Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC122
Insufficient GABA transmission in the K
A. P. Abdala1, M. Dutschmann2, J. M. Bissonnette3, J. Paton1
1. University of Bristol, Bristol, United Kingdom. 2. University of Leeds, Leeds, United Kingdom. 3. Oregon Health and Science University, Portland, Oregon, United States.
Rett syndrome (RTT) is an autistic spectrum disorder caused by mutations in the X-linked gene that encodes the transcription factor methyl-CpG-binding protein 2 (Mecp2). It features respiratory disorders with frequent apnoeas and periodic breathing (Weese-Meyer et al. 2006). The respiratory arrhythmia was successfully reproduced in heterozygous female mice (Mecp2+/-) with deletion of the 3rd and 4th exons (Bissonnette and Knopp, 2008). We demonstrated that augmenting endogenous GABA in the brainstem of Mecp2+/- females markedly reduces apnoeas (Abdala et al. 2010), but the mechanisms have not been fully determined. Since null male mice have prolonged post-inspiratory neuronal activity during apnoeas (Abdala et al. 2010; Stettner et al. 2007), we hypothesized that insufficient GABAA inhibition in the Kölliker-Fuse (KF) nucleus, a key control region of post-inspiratory (post-I) phase duration, underlies these respiratory disorders. All procedures conformed to the UK Home Office guidelines on animals (Scientific Procedures) Act 1986 and were approved by the University of Bristol’s Animal Ethic Committee. Heterozygous females (Mecp2+/-) (n=5) were deeply anaesthetized with 5% halothane and decerebrated. We used an in situ arterially perfused preparation to record phrenic, central vagal (for measurement of post-I) and hypoglossal nerve activity (Paton, 1996). We used a three-barrelled microinjection pipette (<20 µm o.d.) containing glutamate, NO-711 (a GABA reuptake blocker) or fluorescent beads diluted in aCSF in each barrel. Glutamate microinjections helped functional location of the KF nucleus prior to drug injections. Sites were marked with fluorescent beads. In the MeCP2-/+ mice NO-711 (10mM, 60 nl, unilateral) microinjection into KF nucleus decreased the duration of post-I activity to 57±8% (mean±SEM, t test, P<0.05) of the pre-injection level. In addition, NO-711 reduced the coefficient of variability for post-I from 0.82±0.1 to 0.46±0.05 (P=0.02, ANOVA), which was similar to WT (0.39±0.06, P=0.76). Post hoc analysis confirmed that effective injection sites were centred within the KF nucleus; those found outside the KF nucleus were ineffective. These results indicate that the KF nucleus is an essential component for generating the respiratory disorders in this mouse model of RTT. Our findings suggests that: (i) reductions in synaptic inhibition underpin the pathology of the breathing disorders of these mice; (ii) breathing deficiencies are, in part, contained within the Kölliker-Fuse nucleus and; (iii) respiratory deficiency in Mecp2 mice can be rescued.
Where applicable, experiments conform with Society ethical requirements