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Short‐term sustained hypoxia affects synaptic transmission in the nucleus tractus solitarius neurons of juvenile rats

In the present study we evaluated the effects of a short‐term sustained hypoxia [(SH) 24 hours ‐ 10% O2] on intrinsic properties and synaptic transmission of nucleus tractus solitary (NTS) neurons of juvenile Wistar rats (P21). After 24 hours inside hypoxic or normoxic chambers rats were anesthetized, the brains removed and brainstems sliced. Intrinsic properties and excitatory currents of NTS neurons were recorded using whole‐cell patch clamp. SH did not change the resting membrane potential (control: −78.7 ± 2.4 mV n=15; SH: −72.3 ± 3.7 mV n=15), input resistance (control: 1.4 ± 0.4 G Ohm n=8; SH: 1.4 ± 0.4 G Ohm n=9) or capacitance of neurons (control: 14.2 ± 0.9 pF n=17; SH: 12.4 ± 0.8 pF n=15), indicating that SH does not change the intrinsic properties of NTS neurons. However, it was observed an increase in frequency of spontaneous currents (control: 3.6 ± 0.4 Hz n=18; SH: 7.1 ± 1.5 Hz n=15) and in peak amplitude of evoked currents (control: −289 ± 51 pA n=15; SH: −472 ± 64 pA n=15). Moreover, after a train of 5 stimuli, NTS neurons from SH group presented higher depression in glutamatergic events (relative amplitude of evoked currents; control: 100, 44, 34, 32 and 28%; SH: 100, 40, 28, 22 and 17%, *p<0.001, n=15), suggesting that SH affects the vesicular release probability. The data show that short‐term SH increases the spontaneous and evoked neurotransmitter release in the NTS neurons, which may explain, at least in part, the autonomic and respiratory changes observed in this experimental model.