Trigeminal nerve stimulation via facial ice pack application decreased the proportion of asynchronous sympathetic action potentials compared to baseline (9% vs 25%, P<0.01).
Observational (n=16)
Does trigeminal nerve stimulation augment muscle sympathetic nerve activity by synchronizing previously asynchronous action potentials in healthy adults?
Acute cold exposure via trigeminal nerve stimulation increases muscle sympathetic nerve activity by synchronizing previously asynchronous action potentials into bursts.
Absolute Event Rate: 9% vs 25%
p-value: p=<0.01
During acute cold exposure, trigeminal reflex activation increases muscle sympathetic nerve activity (MSNA) to support human circulatory homeostasis. However, the precise neural strategies underpinning trigeminal reflex-mediated rises in MSNA remain unclear. Therefore, this study tested the hypothesis that trigeminal nerve stimulation (TGS) augments MSNA by synchronizing previously asynchronous action potentials (APs) into bursts of MSNA. Also, we explored the contribution of baroreflex mechanisms to alterations in AP synchronicity. In sixteen healthy adults (22 ± 2y; 4 females), we measured muscle sympathetic AP discharge (peroneal microneurography; continuous wavelet transform) and diastolic blood pressure (DBP; Finometer) during 5 minutes of supine baseline (BSL) rest and 3 minutes of TGS (0°C ice pack applied to the face). Sympathetic APs were quantified as either synchronous (coinciding with integrated MSNA bursts) or asynchronous (discharging between integrated MSNA bursts). Sympathetic AP baroreflex threshold gain was quantified as the linear relationship between AP probability and DBP. Sympathetic AP baroreflex sensitivity was measured as the slope of the linear relationship between AP clusters per burst and DBP. One-way mixed-effects analyses of variance and Holm-Šídák post-hoc tests were performed. Data (mean ± SD) are reported for BSL, the first half of TGS (TGS-First) and the second half of TGS (TGS-Second). Compared to BSL (75 ± 6 mmHg), DBP increased during TGS-First (89 ± 10 mmHg, P < 0.01) and TGS-Second (89 ± 7 mmHg, P < 0.01). Compared to BSL (4.6 ± 1.5 clusters/burst), AP clusters/burst increased during TGS-First (6.1 ± 2.0 clusters/burst, P < 0.01) and TGS-Second (5.2 ± 1.2 clusters/burst, P = 0.03). Compared to BSL (e.g., cluster 3: 64 ± 44 %), AP firing probability increased for medium-sized APs during TGS-First (e.g., cluster 3: 127 ± 71 %, P < 0.01) and trended towards an increase during TGS-Second (cluster 3: 79 ± 32 %, P = 0.052). Compared to BSL (25 ± 7 %), the proportion of asynchronous APs decreased during TGS-First (9 ± 4 %, P < 0.01) and TGS-Second (13 ± 6 %, P < 0.01), suggesting greater AP synchronicity. Compared to BSL (e.g., cluster 3: -7.2 ± 4.6 %/mmHg), baroreflex threshold slopes for medium-sized APs decreased during TGS-First (e.g., cluster 3: -3.4 ± 4.3 %/mmHg, P = 0.01), but not TGS-Second (e.g., cluster 3: -8.2 ± 5.0 %/mmHg, P = 0.23). Compared to BSL (-0.07 ± 0.08 AP clusters/burst/mmHg), AP baroreflex sensitivity slope decreased during TGS-First (0.01 ± 0.04 AP clusters/burst/mmHg, P = 0.01), but not TGS-Second (-0.07 ± 0.10 AP clusters/burst/mmHg, P = 0.85). These data suggest that at the onset of TGS the sympathetic nervous system synchronizes previously asynchronous APs into bursts to support rises in MSNA. Also, these data support the hypothesis that AP synchronicity may be regulated by central non-baroreflex mechanisms and/or a distinct yet unexplored baroreflex synchronization mechanism. This work was supported by the Natural Sciences and Engineering Research Council of Canada, Ontario Graduate Scholarship (OGS), and Queen Elizabeth II (QEII) Scholarship. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Lynn et al. (2026) conducted an observational in Healthy adults (n=16). Trigeminal nerve stimulation (0°C ice pack to face) vs. Supine baseline rest was evaluated on Proportion of asynchronous sympathetic action potentials (p=<0.01). Trigeminal nerve stimulation via facial ice pack application decreased the proportion of asynchronous sympathetic action potentials compared to baseline (9% vs 25%, P<0.01).