Brain dopamine and noradrenaline levels in rats submitted to four different aversive behavioral tests

Rats were trained to perform shuttle responses to a buzzer in four different situations: Pseudoconditioning (buzzers and footshocks presented at random), classical conditioning (buzzers and footshocks paired on every trial), avoidance without stimulus pairing (buzzer--shock intervals varied at random, shocks contingent upon the nonemission of a shuttle response to the preceding buzzer), and standard two-way avoidance (buzzers paired to shocks, but the latter omitted every time there was a shuttle to the buzzer). Animals were killed immediately after the last trials and the noradrenaline and dopamine content of their hypothalamus, amygdala, caudate nucleus, and nucleus accumbens was determined. There were falls of dopamine content in the caudate and accumbens and falls of noradrenaline levels in all structures except the caudate after the pseudoconditioning test. Noradrenaline levels were normal, and dopamine levels were partially recovered, in the animals submitted to the other training situations. Thus learning factors (stimulus pairing and/or the avoidance contingency) offset the depleting influence of footshocks per se on both catecholamines in at least the structures studied.