The effects of variable interval schedule on preference and liquid consumption by rats subjected to chronic mild stress / Efeitos do esquema de intervalo variável na preferência e no consumo de líquidos apresentados por ratos submetidos ao chronic mild stress

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The Chronic Mild Stress (CMS) is an experimental animal model of depression induced by the exposure of rats to a set of moderate and uncontrollable aversive stimuli in a long and uninterrupted period of time. The purpose of this study was to investigate the relationship between performance in variable interval schedule of behavior and exposure to the protocol of stress (daily consumption of food and water, changes in body weight, frequency of answers issued in each bar and the frequency of reinforcements obtained when submitted to the same scheme competitor). The study design was composed of three experimental conditions: test consumption and preferably liquid; sessions operating on schedule competitor VI 10 (water) VI 10 (sucrose) and protocol of stress (CMS). Six male rats were used. One subject was used to control weight, not involved in any of the three experimental conditions. Five subjects were submitted to the protocol of stress and tests of consumption and preference of liquids throughout the experiment. Two subjects were submitted to the working sessions (VI competitor VI) before and after CMS and two subjects were submitted to the working sessions before, during and after the CMS. The results were: 1) all subjects showed loss of body weight during the exposure to stressors. 2) The four subjects submitted to the working sessions showed recovery of body weight after the suspension of the protocol. 3) All subjects showed an increase in daily consumption of water and feed during the CMS, despite the loss of weight in this period. 4) Liquid consumption and the percentage of sucrose intake was higher during the CMS for the four subjects submitted to the working sessions, featuring a reduction in the last week of exposure to the protocol of stress. 5) All subjects expressed a greater number of responses in the bar corresponding to sucrose before exposure to CMS. Meanwhile, during and after CMS, a preference for water became outstanding. 6) The subjects received almost all of the planned reinforcements of both magnitudes (sucrose solution or pure water) in the three periods of assessment. We conclude that: 1) the loss of weight during the CMS seems to be related to the combination of aversive stimuli compound by the Protocol of stress and deprivation of water and food intermittent making up this protocol 2) the increase in the total consumption of liquids during the CMS appear to be related to the submission to the working sessions in variable interval before submission to the Protocol 3) the exposure of the subject to a scheme of variable interval, before CMS, slows the decline in the consumption of liquid and increases consumption of fluids during the CMS

ASSUNTO(S)

depression psicologia experimental chronic mild stress chronic mild stress depressao avaliacao do comportamento modelo experimental experimental model

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