With the introduction of molecular approaches into the field of neuroscience an unexpected variety of receptor and ion channel subtypes have been discovered that are developmentally regulated within the central nervous system. The relevance of these findings for the function of neuronal networks is still unclear. In a close combination of studies at the cellular and systems level our laboratory examines how diversity at the cellular level may lead to ontogenetic changes at the network level.

Over the past decade we have analysed cellular mechanisms in neuronal networks that generate rhythmic motor activity in invertebrates and vertebrates. Our current work focusses on the analysis of the in vitro respiratory network in mice. For this purpose we isolate acutely the respiratory network in a transverse plane of the mouse medulla. This brainstem slice preparation contains the essential medullary structures involved in cardio-respiratory control and even after the in vitro isolation generates rhythmic activity in rats and mice of all developmental stages (up to an age of 25 postnatal days). This approach permits a direct comparison of the neuronal mechanisms of rhythmogenesis in newborn and more mature mammals. Our experiments indicate e.g. that the hypoxic response, fast chloride mediated inhibitory synaptic transmission, calcium channels and modulatory processes change postnatally within the respiratory network.

In order to analyze the cellular mechanisms in rhythm generating neural networks we employ the currently available electrophysiological and immunohistochemical techniques. The great advantage of the brainstem slice preparation is that single neurons can be visualized that are embedded in a functional neuronal network using infrared-Normarski optics in conjunction with upright microscopes. Thus, voltage-gated and synaptic whole cell currents, properties of single channels as well as second messenger pathways can be investigated in a functional context to characterize changes in postnatal development of the respiratory network. Our laboratory is particularly interested in understanding developmental alterations of cellular properties involved in the response of the respiratory network to hypoxia. This response elicits a cascade of molecular events which are regulated by endogenously released neuromodulators such as substance P and endorphins and which result in a reconfiguration of the respiratory neuronal network. 

In the future this slice preparation will enable us to further obtain systems and cellular data from functionally identified respiratory neurons. In combination with cell culture and modern molecular techniques (e.g. expression of channel subtypes obtained from respiratory neurons in oocytes) we expect to gain new insights into principle mechanisms of respiratory rhythm generation and the hypoxic response in mammals. Due to the importance of the respiratory system for the survival of any mammal, progress in this field will not only have important scientific, but also clinical implications (e.g. understanding the underlying causes of sleep apnea, periodic breathing, Pickwick syndrome and sudden infant death syndrome "SIDS").

Ramirez, J.M., Quellmalz, U.J.A., Richter, D.W. (1998). The hypoxic response of neurones within the in vitro mammalian respiratory network. J. Physiol 507: 571-582.

Elsen, F., Ramirez, J.M. (1998). Low- and high-voltage activated calcium currents in rhythmic neurons of the isolated respiratory network of mice. J. Neuroscience 18: 10654-10662.

Ramirez, J.M. (1998). Reconfiguration of the respiratory network at the onset of locust flight. J. Neurophysiol. 80.6: 3137-3147.

Ramirez, J.M. (1998). The neuronal control of breathing. New insights and experimental approaches with implications for the investigations of sudden infant death. Saternus, K.S., Karimow, Sch. (eds.). Infant Mortality, Sudden Infant Death (SID), Schmidt-Roemhild, Luebeck, pp.53-66.

Telgkamp, P., Ramirez, J.M. (1999) Differential response of the ventral respiratory group and hypoglossal nucleus to hypoxia in the transverse slice preparation of mice. J. Neurophysiol. 82: 2163-2170.

Ramirez, J.M. Elsen, F.P., Robertson, R.M. (1999). Long-term effects of prior heat shock on neuronal potassium currents recorded in a novel insect ganglion slice preparation. J. Neurophysiol. 81: 795-802
Ramirez, J.M. (1999). The central control of breathing. Biedermann, H. (ed). Manual Medicine, Emke Verlag, 103-112.

Thoby-Brisson, M., Telgkamp, P. Ramirez, J.M. (2000). The role of the hyperpolarization-activated current in modulating rhythmic activity in the isolated respiratory network of mice. J. Neuroscience. 20 (8): 2994-3005.

Lieske, S.P. Thoby-Brisson, M., Telgkamp, P. Ramirez, J.M. (2000). Reconfiguration of the neural network controlling multiple breathing patterns: eupnea, sighs and gasps. Nature Neuroscience 3: 600-7.

Wilken, B., Ramirez, J.M., Probst, I., Richter, D.W., Hanefeld, F. (2000). Anoxic ATP depletion in neonatal mice brainstem is prevented by creatine supplementation. Arch. Diseases in Childhood, Fetal Neonatal Ed. 82: F224-7. 

Wilken B, Ramirez JM, Hanefeld F, Richter DW. (2000). Aminophylline modulation of the mouse respiratory network changes during postnatal maturation. Journal of Applied Physiology 89: 2015-2022.

Thoby-Brisson, M., Ramirez, J.M. (2000). Role of inspiratory pacemaker neurons in mediating the hypoxic response of the respiratory network in vitro. J. Neuroscience 20: 5858-66.

McCrimmon, D.R., Ramirez, J.M., Alford, S., Zuperku, E.J. (2000). Unraveling the mechanisms for respiratory rhythm generation. BioEssays 22: 6-9.

Thoby-Brisson, M, Ramirez, J.M. (2001). Two types of inspiratory pacemaker neurons in the isolated respiratory network of mice. J. Neurophysiol: 86 (1):104-12.

Lieske, S.P., Thoby-Brisson, M., Ramirez, J.M. (2001). Reconfiguration of the central respiratory network under normoxic and hypoxic conditions. Adv Exp Med Biol. 2001; 499: 171-8.

Kelty, J.D., Noseworthy, P.A., Feder, M.E., Robertson, R.M., Ramirez, J.M. (2002). Thermal Preconditioning and HSP72 protect synaptic transmission during thermal stress. J. Neuroscience. Jan 1; 22(1): C193.

Koch, L.E., Koch, H., Stolle, D., Ramirez, J.M., Saternus, K.S. (2002). Heart rate changes in response to mild mechanical irritation of the high cervical spinal cord region in infants. Forensic Science International. In press.

Blitz, D.M., Ramirez, J.M. (2002). Long-term Modulation of Respiratory Network Activity Following Anoxia in Vitro. J. Neurophysiol. 87: 2964-2971.

Ramirez, J.M., Zuperku, E.J., Alheid, G., Lieske S.P., Ptak, C., McCrimmon, D.R. (2002). Respiratory Rhythm Generation. Converging Concepts from In Vitro and In Vivo Approaches? Respiration Physiology and Neurobiology. 131 (1-2): 43-56.

Telgkamp P. Ramirez, J.M. (2002). The Role of Substance P in the Control of respiratory Activity under Normoxic and Hypoxic Conditions In Vitro. J. Neurophysiol. 88: 206-213.

Tryba, A.K, Ramirez, J.M. (2002). The hyperthermic response of the isolated respiratory network of mice. Journal of Neurophysiology: 89 (6): 2975-2983.

Pena, F., Ramirez, J.M. (2002). Endogenous activation of serotonin 2A receptors is required for normal respiratory rhythm generation in vitro. J. Neuroscience; 22(24): 11055-64. 

Ramirez, J.M. (2003). Adaptive properties of motor behavior: The response to changes in developmental and environmental conditions. In: Biedermann H. (editor). Chiropractic Therapy in Infants. Butterworth-Heinemann.

Van Drongelen, W., Koch H., Marcuccilli C.J., Pena, F. Ramirez, J.M. (2003). Synchrony levels during evoked seizure like bursts in mouse neocortical slices, J. Neurophysiology: 90 (3): 1571-1580.

Tryba A.K., Pena, F., Ramirez J.M. (2003). Stabilization of bursting in respiratory pacemaker neurons. J. Neuroscience 23 (8): 3538-3546.

Moseley, A.F., Lieske S.P., Wetzel R.K., James P.F., He S., Shelly D.A., Paul R.J., Boivin, G.P., Witte D.P., Ramirez, J.M., Sweadner, K.J., Lingrel, J.B., (2003). The Na k-AtPase, alpha 2 isoform is expressed in neurons, and its absence disrupts neuronal activity in newborn mice. J. Biol. Chem. 14 278 (7): 5317-5324.