ADENOSINE-DOPAMINE RECEPTOR INTERACTIONS IN THE ISOLATED RAT NODOSE GANGLION BUT NOT IN MEMBRANES OF DORSAL VAGAL COMPLEX

The present study has employed in vitro electrophysiology and radiolig and binding assays to determine whether dopamine and adenosine recepto rs interact with each other on rat vagal afferent neurons. Preincubati on of the isolated rat nodose ganglion with the adenosine A(2a) agonis ts CGS 21 680 or DPMA (Both 1 mu M) resulted in a functional antagonis m of the ability of dopamine to depolarise the preparation. Specifical ly, the concentration-response curve to dopamine was significantly shi fted to the right in the presence of CGS 21 680 and DPMA. On the other hand, adenosine itself, A(1) and A(3) receptor agonists and ATP were all incapable of modulating the electrophysiological response to dopam ine. In contrast to the nodose ganglion, CGS 21 680 did not significan tly affect the ability of the dopamine D-2 ligands quinpirole or raclo pride to displace [I-125]NCQ298 binding to dopamine D-2 receptors in m embranes prepared from rat dorsal brain stem. These data indicate the presence of an interaction between high affinity adenosine A(2) recept ors and dopamine D-2 receptors on the soma of rat vagal afferent neuro ns, whereas the situation in the brain stem remains less clear.