Chronic Intermittent Hypoxia Alters GABAergic Inhibition in Median Preoptic Nucleus (MnPO) Neurons of Rats

Abstract

Chronic intermittent hypoxia (CIH) is an animal model simulating the hypoxemia associated with obstructive sleep apnea (OSA) in humans. Male rats exposed to CIH exhibit increased sympathetic tone and persistent elevations in blood pressure similar to that observed in patients with. In MnPO neurons, CIH reduces GABAa inhibition and, in some neurons, GABAa activation produces excitation. Here, loose patch and perforated patch recordings were conducted in MnPO neurons in response to optogenetic stimulation of GABAergic SFO (efferent) and MnPO (local) neurons to assess the role of GABAergic signaling in these nuclei on MnPO excitability. Our working hypothesis was that CIH would diminish the inhibitory effects of optogenetic stimulation of GABA neurons. This hypothesis was tested using an AAV vector that selectively expresses channel rhodopsin in GABA neurons Using isoflurane (2-3%) anesthesia, male Sprague-Dawley rats (250-350g) received infusions (0.2 μL) of pAAV-mDlx-ChR2-mCherry-Fishell-3 in the SFO or MnPO. After recovery, rats were subjected to 7 days of CIH (0800-1600 hr) or normoxia (Norm). CIH consisted of 6 min cycles (3 min 21% O2, 3 min 10% O2) repeated 10x/hr for 8 hours (during the normal inactive/sleep phase) on 7 consecutive days. For in vitro recordings, rats were anesthetized with isoflurane (2-3%), and sagittal or coronal slices (300 μm) containing MnPO were cut using standard slice procedures. Voltage-clamp loose patch or perforated patch recordings using gramicidin (100 ug/ml in 140 mM K-gluconate) were collected in MnPO neurons in response to optogenetic stimulation of GABAergic neurons (2 ms pulse, 20 Hz, 1 sec). MnPO neurons from CIH-treated rats showed differing responses to GABAergic stimulation while MnPO neurons from Norm-treated rats predominantly exhibited GABAergic inhibition. MnPO neurons from Norm rats exhibited mIPSCs and outward currents in response to muscimol. MnPO neurons from CIH-treated rats show variable mIPSC frequencies and heterogeneous responses to GABAergic neuronal activation in the SFO and MnPO. The results demonstrate that CIH alters the Cl− homeostasis in some MnPO neurons altering their response to GABAa stimulation. These changes may contribute to the increased sympathetic tone and reactivity, as well as the persistent hypertension associated with CIH. Supported by R01 HL155977. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.