LACK OF RELATIONSHIP BETWEEN THALAMIC OSCILLATIONS AND ATTENTION IN RATS - DIFFERENTIAL MODULATION BY AN ALPHA-2 ANTAGONIST

A five-choice serial reaction time (5-CSRT) task was used to assess at tention in rats. In this behavioral paradigm, the rats are required to spatially discriminate a short visual stimulus that will occur random ly in one of five locations while maintaining a sufficient activity le vel. The ability of a rat to maintain attention on the task can be mea sured by counting the choice accuracy (percent correct responses), whe reas the probability of premature responses indicates the level of imp ulsivity. According to previous results [24], rats performing poorly i n the task have a lower choice accuracy and make more premature respon ses than normally behaving individuals, i.e., a clear, inverse correla tion was observed between choice accuracy and impulsiveness of rats. M ethylphenidate, a psychostimulant that has been shown to alleviate the symptoms in attention deficit-hyperactivity disorder (ADHD), improved the choice accuracy of poor performing rats in this task [24]. The pr esent results show that the correlation between choice accuracy and im pulsivity exists also when the rats are tested using a reduced stimulu s intensity or curtailed stimulus duration. The results of a pharmacol ogical experiment suggested that atipamezole (30, 300, or 1000 mu g/kg ), a potent and specific alpha-2 antagonist that is known to increase the activity of monoaminergic systems in the brain, did not affect the percent correct responses in poor performers or in controls tested ei ther at the baseline conditions or at a curtailed stimulus duration (w hich impaired their choice accuracy). At the doses of 300 and 1000 mu g/kg, however, atipamezole slightly increased the probability of prema ture responses in all group of rats. The results of an electrophysiolo gical study indicated that the poor choice accuracy or impulsiveness o f rats is not related to the amount of cortically recorded spike-wave discharges/high voltage spindle (HVS) activity, which reflect thalamo- cortical oscillation. Atipamezole dose-dependently reduced the inciden ce and duration of HVSs. The present data, therefore, indicate that (a ) alpha-a antagonist treatment is not superior to methylphenidate trea tment when investigated using acute administrations of the agents in p oor performers of the 5-CSRT task, and (b) thalamic oscillations are n ot the reason for the attention deficit of rats in this model of ADHD. The relationship between choice accuracy and impulsivity is discussed . (C) 1997 Elsevier Science Inc.