Selective effects of partial striatal 6-OHDA lesions on information processing in the rat

The present study was aimed at characterizing the cognitive deficits caused by the degeneration of nigrostriatal dopamine (DA) pathways by using the additive factor logic [Sternberg, S. (1969) Acta Psychol., 30, 276-315], a powerful reaction time (RT) method developed in humans and recently introduced in the rat [Courtiere, A., Hardouin, J., Hasbroucq, T., Possamai, C.-A. & Vidal, F. (2000) Behav. Process., 50, 113-121]. Long-Evans rats were trained to respond to left or right (lateral) visual cues in a choice RT task. Two task factors, signal intensity and force requirement, were manipulated. Partial bilateral 6-OHDA lesions of DA nerve terminals in the striatum were then performed and their effects tested for up to 7 weeks following surgery. Reaction time was lengthened from the 2nd to the 4th week postlesion. This alteration was independent of force requirement, thereby suggesting that the related motor processes were not influenced by the DA depletion. During the 2nd week postlesion, the RT increase was accompanied by a disappearance of the effect of signal intensity, showing that the lesion altered stimulus-related processes. From the 3rd week the signal intensity effect was re-established although RT was still increased, indicating that the stimulus-related processes had recovered while other central processes were still impaired. From the 5th week after surgery, the lesioned animals had completely recovered from the RT deficits induced by the lesion. These results point at the involvement of striatal DA in sensory and central information processes.