The electrophysiological properties of nicotinic ACh receptors (nAChR) were investigated in acutely dissociated area postrema (AP) neurons of the immature rat brain using the whole-cell patch-clamp recording method. ACh induced a transient inward current exhibiting a strong inward rectification. The ACh response was mimicked by nicotine and cytisine, and was inhibited by nAChR antagonists, but not by 10(-7) M atropine. Muscarinic AChR agonists did not induce any current. We confirmed the Ca2+ permeability of nAChR. These results indicate the presence of nAChR on AP neurons, and suggest that the activation of nAChR play important roles in cardiovascular functions in rats.