O objetivo desse trabalho foi (1) comparar a variação comportamental controlada por duas diferentes contingências de reforçamento positivo (LAG e RDF), (2) observar se a ordem de exposição a essas contingências interfere na instalação e na manutenção da variabilidade, e (3) verificar como a extinção interfere no padrão de variabilidade e sua reinstalação Treze ratos foram divididos em dois grupos, que diferiam entre si devido à ordem de exposição a duas contingências (LAG 5 e RDF), em um procedimento ABACA, onde A foi a primeira contingência de reforçamento em vigor, B a segunda e C extinção. A variabilidade foi analisada sobre seqüências de quatro respostas de pressão a duas barras. Os resultados mostraram que ambas as contingências produziram variabilidade comportamental, sendo os maiores níveis de variação obtidos em RDF, independente da ordem de exposição. A extinção produziu níveis de variabilidade diferentes de acordo com a história de reforçamento dos sujeitos, com um pequeno aumento da variabilidade nos sujeitos expostos a LAG 5. O padrão na fase final não foi afetado pela extinção, sendo típico da contingência em vigor. Esses resultados indicam uma fina sensibilidade aos graus de exigência de variação das contingências, sem interferência da ordem de exposição ou da extinção, quando há uma contingência estabelecida, porém na ausência de contingência (extinção) há um maior controle da história previa de reforçamento nos sujeitos. / The purpose of the present work was to (1) compare the behavioral variability controlled by two different contingencies of positive reinforcement (LAG and RDF), (2) examine whether the order of these contingencies interferes on variability acquisition and maintenance, and (3) establish how extinction intervenes in the pattern of variability and its reacquisition. Thirteen rats were divided into two groups that differed from each other in relation to the order of exposure to two contingencies (LAG 5 and RDF) in an ABACA procedure, where A stood for the first contingency of reinforcement in effect, B for the second and C for the extinction. The variability was evaluated over sequences of four press responses on two levers. The results reveal that both contingencies produced behavioral variability, with the highest levels of variation detected in RDF, whichever the order of exposure. The extinction generated different levels of variability according to the subjects\' reinforcement history, with a small increase in variability in subjects exposed to LAG 5. The pattern in the latest phase was not affected by extinction, being typical of the contingency in effect. These results suggest an acute sensitivity to the variability requirement levels of contingencies, without interference of exposure order or extinction when there is a contingency established. However, in the absence of contingency (extinction) there is a highest control by its previous reinforcement history.

O objetivo desse trabalho foi (1) comparar a variação comportamental controlada por duas diferentes contingências de reforçamento positivo (LAG e RDF), (2) observar se a ordem de exposição a essas contingências interfere na instalação e na manutenção da variabilidade, e (3) verificar como a extinção interfere no padrão de variabilidade e sua reinstalação Treze ratos foram divididos em dois grupos, que diferiam entre si devido à ordem de exposição a duas contingências (LAG 5 e RDF), em um procedimento ABACA, onde A foi a primeira contingência de reforçamento em vigor, B a segunda e C extinção. A variabilidade foi analisada sobre seqüências de quatro respostas de pressão a duas barras. Os resultados mostraram que ambas as contingências produziram variabilidade comportamental, sendo os maiores níveis de variação obtidos em RDF, independente da ordem de exposição. A extinção produziu níveis de variabilidade diferentes de acordo com a história de reforçamento dos sujeitos, com um pequeno aumento da variabilidade nos sujeitos expostos a LAG 5. O padrão na fase final não foi afetado pela extinção, sendo típico da contingência em vigor. Esses resultados indicam uma fina sensibilidade aos graus de exigência de variação das contingências, sem interferência da ordem de exposição ou da extinção, quando há uma contingência estabelecida, porém na ausência de contingência (extinção) há um maior controle da história previa de reforçamento nos sujeitos. / The purpose of the present work was to (1) compare the behavioral variability controlled by two different contingencies of positive reinforcement (LAG and RDF), (2) examine whether the order of these contingencies interferes on variability acquisition and maintenance, and (3) establish how extinction intervenes in the pattern of variability and its reacquisition. Thirteen rats were divided into two groups that differed from each other in relation to the order of exposure to two contingencies (LAG 5 and RDF) in an ABACA procedure, where A stood for the first contingency of reinforcement in effect, B for the second and C for the extinction. The variability was evaluated over sequences of four press responses on two levers. The results reveal that both contingencies produced behavioral variability, with the highest levels of variation detected in RDF, whichever the order of exposure. The extinction generated different levels of variability according to the subjects\' reinforcement history, with a small increase in variability in subjects exposed to LAG 5. The pattern in the latest phase was not affected by extinction, being typical of the contingency in effect. These results suggest an acute sensitivity to the variability requirement levels of contingencies, without interference of exposure order or extinction when there is a contingency established. However, in the absence of contingency (extinction) there is a highest control by its previous reinforcement history.

Recent evidence suggesting that the endogenous cannabinoid (ECB) system can be selectively manipulated to facilitate or impair the extinction of learned behaviours — specifically regarding drug-induced aversive memories — has important consequences for research on opiate withdrawal and abstinence. Data presented here support and expand previous findings that the ECB system has an important function in the extinction of aversively motivated behaviors and is mediated by i) an increase in available endogenous CB1 receptor agonists, primarily anandamide, and ii) the exogenous CB1 receptor agonist Δ9-THC, in a manner that is dependent upon both the dose and route of administration. Experiments demonstrated that the fatty acid amide hydrolase (FAAH) inhibitor, URB597, which blocks deactivation of endogenous CB1 ligands, such as anandamide, significantly facilitated extinction of naloxone-precipitated morphine withdrawal-induced conditioned cue aversion, whereas the CB1 receptor antagonist/inverse agonist SR141716 significantly impaired extinction. Several experiments demonstrated that neither the CB1 antagonist AM251 nor the FAAH inhibitor URB597 had any effect on extinction learning for morphine-induced conditioned cue preference. A method was developed for analysing cannabinoid levels in blood by liquid chromatography/mass spectrometry (LC/MS) to compare bioavailable levels of Δ9-THC and its primary psychoactive metabolite. Experiments were designed to meet three primary objectives: 1) to provide further support for the role of the ECB system in the extinction of aversively-motivated behaviours, 2) to compare bioavailable levels of Δ9-THC and its primary psychoactive metabolite, 11-OH-Δ9-THC, after pulmonary and parenteral administration, and 3) to demonstrate that the route of administration of Δ9-THC can have a significant impact on whether or not it facilitates or impairs extinction learning. Results showed that inhaled Δ9-THC dose- and time-dependently facilitated rates of extinction learning of the conditioned aversion whereas injected Δ9-THC significantly impaired extinction. These data suggest that the route of administration of Δ9-THC has important consequences for its resulting pharmacokinetic and behavioural effects, specifically, that pulmonary exposure facilitates, whereas parenteral exposure impairs, rates of extinction learning for conditioned cue aversion. Thus, pulmonary administration of Δ9-THC may prove more beneficial for pharmacological potentiation of extinction learning for aversive memories, such as those supporting drug-craving/seeking in opiate withdrawal-syndrome. / NSERC and OGS