Action potential amplitude and baroreflex resetting of action potential clusters mediate hypoxia‐induced sympathetic long‐term facilitation

Abstract

Columbia Okanagan in Canada and is mentored by Dr Glen Foster. She is currently investigating neurovascular reflex regulation of arterial blood pressure in response to homeostatic disturbances in oxygen tension. In the future, she aims to continue her research on sympathetic discharge properties and blood pressure governing mechanisms, particularly as it pertains to hypertension development in patients with obstructive sleep apnoea.

Acute hypoxia elicits lasting reductions in the sympathetic action potential transduction of arterial blood pressure in males

“…Average values presented in the current study in Table 1 are similar but do not duplicate those reported previously (Shafer et al., 2022), due to differences in sample size and the longer analysis periods (7 min vs . 5 min in Shafer et al., 2022) required to investigate the effects of sympathetic AP activity on sympathetic transduction of MAP. Written informed consent was obtained from all participants.…”

“…Hypoxia‐induced chemoreflex activation elicits an increase in sympathetic outflow to the skeletal muscle vasculature, which remains elevated even when blood gases return to normal (Foster et al., 2010; Jouett et al., 2017; Ott et al., 2020; Querido et al., 2010, 2011; Shafer et al., 2021, 2022; Steele, Skow et al., 2021; Stuckless et al., 2020; Vermeulen et al., 2020; Xie et al., 2001). Sympathoexcitation during and following hypoxia appears to be mediated by a resetting of the baroreflex to higher operating points (Cooper et al., 2005; Halliwill et al., 2003; Querido et al., 2011; Shafer et al., 2022; Tremblay et al., 2016). Interestingly, parallel changes in vascular resistance are not observed (Morgan et al., 1995; Steele, Skow, et al., 2021; Tamisier et al., 2004), suggesting that the transduction of sympathetic activity may be attenuated during room air recovery.…”

“…Bursts of muscle sympathetic nerve activity (MSNA) are generated by the synchronous firing of varying‐amplitude sympathetic action potentials (APs) (Shoemaker et al., 2018), which can be detected and extracted from the multi‐unit MSNA recordings using wavelet‐based approaches (Salmanpour et al., 2010; Shafer et al., 2022). Examining sympathetic AP activity has provided significant insight into neuronal coding and neural recruitment strategies during reflex stimulation.…”

“…For example, sympathetic activation to physiological stressors appears to be mediated by neural recruitment of previously latent, larger‐diameter sympathetic axons and arterial baroreflex resetting to permit an increased firing frequency of medium‐sized AP subpopulations (Badrov et al., 2015; Klassen et al., 2019, 2020; Ott et al., 2019, 2020; Salmanpour et al., 2011; Steinback et al., 2010). Moreover, a subpopulation of non‐burst‐forming APs exhibiting asynchronous discharge activity between pulse‐synchronous bursts has been identified during periods previously considered ‘neurally silent’ (Klassen et al., 2019; Shafer et al., 2022). Indeed, our group has demonstrated that sympathetic long‐term facilitation following an acute bout of isocapnic hypoxia is mediated by baroreflex resetting of sympathetic AP clusters to higher operating points, a reduction in the percentage of APs firing asynchronously, and a shift toward larger amplitude AP activity (Shafer et al., 2022).…”

“…Moreover, a subpopulation of non‐burst‐forming APs exhibiting asynchronous discharge activity between pulse‐synchronous bursts has been identified during periods previously considered ‘neurally silent’ (Klassen et al., 2019; Shafer et al., 2022). Indeed, our group has demonstrated that sympathetic long‐term facilitation following an acute bout of isocapnic hypoxia is mediated by baroreflex resetting of sympathetic AP clusters to higher operating points, a reduction in the percentage of APs firing asynchronously, and a shift toward larger amplitude AP activity (Shafer et al., 2022).…”