Fig. 6. Microdialysis delivery of buprenorphine decreased adenosine concentrations in the basal forebrain and pontine reticular formation oral part (PnO). (A ) Cresyl-violet stained coronal sections show representative dialysis sites in the PnO and in the substantia innominata (SI) region of the basal forebrain. Arrows indicate the location of each microdialysis membrane. (B ) Time course of a representative experiment showing adenosine concentrations in the SI before (Ringer's solution) and during dialysis delivery of buprenorphine. Each bar represents one sample (30 μl) acquired during 15 min of dialysis. (C ) Chromatograms produced by ultraviolet measurement during the detection of adenosine concentrations ranging from 0 to 200 nM. Each microdialysis experiment began by creating a 5-point standard curve. The standard curve was used to convert ultraviolet absorbance values to concentration of brain adenosine for each microdialysis sample. (D ) Chromatograms resulting from four different measurement conditions. The black trace  illustrates the chromatogram produced when the instrument was injected with Ringer's solution that did not pass through the microdialysis probe (negative control). The green trace  shows a chromatogram reflecting brain adenosine measured during brain microdialysis with Ringer's solution. The blue trace  is a chromatogram produced by measurement of a 100-nM adenosine standard. The red trace  represents a brain sample obtained during dialysis with Ringer's solution + 1 mM erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), an adenosine deaminase inhibitor that increased adenosine (positive control). The key point is that all chromatograms showed the same elution time for adenosine. Thus, the magnitude of the standards (C ) and the elution times (D ) confirm the presence of adenosine in the brain samples.