Réactivité au ‘stress’ et capacité d’adaptation à une situation inhabituelle chez le rat jeune, adulte et âgé

Abstract

Fifty male rats of the Wistar G strain of different age classes (15 young animals aged from 10 to 12 weeks, 20 adults from 13 to 14 months, and 15 old rats aged from 23 to 24 months) were investigated. The free-corticosteroid content of the plasma at rest and after stress induced by Nembutal and ether, and the ability of rats to adapt their behavior to an uncustomary situation of the test were studied. The results obtained give the following conclusions: that age in itself does not greatly alter the basic level of free corticosteroids in the plasma; that the increase of this level following stress varies with stress intensity and with the age of the animal. It appears that the discharge is more important with greater stress intensity. The young rat always reacts to a comparable stress by a higher increase of the free-corticosteroid level than an animal 2-years old; that age does not appreciably alter the percentage of animals which had passed the proposed test; that the younger animals are most often "inhibited", prior to and during learning by experience, by an uncustomary situation; it is among them that the signs of "emotivity" are most frequent; that the adaptation to an uncustomary situation appears, in general, to be associated with a low basic level and with a slight increase, following stress, of the level of free corticosteroids in the plasma.