Neonatal 6-hydroxydopamine-induced dopamine depletions: motor activity and performance in maze learning

Three experiments were performed to study the effect of dopamine (DA) depletions, induced by neonatal intracerebroventricular (ICV) treatment with 6-hydroxydopamine (6-OHDA), upon measures of spontaneous motor activity. Instrumental learning for food reward in an Olton radial arm maze and escape learning from a large, circular water maze were studied also. Motor activity was measured by direct observation of rats in a modified radial arm maze and by use of automated test cages equipped with photocell devices. 6-OHDA-treated rats demonstrated considerable and long-lasting locomotor (ambulation) activity and total activity increases. 6-OHDA-treated rats showed notably less rearing activity than the vehicle-treated rats during the initial 20 min of each 60-min test period. However, over the second half of these 60-min test periods, the 6-OHDA-treated rats demonstrated significantly more rearing activity than the vehicle-treated rats. In the acquisition of the running response, to obtain the 8 food pellets placed in each of the 8 arms of the radial arm maze, 6-OHDA rats showed a retarded acquisition, as measured by the latency and number of arms visited to acquire all eight pellets. 6-OHDA-treated rats failed completely to acquire the Morris-type swim maze task by which they were required to locate a platform just under the water surface in a circular water tank. The neurochemical assays indicated severe DA depletion in several forebrain regions. The present findings add to existing indications of the potential of this DA depletion condition as an animal model of the minimal brain dysfunction syndrome.