Orexin activates neurons in the paraventricular nucleus of the hypothalamus

The paraventricular nucleus (PVN) of the hypothalamus is a critical site for cardiorespiratory homeostasis including reflex sympathetic and respiratory responses to hypoxia. Orexin (Ox)-producing neurons originating from the perifornical hypothalamus project to the PVN. Previous work from our group demonstrated that Ox neurons project to and facilitate the activation of PVN neurons in response to hypoxia. However, the cellular mechanisms underlying this effect are not clear. Our goal is to determine the extent that Ox increases PVN neuronal activity and identify the receptor and intracellular pathway(s) responsible. Neuronal activity was examined in PVN neurons from male 4-wk-old Sprague-Dawley rats via multi-electrode array in PVN slices or dissociated PVN neurons labeled with Fura-2 to measure intracellular Ca 2+ . After a 3-5 min baseline (Bsl) period, we applied vehicle or Ox (10 or 100 nM, 5 min). In PVN slices, application of Ox (100 nM, 5 min) increased extracellular discharge in the majority (60%) of neurons, and across all cells studied significantly elevated discharge. In dissociated neurons whose phenotype was confirmed by their response to high K, we analyzed Ca 2+ event amplitude and frequency relative to each cell's respective Bsl. Immunocytochemistry with a pan-neuronal antibody further confirmed recorded cells were neurons. Compared to the vehicle, 10 & 100 nM Ox significantly and reversibly increased Ca 2+ event amplitude but not frequency. Repetitive application of 100 nM Ox consistently increased intracellular Ca 2+ . Ox receptor 1 and 2 blockade with suvorexant (10 uM) significantly attenuated the elevation of Ca 2+ in response to Ox alone. Overall, our findings suggest that Ox excites PVN neurons to potentially modulate cardiorespiratory responses to hypoxia. R01 HL098602 This abstract was presented at the American Physiology Summit 2025 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.