Stoichiometry of tyrosine hydroxylase phosphorylation in the nigrostriatal and mesolimbic systems in vivo: Effects of acute haloperidol and related compounds

Electrical stimulation of the medial forebrain bundle increases ³²P incorporation into striatal tyrosine hydroxylase (TH) at Ser¹⁹, Ser³¹, and Ser⁴⁰. In the present studies, the effects of acute haloperidol and related drugs on site-specific TH phosphorylation stoichiometry (PS) in the nigrostriatal and mesolimbic systems were determined by quantitative blot immunolabeling using phosphorylation state-specific antibodies. The striatum (Str), substantia nigra (SN), nucleus accumbens (NAc), and ventral tegmental area (VTA) from Sprague-Dawley rats were harvested 30-40 min after a single injection of either vehicle, haloperidol (2 mg/kg), raclopride (2 mg/kg), clozapine (30 mg/kg), or SCH23390 (0.5 mg/kg). In vehicle-injected control rats, Ser¹⁹ PS was 1.5- to 2.5-fold lower in Str and NAc than in SN and VTA, Ser³¹ PS was two- to fourfold higher in Str and NAc than in SN and VTA, and Ser⁴⁰ PS was similar between the terminal field and cell body regions. After haloperidol, Ser⁴⁰ PS increased twofold in Str and NAc, whereas a smaller increase in SN and VTA was observed. The effects of haloperidol on Ser¹⁹ PS were similar to those on Ser⁴⁰ in each region; however, haloperidol treatment increased Ser³¹ PS at least 1.6-fold in all regions. The effects of raclopride on TH PS were comparable to those of haloperidol, whereas clozapine treatment increased TH PS at all sites in all regions. By contrast, the effects of SCH23390 on TH PS were relatively small and restricted to the NAc. The stoichiometries of site-specific TH phosphorylation in vivo are presented for the first time. The nigrostriatal and mesolimbic systems have common features of TH PS, distinguished by differences in TH PS between the terminal field and cell body regions and by dissimilar increases in TH PS in the terminal field and cell body regions after acute haloperidol.