Modulation by Astrocytes of AMPA Currents in the NTS Neurons of Mice Is Reduced by Short Term-Sustained Hypoxia

Abstract

Hypoxia due to reduction in the partial pressure of oxygen in the arterial blood (PaO2) activates the afferents of peripheral chemoreflex to produce cardiovascular and respiratory adjustments to bring PaO2 back to the normal range. Herein we evaluated the possible changes of astrocytic modulation on glutamatergic transmission in NTS neurons of mice submitted to short term-sustained hypoxia (SH). To reach this goal, we used Male C57Bl/6J mice (18-20g), which were submitted to SH (FiO2 0.1) or normoxia for 24 hours. Brainstem slices and whole-cell patch clamp technique were used to evaluate the synaptic transmission in NTS neurons. The intracellular calcium concentration in NTS astrocytes was evaluated by multiphoton microscopy and transgenic Aldh-CRE-GCAMP6f mice (Institutional Ethical Committee Approvals: #016/2018 and #1109/2022R1). SH increased the amplitude of TS-evoked AMPA currents [control: -72.8 ± 13.3 pA ( n = 12) vs SH: -120 ± 14.4 pA ( n = 21)] in NTS neurons with no changes on the rise- or decay-time. SH also increased the amplitude [control: 35.88 ± 7.9 pA ( n = 12) vs SH: 72.74 ± 15.47 pA ( n = 10)] and decay time [control: 61.8 ± 15.2 ms ( n = 9) vs SH: 286 ± 86.7 ms ( n = 10)] of TS evoked-NMDA currents in neurons, while the amplitude of extrasynaptic NMDA currents [control: 28.7 ± 7.4 pA ( n = 10) vs SH: 24.7 ± 3.2 pA ( n = 7)] was not affected. Perfusion with fluoracetate (FAC), a glial metabolism inhibitor, decreased the amplitude of TS-evoked AMPA currents in control group [aCSF: -54.29 ± 16.1 pA vs aCSF + FAC: -24.43 ± 6.82 pA ( n =9)] without affecting AMPA currents in SH neurons [aCSF: -124.5 ± 35.27 pA vs aCSF + FAC: -130.5 ± 50.16 pA ( n =8)]. The passive properties of astrocytes did not change after SH [RMP: -83.73 ± 11.85 mV ( n =10) vs −83.63 ± 11.86 mV ( n =10); Rinput: 123 ± 127.5 MΩ ( n =9) vs 208 ± 212.7 MΩ ( n =10)]. The increase in intracellular calcium concentration induced by AMPA in the astrocytes of control and SH mice was similar [Control: 112.8 ± 15.41 ΔF/F0 (n=68 ROIs) vs SH: 56.38 ± 18.31 ΔF/F0 (n=13 ROIs)]. The data shows that SH increased the evoked glutamatergic currents in NTS neurons of mice, probably due to a reduction in the astrocytic modulation of excitatory transmission by mechanisms apparently independent of astrocytic intracellular calcium. FAPESP (2018/15957-2, 2018/02336-0 and 2022/05237-8), CNPq (309338/2020-4) and CAPES-PROEX (23038.006922/2021-31). 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.