Figure 5. Concentration-effect relation for PPADS in the central chamber on descending inhibitory reflexes.

The effects of 10 µM (top panels), 30 µM (second panels) and 60 µM (third panels) PPADS in the central chamber on IJPs evoked in the anal chamber by distension in the far (oral) chamber (left column) and central chambers (n≥6 in each case). These are compared with the effects of complete synaptic blockade by a 0.25 mM Ca²⁺, 10 mM Mg²⁺ solution in the central chamber on the same responses (n = 6). Synaptic blockade significantly depressed reflexes whether they were evoked in the far or the central chamber, although it was much more effective on reflexes conducted through this chamber than those evoked in it. The effect of PPADS on reflexes conducted through the central chamber from far chamber distension was concentration-dependent with 10 µM having no effect, but even 60 µM PPADS was less effective than complete synaptic blockade. C indicates data obtained in control physiological saline, D indicates data obtained with either PPADS or the low Ca²⁺, high Mg²⁺ solution in the central chamber, W indicates data obtained at least 20 minutes after the solution in the central chamber was returned to control.