Apomorphine- and haloperidol-induced change in 3,4-dihydroxyphenylacetic acid content in the mesolimbic-striatum of the developing rat.

The mesolimbic-striatal content of 3,4-dihydroxyphenylacetic acid (DOPAC) gradually increased with age in the developing rat. An intraperitoneal (i.p.) injection of apomorphine (2 mg/kg) or haloperidol (0.1 mg/kg) caused a significant change in the DOPAC content on day 20 and day 70, but not on day 7. However, a higher dose of apomorphine (10 mg/kg, i.p.) or haloperidol (5 mg/kg, i.p.) as well as that of alpha-flupenthixol (0.5 mg/kg, i.p.) significantly affected the mesolimbic-striatal content of DOPAC in 7-day-old rats. In 24-day-old rats subchronically treated with haloperidol (1 mg/kg to 10 mg/kg for 10 days, s.c.), apomorphine (2 mg/kg, i.p.) produced a significant reduction in the mesolimbic content of DOPAC at the withdrawal stage of the drug, but not in control rats. It is suggested that mesolimbic-striatal dopamine (DA) receptors which are not fully sensitive to DA agonists and antagonists on day 7 reach functional maturity by 20 days of the postnatal age in the rat.