Fig. 1.

Male Sprague Dawley rats received a bilateral microinjection of saporin, dermorphin, or dermorphin–saporin into the RVM. A, B, The animals were tested for responses to non-noxious mechanical stimuli (von Frey filaments) (A) and to noxious radiant heat (B) on days 0 (baseline), 2, 7, 14, and 28 after the microinjection. No significant changes (p > 0.05) were observed in any of the groups of rats over this observation period (ANOVA). C, The response latency to noxious heat applied to the tail (tail-flick reflex using a 52°C water bath) was also determined before dermorphin–saporin and again at day 28 after the microinjection; no change in response latencies was observed. n = 6 rats per group.