Marion E. Frank, Ph.D.Professor of Oral Health and Diagnostic Sciences
Director, Center for Neurosciences
To reveal chemosensory stimulus coding strategies, we study odor and taste identification in humans, and gustatory neurophysiology and behavior in hamsters. The broad goal of our research is to develop fundamental understanding of the functioning of mammalian gustatory and olfactory systems.
In the ever-changing mix of real-world compounds, taste and smell likely evolved to identify stimulus quality at low concentrations. The high concentrations of chemicals used in studies to establish specificity often elicit multiple sensations and may act as reagents, bypassing specific transduction mechanisms. Also, in nature, stimuli are embedded in complex mixtures, but most studies have employed single-component stimuli for ease of study design and data interpretation. Our work on golden hamsters (Mesocricetus auratus), uses behavioral assays (conditioned taste aversion (CTA), intake) and peripheral nerve recordings [chorda tympani (CT), glossopharyngeal (GL)] to challenge candidate peripheral labeled line codes with single, binary and ternary stimuli in the sweet and bitter domains. Our work on humans challenges the human capacity to identify gustatory and olfactory quality with dynamic, complex stimuli at concentrations encountered in natural settings.
Accepting Lab Rotation Students for: Summer '17
Lab Rotation Projects
Students who wish to formulate their own novel questions about the effects of selective adaptation on human odor perception or behavioral/neural analysis of mixture stimuli by hamsters are welcome. In addition the following projects are available:
#1 – Short description of a project and what will be involved in the research: Hamsters are repelled by cycloheximide, a protein synthesis inhibitor. Its aversive potency at concentrations of less than 1 ? M increases dramatically after a single exposure. Yet it is not known whether cycloheximide is a taste stimulus for hamsters. Humans can hardly detect the compound by taste. A rotation project would involve electrophysiological recording from the CT in 2 groups of hamsters, those that had been exposed to cycloheximide and those that had not been exposed to cycloheximide. This project may lead to a thesis project on “induction” of taste receptors for dangerous compounds.
#2 – Short description of a project and important methods that will be learned: Electrophysiological recordings of chorda tympani nerve responses to binary mixtures in hamsters show specific inhibition of sucrose responses by quinine and quinine responses by NaCl. No one has looked at responses to ternary mixtures of NaCl + sucrose + quinine. A lab rotation would involve learning micro-neurosurgical techniques to isolate the chorda tympani nerve, electrophysiological techniques to obtain recordings, computerized analysis techniques to quantify the data, and statistical analysis to evaluate the significance of the data.
#3– Short description of a project and important methods that will be learned: In binary mixtures, identification of a component’s characteristic quality is difficult, and in quaternary mixtures, identification is impossible. This is called mixture suppression. Presenting stimuli in pairs, each stimulus for a few seconds, can rescue an extra component in the second stimulus from mixture suppression. This selective adaptation has been shown for one water-soluble stimulus (label) quartet. No one has looked at other odorous compounds like benzaldehyde (almond), maltol (caramel), methyl anthranilate (grape) and 2-methoxy-3-isobutylpyrazine (green bell pepper). A lab rotation would provide training in testing hypotheses about chemosensory systems by using the human response as the dependent variable. It also requires learning methods of data analysis and statistical evaluation of results.