Suppression of exploratory locomotor activity by the local application of dopamine or l-noradrenaline to the nucleus accumbens of the rat

Abstract

Adult male Sprague-Dawley rats were administered dopamine (DA) or l-noradrenaline ( l-NA) locally into the nucleus accumbens or in the neostriatum. Six minutes following the injections the animals were placed in an open field arena (700×700 mm) and their locomotor activity was recorded every 3 min for maximally 60 min. In the nucleus accumbens both DA (10–160 μg/side) and l-NA (2.5–40 μg/side) produced a suppression of the initial (0–3 min) exploratory locomotor activity in the open field arena. The highest doses of the respective drug, 80–160 μg of DA and 20–40 μg of l-NA, produced stimulation of the locomotor activity at a later time interval (6–9 min). The number of rearings during the initial exploration (0–3 min) was suppressed by DA (10–60 μg/side) as well as by l-NA (2.5–40 μg/side). When administered to the neostriatum, DA (80–160 μg/side) produced a stimulation of locomotor activity, 6–9 min after placement in the open field. The administration of l-NA (20–80 μg/side) to the neostriatum produced a suppression of the exploratory locomotor activity (0–6 min). The number of rearings were reduced by the administration of l-NA (20–80 μg/side) whereas no significant effect was observed after the administration of DA (5–160 μg/side). As assessed in the present experiments DA and l-NA produced identical effects in the nucleus accumbens, l-NA being about 4 times as potent as DA, whereas opposite effects were produced by l-NA and DA when applied to the neostriatum.