Electrical responses to chemosensory stimulation recorded from the vomeronasal duct and the respiratory epithelium in humans

The physiological significance of the human vomeronasal duct (VND) is still unclear. The aim of the present study was to investigate the question whether mucosal responses obtained from the VND are different from those obtained from the respiratory epithelium. There were 15 healthy subjects (8 male, 7 female; age range 19–45 years; 14 normosmic subjects, 1 anosmic subject). All subjects participated in two sessions whereby the first session was used to acquaint them with the experimental conditions. For chemical stimulation, an olfactometer was used which delivered chemical stimulants without altering mechanical or thermal conditions at the stimulated nasal mucosa. For stimulation we used substances previously reported to produce vomeronasal activation (“estra” = estra-1,3,5(10),16-tetraen-3ol and “andro” = androsta-4,16-dien-3-on); in addition, gaseous CO2 was used as a non-odorous, relatively specific stimulant of the trigeminal nerve. Placement of electrodes either in the VND or on the respiratory epithelium was performed under endoscopical guidance. Subjects rated the overall intensity of the stimuli, the strength of trigeminally mediated sensations, and the hedonic tone of the stimulants. Responses could not be recorded from all subjects. For the remaining 7 subjects, intensity was strongest for CO2 stimuli (p < 0.001), whereas no significant difference was observed between “andro” and “estra” (p = 0.33). All three stimulants produced responses at the respiratory epithelium with largest responses obtained after stimulation with CO2. Similar findings were made for recordings inside the VND. Due to the small sample size sexual dimorphisms could not be addressed. In summary, these results seem to indicate that the presently used stimulants produce similar responses at the respiratory epithelium and in the VND which argues against a specific responsiveness of the VND epithelium to chemosensory stimuli although it has to be kept in mind that the effective sample size was small.

Research Highlights
► The current study directly re-investigates results from previous research.
► Stimulants produce similar responses at the respiratory epithelium and in the VND.
► Findings argue against specific responsiveness of the VND to chemosensory stimuli.