Fig. 2.

Effect of D2 dopamine receptor deficiency on extracellular dopamine concentrations in control and coloboma mice. A. Striatal dopamine concentrations were measured by no net flux microdialysis in alert freely moving control (+/+) or coloboma mice (Cm/+) carrying normal (D2^+/+) or knockout (D2^-/-) alleles of the D2 dopamine receptor gene (n=7-8/genotype). There was a significant genotype (+/+ vs Cm/+) × D2 allele interaction effect (F_1,27 = 6.0, p < 0.05). Post hoc analyses using Student's t tests demonstrated that dopamine overflow in normal coloboma mice (Cm/+;D2^+/+) was significantly higher normal control mice (+/+;D2^+/+). No significant difference in dopamine overflow was observed between coloboma mice lacking the D2 dopamine receptor and control mice with or without D2 dopamine receptors (***p < 0.001). B. The extraction fraction, an indirect measure of dopamine reuptake, is the slope of the linear regression analysis of the concentration of dopamine perfused into the microdialysis probe (C_in) versus the perfused dopamine concentration minus the dialysate dopamine concentration (C_in - C_out). No significant differences were observed among the extraction fractions. Values are means ± SEMs.