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Effect of inspired oxygen on periodic breathing in methy-CpG-binding protein 2 (Mecp2) deficient mice

¹Department of Obstetrics and Gynecology and ²Department of Cell and Development Biology, Oregon Health and Sciences University, Portland, Oregon

Submitted 6 August 2007 ; accepted in final form 12 November 2007

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the X-linked gene methyl-CpG-binding protein 2 (Mecp2) that encodes a DNA binding protein involved in gene silencing. Periodic breathing (Cheyne-Stokes respiration) is commonly seen in RTT. Freely moving mice were studied with continuous recording of pleural pressure by telemetry. Episodes of periodic breathing in heterozygous Mecp2 deficient (Mecp2^+/–) female mice (9.4 ± 2.2 h^–1) exceeded those in wild-type (Mecp2^+/+) animals (2.5 ± 0.4 h^–1) (P = 0.010). Exposing Mecp2^+/– animals to 40% oxygen increased the amount of periodic breathing from 118 ± 25 s/30 min in air to 242 ± 57 s/30 min (P = 0.001), and 12% oxygen tended to decrease it (67 ± 29 s/30 min, P = 0.14). Relative hyperoxia and hypoxia did not affect the incidence of periodic breathing in Mecp2^+/+ animals. The ventilation/apnea ratio (V/A) was less at all levels of oxygen in heterozygous Mecp2^+/– females compare with wild type (P = 0.003 to P < 0.001), indicating that their loop gain is larger. V/A in Mecp2^+/– fell from 2.42 ± 0.18 in normoxia to 1.82 ± 0.17 in hyperoxia (P = 0.05) indicating an increase in loop gain with increased oxygen. Hyperoxia did not affect V/A in Mecp2^+/+ mice (3.73 ± 0.28 vs. 3.5 ± 0.28). These results show that periodic breathing in this mouse model of RTT is not dependent on enhanced peripheral chemoreceptor oxygen sensitivity. Rather, the breathing instability is of central origin.

control of respiration; Rett syndrome

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