Comparison of spontaneous and mechanically-stimulated adenosine release in mice.

Rapid adenosine signaling, on the time frame of seconds, has been discovered in the brain that can modulate neurotransmission or blood flow. Rapid adenosine release can occur spontaneously or be evoked after a mechanical stimulation, but these two modes of adenosine have not been compared. Here, we compared spontaneous and mechanically-stimulated adenosine release in the prefrontal cortex, striatum, and hippocampus of anesthetized mice. For spontaneous adenosine, the number of adenosine events in the prefrontal cortex (40 ± 4 per hour) was significantly lower than in the striatum (54 ± 3) or hippocampus (56 ± 3). Similarly, the concentration per transient was lower in the prefrontal cortex but highest in the striatum. For mechanically-stimulated adenosine, the peak concentration in the prefrontal cortex (8 ± 2 μM) and striatum (8 ± 1 μM) were significantly lower than in the hippocampus (16 ± 2 μM). Comparing the two modes, the hippocampus had high mechanically-stimulated concentration and high spontaneous frequency, while the prefrontal cortex had lower spontaneous frequency and mechanically-stimulated release. However, there is no pattern with the striatum and thus no direct correlations between spontaneous and mechanically-stimulated adenosine. Thus, there may be different pools of adenosine or mechanisms of formation for these two modes. Because of the high frequency of spontaneous events and high concentration of mechanically-stimulated release in the hippocampus, there may be some areas that have stronger adenosine signaling and thus stronger neuromodulatory control by adenosine.