The potential role of the nodose ganglion adenosine A1 receptor in regulation of breathing in anaesthetized rats.

The respiratory effects of stimulation of adenosine A(1) receptors were studied in spontaneously breathing rats that were either (1) neurally intact and subsequently bilaterally vagotomized in the neck, or (2) neurally intact and subjected to supranodosal vagotomy or (3) midcervically vagotomized before and after pharmacological blockade of A(1) receptors. Before neural interventions an intravenous bolus of the A(1) receptor agonist N6-cyclopentyladenosine (CPA, 5 microg kg(-1)) decreased breathing rate, tidal volume, mean arterial blood pressure (MAP) and heart rate. After section of the midcervical vagi, CPA still decreased respiratory rate and tidal volume. Supranodose vagotomy abolished the fall in respiratory rate but did not affect the depression of tidal volume. Blockade of A(1) receptors with intravenous doses of DPCPX (100 microg kg(-1)) eliminated all respiratory effects of CPA challenge. In all the neural states, CPA caused significant falls in mean arterial blood pressure and heart rate. DPCPX pre-treatment prevented these cardiovascular effects. The present data suggest that: (1) CPA-evoked activation of A(1) receptors decreases breathing rate and tidal volume and this occurs central to the cervical vagi; (2) supranodosal vagotomy prevents the decrease in breathing rate, which is presumably due to stimulation of nodosal A(1) receptor; and (3) depression of tidal volume and the hypotensive response result from the excitation of central nervous A(1) expressing neurones.