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S4-4 Circadian rhythm generation, expression and entrainment in a molluscan model system
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s4-3 CELLULAR BASIS OF MULTIOSCILLATORY CIRCADIAN SYSTEM IN THE BRAIN. SAT0 HONMA Department of Physiology, Hokkaido University School of Medicine, Sapporo060, Japan The suprachiasmatic nucleus (SCN), the site of the circadian pacemaker in mammals, is composed of GABA and peptide co-localized neurons. In the cultured SCN, concentrations of vasopressin (AVP) and VIP in the medium showed synchronized circadian rhythms. The antimitotic treatment to the organotypic slice culture, but not to the disperse cell culture, desynchronized the two peptide rhythms. Effects of substances in the culture medium on oscillatory coupling were examined in disperse cell culture of rat SCN. By adding serum, AVP rhythm tended to disappear without changing the levels, while VIP rhythm persisted. By reducing glucose concentration, levels of both peptides decreased and rhythms disappeared. Electrical activity in a single neuron measured using multi-electrode dish showed either synchronized or desynchronized circadian rhythm in spontaneous firing rate. Circabidian rhythm was also observed. These results suggest that substances in the culture medium affect the coupling of oscillating cells and the effects depend on the cell type. s4-4 CIRCADIAN RHYTHM GENERATION, EXPRESSION AND ENTRAINMENT IN A MOLLUSCAN MODEL SYSTEM. GENE D. BLOCK, MICHAEL GEUSZ, SAT BIR KHALSA, STEPHAN MICHEL, DAVID WHITMORE NSF Center for Biological Timing, Departmentof Biology, Universityof Virginia, Charlottesville,VA, 22961, U.S.A. A central unresolved question within the neurosciences is identification of the cellular/molecular mechanisms underlying circadian rhythmic&y. Bulla gouldiana, the cloudy bubble snail, has proven unusually competent to address the issues of rhythm generation, entrainment and expression. The eyes of Bulla express a circadian rhythm in spontaneous optic nerve impulse frequency that is generated by approximately 100 neurons at the base of the retina. Each of these neurons is capable of producing a circadian periodicity (Michel et al. Science, 1993). The generation of rhythmicity within these cells engages both molecular translation (Khalsa et al., PNAS 1993) and transcription (Khalsa et al. Am J. Physiol., 1996). Entrainment to light cycles occurs via a change in membrane potential, influx of Ca2’ (McMahon et al. J. Comp. Phsiol., 1986; Khalsa et al. 1988), and a sustained increase in intracellular Ca2’ (Geusz et al. 1994). Rhythm expression appears due to a rhythmic K’ conductance, membrane conductance decreases just before subjective dawn and increases near subjective dusk (Ralph & Block, J. Comp. Physiol., 1991; Michel et al. Science, 1993). NIH NSl5264
Symposium 5. Structure and function of glial cells
s4-3 CELLULAR BASIS OF MULTIOSCILLATORY CIRCADIAN SYSTEM IN THE BRAIN. SAT0 HONMA Department of Physiology, Hokkaido University School of Medicine, Sapporo060, Japan The suprachiasmatic nucleus (SCN), the site of the circadian pacemaker in mammals, is composed of GABA and peptide co-localized neurons. In the cultured SCN, concentrations of vasopressin (AVP) and VIP in the medium showed synchronized circadian rhythms. The antimitotic treatment to the organotypic slice culture, but not to the disperse cell culture, desynchronized the two peptide rhythms. Effects of substances in the culture medium on oscillatory coupling were examined in disperse cell culture of rat SCN. By adding serum, AVP rhythm tended to disappear without changing the levels, while VIP rhythm persisted. By reducing glucose concentration, levels of both peptides decreased and rhythms disappeared. Electrical activity in a single neuron measured using multi-electrode dish showed either synchronized or desynchronized circadian rhythm in spontaneous firing rate. Circabidian rhythm was also observed. These results suggest that substances in the culture medium affect the coupling of oscillating cells and the effects depend on the cell type. s4-4 CIRCADIAN RHYTHM GENERATION, EXPRESSION AND ENTRAINMENT IN A MOLLUSCAN MODEL SYSTEM. GENE D. BLOCK, MICHAEL GEUSZ, SAT BIR KHALSA, STEPHAN MICHEL, DAVID WHITMORE NSF Center for Biological Timing, Departmentof Biology, Universityof Virginia, Charlottesville,VA, 22961, U.S.A. A central unresolved question within the neurosciences is identification of the cellular/molecular mechanisms underlying circadian rhythmic&y. Bulla gouldiana, the cloudy bubble snail, has proven unusually competent to address the issues of rhythm generation, entrainment and expression. The eyes of Bulla express a circadian rhythm in spontaneous optic nerve impulse frequency that is generated by approximately 100 neurons at the base of the retina. Each of these neurons is capable of producing a circadian periodicity (Michel et al. Science, 1993). The generation of rhythmicity within these cells engages both molecular translation (Khalsa et al., PNAS 1993) and transcription (Khalsa et al. Am J. Physiol., 1996). Entrainment to light cycles occurs via a change in membrane potential, influx of Ca2’ (McMahon et al. J. Comp. Phsiol., 1986; Khalsa et al. 1988), and a sustained increase in intracellular Ca2’ (Geusz et al. 1994). Rhythm expression appears due to a rhythmic K’ conductance, membrane conductance decreases just before subjective dawn and increases near subjective dusk (Ralph & Block, J. Comp. Physiol., 1991; Michel et al. Science, 1993). NIH NSl5264
Symposium 5. Structure and function of glial cells