Influence of environmental enrichment in alcohol oral self-administration in rats

Author(s)

Ana Martins Torres Bernardes

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Psicologia (IP/SBD)
• Defense date: 2008-04-18

Examining board members

Maria Teresa de Araujo Silva; Roberto Alves Banaco; Miriam Garcia Mijares

• Advisor: Maria Teresa de Araujo Silva

Abstract

This research investigated the influence of different types of rearing environment on ethanol (ET) self-administration in adult rats. Usually behavioral research is conducted using isolated animals (I), one widely used animal is the rat, a social animal that under normal circumstances lives at large colonies. What kind of effects could this unnatural isolation have? It has been proposed that one major factor in drug abuse and dependence is the lack for alternative reinforcers to the drug. Animals raised in limited environments with few reinforcers (I) consume more morphine, amphetamine and barbital than animals raised in enriched environments (EE), which present different opportunities of behavior. These isolated rats have also been shown to consume more ET; however, there are some contradictory results within studies: some have even shown enhanced consumption in EE rats. The present study proposed to investigate whether differential presence of reinforcers during rearing or concurrently to the presentation of ET would influence its consumption, reiforcer value and demand elasticity. Male Wistar rats were raised either in EE or I. Using a self administration paradigm, consumption and reiforcer value were estimated in a FR2 and Progressive Ratio (PR), respectively. ET was introduced by fade in as sucrose was faded out from the solution, resulting in a 10% ET solution sweetened with saccharin 0,25% as the reinforcer solution. The PR procedure was first conducted using the ET solution and then with just the saccharin solution (vehicle). Anxiety was estimated using the elevated cross maze model, and motor activity was accessed in the activity box. I rats consumed and responded more for ET than EE rats in FR2 schedule. They also presented higher reiforcer value for ET in the PR paradigm, but not for saccharin, when compared to EE rats. There was no significant difference between groups in anxiety levels, but I rats were significantly more active. Using a concurrent model, with ET solution and an isochaloric solution as reiforcers, the demand elasticity was accessed by increasingly VRs, first for the isochaloric alternative, then for the ET solution. The introduction of an isochaloric concurrent reiforcer altered ET consumption of I rats, without affecting EE rats consumption. Groups did not differ in demand elasticity for ET, but it was shown that this demand is relatively inelastic while demand for the isochaloric solution is very elastic, especially for I rats, though. I rats consumed more isochaloric solutions than EE rats. Drug abuse and dependency must be understood using the same laws that regulate so called normal behavior, these phenomena do not belong to a special category, and choice models are essential for that understanding. (AU)