Extracellular ATP can influence cells via activation of P2X purinoceptors, the distribution of which can be altered in the central and peripheral nervous systems following injury or tissue damage. Here we have investigated the effect of a unilateral section of the cervical vagus nerve on the distribution of P2X(1), P2X(2), P2X(3), P2X(4) and P2X(7) receptor subunit immunoreactivity (R-IR) in the dorsal vagal motor nucleus (DVN) and the nucleus ambiguus (NA) in the medulla oblongata. As early as 2 days, and followed up to 14 days, there was a dramatic ipsilateral increase in P2X(1), P2X(2) and P2X(4)R-IR in the cell soma of vagal efferent neurones in the DVN following the nerve section, but not the NA. There were no changes in P2X(3) and P2X(7)R-IR in either nuclei. To test for possible functional consequences of increased P2X receptor levels, whole-cell patch-clamp recordings were made from DVN cells in brainstem slices 4 days following unilateral vagotomy. Application of ATP revealed large cell-to-cell variance in the current amplitude in neurones from both sectioned and control DVN. However, when ATP responses were compared to those elicited by the nicotinic acetylcholine receptor agonist carbachol, the mean ratio of the peak ATP-evoked current to the peak carbachol-evoked current was significantly larger in DVN neurones ipsilateral to the section. Thus the increase in P2XR levels in DVN cells ipsilateral to a nerve section are likely to reflect an increase in expression of functional P2XRs on the cell surface.