Self- and cross-adaptation to chemical stimulation of the nasal trigeminal nerve in the rat

Electrophysiological, multi-unit responses from the ethmoid branch of the trigeminal nerve to chemical stimuli (amyl acetate, d-carvone, l-carvone, l-menthol and toluene) were examined, using self- and cross-adaptation paradigms, to address the question of whether different chemical stimuli may stimulate trigeminal nerve fibers using different ‘receptive pathways’ and thus to suggest whether qualitative distinctions between different compounds may be made by trigeminal chemoreceptors. No adaptation occurred between l-menthol and toluene, suggesting that these two compounds activate different receptive pathways in the trigeminal nerve which may be capable of making qualitative discriminations between these two compounds. Symmetrical adaptation occurred between amyl acetate and d-carvone, amyl acetate and l-carvone, amyl acetate and toluene, and l-carvone and d-carvone suggesting that these compounds may activate the same receptive pathways in the trigeminal nerve which may not be capable of making qualitative discriminations between these compounds. Asymmetrical adaptation occurred between amyl acetate and l-menthol, d-carvone and l-menthol, l-carvone and l-menthol, d-carvone and toluene, and l-carvone and toluene. This implies that the processing of these stimuli by trigeminal nerve fibers may be more complex than anticipated previously.