Pinealectomy attenuates the effect of restraint on plus maze exploration in rats

To investigate a possible stress modulation role of the pineal gland, male Wistar albino rats (200-250 g) were submitted to pinealectomy and divided into four groups one week after surgery: i) sham-operated unrestrained animals (N = 14); ii) pinealectomized unrestrained animals (N = 22); iii) sham-operated animals submitted to 2 h of restraint (N = 52); iv) pinealectomized animals submitted to 2 h of restraint (N = 56). Twenty-four hours later the animals were tested in the elevated plus maze for 5 min. Pinealectomized rats submitted to restraint explored the open arms of the maze to a greater extent than sham-operated restrained rats (mean percent of open arm entries = 26.4 +/- 2.3 vs 18.0 +/- 2.1, mean percent of time spent in the open arms = 11.8 +/- 2.1 vs 6.8 +/- 1.2). Pinealectomized animals not submitted to restraint showed no difference in maze exploration when compared to sham-operated rats (mean percent of open arm entries = 29.3 +/- 3.8 vs 31.1 +/- 5.8, mean percent of time spent in the open arms = 8.8 +/- 1.8 vs 12.5 +/- 2.2). The results, therefore, suggest that the pineal gland may play a modulatory role in the behavioral consequences of stress.