Central CO2 chemoreception: a mechanism involving P2 purinoceptors localized in the ventrolateral medulla of the anaesthetized rat

1. The involvement of P2 purinoceptors in chemosensory function in the vent rolateral regions of the medulla oblongata was investigated in the anaesthe tized rat. We have investigated the effect of antagonizing, or desensitizin g, P2 receptors in the retrofacial area of the ventrolateral medulla on fac tors modifying respiratory activity. 2. Bilateral microinjection of suramin (50 nl, 0.02 M), a P2 purinoceptor a ntagonist, into the retrofacial area in the artificially ventilated rat red uced resting phrenic nerve discharge. It also markedly affected the respons e of the phrenic nerve to increases in arterial CO2. Under conditions of hy per oxic, hypocapnic apnoea, the mean threshold for inducing phrenic nerve activity was raised significantly (from an end-tidal CO2 of 2.5% to 4.5%, n = 9). 3. In addition, the slope of the respiratory response curve to increases in CO2 was reduced after suramin. A similar effect was observed after desensi tization of certain P2X receptors with alpha beta-methyleneATP, As arterial levels of O-2 were greater than 100 mmHg, and an equivalent pattern of res ponse was observed in sino-aortically denervated and vagotomized animals, w e believe any contribution of the peripheral chemoreceptors to be minimal. 4. Our data suggest that respiratory neurones within the retrofacial area ( Botzinger complex) represent part of the central site of action of CO2 on r espiration. Moreover, our observations lead us to suggest that CO2-evoked c hanges in respiration are mediated at least in part by P2X purinoceptors.