TH activity is independently regulated in nigrostriatal pathway.

<p><b>A. Nigral TH inhibition decreases DA tissue content without impact in striatum.</b> AMPT (2.8 nmoles, as methyl ester) was infused unilaterally into the midbrain (coordinates described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029867#s2" target="_blank">methods</a>) of anesthetized rats. Vehicle was infused in the identical coordinates of the contralateral hemisphere. 90 min following AMPT infusion, the striatum and SN were dissected, segregating the hemispheres. Tissue was homogenized in HPLC buffer and DA was normalized to total protein content in the precipitated pellet. Values (mean±SEM) are expressed as pmols DA per mg protein (SN-veh, 42±3; SN-AMPT, 29±4; Str-ipsiveh, 1344±140; Str-ipsi AMPT, 1503±191). Two-tailed Student's paired t-test was used, comparing AMPT-infused hemisphere versus contralateral vehicle-infused hemisphere (<i>n</i> = 6 rats, **<i>p</i> = 0.0036, t = 5.17, df = 5). <b>B. AMPT, at the effective quantity in SN, also reduces striatal DA tissue content with striatal infusion.</b> AMPT (2.8 nmoles as methyl ester), at a quantity sufficient to reducenigral DA tissue content (panel A), also significantly decreases striatal DA tissue content. Values (mean±SEM) are expressed as pmols DA per mg protein (SN-veh, 69±5; SN-AMPT, 37±2; Str-veh, 1911±206; Str-AMPT, 1537±108). Two tailed Student's paired t-test was used, comparing AMPT-infused hemisphere versus contralateral vehicle-infused hemisphere (SN, <i>n</i> = 4 rats, *<i>p</i> = 0.033, t = 3.7, df = 3; Str, <i>n</i> = 5 rats, *<i>p</i> = 0.043, t = 2.9, df = 4). <b>C. Striatal TH inhibition decreases DA tissue content locally without impact in SN.</b> Unilateral AMPT (14 nmoles as methyl ester) infused in striatum significantly decreases striatal DA tissue content without effect in SN. Values (mean±SEM) are expressed as pmols DA per mg protein (Str-veh, 1360±170; Str-AMPT, 1037±98; SN-ipsiveh, 42±5; SN-ipsi AMPT, 40±5). Two tailed Student's paired t-test was used, comparing AMPT-infused hemisphere versus contralateral vehicle-infused hemisphere (<i>n</i> = 5 rats, *<i>p</i> = 0.019, t = 3.8, df = 4).