Nasal Trigeminal Chemoreception: Responses to N-aliphatic Alcohols

Odorant molecules can stimulate nasal trigeminal receptors, but the properties of such molecules which make them effective stimuli are largely unknown. In the present study, we obtained integrated multiunit responses from the ethmoid branch of the rat trigeminal nerve to a homologous series of aliphatic alcohols. Our aim was to determine whether lipid solubility might correlate with stimulus efficacy. Response thresholds (ranging from 3000 ppm for methanol to 3 ppm for octanol) decreased with increasing carbon chain length, suggesting that lipid solubility is important for stimulus effectiveness. One plausible explanation for the importance of lipophilicity is that the more lipid soluble a substance, the more easily it can penetrate epithelial layers to reach chemoreceptive trigeminal nerve endings. Since all stimuli at vapor saturation elicited responses within 0.5 s, and because diffusion of stimulus molecules through epithelium is slow, we speculate that trigeminal nerve endings lie closer to the epithelial surface than previously thought.