Chronic intermittent hypoxia induced increases in central angiotensin II release in the MnPO

The brain is sensitive to Angiotensin II (ANG II) and we have previously shown that ANG II is released by brain slices containing the median preoptic nucleus (MnPO) and subfornical organ (SFO) in an activity dependent manner. In addition, angiotensin II type 1 receptors and angiotensin converting enzyme 1 are upregulated in the MnPO following chronic intermittent hypoxia (CIH), an animal model of obstructive sleep apnea. Here, we investigate changes in ANG II release in the SFO to MnPO pathway following 7-day CIH treatment.Using isoflurane (2-3%) anesthesia, male Sprague-Dawley rats (250-350g) received microinfusions (0.4 μL) of AAV2-hSyn-ChR2(E123A)-eYFP-WPRE in the SFO. After recovery, rats were subjected to 7 days of CIH (0800-1600 hrs) or Normoxia. The CIH protocol 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 sniffer cell measurements, rats were anesthetized with isoflurane (2-3%) and sagittal slices (300 μm) containing the MnPO and SFO were cut using standard in vitro slice procedures. Sniffer cells consisted of Chinese Hamster Ovary cells transfected with a commercially available plasmid for the angiotensin type 1a (AT1a) receptor (Origene Tech.) and R-GECO (Addgene #32462) as previously described. Sniffer cells were placed on the median preoptic nucleus (MnPO) of sagittal in vitro brain slices. Both spontaneous and evoked (SFO stimulation) changes in fluorescent intensity of sniffer cells on the MnPO were measured.Sniffer cell recordings were made from 5 normoxia and 8 CIH treated rats. The frequency of spontaneous sniffer cell activity in slices from normoxic rats (n = 92) was comparable to rates previously reported in Sprague-Dawley rats. Spontaneous sniffer cell activity in slices from CIH treated rats (n = 156) was increased compared to normoxic treated rats (p < 0.05). Furthermore, bath application of TTX (1 uM) reduced, but did not abolish, spontaneous sniffer cell activity in slices from both normoxic (n = 95, p < 0.001) and CIH (n = 108, p < 0.001) treated rats. Incidence of optogenetic evoked responses in sniffer cells were limited in slices from both the normoxic and CIH treated rats and there were no differences detected in these evoked responses.The current study indicates that spontaneous ANG II release in the MnPO 1) is not entirely action potential dependent, 2) is enhanced following 7-days CIH treatment, and 3) the CIH induced increase is action potential dependent. While optogenetic stimulation of SFO increased sniffer cell activity, CIH had no effect evoked release of ANG II in these preliminary studies. Work supported by: P01 HL088052, R01 HL155977 This is the full abstract presented at the American Physiology Summit 2023 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.