The H3 receptor agonist exhibits all   of the following actions EXCEPT: (A) Inhibition of H1receptor induced wakefulness, (B) Increase in H1 mediated gastrin secretion, (C) Inhibition of H1 mediated bronchoconstriction, (D) Negative chronotropic effect on atria
Answer is B. H3 receptors act as pre-synaptic receptors and decrease the release of histamine and other neurotransmitters. These antagonize H1 mediated wakefulness and bronchoconstriction. These also decrease gastrin release and produce negative chronotropic effect. Inverse agonist of H3 receptor (tiprolisant) is approved for Narcolepsy.