Steve Asmus, Ph.D.
B.S., 1988, Cleveland State University, Biology
The Big Question: How do developing neurons produce a functionally-appropriate neurotransmitter, i.e. one that will "communicate" correctly with the target cell?
Background: I am interested in how the nervous system develops. Specifically, I study how developing neurons regulate their production of neurotransmitters, the messenger molecules that control the target cell. A wide variety of neurotransmitters have been discovered, and different types of neurons produce a distinct subset of these molecules. Target cells, in turn, display specific receptors to which the neurotransmitter binds. A neuron must release the appropriate neurotransmitter for proper control of the target cell. Relatively little is known, however, about how the majority of neurons begin to produce the correct neurotransmitter during development.
Specific Aims: Previous research by others has elucidated at least one mechanism whereby neurotransmitters are regulated: the target tissue can radically alter the neurotransmitter produced by a neuron. For example, neurons of the sympathetic nervous system, which controls the "fight-or-flight" response, switch the neurotransmitter that they produce, from norepinephrine to acetylcholine, if they reach sweat glands. Sympathetic neurons connecting to other targets (salivary gland, iris, etc.) continue to produce norepinephrine. I have found that periosteum, the connective tissue surrounding bone, instigates a similar transmitter switch in the developing sympathetic neurons extending to it (Asmus et al., 2000; 2001).
My current project examines the production of tyrosine hydroxylase (TH), the rate-limiting enzyme required for the synthesis of dopamine and the other catecholamine transmitters, in the cerebral cortex of the developing rat brain. A subset of developing cortical interneurons begins to produce TH around two weeks after birth, but the number of these cells decreases during maturation and there are fewer TH-containing cells in the adult cortex. One possible explanation for the rise and fall in the number of cortical TH neurons is that the neurons undergo programmed cell death. To determine if these neurons are dying, we colocalized TH with markers of programmed cell death (DNA fragmentation and active cell death enzymes) (see photos below). We found no evidence that cortical TH neurons undergo cell death. Another explanation is that these neurons decrease TH production as they acquire their mature transmitter phenotype. We currently are exploring a possible transition in the transmitter production of these cells and attempting to identify their embryonic origin. Our most recent findings are presented in Asmus et al., 2008. A more complete understanding of neurotransmitter expression in developing cortical interneurons hopefully will provide insight into neurological disorders such as epilepsy and schizophrenia in which interneuron dysfunction has been implicated.
Techniques: The main techniques that I employ are cryosectioning of fixed tissues, selective cell staining techniques such as immunohistochemistry (using antibodies to visualize molecules of interest) and DNA fragmentation assays, fluorescence microscopy, cell culture, and digital image analysis (see photos below). These techniques are accessible to my student research collaborators and to my students in lab courses.
Collaborative Research: Centre students play an integral role in my research. I have collaborated with 23 students, the majority of whom have gone on to biomedical Ph.D. programs or medical school. My students conduct their research during the summer as paid research assistants and during the academic year for independent study credit. They often present their results at scientific meetings and are coauthors on resulting publications.
Recent Research Articles: (*Undergraduate Centre student collaborators)
Asmus, S.E., H. Tian and S.C. Landis (2001) Induction of cholinergic function in cultured sympathetic neurons by periosteal cells: cellular mechanisms. Developmental Biology, 235: 1-11.
The following are brief descriptions of the courses that I teach. In some cases, more details are given under the course descriptions in Centre's on-line catalog.
FRS 102, Stem Cells, Cloning and You A freshman studies course that examines the scientific, religious, ethical, and public policy issues surrounding stem cell research and cloning. The primary text for the course is Holland et al., The Human Embryonic Stem Cell Debate: Science, Ethics, and Public Policy.
BIO 110, The Unity and Diversity of Life (with lab) An introduction to the foundational principles of biology. This course considers molecules to ecosystems.
BIO 335, Developmental Biology (with lab) A study of the development of animals, primarily vertebrates, from fertilization through organogenesis. Topics include classical embryology and cellular and molecular aspects of development. (Prerequisite: BMB 210). The texts for the course are Gilbert's Developmental Biology and Schoenwolf's Vertebrate and Invert. Embryos: Guide and Atlas of Descriptive and Experimental Development.
BIO 345, Histology (with lab) A study of the microscopic anatomy of vertebrate tissues and organs. Lectures focus on correlating cell organization and physiology with the function of the particular tissue/organ system and on how tissue types function throughout the organism. Lab work includes microscopic identification of tissues and an independent research project. (Prerequisite: BMB 210). The text for the course is Junqueira and Carneiro, Basic Histology: Text and Atlas.
BMB 210, Introduction to Cellular and Molecular Biology (with lab) The structure and function of the macromolecules, organelles and membranes, and the pathways of energy flow and information transfer required for cell function are considered. Organic Chemistry I is a pre- or corequisite. The text for the course is Becker et al., The World of the Cell.
BMB 340, Cell Biology A study of eukaryotic cell structure and function at the molecular level. Topics include membrane structure and function, intracellular compartments, protein sorting, exo- and endocytosis, cell signaling, cytoskeleton, extracellular matrix, cell and molecular mechanisms of development, and cancer. Required for Biochemistry/Molecular Biology majors and an elective for Biology and Chemistry majors. (Prerequisite: BMB 330, Molecular Genetics or permission of the instructor.) The text for the course is Alberts et al., Molecular Biology of the Cell.
BMB 345, Cell Biology Lab (optional lab corresponding to BMB 340) A study of modern cell biology research techniques including mammalian cell culture, immunocytochemistry, programmed cell death assays, fluorescence microscopy, and digital image analysis. Students incorporate their results into primary research-style reports.
BIO 500 and BMB 500, Senior Seminar A study of current research topics in biology and biochemistry/molecular biology, required for all senior Biology and BMB majors, respectively. Students critically analyze and discuss primary research articles. Students hear presentations by scientists from other institutions and meet with them over dinner. Students also work on a research project of their own choosing, culminating in a paper and oral presentation.
Images below were captured with a Zeiss Axiocam digital camera mounted on a Zeiss fluorescence microscope equipped with DIC.
Brain neurons seen through the microscope. Dopamine neurons in the rat substantia nigra are seen here as red triangular and oval shapes with dendrites (arrowheads) extending from the cell bodies (arrows). This brain section was stained immunohistochemically using an antibody that recognizes the dopamine synthesizing enzyme, tyrosine hydroxylase, and a secondary antibody labeled with rhodamine Red-X, a fluorescent red molecule.
Brain neurons seen through the microscope. Dopamine neurons in the rat substantia nigra are seen here as green triangular and oval shapes surrounded by GABA-containing neuronal extensions stained red. This brain section was immunohistochemically double-labeled using antibodies against tyrosine hydroxylase and glutamic acid decarboxylase (GAD), the biosynthetic enzyme for GABA, followed by secondary antibodies labeled with Cy2 (green) and rhodamine Red-X.
Programmed Cell Death in Cultured Cells. The same field of view is seen in A, B, and C. The same two cells present in all three images are identified by arrows. Cancerous Chinese hamster ovary (CHO) cells growing in culture initiate programmed cell death when exposed to ultraviolet light. A. Differential interference contrast (DIC) microscopy reveals all cells in this field of view. B. Immunocytochemical labeling demonstrates that some of the cells contain active caspase-3, an enzyme that triggers the cell death program, indicating that the red cells are dying. C. Fragmented DNA, a hallmark of programmed cell death, is labeled green in two cells (also in A and B, arrows) using the TUNEL technique, which attaches fluorescent molecules to DNA termini. The presence of fragmented DNA suggests that these two green cells are relatively far along in the cell death process.
last updated 6/27/08