The anti-emetic action of the neurokinin1 receptor antagonist CP-99,994 does not require the presence of the area postrema in the dog

Microinjection and ligand binding studies have implicated NK1 receptors in the area postrema (AP) in the emetic response to intragastric copper sulphate that is mediated by abdominal vagal afferents. Because these afferents terminate in the brainstem in the nucleus tractus solitarius in close proximity to the AP or in the AP itself, the results of such studies may be difficult to interpret. The present study has demonstrated in the dog that the emetic response to intragastric copper sulphate is unaffected by AP ablation, demonstrated functionally by absence of an emetic response to apomorphine (100 μg kg−1 i.v.). In AP ablated animals the selective NK1 receptor antagonist CP-99, 994 (1 mg kg−1 i.v.) blocked the emetic response to copper sulphate as it did in intact animals. The results demonstrate that the AP is not involved in the blockade of the emetic response to intragastric copper sulphate by an NK1 receptor antagonist and hence provides further support for other sites proposed such as the nucleus tractus solitarius and central pattern generator.