INSIGHTS INTO GLUTAMATE TRANSPORT DURING METAMORPHOSIS: GLAST LOCALIZATION IN THE PACIFIC ECHINODERM <EM>DENDRASTER EXCENTRICUS</EM>

Echinoderms undergo a profound developmental transition during metamorphosis, in which the larval nervous system is largely dismantled and a distinct adult nervous system forms de novo from the rudiment. While larval neural organization and neurotransmitter distributions have been described in several species, the role and distribution of glutamate transporters such as GLAST during this process remain poorly understood. Glutamate is the principal excitatory neurotransmitter in animal nervous systems, and in vertebrates its extracellular concentration is tightly regulated by high-affinity transporters, including GLAST (EAAT1), predominantly expressed in glial cells. Whether comparable spatial regulation of glutamate uptake occurs during nervous system remodeling in marine invertebrates is unknown. In this study, we investigated the spatial distribution of GLAST immunoreactivity during metamorphosis in the Pacific sand dollar Dendraster excentricus using whole-mount immunofluorescence and fluorescence microscopy. GLAST labeling exhibited a regionally restricted pattern, with stronger signal in the anterior apical region, consistent with areas enriched in larval neural elements. These findings provide the first characterization of GLAST immunoreactivity during metamorphosis in D. excentricus and support the hypothesis that glutamate transport is spatially regulated during this critical developmental transition.