We investigated the pre- and post-synaptic effects of pancreatic polypeptide (PP) on identified pancreas-projecting neurons of the rat dorsal motor nucleus of the vagus, in thin brainstem slices. Perfusion with PP induced a tetrodotoxin- and apamin-sensitive, concentration-dependent outward (22% of neurons) or inward current (21% of neurons) that was accompanied by a decrease in input resistance; PP was also found to affect the amplitude of the action potential afterhyperpolarization. The remaining 57% of neurons were unaffected. PP induced a concentration-dependent inhibition in amplitude of excitatory (N= 22 of 30 neurons) and inhibitory (N=13 of 17 neurons) postsynaptic potentials evoked by electrical stimulation of the adjacent nucleus of the tractus solitarius, with an estimated EC₅₀ of 30nM for both. The inhibition was accompanied by an alteration in the paired pulse ratio, suggesting a presynaptic site of action. PP also decreased the frequency, but not amplitude, of spontaneous excitatory (N=6 of 11 neurons) and inhibitory currents (N=7 of 9 neurons). In 5 neurons, chemical stimulation of the area postrema induced a TTX-sensitive inward (N=3) or biphasic (outward and inward) current (N=2). Superfusion with PP reversibly reduced the amplitude of these chemically-stimulated currents. Regardless of the PP-induced effect, the vast majority of responsive neurons had a multipolar somata morphology with dendrites projecting to areas other than the fourth ventricle or the central canal. These results suggest that pancreas-projecting rat DMV neurons are heterogeneous with respect to their response to PP, which may underlie functional differences in the vagal modulation of pancreatic functions.