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. Author manuscript; available in PMC: 2014 Mar 14.
Published in final edited form as: Prog Pain Res Manag. 1994 Jan 1;2(5):359–371.

Fig. 2.

Fig. 2

This graph shows paw withdrawal latency (PWL) to radiant heat for animals that were untreated (triangles), CNQX-treated (circles), AP7-treated (squares), bicuculline-treated (inverse triangles), and sympathectomized (diamonds) arthritic animals. The response latency of the hindpaw ipsilateral to the inflamed knee joint is represented by filled symbols whereas the contralateral side is represented by unfilled symbols. Before the induction of arthritis or infusion of the antagonists, the withdrawal latencies averaged between 8 and 10 seconds. The receptor antagonists were infused for the duration of the experiment to account for differences in length of effectiveness of the drugs. After one hour infusion of either CNQX (non-NMDA) or AP7 (NMDA) through the dialysis fiber, the PWL increased significantly for both the ipsilateral and the contralateral sides when compared to baseline (paired t test; P ≤ 0.05), suggesting the animals were hypoalgesic. Following the induction of arthritis, untreated and sympathectomized arthritic animals showed a 1–2 second decrease in PWL to radiant heat when compared to baseline at four and eight hours after injection of kaolin and carrageenan. In the animals treated with either CNQX or AP7, there was no further decrease in withdrawal times of either the ipsilateral or contralateral paws after induction of arthritis when compared to the withdrawal times induced by the application of the antagonists. Therefore, the heat hyperalgesia seen in untreated arthritic animals is blocked by the treatment of the spinal cord with either a non-NMDA (CNQX), an NMDA (AP7), or a GABAA (bicuculline) receptor antagonist.