<prompt> The H3 receptor agonist exhibits all of the following actions exceptInhibition of H1 receptors induced wakefulnessIncrease in H1 mediated gastric secretionInhibition of H1 mediated bronchoconstrictionNegative chronotropic effect on atria  <response>: H3 receptors act as presynaptic receptors and decrease the release of histamine and other neurotransmitters. this antagonize H1 mediated wakefulness and bronchoconstriction. these also decrease gastrin release and produced negative chronotropic effect inverse agonist and H3 receptortiprolisant is proved for narcolepsy. Refer KDT 6e p153 