Microinjection of opioid receptor agonists into the nucleus tractus solitarius (NTS) has differential effects on cardiovascular, respiratory and gastrointestinal responses. This can be achieved either by presynaptic modulation of inputs onto neurons or by postsynaptic activation of receptors on neurons in specific regions. Therefore, we sought to determine whether responses of neurons to activation of opioid receptors were dependent upon their location within the NTS. Using whole-cell patch clamp recordings from neurons within the NTS, the mu opioid receptor (MOR) agonist DAMGO (100 nM) hyperpolarized a proportion of neurons in the medial, dorsomedial and dorsolateral NTS, while no postsynaptic responses were observed in remaining subdivisions. DAMGO reduced the amplitude of solitary tract-evoked excitatory postsynaptic potentials (EPSPs) in all neurons tested, regardless of subdivision. The kappa opioid receptor (KOR) agonist U69593 (10-20 µM) also hyperpolarized a small fraction of neurons (6/79) and decreased the amplitude of EPSPs in 50% of neurons. In contrast, the delta-opioid receptor (DOR) agonist DPDPE (1-4 µM) had no presynaptic or postsynaptic effects upon NTS neurons even after pre-incubation with bradykinin. Anatomical data at the light and electron microscopic level complemented electrophysiological observations with respect to MOR location and further showed that MORs were present at both presynaptic and postsynaptic sites in the dorsolateral NTS, often at the same synapse. These data demonstrate site specific responses of neurons to activation of MORs and KORs, which may underlie their ability to modulate different autonomic reflexes.