Intracellular recordings were performed in a midpontine slice preparation of the rat brain containing the mesencephalic trigeminal nucleus (MTN). In spite of the previous demonstration of an adenosine deaminase-containing plexus terminating on this nucleus, adenosine, adenosine 5'-triphosphate (ATP), alpha,beta-methylene ATP (alpha,beta-meATP) and 2-methylthio ATP all failed to influence the membrane potential or input resistance of the MTN cells. Moreover, there was no apparent change in the shape of action potentials in the presence of these drugs, and the accomodation of the firing rate to depolarizing pulses was not affected either.