Inhibition of tyrosine hydroxylase activity suppresses DA levels and daytime PER2 expression in the dorsal striatum. Rats were given three injections of AMPT or saline over 8 h and then killed at either ZT13 (5 h after the last injection) or ZT1 (17 h after the last injection). a, DA content in the dorsal striatum (expressed as picograms of DA/microgram of protein) in AMPT-injected rats (black bars) was significantly decreased at both ZT1 and ZT13 compared with saline-injected rats (white bars; n = 2 per treatment group per ZT; *p < 0.05). b, In the dorsal striatum, AMPT treatment decreased daytime PER2 expression at ZT1 and increased PER2 at ZT13 compared with saline controls (expressed as mean PER2-IR nuclei ± SEM at each ZT; n = 4 per treatment group per ZT; *p < 0.05). c, In the SCN, AMPT treatment had no effect on PER2 expression at either time point.