Effects of 6-hydroxydopamine and 6-hydroxydopa on development of behavior.

Rats treated at birth with 6-hydroxydopamine (6-OHDA) (60 microgram/g, IP) or 6-hydroxydopa (6-OHDOPA X2) (60 microgram/g, IP at birth and 48 hr later) exhibited increases in general activity throughout the initial 5 weeks after birth, with peak activity occurring around 20 days postnatally. Activity changes in the 6-OHDOPAx2 group appeared to be due to increased exploratory behavior (ambulation, climbing, rearing, sniffing), while the 6-OHDA changes appeared to be due to the increased self-directed behavior (eating, grooming, scratching). Despite these behavioral differences there was no obvious difference between treated groups in norepinephrine (NE) levels in the various brain regions, i.e., all treatments resulted in a reduction in neocortical and hippocampal NE and an elevation in cerebellar NE. These findings suggest that noradrenergic neurons may be altered to different degrees by each agent in more discrete brain regions than were tested, or that other neurotransmitter systems may be more selectively altered by either of the drug treatments. Because striatal dopamine was unaltered in any of the groups, however, there is reason to question a previously suggested link between minimal brain dysfunction (MBD) and dopamine depletion in the neonatal brain.