The proposed study will test the hypothesis that chronic changes in extracellular calcium levels will alter the relative concentration or turnover of selected ganglioside species. In the first in vitro phase, extracellular calcium will be manipulated in incubating tissue slices in a physiological medium containing variable calcium (and control) ion concentrations after preloading the tissue with radiolabeled ganglioside precursors. In a subsequent in vivo phase, animals will be injected to maximally label gangliosides, then chronic serum calcium levels will be manipulated by a combination of endocrine surgery and diet control. Gangliosides will be extracted from membranous fractions of cerebrocortical, hippocampal, and thalamic tissue, then purified and separated by two-dimensional thin-layer chromatography. The content of individual gangliosides will be determined by scanning densitometry coupled with computer-assisted image analysis. Turnover of individual ganglioside species will be determined by scanning densitometry of autoradiograms. The ultimate aim of this research is to shed light on the role of gangliosides and their interactions with calcium. This question is of fundamental importance in basic neuroscience, but heightened public interest in dietary calcium gives the topic timely relevance as well.
