Figure 6.

PSCs Ca²⁺ responses are mediated by P2_Y receptors, not muscarinic receptors. A, PSC responsiveness to ventral root stimulation during bath application of the mAChR antagonist, atropine (60 μm). Note that atropine did not prevent PSC Ca²⁺ responses induced by the strong and the weak input stimulations but antagonized responses induced by local application of the mAChR agonist, muscarine (3 μm). The dark trace represents the average of PSC Ca²⁺ responses; and the dotted lines represent SEM. Inset, False color confocal images showing changes in fluorescence of Fluo-4 at the peak of the response. B, Top, PSC Ca²⁺ activity evoked in the presence of the P2_Y receptor antagonist, RB2 (20 μm). Note that no Ca²⁺ responses were evoked in the presence of RB2 either by stimulation of the strong or the weak input. Also, responses induced by local application of the P2_Y receptor agonist, ATP (3 μm), were antagonized. Bottom, Examples of EPPs induced by the strong and weak inputs before and during RB2 application. Note that the lack of PSC Ca²⁺ responses cannot be attributed to the absence of synaptic activity because EPPs were still elicited by motor nerve stimulation. C, Histogram showing PSC Ca²⁺ responses induced by strong and weak inputs and local application of agonists in the different conditions studied.