USE OF HIGH AND LOW RESPONDERS TO NOVELTY IN RAT STUDIES ON THE ROLE OF THE VENTRAL STRIATUM IN RADIAL MAZE PERFORMANCE - EFFECTS OF INTRAACCUMBENS INJECTIONS OF SULPIRIDE

High and low responders to novelty (Wistar rats) were selected with th e help of an open-field test and then equipped with intra-accumbens ca nnulae. They were then tested in a simple four-arm radial maze during 5 successive days, three trials per day, following intra-accumbens inj ections of distilled water or the dopaminergic D2 antagonist (+/-)-sul piride. The injections were given 15 min before the first trial on eac h day. Both types of drug-naive rats reached the same level of perform ance on day 5. However, high responders made more visits, more revisit s, and needed less time to make the first visit than low responders. M oreover, high responders showed their greatest increase in learning 2 days earlier than low responders. It is discussed that these differenc es between high and low responders are not due simply to differences i n locomotor activity, but are due to a subtle, but important, differen ce in the mode of learning between both types. Sulpiride significantly attenuated the learning in both rat types; however, its effect in hig h responders was much less than that in low responders. It is suggeste d that the effects of sulpiride are not due to changes in locomotor ac tivity, motivation, or perception, but are due to a learning deficit. The data are discussed in view of the genetic variation in the neuroch emical and neurobiological makeup of the nucleus accumbens in both typ es.