Tissue slices prepared from the rat frontal cortex and incubated with dopamine at various concentrations for 3–24 h showed significant and concentration-dependent increases in BDNF protein expression [analysis of variance F(2,52)=8.89, P<0.01] after 24 h incubation (). Preliminary experiments showed that the slice preparations incubated in Hibernate A medium remain metabolically active after 24 h, as detected by XTT assay (Sigma Aldrich) and by the incorporation of tritiated myo-inositol into inositol phospholipids when the radiolabel was added from the 24th to the 27th hour of incubation (data not shown). Hence, the BDNFobservations are probably physiologic responses to the agonist.
Fig. 1 Time course for brain-derived neurotrophic factor (BDNF) protein expression in cortical tissue slices. Tissue slices were incubated with dopamine at various concentrations for 3, 12, or 24 h. The data represent the mean±SEM (n =9). Samples collated (more ...)
To determine the brain regional dependence of the dopamine response, tissue slices were prepared from the rat frontal cortex, striatum, or hippocampus and tested with various concentrations of dopamine. Dopamine significantly increased BDNF protein expression in all three tissue preparations (). The lowest concentration of dopamine that induced a significant effect in any brain region was 30 µM. Although the effects in the frontal cortex [F(3,11)=10.01, P < 0.01] were significant only at the highest tested concentration of 300 µM, the striatum effects peaked at 30 µM [F(3,11)=4.638, P < 0.05] and declined thereafter. In the hippocampal tissues, dopamine increased BDNF protein expression [F(3,11)=9.901, P<0.01] through to the highest tested concentration of 300 µM ().
Fig. 2 Brain regional effects of dopamine on brain-derived neurotrophic factor (BDNF) expression in tissue slices. Tissue slices were incubated with dopamine at various concentrations for 24 h and BDNF protein levels were measured by enzyme-linked immunosorbent (more ...)
Dopamine receptor subclass-selective agonists also were tested for possible effects on BDNF protein expression. Tissue slices prepared from the frontal cortex showed no change in BDNF protein expression in comparison with control after treatment with SKF38393 or quinpirole (). In hippocampal [F(2,54)=8.74, P<0.05] and striatal tissue slices [F(2,54)=6.65, P<0.05], SKF38393 produced a significant increase in BDNF protein expression, similar to the effects of dopamine. Quinpirole, however, had no effect on BDNF protein expression in any of these brain regions, implying that the response might be mediated through the D1-like subclass of dopamine receptors.
Fig. 3 Effects of dopamine receptor agonists on brain-derived neurotrophic factor (BDNF) protein expression in vitro. Tissue slices were incubated with dopamine (DA), SKF383893 (SKF), or quinpirole (QUIN) at indicated concentrations for 24 h and the levels of (more ...)
In general, basal concentrations of BDNF protein expression were highest in the hippocampus (50 pg/ml), whereas the levels in the striatum (20 pg/ml) and the frontal cortex (25 pg/ml) were similar (). This pattern of basal activity distribution and agonist responsiveness is reminiscent of D1-like receptor induction of phosphoinositide signaling as previously reported for various parameters of this signaling system.