Evaluation of memory in an elevated T maze: a comparison between spontaneously hypertensive, Wistar-Kyoto and Wistar EPM-1 rats

Four-month old male spontaneously hypertensive (SHR), Wistar-Kyoto (WKY) and Wistar EPM-1 (EPM-1) rats (14-15 animals per group) were tested in an elevated T maze to evaluate memory. Blood pressures of SHR were hyper at the time of experiment (200-235 mmHg). The elevated T maze used consisted of an open arm at right angles with two enclosed arms elevated 50 cm above the ground. Memory was quantified by the escape latency ratio (the ratio of the time it took for the rat to move from the open arm to one of the enclosed arms in the second session to that in the first session) and by the inhibitory avoidance latency (time from being placed at the end of an enclosed arm to move to the open arm, in a 3rd session). No significant differences in escape latency ratios were observed among SHR, WKY and EPM-1 rats. Conversely, SHR presented a significant reduction in inhibitory avoidance latency as compared to those of WKY and EPM-1 rats (mean +/- SEM latency: 65.9 +/- 18.4 s for SHR, 129.9 +/- 21.8 s for WKY animals and 181.2 +/- 11.2 s for EPM-1 rats). These data were discussed in light of the known lowered reaction to aversive environments exhibited by SHR, as compared to WKY and EPM-1 rats

Comparison of anxiety measured in the elevated plus-maze, open-field and social interaction tests between spontaneously hypertensive rats and Wistar EPM-1 rats

On the basis of open-field and plus-maze results it has been proposed that spontaneously hypertensive (SHR) rats are less emotionally reactive than their normotensive controls, Wistar-Kyoto (WKY). However, the proposed anxiolytic characteristics of SHR rats may be questioned in view of the significant hypoactivity presented by WKY rats. In the present study, the behavioral response of spontaneously hypertensive (SHR) and equally active normotensive Wistar EPM-1 (EPM-1) rats (4-month old males, 10-13 animals per group) were evaluated in the open-field, social interaction and elevated plus-maze tests. In the open-field study, no differences were observed for total locomotion frequency and immobility duration, but SHR rats presented a higher central square locomotion frequency (23.8 +/- 2.1 vs 10.3 +/- 1.6) as compared to EPM-1. SHR rats also exhibited a greater duration of social interaction when compared to EPM-1 rats (mean +/- SEM values were 113.9 +/- 8.7 s for SHR vs 72.7 +/- 8.6 s for EPM-1 rats after 8-min observation). In the elevated plus-maze test, SHR rats presented an increased percent of entries (52.8 +/- 3.3 vs 28.3 +/- 4.5) and time in the open arms (65.6 +/- 6.0 vs 11.1 +/- 1.9) as compared to EPM-1 rats, although the total number of arm entries (9.2 +/- 0.9 vs 9.7 +/- 1.0) was unchanged. These results suggest that the anxiolytic behavior of SHR rats in relation to normotensive controls is not related to differences in motility levels