<Ul> <Li> Levocetirizine </Li> </Ul> <Li> Desloratadine (does not cross the blood--brain barrier) </Li> <Li> Pyrilamine (crosses the blood--brain barrier; produces drowsiness) </Li> <P> H - antihistamines, like H - antihistamines, occur as inverse agonists and neutral antagonists . They act on H histamine receptors found mainly in the parietal cells of the gastric mucosa, which are part of the endogenous signaling pathway for gastric acid secretion . Normally, histamine acts on H to stimulate acid secretion; drugs that inhibit H signaling thus reduce the secretion of gastric acid . </P>

Which of the following is not a target of histamine