Animals were euthanized via decapitation at PN60, PN100 and PN150, and the striatum (all ages) and frontal/parietal cortex (PN100, PN150) were dissected and frozen in liquid nitrogen, and then stored at −80 °C until utilized. Tissues were deproteinized by homogenization in 0.1 N perchloric acid containing 3,4-dihydroxybenzylamine (Sigma Chemical Co., St. Louis MO, USA) as an internal standard. Homogenates were sedimented at 26,000 × g for 10 min and supernatants were trace-enriched by alumina adsorption. Dopamine and DOPAC were separated by reverse-phase high performance liquid chromatography, and quantitated by electrochemical detection (Seidler & Slotkin, 1981 (link)), standardized against external standards containing 3,4-dihydroxybenzylamine and known quantities of dopamine (Sigma) and DOPAC (Sigma); values were corrected for recovery of the internal standard. Transmitter utilization was then calculated by the DOPAC/dopamine ratio, so as to assess the proportion of dopamine released into the synapse (Slotkin et al., 2009 (link)). In the frontal/parietal cortex, we simultaneously measured the level of another catecholamine neurotransmitter, norepinephrine.