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 attention in rats. In this behavioral paradigm, the rats are required to spatially discriminate a short visual stimulus that will occur randomly in one of five locations while maintaining a sufficient activity level. The ability of a rat to maintain attention on the task can be measured by counting the choice accuracy (percent correct responses), whereas the probability of premature responses indicates the level of impulsivity. According to previous results [24], rats performing poorly in the task have a lower choice accuracy and make more premature responses than normally behaving individuals, i.e., a clear, inverse correlation was observed between choice accuracy and impulsiveness of rats. Methylphenidate, 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 present results show that the correlation between choice accuracy and impulsivity exists also when the rats are tested using a reduced stimulus intensity or curtailed stimulus duration. The results of a pharmacological experiment suggested that atipamezole (30, 300, or 1000 micrograms/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 either at the baseline conditions or at a curtailed stimulus duration (which impaired their choice accuracy). At the doses of 300 and 1000 micrograms/kg, however, atipamezole slightly increased the probability of premature responses in all group of rats. The results of an electrophysiological study indicated that the poor choice accuracy or impulsiveness of 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 incidence and duration of HVSs. The present data, therefore, indicate that (a) alpha-2 antagonist treatment is not superior to methylphenidate treatment when investigated using acute administrations of the agents in poor performers of the 5-CSRT task, and (b) thalamic oscillations are not the reason for the attention deficit of rats in this model of ADHD. The relationship between choice accuracy and impulsivity is discussed.