commentary review reports meeting abstracts primary research S1 Available online http://respiratory-research.com/content/2/S1 Meeting abstracts Neural control of breathing An Official Satellite of the International Congress of Physiological Sciences (IUPS) 2001, Rotorua, New Zealand, 1–4 September 2001 Received: 2 August 2001 Published: 17 August 2001 Respir Res 2001, 2 (suppl 1):S1–S37 © 2001 BioMed Central Ltd (Print ISSN 1465-9921; Online ISSN 1465-993X) ORAL PRESENTATIONS — SESSION 1 Ontogeny and phylogeny of respiratory control 1.1 Early development of respiratory rhythm generation in mice and chicks J Champagnat , G Fortin, S Jungbluth, V Abadie, F Chatonnet, E Dominquez-del-Toro, L Guimarães UPR 2216 (Neurobiologie Génétique et Intégrative), IFR 2118 (Institut de Neurobiologie Alfred Fessard), CNRS, 91198, Gif-sur-Yvette, France Breathing in mammals starts in the foetus and acquires a vital importance at birth. The ability to produce rhythmic motor behav- iours linked to respiratory function is a property of the brainstem reticular formation, which has been remarkably conserved during the evolution of vertebrates. Therefore, to understand the biological basis of the breathing behavior, we are investigating conservative developmental mechanisms orchestrating the organogenesis of the brainstem. In vertebrates, the hindbrain is one of the vesicles that appears at the anterior end of the neural tube of the embryo. Further morphogenetic subdivision ensues whereby the hindbrain neuroepithelium becomes partitioned into an iterated series of compartments called rhombomeres. The segmentation process is believed to determine neuronal fates by encoding positional infor- mation along the rostro-caudal axis. Before and at the onset of seg- mentation, genes encoding transcription factors such as Hox, Krox-20, kreisler, are expressed in domains corresponding to the limits of future rhombomeres. Inactivation of these genes specifi- cally disturbs the rhombomeric pattern of the hindbrain. The pre- sentation will address the problem of whether this primordial rhombomeric organisation influences later function of respiratory control networks in chicks and mice. Experiments were performed in embryos and after birth in trans- genic mice. They show that, although expression of developmental genes and hindbrain segmentation are transient events of early embryonic development, they are important for the process of res- piratory rhythm generation by brainstem neuronal networks. We have found in chick that at the end of the period of segmentation, the hindbrain contains neuronal rhythm generators that conform to the rhombomeric anatomical pattern. We have also identified a minimal rhombomeric motif allowing the post-segmental maturation of a specific (GABAergic) rhythm-promoting circuit. Furthermore, in vivo and in vitro analysis of neurons in transgenic mice revealed postnatal respiratory phenotypes associated with defects of central pontine and/or afferent respiratory control in Krox-20, Hoxa1 and kreisler mutants. Neonatal respiratory phenotypes are also induced in mice by treatment with low doses of retinoic acid that slightly change the early embryonic development of the Pons. Altogether, these experiments indicate that segmentation-related specifica- tions of the hindbrain rhythmic neuronal network influences the res- piratory patterns after birth. Therefore, early developmental processes have to be taken into account to understand normal and pathological diversity of the breathing behaviour in vertebrates. Acknowledgement: Supported by HFSP RG101/97, ACI (BDPI) 2000, CEE BIO4CT, ICCTI PRAXIS XXI (BD/11299/97). 1.2 Development of gill and lung breathing in amphibia MJ Gdovin , VV Jackson, JC Leiter Division of Life Sciences, University of Texas at San Antonio, TX, USA In the 25 morphological stages of larval bullfrog development there exists a gradual transition from gill to lung ventilation associated with a developmental decrease in the contribution of the skin in gas exchange. Bath application of GABA and/or glycine inhibited gill but not lung burst activities of cranial nerve (CN) VII in the premetamorphic (stages 16–19) in vitro tadpole brainstem prepa- ration [1]. It was proposed that the neural basis of gill rhythmogen- esis involved network inhibition, whereas lung rhythmicity was pacemaker driven [1]. Bath application of a bicuculline/strychnine solution abolished gill and enhanced lung bursting in stages 16–19 in vitro [1]. Bath application of the GABA B receptor antago- nist 2-hydroxy-saclofen disinhibited the lung central pattern genera- tor (CPG) resulting in precocious lung bursting patterns as early as developmental stage 6 [2]. We recorded efferent activity from CN VII and spinal nerve (SN) II in the in vitro tadpole brainstem preparation in three successive devel- opmental groups (3–9; 10–15; 16–19) before and after bath appli- cation of a 10 μM bicuculline and 5 μM strychnine solution. We also exposed the brainstem to bath pH 7.4, 7.8, and 8.2 before and after bath application of bicuculline/strychnine. Bicuculline/strychnine produced lung ventilatory bursts in all developmental stages tested, indicating the presence of the lung CPG as well as excitatory synapses to respiratory motor neurons as early as stage 3. We also designed an experiment to examine the importance of lung ventilation on the developmental shift from gill to lung burst- ing. Two groups of tadpoles were hatched from eggs. Control tad-