Non-handled Rats Research Articles

Adrenocortical function in pregnant rats: Handling and the 24-hour rhythm

The temporal course of the adrenocortical response to handling was determined on Day 16 of pregnancy in previously handled and non-handled rats. Fifteen days of prior handling did not influence the plasma corticosterone response to handling stimulation measured at either the peak or the trough in the 24-hr adrenocortical rhythm. Corticosterone levels in animals sampled at the peak of the 24-hr adrenocortical rhythm were elevated 60 min after handling stimulation which was found to be a function of elevated resting corticosterone levels. In a second experiment the 24-hr adrenocortical rhythm in pregnant animals was characterized by peak values which occurred approximately two hr before darkness but, unlike nonpregnant animals, these peak values were sustained throughout most of the dark period.

Dominance-subordination polarity in early-handled and nonhandled rats

Early-handled and nonhandled rats were paired with members of their own group in adulthood and permitted to compete for food under deprivation conditions. Polarity scores, defined as the winners’ proportion-of-time-at-the-food-container scores minus 50, were higher in the handled group. These results were interpreted in terms of interactions between early-stimulation effects and reinforcement-contingency effects.

Defecation and ambulation in a novel environment as determinants of dominance-subordination polarity in the rat

High and low emotional defecators in cross-classification with high and low emotional ambulators were paired with members of their own group and permitted to compete for food. Polarity scores, defined as the winner’s proportion-of-time-at-the-food-container scores minus 50, followed a pattern similar to that reported in early-handled and nonhandled rats, but only where defecation was the basis for statistical manipulation.

Infantile stimulation and adult exploratory behaviour in the rat: Effects of handling upon visual variation-seeking

Experimental rats were handled daily between birth and weaning; controls were not disturbed during this interval. In adulthood two experiments were run to test for visual exploratory behaviour. Experiment 1 : three degrees of visual stimulus variation were created in a Greek-cross apparatus by having walls painted flat black; flat white; or black, white, and gray. Thirty handled and thirty non-handled subjects were tested. As the degree of stimulus variation increased, the exploratory behaviour of handled rats increased while the exploratory behaviour of the controls was depressed. In addition, handled animals spent significantly more time in the gray and white compartments than did controls. Experiment 2: The Greek cross was painted flat white and two degrees of visual stimulus variation was prepared by varying the illumination in each compartment. Twenty handled and twenty non-handled rats were tested. As the degree of stimulus variation increased, the exploratory behaviour of handled subjects increased while the exploratory behaviour of controls was depressed. In addition, handled rats spent significantly more time in the brightly illuminated compartment than did non-handled controls.