OHSU Physiology and Pharmacology Department

Michael C. Andresen
Professor

Integrative Cellular Neurobiology

click here to enter lab door

Education

Ph.D. 1978, University of Texas Medical Branch
M.S. 1973, San Diego State University
B.S. 1971, University of California, Irvine

Research Interests

Our lab is interested in the neurobiology of visceral sensory integration. Our work deals with a portion of the brain stem called the nucleus of the solitary tract (NTS). Afferents from the visceral organs directly contact the brain at NTS. This information is broadcast from there to distant targets within the CNS. Autonomic reflexes responsible for life support and systems level homeostasis depend on NTS as part of regulation that includes the heart, lungs and gastrointestinal tract. Some of these pathways can be as direct as two central neurons such as the baroreceptor reflex and other vago-vagal reflexes.

Arterial baroreceptors (BR) encode stretch of arteries with each cardiac cycle. This dynamic information about blood pressure and cardiac performance is transmitted to second order neurons in the brain stem at NTS. We study the characteristics of these NTS neurons and synaptic transmission with intracellular methods in an in vitro brain slice. Dyes can be used to visualize the central terminal boutons of BRs within NTS. Questions of particular interest are the identityand interactions of neurotransmitters and their receptors (ionotropic, metabotropic and G-protein coupled signaling); the role of voltage-dependent ion channels and their modulation; and the mechanisms of synaptic transmission and information processing within the nucleus.

Our major technical focus is electrophysiology (patch clamp recording) combined with optical approaches to neurons in slices and dispersed single cells (see additional information by opening the lab door to the left). Our unusual slice preparation allows selective activation of single afferent axons that synapse on the recorded cell and affords near ideal conditions for quantal analysis of neurotransmitter release mechanisms. Currently, we use fluorescent tracers to identify and probe single neurons. For example, we visualize single synaptic boutons from BRs on medial NTS neurons. Combined fluorescence and infrared microscopy enables visual identification and study of specific cell types by patch recordings. Mechanically isolated cells facilitate study of miniature synaptic events originating from attached native boutons. Current major projects focus on use dependent depression of sensory synaptic transmission, accessory co-transmission (ATP, purines, peptides), vanilloid receptors, and general anesthetic actions in NTS. We are interested in roles played by intrinsic cellular differences in sensory neurons with myelinated and unmyelinated axons in the information transfer to the CNS as well as local intra-NTS circuit properties.

Recent Publications

Bailey, T.W.; Jin, Y.-H.; Appleyard, S.M., Andresen, M.C. Organization and properties of GABAergic neurons in solitary tract nucleus (NTS). J. Neurophysiology Apr;99(4):1712-22, 2008. PMID: 18272881

McDougall, S.J.; Bailey, T.W.; Mendelowitz, D; Andresen, M.C. Propofol enhances both tonic and phasic GABAA transmission onto second-order neurons of the solitary tract nucleus (NTS). Neuropharmacology 54:552-563, 2008. PMID: 18082229

Peters, J. H.; McDougall, S.J.; Mendelowitz, D; Koop, D.R.; Andresen, M.C. Isoflurane differentially modulates inhibitory and excitatory synaptic transmission to the solitary tract nucleus. Anesthesiology 108:675-683, 2008 PMID: 18362600

Appleyard, S.M., Marks, D.; Kobayashi, K., Okano, H., Low, M.J., Andresen, M.C. Visceral afferents directly activate catecholamine neurons in the solitary tract nucleus. J. Neuroscience. 27: 13292-13302. 2007. PMID: 18045923

Bailey, T.W.; Hermes, S.M.; Whittier, K.L.; Aicher, S.A.; Andresen, M.C. A-type potassium channels differentially tune afferent pathways from solitary tract nucleus to caudal ventrolateral medulla or paraventricular hypothalamus. J. Physiology, 582 (2): 613-628, 2007.

Bailey, T.W.; Hermes, S.M.; Andresen, M.C.; Aicher, S.A. Cranial visceral afferent pathways through the nucleus of the solitary tract to caudal ventrolateral medulla or paraventricular hypothalamus: Target-specific synaptic reliability and convergence patterns. J. Neuroscience 26 11893-11902, 2006.

Bailey, T.W.; Jin, Y.-H.; Doyle, M.W.; Smith, S.M.; Andresen, M.C. Vasopressin inhibits glutamate release via two distinct modes in the brainstem. J. Neuroscience 26(23): 6131-6142, 2006.

Click here for PubMed bibliography.

revised 04-02-2008