The development of response to continuous auditory stimulation in rats treated neonatally with 6-hydroxydopamine

This study investigated biochemical substrates of the continuous stimulation effect, i.e. the developmental phenomenon whereby continuous stimulation depresses arousal level. Neonatal rats were injected intracisternally with 6-hydroxydopamine. Motility, heart rate, and brain amines were measured in theses animals, as well as in injected and noninjected control animals, at 14 and 28 days of age in an own-control design with and without continuous auditory stimulation. Brain norepinephrine was significantly and inversely related to the magnitude of the continuous stimulation effect and experimental-control differences increased with age. These results indicate that an intact catecholaminergic system is necessary for the mediation of increased arousal during stimulation.