As an undergraduate at George Mason University, I participated in research projects involving functional genomics, specifically in drug addiction models and hepatotoxicity, using cDNA microarray technology. My research interests included ion channels involved in synaptic transmission and mechanisms and the role of synaptic plasticity.  I am also interested in ion channels in peripheral terminals of sensory systems-pain & heat. 

Laboratory Rotations:

Effects of polyunsaturated fatty acids on capsaicin channel function
Gerard Ahern, Ph.D.

Omega-3 (n-3) polyunsaturated fatty acids (PUFAs) are essential dietary fatty acids shown to have analgesic properties.  Because of a similarity in structure to known endogenous activators of the capsaicin receptor (TRPV1), we reasoned that TRPV1 function may be regulated by n-3 PUFAs.  This hypothesis was tested with TRPV1 in a Xenopus oocyte expression system and in native channels in cultured sensory neurons.  We compared the ability of different dietary fatty acids (saturated, mono, and PUFAs) to modulate agonist-evoked currents.   We found that all unsaturated fatty acids blocked capsaicin-induced currents. In contrast, PUFAs enhanced the current evoked by protons, which have extracellular binding sites.  These results suggest that PUFAs act at intracellular site(s).   Significantly, after stimulation of PKC, PUFAs activated TRPV1 and this effect was more pronounced with the n-3 PUFAs.  Similarly, in capsaicin-sensitive neurons, n-3 PUFAs alone evoked inward, capsazepine-sensitive currents but did not block currents evoked by endogenous agonist N-arachidonyl-dopamine (NADA). However, pre-treatment with n-3 PUFAs completely blocked the NADA evoked Ca²⁺ rise in sensory neurons.  These results suggest that under normal physiological conditions, n-3 fatty acids may partially elicit their analgesic effects by first activating and then desensitizing the TRPV1 channel.

Potential role of serum-inducible kinase (SNK) in synaptic plasticity
Dan Pak, Ph.D.

Long-term changes in synaptic activity are thought to underlie the persistent behavior involved in learning and memory, and drug addiction.  Recent reports show SNK induction by synaptic activity causes synaptic plasticity and changes in dendritic spine morphology.  Changes in synaptic composition may involve changes of synaptic receptors at spines, so we are attempting to identify the potential role of SNK in receptor internalization.  Our preliminary data indicates SNK associates with players involved in AMPA receptor internalization, such as NSF and clathrin adaptors.  These interactions were found using co-immunoprecipitation by pulling down whole brain lysates with GST-SNK fusion proteins, and then probing with antibodies for NSF and clathrin adaptors in western blots.

Recent reports have shown a specific interaction between AMPA receptors with clathrin adaptors and NSF, which were shown to have effects on AMPA receptor internalization and synaptic plasticity, thus our near future goal is to determine a physiological role of SNK and receptor internalization, specially looking at glutamate receptors.  We will attempt to do this using immunocytochemistry while inducing SNK or kinase dead form of SNK in neuronal cultures and cell lines expressing glutamate receptors.

Why do our cells need to express more than one NR2 subunit?
Stefano Vicini, Ph.D. (Department of Physiology)

I am currently doing my third rotation with Dr. Vicini.  A major focus in this project is to determine the physiological role of NMDA receptor heterogeneity of the NR2 subunit.  Using electrophysiological, molecular, and anatomical studies in transgenic mice lacking specific NR2 subunits, we will determine the role of NR2 subunits in excitatory synaptic efficacy, and possible compensatory mechanisms that may occur due to the absence of NR2 proteins.  Such approaches will allow us to test our leading hypothesis that the heterogeneity of molecular forms of NMDARs at excitatory synapses has a physiologic role in determining the efficacy of excitatory synaptic transmission and, in turn, plasticity.