Figure 7. The adenosine released by electrical stimulation modulates parallel fibre–Purkinje cell synaptic transmission.
Parallel fibre (PF) EPSPs were evoked every 10 s by a stimulating electrode placed on the surface of the molecular layer and recorded with an extracellular electrode. A, graph plotting PF EPSP amplitude against time. Application of 1 μm 8CPT, to block A1 receptors, increased EPSP amplitude by ∼30%. B, superimposed traces from an adenosine biosensor in control and in the presence of 1 μm 8CPT. Adenosine release was evoked by a 7 s stimulus at the arrow. Application of 8CPT increased adenosine release by 43%. C, graph plotting PF EPSP (evoked every 10 s) amplitude against time. At the asterisk a train of stimuli was delivered (10 s, 20 Hz) to cause adenosine release. Following the train there was a marked reduction in PF EPSP amplitude followed by a slow recovery back to control amplitude (PF EPSP amplitude during the train is not plotted). The time course of PF EPSP amplitude recovery was ∼150 s which is very similar to the time course of adenosine release. Application of the A1 receptor antagonist 8CPT increased PF EPSP amplitude by ∼25% and also markedly speeded recovery following a train of stimuli (∼50 s). Thus, the slow component of recovery results from the released adenosine activating A1 receptors. D, graph summarizing data from 6 recordings. Following blockade of A1 receptors there was significant speeding of EPSP recovery.