An autumn-enhanced mucotropic action of inhaled terpenes and related volatile agents

Odorant stimulation of secretory and neural processes in the salamander olfactory mucosa

Topical application of the odorants guaiacol (10(-3) mol/l, 1-30 min) and 2-isobutyl-3-methoxypyrazine (IBMP, 10(-5)-10(-3) mol/l, 15 min) caused time- and concentration-dependent reductions in the secretory granule content of acinar cells of the superficial Bowman's glands (sBG) and moderate to extensive vacuolation in acinar cells of sBG and deep olfactory glands (dG). Topical application of 9.8 mg/ml scopolamine 10 min before 10(-4) mol/l IBMP significantly reduced the amount of secretory granule depletion from sBG compared to that seen with IBMP alone and resulted in less extensive vacuolation in sBG and dG acinar cells. The i.p. injection of 42 mg/kg propranolol 10 min before topical application of 10(-4) mol/l IBMP had no effect on the action of IBMP. Guaiacol and IBMP also had time- and concentration-dependent effects on the secretory activity of sustentacular cells in the olfactory epithelium. The protrusion of secretory material into the mucociliary matrix that covers the epithelial surface and vacuolation within the secretory material resulted from odorant application. Scopolamine and propranolol had no effects on the action of IBMP on sustentacular cell secretory activity. When applied in the vapor phase, guaiacol elicited action potentials recorded from individual olfactory receptor neurons; the impulse frequency was concentration-dependent and showed tonic and phasic components when the duration of stimulation was varied. Low to moderate concentrations of IBMP delivered in the vapor phase evoked monophasic negative slow voltage transients recorded from the surface of the olfactory mucosa. The amplitudes of these transients increased with increasing stimulus concentrations. Higher concentrations or longer stimulus durations evoked longer-latency positive-voltage generating processes and negative afterpotentials. The properties of the electrophysiological responses to both odorants were characteristic of responses evoked by a wide variety of 'typical' odorants.