Undergraduate Research Fellows

Cesareo Blanco

Different species of birds are known to have different sound localizing ability. These differences can be seen at the anatomical level through comparisons of the nuclei of the auditory brainstem.

The barn owl (Tyto alba) is known for it's ability to locate sound for predatory purposes. They use interaural time difference (ITD) as a means to locate sound in complete darkness. Signals from both ears are first combined with respect to ITD in the nucleus laminaris (NL). The NL is where the axonal afferents from the ipsilateral and contralateral cochlear nucleus magnocellularis (NM) interdigitate (Carr, Konishi, 1988). The NM afferents form a series of delay lines that result in a map of ITDs in NL. The neurons of the NL act as coincidence detectors of impulses sent from the NM, maximally firing when stimulated from both Nms simultaneously.

Comparisons between the NL of barn owls and chickens which have non-specialized auditory systems have shown differences in NL structure. The NL of the chicken can be described as a monolayer or lamina of neurons where ITDs are also mapped. The barn owl however possesses a wider more distributed NL structure. This anatomical difference can be correlated with the barn owl's superior ability to localize sound.

Parakeets are known to have the ability to detect complex sound. They have also shown highly tuned response to ITD (Amagai, et al. 1996). Preliminary anatomical data has shown that the structure of the NL lies somewhere in between of the two extremes represented by the chicken and barn owl (Kubke, et al. 1996). It is therefore important to investigate the anatomy of this nucleus in the parakeet, to correlate the anatomy of the structures with physiological studies in progress.

This summer I will be processing serial sections using the antibody against calbindin. This antibody labels cells from the NL but not cells from the NM. NM cells will be visualized by staining with neutral red or other histological stains. Camera lucida drawings of each section and the sound localization nuclei within each section will then be digitized and manipulated through the use of NIH Image, Macromedia's Extreme 3D, and similar software in order to obtain a fluid, three dimensional computer model of the different auditory nuclei of the parakeet's brainstem.

Upon completion of the computer model of the nuclei, the individual cell types within the NL will be modeled in a similar fashion to be analyzed in conjunction with the original three dimensional model of the auditory brainstem to determine the relative position of the different cell types within the tonotopic axis. Later in the summer, biotilinated dextran amine (BDA) injections will be used to label axonal afferents from both the ipsilateral and contralateral NMs which interdigitate in the NLs. Camera lucida and confocal microscopy images will be obtained from these labeled axonal afferents and will be digitized in order to perform similar three dimensional reconstructions. The relative patterns and position in which they interdigitate in the NL will also be correlated the NL cellular organization.

This union of physiological experiments with three dimensional anatomical models is valuable because it will be possible to correlate physiological properties with specific anatomical characteristics.

Questions or comments can be directed to blanco@zool.umd.edu

Jason Denkevitz

Manihot esculenta, or cassava, is a pan-tropical staple crop consumed by 300 to 500 million people daily. The plant is indigenous to South America and has subsequently been introduced worldwide. Cassava, known in the United States as tapioca or yuca, is a rich source of the cyanogenic glucosides linamarin and lotaustralin. Once ingested, the cyanide moiety is cleaved via linamarase and hydrogen cyanide is formed and circulated throughout the bloodstream. The body converts ingested cyanide to thiocyanate via the enzyme rhodanase.

Hypothyroidism is a condition found throughout the world and is associated with low iodine intakes. In some populations, low iodine intakes are associated with high serum thiocyanate levels.It is believed dietary cyanogenic glucosides are among the most significant natural biological sources of cyanide and elevated serum thiocyanates. Thiocyanate is also present in cigarette smoke and increased blood SCN levels have been detected in smokers. Swine are an excellent model for human metabolic processes and young swine are expected to show the greatest thyroid responses to any elevations in serum thiocyanate.

In many studies testing the effects of cyanogenic glucosides and cyanides on thyroid function, the levels of these compounds used are not relevant to normal biological intake such as that ingested by eating foods containing cyanogenic glucosides.I wish to test the physiological effects of biologically relevant levels of these compounds and their resulting metabolic byproduct, thiocyanate, on several indices of thyroid function in an in vivo system. To accomplish this, I am using a sample of 24 piglets.

The central hypothesis of this study is that treated animals will express hypothyroidism relative to control animals as measured by a selected set of response variables: thyroid stimulating hormone (or thyrotropin), thyroxine, triodothyronine (or T3),tetraiodothyronine, thyroxine-binding globulin, albumin, and blood serum thiocyanate levels. The null hypothesis is that treatments will not influence thyroid function relative to control animals.

Twenty four miniature swine (Sus domesticus) siblings, Pittman-Moore strain (or similar variety) are to be studied. 8 animals will be assigned to the control group and will receive a water placebo. In addition, 8 animals will be assigned to the first treatment group and will receive a treatment of cassava-based cyanogenic glucosides (linimarin and lotustralin). 8 animals will be assigned to the second treatment group and will receive a comparable concentration of inorganic HCN. Phenotypic effects of the cyanogenic glucosides and inorganic cyanide will be studied by looking for the following changes in levels (absolute amounts) of TSH, T3, and T4 hormones, changes in the amount of glycoproteins (for example thyroxine-binding globulin) and proteins (for example, albumin),and changes in mitochondria size and number.Possible genotypic effects of the cyanogenic glucosides and inorganic cyanide will be examined by looking for changes in electrophoretic patterns of glycoproteins and albumin.

This data set should tell us more of the practical effects of cyanogenic glucosides when given in biologically and anthropologically relavent dosages.

Any comments/questions/feedback should be addressed to denkevit@zool.umd.edu

Jessica Fields will be working with Dr. William Hodos on changes in visual acuity associated with age. Specifically, Jessica will assess the effects hormonal treatments during development on the retina of Japanese quail. She will look for masculine or feminine traits in the retina associated with her treatments and their affect on age-related changes in visual acuity.

Jeannie Lee will be studying inducible DAN cross-linking agents with Dr. Steve Rokita in the Department of Chemistry and Biochemistry. Jeannie points out that therapeutic agents for cancer have significant side effects and that there is an acute need for anti-cancer agents that have less negative effects. She will be trying to develop agents that will become crosslinking compounds until they reach their targets. By appropriate chemical modification she hopes to transform one such crosslinnking agent into one that will only crosslink when bound to DNA.

Edward Lee

Bowerbirds are amoung the few avian species in which males make no material contribution to offspring and in which female choice of males appears especially dependent on the genetic contribution of males. How males court females and a criteria which females use to choose a male are key elements in understanding the functional significance of mate choice. Models of sexual selection predict that females use male displays in assessing his quality as a sire. Studies have shown that females mate with males that perform more aggressive (intensive) displays because aggressiveness in display is an indication of the overall vigor of the male that can be passed on to offspring. However, if this is true, the males are faced with a problem. How do they effectively display their genes without compromising the sense of safety in the female; in other words, scaring her off. Several years ago a study of the spotted (Chlamydera maculata) and great (Chlamydera nuchalis) bowerbirds was conducted to explore this paradox. This study concluded that males modulate their displays to ameliorate its threatening appearance. This behavior, referred to as threat reduction, is most evident in spotted courtships. In following the logic of threat reduction, the spotted female positions herself facing the bower wall instead of the bower opening as in other species such as great bowerbirds. She then observes the male's highly aggressive display from behind a see through wall which offers protection to the female.

In the proposed research I will study the behavior of the fawn breasted (C. cerveniventris) and yellow breasted (C. lauterbachi) bowerbirds. The hypothesis I will test is, if males of these two species modulate displays as has been observed in the two other Chlamydera species. I predict that court size should be correlated with the intensity of display. Thus species with small courts should have less intense displays because males are near females during display. To compensate in showing genetic quality with reduced intensity of display, males may court longer or display a behavior known as "head turning."

I will test this hypothesis by using court measurements previously taken in the field and the intensity of displays to construct a linear plot that shows a proportional relationship in the four Chlamydera species. The intensity of display is defined as the frequency and duration of wing flapping, head twitching, decoration throwing and movement along the bower wall; greater frequencies of which corresponds to greater intensity. Frequencies will be measured by counting the number of times a behavior is observed in the time frame of the courtship. Then the frequencies will be converted to rates. Durations will be timed with a stop watch. The rates of each diplay will be compared and plotted on a graph with its corresponding court size. From these results we may determine that a proportional relationship between court size and intensity of display indeed exists using an analysis of variance. Furthermore we may observe that the conflict between performing an aggressive display and reducing its threatening appearence to the female is consolidated through compensating behaviors such as head turning and longer courtships.

Gila Neta will work with Dr. Sue Carter in the Zoology Department. Gila will study female aggressiveness in the prairie vole. Female behavior, including aggressiveness, is affected by hormones like vasopressin. Gila will test the effects of vasopressin on female territoriality and aggression. This study will shed light on the effects hormones have on behavior in mammals.

Alexandra Newman is working with Dr. Dan Stein of the Microbiology Department on lipooligosaccharide structures (LOS) in the membrane of Neisseria gonorrhoeae. This organism is the causative agent of sexually transmitted gonorrhea. The LOS component of the organism's membrane determines the virulence of infection. Alexandra will examine how LOS affects the susceptibility of the organism to the killing action of human serum.

Tami Panhius is working with Dr. Gerald Wilkinson on the evolution and neuroanatomical correlates in contests of stalk-eyed flies. Tami will study aggressive behavior in stalk-eyed flies and correlate eye span with parameters such as contest duration and injury. She believes that flies with smaller eye spans will be injured more and have longer contestes that flies with wider eye spans. Her work will reveal more about agressive behavior in animals.

Kinnari Patel

With the support of The Howard Hughes Fellowship, I plan to complete a honors thesis concerning the prairie vole (Microtus ochrogaster),a small, mouse like rodent of the midwestern U.S. that exhibits monogamous behavior characterized by partner preference and aggression. Specifically, I will examine the prairie vole for the abundance of vasopressin (ADH) receptors on the collecting ducts of the kidney and glucocorticoid receptors (type 2 that detect corticosterone) on the adrenal cortex once developmental changes in hormone levels have occurred. Histological techniques will be used to determine whether group differences exist in the kidneys and adrenal glands of experimental and control groups. I am excited about the project and the support I am getting from The Howard Hughes Fellowship.

Questions or comments can be directed to Kinnari Patel at: kinnari@wam.umd.edu

<!-img align=left vspace=4 hspace=4 src=crezende.gif alt="[picture of C. Rezende]"> Christian Rezende is spending the summer in D. Sam Joseph's lab studying Salmonella. Christian will attempt to determine whether or not Salmonella use trehalose as an osmotic effector to protect itself from osmotic stress during dehydration. Christian's work may identify mechanisms of bacterial resistance to dessication and provide new avenues for bacteriacidal agents to be developed. It is worth pointing out that Christian delayed his graduation in May 1996 so that he could conduct this research project. This demonstrates the dedication that some of our students have toward their education.

Ashley Ross is working with Dr. Jason Kahn in Biochemistry. He is studying the structure of the DNA which is looped by the lac repressor protein. The lac repressor protein is responsible for inhibiting the transcription of the lac gene and is considered a model for this type of repression. Ashley intends to describe the shape of the DNA sequences which are most effectively bound by this Lac repressor protein. This work will also help define the conditions under which looped protein-DNA copmplexes are formed.

Mary Rubin is working the the Biochemistry Department with Sarah Woodson. Mary is embarking on an ambitious project investigating the ability of Escherichia coli intervening sequences (EC-IVS) to integrate into rRNA in vivo. These intervening sequences can self-splice in vitro readily.

Ori Shokek is studying formation of secondary amide carbon enolates by C- silylation in Dr. Jeff Davis's lab in the Department of Biochemistry. Ori will be working specifically on the production of unnatural amino acid and peptide derivatives which may have importance as pharmaceuticals or other useful agents.

Chris Vaccari is working with Sue Carter in Zoology to quantify the effects of postnatal vasopressin treatment on the vasopressin and oxytocin receptors in the brains of prairie voles. Previous work has hsown that these hormone levels can alter behavior in significant ways. The action of hormones depends not only on the level of the hormones but also on the levels of receptors present on target cells. Chris will use newly produced cDNAs to hybridize to frozen sections of vole brain. This way he will be able to distinguish between different types of vasopressin/oxytocin receptors.

Suneth Wijetunga is working with Dr. Spencer Benson in the Microbiology Department to analyze the E. coli IMP gene. IMP, or increased membrane permeability, apparently controls the permeability of the E. coli membrane. A mutation in this gene causes increased permeability making the cells more susceptible to antibiotics and detergents. Suneth will be investigating the expression of the imp gene and how that expression is regulated.

My name is Ghazaleh Zardoost and I am a double degree undergraduate student in Biochemistry and Psychology. I am currently working under the supervision of Dr. Kahn in Department of Biochemistry on my honors project. My e-mail address is ghaz@wam.umd.edu

Project Summary: DNA bending may be important in transcription initiation. If the DNA is bent, it could change protein-DNA interactions and also alter protein- protein contacts. The primary goal is to understand the DNA bending patterns and properties associated with the binding of E.coli RNA polymerase. The binding of RNA polymerase to a specific DNA sequence (called the promoter), is a process that takes place when genetic information (DNA) needs to be transcribed into RNA, which then becomes translated into proteins that are used by the organism. In this project, we are interested in what happens at the stage of transcription, specifically, the interactions between RNA polymerase and the promoter. The goal of the above agenda is to essentially answer the question of what is advantageous about a particular geometry with regard to the function of the enzyme (RNA polymerase) and the promoter in gene regulation and transcription. The techniques developed within this study could then be applied to other higher-order DNA-protein complexes even with impure mixtures. Little is still known about the exact nature of these interactions and their kinetics. Research on this topic is not only fascinating, but also a necessity for the advancement of knowledge about various genetic diseases that affect many people. With the present in vitro studies, the results can lead to future in vivo studies.-->