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Office: W224 Anatomy/Zoology
Phone: 970-491-1672
Fax: 970-491-7907
Email: Stuart.Tobet@colostate.edu ​​

Stuart Tobet, PhD

​Professor, Department of Biomedical Sciences
Program in Cell and Molecular Biology
Front Range Neuroscience Group
School of Biomedical Engineering
Colorado State University

Education


PhD, Massachusetts Institute of Technology
SM, Massachusetts Institute of Technology
BS, Tulane University 

Overview


The long-term goal of Tobet’s research is to determine cellular and molecular events underlying the interactions of cells for organ function. This now ranges from the differentiation of regions of the brain that underlie neuroendocrine function to breast cancer cells and cells in the mammalian intestine.

Through a number of collaborations, Tobet started bringing new biomedical engineering approaches to the biological problems that he has been studying. These techniques include the use of microfluidic devices, biosensors, and multi-modal imaging. The combination opens new vistas. In one case, his group is exploring the interactions of neuro, immune, and microbial components of the mammalian intestines. Different groups have studied these components independently, but unifying models have been elusive. Using 25+ years of ex vivo tissue experience an ex vivo model was developed that maintains the functions of multiple physiological components. By combining such an ex vivo slice model with microfluidics to sample chemical environments for some molecules and biosensors for others, they are characterizing key signaling events between components. The use of fluorescent transgenic mice (promoter selective GFP) that highlight neurons versus immune cells allow plans for following the behaviors of cells in response to specific chemical signals. Devices are being designed that will allow us to use dual flow microfluidic channels to match oxygen concentrations for different departments of the same tissue. For example, the lumen of the intestines function at low oxygen (virtually anaerobic), while the tissue wall functions between 1 and 10% based on blood supply. When these devices are designed with microscopy in mind, investigators can follow changes in extracellular matrix collagen live using second harmonic imaging. This is a label-free imaging method with great power to help decipher impacts of pathogenic stimuli in the intestine.

Neuroendocrine structures are important because they regulate behavior and homeostasis and are susceptible to a variety of diseases or syndromes such as Kallmann’s or Prader-Willi. Tobet began his career by examining the long-term consequences of early hormone action on sexual behaviors, reproductive physiology, and hypothalamic structure. He proceeded to focus on molecular actions of gonadal steroids during critical periods of hormone action. The group is now determining how diverse signals affect cell position in multiple ex vivo model systems. Cellular organization and differentiation in brain follow several courses leading to primarily layered (e.g., cerebral or cerebellar cortices) or nuclear (cell groupings within the thalamus and hypothalamus) structures. We concentrate on the formation of nuclear structure using the preoptic area (POA), and ventromedial (VMN) and paraventricular (PVN) nuclei of the hypothalamus as model systems. These nuclei are key for regulating homeostatic, neuroendocrine, and behavioral functions. Cells migrate to specific positions within these nuclei characterized by neurochemical environment, phenotype of neighboring cells, and the pattern of anatomical connections. They are within a region, the hypothalamus, where gonadal steroid hormones dramatically influence development and where hormone-concentrating cells dramatically affect physiology and behavior. Model systems have allowed Tobet and colleagues to follow nuclear formation in vitro (video microscopy) where it is easily accessible to manipulation. Live video microscopy allowed the discovery of the first evidence of sex differences in neuronal migration. Now, it is providing for examination of hypotheses of the mechanism(s) of sex differences. Finally, studies of the developing PVN led Tobet to examine the vascular development of this key nuclear group in the hypothalamus. Although the strikingly dense vascularity of this region has been known for over 70 years, its development remains a mystery. The group is interested in factors that regulate the vascular development of this region and examine key aspects of blood brain barrier function related to its development and potential susceptibility to disorder. As the PVN lies at the co-morbidity crossroad of mood disorders, cardiovascular disorders, and obesity, disturbances in vascular function in this region may provide a here-to-fore unappreciated mechanism with high levels of clinical significance. 

Research Interests -- Determination of Cell Positions in the Developing Neuroendocrine Brain


The long-term goal of my research is to determine cellular and molecular events underlying the differentiation of regions of the brain that underlie neuroendocrine function. Neuroendocrine structures are important because they regulate behavior and hoemostasis and are susceptible to a variety of diseases or syndromes such as Kallmann's, Prader-Willi, or Rubenstein-Taybi. I began my career by examining the long-term consequences of early hormone action on sexual behaviors, reproductive physiology, and hypothalamic structure. I proceeded to focus on molecular actions of gonadal steroids during critical periods of hormone action. We are now determining how multiple signals affect migration and cell position in the developing nervous system.

Cellular organization and differentiation may follow several courses leading to primarily layered (e.g., cerebral or cerebellar cortices) or nuclear (cell groupings within the thalamus and hypothalamus) structures. We concentrate on the formation of nuclear structures using the ventromedial and paraventricular nuclei of the hypothalamus (VMH and PVN) as model systems. The VMH and PVN are part of complex neural circuitries that regulate homeostatic, neuroendocrine, and behavioral functions. They migrate to specific positions within the respective nuclei characterized by neurochemical environment, phenotype of neighboring cells, and the pattern of anatomical connections. Our model system allows us to follow the formation of nuclei in vitro (video microscopy) and is easily accessible to manipulation. Our discovery of a unique relationship of the neurotransmitter GABA to the developing VMH, and more recently the PVN, has led to hypotheses that are being tested directly through pharmacological manipulations and selecting transgenic mouse models. In particular, we are taking advantage of two lines of gene-disrupted mice. In one line, a single gene-deletion (the nuclear orphan receptor, steroidogenic factor-1 or SF-1) leads to failure of VMH formation. In the other, the R1 subunit of the GABABreceptor is disrupted and GABABreceptors are functionally impaired. The unique targeting of the SF-1 gene to the VMH also leads to our efforts to examine transgenic mice in which green fluorescent protein (GFP) expression is driven by the SF-1 gene promoter and another line of mice in which GFP expression is driven by the NPY promoter (see images).


 

We are also studying GABAergic mechanisms in the development of neurons that synthesize gonadotropin-releasing hormone (GnRH). During embryonic development, neurons containing GnRH migrate from the
nasal compartment, across the cribriform plate, into the brain to reside in the basal forebrain. Over their early migration, we have found GABA either in neighboring cells or within GnRH neurons in mice, rats, humans and lamprey. Using pharmacology and a unique in vitro slice paradigm that keeps the relationship of the head and brain intact, we are testing mechanisms of migration directly. Here again, we are taking advantage of lines of transgenic and gene-disrupted mice. In particular, we are examining GnRH neuron migration in mice deficient in the netrin-1 receptor, deleted in colon cancer (DCC). In addition, we are using live video microscopy to examine the migration of GnRH neurons that are revealed by GFP expression driven by the GnRH gene promoter. We are characterizing intracellular, extracellular, and cell surface molecules as they relate to this instance of neuronal migration from the periphery into the CNS, a unique event.

Finally, we were led to examine the role of gonadal steroids in cell migration when a monoclonal antibody we generated revealed sex differences in antigen expression in radial glia in the hypothalamus of perinatal rats. We further discovered a transient radial glial scaffold that reaches from the lateral ventricles across the anterior commissure through the sexually dimorphic preoptic/anterior hypothalamus (POAA/AH) to the pial surface at its base. We are exploring which cells might utilize this unique radial glial pathway using im

munocytochemical and live video microscopy techniques. We are particularly focused on following the migratory behavior of cells that might contribute to sex differences in structure or function. Our live video microscopy allowed us to discover the first evidence of sex differences in neuronal mi

gration. Now, it is providing for our examination of hypotheses of the mechanism(s) of sex differences. By focusing our efforts primarily in murine models, we combine the utility of in vitro work and pharmacology with the power of mouse genetics. Thus we are taking advantage of different transgenic mice or mice in which selected genes have been disrupted (e.g., SF-1 mentioned above, and others) to explore the importance of specific steroid hormone systems in the POA/AH.

Representative Publications


For a complete list of publications, please visit: Tobet S PubMed

Human colon functionex vivo: Dependance on oxygen and sensitivity to antibiotic. Schwerdtfeger LA, Nealon NJ, Ryan EP, Tobet SA. PLOS One. 2019 May 16; 14(5):e0217170. doi: 10.1371/journal.pone.0217170.      
 
From organotopic cluture to body-on-a-chip: A neuroendocrine perspective.
Schwerdtfeger LA, Tobet SA. J Neuroendocrinol. 2019 Mar;31(3):e12650. doi: 10.111/jne.12650.     
 
An organotypic slice model for ex vivo study of neural, immune, and microbial interactions of mouse intestine. Schwerdtfeger LA, Ryan EP, Tobet SA. Am J Physiol Gastrointest Liver Physiol. 2016 Feb 15;310(4):G240-8. doi: 10.1152/ajpgi.00299.2015. 
 
Spatiotemporal norepinephrine mapping using a high-density CMOS microelectrode array. Wydallis JB, Feeny RM, Wilson W, Kern T, Chen T, Tobet S, Reynolds MM, Henry CS.
Lab Chip. 2015 Oct 21;15(20):4075-82. doi: 10.1039/c5lc00778j. 
 
Development of the blood-brain barrier within the paraventricular nucleus of the hypothalamus: influence of fetal glucocorticoid excess. Frahm KA, Tobet SA. Brain Struct Funct. 2015 Jul;220(4):2225-34. doi: 10.1007/s00429-014-0787-8. 
 
Fetal hormonal programming of sex differences in depression: linking women's mental health with sex differences in the brain across the lifespan. Goldstein JM, Holsen L, Handa R, Tobet S. Front Neurosci. 2014 Sep 8;8:247. doi: 10.3389/fnins.2014.00247.
 
Disruption of fetal hormonal programming (prenatal stress) implicates shared risk for sex differences in depression and cardiovascular disease. Goldstein JM, Handa RJ, Tobet SA. Front Neuroendocrinol. 2014 Jan;35(1):140-58. doi: 10.1016/j.yfrne.2013.12.001.
 
The vasculature within the paraventricular nucleus of the hypothalamus in mice varies as a function of development, subnuclear location, and GABA signaling. Frahm KA, Schow MJ, Tobet SA. Horm Metab Res. 2012 Jul;44(8):619-24. doi: 10.1055/s-0032-1304624.