INCREASED DOPAMINE RELEASE INVIVO IN NUCLEUS-ACCUMBENS AND CAUDATE-NUCLEUS OF THE RAT DURING DRINKING - A MICRODIALYSIS STUDY

Changes in dopamine release and metabolism during drinking in thirsty rats were studied using in vivo microdialysis. Animals were maintained on controlled water (1 h per day) and trained to lick for water in a behavioural box. Microdialysis probes were then inserted into the left nucleus accumbens and right caudate nucleus through previously implanted guide cannulae, and the following day animals were connected for dialysis perfusion, during which they were allowed 1 h free access to water. Dopamine, and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, increased in both nucleus accumbens and caudate nucleus in association with drinking, but the 5-hydroxytryptamine metabolite, 5-hydroxyindoleacetic acid, only increased in the caudate nucleus. There was a direct correlation between the maximum dopamine release in nucleus accumbens and the maximum licking rate per 10-min period, but the maximum increase in dopamine did not occur until after the period of maximum licking. Increases in 3,4-dihydroxyphenylacetic acid and homovanillic acid were further delayed (by 20 and 30 min, respectively). In the caudate, changes in 5-hydroxyindoleacetic acid showed a very similar time-course to those of 3,4-dihydroxyphenylacetic acid. These data show that dopamine systems in both nucleus accumbens and and caudate nucleus are activated in relation to drinking in thirsty rats. In addition, they indicate that 5-hydroxytryptamine systems in the caudate nucleus, but not in nucleus accumbens, may also be involved. The support that the results provide for the hypothesized connection between reward and limbic dopamine is discussed.