Projects of the 2002 Fellows:
Each of us has chosen a research project that we study for the 14 weeks that we spend at the Marine Biological Laboratory. The following section describes these projects.
Rooma Desai, Ph.D.
Isolation of K+ Currents Underlying the "Chopper Response" of Principal Cells of the Lateral Superior Olive (LSO)
The central processing of binaural information for sound localization involves the comparison of converging neural inputs from both ears. The two basic cues used in binaural sound localization are interaural time difference (ITD) for low frequency sound and interaural level (intensity) difference (ILD) for high frequency sound. Some (but not all) neurons of the superior olivary complex (SOC), are the first station in the ascending mammalian brainstem auditory pathway that receives projections from both ears. The SOC consists of three well-defined nuclei: the lateral superior olive (LSO), the medial superior olive (MSO), and the medial nucleus of the trapezoid body (MNTB). In vivo experiments indicate that the neurons of LSO encode the ILD coding for sound localization. Since K+ channels are known to control the shape and firing rate of action potentials by a neuron, I am interested in studying the possible role of K+ channels in ILD coding by the LSO neurons. I am using whole cell patch clamp technique in a living brainstem slice preparation to identify the different K+ currents present, and study how these K+ currents are modulated within LSO neurons upon stimulation with excitatory or/and inhibitory signals.
Sunil Gandhi
Visualizing the Post-Fusion Movement of Synaptic Vesicle Membrane Proteins with Evanescent Wave Fluorescence Microscopy
To release neurotransmitter, a synaptic vesicle forms a pore with the cell surface. Afterwards, the fusion pore can either close (kiss-and-run) or dilate (classical fusion). Closure of the pore seems advantageous to dilation because it would preserve the shape and protein makeup of the vesicle. This summer I am testing this assumption by asking: when a vesicle fuses, do its proteins diffuse into the cell surface or do they stay together as a patch? Using the giant synapse of the goldfish retinal bipolar cell as a preparation, I track the real-time movement of a recombinant, fluorescently tagged synaptic vesicle protein (VAMP-2) with total internal reflection fluorescence microscopy (TIRFM).
Matthias Gruhn, Ph.D.
Correlation of Extracellular Nerve Recordings and Behavioral Activity in Live Crayfish Using Implantable Electrodes and High-Speed Video Technology
The escape response of crayfish has been a neuronal circuit used to elucidate various neuronal principles in the past fifty years. However, there is still a gap of knowledge between the in vivo vs. the in vitro activity within the nervous system of crayfish, especially when they are freely behaving.
I am interested in looking at the nerve activity in abdominal nerves of the crayfish with chronically implanted electrodes to study neuronal activity in live and behaving animals. These signals are then matched with video images of the tethered crayfish while it is moving freely in a small aquarium. Specifically, I am interested in different versions of the tail-flip escape response and variations in the in vivo nerve activity during the tail-flips.
Beate Mittmann, M.S.
The Development of the Nervous System in the Horseshoe Crab, Limulus polyphemus (Chelicerata, Ziphosura) and its Implication for Arthropod Relationships
I am working as comparative zoologist mainly in the field of Evolutionary Developmental Biology with focus on evolution and relationships of arthropods (Insecta, Crustacea, Myriapoda and Chelicerata). Beside classical methods (SEM, palaeontology, drawings etc.) I am studying spatial and temporal gene expression patterns of several genes in chelicerates (primarily in the horseshoe crab Limulus polyphemus), in crustaceans (Triops cancriformis) and in insects (apterygote insects like the silverfish Lepisma saccharina and several species of collembolans). These gene expression patterns are used as character for comparative studies to figure out the evolutionary path of the arthropod groups. We can expect them to show many ancestral characters, which then can be compared with specimen from other groups.
During the Grass Fellowship, I investigate the early neurogenesis (ganglia formation) in horseshoe crabs.
Gonzalo Garcia de Polavieja, Ph.D.
Behavioral Algorithm and Circuitry for Visual Motion Detection in the Leech
Leeches orient themselves to the origin of a source of water ripples using the direction of moving bars of light. To detect the direction of these moving bars of light, the leech nervous system has to distinguish the temporal order of inputs coming from photoreceptors at different points in space. I use optical imaging techniques and intracellular recordings to study leech vision and in particular the visual motion detection pathway.
Dima Rinberg, Ph.D.
Optical recording of multineuron activity using ballistic delivery of voltage sensitive dyes
Staining cells with dye by means of ballistic delivery of micron size beads covered with the dye may solve the problem of staining multiple cells while maintaining minimal background noise. This gives hope to record spikes from multiple cells optically. While developing a new technique, I am interested in understanding the olfactory information processing and learning in a terrestrial mollusk the slug, Limax maximus.
Adrian Rodriguez-Contreras, Ph.D.
Intrinsic Properties, Morphology and Distribution of Inhibitory Neurons in the Midbrain Auditory Pathway of Chicken
The auditory system of birds and other vertebrates is characterized by a precise organization of excitatory and inhibitory connections. Seemingly unrelated species such as the domestic chicken (Gallus domesticus) and the barn owl (Tyto alba) share this general organization. Studies of sound localization in the inferior colliculus of barn owls suggest a topographic organization into a map of auditory space. The distribution of GABAergic cell bodies and nerve terminals in this auditory region has been described previously and shown to be similar in both species. What is the relationship between the intrinsic properties of neurons and the functional organization of this midbrain region? Is there any relationship between the morphology of a neuron and its electrical properties? My goal for the summer is to identify and characterize neurons that use GABA as neurotransmitter in the inferior colliculus of the chicken. To achieve this, I am developing a brain slice preparation that allows the combination of anatomical and electrophysiological techniques.
Michael S. Smotherman, Ph.D.
Pharmacological stimulation of chromatophore motoneurons in the cephalopod brain.
Cephalopods are unique in their ability to rapidly change their body coloration. Color-changing behavior provides camouflage for the animal and is used for intraspecific communication. Color patterns are controlled neurally and initiated by cells in specific regions of the brain, the chromatophore lobes, which receive multiple inputs from a complex circuitry that integrates visual, vestibular and hormonal influences. My research seeks to elucidate the neural correlates of color changing behavior and especially how sensory information is integrated centrally and leads to changes in behavior. The current project studies the effects of applying specific neurotransmitters to the motoneurons and assessing their effects on whole-body color patterns. Once transmitters are identified, the source of these inputs to the chromatophore lobes can be traced retrogradely.
Damian Wheeler
Multiprotein Complex Signaling from Synapse to Nucleus
Long-term changes in neuronal function in response to synaptic activation play very important roles in brain development and in the adult. These changes require alterations in gene expression profiles in response to activation of post-synaptic receptors.
I am interested in how synaptic activation produces local changes in the post-synaptic region that signal to the nucleus to alter gene expression. To investigate this I am developing a new technique that uses antibody-coated magnetic beads for affinity-purification of post-synaptic densities (PSD's) from primary cultured cortical and hippocampal neurons. Using biochemical techniques, I am examining synaptic activation-induced post-translational modifications and alterations in the abundance of specific PSD proteins (ie. CaMKII, MAPK). The ultimate goal of this project is to gain insight into the functional role of the multiprotein complex associated with post-synaptic receptors in long-term neuronal plasticity.
