Antigen depolarizes guinea pig bronchial parasympathetic ganglion neurons by activation of histamine H₁ receptors

Studies were carried out to evaluate the mechanism by which neurotransmission through airway parasympathetic ganglia may be modulated during immediate hypersensitivity reactions. Guinea pigs were passively sensitized by injection of guinea pig serum containing high-titer anti- ovalbumin antibodies. Intracellular recordings were obtained from intrinsic parasympathetic ganglion neurons from the right mainstem bronchus in vitro. Ovalbumin (10 μg/ml) elicited a membrane potential depolarization and changes in membrane resistance in bronchial ganglion neurons from passively sensitized guinea pigs. Histamine mimicked the depolarizing effect of ovalbumin in a concentration-dependent manner (0.1-10 μM) and caused a transient increase and decrease in membrane resistance. Pyrilamine, a histamine H₁-receptor antagonist, inhibited the histamine-induced membrane depolarization and decrease in resistance. By contrast, blocking histamine H₂ and H₃ receptors did not inhibit histamine-induced depolarization. Pyrilamine also reduced the antigen-induced depolarization of ganglion neurons, demonstrating a role for histamine H₁ receptors in this response. The data provide evidence that the antigen-induced depolarization of airway ganglion neurons is secondary to an antigen-antibody interaction on intrinsic mast cells and the consequential effect of histamine on H₁ receptors. These studies demonstrate that histamine released during an immediate hypersensitivity reaction has direct effects on airway parasympathetic nerves.