Figure 2. D₁ stimulation increases free cAMP concentration to higher levels in striatal neurones than in cortical neurones.

A, prefrontal cortical neurones in a mouse brain slice were transduced for expression of Epac1-camps and imaged by two-photon laser-scanning microscopy. Images show the raw fluorescence at 535 nm (left, in grey scale) and the ratio (in pseudocolour) indicating the change in conformation of Epac1-camps following binding to cAMP, at the times indicated by the arrows on the graph below. Each trace on the graphs indicates F480/F535 emission ratio measurements on regions indicated by the colour contour drawn on the raw images; thin traces in black correspond to cells outside the displayed region; the thick black line represents the average of all the traces. Forskolin increased the ratio to a moderate level and the non-specific inhibition of phosphodiesterases with IBMX resulted in a stronger response. B, as for A, except that the pyramidal cortical neurones were transduced with Epac2-camps300. SKF38393 triggered a clear response, which was further increased by forskolin. C, medium spiny neurones of the striatum transduced for Epac1-camps expression were imaged by two-photon laser-scanning microscopy. Traces are separated into two plots on the basis of the response to either the A_2A agonist CGS21680 or to the D₁ agonist SKF38393. SKF38393 (1 μm), CGS21680 (1 μm), forskolin (13 μm) and forskolin (13 μm) + IBMX (200 μm) were added to the bath during the time represented by the horizontal bar.