Dopamine receptors in a rat model of minimal brain dysfunction

A model of minimal brain dysfunction (MBD) in rats based on injection of 6-OH-dopamine (DA) intracisternally on the 5th day of life has been described previously. Since 6-OH-DA pretreatment has been reported in adult rats to lead to a compensatory rise in DA receptor number, we measured DA receptor number in animals treated with 6-OH-DA on the 5th day of life, after completion of behavioral observations on days 17, 20 and 23 of life. Rats pretreated with 6-OH-DA at day 5 were found, on sacrifice on day 23, to have a mean increase of about 20% in caudate spiperone binding. There was a significant correlation between spiperone binding and gross activity in 6-OH-DA-treated animals but not in untreated animals. Since the significant correlation between receptor number and gross activity is negative and DA receptor stimulators are known to increase activity, it appears that receptor number changes are not directly related to hyperactivity.