thermal thresholds in inflamed wildtype mice, but reversed thermal hyperalgesia in P2Y1-/- mice. D) Hindpaw injection of MRS2500, a P2Y1 antagonist, in inflamed wildtype mice acutely reversed thermal hyperalgesia compared to saline injection. Injection of either IDP (E) or UDPG (F) into the inflamed hindpaw reversed inflammation-evoked thermal hyperalgesia. n = 10 mice/cohort.

Mentions: Our analysis of nucleotide signaling in isolated neurons suggests that P2YGi receptors have inhibitory actions in sensory neurons, whereas P2Y1 is excitatory. To determine the impact of these receptors on nociceptive signaling in vivo, we examined the effects of P2Y agonists on behavioral responses to noxious heat using the Hargreaves test in naïve mice and after inducing inflammation by injecting complete Freund's adjuvant (CFA) into the plantar surface of the hindpaw. Baseline paw withdrawal latencies were not different between wildtype and P2Y1-/- mice (Figure 5A), and both wildtype and mutant mice developed persistent thermal hyperalgesia after CFA injection. However, mutant mice were significantly less sensitized than wildtype at the peak of hyperalgesia on day 3, suggesting that the sensitization of nociceptors by inflammatory injury is modestly impaired in the absence of P2Y1 signaling.


Gi- and Gq-coupled ADP (P2Y) receptors act in opposition to modulate nociceptive signaling and inflammatory pain behavior.

Malin SA, Molliver DC - Mol Pain (2010)

ADP has opposing effects on behavioral nociceptive thresholds in the presence and absence of P2Y1. ADP has opposite effects on withdrawal latencies to noxious heat stimuli (Hargreaves test) in the presence and absence of P2Y1. A) P2Y1-/- mice show a deficit in thermal hyperalgesia at day 3 following CFA injection, compared to wildtype mice. B) Injection of ADP into the hindpaw of naïve mice caused thermal hyperalgesia in wildtype mice, but hypoalgesia in P2Y1-/- mice. C) Mice were injected with ADP in the hindpaw three days after CFA injection and thermal response thresholds were measured. ADP injection had no effect on thermal thresholds in inflamed wildtype mice, but reversed thermal hyperalgesia in P2Y1-/- mice. D) Hindpaw injection of MRS2500, a P2Y1 antagonist, in inflamed wildtype mice acutely reversed thermal hyperalgesia compared to saline injection. Injection of either IDP (E) or UDPG (F) into the inflamed hindpaw reversed inflammation-evoked thermal hyperalgesia. n = 10 mice/cohort.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2865444&req=5

Figure 5: ADP has opposing effects on behavioral nociceptive thresholds in the presence and absence of P2Y1. ADP has opposite effects on withdrawal latencies to noxious heat stimuli (Hargreaves test) in the presence and absence of P2Y1. A) P2Y1-/- mice show a deficit in thermal hyperalgesia at day 3 following CFA injection, compared to wildtype mice. B) Injection of ADP into the hindpaw of naïve mice caused thermal hyperalgesia in wildtype mice, but hypoalgesia in P2Y1-/- mice. C) Mice were injected with ADP in the hindpaw three days after CFA injection and thermal response thresholds were measured. ADP injection had no effect on thermal thresholds in inflamed wildtype mice, but reversed thermal hyperalgesia in P2Y1-/- mice. D) Hindpaw injection of MRS2500, a P2Y1 antagonist, in inflamed wildtype mice acutely reversed thermal hyperalgesia compared to saline injection. Injection of either IDP (E) or UDPG (F) into the inflamed hindpaw reversed inflammation-evoked thermal hyperalgesia. n = 10 mice/cohort.
Mentions: Our analysis of nucleotide signaling in isolated neurons suggests that P2YGi receptors have inhibitory actions in sensory neurons, whereas P2Y1 is excitatory. To determine the impact of these receptors on nociceptive signaling in vivo, we examined the effects of P2Y agonists on behavioral responses to noxious heat using the Hargreaves test in naïve mice and after inducing inflammation by injecting complete Freund's adjuvant (CFA) into the plantar surface of the hindpaw. Baseline paw withdrawal latencies were not different between wildtype and P2Y1-/- mice (Figure 5A), and both wildtype and mutant mice developed persistent thermal hyperalgesia after CFA injection. However, mutant mice were significantly less sensitized than wildtype at the peak of hyperalgesia on day 3, suggesting that the sensitization of nociceptors by inflammatory injury is modestly impaired in the absence of P2Y1 signaling.

Bottom Line: Agonists for these receptors inhibit nociceptive signaling in isolated neurons and reduce behavioral hyperalgesia in vivo.Anti-nociceptive actions of these receptors appear to be antagonized by the Gq-coupled ADP receptor, P2Y1, which is required for the full expression of inflammatory hyperalgesia.Taken together, our data suggest that Gi-coupled P2Y receptors are broadly expressed in nociceptors, inhibit nociceptive signaling in vivo, and represent potential targets for the development of novel analgesic drugs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dept Medicine; Dept Neurobiology, University of Pittsburgh, Pittsburgh, PA, USA. sachamalin@gmail.com

ABSTRACT

Background: Investigations of nucleotide signaling in nociception to date have focused on actions of adenosine triphosphate (ATP). Both ATP-gated ion channels (P2X receptors) and G protein-coupled (P2Y) receptors contribute to nociceptive signaling in peripheral sensory neurons. In addition, several studies have implicated the Gq-coupled adenosine diphosphate (ADP) receptor P2Y1 in sensory transduction. In this study, we examined the expression and function of P2Y1 and the Gi-coupled receptors P2Y12, P2Y13 and P2Y14 in sensory neurons to determine their contribution to nociception.

Results: We detected mRNA and protein for ADP receptors P2Y12 and P2Y13 in mouse dorsal root ganglia (DRG). P2Y14, a homologous Gi-coupled nucleotide receptor, is also expressed in DRG. Immunohistochemical analysis of receptor distribution indicated that these receptors are widely expressed in nociceptive neurons. Using ratiometric calcium imaging, we found that ADP evokes increases in intracellular calcium in isolated DRG neurons and also produces a pertussis toxin-sensitive inhibition of depolarization-evoked calcium transients. The inhibitory effect of ADP was unaltered in the presence of the selective P2Y1 antagonist MRS2179 and in neurons isolated from P2Y1 knockout mice, whereas ADP-evoked calcium transients were greatly reduced. Analysis of behavioral responses to noxious heat before and after inflammatory injury (injection of complete Freund's adjuvant into the hindpaw) revealed that P2Y1 is required for the full expression of inflammatory hyperalgesia, whereas local injection of agonists for Gi-coupled P2Y receptors reduced hyperalgesia.

Conclusions: We report that Gi-coupled P2Y receptors are widely expressed in peripheral sensory neurons. Agonists for these receptors inhibit nociceptive signaling in isolated neurons and reduce behavioral hyperalgesia in vivo. Anti-nociceptive actions of these receptors appear to be antagonized by the Gq-coupled ADP receptor, P2Y1, which is required for the full expression of inflammatory hyperalgesia. We propose that nociceptor sensitivity is modulated by the integration of nucleotide signaling through Gq- and Gi-coupled P2Y receptors, and this balance is altered in response to inflammatory injury. Taken together, our data suggest that Gi-coupled P2Y receptors are broadly expressed in nociceptors, inhibit nociceptive signaling in vivo, and represent potential targets for the development of novel analgesic drugs.

Show MeSH
Related in: MedlinePlus