Table 3.

Interactions of serotonin and dopamine signaling pathways on DARPP-32 phosphorylation in slices

	Thr34	Thr75	Ser137
Control	100 (17.0)	100 (5.0)	100 (3.9)
Serotonin	342 (26.7)**	76 (7.5)**	141 (6.0)**
SKF 82958 (D1 agonist)	552 (59.1)**	63 (1.7)**	105 (14.7)
SKF 82958 + serotonin	717 (42.4)**#§	56 (1.1)**#§	121 (14.4)
Quinpirole (D2 agonist)	65 (4.7)**	112 (8.5)	135 (5.1)*
Quinpirole + serotonin	125 (12.7)169†	106 (13.2)167	186 (11.1)**#†
MPTP treatment	93 (8.7)	118 (9.3)	104 (7.9)
MPTP-treatment + serotonin	307 (44.1)**	80 (9.2)*	154 (21.1)**

SKF 82958 (10 μM), a D₁ receptor agonist, or quinpirole (10 μM), a D₂ receptor agonist, was applied 10 min before serotonin (100 μM). MPTP (50 mg/kg, i.p.) was administered i.p. four times at 12-h intervals, 4 weeks before the slice experiment. This pretreatment caused a 85–93% reduction in the levels of tyrosine hydroxylase in striatum. Data represent means (± SEM) (n = 16–30). 

^*, P < 0.05; 

^**, P < 0.01; 

^**, P < 0.001 compared with control;  

^#, P < 0.05;  

¹⁶⁷, P < 0.01; 

¹⁶⁹, P < 0.001 compared with serotonin alone;  

^§, P < 0.05 compared with SKF 82958 alone;  

^†, P < 0.05 compared with quinpirole alone; one-way ANOVA followed by Dunnett's test.