Fig. 7. Dialysis administration of SPA decreased acetylcholine release. (A ) Time course of a typical experiment. (Inset ) Sagittal view of cat brain with a dialysis probe delivering sulfophenyladenosine (SPA, 8.8 mm) into the medial pontine reticular formation (mPRF) and dialysis samples containing acetylcholine (ACh) collected every 10 min. Bars represent amount of acetylcholine detected in each 30-μl sample. Mean ± SD acetylcholine during dialysis with Ringer's solution (control) was 0.22 ± 0.02 pmol/10 min of dialysis. Mean ± SD acetylcholine during dialysis with SPA was 0.17 ± 0.04 pmol/10 min. (B ) Comparison of acetylcholine release during mPRF dialysis with Ringer's solution (n = 40 dialysis samples) and during dialysis with 0.088 mm SPA (n = 40) and 8.8 mm SPA (n = 40). Data were obtained from four experiments in four cats. Analysis of variance followed by Tukey-Kramer post hoc  analysis demonstrate a statistically significant decrease in acetylcholine release below Ringer's solution levels following dialysis of 8.8 mm SPA (*P < 0.01).