Riluzole disrupts respiratory rhythm generation in neonatal mice

Leanne McKay1,2, Carine Vias2, Valerie Mezieres2, Gilles Fortin2, Jean Champagnat2. 1University of Glasgow, Glasgow, United Kingdom, 2CNRS, Gif-Sur-Yvette, France.

At birth, the mammalian respiratory system is immature. In mice, breathing pattern is fragile and highly variable during postnatal days 1-3 (P1-3). Around P3, the respiratory system undergoes a step in maturity when breathing becomes less variable and increases in frequency. The neural mechanisms underlying this maturity step are unknown. There is emerging evidence that two distinct brainstem oscillators (preBötC and RTN/pFRG) play a critical role in generating respiratory rhythm but little is known of the interaction between these oscillators during development and early postnatal life when the respiratory system is fragile. Riluzole, a blocker of persistent sodium currents, has been shown to perturb pacemaker properties of neurons within the respiratory system. To investigate the effects of riluzole on neonatal breathing patterns in-vivo we subcutaneously injected neonatal swiss mice (P0-P14) with riluzole (10mg/kg) or physiological saline as control. The animals were continuously monitored post injection and breathing was recorded by closed plethysmography at regular intervals from 5 minutes post injection to 2 hours post injection. At each time point, box temperature, animal temperature, movement, time to upright and mastication were recorded. Pups treated with riluzole at P0-P3, exhibited an increased variability in breathing pattern, characterized by either a decrease in respiratory frequency or an increase in the number of apneas or hyperpneas, compared to pups injected with saline. From P3-P5, riluzole either increased breathing pattern variability or had no effect, compared to saline injected animals. From P5 onwards, riluzole had no effect on breathing pattern compared to saline injected pups. The breathing pattern after riluzole injection in the P0-P3 mice was reminiscent of the Krox20-/- mutant respiratory phenotype. Krox20-/- mutants have brainstem anatomical malformations that may include elimination of the RTN/pFRG but not the preBötC. These malformations lead to a life threatening phenotype of apnoeic breathing. This suggests that the RTN/pFRG may have a necessary role in the respiratory system immediately after birth and that it could be a target of riluzole during P0-P3.