Parkinson's disease (PD) patients often suffer from visuospatial deficits, which may results from a disruption of the representation of external space. The lateralised choice reaction time (CRT) task is an operant task for rodents in which similar visuospatial deficits can be assessed. Specific parameters in this task are disrupted after unilateral nigrostriatal injections of 6-hydroxydopamine (6-OHDA), directly linked to the severe striatal dopamine (DA) depletion that inevitably follows this type of lesion. However, studies have demonstrated that this type of lesion also affects the serotonergic (5HT) and noradrenergic (NA) midbrain pathways. The influence of these systems on visuospatial parameters in the CRT task had not yet been investigated.To this end, rats were pretrained on the CRT task before receiving selective lesions of the DAergic system, either alone or in combination with bilateral depletion of the NA-or 5HT system. All rats with a 6-OHDA lesion displayed a gradual decline in the selection, initiation and execution of lateralised movements on the side contralateral to the lesion compared to sham-lesion controls. They also displayed a reduced number of useable trials as well as an increased number of procedural errors. Interestingly, the group with an additional noradrenergic lesion was significantly slower in reacting to lateralised stimuli throughout the testing period, as compared to the other two groups with a 6-OHDA lesion. There was however, no pronounced difference between the three different lesion groups in any other parameters assessed in the task.These data confirm previous findings demonstrating that that majority of the parameters assessed in the lateralised CRT task are strongly dependent on DA. However, an important new finding in this study is the illustration of a putative role for the NAergic system in contributing to the attentive performance influencing the animals' capacity to react to the presented lateralised stimuli.

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