Figure 2. Suramin blockade of P2 receptors in the NTS selectively attenuates the reflex bradycardia in response to peripheral chemoreceptor but not pharyngo-oesophageal receptor stimulation.

A representative WHBP in which CN stimulation of peripheral chemoreceptors (top) evoked a decrease in PNA cycle length and bradycardia. The cardiac, but not the respiratory component of this response was attenuated by suramin (100 pmol). The attenuating effect of suramin on the chemoreceptor reflex bradycardia was abolished after 15 min. Distension of pharyngo-oesophageal junction (PO; bottom) using a small balloon caused an increase in PNA cycle length and bradycardia that persisted after an NTS microinjection of suramin. Note that the persistence of the latter response occurred at a time when the chemoreceptor reflex-mediated bradycardia was attenuated. HR, heart rate; PP, perfusion pressure.