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.

Effects of age and isolation on the evolution of catalepsy during chronic haloperidol treatment.

Sixteen young (5 months) and 16 old (20-24 months) male Wistar rats, housed together or in individual cages were observed for cataleptic behavior 10, 20 and 30 days after the beginning of chronic haloperidol treatment (1.0 mg/kg, twice daily, for 30 days). Catalepsy was measured by the bar test. Age increased the duration of haloperidol-induced catalepsy of isolated and group-housed rats in the three observation sessions (old-isolated = 7.4 +/- 0.2; old-group housed = 7.5 +/- 0.1; young-isolated = 6.3 +/- 0.2; young-group housed = 6.8 +/- 0.2 In seconds in session 1, for example). Conversely, isolation did not modify the sensitivity to the cataleptic effect of haloperidol. Even more important, no differences in duration of haloperidol-induced catalepsy were observed among the three sessions for each group. The results indicate that under the experimental conditions employed the animals did not develop tolerance nor sensitization to haloperidol-induced catalepsy. In addition, neither age nor isolation modified the absence of effects of repeated haloperidol treatment on the catalepsy behavior of rats.

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-age (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(T) 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 ñ 0.3 s; T1 = 3.8 ñ 0.3s; T2 = 3.3 ñ 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

Effects of age and isolation on the evolution of catalepsy during chronic haloperidol treatment

Sixteen young (5 months) and 16 old (20-24 months) male Wistar rats, housed together or in individual cages were observed for cataleptic behavior 10, 20 and 30 days after the beginning of chronic haloperidol treatment (1.0 mg/kg, twice daily, for 30 days). Catalepsy was measured by the bar test. Age increased the duration of haloperidol-induced catalepsy of isolated and group-housed rats in the three observation sessions (old-isolated = 7.4 ñ 0.2; old-group housed = 7.5 ñ 0.1; young-isolated =6.3 ñ 0.2; young-group housed = 6.8 ñ 0.2 In seconds in session 1, for example). Conversely, isolation did not modify the sensitivity to the sensitivity to the cataleptic effect of haloperidol. Even more important, no differences in duration of haloperidol-induced catalepsy were observed among the three sessions for each group. The resultss indicate that under the experimental conditions employed the animals did not develop tolerance nor sensitization to haloperidol-induced catalepsy. In addition, neither age nor isolation modified the absence of effects of repeated haloperidol treatment on the catalepsy behavior of rats

Evaluation of memory and anxiety in rats observed in the elevated plus-maze: effects of age and isolation.

Twenty young (5 months) and 20 old (20-24 months) male Wistar rats, isolated or group housed, were tested in the elevated plus-maze to evaluate memory and anxiety. Memory was quantified by transfer latency (the time it took for the rat to move from the open arm to the enclosed arm) and anxiety by percent entries into the open arms. Isolation decreased the transfer latency of old (session 1 = 119.33 +/- 0.44 s; session 3 = 49.67 +/- 12.12 s) and young (session 1 = 111.20 +/- 8.80 s; session 3 = 55.90 +/- 13.60 s) rats, but did not modify percent entries into the open arms (old-isolated = 5.56 +/- 5.56; old-group housed = 10.18 +/- 7.05; young-isolated = 35.16 +/- 8.98; young-group housed = 33.21 +/- 8.11). Conversely, aging decreased percent entries into the open arms but did not affect the transfer latency of isolated or group-housed animals. The results indicate that the plus-maze test, unlike other methods for memory evaluation, does not discriminate between young and old rats. They also suggest that age increases anxiety and that isolation increases memory levels, but that there is no interaction between age and isolation with regard to their effect on memory and anxiety in rats.

Evaluation of memory and anxiety in rats observed in the elevated plus-maze: effects of age and isolation

Twenty young(5months)and 20 old(20-24 months) male Wistar rats, isolated or group housed, were tested in the elevated plus-maze to elevated memory and anxiety. Memory was quantified by transfer latency (the time it took for the rat move from the open arm to the enclosed arm) and anxiety by percent entries into the openarms. Isolation decreased the transfer latency of old (session 1 - 119,33 ñ 0.44s; session 3 - 49,67 ñ 12.12s) and young (session 1 -111.20 ñ 8.80s; session 3 -55.90 ñ 13.60s) rats, but did not modify percent entries into the open arms (old-isolated - 5.56 ñ 5.56; old-group housed - 10.18 ñ7.05; young isolated - 35.16 ñ 8.98; young - group housed - 33.21 ñ 8.11). Conversely, aging decreased percent entries into the open arms but did not affect the transfer latency of isolated or group-housed animals. The results indicate that the plus-maze test, unlike other methods for memory evaluation, does not discriminate between young and rats. They also suggest that age increases anxiety and that isolation increases memory levels, but that there is no interaction between age and isolation with regard to their effect on memory and anxiety in rats