Effect of age on antinociceptive effects of elevated plus-maze exposure

It has been suggested that anxiety may be a critical factor in certain forms of non-opioid environmental analgesia. Furthermore, age has been reported to increase the anxiety levels in rats as measured in the elevated plus-maze. In the present investigation 10 young (3 months), 10 middle-aged (14-16 months) and 10 old (28-30 months) male Wistar rats were tested by the tail withdrawal assay of nociception before (baseline), and at 0 (T1) and 10 (T2) min after a 5-min exposure to the elevated plus-maze apparatus. Only old rats presented an increase in tail withdrawal latencies after elevated plus-maze exposure, even though this effect was statistically significant only immediately after exposure to the apparatus (baseline = 2.5 +/- 0.3 s; T1 = 3.8 +/- 0.3 s; T2 = 3.3 +/- 0.4 s). The results indicate that exposure to the elevated plus-maze induces a rapidly reversed and age-dependent antinociception in rats. They are also consistent with the proposed greater sensitivity of old rats to anxiogenic effects of the plus-maze.