Ablation of the area postrema and emesis.

The emetic action of dopamine, norepinephrine, epinephrine, nicotine, dimethylphenyl-piperazinium (DMPP), and 4-m-chlorophenylcarbamoyloxy-2-butynyltrimethylammonium (McN-A-343) injected intracerebroventricularly (i.c.v.) to the unanesthetized cat was investigated and compared. ED50 values (mg) were as follows: nicotine, 0.011; epinephrine, 0.047; norepinephrine, 0.57; DMPP, 0.9; dopamine, 1.66; and McN-A-343, 4.42. The most potent was nicotine, whereas the least active McN-A-343. On the other hand, DMPP produced the longest emetic response, about 30 min, while McN-A-343-induced emesis lasted up to 1 min. The ablation of the area postrema abolished the emetic response to i.c.v. dopamine, norepinephrine, epinephrine, nicotine, and DMPP. However, the emetic response to i.c.v. McN-A-343 was significantly reduced in cats with an ablated area postrema. Taken together, the results obtained show that the area postrema is almost always involved in the central regulation of emesis and that the area postrema represents, in most cats, a common site of confluence of different inputs subserving the emesis.