Effect of prestimulation on avoidance responding in rats, and hormonal dependence of the effect

Rats were tested daily in a free-operant avoidance task and were found to make more avoidance responses in sessions preceded by a brief period of prestimulation than in control sessions. Footshock, air blast, and handling were effective sources of prestimulation for this effect. Further experiments showed that the effect of prestimulation depended on the presence of circulating mineralocorticoid and not on any other adrenal or pituitary hormone. Adrenalectomy, but not hypophysectomy, abolished the effect. The effect was also abolished in intact rats by maintaining them on saline drinking fluid, a procedure that inhibits mineralocorticoid production. In either adrenalectomized rats or intact, saline-maintained rats, injection of mineralocorticoid permitted the effect of prestimulation to reappear while leaving the nonprestimulated response rate unaffected.