One-way avoidance learning in female inbred Roman high- and low-avoidance rats: effects of bilateral electrolytic central amygdala lesions.

Female inbred Roman high- (RHA-I) and low- (RLA-I) avoidance rats show differences in one-way avoidance learning only when the task implies a highly aversive situation (1s in the "non-shock"-associated safe compartment, as opposed to 30s). These between-strain differences seem to depend on strain differences in emotionality, given that: (i) they are abolished by IP administration of the GABAergic anxiolytic diazepam (Torres et al. [32]) and (ii) avoidance responding appears to correlate with cellular density in the basolateral amygdala (Gómez et al. [9]). In the present study we further analyzed whether the implication of the amygdala in one-way avoidance depends on the experimental situation aversiveness (30s vs. 1s in safety). After bilateral electrolytic lesions (1mA; 20s) of the central amygdala (CeA), RHA-I and RLA-I rats were exposed to a danger compartment (where they received a warning signal - 88dB tone - followed by a 1mA electric foot-shock), and a safe compartment, where these stimuli were not presented. The number of trials needed to reach 5 consecutive avoidance responses was used as dependent variable. Sham lesioned RLA-I rats showed poorer performance than sham lesioned RHA-I rats only under the 1s condition. The CeA lesion disrupted the avoidance response only in 1s groups, abolishing the between-strain performance differences observed under this condition. These results indicate the implication of CeA in one-way avoidance performance, and suggest a reciprocal modulation of fear and reinforcement (i.e. fear relief) in this form of aversive learning.

The partial reinforcement extinction effect (PREE) in female Roman high- (RHA-I) and low-avoidance (RLA-I) rats.

The present experiment was designed with the goal of studying the partial reinforcement extinction effect (PREE) in female inbred Roman high- (RHA-I) and low-avoidance (RLA-I) rats. Two groups of RHA-I and two of RLA-I food-deprived animals were placed in a straight alley where they were partially or continuously reinforced. Once the animals reached the acquisition criterion, they were exposed to an extinction phase where the reinforcement was omitted. During the extinction phase RHA-I animals continuously reinforced during acquisition exhibited more resistance to extinction than their RLA-I counterparts, whereas only RLA-I rats partially reinforced during acquisition showed an increased resistance to extinction in comparison to continuously reinforced control RLA-I rats, this PREE being absent in RHA-I animals. These results are discussed within the framework of PREE theories that account for this effect by using emotional mechanisms, as pertains to the repeatedly observed RHA-RLA differences in emotional reactivity.