Active control and its stress effects

The effects of 5-fold injections of normal saline were studied in Wistar rats in two conditioned reflex situations: defense and alimentary. Intact animals developed conditioned pain avoidance reflex in repeated tail-flick test after 60 presentations over 3 days. Two injections of normal saline were sufficient for the formation of a stable negative stress status in experimental rats, which manifested by a drastic increase in tactile sensitivity persisting for 5 days after discontinuation of injections. Only 15% experimental rats vs. 40% intact animals developed the food-procuring response in a multialternative maze. Presumably, repeated injections of normal saline should be regarded as a potent negative stress factor modulating animals behavior, and these signs should be taken into consideration, when interpreting the effects observed in pharmacological investigations.