Exposure to a 10% hypoxia challenge and vagus nerve stimulation (20Hz, 20mA) increased calcium activity in nTS-CRH terminals, correlating with changes in mean arterial pressure and heart rate.
In vivo imaging demonstrates that CRH-positive inputs in the nTS are actively involved during both systemic hypoxia and vagal afferent stimulation, correlating with changes in cardiorespiratory parameters.
Peripheral cardiorespiratory reflexes in response to hypoxia are processed and integrated in the nucleus tractus solitarii (nTS). We and others have previously shown that CRH inputs into the nTS are critical in modulating nTS synaptic and neuronal activity in normoxia and during hypoxia bouts, as well as cardiovascular function. However, the in vivo activation of these CRH fibers within the nTS in coordination with reflex -mediated alterations of cardiorespiratory parameters is unknown. We hypothesize that CRH fibers will increase activity during hypoxia. To evaluate circuit dynamics in vivo, we crossed CRH-Cre mice (B6(Cg)-Crhtm1(cre)Zjh/J) with a Cre-dependent GCaMP (B6J.Cg-Gt(ROSA)26Sortm95.1(CAG-GCaMP6f)Hze/MwarJ) reporter line to globally express GCaMP in all CRH neurons in the brain. Mice were instrumented with a femoral arterial catheter to monitor blood pressure and diaphragmatic electrodes for respiratory EMG recording. Furthermore, a bipolar electrode was implanted on the cervical vagus nerve to evaluate visceral afferent integration in the nTS. The dorsal brainstem was exposed, and a fiber optic probe was positioned over the nTS to record calcium activity specifically from CRH-putative fibers and terminals via fiber photometry. When exposed to a 10% hypoxia challenge (40 sec), mice exhibited a transient increase in mean arterial pressure (MAP) that correlated with a persistent increase in calcium activity in the nTS-CRH terminals. Electrical stimulation of the vagus nerve (20Hz, 20mA) caused a biphasic response during the stimulation; an initial increase in CRH fiber calcium activity at the beginning of the stimulation, followed by a decrease at the end. The decrease occurred alongside a reduction in MAP, HR, and respiratory frequency. Overall, these data indicate that CRH-positive inputs in the nTS are actively involved during both systemic hypoxia and vagal afferent stimulation. Further research is needed to clarify their specific roles in influencing MAP, HR, and respiration, and to better understand their functions within the nTS circuitry. 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.
Filho et al. (Fri,) conducted a other in Cardiorespiratory reflexes. Hypoxia challenge and vagus nerve stimulation was evaluated on Calcium activity in nTS-CRH terminals and cardiorespiratory parameters. Exposure to a 10% hypoxia challenge and vagus nerve stimulation (20Hz, 20mA) increased calcium activity in nTS-CRH terminals, correlating with changes in mean arterial pressure and heart rate.