Objective: To explore the impact of intermittent hypoxia on long-term facilitation (LTF) of hypoglossal nerve discharge.
Methods: Twelve adult SD rats were divided into the experimental group (CIH group, n = 6) and the control group (normoxia group, n = 6) by the random number table. The rats in the CIH group were fed in the intermittent hypoxia animal chambers, while the control group was placed in the normoxia animal chambers for 8 h per day (from 8:00 AM to 4:00 PM) for 4 consecutive weeks. After that, 5 min×3 stimulations of acute intermittent hypoxia (AIH) were administered and the hypoglossal never signals were recorded before and after AIH.
Results: The baseline frequency and average peak amplitude of hypoglossal nerve discharge in the CIH experimental group were significantly greater than those in the control group. The discharge frequency in the CIH and the control groups was (73 ± 13) Hz, and (58 ± 11) Hz, respectively(P < 0.05); and the discharge amplitude in the 2 groups was (4.6 ± 1.1) µV, and (3.3 ± 0.7) µV, respectively(P < 0.05). After intervention with AIH, the frequency and the average peak amplitude of the hypoglossal nerve discharge in the experimental and the control groups were significantly increased(all P < 0.05). The increased discharge lasted more than 1 h and this typical phenomenon was referred to as LTF. In the CIH group, the discharge frequency before and after exposure to AIH was (68 ± 16) Hz and (133 ± 20) Hz, respectively; and the discharge amplitude was (4.6 ± 1.1) µV and (8.9 ± 1.4) µV, respectively. In the control group, the discharge frequency before and after AIH was (59 ± 12) Hz and (102 ± 16) Hz, respectively; and the discharge amplitude was (3.3 ± 0.7) µV and (4.5 ± 0.7) µV, respectively(P < 0.05). After AIH stimulation, the enhanced respiratory intensity of rats in CIH group was much higher than that in the control group [(408 ± 149)% vs (242 ± 31)%, P < 0.05].
Conclusion: Both AIH and CIH can induce LTF of the hypoglossal nerve discharge, while the induction of LTF by AIH can be strengthened by CIH.