| Evidence Sentence: |
Acupuncture also has brief (1-2 h) antinociceptive effects in mice and these effects are dependent on localized adenosine A1 receptor (A1R) activation. |
| Evidence Sentence: |
Since A1R activation in peripheral tissues, including at the Zusanli acupuncture point (which is anatomically close to Weizhong; Figure 1A'), had brief antinociceptive effects in rodents, we first sought to determine if A1R activation at Weizhong also had antinociceptive effects. |
| Evidence Sentence: |
In contrast, CPA had no effect in either hindpaw of A1R-/- mice (Figure 1B). |
| Evidence Sentence: |
Additionally, CPA did not affect mechanical sensitivity in naive (non-sensitized) wild-type or A1R-/- mice (Figure 1C). |
| Evidence Sentence: |
Taken together, these data reveal that activation of A1R at the Weizhong acupuncture point can locally inhibit nociception. |
| Evidence Sentence: |
Given our previous work with PAP:an ectonucleotidase that hydrolyzes AMP to adenosine and activates A1R for days following a single spinal injection :we hypothesized it might be possible to enzymatically hydrolyze the pool of AMP to adenosine and inhibit nociception without performing acupuncture. |
| Evidence Sentence: |
Importantly, hPAP did not affect thermal sensitivity in A1R-/- mice, demonstrating a critical requirement for A1R activation (Figure 2A). |
| Evidence Sentence: |
These results are the first to reveal that a single, peripheral injection of hPAP locally inhibits nociception for an extended period of time by engaging an A1R-dependent mechanism that is common to acupuncture. |
| Evidence Sentence: |
To determine if the long-lasting antinociceptive effects of hPAP were due to sustained A1R activation, we next injected hPAP (250 mU) into the popliteal fossa of wild-type mice, then 48 h later injected (i.p.) |
| Evidence Sentence: |
These data indicate the local antinociceptive effects of hPAP are due to sustained A1R activation. |
| Evidence Sentence: |
We previously found that the antinociceptive effects of hPAP, when injected intrathecally, were due to A1R activation and phospholipase C (PLC)-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate. |
| Evidence Sentence: |
Strikingly, thermal sensitivity returned to baseline levels and mechanical sensitivity returned almost to baseline for three days in wild-type mice but not A1R-/- mice (Figure 4A,B). |
| Evidence Sentence: |
Likewise, in the spared nerve injury (SNI) model of neuropathic pain, hPAP (250 mU) inhibited thermal and mechanical hypersensitivity for three days in the ipsilateral (injured) hindpaw of wild-type mice but not A1R-/- mice (Figure 4C,D). |
| Evidence Sentence: |
Collectively, these data indicate that hPAP has localized, long-lasting, A1R-dependent antinociceptive effects in two models of chronic pain when injected peripherally. |
| Evidence Sentence: |
To determine if peripheral injection of hPAP could preemptively inhibit pain hypersensitivity, as occurs when hPAP is injected intrathecally, we injected hPAP (250 mU) into the popliteal fossa of wild-type and A1R-/- mice and performed the SNI surgery the following day. |
| Evidence Sentence: |
hPAP reduced nerve-injury induced thermal hyperalgesia for two days in wild-type but not A1R-/- mice (Figure 4E). |
| Evidence Sentence: |
There are several possible reasons why hPAP (250 mU) consistently had antinociceptive effects that lasted three days but not longer: 1) hPAP depleted the local AMP pool, 2) A1R desensitized or 3) hPAP protein lost catalytic activity or washed out. |
| Evidence Sentence: |
To distinguish between these possibilities, we injected wild-type mice and A1R-/- mice with hPAP (250 mU) then injected these same mice with a second dose (250 mU) three days later. |
| Evidence Sentence: |
We reasoned that the second hPAP injection should have no antinociceptive effects if the first hPAP injection depleted AMP or desensitized A1R. |
| Evidence Sentence: |
On the contrary, thermal withdrawal latency increased in the ipsilateral hindpaw after the second hPAP injection and remained significantly elevated for four more days in wild-type mice but not A1R-/- mice (Figure 5A). |
| Evidence Sentence: |
These data reveal that PAPupuncture duration can be extended in naive and sensitized animals by injecting additional enzyme and that duration is not limited by substrate availability or A1R desensitization. |
| Evidence Sentence: |
To test this, we injected a selective A1R agonist, N6-cyclopentyladenosine (CPA), into the popliteal fossa of wild-type mice and A1R-/- mice while monitoring noxious thermal and mechanical sensitivity. |
| Evidence Sentence: |
Antinociception could be transiently boosted with additional substrate (AMP) or transiently blocked with an A1R antagonist or an inhibitor of phospholipase C. This novel therapeutic approach:which we term PAPupuncture:locally inhibits pain for an extended period of time (100x acupuncture), exploits a molecular mechanism that is common to acupuncture, yet does not require acupuncture needle stimulation. |
| Evidence Sentence: |
vehicle or a selective A1R antagonist, 8-cyclopentyl-1,3-dipropylxanthine (CPX). |
| Evidence Sentence: |
Here, we found that injection of PAP into the popliteal fossa:a space behind the knee that encompasses the Weizhong acupuncture point:had dose- and A1R-dependent antinociceptive effects in mouse models of acute and chronic pain. |
