Responses to the activation of different intranasal trigeminal receptors: Evidence from behavioral, peripheral and central levels.

AIM

There are various receptors that mediate intranasal trigeminal sensations. However, few studies compare the response patterns across different receptor activations.

METHODS

We recorded negative mucosal potentials (NMPs) in 24 healthy participants and event-related potentials (ERPs) in 17 participants during exposure to five odors that trigger trigeminal sensations and one olfactory stimulus. Additionally, 10 participants completed a continuous odor intensity rating task.

RESULTS

We observed a significant effect of odor type on NMP amplitudes (F=13.51-21.88, p's < 0.01), with cyclohexanone (TRPV1) and CO2 (TRPV1 +A1) inducing greater N1 and/or P1N1 amplitudes than other stimuli (t = 3.28-7.54, p's < 0.05). Similar differences were seen in ERP amplitudes (F=3.69-12.25, p's < 0.05), with cyclohexanone showing greater P2 and/or N1P2 amplitudes than PEA (odorant), carvacrol (TRPV3 +A1), and perillaldehyde (TRPA1) (t = 3.13-4.10, p's < 0.05). CO2 also produced greater amplitudes than carvacrol (t = 3.53-4.42, p's < 0.05). In the odor intensity rating task, cyclohexanone, CO2, and isopulegol (TRPM8 +TRPA1) had higher peak ratings, steeper slopes, and/or shorter latencies (F=6.15-13.86, p's < 0.01; t = 3.14-7.76, p's < 0.05).

CONCLUSIONS

Activation of different intranasal trigeminal receptors yields varied responses. Notably, stimuli involving TRPV1 activation, linked to irritation or pain, elicited stronger behavioral and neural activity compared to stimuli involving other receptors, even when controlling for rated stimulus intensity. This emphasizes TRPV1's significance in survival adaptation. Future studies should test different sets of stimulants to verify the robustness of these findings.