Behavioral and electrocortical activity in rats after neonatal intraventricular 6-hydroxydropamine administration

Intraventricular injections of 6-hydroxydopamine (6-OHDA) to newborn rats resulted in a nearly complete disappearance of catecholamines in brain regions containing nerve terminals. In the hypothalamus, however, dopamine was only decreased to 60% of control levels. The exploratory (rearing and crossing) and some of the automatic type behavioral activities (grooming, chewing and gnawing), the duration of neocortical synchronization and hippocampal theta frequency were measured during light and dark periods in adulthood. Decreased exploratory and increased automatic behavioral activities were found in both light and dark periods and a high incidence of synchronization and a lowered hippocampal theta frequency in the light phase when the animals were repeatedly subjected to a strange environment. The light-dark rhythmicity of exploratory and hippocampal activity remained intact in the 6-OHDA treated rats. Furthermore, the diurnal periodicity of general motor activity was also normal. It was concluded that contrary to the active involvement of prepontine catecholamine structures in the behavioral and electrocortical responses in a novel situation, their role in controlling the light-dark rhythmical processes may not be essential.