| Abstrakt: |
Abstract Using double in situ hybridization, we found extensive coexpression of dopamine D1 and D3 receptor (D1 R and D3 R) mRNAs in neurons of the island of Calleja major (ICjM) and ventromedial shell of nucleus accumbens (ShV), respectively. Thus, at least 79 and 63% of D3 R mRNA‐expressing neurons in ICjM and ShV also expressed the D1 R mRNA. Coexpression of D1 R and D3 R mRNAs was found to occur in substance P (SP) mRNA‐expressing neurons in both areas, suggesting SP mRNA as a marker of the activity of coexpressing neurons. Administration of SKF 38393, a D1 R receptor agonist, increased c‐fos mRNA in ICjM, whereas administration of quinpirole, a D2 R/D3 R agonist, decreased it; SCH 23390, a D1 R antagonist and nafadotride, a preferential D3 R antagonist, given alone, had effects opposite to those of the corresponding agonists. These data indicate that basal c‐fos expression in ICjM is maintained by endogenous dopamine acting tonically upon two receptor subtypes subserving opposite effects on the same cell. However, in ShV, whereas SKF 38393 also increased c‐fos mRNA, quinpirole had no effect, a difference presumably reflecting the lower fraction of neurons coexpressing D1 R and D3 R in this area. In contrast, in ShV from reserpine‐treated rats, SKF 38393 increased SP mRNA and quinpirole potentiated this effect. These contrasting interactions of D1 R‐ and D3 R‐mediated signalling events, i.e. in either opposite or synergistic directions, most likely occurring at the single cell level, may serve to increase the dopamine response threshold of the target cells in ICjM and to maintain a strong tonic activity of ShV neurons. [ABSTRACT FROM AUTHOR] |
